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Precambrian Research 234 (2013) 322– 350

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Precambrian Research

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ow long-lived is ultrahigh temperature (UHT) metamorphism? Constraintsrom zircon and monazite geochronology in the Eastern Ghats orogenic belt, India

.J. Korhonena,∗, C. Clarka, M. Brownb, S. Bhattacharyac, R. Taylora

Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, AustraliaLaboratory for Crustal Petrology, Department of Geology, University of Maryland, College Park, MD 20742, USAGeological Studies Unit, Indian Statistical Institute, Kolkata, India

r t i c l e i n f o

rticle history:eceived 2 March 2012eceived in revised form 4 December 2012ccepted 5 December 2012vailable online 20 December 2012

eywords:astern Ghatseochronology

ndiaonaziteHT metamorphismircon

a b s t r a c t

Along the coast of Peninsular India, the Eastern Ghats expose a deep crustal section through a com-posite Proterozoic orogenic belt. To quantify the late Mesoproterozoic–early Neoproterozoic pressure(P)–temperature (T)–time (t) evolution of the Eastern Ghats Province, new SHRIMP U–Pb zircon andmonazite age data from multiple localities are reported and integrated with the results of phase equilib-ria modelling. Samples of residual granulite, migmatite and enderbite yield a spread of weighted mean207Pb/206Pb zircon and monazite ages between ca 970 and ca 930 Ma. Based on ranges of spot agesfrom several samples, the late prograde to peak ultrahigh temperature (UHT) metamorphism (counter-clockwise evolution (CCW) to T >950 ◦C at P >8 kbar) and initial cooling is interpreted to have occurredbetween ca 1130 and ca 970 Ma. Regionally extensive enderbite and charnockite magmas were emplacedinto the hot, suprasolidus crust around the time of peak metamorphism. For the residual granulites andmigmatites the retrograde P–T–t path is characterized by close-to-isobaric cooling to the variable butelevated solidi for different samples. Weighted mean ages between ca 970 and ca 930 Ma in several sam-ples are interpreted to record the timing of crystallization of melt trapped by the percolation thresholdin each of these samples. Two additional weighted mean ages of ca 980 Ma (from Korhonen F.J., Saw,A.K., Clark, C., Brown, M., Bhattacharya, S., 2011. New constraints on UHT metamorphism in the EasternGhats Province through the application of phase equilibria modelling and in situ geochronology. Gond-
wana Research 20, 764–781) extend this range back in time by 10 My. The variability in the calculatedweighted mean ages across the region is interpreted to be due mainly to differences in the temperatureof the elevated solidus from sample to sample, suggesting a slow cooling rate of ∼1 ◦C/My during the ret-rograde stage of this long-lived UHT metamorphism. These results demonstrate that the Eastern GhatsProvince sustained UHT conditions (T >900 ◦C) for �50 My, and perhaps for as long as 200 Ma from ca1130 to 930 Ma, during a single CCW tectono-metamorphic event.
. Introduction

Increasingly ultrahigh temperature (UHT) metamorphism (T900 ◦C) is recognized from the exhumed hinterlands of orogensHarley, 1998; Brown, 2006, 2007; Kelsey, 2008). The recogni-ion that the crust can achieve and sustain temperatures >900 ◦Cas significant implications for crustal evolution, including growthnd differentiation, and for tectonics, due to the weakening andtrengthening effect of melting and melt loss, respectively, on
rustal rheology. However, there is little consensus on how andt what rate the heat for such extreme metamorphism is generatedr for how long temperatures >900 ◦C are sustained.
∗ Corresponding author at: Geological Survey of Western Australia, East Perth,A 6004, Australia. Tel.: +61 8 9222 3482; fax: +61 8 9222 3633.

E-mail address: [email protected] (F.J. Korhonen).

301-9268/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rittp://dx.doi.org/10.1016/j.precamres.2012.12.001

Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.

The Eastern Ghats Province, a subdivision of the EasternGhats orogenic belt in India, is characterized by the widespreadoccurrence of late Mesoproterozoic–early Neoproterozoic UHTmetamorphism. However, conflicting petrologic and structuralinterpretations relating to the pressure (P)–temperature (T)–time(t) evolution of the Province (counter-clockwise (CCW) versusclockwise (CW)) and difficulties in deciphering the geologic sig-nificance of ages that span a range from the late Mesoproterozoicto the early Neoproterozoic (a single versus a polyphase meta-morphic evolution) have led to the development of contrastingtectono-metamorphic models for the Province. As a result of theseconflicting interpretations the Eastern Ghats Province providesan ideal location for an integrated investigation of the petrologic
and chronologic evolution of the UHT metamorphism, using state-of-the-art petrologic phase equilibria modelling combined withpetrographically constrained accessory mineral U–Pb geochronol-ogy, to resolve the controversy.
ghts reserved.

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F.J. Korhonen et al. / Precamb

In this contribution, new Sensitive High Resolution Ion Micro-robe (SHRIMP) U–Th–Pb age data from zircon and monazite areeported from several localities in the Eastern Ghats Province. Thesege data are retrieved from zircon and monazite grains individu-lly chosen from thin sections so that the results can be integratedith the results of quantitative phase equilibria modelling to defineell-constrained P–T–t paths. These integrated results allow an

ssessment of the geologic significance of the ages in relation tohe apparently prolonged prograde and retrograde evolution atHT metamorphic conditions. The new ages provide limits on

he timing of UHT metamorphism and determine when crystal-ization of the last vestiges of melt trapped by the percolationhreshold occurred in residual UHT granulites as they crossed thelevated solidus during cooling. Such data from individual locali-ies show that the evolution for the Province can be characterizedy a broadly similar CCW P–T path and provides an explanation forhe spread of ages within the context of a single UHT metamor-hic event characterized by slow cooling after the metamorphiceak.

. Regional geology

The Eastern Ghats extends over 1000 km along the eastern coastf Peninsular India (Fig. 1a) and exposes a deep crustal sectionhrough a composite Proterozoic orogenic belt. Based on geologi-al and isotopic data the Eastern Ghats Belt has been separated intoour discrete crustal provinces with contrasting histories (Rickerst al., 2001a; Dobmeier and Raith, 2003), despite broad lithologicalimilarities.

The Eastern Ghats Province (Fig. 1a), as proposed by Dobmeiernd Raith (2003), is the largest crustal province located in theentral and northern parts of the belt. Previous petrologic studiesn the Eastern Ghats Province have estimated peak UHT condi-ions for the late Mesoproterozoic–early Neoproterozoic orogenicvent to be greater than 950 ◦C and 9 kbar, but both CW andCW P–T–t paths have been proposed from different localitiese.g. Lal et al., 1987; Kamineni and Rao, 1988; Sengupta et al.,990; Dasgupta et al., 1995; Sen et al., 1995; Mukhopadhyay andhattacharya, 1997; Mohan et al., 1997; Shaw and Arima, 1997;ose et al., 2000, 2006; Rickers et al., 2001b; Bhattacharya andar, 2002; Sarkar et al., 2003; Das et al., 2006, 2011; Bose andas, 2007; Nasipuri et al., 2008; Korhonen et al., 2011; Dharmaao et al., 2012a). In addition to contrasting P–T–t paths, therere disparities in the number of metamorphic events recognizednd in the timing and duration of the UHT metamorphism. As

result of the ambiguity, conflicting tectono-metamorphic mod-ls have been proposed for the evolution of the Eastern Ghatsrovince.

Evidence for granulite facies metamorphism and felsic magma-ism between ca 1000 and ca 950 Ma has been well documentedGrew and Manton, 1986; Shaw et al., 1997; Mezger and Cosca,999; Bhattacharya et al., 2003; Simmat and Raith, 2008; Dast al., 2011; Korhonen et al., 2011; Bose et al., 2011). However,lder ages ranging from ca 1400 Ma (U–Pb in zircon, Pb–Pb ineldspar–reviewed in Simmat and Raith, 2008) to ca 1250–1100 MaTh–U–Pb chemical ages from monazite – Simmat and Raith, 2008)ave been interpreted to date an early UHT metamorphic eventM1). In these studies, close-to-isobaric cooling to ∼750–800 ◦C isnferred to have followed the metamorphic peak for this early UHTvent. A later pervasive granulite facies event (M2) is argued toave occurred at ca 1000–950 Ma, reaching conditions of ∼850 ◦C
nd 8 kbar and characterized by near-isothermal decompressiono ∼5 kbar following the metamorphic peak (see Dasgupta andengupta, 2003; Simmat and Raith, 2008; Bose et al., 2011). Inontrast to this polyphase interpretation for the Eastern Ghats
esearch 234 (2013) 322– 350 323

Province, the UHT metamorphism has been interpreted as a singlelong-lived event in the late Mesoproterozoic to early Neoprotero-zoic (e.g. Korhonen et al., 2011; Gupta, 2011; Dharma Rao et al.,2012a).

The present study area is in the central part of the Eastern GhatsProvince (Fig. 1), in Domain II of Rickers et al. (2001a). The dom-inant rocks include migmatitic sillimanite–garnet-bearing gneiss(referred to locally as khondalite), orthopyroxene-free garnetif-erous quartzofeldspathic gneiss (referred to locally as leptynite),orthopyroxene-bearing charnockitic and enderbitic quartzofelds-pathic gneiss, and two-pyroxene mafic granulite. Small lensesof calc-silicate and high Mg–Al granulites also occur in thegneisses.

The P–T–t histories proposed in previous studies that specif-ically relate to the new results presented here are summarizedin more detail below. Unless otherwise indicated, these interpre-tations have relied on petrogenetic grids in simplified chemicalsystems and conventional thermobarometry to determine P–T con-ditions. The P–T–t evolution of the samples dated in this study hasbeen evaluated using state-of-the-art phase equilibria modellingin the Na2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3(NCKFMASHTO) chemical system, and will be presented indetail in future contributions (Korhonen, Brown and Clark,unpublished data), although the results critical to a properinterpretation of the new ages are summarized later in thispaper.

3. Geochronological methods

3.1. SHRIMP U–Pb zircon

Zircon grains were separated from crushed rock samples byconventional magnetic and heavy liquid separation. In addition,selected zircon grains from two samples (EGB-09-01, -19) weredrilled from polished thin sections. Handpicked grains and thin sec-tion fragments were mounted in epoxy resin discs. Each mountwas imaged using a cathodoluminscence (CL) detector fitted toa Phillips XL30 scanning electron microscope at a working dis-tance of 15 mm and using an accelerating voltage of 12 kV, whichhighlights distortions in the crystal lattice that are related to trace-element distribution and/or radiation damage (e.g. Nasdala et al.,2003; Rubatto and Gebauer, 2000). The mounts were then ultrason-ically cleaned in ethanol, petroleum ether and detergent (Decon),rinsed in distilled and deionized water, and dried in an oven at60 ◦C. The polished surface of each mount was then coated with athin membrane of gold producing a resistivity of 10–20 � acrossthe disc.

Zircon U–Th–Pb isotope data were collected using the SHRIMPII based in the John de Laeter Centre of Mass Spectrometry, Perth,Western Australia. The sensitivity for Pb isotopes in zircon usingSHRIMP II was 21 cps/ppm/nA, the primary beam current was2.5–3.0 nA and mass resolution was ∼5000. Correction of mea-sured isotope ratios for common Pb was based on the measured204Pb in each sample and routinely represented a <1% correctionto the 206Pb counts. Corrections for common Pb were estimatedfrom 204Pb counts and the Stacey and Kramers (1975) commonPb model for the approximate U–Pb age of each analysis. Pb/Uisotope ratios were corrected for instrumental interelement dis-crimination using the observed covariation between Pb+/U+ andUO+/U+ (Compston et al., 1984; Hinthorne et al., 1979) deter-
mined from interspersed analyses of the standard zircon BR266.BR266 is a single zircon megacryst from Sri Lanka with an age of559 ± 0.3 Ma, 206Pb/238U = 0.09059, U and Th contents of 909 and201 ppm, respectively (Stern, 2001).

324 F.J. Korhonen et al. / Precambrian Research 234 (2013) 322– 350

Fig. 1. (a) Simplified geological map of the Eastern Ghats Province; modified after Ramakrishnan et al. (1998) and Rickers et al. (2001a). Stars indicate study areas. (b) GoogleEarth image showing sample locations in the northern sector. ** Sunki samples described in Korhonen et al. (2011). (c) Google Earth image showing sample locations in thec ctor.

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.2. SHRIMP U–Pb monazite

Thin section fragments with selected monazite grains from sam-les EGB-10-82 and -84 were cast with chips of the India monazitetandard Ind-1 (509 Ma, 206Pb/238U = 0.082133; Korhonen et al.,011), and were prepared in a similar way to the zircon mounts.onazite elemental mapping for Ce, Y, Th, U and Pb was under-

aken using the JEOL JXA-8530F Electron Probe Microanalyzer at
he Centre for Microscopy, Characterisation and Analysis, Univer-ity of Western Australia. An accelerating voltage of 15 kV and
current of 200 nA with a step size of 0.5 �m in both the xnd y directions were used for elemental mapping. Maps were

processed in NIH Image using the Fire lookup table, and all mapswere processed to the same degree so colour intensities are directlycomparable between grains. Monazite grains from samples EGB-09-04, -10-72, and -74 were imaged using a backscatter electron(BSE) detector fitted to a Phillips XL30 scanning electron micro-scope at a working distance of 5 mm and using an acceleratingvoltage of 20 kV. U–Pb isotope measurements were carried outusing the SHRIMP II, and analysed with ∼0.5 nA O2

− primary beam
focused on to ∼10 �m spots, a 5-scan duty cycle, and a massresolution of ∼5000 (a more detailed description of the CurtinSHRIMP procedure for monazite analysis is provided by Foster et al.(2000)).

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. Sample descriptions

.1. Samples from the northern sector of the study areaSalur–Pachipenta–Sunki)

The localities comprising the northern sector of the study areare shown on Fig. 1a as point ‘N’. Three samples were collectedrom two localities (Fig. 1b). Samples EGB-10-71 and EGB-10-72ere collected ∼9 km to the west of Salur. Sample EGB-10-74 was

ollected ∼6 km to the south, near Pachipenta. This area compriseselitic migmatites and granulite facies metapelitic to semipeliteneisses with minor enderbite–charnockite, calc-silicate gneissesnd metaquartzites. A garnetiferous gneiss intrudes the metased-mentary gneisses and is exposed east of the sample localitiesMukhopadhyay and Bhattacharya, 1997).

Mukhopadhyay and Bhattacharya (1997) documented threehases of deformation in this area. The earliest two phases repre-ent a progressive deformation associated with prograde heatingnd crustal melting along a CCW P–T–t path. Weakly foliated patchnd vein leucosomes in some outcrops indicate ongoing deforma-ion at the time of melt crystallization. The progressive deformations expressed as isoclinal folds (D1a) with strongly attenuatedimbs forming an axial planar gneissosity (D1b) and reclined foldsD2) that refolded the early structures to produce the map-scalenterference patterns (Mukhopadhyay and Bhattacharya, 1997).

esoscopic dome and basin structures in calc-silicate gneissesre due to interference between the early folds and later openpright folds (D3). Peak metamorphic conditions were achievedyn- to post-D2 and were estimated to be 8 kbar and 850 ◦C byukhopadhyay and Bhattacharya (1997) based on inferences fromicrostructures and the stability of univariant mineral reactions in

etrogenetic grids calculated for simplified chemical systems.A more robust approach was used by Korhonen et al. (2011)

n a study from a locality ∼10 km southwest of Sunki (Fig. 1b), tohe west-southwest of Salur in the metasedimentary gneisses of

ukhopadhyay and Bhattacharya (1997). Korhonen et al. (2011)inked microstructures from two high Mg–Al granulite samples

ith phase assemblage fields in P–T pseudosections (isochemi-al phase diagrams) calculated for individually constrained H2Ond Fe2O3 contents as appropriate to each sample. For one sam-le, the peak metamorphic phase assemblage was interpreted toe garnet + orthopyroxene + quartz + ilmenite + melt and the post-eak evolution involved recrystallization of garnet and the growthf orthopyroxene, sillimanite, cordierite and biotite. In the sec-nd sample, the peak metamorphic phase assemblage comprisedbundant elongate orthopyroxene porphyroblasts, rare grains ofpinel and sparse isolated coarse-grained sillimanite, inferred toave been in equilibrium with melt. The post-peak evolution

nvolved growth of sillimanite with biotite, likely at the expensef orthopyroxene, followed by growth of cordierite and a fine-rained cordierite–K-feldspar intergrowth. Using phase equilibriaodelling, Korhonen et al. (2011) constrain peak conditions to

ave been in excess of 950 ◦C and 9.5 kbar, followed by decom-ression and minor cooling to the elevated solidus at ∼900 ◦C and.5 kbar. Monazite analysed in situ with the SHRIMP yielded aeighted mean 207Pb/235U age of ca 980 Ma (Table 1), which was

nterpreted to broadly constrain the timing of high-temperatureonazite growth during decompression and crystallization of melt

rapped by the percolation threshold during a single UHT metamor-hic event. These authors interpreted the spread of 207Pb/235U spotges that extended from ca 1043 to ca 922 Ma as evidence for pro-racted monazite growth during the high-temperature retrograde
volution, implying very slow cooling at a rate of <1 ◦C/Ma afterecompression and possibly diffusive lead loss.
The samples considered in the present study were collectedrom the metasedimentary gneisses described in Mukhopadhyay

esearch 234 (2013) 322– 350 325

and Bhattacharya (1997). These authors interpreted the massif ofintrusive gneiss exposed east of the sample localities to have beenderived by melting of a deeper crustal source early during the pro-grade metamorphic history.

4.1.1. EGB-10-71 (N18◦31′33.1′′, E083◦7′34.5′′)Sample EGB-10-71 is an enderbite comprising

orthopyroxene–quartz–magnetite–plagioclase–K-feldspar, withaccessory zircon and ilmenite. The enderbite has intrusive anddiffuse contacts with the host migmatitic gneiss (Fig. 2a), althoughleucocratic material derived from the host gneiss also back-veinsinto the enderbite (Fig. 2b). The enderbite contains small leu-cocratic patches (±orthopyroxene) that suggest in situ melting(Fig. 2a and c). Orthopyroxene commonly occurs where thesepatches coalesce into a larger network (Fig. 2c).

Zircon mainly occurs along grain boundaries in the leucocraticlayers and along grain boundaries with orthopyroxene. Inspectionof separated zircon grains from this sample by CL imaging revealedboth zoned and homogeneous grains (Fig. 3a). Some grains containdiscrete weakly luminescent structural cores, commonly less than15 �m in size (Fig. 3a and b). Larger cores may preserve oscillatoryzoning (Fig. 3c). The dark cores are surrounded by more lumines-cent rims, which may be overgrown or truncated by thicker, lessluminescent outer rims (Fig. 3a–c). These outer rims have similarCL characteristics to the homogenous grains (Fig. 3a).

4.1.2. EGB-10-72 (N18◦31′33.7′′, E083◦7′35.3′′)Sample EGB-10-72 is a garnet–cordierite migmatitic gneiss

closely associated with intrusive enderbite similar to sam-ple EGB-10-71. The mineral assemblage in this sample isgarnet–sillimanite–cordierite–biotite–quartz–plagioclase–biotite–titanohematite, with accessory magnetite, zircon and monazite. Agarnet-rich selvedge ∼5 cm in thickness occurs at the contact withenderbite (Fig. 2d).

Zircon is distributed throughout the sample, but most com-monly occurs along grain boundaries and as inclusions incoarse-grained quartz in leucosomes, and as inclusions in cordieriteand garnet. Monazite also occurs throughout the sample, and maybe more concentrated in monazite-rich layers parallel to the folia-tion. Monazite grains generally occur along grain boundaries withquartz, cordierite and titanohematite, and along fractures withingarnet porphyroblasts.

CL imaging of zircon separates from this sample show weaklyluminescent and resorbed cores, which are overgrown by morebrightly luminescent rims (Fig. 3d). In some grains, these over-growths may display oscillatory zoning (Fig. 3e). A less luminescentovergrowth is also present in some grains (Fig. 3d–f). Grains of mod-erately luminescent zircon with only relics of brighter cores werealso observed (Fig. 3f). Monazite separates do not show obviouscompositional zoning based on BSE imaging.

4.1.3. EGB-10-74 (N18◦28′45.5′′, E083◦6′19.4′′)Sample EGB-10-74 was collected from a quarry comprising stro-

matic metatexite migmatite with a vertical E–W-trending foliation.Layers in the outcrop preserve isoclinal folds with a steep axial pla-nar gneissosity parallel to the foliation, consistent with a compositeplanar fabric (Fig. 2e), similar to the S1a and S1b fabrics describedby Mukhopadhyay and Bhattacharya (1997). In some places atoutcrop, an anastomosing network of leucosome in patch or veinmigmatite has a foliation defined by fine-grained biotite, althoughcoarse-grained biotite aggregates in the centre of the leucosomes
may be oriented at any angle (Fig. 2f). These leucosomes are inter-preted to post-date the deformation associated with the stronglyattenuated D1 fold limbs and the composite S1a/S1b fabric. Thus, themelting recorded by the patch and vein migmatite is interpreted to


Table 1Summary of U–Pb zircon and monazite ages from this study.

Sample Location Mineral Age (Ma)* Comments

Northern sector of the study area (Salur–Pachipenta–Sunki)EGB-10-71 (enderbite) N18◦31′33.1′′

E083◦7′34.5′′Zircon 954 ± 14b Approximate age of crystallization of low-volume in situ melt

will be slightly younger than weighted mean age** defined by31 concordant (<10% discordance) analyses from overgrowthdomains. Two concordant core analyses yield spot ages of ca1009 and ca 973 Ma; broadly interpreted as the timing ofenderbite emplacement.

EGB-10-72 (migmatitic gneiss) N18◦31′33.7′′

E083◦7′35.3′′Zircon 950 ± 17b

1516 ± 34c

613 ± 93c

Approximate age of melt crystallization at conditions ofelevated solidus during high-temperature metamorphismdefined by weighted mean age** of nine concordant rimanalyses (MSWD = 1.4). Anomalously old spot ages (ca 1195, ca1146, and ca 1025 Ma) not included in the calculation of theweighted mean age imply older zircon growth, possibly duringa protracted high-temperature event. An older population(1514–1220 Ma) plots in a discordant array with poorlydefined intercepts: the upper intercept age corresponding toinherited grains and the lower intercept age implyingNeoproterozic Pb-loss.

Monazite 966 ± 6b Approximate age of melt crystallization at conditions ofelevated solidus during high-temperature metamorphismdefined by weighted mean age** of 24 concordant analyses(MSWD = 1.0).


E083◦6′19.4′′Zircon 1005 ± 22 to

874 ± 20aProtracted zircon growth during the high-temperatureretrograde evolution observed in zircon cores andovergrowths.

Monazite 980 ± 15 to921 ± 15a

633 ± 17b

533 ± 12b

Range of spot ages reflects protracted monazite growth duringthe high-temperature retrograde evolution to conditions of theelevated solidus from ca 980 to 920 Ma. The youngest agepopulation from 11 grains (n = 12; 533 ± 12 Ma) impliesmonazite growth during the younger Pan-Africantectonothermal event. The intermediate age population of ca633 Ma either corresponds to localized monazite growthduring a Neoproterozoic metamorphic event or mixingbetween the older and younger age populations.

SK2-6-05d ∼N18◦30′1.3′′

∼E83◦2′53.6Monazite 979 ± 8b Approximate age of melt crystallization at conditions of

elevated solidus during high-temperature metamorphismdefined by weighted mean age** of 23 concordant analyses(MSWD = 0.41).

D1-3-S3d ∼N18◦30′1.3′′

∼E83◦2′53.6Monazite 1042 ± 41b Weighted mean age based on analyses (n = 3) from a single

monazite grain included in an orthopyroxene porphyroblast;interpreted to date the late prograde growth of peakmetamorphic minerals.

977 ± 13b Approximate age of melt crystallization at conditions ofelevated solidus during high-temperature metamorphismdefined by weighted mean age** of 23 concordant analyses(MSWD = 1.11).

Central sector of the study area (Anantagiri–Sunkarametta)EGB-09-38 (sapphirine-bearing high

Mg–Al granulite)N18◦14′8.0′′

E083◦0′41.6′′Zircon 1120 ± 41 to

794 ± 119aRange of concordant spot ages from metamorphicovergrowths reflects protracted zircon growth during thehigh-temperature retrograde evolution. All analyses fromovergrowth domains (n = 23) yield a poorly constrained andshallow discordia with an upper intercept age of 1007 ± 97,broadly consistent with the timing of high-temperaturemetamorphism in other samples, and a lower intercept of566 ± 320 Ma, suggesting possible overprinting associatedwith Pan-African tectonism. However, the errors of thediscordia line do not permit a meaningful interpretation.

EGB-09-39 (sapphirine-bearing highMg–Al granulite)

N18◦14′12.3′′

E083◦0′48.2′′Zircon 970 ± 28b Approximate age of melt crystallization at conditions of

elevated solidus during high-temperature metamorphismdefined by weighted mean age** of 10 concordant rim analyses(MSWD = 1.1). Two older concordant spot ages (ca 1059, ca1055) from metamorphic rims imply protracted zircon growth.

EGB-10-82 (high Mg–Al granulite) N18◦16′22.6′′

E082◦57′21.9′′Monazite 953 ± 7b Approximate age of melt crystallization at conditions of

elevated solidus during high-temperature metamorphismdefined by weighted mean age of 37 concordant analyses(MSWD = 1.7).

EGB-10-84 (high Mg–Al granulite) N18◦16′22.6′′

E082◦57′21.9′′Monazite 948 ± 5b Approximate age of melt crystallization at conditions of

elevated solidus during high-temperature metamorphismdefined by weighted mean age of 33 concordant analyses(MSWD = 1.6).

F.J. Korhonen et al. / Precambrian Research 234 (2013) 322– 350 327

Table 1 (Continued)

Sample Location Mineral Age (Ma)* Comments

Southern sector of the study area (Paderu–Gangaraja Madugula)EGB-09-01 (migmatitic gneiss) N18◦2′10.4′′

E082◦33′38.7′′Zircon 929 ± 17b Approximate age of melt crystallization at conditions of

elevated solidus during high-temperature metamorphismdefined by weighted mean age of 22 concordant rim analyses(MSWD = 1.0).


E082◦33′23.5′′Monazite 968 ± 20b

822 ± 31bWeighted mean age of ca 968 Ma approximates age of meltcrystallization at conditions of elevated solidus duringhigh-temperature metamorphism (13 concordant rim analysesfrom four grains; MSWD = 2.0). Weighted mean age of ca822 Ma from one grain may be related monazite growth duringlater fluid infiltration.

EGB-09-19 (granite with garnetschlieren)

N18◦3′11.8′′

E082◦33′10.7′′Zircon 1129 ± 46 to

885 ± 15a

1620 + 44/−45c

855 + 14/−15c

Range of concordant spot ages from metamorphicovergrowths (n = 8) reflects protracted zircon growth duringthe high-temperature retrograde evolution. Approximate ageof melt crystallization at conditions of elevated solidus isapproximated by three concordant rim analyses yielding agesof 965–960 Ma. Four younger ages (909–885 Ma) from threegrains occurring along fractures in garnet are interpreted asthe final release of fluids associated with the waning stages ofmetamorphism at greater depth (also lower intercept age ofdiscordia line; MSWD = 1.2). Upper intercept age of discordialine is age of inherited grains.

* Age = 207Pb*/206Pb* age:a Age range reflecting protracted growth.b Weighted mean age.

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c Regression age.** Approximate age of melt crystallization at the solidus will be younger than calcd From Korhonen et al. (2011).

e syn-D2 with the fabric developing as the melt crystallized lateuring D2.

Sample EGB-10-74 is a garnet-bearing stromatic metatex-te migmatite. The mineral assemblage in this sample is garnet–illimanite–biotite–quartz–plagioclase–titanohematite–magnetiteinor cordierite and orthopyroxene with accessory zircon andonazite are also present. Zircon is most common in leuco-

omes, occurring along grain boundaries and as inclusions inoarse-grained quartz. Trace monazite occurs throughout theample, CL imaging shows that zircon separates from this sampleave discrete structural cores, which are typically overgrown byore brightly luminescent rims (Fig. 3g and h). However, some

rains show a less luminescent overgrowth (Fig. 3i). BSE imagingf monazite separates does not reveal obvious compositionaloning.

.2. Samples from the central sector of the study areaAnantagiri–Sunkarametta)

The localities in the central sector of the study area are shownn Fig. 1a as point ‘C’. Samples EGB-09-38 and EGB-09-39 were col-ected just east of Anantagiri (Fig. 1c). This area is characterized bylongate NE–SW-trending bodies of pelitic migmatite, charnockite,nd garnetiferous quartzofeldspathic gneiss with gradational con-acts. Mafic granulites occur as lenses within the gneisses. Minorapphirine-bearing, high Mg–Al granulites in the Anantagiri areaypically occur as enclaves within charnockite (e.g. Fig. 4a). The out-rops generally have moderate to steeply dipping foliation, parallelo the rock contacts.

Petrologic interpretations from sapphirine-bearing granulitesave been used by Sengupta et al. (1990) to propose a CCW P–T–tvolution for this area, with a high-T/low-P prograde path reach-ng peak P–T conditions of 8.3 kbar above 950 ◦C, followed by near
sobaric cooling to ∼675 ◦C and 7.5 kbar, and a final decompressionegment from 7.5 to 4.5 kbar. Dasgputa et al. (1991) proposed aroadly similar retrograde P–T–t path for mafic granulites in therea.
weighted mean age; see text for further discussion.

The interpretation of a CCW P–T–t evolution by Senguptaet al. (1990) relies on the inference that tiny inclu-sions of spinel in sapphirine record a reaction such asrutile + spinel + quartz → sapphirine + ilmenite, which they calcu-lated to occur at pressures <3 kbar for temperatures of 700–900 ◦C.Given the involvement of rutile, this calculated stability is veryunlikely to be correct, and the occurrence of spinel inclusions insapphirine in aluminous granulites that have followed a clockwiseP–T–t evolution from pressures >10 kbar is well documented (e.g.Galli et al., 2011). To address this potential ambiguity, the P–T–tevolution of the samples dated in this study from these localitieshas been evaluated using phase equilibria modelling. Although theresults of this modelling will be presented in detail elsewhere, theresults indicate peak conditions >950 ◦C at between 7 and 9 kbarfollowed by near isobaric cooling to the elevated solidus at ∼950 ◦C(Korhonen, Brown and Clark, unpublished data).

Samples EGB-10-82 and EGB-10-84 were collected approx-imately 7 km northwest of Anantagiri and 1.5 km west ofSunkarametta (Fig. 1c), separated by ∼2 m in the same out-crop. This area exposes migmatitic gneiss, mafic granulite,and charnockite–enderbite. High Mg–Al granulite (±sapphirine)occurs as small elongate bodies within the dominant migmatiticgneiss near the margins with mafic and enderbitic gran-ulites (Bose et al., 2000). Bose et al. (2000) have interpretedorthopyroxene–cordierite and orthopyroxene–spinel associationsin massive and migmatitic high Mg–Al granulites from this localityin terms of prograde melting of biotite–plagioclase–quartz-bearingprotoliths at ∼6–8 kbar and temperatures in excess of 850 ◦C, withpeak metamorphic conditions reaching 9 kbar and 950 ◦C, followedby slight decompression and cooling to ∼700–750 ◦C (see also Boseet al., 2006). Similar results have been obtained from the samplesdated in this study using phase equilibria modelling, with estimatedpeak conditions near 950 ◦C and 8 kbar followed by near isobariccooling (Korhonen, Brown and Clark, unpublished data).

Geochronological data from this general area have been recentlyreported by Das et al. (2011) and Bose et al. (2011; Domain2). Oscillatory-zoned zircon cores that yield near-concordant207Pb/206Pb ages ranging from ca 1780 to ca 1700 Ma are


Fig. 2. Field photographs from the northern sector of the study area. (a) Enderbite with intrusive and diffuse contacts with the host gneiss. Arrows denote small leucocraticpatches (±orthopyroxene) consistent with in situ partial melting. (b) Leucocratic material derived from the host migmatitic gneiss back-veins into the enderbite. (c) Leucocraticpatches in enderbite. Orthopyroxene (opx) commonly occurs where these patches coalesce into a larger network. (d) Contact between migmatitic gneiss and enderbite ismarked by a garnet-rich selvedge. (e) Layering in stromatic metatexite migmatites (S1a) preserves isoclinal folds with a steep axial planar gneissosity (S1b) parallel to thefoliation, consistent with a composite planar fabric (S1a/S1b). (f) Patch migmatite with S1a foliation is crosscut by leucosomes with S1b foliation defined by fine-grained biotite.Both the S1a foliation in the host and the S1b foliation in the leucosomes are crosscut by the composite S1a/S1b fabric.


Fig. 3. Representative cathodoluminescence (CL) images of zircons from all samples and SHRIMP analytical spots (ellipses). Sample name is displayed and grain numbersrefer to the analyses presented in tables. 207Pb/206Pb ages are quoted, those marked with asterisks (*) are >10% discordant.

330 F.J. Korhonen et al. / Precambrian R

Fig. 4. Field photographs from the central and southern sectors of the study area.(a) Minor sapphirine-bearing, high Mg–Al granulites in the Anantagiri area typicallyoccur as enclaves within charnockite. (b) Orthopyroxene-rich granulite from theSunkarametta area, occurring as a layer within migmatitic gneiss. (c) Compositionallayering in residual granulite from the Sunkarametta area, with a distinct cordierite-rich domain on the left of the photograph and a cordierite-poor, garnet-rich domainon the right.

esearch 234 (2013) 322– 350

interpreted to record magmatic events in the source of these detri-tal grains. Discordant ages of 1600–1100 Ma are inferred to bemixing ages resulting from UHT metamorphism at 1030–990 Ma(M1), based on chemical dates of monazite inclusions in orthopy-roxene. A second phase of granulite metamorphism (M2) wascharacterized by significant zircon growth at 980–900 Ma, pre-ceded and/or contemporaneous with emplacement of voluminousgranite at 990–980 Ma.

4.2.1. EGB-09-38 (N18◦14′8.0′′, E083◦0′41.6′′)Sample EGB-09-38 is a sapphirine-bearing gran-

ulite. The mineral assemblage in this sample comprisessapphirine–garnet–orthopyroxene–sillimanite–cordierite–spinel–magnetite–rutile–quartz–plagioclase–K-feldspar. Zircon generallyoccurs along grain boundaries and as inclusions in quartz andcordierite.

CL imaging of zircon separates from this sample show bothzoned and homogeneous grains (Fig. 3j). Many grains containweakly luminescent and resorbed cores; some with well developedoscillatory zoning. These dark cores are commonly surrounded bybrightly luminescent overgrowth domains, which have similar CLcharacteristics to the homogenous grains (Fig. 3j).

4.2.2. EGB-09-39 (N18◦14′12.3′′, E083◦0′48.2′′)This sample is similar to sample EGB-09-38. Zircon sepa-

rates typically display weakly luminescent, oscillatory-zoned cores,which are overgrown by more brightly luminescent rims (Fig. 3k).

4.2.3. EGB-10-82 (N18◦16′22.6′′, E082◦57′21.9′′)Sample EGB-10-82 is an orthopyroxene-rich granulite,

occurring as a layer within migmatitic gneiss (Fig. 4b).The mineral assemblage in this sample is composed oforthopyroxene–sillimanite–cordierite–rutile–quartz–plagioclase–K-feldspar–biotite–ilmenite.

Monazite grains were analysed in situ to preserve the petrologiccontext. Monazite grains are closely associated with cordierite ororthopyroxene, occurring either along grain boundaries (Fig. 5a,c and d) or as inclusions (Fig. 5b). Some grains are chemicallyhomogeneous (e.g. Fig. 6e and l), whereas other grains show com-positional zoning in Y with relative enrichment in the core regionsand depletion in overgrowth domains (e.g. Fig. 6c and f). Thinouter rims with Y enrichment may also be preserved. The Y-poordomains are typically associated with a slight increase in Th con-tent, whereas variations in Ce, Pb, and U are less pronounced.Monazite grains do not show a correlation between petrographicsetting and chemical zoning.

4.2.4. EGB-10-84 (N18◦16′22.6′′, E082◦57′21.9′′)This sample is similar to sample EGB-10-82, collected

from the same outcrop. The mineral assemblage comprisesorthopyroxene–sillimanite–cordierite–rutile–quartz–plagioclase–K-feldspar–biotite. Minor garnet and sapphirine are also presentin discrete layers.

Monazite grains selected for in situ analysis occur as inclu-sions in garnet (Fig. 5e), sillimanite (Fig. 5h), orthopyroxene andcordierite, and within and closely associated with cordierite + K-feldspar intergrowths (Fig. 5f, g, and i). Elemental mapping ofmonazite in this sample reveals that most of the analysed monazitegrains are chemically homogeneous (e.g. Fig. 6m–p), although thinY-rich overgrowths are present on some grains. One grain showsevidence for oscillatory zoning in the core, which is truncated by
a thin Y-depleted overgrowth. Two grains hosted in garnet (Fig. 6rand s) have Y-enriched core domains with cuspate embaymentssurrounded by Y-depleted overgrowths. These features suggestfluid-assisted dissolution and reprecipitation.


F amplem

4(

sasw0miecgpMdcB

Pf

ig. 5. Photomicrographs of representative monazite grains analysed in situ from sonazite grains listed in Tables 8 and 9.

.3. Samples from the southern sector of the study areaPaderu–Gangaraja Madugula)

The localities in the southern sector of the study area arehown on Fig. 1a as point ‘S’. Sample EGB-09-01 was collectedbout 4 km northeast of Gangaraja Madugula, approximately 12 kmouthwest of Paderu (Fig. 1d). Samples EGB-09-04 and EGB-09-19ere collected about 2 km north–northwest of sample EGB-09-

1, separated by about 400 m (Fig. 1d). This area exposes peliticigmatite (e.g. Fig. 4c), mafic granulite, charnockite–enderbite, and

ntrusive granites. Rare high Mg–Al granulites (±sapphirine) gen-rally occur as small blocks and folded layers within massif-typeharnockite–enderbite bodies and granites. Orthopyroxene-freeranites in this area have been linked to the pelitic granulites byrograde high-temperature hydrate-breakdown melting in high-g pelitic and greywacke protoliths, followed by high-temperature

ecompression from ∼10 to ∼8 kbar at 1000 ◦C and subsequentooling from >900 ◦C to ∼600 ◦C (Bhattacharya and Kar, 2002;
hattacharya et al., 2003).
Various P–T–t paths have been proposed for the Paderu area.reliminary phase equilibria modelling predicts peak conditionsor sample EGB-09-01 to be >860 ◦C at 6–11 kbar, and a retrograde

s EGB-10-82 and -84. Samples numbers and grains are labelled, and correspond to

trajectory of near-isobaric cooling just prior to conditions of finalcrystallization of melt trapped by the percolation threshold. SampleEGB-09-04 records higher peak metamorphic conditions of ∼945 ◦Cand 8.3 kbar. The preserved assemblage in this sample provides atight constraint on the solidus conditions where the last melt crys-tallized, estimated at ∼900 ◦C and 8.3 kbar (Korhonen, Brown andClark, unpublished data).

A study of sapphirine-bearing granulites near GangarajaMadugula by Mohan et al. (1997) constrained peak metamorphicP–T conditions to have been >900 ◦C at 8.4 kbar. Following peakmetamorphism, these authors proposed a retrograde path charac-terized by a decrease in pressure of up to 3 kbar with cooling of150–200 ◦C. A history of high-temperature decompression follow-ing peak UHT metamorphism has also been proposed by DharmaRao et al. (2012a) for samples collected ∼2 km northeast of Paderu.These authors use the results of phase equilibria modelling inNCKFMASH and thermobarometry to propose peak metamorphicconditions >1000 ◦C and >10 kbar, followed by decompression to
pressures <10 kbar, and subsequent near-isobaric cooling to tem-peratures <900 ◦C. In contrast to these studies, Sengupta et al.(2004) reinterpreted the data of Bhattacharya and Kar (2002) andBhattacharya et al. (2003) to suggest decompression from a lower


Fig. 6. Yttrium X-ray compositional maps and SHRIMP analytical spots (ellipses) of monazite grains from samples EGB-10-82 and -84. Samples numbers are abbreviated to‘82 mXX’ and ‘84 mXX’, respectively, where ‘XX’ refers to monazite grains listed in Tables 8 and 9. Maps were processed in NIH Image using the Fire lookup table, and allmaps were processed to the same degree so colour intensities are directly comparable between grains. Scale bar is 20 �m. (For interpretation of the references to colour inthis figure legend, the reader is referred to the web version of this article.)

rian R

ppB∼a

4

afsbA(tmcNao

4

afsr((i

4

afisn

acinais

5

i6cCvot2

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5

faft


ressure of ∼7–8 kbar at 850 ◦C, inferred to postdate cooling fromeak UHT conditions along a general CCW P–T–t path. Pal andose (1997) also proposed a CCW path, reaching peak conditions of1000 ◦C and 9.5 kbar, followed by near-isobaric cooling to 900 ◦Cnd 9 kbar.

.3.1. EGB-09-01 (N18◦2′10.4′′, E082◦33′38.7′′)Sample EGB-09-01 is a migmatitic gneiss with a mineral

ssemblage comprising garnet–orthopyroxene–magnetite–K-eldspar–biotite–quartz–plagioclase–ilmenite. Zircon grainselected for in situ analysis occur as inclusions and along grainoundaries of quartz and plagioclase in leucosomes (Fig. 7a–c).

single grain (A-6) occurs as an inclusion at the edge of garnetFig. 7c). CL imaging of the zircon grains from this sample revealedhe presence of weakly luminescent, oscillatory-zoned cores in

any grains (Fig. 3l). These cores were commonly truncated andompletely overgrown by more brightly luminescent rims (Fig. 3l).early homogenous grains of moderately luminescent zircon werelso observed, although in some grains there is a slightly darkervergrowth (Fig. 3m).

.3.2. EGB-09-04 (N18◦3′15.8′′, E082◦33′23.5′′)This sample is a migmatitic gneiss (Fig. 4c) with a mineral

ssemblage of garnet–orthopyroxene–cordierite–sillimanite–K-eldspar–biotite–plagioclase–quartz–rutile. Monazite grainselected for in situ analysis are closely associated with orthopy-oxene, occurring along grain boundaries (Fig. 7d), as inclusionsFig. 7e), or within a fine-grained intergrowth of sillimanite + quartz±biotite) replacing the orthopyroxene (Fig. 7f). BSE imaging ofn situ monazite grains reveals that the monazite is unzoned.

.3.3. EGB-09-19 (N18◦3′11.8′′, E082◦33′10.7′′)Sample EGB-09-19 is a foliated garnet-bearing granite, collected

bout 2 km northwest of sample EGB-09-01 (Fig. 1d). Schlieren ofne-grained garnet are abundant and define the foliation in thisample. Quartz, plagioclase, K-feldspar, biotite, ilmenite and mag-etite are also present.

The petrographic settings for the zircon grains selected for in situnalyses are either along grain boundaries of quartz and plagio-lase or included in garnet along cracks or along edges of magnetitenclusions. CL imaging shows that the grains display brightly lumi-escent cores, some with oscillatory zoning (Fig. 3n). These coresre commonly overgrown by less luminescent rims. Zircon grainsn this sample are more fractured than grains in other samples. Inome grains, the fractures occur only in the core regions (Fig. 3o).

. Results

U–Pb isotope ages for zircon and monazite are summarizedn Table 1, together with the monazite ages from samples SK2--05 and D1-3-S3 reported in Korhonen et al. (2011), and theomplete data for the new samples are reported in Tables 2–13.oncordia regressions, concordia age and weighted average agealues were calculated with ISOPLOT v3 (Ludwig, 2003) and plottedn Tera-Wasserberg concordia diagrams (Fig. 8a–q) and conven-ional concordia diagrams (Fig. 8r). Unless otherwise indicated,07Pb/206Pb spot ages (±1�) are reported. Analyses described asconcordant’ refer to <10% discordance.

.1. EGB-10-71

Thirty-seven cores and rims from 29 zircon grains were analysed
rom sample EGB-10-71 (Fig. 8a, Table 2). Thirty-three analysesre <10% discordant, which yield a range of 207Pb/206Pb spot agesrom 1042 ± 28 to 842 ± 30 Ma. The weakly luminescent struc-ural cores were typically too small to analyse, but two concordant
esearch 234 (2013) 322– 350 333

analyses from dark, oscillatory-zoned cores yield 207Pb/206Pb spotages of 1009 ± 22 and 973 ± 24 Ma. These ages are interpreted asapproximating the timing of enderbite crystallization. The concord-ant analyses from overgrowth domains (n = 31) yield a weightedmean 207Pb/206Pb age of 954 ± 14 Ma (95% confidence, MSWD = 1.5;Fig. 8b), corresponding to new zircon growth during UHT metamor-phism. There is no systematic age difference between the brightlyluminescent domains and the less luminescent domains character-istic of the outer rims and homogenous grains (Table 2).

5.2. EGB-10-72

Twenty-six cores and rims from twenty-three zircon grainswere analysed from sample EGB-10-72 (Fig. 8c, Table 3). Theanalyses reveal two distinct age populations. An older popu-lation with 207Pb/206Pb spot ages ranging from 1514 ± 15 to1220 ± 17 Ma plots in a discordant array with poorly defined upperand lower intercepts of 1516 ± 34 and 613 ± 93 Ma, respectively(±2�, MSWD = 5.0; Fig. 8d). The array is broadly consistent withthe inheritance of late Mesoproterozoic detrital zircons affectedby a possible Pan-African thermal disturbance (ca 550–500 Ma;e.g. Mezger and Cosca, 1999; Gupta, 2011). Nine analyses from ayounger, concordant population yield a weighted mean 207Pb/206Pbage of 950 ± 17 Ma (95% confidence, MSWD = 1.4; Fig. 8e). Five con-cordant analyses, three of which correspond to anomalously old207Pb/206Pb spot ages of 1195 ± 17, 1146 ± 16, and 1025 ± 19 Ma,and two which yield younger 207Pb/206Pb spot ages of 851 ± 48 and488 ± 30 Ma, were not included in the calculation of the weightedmean age because they are outliers based on 1� uncertainties. Theobservation that the group of nine concordant analyses are fromrims is consistent with an interpretation that these ages date newzircon growth during UHT metamorphism.

Twenty-five analyses from multiple monazite grains yield aspread of 207Pb/206Pb spot ages ranging between 1001 ± 17 and915 ± 16 Ma (Fig. 8f, Table 4). All of the analyses are <10% dis-cordant. The youngest spot age of 915 ± 16 Ma is outside the1� uncertainties of the other analyses, and is therefore consid-ered to be an outlier. The remaining analyses define a weightedmean 207Pb/206Pb age of 966 ± 6 Ma, MSWD = 1.0 (95% confidence,MSWD = 1.0; Fig. 8f).

5.3. EGB-10-74

Thirty-three analyses from twenty-four zircon grains wereobtained from sample EGB-10-74 (Fig. 8g, Table 5). All of the anal-yses are <10% discordant. The three youngest spot ages (816 ± 19,803 ± 30 and 753 ± 55 Ma) are outliers with respect to the otheranalyses based on 1� uncertainties. Excluding these three ages,twenty-three analyses from overgrowth domains have a range of207Pb/206Pb spot ages from 1001 ± 28 to 874 ± 20 Ma, and sevenanalyses from the core domains have a similar spread of ages from1005 ± 22 to 893 ± 26 Ma (Fig. 8g).

Twenty-five analyses from sixteen monazite grains yielda spread of 207Pb/206Pb spot ages ranging from 980 ± 15 to519 ± 20 Ma (Fig. 8h, Table 6). All of the analyses are <10% dis-cordant. The analyses define four 207Pb/206Pb age populations of980–941 Ma (n = 3; Fig. 8i), 934–921 Ma (n = 4; Fig. 8i), 656–614 Ma(n = 6), and 551–519 Ma (n = 12; Fig. 8h). The oldest populationcorresponds to spot ages from a single grain, whereas the four207Pb/206Pb spot ages from 934 ± 11 to 921 ± 15 Ma are fromthree different grains. These two age populations are inter-
preted as evidence for protracted monazite growth during thehigh-temperature retrograde evolution to the solidus from ca980 to ca 920 Ma. The youngest age population from 11 grains(n = 12) has a weighted mean 207Pb/206Pb age of 533 ± 12 Ma (95%


Fig. 7. Photomicrographs of selected zircon and monazite grains analysed in situ from samples EGB-09-01 and 04, respectively.

Table 2Ion microprobe results for zircons from sample EGB-10-71.

Spot Domain 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date (Ma) ±1� Date (Ma) ±1�

3.1 M m 154 83 0.56 0.149 7.585 0.946 0.06713 1.44747 798 7 842 30 5.524.1 M m 155 69 0.46 0.330 6.566 0.954 0.06855 1.65284 914 8 885 34 −3.5

9.1 M m 118 53 0.46 0.253 6.216 1.023 0.06881 1.73719 962 9 893 36 −8.314.1 M m 144 63 0.45 0.410 6.487 0.981 0.06890 1.87719 924 8 896 39 −3.410.1 M m 109 60 0.57 0.426 6.445 1.059 0.06900 2.56186 930 9 899 53 −3.728.1 M m 155 71 0.48 0.304 6.423 0.960 0.06942 1.61657 933 8 911 33 −2.523.1 M m 145 68 0.48 0.474 6.509 0.971 0.06945 1.86935 921 8 912 38 −1.121.1 M m 136 67 0.51 0.291 6.320 0.987 0.06950 1.65757 947 9 914 34 −3.925.1 M m 155 81 0.54 0.421 6.220 1.483 0.06951 1.75623 961 13 914 36 −5.615.1 M m 144 64 0.46 0.142 6.924 0.972 0.07001 1.36017 870 8 929 28 6.813.1 M m 217 126 0.60 0.192 6.392 0.882 0.07002 1.70181 937 8 929 35 −0.920.1 M m 197 107 0.56 0.080 6.372 0.946 0.07032 1.31689 940 8 938 27 −0.226.1 M m 146 69 0.49 0.258 6.718 1.666 0.07058 1.58879 895 14 945 33 5.7

8.1 M m 149 46 0.32 0.276 6.209 0.968 0.07065 2.04291 963 9 947 42 −1.712.1 M m 164 87 0.55 0.284 6.382 0.946 0.07092 1.50749 938 8 955 31 1.9

7.1 M m 196 127 0.67 0.115 6.282 0.900 0.07103 1.16849 952 8 958 24 0.716.1 M m 148 73 0.51 0.315 6.062 1.354 0.07105 1.63757 984 12 959 33 −2.922.1 M m 165 74 0.46 0.162 6.627 0.992 0.07123 2.00583 906 8 964 41 6.529.1 M m 148 65 0.45 0.143 6.426 0.970 0.07129 1.35387 932 8 966 28 3.7

1.1 M m 174 85 0.51 0.133 6.246 0.918 0.07145 1.15456 957 8 970 24 1.427.1 M m 178 84 0.48 0.103 6.240 0.949 0.07167 1.07965 958 8 977 22 2.011.1 M m 147 63 0.44 0.037 6.314 0.968 0.07244 1.15209 948 9 998 23 5.417.1 M m 126 59 0.49 0.115 6.429 1.008 0.07248 1.33721 932 9 999 27 7.3

4.1 M m 126 61 0.50 0.120 6.299 0.998 0.07278 1.36866 950 9 1008 28 6.218.1 M m 141 67 0.49 −0.181 6.038 0.980 0.07403 1.37479 988 9 1042 28 5.619.1 M b 116 73 0.65 0.353 6.481 1.028 0.06981 1.81340 925 9 923 37 −0.3

8.2 M b 115 35 0.32 0.348 6.280 1.027 0.07095 1.68452 953 9 956 34 0.46.2 C m 175 104 0.61 0.327 6.424 0.940 0.06791 1.65851 933 8 866 34 −8.3

27.2 C m 199 80 0.41 0.181 6.490 1.272 0.07169 2.03354 924 11 977 41 5.91.2 C b 65 33 0.53 0.381 6.107 1.228 0.07039 3.67475 978 11 940 75 −4.34.2 C b 45 22 0.50 0.423 5.945 1.424 0.07156 4.21582 1002 13 973 86 −3.2

Ages not included in calculation of weighted mean age10.2 C d 170 74 0.45 0.093 6.232 0.930 0.07155 1.17035 959 8 973 24 1.5

9.2 C d 150 76 0.53 0.035 6.258 0.969 0.07283 1.10397 956 9 1009 22 5.76.1* D 172 92 0.55 0.142 9.189 0.924 0.06469 1.63342 666 6 764 34 13.57.2* D 97 56 0.60 0.746 6.595 2.087 0.06489 2.95759 910 18 771 62 −19.42.1* D 113 61 0.56 1.527 6.336 1.067 0.06610 4.63860 945 9 809 97 −18.05.1* D 132 68 0.53 0.681 6.311 1.375 0.06789 2.98911 948 12 865 62 −10.3

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.C, core analysis; M, metamorphic growth; D, >10% discordant; luminescence: m, moderate; b, bright; d, dark.

* Analyses with >10% discordance. Data arranged according to increasing 207Pb/206Pb age within domain groups.





2.2 M 234 68 0.30 0.379 6.378 1.099 0.06862 1.46285 939 10 887 30 −6.29.1 M 160 119 0.77 0.184 6.381 0.939 0.07024 1.33839 938 8 935 27 −0.36.1 M 498 68 0.14 0.146 6.486 0.755 0.07045 0.69350 924 6 941 14 1.97.1 M 535 80 0.16 0.065 6.318 1.229 0.07048 0.57783 947 11 942 12 −0.6

13.1 M 309 39 0.13 0.196 6.285 0.847 0.07083 0.94553 952 7 952 19 0.121.1 M 205 65 0.33 0.252 6.538 1.494 0.07121 1.29404 918 13 963 26 5.115.1 M 519 72 0.14 0.000 6.318 0.962 0.07134 1.19899 947 8 967 24 2.220.1 M 223 121 0.56 0.036 6.181 0.943 0.07196 1.12921 967 8 985 23 2.0

8.1 M 175 94 0.56 0.114 6.287 1.565 0.07203 1.15218 952 14 987 23 3.8

Ages not included in calculation of weighted mean age2.1 M 342 57 0.17 0.126 11.809 0.818 0.05690 1.34820 524 4 488 30 −7.81.1 M 122 88 0.75 0.527 6.778 1.407 0.06743 2.30017 887 12 851 48 −4.5

22.1 M 267 62 0.24 0.084 5.902 0.860 0.07338 0.93721 1009 8 1025 19 1.623.1 M 325 72 0.23 0.135 5.489 1.179 0.07795 0.82422 1079 12 1146 16 6.312.1 M 355 55 0.16 0.212 5.081 1.437 0.07991 0.83940 1158 15 1195 17 3.4

4.2 M 768 36 0.05 0.043 4.478 1.040 0.08925 0.72036 1299 12 1410 14 8.619.1 M 805 32 0.04 0.033 4.263 0.862 0.09104 0.62542 1358 11 1447 12 6.8

4.1 M 642 65 0.11 0.060 4.233 1.135 0.09192 0.45525 1367 14 1466 9 7.511.1 M 583 43 0.08 0.033 3.991 0.992 0.09331 0.40108 1442 13 1494 8 3.9

5.1 M 538 51 0.10 0.011 3.816 1.598 0.09431 0.77902 1500 21 1514 15 1.017.1* D 143 103 0.74 0.453 6.501 0.955 0.06710 3.43224 922 8 841 71 −10.416.1* D 294 93 0.33 0.114 6.303 0.834 0.08093 0.86974 949 7 1220 17 23.8

3.1* D 746 36 0.05 0.077 4.854 1.480 0.08747 0.81044 1207 16 1371 16 13.118.1* D 634 33 0.05 −0.022 4.961 0.913 0.08754 0.39941 1184 10 1372 8 15.0

6.2* D 327 66 0.21 0.032 4.644 1.266 0.08958 0.86525 1257 14 1416 17 12.414.1* D 539 39 0.08 0.013 4.555 0.765 0.09028 1.48972 1279 9 1431 28 11.710.1* D 359 91 0.26 0.043 4.794 1.239 0.09127 1.20329 1221 14 1452 23 17.4

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.M, metamorphic growth; D, >10% discordant.

* Analyses with >10% discordance. Data arranged according to increasing 207Pb/206Pb age within domain groups.

Table 4Ion microprobe results for monazite from sample EGB-10-72.

Spot 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)


72-1.1 2735 71,037 26.8 −0.102 6.194 0.636 0.07048 0.50990 965 6 942 10 −1.672-10.1 1576 49,920 32.7 −0.128 6.234 0.725 0.07065 0.66877 959 6 947 14 −0.972-15.1 558 115,064 213.0 −1.100 6.131 1.040 0.07077 1.14111 974 9 951 23 −1.772-4.1 765 139,019 187.7 −0.599 6.328 0.947 0.07097 1.05720 946 8 956 22 0.872-25.1 2952 39,351 13.8 −0.087 6.229 0.631 0.07097 0.49494 960 6 957 10 −0.272-3.1 2303 94,795 42.5 −0.326 6.304 0.671 0.07107 0.57541 949 6 959 12 0.772-24.1 3549 66,344 19.3 −0.010 6.230 0.615 0.07116 0.46824 960 5 962 10 0.272-23.1 1262 57,847 47.4 −0.381 6.178 1.100 0.07119 0.74420 967 10 963 15 −0.372-11.1 743 59,303 82.5 −0.335 6.076 0.921 0.07120 0.96345 982 8 963 20 −1.472-14.1 1675 56,930 35.1 −0.200 6.328 0.710 0.07120 0.65256 946 6 963 13 1.372-22.1 769 82,544 111.0 −0.864 6.136 0.942 0.07122 0.95411 973 9 964 19 −0.772-6.1 2153 58,992 28.3 −0.055 6.151 0.676 0.07128 0.58084 971 6 966 12 −0.472-16.1 1445 51,378 36.7 −0.202 6.242 0.737 0.07129 0.68911 958 7 966 14 0.672-21.1 1026 74,492 75.1 −0.243 6.119 0.824 0.07137 0.83592 976 7 968 17 −0.672-9.1 860 63,481 76.3 −0.542 6.166 0.893 0.07145 0.91789 969 8 970 19 0.172-20.1 1336 73,107 56.5 −0.223 6.360 0.761 0.07148 0.74173 941 7 971 15 2.272-17.1 1202 59,650 51.3 −0.192 6.354 0.794 0.07171 0.78642 942 7 978 16 2.672-19.1 777 61,406 81.6 −0.527 6.161 0.890 0.07171 0.92123 970 8 978 19 0.672-7.1 807 67,958 87.0 −0.286 6.125 0.899 0.07180 0.93192 975 8 980 19 0.472-18.1 696 83,926 124.7 −0.644 6.251 0.954 0.07200 1.02801 957 8 986 21 2.172-12.1 748 77,297 106.8 −0.739 6.065 0.936 0.07200 0.96661 984 9 986 20 0.172-5.1 974 58,861 62.4 −0.265 6.319 0.858 0.07211 0.88491 947 8 989 18 3.072-13.1 1509 47,226 32.3 −0.138 6.171 0.725 0.07223 0.66360 968 7 992 13 1.772.8.1 1137 76,566 69.6 −0.313 6.355 0.807 0.07252 0.81741 942 7 1001 17 4.3

Age not included in calculation of weighted mean age72-2.1 1194 77,833 67.3 −0.526 6.621 0.788 0.06956 0.79737 907 7 915 16 0.7

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.Data arranged according to increasing 207Pb/206Pb age within domain groups.


Fig. 8. U–Pb concordia plots of zircon and monazite analyses.


Fig. 8. ( Continued ).


Fig. 8. ( Continued ).





10.1 M 233 6 0.03 0.621 7.694 0.874 0.06435 2.59470 788 6 753 55 −4.920.1 M 197 3 0.02 0.188 8.082 0.899 0.06588 1.41077 752 6 803 30 6.7

6.1 M 445 12 0.03 0.158 7.776 0.796 0.06631 0.91448 780 6 816 19 4.716.2 M 268 203 0.78 0.140 6.547 0.837 0.06817 0.97077 916 7 874 20 −5.224.1 M 334 31 0.10 0.208 6.756 1.144 0.06823 1.55983 890 10 876 32 −1.7

2.1 M 274 121 0.45 0.068 6.774 1.172 0.06827 1.65649 888 10 877 34 −1.312.1 M 591 12 0.02 0.100 6.791 1.125 0.06898 0.68256 886 9 898 14 1.511.1 M 255 1 0.00 0.084 6.633 0.853 0.06908 0.96278 905 7 901 20 −0.5

3.1 M 489 74 0.16 0.014 6.873 0.802 0.06919 1.11537 876 7 905 23 3.418.1 M 362 127 0.36 0.131 6.197 1.143 0.06959 0.82277 964 10 916 17 −5.715.1 M 475 27 0.06 0.068 6.564 0.774 0.06960 0.93718 914 7 916 19 0.3

5.1 M 427 81 0.20 0.042 6.551 0.794 0.06974 0.63343 916 7 921 13 0.622.1 M 250 107 0.44 0.185 6.462 0.857 0.06987 1.74617 928 7 925 36 −0.413.1 M 308 49 0.16 0.549 6.437 1.071 0.06998 1.95197 931 9 928 40 −0.4

9.1 M 337 117 0.36 0.222 6.275 1.238 0.07002 1.01397 953 11 929 21 −2.823.1 M 711 12 0.02 0.008 6.401 0.965 0.07035 0.52660 936 8 939 11 0.317.1 M 593 47 0.08 0.090 6.370 0.752 0.07068 0.60092 940 7 948 12 0.9

8.1 M 634 54 0.09 0.127 6.071 0.871 0.07076 0.61012 983 8 950 12 −3.71.2 M 531 213 0.41 0.229 5.926 0.860 0.07098 1.66648 1005 8 957 34 −5.58.3 M 480 12 0.03 0.110 6.041 0.780 0.07101 0.68939 987 7 958 14 −3.34.1 M 263 122 0.48 0.119 6.090 1.149 0.07152 0.90047 980 10 972 18 −0.91.1 M 708 80 0.12 0.012 6.325 1.277 0.07157 0.62359 946 11 974 13 3.0

21.1 M 439 87 0.20 0.022 6.015 0.784 0.07180 0.60890 991 7 980 12 −1.214.1 M 360 141 0.40 0.093 6.103 0.969 0.07231 0.71290 978 9 995 14 1.819.1 M 266 154 0.60 0.121 6.075 1.214 0.07236 0.90717 982 11 996 18 1.5

7.1 M 386 73 0.19 0.117 6.201 1.168 0.07252 1.36230 964 10 1001 28 4.01.3 C 641 53 0.09 0.236 6.443 0.809 0.06881 1.27076 930 7 893 26 −4.4

12.2 C 1017 12 0.01 −0.010 6.207 0.938 0.07056 0.39537 963 8 945 8 −2.123.2 C 453 82 0.19 0.180 6.279 0.787 0.07080 0.82901 953 7 952 17 −0.110.2 C 340 91 0.28 0.092 5.987 0.822 0.07083 0.83075 996 8 952 17 −4.916.1 C 480 31 0.07 0.081 6.124 0.787 0.07112 0.59056 975 7 961 12 −1.6

8.2 C 288 160 0.57 0.000 6.151 1.396 0.07225 0.72076 971 13 993 15 2.417.2 C 752 43 0.06 0.027 6.194 0.953 0.07267 1.07310 965 9 1005 22 4.3

I 38U/20

A rom thC Pb/20

cds6mgb

5

aataaaFntlldammto2

on microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(2

ll errors are at the 1� level; f204% is the percentage of common 206Pb, estimated f, core analysis; M, metamorphic growth; data arranged according to increasing 207

onfidence, MSWD = 0.25; Fig. 8h), indicating monazite growthuring the younger Pan-African tectonothermal event. Six analy-es from five grains define a weighted mean 207Pb/206Pb age of33 ± 17 Ma (95% confidence, MSWD = 0.6; Table 1). This inter-ediate age population either corresponds to localized monazite

rowth during a Neoproterozoic metamorphic event or mixingetween the older and younger age populations.

.4. EGB-09-38

Forty-two cores and rims from thirty-eight zircon grains werenalysed from this sample. Twenty analyses are <10% discord-nt, which yield a range of 207Pb/206Pb spot ages from 2039 ± 95o 794 ± 119 Ma (Fig. 8j, Table 7). Older spot ages are typicallyssociated with core domains (ca 2039–1153 Ma; n = 9), whereasges obtained from brightly luminescent overgrowth domainsre younger, ranging from 1120 ± 41 to 794 ± 119 Ma (n = 10;ig. 8k). A single age from the core domain of a brightly lumi-escent grain yields an age of 1517 ± 151 Ma. The dataset fromhe overgrowth domain yields a poorly constrained and shal-ow discordia with an upper intercept age of 1007 ± 97 and aower intercept of 566 ± 320 Ma (not shown). This discordia lineoes not permit a meaningful estimate of the intercept ages,lthough the upper intercept age is broadly consistent with meta-orphic ages from the other samples. The lower intercept age
ay reflect overprinting associated with the younger Pan-African
ectonothermal event, as suggested by the rutile 206Pb/238U agef 451 ± 5 Ma for this sample (sample EB-38 of Taylor et al.,012).

6Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).e measured 204Pb; grain spot is the individual grain and analysis identification.

6Pb age within domain groups.

5.5. EGB-09-39

Forty-one analyses from thirty-nine zircon grains were obtainedfrom sample EGB-09-39 (Fig. 8l, Table 8). Seven concordant anal-yses from core domains yield 207Pb/206Pb spot ages ranging from1813 ± 180 to 954 ± 27 Ma. Twelve concordant analyses from theovergrowth domains correspond to 207Pb/206Pb spot ages between1059 ± 67 and 756 ± 47 Ma. Excluding the youngest spot age of954 ± 27 Ma from a core domain, the ages from the metamorphicovergrowths are younger than the cores. Ten of these analysesdefine a weighted mean 207Pb/206Pb age of 970 ± 28 Ma (95% con-fidence, MSWD = 1.1; Fig. 8m). The two youngest spot ages of772 ± 163 and 756 ± 47 Ma were not included in the calculation ofthe weighted mean age. In contrast to sample EGB-09-38, the zir-con age data in this sample provide little evidence for Pan-Africanoverprinting, despite a rutile 206Pb/238U age of 449 ± 6 Ma for thissample (sample EB-39 of Taylor et al., 2012).

5.6. EGB-10-82

Thirty-nine analyses from ten monazite grains were performedin situ to preserve their petrographic context (Table 9). Thirty-seven concordant analyses yield a spread of 207Pb/206Pb spot agesranging between 996 ± 14 and 902 ± 13 Ma (Fig. 8n, Table 9). Thespread of ages does not correlate with petrographic setting or
systematic differences in Y or Th zoning (Table 9 and Fig. 6a–iand l). These analyses define a weighted mean 207Pb/206Pb ageof 953 ± 7 Ma (95% confidence, MSWD = 1.7; Fig. 8n). The twoyoungest spot ages of 874 ± 20 and 854 ± 22 Ma are −9.7% and



Spot 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)


ca 533 Ma group74-11.1 2098 87,697 43.2 −0.510 11.369 0.705 0.05844 0.92764 543 4 546 20 0.474-12.2 1181 71,972 62.9 −0.728 10.996 0.842 0.05856 1.18310 561 5 551 26 −1.574-13.1 1865 73,043 40.5 −0.517 11.941 0.731 0.05787 0.97536 518 4 525 21 1.074-14.1 1716 79,060 47.6 −0.697 11.674 0.754 0.05817 0.99193 530 4 536 22 1.074-15.1 2076 73,667 36.7 −0.120 11.873 0.696 0.05818 0.91841 521 3 537 20 2.474-16.1 2021 65,839 33.7 −0.468 11.734 0.712 0.05772 0.91165 527 4 519 20 −1.274-3.1 1384 82,169 61.4 −0.363 11.586 1.277 0.05803 1.06839 534 7 531 23 −0.574-4.1 1663 85,406 53.1 −0.450 11.539 0.745 0.05849 1.02616 536 4 548 22 1.874-5.2 1413 104,135 76.2 −0.547 11.619 0.924 0.05827 1.38040 532 5 540 30 1.174-7.1 1836 76,821 43.2 −0.226 11.873 0.713 0.05781 0.95880 521 4 522 21 0.274-7.2 1784 74,643 43.2 −0.327 11.968 1.016 0.05776 0.95313 517 5 521 21 0.574-8.2 1663 130,059 80.8 −0.790 11.732 0.755 0.05799 1.03242 527 4 529 23 0.3

ca 633 Ma group74-9.1 1675 93,835 57.9 −0.522 9.944 0.733 0.06028 0.90176 618 4 614 19 −0.574-12.1 1446 64,686 46.2 −0.254 9.973 0.752 0.06051 0.95606 616 4 622 21 0.874-3.3 1695 78,685 48.0 −0.356 9.638 0.761 0.06076 0.87534 636 5 631 19 −0.774-8.1 1533 125,694 84.7 −0.799 9.653 0.768 0.06106 0.95222 635 5 641 20 0.774-2.1 1368 81,759 61.7 −0.567 9.496 4.218 0.06122 1.53515 645 26 647 33 0.274-3.2 1360 85,286 64.8 −0.721 9.368 0.790 0.06148 0.94838 654 5 656 20 0.3

Ages not included in calculation of weighted mean ages74-5.1 1482 84,231 58.7 −0.160 6.402 0.745 0.06974 0.73224 936 6 921 15 −1.174-5.3 1449 85,005 60.6 −0.241 6.448 0.751 0.06982 1.46201 929 6 923 30 −0.574-1.1 1456 89,337 63.4 −0.286 6.423 0.744 0.07009 0.72753 933 6 931 15 −0.174-10.1 2936 67,397 23.7 −0.216 6.453 0.645 0.07018 0.52503 929 6 934 11 0.474-6.2 3803 59,890 16.3 −0.036 6.088 0.613 0.07044 0.46119 980 6 941 9 −2.874-6.1 1241 95,032 79.1 −0.346 6.076 0.804 0.07179 0.80855 982 7 980 16 −0.274-6.3 1507 75,466 51.8 −0.258 6.066 0.755 0.07179 0.73864 984 7 980 15 −0.3

I 38U/20

A rom thD

−c

5

g2

(p<mFu(yamwo

5

saT9

5

s

on microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(2

ll errors are at the 1� level; f204% is the percentage of common 206Pb, estimated fata arranged according to increasing 207Pb/206Pb age within domain groups.

17.9% discordant, respectively, and were not included in the cal-ulation of the weighted mean age.

.7. EGB-10-84

Thirty-four analyses performed in situ from nine monaziterains yield similar results to sample EGB-10-82, with a spread of07Pb/206Pb spot ages ranging between 990 ± 14 and 883 ± 12 MaFig. 8o, Table 10). There is no detectable correlation between age,etrographic setting, or chemical zoning. All of the analyses are10% discordant. Thirty-three of the analyses define a weightedean 207Pb/206Pb age of 948 ± 5 Ma (95% confidence, MSWD = 1.6;

ig. 8o). The youngest spot age of 883 ± 12 Ma is just within the 1�ncertainties of the other analyses, but has the highest discordance−7.7%). Therefore this spot age is considered to be anomalouslyoung and was not included in the calculation of the weighted meange. Two monazite grains included in garnet show cuspate embay-ents in core domains (Fig. 6r and s). These features are consistentith fluid-assisted dissolution and reprecipitation in the presence

f melt or fluid derived from crystallizing rocks at depth.

.8. EGB-09-01

Twenty-six analyses from eight zircon grains were analysed initu. Twenty-two analyses from metamorphic overgrowths yield

range of 207Pb/206Pb ages 990 ± 42 to 832 ± 51 Ma (Fig. 8p,able 11), which define a weighted mean 207Pb/206Pb age of29 ± 17 Ma (95% confidence, MSWD = 1.0; Fig. 8p).

.9. EGB-09-04

Nineteen monazite analyses from five grains were analysed initu. 207Pb/206Pb spot ages range from 1014 ± 27 to 804 ± 37 Ma

6Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).e measured 204Pb; grain spot is the individual grain and analysis identification.

(Fig. 8q, Table 12). All of the analyses are <10% discordant. Thirteenanalyses from four grains define a weighted mean 207Pb/206Pb ageof 968 ± 20 Ma (95% confidence, MSWD = 2.0; Fig. 8q). One grainalong the grain boundary between orthopyroxene and quartz yieldssignificantly younger spot ages (836–804 Ma; Fig. 8q), defining aweighted mean 207Pb/206Pb age of 822 ± 31 Ma (95% confidence,MSWD = 0.12; Table 1).

5.10. EGB-09-19

Twenty-two analyses from eleven zircon grains were per-formed in situ. The 207Pb/206Pb spot ages range from 1754 ± 44 to885 ± 15 Ma (Fig. 8r, Table 13), and eighteen of the analyses plot in adiscordant array with upper and lower intercepts of 1620 + 44/−45and 855 + 14/−15 Ma, respectively (±2�, MSWD = 1.2; Fig. 8r). Eightanalyses from weakly luminescent overgrowths in five grains are<10% discordant, yielding ages from 1129 ± 46 to 885 ± 15 Ma(Fig. 8r). Four of these analyses from three grains occurringalong fractures in garnet correspond to the youngest spot ages(909–885 Ma). The other four analyses yield distinctly older agesfrom 1129 ± 46 to 960 ± 17 Ma, although three of the grains yieldspot ages of 965–960 Ma. These three grains occur along a fracturein garnet, as an inclusion in quartz, and along a grain boundarybetween garnet and quartz.

6. Discussion

6.1. Age and duration of UHT metamorphism

Each of the samples dated in this study yields data that pro-vides constraints on the age and duration of UHT metamorphismin the Eastern Ghats Province. The data are of four types: (1) dis-crete, concordant populations of zircon overgrowths on older cores;





Rims13.1 M 20 479 24.55 0.351 7.389 2.134 0.06562 5.69444 818 16 794 119 −3.218.1 M 73 277 3.90 1.689 7.000 1.194 0.06813 8.03203 861 10 873 166 1.43.1 M 68 97 1.47 0.359 6.023 1.194 0.06975 2.75942 990 11 921 57 −8.15.1 M 75 108 1.48 0.000 6.172 5.107 0.07017 4.40857 968 46 933 90 −4.014.1 M 23 564 25.71 0.266 6.442 1.957 0.07024 4.34685 930 17 935 89 0.67.1 M 43 38 0.91 −0.123 5.742 1.432 0.07181 3.94272 1035 14 981 80 −6.022.1 M 53 170 3.31 0.089 5.926 2.260 0.07367 3.42564 1005 21 1032 69 2.82.1 M 77 112 1.50 0.360 6.066 1.246 0.07389 3.16600 984 11 1038 64 5.715.1 M 511 45 0.09 −0.010 5.781 2.628 0.07602 1.81908 1029 25 1095 36 6.617.1 M 50 90 1.86 −0.100 5.215 3.135 0.07694 2.03516 1131 33 1120 41 −1.18.1 M 193 359 1.92 0.072 4.005 10.427 0.09447 8.02073 1437 134 1517 151 5.924.1* D 20 183 9.40 1.422 5.742 2.179 0.05421 10.30584 1035 21 380 232 −186.912.1* D 20 554 28.75 1.560 6.239 2.208 0.06178 10.12869 958 20 666 217 −47.223.1* D 20 586 30.76 1.256 5.852 2.183 0.06306 9.04775 1017 21 710 192 −46.79.1* D 41 330 8.34 0.997 6.073 2.695 0.06428 7.77660 983 25 751 164 −33.34.1* D 72 111 1.59 1.215 5.800 1.279 0.06695 4.46968 1025 12 836 93 −24.516.1* D 18 519 30.51 −0.378 6.748 4.178 0.07194 5.54978 891 35 984 113 10.26.1* D 25 4 0.17 −1.300 7.013 2.090 0.07550 7.71740 859 17 1082 155 22.021.1* D 52 478 9.58 0.709 6.761 1.522 0.07942 5.71184 889 13 1183 113 26.620.1* D 19 410 22.70 −0.642 5.996 2.198 0.08069 6.86631 994 20 1214 135 19.519.1* D 26 603 23.70 −0.581 5.313 5.892 0.08164 7.78113 1112 60 1237 153 11.01.1* D 15 376 25.76 −0.423 6.615 2.623 0.08610 5.38522 907 22 1340 104 34.611.1* D 71 74 1.08 3.737 6.298 3.597 0.08628 13.33606 950 32 1344 258 31.5

CoresC.6 C 702 18 0.03 −0.030 5.428 4.401 0.07825 4.33413 1090 44 1153 86 6.0C.5 C 1035 45 0.04 −0.018 3.836 4.062 0.08803 11.05782 1493 54 1383 212 −8.9C.8 C 957 71 0.08 0.040 4.423 3.918 0.08925 3.38297 1314 47 1410 65 7.5C.10 C 903 28 0.03 0.015 3.456 2.355 0.09906 3.65671 1638 34 1607 68 −2.2C.2 C 1772 132 0.08 0.006 3.392 3.040 0.10055 3.56379 1665 45 1634 66 −2.2C.14 C 1536 16 0.01 0.000 3.315 4.316 0.10216 5.47877 1700 64 1664 101 −2.5C.21.1 C 780 20 0.03 0.003 3.105 2.806 0.10234 2.38012 1800 44 1667 44 −9.1C.15 C 610 21 0.04 0.014 3.075 1.495 0.10846 4.15159 1815 24 1774 76 −2.7C.7 C 865 15 0.02 0.002 2.650 2.628 0.12571 5.37500 2064 46 2039 95 −1.5C.15A* D 683 38 0.06 −0.005 4.242 1.693 0.07855 6.34334 1365 21 1161 126 −19.5C.11* D 829 21 0.03 −0.020 5.419 3.030 0.08729 5.82384 1092 30 1367 112 21.9C.1* D 767 44 0.06 −0.019 4.611 1.443 0.09160 2.48233 1265 17 1459 47 14.6C.15B* D 673 27 0.04 0.141 5.330 4.764 0.09336 7.27513 1108 49 1495 138 28.1C.3* D 874 33 0.04 −0.004 4.658 2.887 0.09601 7.25674 1254 33 1548 136 20.9C.16* D 506 35 0.07 0.027 4.025 6.005 0.10002 2.97534 1430 77 1625 55 13.3C.5* D 640 31 0.05 −0.049 4.876 6.228 0.10124 10.37017 1203 68 1647 192 29.5C.4* D 561 53 0.10 0.051 4.461 6.019 0.10671 4.75573 1304 71 1744 87 27.8C.9* D 794 29 0.04 −0.023 3.600 2.809 0.10697 4.33704 1580 39 1749 79 10.9C.13* D 1256 19 0.02 0.002 2.661 2.015 0.10802 2.79453 2056 35 1766 51 −19.2

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.C

06Pb a

(aicaaiPNa

6(

sa(st

, core analysis; M, metamorphic growth; D, >10% discordant.* Analyses with >10% discordance. Data arranged according to increasing 207Pb/2

2) ranges of concordant zircon spot ages with weighted meanges from discrete, concordant populations; (3) upper and lowerntercept ages of discordant arrays of partially reset inherited zir-on cores and metamorphic rims that approximate concordantnalyses; and, (4) discrete, concordant populations from monazitenalysed in situ and as grain separates. These results have directmplications for models of the UHT evolution of the Eastern Ghatsrovince. Distinctly younger age populations associated with lateeoproterozoic overprinting do not bear on the UHT evolution andre not further considered.

.1.1. Northern sector of the study areaSalur–Pachipenta–Sunki)

Zircon and monazite from the three samples in the northernector of the study area (EGB-10-71, -72, -74) yield broadly similar
ge results. The range in zircon spot ages from sample EGB-10-711042 ± 28 to 842 ± 30 Ma) is within error of the spot ages fromample EGB-10-74 (1005 ± 22 to 874 ± 20 Ma), and implies pro-racted growth during a high-temperature history. Zircon from
ge within domain groups.

EGB-10-72 yields a weighted mean age of 950 ± 17 Ma. Monazitespot ages are less scattered as compared to zircon. Monazite fromsample EGB-10-74 yields spot ages from 980 ± 15 to 921 ± 15 Ma,although monazite from sample EGB-10-72 defines a weightedmean age of 964 ± 7 Ma. These age populations are interpretedas evidence for protracted monazite growth during the high-temperature retrograde evolution to the solidus from ca 980 to ca920 Ma.

Monazite analyses from two high Mg–Al granulites near Sunki,reported in Korhonen et al. (2011), show slight reverse discordance,indicating excess 206Pb. For this reason, 207Pb/235U ages were con-sidered to be more reliable, as excess 206Pb does not affect the207Pb/235U ratio (e.g. Kirkland et al., 2009). Monazite from bothsamples yielded weighted mean ages of ca 980 Ma, with a spread of207Pb/235U spot ages from ca 1043 to ca 922 Ma. A monazite inclu-
sion in an orthopyroxene porphyroblast was interpreted to date thelate prograde growth of the peak minerals at ca 1042 Ma. Althoughzircon and monazite from the samples in the present study yieldyounger weighted mean ages as compared to the data from the





Rims23.1 M 168 199 1.22 0.000 6.372 0.891 0.06982 1.18877 940 8 923 24 −1.914.1 M 36 358 10.18 1.242 6.774 1.782 0.06985 6.25762 888 15 924 129 4.22.1 M 307 179 0.60 0.791 6.288 6.606 0.07008 4.99267 951 58 931 102 −2.46.1 M 47 471 10.36 0.825 6.191 1.582 0.07056 4.24194 965 14 945 87 −2.311.1 M 50 426 8.78 −0.303 5.765 1.389 0.07164 2.72176 1031 13 976 55 −6.217.1 M 255 408 1.65 −0.058 6.300 0.845 0.07166 1.18090 950 7 976 24 2.94.1 M 211 154 0.75 −0.076 5.758 3.686 0.07306 5.74584 1032 35 1015 116 −1.816.1 M 68 74 1.12 −0.081 5.837 2.325 0.07380 3.48057 1019 22 1036 70 1.75.1 M 64 62 1.00 −0.318 5.675 2.644 0.07451 2.34629 1046 26 1055 47 0.99.1 M 264 283 1.11 0.000 5.555 3.715 0.07463 3.33568 1067 37 1059 67 −0.9

Rim ages not included in calculation of weighted mean age19.1 M 131 323 2.54 0.252 7.660 0.941 0.06445 2.20482 791 7 756 47 −4.98.1 M 44 811 18.94 1.081 8.152 1.528 0.06494 7.72196 746 11 772 163 3.620.1* D 53 404 7.82 1.153 6.058 1.978 0.06358 6.60632 985 18 728 140 −38.121.1* D 89 196 2.27 0.488 6.212 2.408 0.06657 3.47858 962 22 824 73 −18.03.1* D 143 82 0.59 0.080 8.448 2.044 0.06679 3.19249 721 14 831 67 14.012.1* D 43 322 7.73 1.287 10.432 1.508 0.06773 7.16697 590 9 860 149 32.815.1* D 37 386 10.69 0.000 5.682 1.534 0.07103 4.87412 1045 15 958 100 −9.818.1* D 70 243 3.56 −0.192 5.162 7.107 0.07198 2.83469 1141 74 985 58 −17.313.1* D 26 531 21.21 0.234 6.609 1.868 0.07323 3.85807 908 16 1020 78 11.810.1* D 24 569 24.99 −0.520 6.517 1.972 0.07323 6.41161 920 17 1020 130 10.51.1* D 41 767 19.22 −0.482 5.940 1.630 0.07776 3.68088 1003 15 1141 73 13.022.1* D 63 987 16.08 0.000 5.854 1.222 0.07900 3.73158 1017 11 1172 74 14.37.1* D 45 413 9.43 0.530 6.211 4.441 0.07910 6.27673 962 40 1175 124 19.4

CoresC.10 C 906 38 0.04 −0.019 6.686 1.445 0.07088 1.30674 899 12 954 27 6.2C.3 C 848 169 0.21 −0.009 4.260 4.095 0.08533 4.05457 1359 50 1323 79 −3.0C.5 C 317 90 0.29 −0.011 4.393 6.599 0.08567 4.25081 1322 79 1331 82 0.7C.15 C 1216 174 0.15 0.009 3.275 2.489 0.10011 1.52481 1718 38 1626 28 −6.4C.2 C 547 59 0.11 0.031 3.210 1.561 0.10327 2.57144 1748 24 1684 47 −4.4C.9 C 485 50 0.11 0.061 3.001 3.840 0.10787 4.05563 1854 62 1764 74 −5.9C.8 C 924 87 0.10 0.023 3.146 7.177 0.11085 9.93569 1779 112 1813 180 2.2C.1B* D 1121 439 0.40 −0.014 6.214 6.947 0.06789 7.35875 962 62 865 153 −12.0C.1* D 710 374 0.54 0.071 7.609 1.158 0.06918 0.94572 796 9 904 19 12.7C.1C* D 737 333 0.47 0.018 7.298 0.824 0.07136 8.58796 828 6 968 175 15.4C.4* D 553 178 0.33 −0.020 6.635 3.348 0.07427 4.18336 905 28 1049 84 14.7C.7* D 845 68 0.08 0.016 5.318 4.583 0.08533 5.85080 1111 47 1323 113 17.5C.13* D 727 121 0.17 0.032 5.130 4.363 0.08680 6.37585 1148 46 1356 123 16.7C.14* D 982 285 0.30 0.016 5.045 2.327 0.09166 5.78754 1166 25 1460 110 22.0C.16* D 693 133 0.20 0.020 2.787 2.862 0.10184 3.75241 1977 49 1658 69 −22.4C.6* D 680 92 0.14 −0.018 2.655 2.865 0.10243 2.31609 2061 51 1669 43 −27.5C.12* D 592 187 0.33 0.036 2.621 0.667 0.10741 5.14972 2083 12 1756 94 −21.8C.11* D 674 50 0.08 0.008 3.376 2.137 0.11561 5.39177 1673 31 1889 97 13.0

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).A rom thC oderat

06Pb a

SS((mspfs

grcitbctt

ll errors are at the 1� level; f204% is the percentage of common 206Pb, estimated f, core analysis; M, metamorphic growth; D, >10% discordant; luminescence: m, m

* Analyses with >10% discordance. Data arranged according to increasing 207Pb/2

unki high Mg–Al granulites, the spread in monazite spot ages fromunki is similar to the range of zircon spot ages in the enderbitesample EGB-10-71; Fig. 8a, Table 2) and in the host migmatitesamples EGB-10-72, -74; Fig. 8c and g, Tables 3 and 5). Further-

ore, the weighted mean monazite ages of ca 980 Ma are broadlyimilar to two 207Pb/206Pb spot ages from zircon cores in sam-le EGB-10-71 (Table 2). A similar age of ca 979 Ma was reportedor emplacement of porphyritic charnockite collected about 60 kmouth of this area by Grew and Manton (1986).

The breakdown of LREE- and Zr-bearing phases during the pro-rade history may result in the growth of monazite and zircon,espectively, prior to peak metamorphism. Therefore the spread ofoncordant spot ages in each sample is likely to have geologic signif-cance, and may record protracted accessory mineral growth duringhe early high-to-ultrahigh temperature history. Nevertheless, the
ulk of zircon and monazite growth is predicted to occur duringrystallization of residual melt (cf. Kelsey et al., 2008) retained athe melt percolation threshold (Cheadle et al., 2004). Therefore,he weighted mean ages are interpreted as statistically valid; they
e measured 204Pb; grain spot is the individual grain and analysis identification.e; b, bright; d, dark.ge within domain groups.

will typically record the timing of melt crystallization close to thesolidus, possibly by diffusive loss of H2O (cf. White and Powell,2010), even though accessory mineral growth will have occurredover a range of temperature (cf. Kelsey et al., 2008) and, therefore,time according to the cooling rate.

Although the monazite and zircon weighted mean ages of ca966 and 950 Ma in sample EGB-10-72 overlap at 2� uncertainty,and the range of spot ages for each is similar, within the concord-ant age population the oldest of the monazite spot ages is older thanthe oldest of the zircon spot ages in the same sample (Fig. 8e and f).The same is broadly true for the range of spot ages for monazite andzircon in sample EGB-10-74, although in this case the zircon agesextend to <900 Ma. These observations contrast with the postu-late that zircon growth in residual pelites typically begins at highertemperatures than monazite (cf. Kelsey et al., 2008). In addition, the
Sunki samples yield weighted mean ages from monazite that areolder than the monazite weighted mean age from sample EGB-10-72. Thus, residual melt in the Sunki rocks may have been trappedby the percolation threshold earlier than in the migmatite sample.



Spot Setting Fig. 5 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date(Ma)

±1� Date(Ma)

±1�

3.1 in cd (a) 3065 120,048 40.5 0.309 6.672 1.341 0.07113 0.54363 900 11 961 11 6.83.2 701 146,365 215.9 1.137 6.317 1.404 0.06919 1.09731 947 13 904 23 −5.13.3 2126 121,220 58.9 0.375 6.478 1.141 0.07100 0.63018 925 10 958 13 3.6

4.1 in cd (b) 2690 116,027 44.6 0.223 6.330 1.112 0.07038 0.56651 946 10 940 12 −0.7

4.2 2105 132,248 64.9 0.430 6.084 1.149 0.07031 0.63182 981 10 937 13 −5.04.3 2618 131,902 52.1 0.309 6.398 1.345 0.07065 0.94788 936 12 947 19 1.34.4 1255 156,864 129.2 0.926 6.751 1.260 0.07092 0.88297 890 11 955 18 7.2

6.1 in opx,adj tocd

(c) 3502 123,409 36.4 0.219 6.452 1.211 0.07134 0.75920 929 10 967 15 4.3

6.2 902 226,630 259.6 1.321 6.416 1.336 0.07213 0.99531 934 12 990 20 6.1

7.1 in opx,adj tocd

(d) 2484 123,583 51.4 0.238 6.618 1.388 0.07098 0.58623 907 12 957 12 5.6

7.2* 940 216,404 237.8 1.316 6.281 1.315 0.06818 0.97622 952 12 874 20 −9.77.3 1587 115,888 75.5 0.373 6.389 1.180 0.07175 0.71367 937 10 979 15 4.67.4* 788 183,986 241.3 1.363 5.985 1.363 0.06753 1.03590 996 13 854 22 −17.9

8.1 in opx,adj. tocd

(i) 893 128,683 148.8 0.801 6.161 1.331 0.07188 0.97292 970 12 983 20 1.4

8.3 1399 124,626 92.1 0.479 6.399 1.208 0.07143 0.77685 936 11 970 16 3.78.4 2245 117,877 54.3 0.309 6.323 1.124 0.07094 0.58772 946 10 956 12 1.0

12.1 opx–sill,near cd

(e) 1652 85,131 53.2 0.340 6.395 1.174 0.07069 1.27097 937 10 949 26 1.4

12.2 1662 82,058 51.0 0.186 6.408 1.172 0.07066 0.70757 935 10 948 14 1.412.3 1615 87,155 55.7 0.332 6.324 1.174 0.07097 0.69961 946 10 956 14 1.112.4 1664 91,794 57.0 0.357 6.277 1.414 0.07074 0.69725 953 13 950 14 −0.312.5 1683 86,175 52.9 0.222 6.392 1.169 0.07018 0.69764 937 10 933 14 −0.412.6 1629 81,877 51.9 0.181 6.395 1.172 0.07092 0.70410 937 10 955 14 2.1

13.1 opx–sill (f) 1201 92,063 79.2 0.417 6.464 1.217 0.07015 0.79762 927 11 933 16 0.6

13.2 1294 102,949 82.2 0.288 6.150 1.224 0.07170 0.78397 971 11 977 16 0.713.3 2201 83,545 39.2 0.208 6.576 1.139 0.06912 0.65206 913 10 902 13 −1.213.4 1284 97,972 78.8 0.451 6.492 1.263 0.07034 0.80152 924 11 938 16 1.713.5 1076 91,575 88.0 0.369 6.244 1.735 0.07066 0.89769 958 15 947 18 −1.113.6 1128 95,306 87.3 0.375 6.418 1.256 0.07045 0.87001 933 11 941 18 0.9

17.1 opx–sill (h) 1243 85,794 71.3 0.425 6.401 1.482 0.07087 0.76445 936 13 954 16 2.0

17.2 1530 103,934 70.2 0.491 6.350 1.174 0.07236 0.68569 943 10 996 14 5.817.3 1216 89,023 75.7 0.400 6.433 1.218 0.07104 1.22763 931 11 958 25 3.0

18.1 cd, nearopx–sill

(g) 911 100,031 113.5 0.545 6.434 1.277 0.07114 0.89696 931 11 962 18 3.4

18.2 1198 106,481 91.9 0.540 6.468 1.545 0.07180 0.80384 927 13 980 16 5.918.3 1240 89,124 74.3 0.590 6.708 1.224 0.06965 0.81907 896 10 918 17 2.6

19.1 cd, nearopx–sill

(l) 1135 96,761 88.1 0.426 6.384 1.227 0.07002 0.81595 938 11 929 17 −1.1

19.2 1092 96,419 91.2 0.577 6.460 1.779 0.07051 0.82841 928 15 943 17 1.819.3 1001 97,790 100.9 0.549 6.390 1.255 0.07131 0.85946 937 11 966 18 3.219.4 1053 95,489 93.7 0.442 6.477 1.238 0.07124 0.83573 926 11 964 17 4.319.5 1053 95,564 93.8 0.613 6.381 1.250 0.07151 0.83793 939 11 972 17 3.7

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).A 206 m the 204

aa

ghted

AbEe

iz

ll errors are at the 1� level; f204% is the percentage of common Pb, estimated frorranged by analysis in order to preserve petrographic setting informationdj., ajdacent to; cd, cordierite; opx, orthopyroxene; sill, sillimanite.

* Analyses with >10% discordance, which were not included in calculation of wei

s a result, during cooling the residual melt in these rocks may haveecome saturated in LREE at a higher temperature than in sampleGB-10-72, which, in turn, may have led to growth of monazite
arlier.
The timing of enderbite emplacement (sample EGB-10-71) isnferred from two concordant analyses from dark, oscillatory-oned cores that yield ages of 1009 ± 22 and 973 ± 24 Ma. These

measured Pb; grain spot is the individual grain and analysis identification. Data

mean age.

ages are consistent with the timing of the dominant charnockite-forming event in the Eastern Ghats Province at ca 1000–900 Ma(reviewed in Rajesh, 2012). In this interpretation, emplacement
of enderbite into the surrounding pelitic migmatite gneisses (asrepresented by sample EGB-10-72) was contemporaneous withthe immediate post-peak P–T conditions recorded at ca 980 Ma inhigh Mg–Al granulites at the Sunki locality to the west-southwest



Spot Setting Fig. 5 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date(Ma)

±1� Date(Ma)

±1�

1.1 in g (s) 2065 95,006 47.5 0.205 6.527 1.491 0.07041 0.56319 919 13 940 12 2.51.2** 3793 97,282 26.5 0.131 6.324 1.170 0.06848 0.55934 946 10 883 12 −7.71.3 2359 91,374 40.0 0.198 6.440 1.145 0.07062 0.49578 930 10 946 10 1.81.4 2438 98,791 41.9 0.126 6.442 1.156 0.07046 0.51819 930 10 942 11 1.31.5 2043 91,926 46.5 0.265 6.234 1.319 0.07106 0.55408 959 12 959 11 0.0

2.1 in g (r) 2559 105,079 42.4 0.281 6.457 1.337 0.07015 0.51901 928 12 933 11 0.52.2 2568 98,141 39.5 0.153 6.520 1.144 0.07002 0.49515 920 10 929 10 1.02.3 3656 88,709 25.1 −0.046 6.402 1.153 0.07116 0.51698 936 10 962 11 2.9

3.1 in cd (j) 2730 85,182 32.2 0.200 6.351 1.142 0.07026 0.48429 943 10 936 10 −0.83.2 2615 80,572 31.8 0.151 6.360 1.472 0.07076 0.47309 941 13 951 10 1.03.3 2609 85,860 34.0 0.233 6.315 1.247 0.07115 0.47505 948 11 962 10 1.6

4.1 in q,nearcd–kfs

(k) 1317 88,445 69.4 0.342 6.392 1.218 0.07214 0.67329 937 11 990 14 5.7

4.2 2399 76,086 32.8 0.188 6.442 1.302 0.07058 0.49448 930 11 945 10 1.74.3 2564 70,241 28.3 0.075 6.458 1.144 0.07046 0.49590 928 10 942 10 1.6

8.1 adj. tocd andopx

(o) 2393 83,537 36.1 0.143 6.371 1.303 0.07056 0.87869 940 11 945 18 0.6

8.2 2565 73,369 29.6 0.145 6.423 1.143 0.07004 0.49220 933 10 930 10 −0.48.3 2575 80,139 32.2 0.142 6.467 1.299 0.07014 0.94039 927 11 932 19 0.7

9.1 in opx (m) 2528 83,229 34.0 0.232 6.430 1.148 0.07031 0.50667 932 10 937 10 0.69.2 1956 83,630 44.2 0.108 6.294 1.420 0.07124 0.55358 950 13 964 11 1.5

10.1 cd–kfs (p) 2291 81,392 36.7 0.128 6.363 1.301 0.07052 0.51794 941 11 943 11 0.310.2 2240 85,519 39.5 0.203 6.407 1.158 0.07092 0.52671 935 10 955 11 2.310.3 2284 81,786 37.0 0.212 6.318 1.155 0.07084 0.51757 947 10 953 11 0.6

11.1 adj. tocoarsesill

(q) 1660 93,452 58.2 0.283 6.447 1.184 0.07134 0.59091 930 10 967 12 4.2

11.2 2793 92,531 34.2 0.183 6.320 1.137 0.07071 0.46347 947 10 949 9 0.211.3 4127 94,587 23.7 0.111 6.300 1.191 0.07125 0.38688 950 11 965 8 1.711.4 2464 92,665 38.9 0.218 6.317 1.284 0.06981 0.50680 947 11 923 10 −2.911.5 2744 88,025 33.1 0.120 6.491 1.137 0.06999 0.47115 924 10 928 10 0.511.6 2413 87,889 37.6 0.190 6.395 1.150 0.07023 0.91806 937 10 935 19 −0.2

12.1 q, nearcd–kfs

(n) 2686 98,346 37.8 0.190 6.430 1.303 0.07114 0.49245 932 11 961 10 3.3

12.2 2769 96,083 35.9 0.137 6.454 1.139 0.07079 0.47564 929 10 951 10 2.612.3 2680 96,455 37.2 0.106 6.375 1.143 0.07085 0.48143 939 10 953 10 1.512.4 2969 91,736 31.9 0.158 6.336 1.235 0.07033 0.46010 945 11 938 9 −0.812.5 2736 89,899 33.9 0.157 6.380 1.157 0.07059 0.47620 939 10 946 10 0.812.6 2379 95,979 41.7 0.155 6.278 1.355 0.07095 0.50659 953 12 956 10 0.4

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification. Dataarranged by analysis in order to preserve petrographic setting information.a artz; s

((iBPfmp1tuistca

dj., ajdacent to; cd, cordierite; g, garnet; kfs, K-feldspar;opx, orthopyroxene; q, qu** Not included in calculation of weighted mean age.

Fig. 1b). At Sunki, the peak P–T conditions of T >950 ◦C at P >9.5 kbarKorhonen et al., 2011) were followed by close-to-isobaric cool-ng to the solidus (Fig. 9a, P–T–t paths ND1 and NSK; Korhonen,rown and Clark, unpublished data). In the absence of quantitative–T data from the migmatites, by analogy with the P–T–t pathor the high Mg–Al granulites at Sunki we interpret the younger

onazite and zircon weighted mean ages from migmatite sam-les EGB-10-72 and -74 to be consistent with a period of ca5–30 My of close-to-isobaric cooling from the peak P–T conditionso a lower temperature solidus than that for the highly resid-al granulites. Further, we infer that the enderbite was emplaced

nto suprasolidus crust at a temperature that must have been the
ame as or more likely hotter than the ambient temperature ofhe host rocks as suggested by field observations showing diffuseontacts between the enderbite and leucosome from migmatitend back-veining of leucosome into enderbite (Fig. 2a and b).
ill, sillimanite.

Subsequent low-volume melting of the crystallized enderbite in situ(Fig. 2a (arrows) and c) may have been facilitated by fluids releasedduring progressive crystallization of melt trapped by the percola-tion threshold in the host migmatites during around ca 950 Ma,consistent with growth of zircon in samples EGB-10-71 and -72.

Alternatively, the sparse number of zircon cores analysed inthe enderbite sample (EGB-10-71) leaves open the possibility thatthe enderbite may have been emplaced significantly before theUHT metamorphism, in which case all the spot ages obtained fromthis sample would be interpreted as related to the UHT metamor-phic event. Elsewhere in the Eastern Ghats orogenic belt an oldercharnockite-forming event has been identified at ca 1700–1600 Ma
(Dharma Rao et al., 2012b; Rajesh, 2012). However, the field obser-vations at this locality (Fig. 2) and the available zircon data fromthis sample are most simply interpreted as emplacement of theenderbite magma at ca 980 Ma during the UHT metamorphic event



Spot Setting Domain 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date(Ma)

±1� Date(Ma)

±1�

A-2.2 q (rim) M 108 256 2.45 0.932 5.997 3.598 0.06955 5.94983 994 33 915 122 −9.3A-2.1 M 98 254 2.69 0.000 6.157 2.965 0.07187 1.71904 970 27 982 35 1.3

A-3.5 q–ilmboundary

M 1392 120 0.09 1.183 6.637 2.377 0.06834 2.41512 905 20 879 50 −3.2

A-3.2 M 96 299 3.23 −0.088 6.538 2.377 0.06846 1.98773 917 20 882 41 −4.3A-3.6 M 1444 197 0.14 0.671 6.771 2.225 0.06957 0.89204 888 18 916 18 3.2A-3.7 M 1060 167 0.16 1.419 6.078 2.356 0.06990 1.35037 982 21 926 28 −6.6A-3.3 M 97 281 2.99 1.406 6.584 2.396 0.07120 4.40622 912 20 963 90 5.7

A-4.4 q–ilmboundary

M 141 199 1.46 0.733 6.675 2.349 0.06752 4.33028 900 20 854 90 −5.8

A-4.2 M 66 169 2.66 0.119 6.936 2.446 0.06999 2.40787 868 20 928 49 6.9A-4.3 M 97 304 3.25 0.000 6.495 2.389 0.07210 2.94411 923 21 989 60 7.1

A-5.1 ilm–biboundary

M 156 309 2.04 1.510 6.448 2.336 0.07019 4.03425 929 20 934 83 0.5

A-5.3 M 100 257 2.65 0.251 6.584 2.380 0.07127 2.36313 911 20 965 48 6.0A-5.2 M 167 351 2.17 −0.092 6.532 2.555 0.07165 1.41173 918 22 976 29 6.4A-5.5 M 119 403 3.50 0.247 6.545 2.369 0.07205 2.31391 917 20 987 47 7.7A-5.4 M 92 288 3.23 −0.365 6.221 3.510 0.07211 4.89724 961 31 989 100 3.1

A-6.1 g (rim) M 115 219 1.97 1.720 6.762 2.580 0.06722 4.96702 889 21 845 103 −5.6A-6.3 M 695 237 0.35 0.369 6.096 2.938 0.07040 1.94232 979 27 940 40 −4.5A-6.2 M 103 258 2.59 −0.166 6.652 2.590 0.07216 2.07153 903 22 990 42 9.5

A-7.1 in q M 268 282 1.09 0.265 6.441 2.278 0.06988 1.54221 930 20 925 32 −0.6

A-8.3 inmyrmekite

M 112 385 3.55 0.292 6.768 2.354 0.06682 2.43435 888 20 832 51 −7.2

A-8.2 M 136 501 3.79 0.179 6.810 2.329 0.06835 1.89221 883 19 879 39 −0.5

A-9.2 in pl M 145 549 3.90 0.301 6.779 2.330 0.06839 2.17350 887 19 881 45 −0.8

Ages not included in calculation of weighted mean ageA-3.4* q–ilm

boundaryD 114 226 2.06 1.511 6.655 2.386 0.07763 6.98370 902 20 1137 139 22.1

A-3.1* D 125 256 2.12 11.781 6.553 3.275 0.08303 28.10157 916 28 1270 548 29.9

A-4.1* q–ilmboundary

D 68 176 2.69 3.637 6.534 2.559 0.08468 7.85040 918 22 1308 152 32.0

A-8.1* inmyrmekite

D 155 521 3.48 4.482 6.563 2.465 0.08361 7.98266 914 21 1283 155 30.8

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.adj., ajdacent to; cd, cordierite; opx, orthopyroxene; sill, sillimanite.M pl, p2

f9

7bptctos(ttcdwttTo

, metamorphic growth; D, >10% discordant; bi, biotite; g, garnet; ilm, ilmenite;07Pb/206Pb age within grains.

* Analyses with >10% discordance.

ollowed by limited in situ anatexis and new zircon growth at ca50 Ma.

Field observations of the outcrop from which sample EGB-10-4 was collected constrain the timing of partial melting recordedy folded stromatic migmatite and patch migmatite to be syn-D2,robably corresponding to a late stage in the crystallization of meltrapped by the percolation threshold (Fig. 2e and f). The age of meltrystallization is interpreted at ca 950 Ma broadly constrains theiming of D2. The timing of syn- to post-D1a melting may haveccurred as early as ca 980 Ma, but the sparse occurrence of olderpot ages from zircon overgrowths in samples EGB-10-71 and -72ca 1195 to ca 1025 Ma) implies protracted zircon growth duringhe prograde history and/or during ongoing partial melting at closeo peak metamorphic conditions. The absence of ages older thana 1005 Ma in sample EGB-10-74 likely reflects enhanced zirconissolution in this sample, such that most inherited zircon grainsere dissolved into the melt during prograde metamorphism to

he peak UHT conditions, as indicated by fewer inherited cores inhis sample as compared to other samples (e.g. EGB-10-72; Fig. 3).he ca 1005 Ma age may provide an upper constraint on the timingf peak UHT metamorphic conditions in this sample.

lagioclase; q, quartz. Data arranged by (1) domain, (2) grains, and (3) increasing

6.1.2. Central sector of the study area (Anantagiri–Sunkarametta)Older (ca 970 Ma) and younger (ca 950 Ma) age populations are

also present in the central sector. The two sapphirine-bearing, highMg–Al granulite samples from Anantagiri (samples EGB-09-38, -39) show a broadly similar range of zircon spot ages (Fig. 8j andl). Zircon rim analyses from sample EGB-09-38 yielded spot agesranging from 1120 ± 41 to 794 ± 119 Ma. Broadly similar resultswere obtained from sample EGB-09-39, with spot ages between1059 ± 67 and 756 ± 47 Ma and a weighted mean 207Pb/206Pb ageof 970 ± 28 Ma; the weighted mean age is interpreted to recordthe age of final crystallization of residual melt following close-to-isobaric cooling to the solidus (Fig. 9a, P–T–t path C39; Korhonen,Brown and Clark, unpublished data).

Monazite from the high Mg–Al granulites from Sunkaram-etta yielded slightly younger ages, with weighted mean ages of953 ± 7 Ma for sample EGB-10-82 and 948 ± 5 Ma for sample EGB-10-84 (Table 1). The probabilities of fit for these calculated ages are
very low (=0.004 and 0.015, respectively), implying that the uncer-tainties on the individual data do not account for the protracted agespread. Although only one discrete age population may be resolved,the range of protracted ages is interpreted to have geologic



Spot Setting 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date(Ma)

±1� Date(Ma)

±1�

ca 822 Ma groupA-1.6 opx–q

boundary468 51,665 114.0 0.479 7.480 1.902 0.06594 1.77573 809 14 804 37 −0.6

A-1.2 796 107,757 139.9 0.968 7.559 2.057 0.06609 2.09636 801 15 809 44 1.1A-1.4 227 11,124 50.7 0.214 7.501 2.399 0.06631 2.69181 807 18 816 56 1.2A-1.1 293 25,976 91.7 −0.684 7.358 2.112 0.06652 1.68282 821 16 823 35 0.2A-1.5 276 19,958 74.6 0.141 7.255 1.984 0.06686 1.54167 832 15 833 32 0.1A-1.3 299 22,775 78.6 0.566 7.393 2.352 0.06695 1.62681 818 18 836 34 2.3

ca 968 Ma groupB-1.5 opx–q

boundary679 34,832 53.0 0.274 6.696 9.795 0.06848 9.27874 897 82 883 192 −1.7

B-1.2 699 39,094 57.8 0.044 6.351 1.879 0.06963 0.87129 943 16 917 18 −3.0B-1.1 604 42,175 72.1 0.316 6.154 1.899 0.07051 1.22110 971 17 943 25 −3.1B-1.6 751 36,494 50.2 0.313 6.217 2.758 0.07100 2.62466 961 25 957 54 −0.5B-1.3 563 42,293 77.6 0.031 6.185 1.909 0.07190 1.79867 966 17 983 37 1.9B-1.7 594 40,420 70.3 0.050 6.167 5.223 0.07242 3.35466 969 47 998 68 3.1B-1.4 534 41,071 79.4 0.808 6.258 1.916 0.07298 1.33295 956 17 1014 27 6.1

B-4.4 opx–sill 638 38,691 62.6 −0.061 6.130 1.892 0.07093 0.87803 974 17 955 18 −2.1B-4.1 690 36,545 54.8 0.001 6.268 1.883 0.07247 0.89090 954 17 999 18 4.8B-4.3 800 37,682 48.7 0.646 6.271 1.869 0.07254 0.92571 954 17 1001 19 5.1B-4.2 643 37,197 59.8 0.561 6.181 2.116 0.07266 1.30116 967 19 1005 26 4.1

B-5.1 opx–sill 694 38,950 58.0 0.146 6.181 1.886 0.07161 0.89127 967 17 975 18 0.9

B-6.1 in opx 661 39,717 62.1 0.215 6.192 1.891 0.07033 0.85697 965 17 938 18 −3.1

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.oD

snatlKmaat

dTrafds1h

6M

0ssSwttis

px, orthopyroxene; q, quartz; sill, sillimanite.ata arranged according to increasing 207Pb/206Pb age within grains.

ignificance. The majority of monazite is inferred to have grownear the conditions of the solidus, therefore the weighted meanges are interpreted to be statistically valid ages that record theiming of final crystallization of residual melt following a CCW evo-ution and cooling to the solidus (Fig. 9a, P–T–t paths C82 and C82;orhonen, Brown and Clark, unpublished data). Cuspate embay-ents in core domains of two monazite inclusions in garnet (Fig. 6r

nd s) indicate that fluid-assisted dissolution of pre-existing grainsnd reprecipitation in the presence of melt also occurred duringhe high-temperature retrograde evolution.

Additional age information for the Sunkarametta locality iserived from sample EG-San3A from the study of Bose et al. (2011).his orthopyroxene-bearing quartzofeldspathic orthogneiss has aeported location about 120 m southwest of samples EGB-10-82nd EGB-10-84. It yields a range of discordant 207Pb/206Pb spot agesrom recrystallized domains in zircon from ca 1600 to ca 1100 Ma,efining a lower intercept age of 1008 ± 49 Ma. Near-concordantpot ages from undisturbed oscillatory-zoned grains range from ca025 to ca 950 Ma. A single spot age from an overgrowth domainas an age of ca 980 Ma.

.1.3. Southern sector of the study area (Paderu–Gangarajaadugula)

The monazite weighted mean age of 968 ± 20 Ma in sample EGB-9-04 is older than the zircon weighted mean age of 929 ± 17 Ma inample EGB-09-01 (Table 1), although these samples yield a broadlyimilar range of concordant spot ages. Similar to the samples fromunkarametta in the central sector, the probability of fit for theeighted mean age in sample EG-09-04 is low (=0.02). However,

he weighted mean age is interpreted to be statistically valid ando record the timing of final crystallization of residual melt, assum-ng that the majority of accessory phase growth occurred near theolidus. The weighted mean ages from samples EGB-09-01 and -04

are within error of the ca 980–970 Ma and ca 950 Ma ages recordedin samples from the northern and central sectors of the study area.

Sample EGB-09-04 records peak metamorphic conditions of∼945 ◦C and 8.3 kbar followed by close-to-isobaric cooling to thesolidus at 900 ◦C (Fig. 9a, P–T–t path S; Korhonen, Brown andClark, unpublished data). Sample EGB-09-01 preserves evidencefor close-to-isobaric cooling just above the solidus, although esti-mates for peak conditions are more poorly constrained at >860 ◦C at6–11 kbar, with the minimum temperature defined by the solidus(Fig. 9a). Although the temperature of the solidus will be sensi-tive to the H2O content used in the phase equilibria modelling, themineral assemblages in these samples provide tight constraints onthe appropriate H2O content to be used in the modelling. Sincethe majority of accessory phase growth is predicted to occur closeto the solidus, the ∼40 ◦C difference in the predicted temperatureof the solidi for these two samples would have resulted in a sig-nificant age difference if the cooling rate was sufficiently slow.Mezger and Cosca (1999) proposed a cooling rate of 3 ◦C/My basedon monazite and titanite ages from the northern part of the EasternGhats Province, which would result in an age difference of 13 Mafor this scenario. A lower cooling rate of 1 ◦C/My could account forthe 40 My difference between the monazite weighted mean age of968 ± 20 Ma in sample EGB-09-04 and the zircon weighted meanage of 929 ± 17 Ma in sample EGB-09-01 (Fig. 9b).

The zircon age results from sample EGB-09-19 are more ambigu-ous. Three grains yield spot ages of ca 965 to ca 960 Ma (Table 13),and are within uncertainty of the ca 950 Ma ages recorded in othersamples. However, there is also evidence for a younger history, asindicated by the lower intercept age of 855 + 14/−15 Ma (Fig. 8p)
and the younger population from the concordant analyses (spotages from ca 909 to ca 885 Ma, Table 13). Sparse evidence for ayounger overprinting event is also recorded by a monazite grainalong the grain boundary between orthopyroxene and quartz in



Spot Setting Domain 238U (ppm) 232Th (ppm) 232Th/238U f204% 238U/206Pb* ±� (%) 207Pb*/206Pb* ±� (%) 238U/206Pb* 207Pb*/206Pb* Disc. (%)

Date(Ma)

±1� Date(Ma)

±1�

A-1.2 q (rim) M 720 88 0.13 0.026 6.839 1.155 0.07114 0.59522 880 10 962 12 9.1

A-3.1 adj. g, q M 598 138 0.24 0.012 6.334 2.543 0.07127 2.35148 945 22 965 48 2.3A-3.2 M 534 87 0.17 0.055 5.694 1.878 0.07732 2.29184 1043 18 1129 46 8.3

A-4.2 in g (nearilm)

M 664 143 0.22 −0.013 6.852 0.687 0.06854 0.73416 878 6 885 15 0.8

A-4.3 M 578 118 0.21 0.014 6.843 1.070 0.06932 0.74891 879 9 908 15 3.4A-4.1 M 557 126 0.23 0.039 6.677 1.018 0.07110 0.81765 900 9 960 17 6.8

A-5.2 in g (nearcrack)

M 979 112 0.12 0.128 7.025 0.764 0.06913 0.72560 858 6 903 15 5.3

B-5.1 M 737 156 0.22 −0.031 6.757 0.618 0.06933 0.66756 890 5 909 14 2.2

A-2.1 in q C 574 438 0.79 0.195 3.454 1.181 0.10101 1.21948 1639 17 1643 23 0.2

A-1.1* q (rim) D 1066 108 0.10 0.186 6.240 1.354 0.07464 2.22808 958 12 1059 45 10.2

A-6.1* q (rim) D 422 246 0.60 0.057 3.645 4.125 0.08496 11.26076 1563 57 1315 218 −21.3A-6.2* D 236 172 0.75 0.210 4.291 3.209 0.09892 6.95951 1350 39 1604 130 17.5A-6.3* D 221 178 0.83 −0.020 2.443 12.700 0.10156 7.84884 2212 238 1653 145 −40.0

B-1.3* q–plboundary

D 426 66 0.16 0.161 5.610 1.714 0.07915 1.72838 1057 17 1176 34 10.9

B-1.1* D 99 69 0.72 0.162 2.350 27.890 0.09386 15.49731 2285 537 1505 293 −61.8B-1.2* D 131 95 0.75 −0.043 2.682 2.809 0.10729 2.39624 2043 49 1754 44 −19.2

B-2.4* in g (nearcrack)

D 697 77 0.11 0.062 5.844 2.722 0.07855 1.59053 1018 26 1161 32 13.3

B-2.1* D 968 127 0.14 0.020 5.670 4.774 0.08360 8.58502 1047 46 1283 167 19.9B-2.5* D 460 331 0.74 −0.022 4.370 1.523 0.09251 0.63013 1328 18 1478 12 11.2


D 985 41 0.04 0.014 5.733 1.761 0.07809 1.87266 1037 17 1149 37 10.6

B-3.1* D 741 227 0.32 −0.015 4.724 3.442 0.08729 4.70006 1238 39 1367 90 10.4


D 282 177 0.65 0.011 3.082 1.211 0.10079 2.26358 1812 19 1639 42 −12.1

Ion microprobe U–Pb data. Disc (%) is the age discordance as defined = 100 × (1 − [(238U/206Pb date) − (207Pb/206Pb date)]/(207Pb/206Pb date)).All errors are at the 1� level; f204% is the percentage of common 206Pb, estimated from the measured 204Pb; grain spot is the individual grain and analysis identification.C ite; pl

3) incr

sanz(aAaodtt

6

UPolssptwti

, core analysis; M, metamorphic growth; D, >10% discordant; g, garnet; ilm, ilmen* Analyses with >10% discordance. Data arranged by (1) domain, (2) grains, and (

ample EGB-09-04 (weighted mean age of 822 ± 31 Ma; Table 1),nd spot ages younger than ca 900 Ma recorded in samples from theorthern and central sectors of the study area. Similar ages fromircon and monazite have been interpreted by Simmat and Raith2008) to date local- to regional-scale ductile to brittle deformationnd associated fluid infiltration during the interval ca 900–750 Ma.lternatively, these ages could be related to the release of fluidsssociated with the waning stages of cooling and crystallizationf residual melt trapped by the percolation threshold at greaterepth in the orogeny, since the decay in the thermal structure ofhe orogeny is expected to young downwards to greater depth withime.

.2. Implications for the Eastern Ghats Province

Each of the sample localities in this study preserves evidence forHT metamorphism. Conditions of peak metamorphism from theaderu locality (samples EGB-09-01, -04) in the southern sectorf the study area are estimated to be ∼945 ◦C and 8.3 kbar, fol-owed by close-to-isobaric cooling to conditions of the elevatedolidus (Fig. 9a). Modelling results from samples in the centralector yield similar constraints (Fig. 9a). Peak conditions for sam-les from the Sunki locality in the northern sector were estimated
o be in excess of 950 ◦C and 9.5 kbar, although pressure was notell constrained (Korhonen et al., 2011). In many samples from all
hree sectors of the Eastern Ghats Province, cordierite–K-feldsparntergrowths occur. These are interpreted to represent peak to

, plagioclase; q, quartz.easing 207Pb/206Pb age within grains.

immediate post-peak retrograde reaction between osumilite andmelt and together with the early development of cordierite in somesamples requires that the prograde evolution was one of coevalincreasing temperature and increasing pressure (Korhonen, Brownand Clark, unpublished data). A reinvestigation of the Sunki sam-ples suggests that the pressure estimated by Korhonen et al. (2011)may have been high. New results indicate that the peak and retro-grade P–T–t conditions recorded in the Sunki samples are similar tothose retrieved from samples from the central and southern sectorsof the study area, as summarized in Fig. 9a. In summary, all samplesexhibit close-to-isobaric cooling to the solidus from broadly similarpeak P–T conditions and several define CCW P–T–t paths (Korho-nen, Brown and Clark, unpublished data). Thus, the results fromthis study demonstrate that widely spaced localities in the east-ern Ghats Province share a broadly similar tectono-metamorphichistory.

The spread of concordant 207Pb/206Pb spot ages between ca 1130and ca 980 Ma is interpreted as the approximate time span forreaching the peak of UHT metamorphism and cooling to tempera-tures close to the elevated solidi for the samples where it is inferredthat most new accessory mineral growth occurred; this implies along period of heating to and slow cooling from peak UHT con-ditions. Following the peak of UHT metamorphism, most samples
record close-to-isobaric cooling to an elevated solidus between ∼8and ∼7.5 kbar (Fig. 10). These residual granulites yield a spreadof weighted mean 207Pb/206Pb ages, ranging from ca 980 to ca930 Ma; they are interpreted as the best estimate for the timing of


Fig. 9. P–T–t evolution of studied samples. (a) P–T paths and pos-itions of the solidi constrained by phase equilibria modelling in theNa2O–CaO–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–Fe2O3 (NCKFMASHTO)chemical system. Methodology for modelling similar to that reported in Korhonenet al. (2011); the detailed results from this study will be presented elsewhere(Korhonen, Brown and Clark, unpublished data). Patterns for the solidi are shownin the legend and labelled with italic text. P–T–t paths are colour-coded arrows,correlated with the colour of the solidus. Results from the northern, central andsouthern sectors denoted by ‘Nxx’, ‘Cxx’ and ‘Sxx’, respectively, where xx refers tolast two digits of sample number. (b) Weighted mean 207Pb/206Pb age (Ma) versusestimated temperature of solidus (◦C) along P–T paths shown in Fig. 10a. Error barsfor age data are 95% confidence intervals and solidus temperature are ∼1�. (Forit

cosfa

a(nma

800 850 900 950 1000 1050

6

7

8

9

10

P (k

ba

r)

T (°C)

S01 C39S04

C84

C82

ND1NSK

Peak conditions

>>950°C, ~8 kbar

ca 930 ....... 980 Ma

929 ± 17 Ma

Fig. 10. Summary P–T–t path for the Eastern Ghats Province as a whole. The vari-

nterpretation of the references to colour in this figure legend, the reader is referredo the web version of this article.)

rystallization of residual melt trapped by the percolation thresh-ld and since the temperature of the solidus varies for each sample,o there is a range of ages (Fig. 9b). Thus, the temperature intervalrom the peak of UHT metamorphism to the solidus for each samplelso varies (Fig. 10).

There are similarities between the results presented herend the ages reported by Bose et al. (2011) and Das et al.
2011). These two studies interpreted oscillatory-zoned zircon withear-concordant ages ranging from ca 1780 to ca 1700 Ma to recordagmatic events in the source of the detrital grains, and discordant
ges from ca 1600 to ca 1100 Ma to represent mixing ages resulting

ability in the calculated weighted mean ages between the samples results mainlyfrom differences in the temperature of the solidi. See text for additional details.

from M1 UHT metamorphism and these detrital cores. The timing ofM1 UHT metamorphism was constrained to be ca 1030 to ca 990 Ma,based on chemical dates of monazite inclusions in orthopyrox-ene. Near concordant spot ages from zircon overgrowths betweenca 1000 and ca 900 Ma were interpreted by Bose et al. (2011) torecord a second granulite metamorphism (M2), which was pre-ceded and/or accompanied by emplacement of voluminous graniteat ca 990 Ma. However, it is likely that these two ‘events’ are partof one continuous P–T–t evolution through peak UHT metamorphicconditions. Das et al. (2011) estimated the timing of the M2 event tobe 953 ± 6 Ma based on seven concordant analyses from neoblasticzircon grains and overgrowths on pre-existing zircon, and explicitlyinfer that M2 was a separate tectonothermal event superimposedon UHT granulites that had already cooled from the M1 thermalpeak. Zircon growth at ca 900 Ma was interpreted by them to beassociated with later fluid-induced retrogression associated withmelt crystallization, whereas Bose et al. (2011) left open the possi-bility of younger ages being due to later tectonothermal reworkingor a Pan-African overprint.

The new results presented in this study allow for a more com-plete interpretation of the evolution of the Eastern Ghats Province.An important outcome is the inference that the age populationsbetween ca 1130 Ma and ca 930 Ma correspond to a single pro-grade, peak and retrograde metamorphic evolution, characterizedby close-to-isobaric cooling from peak UHT conditions to differentsolidi for individual samples (Fig. 10). The timing of final melt crys-tallization in each sample is broadly constrained by the monaziteand zircon weighted mean ages. However, the range of spot agesdoes suggest protracted accessory mineral growth during a long-lived high-temperature evolution involving an extended period ofheating followed by slow cooling and the possibility of ingress offluids from deeper in the crust. The variability in the calculatedweighted mean ages between the samples results mainly from dif-
ferences in the temperature of the solidi (e.g. Fig. 9b). In a slowlycooled terrane, these differences may result in distinct age popula-tions as proposed by Reno et al. (2012) and confirmed in this study.The dominant age population of ca 960 to ca 950 Ma that occurs

rian R

tBMfibbtii

EtitcbpCstmgEd2icFca

7

g9oeBaempttepyeArte

A

chaAaott


hroughout the Eastern Ghats Province (this study; Das et al., 2011;ose et al., 2011; Simmat and Raith, 2008; Bhattacharya et al., 2003;ezger and Cosca, 1999) might reflect broadly similar conditions of

nal melt crystallization in many parts of the Province, as suggestedy the cluster of solidi between 930–960 ◦C at 7.5–8 kbar predictedy the results of the phase equilibria modelling for the samples inhis study (Fig. 9). The emplacement of voluminous pophyritic gran-tes across the region between ca 985 and ca 955 Ma (summarizedn Dobmeier and Raith, 2003) is consistent with this interpretation.

The results from the Salur and Pachipenta localities (samplesGB-10-71, -72, -74) provide insight into the timing and condi-ions of enderbite emplacement. The charnockites and enderbitesn the Eastern Ghats Province are interpreted to be derived by par-ial melting of a hornblende-rich mafic source, with massif-typeharnockite representing the segregated partial melt and ender-ites representing a mixture composed of melt and entrainederitectic ± residual solids (Kar et al., 2003; Bhattacharya andhaudhary, 2010). Hornblende-breakdown melting of a maficource implies temperatures >900 ◦C, and the geochemistry of Pro-erozoic charnockites from Paderu and Sunki is consistent with

elting at relatively shallow depths in the stability field of pla-ioclase, as compared to Archaean charnockites elsewhere in theastern Ghats Province which were derived by melting at greaterepth in the stability field of garnet (Bhattacharya and Chaudhary,010). Thus, the petrogenesis of the charnockites and enderbites

s consistent with emplacement of magmas into hot, suprasolidusrust at ca 980 Ma during a single UHT tectono-metamorphic event.inal melt crystallization in the host rocks at ca 950 Ma further indi-ates that suprasolidus conditions in the crust were maintained forn additional 30 My.

. Conclusions

The Eastern Ghats Province records a single long-lived high-rade metamorphic evolution in the interval ca 1130 Ma to ca30 Ma. The timing of peak UHT metamorphism is estimated to belder than 980 Ma and possibly as old as 1042 ± 41 Ma (Korhonent al., 2011), consistent with the estimate of 1030–990 Ma fromose et al. (2011), with P–T conditions estimated to be >950 ◦Cnd ∼8 kbar. These peak metamorphic conditions preceded themplacement of regionally extensive charnockite–enderbite mag-as at ca 980 Ma. The predominant zircon and monazite age

opulations across the region in the interval ca 980–930 Ma recordhe immediate post-peak evolution, characterized by slow close-o-isobaric cooling from peak UHT conditions to ∼7.5 kbar at thelevated solidus for each sample (Fig. 10). Differences in the tem-erature of the solidi are responsible for the variability in theseounger age populations across the region (Fig. 9b), and the differ-nces in age are consistent with slow cooling at a rate of ∼1 ◦C/My.ges younger than ca 930 Ma are more enigmatic, but may beelated to the release of fluids associated with final melt crystalliza-ion at depth during the waning stages of this tectono-metamorphicvent.

cknowledgements

We would like to thank S. Dasgupta, B. Reno and S. Gupta forritical comments on an earlier version of this paper, and editorialandling by M. Satish-Kumar. SHRIMP analyses were undertakent the John de Laeter Centre for Mass Spectrometry, a Westernustralian state government supported Centre of Excellence. We
lso acknowledge the facilities, scientific and technical assistancef the Centre for Materials Research at Curtin University, andhe Australian Microscopy & Microanalysis Research Facility athe Centre for Microscopy, Characterisation & Analysis at the
esearch 234 (2013) 322– 350 349

University of Western Australia. We thank A. Josephs for assistancewith the SHRIMP at Curtin University. This project was fundedthrough the DIISR Australia–India Strategic Fund project ST030046.C. Clark acknowledges salary and research support from DECRA(DE120103067).

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