HP–UHP Metamorphic Belt in the East Kunlun Orogen: Final ...€¦ · Kunlun, the west part of the Qinling–Qilian–Kunlun Mountains (Fig. 1), is a long-lived orogenic belt with

HPndashUHP Metamorphic Belt in the East Kunlun

Orogen Final Closure of the Proto-Tethys Ocean

and Formation of the Pan-North-China

Continent

Shuguang Song 1 Hengzhe Bi1 Shengsheng Qi2 Liming Yang1

Mark B Allen3 Yaoling Niu3 Li Su4 and Wufu Li2

1MOE Key Laboratory of Orogenic Belt and Crustal Evolution School of Earth and Space Sciences Peking

University Beijing 100871 China 2Qinghai Bureau of Geological Survey Xining 810012 China 3Department of

Earth Sciences Durham University Durham DH1 3LE UK 4Institute of Earth Science and State Key Laboratory of

Geological Processes and Mineral Resources Chinese University of Geosciences Beijing 100083 China

Corresponding author E-mail sgsongpkueducn

Received April 8 2018 Accepted September 12 2018

ABSTRACT

The East Kunlun Orogen the northwestern part of the Central China Orogenic Belt is a long-livedaccretionary orogenic belt that records the evolution and eventual destruction of branches of the

Tethys Ocean from the Cambrian to the Triassic Here we report an Early Paleozoic eclogite belt that

extends for 500 km within the East Kunlun Orogen This belt consists of eclogite blocks metasedi-

mentary rocks and minor serpentinite blocks accompanied by ophiolites (530ndash460 Ma) and concur-

rent arc volcanic sequences and granitic plutons Geochemical data show that the eclogites have

normal mid-ocean ridge basalt- to ocean island basalt-like compositions UndashPb dating of metamorph-

ic zircons from eclogites and their surrounding rocks gave peak and retrograde metamorphic ages of430ndash410 Ma Coesite pseudomorphs in garnet quartz exsolution rods in omphacite and PndashT calcula-

tions suggest that some eclogites experienced ultrahigh-pressure (UHP) metamorphic conditions at

29ndash30 kbar and 610ndash675C these could represent oceanic crust subducted to and exhumed from

coesite-forming depths (100ndash120 km) The UHP metamorphic eclogite belt in the East Kunlun Orogen

may represent the final closure of the Proto-Tethys Ocean (opening at 580 Ma subduction initiating

at 520 Ma) at 430ndash410 Ma in the East Kunlun with the formation of the Pan-North-China Continentin the Early Paleozoic and expansion of the Paleo-Tethys Ocean in the south

Key words eclogite belt ultrahigh-pressure metamorphism Proto-Tethys Ocean East KunlunOrogen

INTRODUCTION

Eclogites carry information that is critical in understand-ing orogenic processes (eg Ernst 1988 Carswell 1990

Ernst amp Liou 1995) Together with ophiolites arc mag-

matism and the sedimentary fill of accretionary prisms

eclogites characterize orogenic belts associated

with paleo-ocean subduction (eg Agard et al 2009

Song et al 2013) and provide valuable information on

the processes and conditions of subduction andexhumation

The Proto-Tethys Ocean is an inconsistently used

concept for a supposed predecessor of the Paleo-Tethys Ocean which separated some blocks (eg the

QaidamndashQilian South China) from the northern mar-

gins of Gondwana in the Neoproterozoic (eg Li et al

2008 von Raumer amp Stampfli 2008 Xu et al 2015)

The evolution of Proto-Tethys is however ambiguous

concerning the timing of its opening and closing aswell as geological processes in the course of its shrink-

ing and transition to the Paleo-Tethys Ocean

J O U R N A L O F

P E T R O L O G Y

Journal of Petrology 2018 Vol 59 No 11 2043ndash2060

doi 101093petrologyegy089

Advance Access Publication Date 20 September 2018

Original Article

nloaded from httpsacadem

icoupcompetrologyarticle-abstract591120435104339 by U

niversity of Durham

user on 01 January 2019

The QinlingndashQilianndashKunlun orogenic belt (or the

Central China Orogenic Belt) lies in the central part of

China and is considered to have resulted from the con-

sumption of the Proto-Tethys (eg Yin amp Harrison 2000

Dong amp Santosh 2016 Song et al 2017) The EastKunlun the west part of the QinlingndashQilianndashKunlun

Mountains (Fig 1) is a long-lived orogenic belt with a

history from Cambrian to Triassic times which records

the orogenic evolution of the Proto- and Paleo-Tethys

oceans and holds the key to understanding the evolu-

tion of the ancient Tethys Ocean and formation of the

Chinese continent Eclogite blocks were reported byMeng et al (2013) and subsequently by Qi et al (2016)

at Wenquan in the east and by Qi et al (2014) at

Xiarihamu in the west of the East Kunlun Orogen (EKO)

(Fig 1) With the addition of a newly discovered

eclogite-bearing locality at Kehete in the mid-east a

500 km long eclogite-bearing high-pressure meta-morphic belt can be recognized within the EKO In this

study we present petrological geochemical and geo-

chronological studies of this eclogite belt We have

determined for the first time that some of the EKO eclo-

gites have experienced UHP metamorphism in

SilurianndashDevonian times This eclogite belt togetherwith accompanying ophiolites and arc volcanic rocks

represents the final closure of the Proto-Tethys Ocean

and continued convergence between fragments of

Eastern Gondwanaland and the North ChinandashTarim

continent

Mineral abbreviations are after Whitney amp Evans

(2010)

GEOLOGICAL SETTING AND PETROGRAPHY

The East Kunlun Orogen lies south of the Qaidam Block

(Fig 1) The basement of the Qaidam Block is largely

covered by thick sedimentary successions of a

Mesozoic to Cenozoic intracontinental basin The

Precambrian crystalline basement is mainly exposed at

the north and south margins of the block To the north

of the Qaidam Block is the North Qaidam ultrahigh-pressure metamorphic (UHPM) belt which consists of

various types of eclogite garnet peridotite coesite-

bearing metapelite and granitic gneiss The North

Qaidam UHPM belt is a continental collision zone

recording that the Qaidam Block had subducted north-

wards to depths of 200 km at 440ndash425 Ma (eg Song

et al 2014 and references therein) Further north theQilian Orogen consists of the South Qilian oceanic

accretionary belt the Central Qilian Block and the North

Qilian oceanic accretionary belt The South Qilian

oceanic accretionary belt (SQAB) is composed of

Cambrian ophiolites (535ndash500 Ma) and an Ordovician

intra-oceanic arc complex (470ndash440 Ma) (eg Songet al 2017 Zhang et al 2017) without high-pressure

rocks The North Qilian oceanic accretionary belt

(NQAB) consists of 550ndash450 Ma ophiolites 520ndash440 Ma

continental arc volcanic and plutonic rocks and 500ndash

440 Ma high-pressure metamorphic rocks Carpholite in

metapelites and lawsonite in eclogites and blueschistssuggest relatively cold oceanic subduction and high-

pressurelow-temperature (HPLT) metamorphism

(Song et al 2007 Zhang et al 2007) Therefore three

subparallel HPndashUHP belts are exposed in a 400 km wide

region in the northern Tibetan Plateau (Fig 1) These

HPndashUHP belts together with associated ophiolites and

arc rocks record the evolution of the northern Proto-Tethys Ocean from ocean-floor subduction and con-

sumption to subsequent continental collision (Song

et al 2006 2014)

The East Kunlun Orogen records a long and complex

history from Cambrian to Triassic times (Dong et al

Fig 1 Simplified geological map of the northern Tibetan Plateau showing HPndashUHP metamorphic terranes in three orogenic beltsCAOB Central Asian Orogenic Belt CCOB Central China Orogenic Belt HOB Himalayan Orogenic Belt NCC North China CratonNQ-SP North QiangtangndashSongpan Block SCC South China Craton QLB QiangtangndashLhasa Block TB Tarim Block NQAB NorthQilian Accretionary Belt SQAB South Qilian Accretionary Belt NQUB North Qaidam UHPM Belt EKO East Kunlun Orogen CQBCentral Qilian Block

2044 Journal of Petrology 2018 Vol 59 No 11

niversity of Durham

2018 Li et al 2018) It mainly consists of (1) an Early

Paleozoic accretionary complex at the southwestern

margin of the Qaidam Block (2) the Arsquonyemaqen accre-

tionary complex in the south (3) Precambrian base-

ment (the South Kunlun Block) and (4) Triassic volcanicand plutonic rocks distributed throughout the East

Kunlun Orogen Ophiolites in the Early Paleozoic accre-

tionary complex formed over a long period from 537 to

460 Ma (Yang et al 1996 Bian et al 2004 Meng et al

2015 Qi et al 2016 Li et al 2018) the same as ophio-

lites in the QilianndashQaidam region to the north (Song

et al 2013) The types of ophiolite are not well docu-mented partly because most ophiolites are strongly

deformed and fragmented Basalts with pillow structure

show characteristics of normal- to enriched-mid-ocean

ridge basalt (N- to E-MORB) affinity (Yang et al 1996

Qi et al 2016) most probably representative of MORB-

type ophiolites (eg Topuz et al 2018) Arc volcanicrocks include Alaskan-type ultramaficndashmafic intrusions

with CundashNi ore-deposits andesitesndashrhyolites and

granites with SilurianndashDevonian ages (450ndash400 Ma) (eg

Zhu et al 2006 Wang et al 2014) Three eclogite-

bearing regions from east to west Wenquan Kehete

and Xiarihamu are distributed discontinuously along

the Early Paleozoic accretionary belt (Fig 1) TheArsquonyemaqen accretionary complex in the south is main-

ly a melange belt with 460ndash308 Ma ophiolitic fragments

(Bian et al 2004 Yang et al 2004) The Precambrian

basement in the EKO mainly consists of 1200ndash950 Ma

Mesoproterozoic granitic gneisses Detrital zircons from

metapelite (KL33) yielded an age peak at 2482 Ma with

secondary age groups of 2686ndash2505 and 2180ndash1054 Madetrital zircons from late Neoproterozoic sedimentary

rocks (Golmud region) yield a major age group of 1465ndash

802 Ma and three minor age groups of 1892ndash1758

2502ndash2431 and 3308 Ma (authorrsquos unpublished data)

All eclogites in the three terranes occur as lens-

shaped blocks of varying size (5ndash100 m in length) withinmetasedimentary hosts including metapelite and mar-

ble (Fig 2andashd) A serpentinite block has also been

Fig 2 Field photographs and photomicrographs of the eclogite belt in the EKO (a) Eclogite block within garnetndashmica schist (meta-pelite) from Kehete terrane (b) Eclogite block with weak alteration (Kehete terrane) (c) Eclogite blocks with marble (Xiarihamu ter-rane) (d) Eclogite blocks within metapelite (Xiarihamu terrane) (e) Photomicrograph of eclogite with the mineral assemblagegarnet (Grt) omphacite (Omp) phengite (Phn) rutile (Rt) and quartz (16KL13) (f) Coesite-pseudomorphs (Coe-P) in omphacite (g)Coesite-pseudomorph (Coe-P) in garnet [Note Omp rims decompressed into symplectitic low-Na clinopyroxene (Cpx) and oligo-clase (Oli) and further replaced by amphibole (Amp)] (h) Densely packed quartz exsolution rods in Omp (i) Amphibolite-faciesretrogression of eclogite in the Xiarihamu terrane with omphacite replaced by amphibole and rutile (Rt) by titanite (Ttn)

Journal of Petrology 2018 Vol 59 No 11 2045

niversity of Durham

discovered in the Kehete terrane The metapelite sam-

ples have a schistose structure with red grains of gar-

net and foliated mica in outcrop The rocks are

composed of garnet (5ndash15) muscovite (20ndash30) bio-

tite (5ndash10) quartz (35ndash45) plagioclase (10) andminor tourmaline zircon and rutile Most rutile grains

in the matrix are replaced by titanite andor ilmenite No

granitic gneiss has been found in the eclogite-bearing

high-pressure terranes The rock assemblage plus

some serpentinite massifs suggests an oceanic-type

subduction melange

Most eclogite samples in the east section of the HPndashUHP belt are fresh They show granoblastic textures with

a mineral assemblage of garnet omphacite rutile quartz

and minor phengite without obvious foliation Garnet

occurs as euhedral crystals with rare zircon and rutile

inclusions (Fig 2e and f) Coesite pseudomorphs are

observed as inclusions in garnet (Fig 2g) Most ompha-cite crystals contain densely packed oriented quartz rods

(Fig 2h) Omphacite crystals are commonly replaced by

Cpx thorn Oli symplectites and further by amphibole and ru-

tile is replaced by titanite suggesting that these eclogite

samples are overprinted by later decompression and

amphibolite-facies retrogression (Fig 2i)

ANALYTICAL METHODS

Mineral compositionsPolished thin sections were produced from representa-tive pieces of the studied samples and were examined

in detail using a petrographic microscope Mineral com-

positions were analysed using an electron probe micro-

analyzer (EPMA) (JEOL JXA-8100) at Peking University

operated at 15 kV acceleration voltage with 20 nA beam

current and 1ndash5 lm beam spot Routine analyses wereobtained by counting for 20 s at peak and 5 s on back-

ground Synthetic silica (Si) and spessartine (Mn) nat-

ural sanidine (K) pyrope (Mg) andradite (Fe and Ca)

albite (Na and Al) and rutile (Ti) were used as standards

Ferric iron in minerals was determined based on the

scheme of Droop (1987)

Whole-rock major and trace elementsOn the basis of careful petrographic observations we

selected 18 samples for whole-rock major and trace

element analyses The whole-rock major element

oxides were analyzed using a Leeman Prodigy induct-

ively coupled plasma optical emission spectroscopy

system (ICP-OES) at the China University of

Geosciences Beijing (CUGB) The analytical precisions(1r) for most major elements based on master stand-

ards GSR-1 GSR-3 GSR-5 (national geological stand-

ard reference materials of China) and USGS AGV-2 are

better than 1 except for TiO2 (15) and P2O5

(20) Loss on ignition (LOI) was determined by plac-

ing 1 g of sample powder in a furnace at 1000C for sev-eral hours before being cooled in a desiccator and

reweighed (Song et al 2010)

The trace element compositions of Haolaoluchang

volcanic samples were determined by inductively

coupled plasma mass spectrometry (ICP-MS) using an

Agilent-7500a quadrupole system in the Institute of

Earth Science CUGB About 40 mg power for each sam-ple was dissolved in a distilled acid mixture (11 HNO3ndash

HF) in a Teflon digesting vessel and heated on a hot-

plate at 185C for 48 h using high-pressure bombs for

digestionndashdissolution The sample was then evaporated

to incipient dryness refluxed with 1 ml 6N HNO3 and

heated again to incipient dryness The sample was

again dissolved in 2 ml of 3N HNO3 in a high-pressurebomb at 165C for a further 24 h to ensure complete dis-

solution Such digested samples were finally diluted

with Milli-Q water to a dilution factor of 2000 in 2

HNO3 solution for analysis Master standards (GSR-1

GSR-3 GSR-5 and USGS AGV-2) were used to monitor

the analytical accuracy and precision Analytical accur-acy as indicated by a relative difference between meas-

ured and recommended values is better than 5 for

most elements and 10ndash15 for Cu Zn Gd and Ta

Zircon preparation and UndashThndashPb analysisThe samples were crushed and sieved to 300 lm forthe first separation and then to 100 lm for the second

separation Zircons were separated by combining mag-

netic and heavy liquid methods before finally hand-

picking under a binocular microscope Zircon grains to-

gether with zircon standard 91500 were mounted in

epoxy mounts which were then polished to section thecrystals in half for analysis All zircons were docu-

mented with transmitted and reflected light micro-

graphs as well as cathodoluminescence (CL) images to

reveal their internal structures and the mount was

vacuum-coated with high-purity gold prior to secondary

ion mass spectrometry (SIMS) analysis The CL images

were obtained on an FEI Philips XL30 SFEG SEM with2 min scanning time at conditions of 15 kV and 20 nA at

Peking University

Measurements of U Th and Pb were conducted

using the Cameca IMS-1280 SIMS system at the

Institute of Geology and Geophysics Chinese Academy

of Sciences in Beijing UndashThndashPb ratios and absoluteabundances were determined relative to the standard

zircon 91500 (Wiedenbeck et al 1995) analyses of

which were interspersed with those of unknown grains

using operating and data processing procedures similar

to those described by Li et al (2009) A long-term uncer-

tainty of 15 (1RSD) for 206Pb238U measurements of

the standard zircons was propagated to the unknowns(Li et al 2010) despite the fact that the measured206Pb238U error in a specific session is generally around

1 (1RSD) or less Measured compositions were cor-

rected for common Pb using non-radiogenic 204Pb

Corrections are sufficiently small to be insensitive to the

choice of common Pb composition and an average ofthe present-day crustal composition (Stacey amp Kramers

1975) was used for the common Pb assuming that the

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common Pb is largely surface contamination introduced

during sample preparation Uncertainties on individual

analyses in data tables are reported at a 1r level mean

ages for pooled UPb (and PbPb) analyses are quoted

with a 95 confidence interval Data reduction was

carried out using the IsoplotEx v 249 program

(Ludwig 2003)

Measurements of UndashPb in zircons by laser ablation

(LA)-ICP-MS were carried out on an Agilent-7500a quad-

rupole ICP-MS system coupled with a New Wave SSUP193 laser sampler at the China University of

Geosciences Beijing Laser spot size of 36 lm laser en-

ergy density of 85 J cmndash2 and a repetition rate of 10 Hz

were applied for analysis National Institute of

Standards and Technology 610 glass and zircon stand-

ard 91500 (Wiedenbeck et al 1995) were used as exter-

nal standards Si as an internal standard and zirconstandard Qinghu zircon as the secondary standard The

software GLITTER (ver 44 Macquarie University) was

used to process the isotopic ratios and element concen-

trations of zircons The common lead correction was

made following Andersen (2002) Age calculations and

plots of concordia diagrams were made using IsoplotEx v 30 program (Ludwig 2003) Analytical details

have been described by Song et al (2010)

MINERAL AND WHOLE-ROCK CHEMISTRY

Chemical compositions of representative metamorphic

minerals are listed in Tables 1ndash3 Garnets in eclogites

from the three eclogite terranes show varying composi-tions (Fig 3a) Eclogitic garnets in the Kehete terrrane

are homogeneous in composition whereas garnets in

eclogites from the Xiarihamu terrane display weak

Table 3 Representative analyses of phengite in eclogites fromKehete Terane East Kunlun Orogen

Sample 16KL13-1 16KL27-1 16KL27-1 16KL27-1 16KL27A-1

SiO2 5596 5342 5248 5324 5465TiO2 094 069 067 073 068Al2O3 2488 2699 2778 2804 2611Cr2O3 000 007 002 006 000FeO 163 200 197 174 178MnO 002 003 001 000 001NiO 002 000 001 002 002MgO 476 395 314 352 416CaO 000 002 002 003 001Na2O 012 036 031 061 038K2O 860 924 895 802 872Total 9693 9676 9637 9601 9652Calculation using 12 oxygenSi 3591 3466 3447 3452 3533Ti 0045 0034 0033 0036 0033Al 1882 2064 2150 2142 1989Cr 0000 0004 0001 0003 0000Fe 0087 0109 0108 0094 0096Mn 0001 0002 0001 0000 0001Ni 0001 0000 0001 0001 0001Mg 0455 0382 0307 0340 0401Ca 0000 0001 0001 0002 0001Na 0015 0045 0039 0077 0048K 0704 0765 0750 0663 0719Sum 6782 6871 6839 6810 6822

Fig 3 Diagrams showing compositional variation of garnet (a) clinopyroxene (b) and amphibole (c) from the East Kunlun eclogite belt

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Table 5 Whole-rock compositions of eclogites from East Kunlun Orogen

Sample 16KL-13 KL-14 KL-15 KL-16 KL-20 KL-23 KL-24 KL-26 KL-27 KL-37 KL-38 KL-40 KL-43 KL-44Location Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete Hekete

Major elements (wt )

SiO2 4722 4687 4672 5059 4721 4680 4709 4685 4859 4928 5090 4909 4827 4601

TiO2 347 243 147 201 286 271 281 397 183 179 170 208 235 254

Al2O3 1340 1449 1678 1503 1266 1391 1358 1287 1452 1420 1381 1438 1389 1413

TFe2O3 1660 1536 1284 1316 1613 1830 1839 1488 1430 1382 1351 1516 1574 1727

MnO 023 021 018 017 022 027 027 016 019 019 018 021 021 027

MgO 561 654 806 664 604 587 574 758 713 727 681 682 704 708

CaO 897 987 1173 917 1099 966 973 993 994 1007 958 938 911 951

Na2O 226 220 163 147 206 199 188 276 221 217 200 197 127 191

K2O 053 080 016 026 070 039 027 011 053 041 038 020 063 053

P2O5 044 028 006 050 030 027 031 032 014 012 014 021 020 025

LOl 062 054 029 024 069 005 006 048 046 039 033 022 103 058

Total 9934 9960 9994 9925 9987 10011 10002 9991 9985 9971 9936 9973 9974 10008

Trace elements (ppm)

Li 9572 11886 12266 10178 3894 7328 6108 2246 2134 11988 12776 2892 16782 265Sc 352 3618 3706 2312 3586 4032 4038 2888 348 3562 3274 356 3348 3448

V 4202 3668 2428 1993 4378 3894 3832 5282 2774 3064 2826 284 2844 315

Cr 7132 689 194 9732 14688 307 3398 5482 141 1561 1398 12842 11698 9824

Co 493 5016 4392 4536 4848 4844 5564 3826 5522 5112 4826 4526 5738 4488

Ni 414 4508 532 5226 6796 2436 3746 387 8176 8058 8646 579 903 6034

Cu 4476 4946 2268 2888 935 6482 6744 15508 9614 7452 7684 4794 7308 6132

Zn 10278 969 6614 1069 10738 10776 10948 731 8696 909 858 8048 9664 9938

Ga 225 2118 16002 2804 2204 2100 2044 2926 1905 1899 17586 17872 18384 1898

Rb 2202 284 6744 8066 15188 1708 11748 4922 2324 14978 12254 6686 3172 2692

Sr 16548 19216 11096 12438 386 2052 2124 3262 1622 13484 12542 1382 1371 13072

Y 4206 359 2474 223 3564 392 3976 2444 2738 2618 2518 3094 3544 352Zr 19975 14103 9359 10695 10074 16444 18717 18054 10537 9221 9523 11108 14079 14873

Nb 3468 2603 971 1838 1879 2198 2223 3449 1264 1127 1064 1352 1701 1570

Cs 1375 1088 0158 0786 0835 0754 0499 0227 1255 1550 1379 0750 2662 0399

Ba 6272 8378 1751 416 2078 4048 3796 13422 5768 674 6226 3002 455 5514

La 2638 19054 3776 14356 17228 9786 1494 18414 891 7704 8266 11246 1209 13884

Ce 5586 4082 8954 3078 4028 2136 3308 3884 2008 17132 17986 2548 2656 3116

Pr 7496 5542 13392 4258 5888 3138 4662 5316 2914 247 253 3608 3754 443

Nd 3268 2428 6874 19092 2706 15296 215 2352 1363 1178 11886 16594 17056 2024

Sm 7578 5966 261 4584 7006 4946 5992 5704 3848 363 3556 4388 4716 5346

Eu 2432 1881 1122 1562 2460 1850 2056 2272 1458 1416 1388 1556 1666 1874

Gd 8028 6520 3732 4798 7470 6596 7110 5628 4636 4502 4448 5110 5734 6274

Tb 1297 1079 0685 0749 1196 1172 1210 0852 0796 0771 0760 0881 1017 1053

Dy 8140 6882 4638 4562 7302 7548 7732 4982 5144 4932 4866 5776 6604 6608

Ho 1661 1396 0983 0899 1419 1548 1572 0962 1058 1013 0995 1194 1351 1333

Er 4596 3876 2808 2444 3824 4274 4360 2590 2958 2804 2754 3332 3804 3690

Tm 0640 0546 0402 0339 0515 0598 0608 0353 0413 0393 0385 0465 0534 0512

Yb 4072 3444 2602 2126 3152 3762 3852 2250 2616 2472 2436 2940 3344 3208

Lu 0599 0499 0389 0307 0453 0555 0569 0335 0385 0366 0363 0437 0497 0473

Hf 4822 3698 2402 2673 2730 4085 4668 4307 2650 2339 2447 2749 3440 3587

Ta 2096 1637 0604 1143 1161 1308 1334 2121 0840 0646 0617 0779 1000 0939

Pb 2380 11698 10046 12590 11400 10740 10700 4966 10204 5130 3214 6572 7828 9052

Th 2396 1733 0312 1512 2372 1647 1784 1746 0927 1016 1124 1545 1642 1634

U 0727 0637 0487 0505 1225 1084 1275 0624 0351 0324 0320 0389 0677 0454

(continued)

niversity of Durham

Table 5 Continued

Sample 16KL-52 KL-53 KL-54 KL-56 KL-64 KL-80 KL-81 KL-83 KL-84 KL-91 KL-92

Location Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu Xiarihamu

SiO2 4575 5053 5019 4899 5050 5088 5163 5181 5100 4611 4518

TiO2 627 118 124 142 102 082 104 162 104 294 304

Al2O3 1232 1271 1346 1359 1312 1285 1263 1245 1262 1339 1269

TFe2O3 1585 1274 1214 1440 1191 1078 1159 1419 1216 1749 1820

MnO 022 018 017 020 017 020 017 023 023 021 021

MgO 656 723 790 692 818 831 798 616 763 649 692

CaO 978 1088 1167 1112 1104 1050 1023 998 1175 1076 1111

Na2O 270 246 157 212 193 237 211 226 171 203 215

K2O 008 052 028 022 034 050 026 018 019 011 011

P2O5 022 009 009 011 009 006 007 013 008 025 026

LOl 004 057 052 035 083 180 125 009 060 009 011

Total 9979 9909 9922 9945 9913 9908 9895 9902 9901 9986 9999

Li 1944 2224 15276 206 13855 2476 2462 16776 5504 1212 11144

Sc 4538 3908 3728 423 38006 3618 364 3834 3568 3886 4226

V 6744 3368 3166 3706 309467 2634 3088 3656 302 4558 4944Cr 482 16014 2154 1739 2403 3346 3488 9482 3376 2038 5848

Co 4644 4498 4606 5722 46691 4222 4332 4528 4534 5154 5438

Ni 352 698 9464 8472 97653 11064 12616 7074 12484 448 6642

Cu 6566 7786 7582 19426 88127 3152 6986 16992 9146 428 4938

Zn 8456 763 708 7872 74589 701 7436 8168 6692 8994 9226

Ga 18862 15562 15586 16292 15152 1365 14518 15392 12792 16952 1781

Rb 3098 12226 8616 8544 14571 219 7682 3848 5186 2002 10938

Sr 6548 2294 15282 17012 1649 2614 2102 134 1417 382 3448Y 4226 2096 19976 248 18359 15078 17646 3042 17688 14978 15802

Zr 16917 6414 6223 7421 4749 3555 4908 9263 4860 8445 8893

Nb 3260 367 556 644 294 235 367 968 300 894 964

Cs 0615 2216 15434 07876 0602 12818 09232 0278 0691 0345 0245

Ba 10826 2124 453 4216 66105 9992 5896 77140 27220 17066 11088

La 11314 3796 4912 604 4003 3596 3064 7746 3018 7808 7788

Ce 2534 9408 11384 13836 8865 7296 7426 17332 7570 17588 17916

Pr 3742 1485 17252 2056 1321 1077 1187 2520 1211 2558 2618

Nd 17958 7498 8308 9960 6504 5216 6018 11776 6140 11804 12158

Sm 508 2408 2482 2936 2060 1612 19178 3448 1958 2812 2946

Eu 1565 0919 0899 1079 0753 0619 0731 1181 0718 1138 1144

Gd 6004 3122 3006 3672 2615 2104 2452 4332 2456 2982 3134

Tb 1078 0559 0535 0653 0482 0386 0444 0777 0448 0462 0493

Dy 7510 3742 3560 4414 3233 2602 3068 5242 3016 2852 3040

Ho 1639 0796 0747 0945 0680 0563 0667 1127 0650 0574 0613

Er 4752 2286 2126 2706 1938 1658 1939 3284 1879 1557 1646

Tm 0689 0324 0300 0390 0276 0239 0276 0468 0268 0205 0218

Yb 4474 2084 1919 2506 1780 1584 1802 3010 1728 1246 1334

Lu 0670 0311 0282 0372 0270 0238 0267 0446 0260 0178 0192

Hf 4135 1524 1484 1770 1144 0844 1161 2186 1137 2611 2718

Ta 1736 0217 0376 0670 0179 0138 0549 0532 0176 0535 0528

Pb 1176 4966 1944 2964 4503 1712 1565 0838 0704 0579 0446

Th 0931 0457 0637 0693 0407 0282 0340 0972 0337 0114 0128

U 0199 0283 0291 0363 0204 0095 0124 0314 0113 0112 0033

niversity of Durham

chemical zoning the XMn [frac14 Mn(Fe thorn Mg thorn Ca thorn Mn)]

values decrease slightly from core to rim and XMg [frac14Mg(Fe thorn Mg thorn Ca thorn Mn)] exhibits reversed zoning

Omphacite in eclogites from the Kehete and Wenquan

terranes have higher jadeite contents than that from the

Xiarihamu terrane (Table 2 Fig 3b) Phengite is a minor

phase found only in the eclogites from the Kehete ter-

rane Si contents in phengite vary from 344 to 359 Siatoms per formula unit (apfu) based on 11 oxygens

(Table 3)

Amphibole is a retrograde phase in eclogites from all

the three terranes Hbl thorn Pl occurs as a symplectite or

symplectitic coronas after garnet and omphacite

(Fig 2g and i) Results of EPMA (Fig 3c Table 4) indi-

cate that they show wide compositional variations butthere is no significant difference between coronas and

coarse amphibole grains in the matrix

Twenty-six eclogite samples (14 from the Kehete ter-

rane in the east and 12 from the Xiarihamu terrane in

the west) were selected for whole-rock compositional

analysis at the China University of Geosciences Beijing(Table 5) All eclogite samples are predominantly bas-

altic with SiO2 (4601ndash510 wt ) TiO2 (084ndash627 wt )

MgO (561ndash831 wt ) CaO (897ndash1173 wt ) and Na2O

(127ndash270 wt ) In a (NbY) vs (ZrTiO2) diagram

(Winchester amp Floyd 1976) five samples plot in the al-

kaline field whereas others plot in the subalkaline field

(Fig 4a) Discrimination diagrams as well as trace

element patterns show that the eclogites from the

Kehete terrane have the geochemical characteristics ofenriched mid-ocean ridge basalts (E-MORB) to ocean-

island basalts (OIB) or within-plate basalts (WPB)

whereas eclogites from the Xiarihamu terrane are simi-

lar to E-MORB and N-MORB (Figs 4bndashd and 5) The geo-

chemical characteristics of these eclogites suggest that

their protoliths were oceanic crust (including seamount)basalts

METAMORPHIC PndashT PATHS

Three stages of metamorphism of eclogites in the EastKunlun can be identified peak stage I with a mineral as-

semblage of garnet thorn Omp thorn CoeQtz thorn Rutile 6

Phengite stage II decompression of omphacite at dry

conditions to Cpx2thornoligoclase stage III amphibolite

overprinting with addition of H2O in the mid-crust

Coesite pseudomorphs and quartz exsolution rods in

Omp suggest UHP conditions during the peak stage ofmetamorphism GrtndashOpmndashPhn geothermobarometry

(Krogh Ravna amp Terry 2004) also indicates UHP condi-

tions of Pfrac14 291ndash303 GPa and Tfrac14610ndash675C (Fig 6)

The PndashT conditions of omphacite decompression into

Cpx2thornoligoclase cannot be precisely determined but

should lie below the stability curve of Jadeite thorn Quartzfrac14 Albite The amphibolite-facies retrogression is

marked by varying degrees of amphibolitization in all

Fig 4 Discrimination diagrams for eclogites from the EKO (a) NbY vs ZrTi after Winchester amp Floyd (1976) for rock classification(b) TaYb vs ThYb (modified after Pearce 1982) The compositions of modern normal mid-ocean ridge basalts (N-MORB) enrichedmid-ocean ridge basalts (E-MORB) and ocean-island basalts (OIB) are from Sun amp McDonough (1989) (c) HfndashThndashTa discriminationdiagram of Wood (1980) (d) NbndashZrndashY discrimination diagram of Meschede (1986)

niversity of Durham

eclogite blocks with the retrograde assemblage Hbl thornEp thorn Pl at 600C and 06 GPa Therefore eclogites

from the EKO record a clockwise PndashT path from subduc-

tion to exhumation (Fig 7)

HPndashUHP METAMORPHIC AGES

Three eclogites and two garnetndashmica schist samples

(three from the Kehete terrane and two from the

Xiarihamu terrane) were selected for zircon UndashPb dating

(Supplementary Data Appendix Tables S1 and S2 sup-

plementary data are available for downloading at http

wwwpetrologyoxfordjournalsorg)

Zircons separated from the eclogite blocks (samples16KL13 and 16KL27 from Kehete and 16KL87 from

Xiarihamu) are round to ovoid crystals and have a

diameter of 50ndash150 lm They all show a typical meta-

morphic origin with oval shapes and fir-tree and radial

sector zoning in CL images (Fig 8) Garnet thorn omphacite

thorn rutile inclusions were identified by Raman

Fig 5 Primitive mantle-normalized multi-element patterns foreclogites from the Kehete terrane (a) and the Xiarihamu ter-rane (b) Normalization values are from Sun amp McDonough(1989)

Fig 7 PndashTndasht path of eclogites in the EKO ZE zeolite facies PPprehnitendashpumpellyite facies EA epidote amphibolite faciesAM amphibolite facies GR granulite facies HGR high-pres-sure granulite facies BS blueschist facies Amp EC amphiboleeclogite facies Ep-EC epidote eclogite facies Lw-EC lawsoniteeclogite facies (after Liou et al 1998)

Fig 6 PndashT diagrams for three eclogite samples from the Hekete terrane with the assemblage Grt thorn Omp thorn Phn Calculation wasperformed using lsquoP-T calc eclogitersquo of Krogh Ravna amp Terry (2004)

niversity of Durham

spectroscopy (Fig 8a and b) The U content in zircon

varies from 220 to 1487 ppm (mostly 300ndash600 ppm)with ThU ratios of 002ndash043 Thirty-two analyses of

16KL13 yield a concordia age of 4275 6 21 Ma (MSWD

frac14 036) 30 analyses of 16KL27 yield a concordia age of

4255 6 22 Ma (MSWD frac14 0069) and 30 analyses of

16KL87 4277 6 22 Ma (MSWD frac14 053) (Fig 9) These

ages suggest that the eclogites in the East Kunlunformed in a narrow age range of 428ndash425 Ma the same

as eclogites (428 6 2 Ma) from the Wenquan Terrane in

the easternmost EKO (Meng et al 2013)

Zircons in the two metapelitic samples (garnetndashmica

schists) (16KL39 from the east section and 16KL85 fromthe west section) show clear internal zoning with inher-

ited detrital cores and metamorphic rims (Fig 8)

Garnet and rutile inclusions were detected in the meta-

morphic rims by Raman spectroscopy (Fig 8b and c) In

sample 16KL39 from the east section of the East Kunlun

eclogite belt a total of 77 zircon grains were analyzedand 61 core analyses yielded 206Pb238U ages varying

from 453 6 5 to 971 6 10 Ma with peaks at 465 512

603 712 834 and 923 Ma Sixteen zircon rims in sample

Fig 8 Photomicrographs and cathodoluminescence (CL) images of zircons from the eclogites and metapelites in the EKO (a)Garnet and rutile inclusions in zircon from eclogite (16KL27) (b) Garnet inclusion in the rim domain of zircon from metapelite(16KL39) (c) Rutile inclusions in zircon from metapelite (16KL39) (d) CL images of zircons from eclogites omphacite (Omp) inclu-sion should be noted (e) CL images of zircons from metapelites The corendashrim structure and dark luminance of the rim domainsshould be noted

niversity of Durham

16KL39 have significantly low ThU ratios (001ndash006)

Twelve analyses form a concordia age of 4273 6 14 Ma(MSWD frac14 010) (Fig 10andashc) which is consistent with

the metamorphic ages of the eclogites Another four

analyses gave a younger mean age of 4105 6 2 Ma

(MSWD frac14 005) which may represent the amphibolite-

facies retrograde age of the HP belt Forty-five analyses

of zircon cores from sample 16KL85 yielded similar

ages ranging from 469 to 1162 Ma Six analyses of zir-

con rims gave a concordia age of 4275 6 2 Ma (MSWD

frac14 009) (Fig 10dndashf) the same as the ages of the

eclogites

DISCUSSION

The conditions of UHP metamorphism in theEast Kunlun OrogenThe 500 km long eclogite belt indicates the existence of

HPndashUHP metamorphism in a subduction zone associ-

ated with the East Kunlun Orogen Its rock assemblage

together with ophiolite and arc-volcanic rocks along this

belt suggests a tectonic melange and accretionary

complex that combines oceanic subduction and contin-

ental collision Peak metamorphic conditions are withinthe coesite stability field evidenced by quartz exsolu-

tion rods in Omp coesite pseudomorphs in garnet and

omphacite and PndashT calculations using the GrtndashOmpndash

Phn geothermobarometer of Krogh Ravna amp Terry

(2004) The metamorphic PndashTndasht path of the eclogite

shows a clockwise decompression path suggestingthat the eclogite blocks were exhumed from depths of

100ndash120 km

Evolution of the Proto-Tethys Ocean and forma-tion of the Pan-North-China ContinentThe remnants of the Early Paleozoic QinlingndashQilianndash

Kunlun Ocean preserved in the present-day Chinese

continent represent part of the Proto-Tethys Ocean

(Mattern amp Schneider 2000 von Raumer amp Stampfli2008 Stampfli et al 2013) All blocks in this region

including the South Kunlun Block QaidamndashQuangji

Block Central Qilian Block South China Block and

North Qilian Block which have been referred to as peri-

Gondwana have similar Precambrian basements

(records of 12ndash09 Ga orogenic assembly and 085ndash

07 Ga rifting of Rodinia) They are believed to have dis-persed from East Gondwanaland during breakup of the

Rodinia supercontinent (Yin amp Harrison 2000 Gehrels

et al 2003 Cawood et al 2007 2013 von Raumer amp

Stampfli 2008 Song et al 2012 2014 Han et al 2016

Xu et al 2016) in the late Neoproterozoic as recorded

by the 600ndash580 Ma rift-related volcano-sedimentarysequence and the oldest ophiolite (550 Ma) in the Qilian

orogen (Song et al 2013 Xu et al 2015)

The remnants of the Proto-Tethys Ocean preserved

in the northern Tibetan Plateau can be divided into the

Qilian Ocean in the north and the East Kunlun Ocean in

the south separated by the Qaidam Block Subparallel

oceanic-type accretionary belts and continental-typecollisional zones together with the three HP and UHP

metamorphic belts (Fig 1) suggest that the Proto-

Tethys Ocean must have experienced an evolution from

initial subduction at 520 Ma to final closure at

410 Ma The Qilian Ocean between the NCCndashTarim

and Qaidam blocks started to subduct at 520 Maand closed at 440 Ma followed by the northward con-

tinental subductionndashcollision of the Qaidam block at

Fig 9 Concordia diagrams for eclogites in the EKO

niversity of Durham

440ndash420 Ma (Song et al 2013 2014) Ophiolites in the

EKO record formation ages of 540ndash460 Ma (eg Yanget al 1996 Meng et al 2015 Qi et al 2016 Li et al

2017) suggesting that the Kunlun Ocean between the

Qaidam and South Kunlun blocks had a similar history

to the Qilian Ocean in the north Arc volcanic rocks

suggest that the East Kunlun Ocean may have started

subduction at 450 Ma Ages of the Kunlun UPndashUHPbelt reveal that the Proto-Tethys Ocean finally closed at

428ndash410 Ma resulting in the formation of a united con-

tinent in North China by the end of Early Paleozoic

named lsquothe Pan-North-China Continentrsquo

Transition from Proto-Tethys to Paleo-Tethys inthe Northern Tibetan PlateauThe Proto-Tethys Ocean is generally considered to have

initiated at 550 Ma between the continents of Laurasia

and Gondwana (von Raumer amp Stampfli 2008 Song

et al 2013) However the transition from Proto-Tethys

to Paleo-Tethys is always ambiguous because there is

no clear subdivision of these two periods of oceanicspreading As shown in Fig 11 after closure of the

Proto-Tethys Ocean at 420ndash410 Ma in the East Kunlun

Fig 10 Concordia and histograms showing the age distribution of detrital zircons from two metapelite samples in the EKOSample 16KL39 is from the Kehete terrane and 16KL85 is from the Xiarihamu terrane

Fig 11 Schematic illustration of the evolution from the Proto-Tethys to the Neo-Tethys oceans and the formation of the Pan-North-China Continent (PNCC) 1 UHP metamorphic ages ofSouth Altun (Liu et al 2012) 2 HP metamorphic ages of eclog-ite and blueschist of North Qilian (Song et al 2006 Zhanget al 2007) 3 UHP metamorphic ages of North Qinling (Liu

et al 2016) 4 UHP metamorphic ages of North Qaidam (Songet al 2014) 5 HPndashUHP metamorphic ages of East Kunlun(Meng et al 2013 Qi et al 2014 this study) 6 UHP meta-morphic ages of DabiendashSulu (Li et al 1993 Liu et al 2006) 7HP metamorphic ages of eclogite and blueschist of NorthQiangtang (Zhai et al 2011) 8 HP metamorphic ages of blues-chists in Lanchangjiang (Wang et al in press) SA SouthAltun QL Qilian Block NQ North Qinling SK South KunlunNQ-SP North QiangtangndashSongpan SQ-LS South QiangtangndashLhasa

niversity of Durham

orogen a wide Paleo-Tethys Ocean which was named

the lsquoRheic Oceanrsquo by von Raumer amp Stampfli (2008)

developed in the Late Paleozoic in the south and east be-

tween Gondwana and the Pan-North-China Continent (or

Hunic terranes von Raumer et al 2003) Ophiolites inthe Arsquonyemaqen accretionary belt of the East Kunlan

(eg Yang et al 1996 Bian et al 2004) and in Central

Qiangtang (Zhai et al 2016) suggest that the oceanic

crust of the Paleo-Tethys Ocean could be as old as

500 Ma The Paleo-Tethys Ocean had closed by 220 Ma

marked by collision between the South China and North

China blocks in the north (eg Li et al 1993 Liu et al2006) and between the South QiangtangndashSibomasu

blocks and South ChinandashNorth Qiangtang blocks in the

south (Zhai et al 2011 Wang et al 2018) (Fig 11)

CONCLUSIONS

(1) The eclogite belt consists of eclogite blocks metape-

lites marble and minor serpentinite blocks and extends

laterally for 500 km within the Kunlun orogenic belt

All eclogites show geochemical characteristics with E-

MORB and OIB affinities

(2) Coesite pseudomorphs quartz exsolution in

omphacite and PndashT calculations reveal that the EastKunlun eclogites experienced UHP metamorphism at

conditions of 29ndash30 kbar and 610ndash675C Zircon UndashPb

analyses show they formed at 430ndash410 Ma

(3) The East Kunlun eclogite belt was produced in re-

sponse to final closure of the Proto-Tethys Ocean at the

end of the Early Paleozoic

ACKNOWLEDGEMENTS

We thank Xianhua Li and his group for help with the

secondary ion mass spectrometry UndashPb dating of zir-

cons and Xiaoli Li for help with electron microprobe

analysis We also thank Hannes Brueckner Gueltekin

Topuz and an anonymous reviewer as well as EditorAlasdair Skelton for their constructive comments

which significantly improved the quality of the paper

FUNDING

This research was financially supported by the Major

State Basic Research Development Program(2015CB856105) and the National Natural Science

Foundation of China (grants 41572040 and 41372060)

SUPPLEMENTARY DATA

Supplementary data for this paper are available at

Journal of Petrology online

REFERENCES

Agard P Yamato P Jolivet L amp Burov E (2009) Exhumationof oceanic blueschists and eclogites in subduction zonestiming and mechanisms Earth-Science Reviews 92 53ndash79

Andersen T (2002) Correction of common lead in U-Pb analy-ses that do not report 204Pb Chemical Geology 192 59ndash79

Bian Q-T Li D-H Pospelov I Yin L-M Li H-S Zhao D-S Chang C-F Luo X-Q Gao S-L Astrakhantsev O ampChamov N (2004) Age geochemistry and tectonic settingof Buqingshan ophiolites North QinghaindashTibet PlateauChina Journal of Asian Earth Sciences 23 577ndash596

Carswell D A (1990) Eclogite Facies Rocks Glasgow BlackieNew York Chapman amp Hall 396 pp

Cawood P A Johnson M R W amp Nemchin A A (2007)Early Paleozoic orogenesis along the Indian margin ofGondwana tectonic response to Gondwana assemblyEarth and Planetary Science Letters 255 70ndash84

Cawood P A Wang Y Xu Y amp Zhao G (2013) LocatingSouth China in Rodinia and Gondwana a fragment ofgreater India lithosphere Geology 41 903ndash906

Dong Y amp Santosh M (2016) Tectonic architecture and mul-tiple orogeny of the Qinling Orogenic Belt Central ChinaGondwana Research 29 1ndash40

Dong Y He D Sun S Liu X Zhou X Zhang F Yang ZCheng B Zhao G amp Li J (2018) Subduction and accre-tionary tectonics of the East Kunlun orogen western seg-ment of the Central China Orogenic System Earth-ScienceReviews doi101016jearscirev201712006

Droop G T R (1987) A general equation for estimating Fe3thorn

concentrations in ferromagnesian silicates and oxides frommicroprobe analyses using stoichiometric criteriaMineralogical Magazine 51 431ndash435

Ernst W G (1988) Tectonic history of subduction zonesinferred from retrograde blueschist PndashT paths Geology 161081ndash1084

Ernst W G amp Liou J G (1995) Contrasting plate-tectonicstyles of the QinlingndashDabiendashSulu and Franciscan meta-morphic belts Geology 23 353ndash356

Gehrels G E Yin A amp Wang X F (2003) Detrital-zircon geo-chronology of the northeastern Tibetan plateau GeologicalSociety of America Bulletin 115 881ndash896

Han Y Zhao G Cawood P A Sun M Eizenhofer P R HouW Zhang X amp Liu Q (2016) Tarim and North China cratonslinked to northern Gondwana through switching accretionarytectonics and collisional orogenesis Geology 44 95ndash98

Krogh Ravna E J amp Terry M P (2004) Geothermobarometryof UHP and HP eclogites and schistsmdashan evaluation of equi-libria among garnetndashclinopyroxenendashkyanitendashphengitendashcoe-sitequartz Journal of Metamorphic Geology 22 579ndash592

Li Q L Li X H Liu Y Tang G Q Yang J H amp Zhu W G(2010) Precise UndashPb and PbndashPb dating of Phanerozoic bad-deleyite by SIMS with oxygen flooding technique Journalof Analytical Atomic Spectrometry 25 1107ndash1113

Li R Pei X Li Z Pei L Chen G Wei B Chen Y Liu C ampWang M (2018) Cambrian (510 Ma) ophiolites of the EastKunlun orogen China a case study from the Acite ophiolitictectonic melange International Geology Review 602063ndash2083

Li S Xiao Y Liou D Chen Y Ge N Zhang Z Sun S-SCong B Zhang R Hart S R amp Wang S (1993) Collisionof the North China and Yangtse Blocks and formation ofcoesite-bearing eclogites timing and processes ChemicalGeology 109 89ndash111

Li S Zhao S Liu X Cao H Yu S Li X Somerville I YuS amp Suo Y (2018) Closure of the Proto-Tethys Ocean andEarly Paleozoic amalgamation of microcontinental blocks inEast Asia Earth-Science Reviews doi 101016jearscirev201701011

Li X H Liu Y Li Q L Guo C H amp Chamberlain K R (2009)Precise determination of Phanerozoic zircon PbPb age bymulti-collector SIMS without external standardization

niversity of Durham

Geochemistry Geophysics Geosystems 10 doi1010292009GC002400

Li Z X Bogdanova S V Collins A S Davidson A DeWaele B Ernst R E Fitzsimons I C W Fuck R AGladkochub D P Jacobs J Karlstrom K E Lu SNatapov L M Pease V Pisarevsky S A Thrane K ampVernikovsky V (2008) Assembly configuration andbreak-up history of Rodinia a synthesis PrecambrianResearch 160 179ndash210

Liou J G Zhang R Y Ernst W G Rumble D amp MaruyamaS (1998) High-pressure minerals from deeply subductedmetamorphic rocks In Hemley R J (ed)Ultrahigh-Pressure Mineralogy Physics and Chemistry ofthe Earthrsquos Deep Interior Mineralogical Society of AmericaReviews in Mineralogy 37 33ndash96

Liu D Jian P Kroner A amp Xu S (2006) Dating of progrademetamorphic events deciphered from episodic zircongrowth in rocks of the DabiendashSulu UHP complex ChinaEarth and Planetary Science Letters 250 650ndash666

Liu L Wang C Cao Y T Chen D L Kang L Yang W Q ampZhu X H (2012) Geochronology of multi-stage meta-morphic events Constraints on episodic zircon growth fromthe UHP eclogite in the South Altyn NW China Lithos 13610ndash26

Liu L Liao X Wang Y Wang C Santosh M Yang MZhang C amp Chen D (2016) Early Paleozoic tectonic evolu-tion of the North Qinling Orogenic Belt in Central ChinaInsights on continental deep subduction and multiphase ex-humation Earth-Science Reviews 159 58ndash81

Ludwig K R (2003) Userrsquos Manual for Isoplot 300 AGeochronological Toolkit for Microsoft Excel BerkeleyGeochronology Center Special Publication 4

Mattern F amp Schneider W (2000) Suturing of the Proto- andPaleo-Tethys oceans in the western Kunlun (XinjiangChina) Journal of Asian Earth Sciences 18 637ndash650

Meng F Zhang J amp Cui M (2013) Discovery of EarlyPaleozoic eclogite from the East Kunlun Western China andits tectonic significance Gondwana Research 23 825ndash836

Meng F Cui M Wu X amp Ren Y (2015) Heishan maficndashultra-mafic rocks in the Qimantag area of Eastern Kunlun NWChina remnants of an early Paleozoic incipient island arcGondwana Research 27 745ndash759

Meschede M (1986) A method of discriminating between differ-ent types of mid-ocean ridge basalts and continental tholeiiteswith the NbndashZrndashY diagram Chemical Geology 56 207ndash218

Pearce J A (1982) Trace element characteristics of lavas fromdestructive plate boundaries In Thorpe R S (ed)Andesites New York John Wiley pp 525ndash548

Qi S S Song S G Shi L C Cai H J amp Hu J C (2014)Discovery and its geological significance of Early Paleozoicedogite in XiarihamundashSuhaitu area western part of the EastKunlun Acta Petrologica Sinica 30 3345ndash3356

Qi X Yang J amp Fan X (2016) Age geochemical characteris-tics and tectonic significance of Changshishan ophiolite incentral East Kunlun tectonic melange belt along the east sec-tion of East Kunlun Mountains Geology in China 43797ndash816 (in Chinese with English abstract)

Song S Niu Y Su L Zhang C amp Zhang L (2014)Continental orogenesis from ocean subduction continentcollisionsubduction to orogen collapse and orogen recy-cling the example of the North Qaidam UHPM belt NWChina Earth-Science Reviews 129 59ndash84

Song S G Zhang L F Niu Y L Su L Song B A amp Liu DY (2006) Evolution from oceanic subduction to continentalcollision a case study from the Northern Tibetan Plateaubased on geochemical and geochronological data Journalof Petrology 47 435ndash455

Song S G Zhang L F Niu Y Wei C J Liou J G amp Shu GM (2007) Eclogite and carpholite-bearing metasedimentaryrocks in the North Qilian suture zone NW China implica-tions for early Palaeozoic cold oceanic subduction and watertransport into mantle Journal of Metamorphic Geology 25547ndash563

Song S G Niu Y L Wei C J Ji J Q amp Su L (2010)Metamorphism anatexis zircon ages and tectonic evolutionof the Gongshan block in the northern IndochinacontinentmdashAn eastern extension of the Lhasa Block Lithos120 327ndash346

Song S G Su L Li X H Niu Y L amp Zhang L F (2012)Grenville-age orogenesis in the QaidamndashQilian block thelink between South China and Tarim Precambrian Research220ndash221 9ndash22

Song S G Niu Y L Su L amp Xia X H (2013) Tectonics of theNorth Qilian orogen NW China Gondwana Research 231378ndash1401

Song S G Yang L M Zhang Y Q Niu Y L Wang C SuL amp Gao Y L (2017) Qi-Qin Accretionary Belt in CentralChina Orogen accretion by trench jam of oceanic plateauand formation of intra-oceanic arc in the Early PaleozoicQin-Qi-Kun Ocean Science Bulletin 62 1035ndash1038

Stacey J S amp Kramers J D (1975) Approximation of terres-trial lead isotope evolution by a two-stage model Earth andPlanetary Science Letters 26 207ndash221

Stampfli G M Hochard C Verard C Wilhem C amp vonRaumer J (2013) The formation of Pangea Tectonophysics593 1ndash19

Sun S S amp McDonough W F (1989) Chemical and isotopicsystematics of oceanic basalts implications for mantle com-position and processes In Saunders A Damp Norry M J(eds) Magmatism in the Ocean Basins Geological SocietyLondon Special Publications 42 313ndash345

Topuz G Okay A I Schwarz W H Sunal G Altherr R ampKylander-Clark A R C (2018) A middle Permian ophiolitefragment in Late Triassic greenschist- to blueschist-faciesrocks in NW Turkey An earlier pulse ofsuprasubduction-zone ophiolite formation in the Tethyanbelt Lithos 300ndash301 121ndash135

von Raumer J F amp Stampfli G M (2008) The birth of theRheic Oceanmdashearly Palaeozoic subsidence patterns andsubsequent tectonic plate scenarios Tectonophysics 4619ndash20

von Raumer J F Stampfli G M amp Bussy F (2003)Gondwana-derived microcontinentsmdashthe constituents ofthe Variscan and Alpine collisional orogens Tectonophysics365 7ndash22

Wang F Liu F Schertl H-P Liu P Jia L Cai J amp Liu L(2018) Paleo-Tethyan tectonic evolution of Lancangjiangmetamorphic complex evidence from SHRIMP UndashPb zircondating and 40Ar39Ar isotope geochronology of blueschistsin XiaoheijiangndashXiayun area Southeastern Tibetan PlateauGondwana Research in press

Wang G Sun F amp Li B (2014) Zircon UndashPb geochronologyand geochemistry of the maficndashultramafic intrusion inXiarihamu CundashNi deposit from East Kunlun with implica-tions for geodynamic setting Earth Science Frontier 21381ndash401 (in Chinese with English abstract)

Whitney D L amp Evans B W (2010) Abbreviations for namesof rock-forming minerals American Mineralogist 95185ndash187

Wiedenbeck M Alle P Corfu F Griffin W L Meier MOberli F Vonquadt A Roddick J C amp Spiegel W (1995)Three natural zircon standards for UndashThndashPb LundashHftrace-element and REE analyses Geostandards andGeoanalytical Research 19 1ndash23

niversity of Durham

Winchester J A amp Floyd P A (1976) Geochemical magmatype discrimination application to altered and metamor-phosed basic igneous rocks Earth and Planetary ScienceLetters 28 459ndash469

Wood D A (1980) The application of a ThndashHfndashTa diagram toproblems of tectonomagmatic classification and to estab-lishing the nature of crustal contamination of basaltic lavasof the British Tertiary Volcanic Province Earth and PlanetaryScience Letters 50 11ndash30

Xu X Song S G Su L Li Z X Niu Y L amp Allen M B(2015) The 600ndash580 Ma continental rift basalts in NorthQilian Shan northwest China links between theQilianndashQaidam block and SE Australia and the recon-struction of East Gondwana Precambrian Research 25747ndash64

Xu X Song S G Allen M B Ernst R E Niu Y L amp Su L(2016) An 850ndash820 Ma LIP dismembered duringbreakup of the Rodinia supercontinent and destroyed byEarly Paleozoic continental subduction in the northernTibetan Plateau NW China Precambrian Research 28252ndash73

Yang J S Robinson T Jiang C F amp Xu Z Q (1996)Ophiolites of the Kunlun Mountains China and their tectonicimplications Tectonophysics 258 215ndash231

Yang J-S Wang X-B Shi R D Xu Z Q amp Wu C L (2004)The Durrsquongoi ophiolite in East Kunlun north QinghaindashTibet

Platea fragment of paleo-Tethyan oceanic crust Geology inChina 31 225ndash239

Yin A amp Harrison T M (2000) Geologic evolution of theHimalayanndashTibetan orogen Annual Review of Earth andPlanetary Sciences 28 211ndash280

Zhang J X Meng F C amp Wan Y S (2007) A cold EarlyPalaeozoic subduction zone in the North Qilian MountainsNW China petrological and UndashPb geochronological con-straints Journal of Metamorphic Geology 25 285ndash304

Zhang Y Q Song S G Yang L M Su L Niu Y L Allen MB amp Xu X (2017) Basalts and picrites from a plume-typeophiolite in the South Qilian Accretionary Belt QilianOrogen Accretion of a Cambrian Oceanic Plateau Lithos278 97ndash110

Zhai Q G Zhang R Y Jahn B M Li C Song S G amp WangJ (2011) Triassic eclogites from central Qiangtang north-ern Tibet China petrology geochronology and meta-morphic PndashT path Lithos 125 173ndash189

Zhai Q-G Jahn B-M Wang J Hu P-y Chung S-L LeeH-y Tang S-h amp Tang Y (2016) Oldest Paleo-Tethyanophiolitic melange in the Tibetan Plateau GeologicalSociety of America Bulletin 128 355ndash373

Zhu Y Lin Q Jia C amp Wang G (2006) SHRIMP zircon UndashPbage and significance of Early Paleozoic volcanic rocks inEast Kunlun Orogen Qinghai Province China Science inChina Series D 49 88ndash96

niversity of Durham

egy089-TF1

egy089-TF2