Archean komatiite volcanism controlled by theevolution of early continentsDavid R. Molea,b,1,2, Marco L. Fiorentinia, Nicolas Thebauda, Kevin F. Cassidya, T. Campbell McCuaiga,Christopher L. Kirklandc, Sandra S. Romanoc, Michael P. Doubliera,c, Elena A. Belousovad, Stephen J. Barnese,and John Millera

aCentre for Exploration Targeting, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems, School of Earth and Environment,University of Western Australia, Perth, WA 6009, Australia; bDepartment of Applied Geology, Curtin University, Bentley, WA 6102, Australia; cGeologicalSurvey of Western Australia, Department of Mines and Petroleum, East Perth, WA 6004, Australia; dKey Centre for the Geochemical Evolution andMetallogeny of Continents, Australian Research Council Centre of Excellence for Core to Crust Fluid Systems, Macquarie University, North Ryde NSW 2109,Australia; and eEarth Science and Resource Engineering, Commonwealth Scientific and Industrial Research Organization (CSIRO), Kensington, Perth, WA 6151,Australia

Edited by Norman H. Sleep, Stanford University, Stanford, CA, and approved April 14, 2014 (received for review January 7, 2014)

The generation and evolution of Earth’s continental crust hasplayed a fundamental role in the development of the planet. Itsformation modified the composition of the mantle, contributed tothe establishment of the atmosphere, and led to the creation ofecological niches important for early life. Here we show that in theArchean, the formation and stabilization of continents also con-trolled the location, geochemistry, and volcanology of the hottestpreserved lavas on Earth: komatiites. These magmas typically rep-resent 50–30% partial melting of the mantle and subsequentlyrecord important information on the thermal and chemical evolu-tion of the Archean–Proterozoic Earth. As a result, it is vital toconstrain and understand the processes that govern their localiza-tion and emplacement. Here, we combined Lu-Hf isotopes andU-Pb geochronology to map the four-dimensional evolution of theYilgarn Craton, Western Australia, and reveal the progressive de-velopment of an Archean microcontinent. Our results show that inthe early Earth, relatively small crustal blocks, analogous to modernmicroplates, progressively amalgamated to form larger continen-tal masses, and eventually the first cratons. This cratonization pro-cess drove the hottest and most voluminous komatiite eruptionsto the edge of established continental blocks. The dynamic evolu-tion of the early continents thus directly influenced the addition ofdeep mantle material to the Archean crust, oceans, and atmo-sphere, while also providing a fundamental control on the distri-bution of major magmatic ore deposits.

crustal evolution | lithosphere | architecture | mantle plumes |Ni-Cu-PGE deposits

Volcanism on Earth is the dynamic surface expression of ourplanet’s thermal cycle, with heat created from radioactive

decay and lost through mantle convection (1). In the Archeaneon (>2.5 bya), Earth’s heat flux was significantly higher thanthat observed today (1, 2) due to the combined effects of a moreradioactive mantle (1, 3) and residual heat from planetary ac-cretion (4). This resulted in the eruption of komatiites: ultra-hightemperature, low-viscosity lavas with MgO >18% and eruptiontemperatures >1,600 °C (5) formed from mantle plumes (1, 2, 6).These rare, ancient magmas are dominantly restricted to theearly history of the planet (3.5–1.5 Ga; ref. 7) and represent theremnants of huge volcanic flow fields (8) consisting of the hottestlavas preserved on Earth (5, 9, 10). These now-extinct volcanicsystems and flow complexes had the potential to cover significantportions of the early continents, and were likely analogous tolarge igneous provinces in size and magma volume (11, 12).Komatiites are vital to our understanding of Earth’s thermalevolution (1–3, 7, 13–16), and represent a window into the dy-namic secular development of the mantle throughout the earlyhistory of our planet (5). Subsequently, understanding the physicaland chemical processes that govern their localization, volcanology,and geochemistry is vital in deciphering this information.

In the Yilgarn Craton of Western Australia (Fig. 1), two majorpulses of komatiite activity occurred at ∼2.9 Ga (southern YouanmiTerrane; refs. 17–19) and 2.7 Ga (Kalgoorlie Terrane, EasternGoldfields Superterrane; refs. 5, 10). These represent twoseparate plume events that impinged onto preexisting continentalcrust (20–23), with the resulting magmas heterogeneously dis-tributed across the craton (8, 10, 17–19, 23, 24). In this study,we provide the first evidence of a fundamental relationshipbetween the spatiotemporal variation in komatiite abundance,geochemistry, and volcanology and the evolution of an Archeanmicrocontinent, reflected in the changing isotopic composition ofthe crust.We used Lu-Hf and U-Pb isotopic techniques on multiple

magmatic and inherited zircon populations from granitoid rocksand felsic volcanic units, which represent the exposed Archeancrust of the Yilgarn Craton. All zircon grains were dated usingthe sensitive high-resolution ion microprobe (SHRIMP), beforein situ laser ablation inductively coupled plasma mass-spectrometry(LA-ICP-MS) analysis for Lu-Hf isotopes. The Lu-Hf isotopicdata are expressed as eHf, which denotes the derivation of the176Hf/177Hf ratio of the sample from the contemporaneous ratio

Significance

Komatiites are rare, ultra-high-temperature (∼1,600 °C) lavasthat were erupted in large volumes 3.5–1.5 bya but only veryrarely since. They are the signature rock type of a hotter earlyEarth. However, the hottest, most extensive komatiites havea very restricted distribution in particular linear belts withinpreserved Archean crust. This study used a combination of dif-ferent radiogenic isotopes to map the boundaries of Archeanmicrocontinents in space and time, identifying the microplatesthat form the building blocks of Precambrian cratons. Isotopicmapping demonstrates that the major komatiite belts are lo-cated along these crustal boundaries. Subsequently, the evo-lution of the early continents controlled the location andextent of major volcanic events, crustal heat flow, and majorore deposit provinces.

Author contributions: D.R.M., M.L.F., and J.M. designed the research project; D.R.M., N.T.,S.S.R., and M.P.D. performed research; D.R.M., M.L.F., K.F.C., T.C.M., C.L.K., and S.J.B.analyzed data; D.R.M. wrote the paper; N.T., K.F.C., T.C.M., C.L.K., and J.M. performedregional geological analysis; S.S.R. and M.P.D. performed regional geological analysis andmapping; E.A.B. provided assistance with operation of analytical equipment and datareduction; and S.J.B. provided access to the CSIRO komatiite database.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.1Present address: Earth Science and Resource Engineering, Commonwealth Scientific andIndustrial Research Organization (CSIRO), Kensington, Perth, WA 6151, Australia.

2To whom correspondence should be addressed. E-mail: david.mole@csiro.au.

This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1400273111/-/DCSupplemental.

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of the chondritic uniform reservoir (CHUR), multiplied by 104.The term “juvenile” refers to crustal material that plots on orclose to the depleted mantle evolution line, suggesting derivationfrom a depleted mantle source. In contrast, “reworked” refersto the remobilization of preexisting crust by partial meltingand/or erosion and sedimentation (25, 26). Complete sample in-formation, methodology, and geochemical datasets (U-Pb, Lu-Hf,and komatiite) are available in the Supporting Information,Figs. S1–S3, and Tables S1–S4.The Lu-Hf data are displayed as a series of time-slice contour

maps, which show “snapshots” of the changing source and age ofthe crust at 3,050–2,820; 2,820–2,720; and 2,720–2,600 Ma [Figs. 2–4; intervals based on the work of Mole et al. (21); full Hf dataset

displayed in Fig. S4]. In these maps, point data representing themedian eHf value of granites and felsic volcanics are plotted ascontour maps that show the spatial extent of “blocks” of specific Lu-Hf isotopic character and their evolution through time. This methodis based on previous isotopic mapping of the Yilgarn Craton usingthe analogous Sm-Nd system (27). Importantly, the Lu-Hf datapresented here replicate the features of the Sm-Nd work (27, 28),with the added ability to look further back in time due to the in situanalysis of abundant inherited zircons (21).The variable isotopic signatures of the crust (Figs. 2–4) can be

interpreted as proxies for lithospheric thickness (Figs. 5 and 6;ref. 29), where young, juvenile eHf values (eHf > 0) indicaterelatively thin lithosphere and old, reworked values (eHf < 0)reflect thicker lithosphere (29, 30); a pattern observed in themodern-day western United States (29–32). Here, this informa-tion is combined to document the four-dimensional lithosphericarchitecture of the Yilgarn Craton and development of an Archeanmicrocontinent.

ResultsThe first time slice (T1 − 3,050–2,820 Ma; Fig. 2) shows the litho-spheric architecture at the time of ∼2.9 Ga komatiite emplacementin the southern Youanmi Terrane. The Lu-Hf mapping identifiesthree lithospheric blocks: Marda, Hyden, and Lake Johnston. TheMarda and Hyden blocks dominantly comprise reworked oldercrust, with eHf −6.0 and −4.0, respectively. In contrast, the LakeJohnston block comprises younger, more juvenile material, witheHf +2.0. This protocratonic lithospheric architecture exerts afirst-order control on the localization of the ∼2.9 Ga high-MgOkomatiites of the Forrestania (17) and Lake Johnston (10, 19, 33)greenstone belts. These komatiites occur in the juvenile LakeJohnston block, primarily along the margin of the older Hydenblock (Fig. 2). Within the Marda block to the north, komatiitesare largely absent and the greenstone stratigraphy is almost ex-clusively comprised of basalt (24). No known volcanic units fromthis time are preserved in the Hyden block.The second time slice (T2 − 2,820–2,720 Ma; Fig. 3) images

the lithospheric architecture of the craton at a time when nosignificant evidence of komatiite magmatism is recorded. Sixcrustal blocks can be identified: Barlee, Marda, Hyden, Corrigin,Lake Johnston, and Eastern Goldfields. The Barlee block showsa bimodal eHf distribution, with peaks at 0 and +3.0. In relation

Fig. 1. Map of the Archean Yilgarn Craton showing the basic granite-greenstone bedrock geology and location of the ∼2.9 and 2.7 Ga komatiitelocalities. Individual terranes/domains (39, 40) are labeled. Greenstone beltsare labeled as follows: MD, Marda–Diemals; SC, Southern Cross; FO, For-restania; LJ, Lake Johnston; RAV, Ravensthorpe; AW, Agnew–Wiluna; andKAL, Kalgoorlie/Kambalda. Komatiite localities are from Barnes and Fior-entini (10) (Table S4).

Fig. 2. Lu-Hf (eHf) map of the Yilgarn Craton at 3,050–2,820 Ma. (A) Hf isotope map with the location of sample sites and komatiite localities. (B) Interpretivemap of the area, showing the individual crustal blocks identified from the Hf isotope map and corresponding probability density plots. The blue curverepresents the median eHf for discrete temporal groups (ng), whereas the red curve represents all of the individual grain analyses (na). Dark gray polygonsshown in the background of all maps represent supracrustal belts (Fig. 1).

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to the first time slice, the Hyden block has extended north andmerged with the Marda block, although its western extentappears to have been rejuvenated by mantle input (Corriginblock – eHf ∼0). The result is a narrow block of old, reworkedcrust with eHf peaks at −4.3 and −2.3. The Marda block remainsold and unradiogenic, with a major eHf peak at −4.0. TheLake Johnston block has been significantly reworked since 3,050–2,820 Ma, as demonstrated by the lower eHf at −0.5 (Fig. 3). TheEastern Goldfields is now identifiable as a crustal block, and ismore juvenile than the blocks to the west, displaying a bimodaleHf distribution with peaks at +2.0 and +4.0. Overall, thesecond time slice shows reworking throughout the core area of theWest Yilgarn and addition of juvenile material at the northern,western, and eastern edges.The third time slice (T3 − 2,720–2,600 Ma; Fig. 4) represents the

lithospheric architecture at the time of voluminous ∼2.7 Gakomatiite volcanism in the Kalgoorlie Terrane of the Eastern

Goldfields Superterrane (10, 33). Two major lithospheric blocks arepresent at this time: the Eastern Goldfields and the West Yilgarn(Fig. 4). The Eastern Goldfields block comprises a bimodal eHfdistribution, with the majority of material at +2.0, and a notableminor peak at −2.0. The West Yilgarn is the result of the pro-gressive cratonization of the individual blocks identified in timeslices T1 and T2. It has a eHf distribution with peaks at −2.4(major) and +1.8, −5.5, and −8.0 (minor). These variable sourcesreflect the complex history of the West Yilgarn as well as theintracratonic signature of the individual blocks from which itderives (Fig. 4). Overall, it appears that the majority of the WestYilgarn formed from a source ∼800 Ma (Marda) to 200 Ma (LakeJohnston) older than that of the Eastern Goldfields (Fig. S4).

DiscussionIn the Yilgarn Craton, high-flux, thick channelized komatiites withaverage whole-rock MgO contents >30% only occur in greenstone

Fig. 3. Lu-Hf (eHf) map of the Yilgarn Craton at 2,820–2,720 Ma. (A) Hf isotope map with the location of sample sites and komatiite localities. (B) Interpretivemap of the area, showing the individual crustal blocks identified from the Hf isotope map and corresponding probability density plots. The blue curverepresents the median eHf for discrete temporal groups (ng), whereas the red curve represents all of the individual grain analyses (na). Dark gray polygonsshown in the background of all maps represent supracrustal belts (Fig. 1).

Fig. 4. Lu-Hf (eHf) map of the Yilgarn Craton at 2,720–2,600 Ma. (A) Hf isotope map with the location of sample sites and komatiite localities. (B) Interpretivemap of the area, showing the individual crustal blocks identified from the Hf isotope map and corresponding probability density plots. The blue curverepresents the median eHf for discrete temporal groups (ng), whereas the red curve represents all of the individual grain analyses (na). Dark gray polygonsshown in the background of all maps represent supracrustal belts (Fig. 1).

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belts located at the interface between juvenile and reworked crustaldomains (Figs. 2 and 4). Preexisting lithospheric weaknesses atthese craton margins (10, 34, 35) led to crustal attenuation,major intracontinental rifts, and high-flux magma transportthrough associated translithospheric conduits (10, 34). Ultra-mafic magmas rapidly ascended from mantle to surface withoutsignificant ponding or differentiation in the lithosphere (Figs. 5and 6) (34, 35), and formed giant, high-flux komatiite flow fieldsthat contain large nickel-sulfide ore reserves (5, 33). At ∼2.9 Gain the juvenile Lake Johnston block, channelized high-MgOkomatiites erupted to form thick olivine cumulate bodies that arenow preserved in the Forrestania (17), Lake Johnston (10, 19,33), and Ravensthorpe (36) greenstone belts. Their setting isconsistent with the occurrence of a paleocraton margin at theHyden–Lake Johnston block boundary at ∼2.9 Ga (Figs. 2 and5). Between ∼2.9 and 2.7 Ga, the focus of hot and voluminouskomatiite magmatism shifted to the east toward the KalgoorlieTerrane of the Eastern Goldfields (Fig. 6), following the marginof the growing continent.Conversely, plume-derived magmas that erupted in “intra-

continent” settings (Figs. 5 and 6) formed abundant basalts andonly low-flux, thin komatiites with average MgO values typically<30% (10, 33), as demonstrated by the greenstone belts of theMarda block at ∼2.9 Ga (24) and in the Kurnalpi Terrane at ∼2.7Ga (10). In this setting, magmas rose through thick reworkedlithosphere (Marda) or thinner juvenile (Kurnalpi) crust that wasnot adjacent to an older, thicker crustal block at the time ofmagmatism (Figs. 2 and 4). Consequently, eruptions were notsufficiently voluminous or continuous to form the giant komatiiteflow fields and related nickel mineralization that is associatedwith craton margins.The komatiites of the Southern Cross greenstone belt (18) form

an intermediate group between the intracontinent (low-MgO, un-channelized) and the continent edge (high-MgO, channelized) typekomatiites. These magmas have high-MgO contents (18), but are

unchannelized, cumulate-poor, and unmineralized (18). We suggestthat, due to the unique location of the Southern Cross greenstonebelt between the reworked Hyden and Marda blocks (Fig. 2),magmas were focused enough to form high-MgO komatiites, butnot to the extent needed for high-flux, continuous eruptions.The heterogeneous nature of komatiite magmatism at ∼2.9

and 2.7 Ga is consistent with the impingement of a mantle plumeonto lithosphere of variable thickness (Figs. 5 and 6). The iso-topic architecture constrained in this study indicates that the∼2.9 and 2.7 Ga komatiites were emplaced in similar geodynamicsettings, at the margins of thick crustal domains (Figs. 2–6).Consequently, the melting dynamics of the underlying mantleand the petrogenetic signature of the komatiites would also beexpected to be similar. However, although both Munro- andBarberton-type komatiites were erupted in the Lake Johnstonblock at ∼2.9 Ga (17–19, 36), only Munro-type komatiite magma-tism is recorded in the Kalgoorlie Terrane at ∼2.7 Ga (10, 19, 33).Barberton-type komatiites contain notably depleted aluminum

concentrations (Al2O3/TiO2 ∼10) in relation to Munro-type mag-mas (Al2O3/TiO2 ∼20). These compositional differences reflectthe conditions under which the melts separated from their plumesources (2, 5). Barberton-type komatiites formed in the garnetstability zone, at a depth of ∼450–300 km (37); whereas, Munro-type komatiites segregated from their mantle sources at <300 kmdepth, although high-percentage partial melts (>30%) only formedat <150 km depth (2, 5). A possible explanation for the occurrenceof Barberton-type komatiites in the ∼2.9 Ga sequences is thesecular cooling of the Earth; melt generation at >300 km isonly possible in the hotter, older mantle (13). This hypothesis issupported by the well-constrained global decline of Barberton-type komatiite magmatism from 3.5 to 2.7 Ga (2, 5). However, itis unlikely that sufficient global cooling occurred between ∼2.9 and2.7 Ga to affect the source depth of the Yilgarn komatiites (1, 2).An alternative scenario considers the spatiotemporal vari-

ability in komatiite type as a consequence of petrogenetic

Fig. 5. Isotopic cross-section and interpreted lithospheric ar-chitecture during the emplacement of ∼2.9 Ga komatiites inthe southern Youanmi Terrane. (A) eHf map showing the iso-topic architecture at the time of the ∼2.9 Ga plume emplace-ment, with the approximate extent of the plume head (red)and tail (yellow) shown for scale; (B) isotopic cross-section (A–A′) documenting the changing eHf of the crust from east towest (circles represent median; squares represent individualanalyses) together with the occurrence and MgO content (Ta-ble S4) of ultramafic–mafic magmatism; and (C) interpretedlithospheric architecture based on the changing isotopicproperties of the crust. The white ellipses represent thetypes of magma available in a particular area and thedashed lines show the approximate limits of their sourceregions. TiO2 vs. Al2O3 data (17, 19) are shown for komatiitesof the relevant greenstone belts, demonstrating the pro-gressive eastward homogenization of Barberton-type melts.The location of the continent core and continent edge areshown based on the Lu-Hf data. The eruption of komatiitewould likely have been facilitated by plume-related exten-sion at this interface. Approximate thickness values for de-veloped Archean lithosphere (∼250–150 km) were taken fromBoyd et al. (41), Artemieva and Mooney (42), and Begg et al.(43). The approximate scale of the plume head (∼1,600 km),tail (200–100 km), and thickness (∼150–100 km) were takenfrom Campbell et al. (15). Note that the plume-tail mate-rial moves above the plume head, despite impacting thelithosphere later, as it is hotter, more buoyant, and sub-sequently emplaced at higher flux (15).

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filtering by thick lithosphere. The relative architecture betweenthe ∼2.9 Ga Hyden−Lake Johnston and ∼2.7 Ga West Yilgarn−Eastern Goldfields blocks is fundamentally similar (Figs. 5 and 6).However, the less-reworked nature of the Lake Johnstonblock at ∼2.7 Ga (Fig. 4) suggests that the ∼2.9 Ga Hydenblock was thicker than this part of the ∼2.7 Ga West Yilgarnblock (Figs. 5 and 6); an inference supported by magnetotelluricdata (38). Consequently, at ∼2.9 Ga, the >150-km-thick litho-sphere of the Hyden block prevented the segregation of high-percentage (∼50–30%) partial melt Munro-type magmas (MH)and restricted melt generation to Barberton- and low-percentagepartial melt (<30%) Munro-type magmas (ML; Fig. 5). The lackof large quantities of Munro-type melt, together with the closeproximity of the craton margin (Fig. 5), ensured Barberton-typemelts were erupted in the Forrestania greenstone belt (17) be-fore significant dilution by the upper high-percentage partial meltMunro-type magmas could occur. The eastward position of theLake Johnston greenstone belt allowed homogenization of theBarberton–Munro melts, resulting in magmas with intermediatecompositions (19) (Fig. 5).In contrast, at ∼2.7 Ga in the Eastern Goldfields, due to the

shallower nature of the Lake Johnston block, Barberton-typemagmas generated under the Hyden block would have had to travel∼300–200 km laterally through both low- and high-percentagepartial-melt Munro-type sources (Fig. 6). Subsequently, theBarberton-type signature was diluted to the extent that onlyMunro-type komatiites were erupted in the Eastern Goldfields (9).A Phanerozoic analog for the relationship between litho-

spheric architecture and magmatism in the Yilgarn Craton at∼2.9 and 2.7 Ga is the ∼17 Ma (31, 32) continental plume settingat Yellowstone in the western United States. The overlying litho-sphere comprises the old, thick Archean Wyoming Craton to theeast and the thinner Mesozoic–Paleozoic-accreted oceanic ter-ranes to the west (29–31). The westward movement of the NorthAmerican plate (∼2 cm/y; ref. 31) traversed this lithospheric

architecture over the stationary plume, resulting in variations inthe character, frequency, and isotopic signature of volcanism (29,31, 32). Under the younger, thinner accreted terranes in the west,the plume ascends to higher levels allowing the formation oflarge volumes of decompression melt (29, 31, 32, 34, 35) and ajuvenile (eNd +4, eHf +10; ref. 29) volcanic sequence domi-nated by basaltic (including the Columbia River basalts; ref. 32)and minor felsic magmatism. This setting is a modern analog tothe high-MgO, voluminous continent-edge–type komatiite vol-canism observed in the Yilgarn Craton. To the east, where theYellowstone plume impinges on thick, old Archean lithosphere,less decompression melting occurs. This relatively small amountof mantle melt infiltrates the overlying lithosphere, where it iscontaminated by more unradiogenic continental material. Thisprocess leads to evolved (eNd −11, eHf −10; ref. 29) felsic-onlyvolcanism, similar to that recorded in the Marda block at ∼2.7Ga (24) (eHf −7 to −2; Table S2). This architecture is a modernanalog to the intracontinent Archean settings, where komatiitemagmatism is largely absent.This study demonstrates that the dynamic evolution of the

early continents controlled the location, geochemistry, metal-logeny, and volcanology of komatiites. An analogous processcontinues to operate in the modern Earth (30, 32, 34), and hasbeen fundamental to the transfer of deep mantle material tothe continental crust, oceans, and atmosphere throughout thehistory of the planet.

Materials and MethodsWe report here on new U-Pb geochronology (36 samples) and Lu-Hf isotopicdata (84 samples) from the Yilgarn Craton of Western Australia (Tables S2and S3). The U-Pb zircon geochronology was performed on the sensitivehigh-resolution ion microprobes at the John de Laeter Centre of MassSpectrometry at Curtin University, Western Australia. Following precisedating of the magmatic and inherited zircon populations from sampledgranites and felsic volcanics, >900 in situ Lu-Hf isotopic analyses were carriedout at the Centre for the Geochemical Evolution and Metallogeny of

Fig. 6. Isotopic cross-sections and interpreted lithosphericarchitecture during the emplacement of the ∼2.7 Ga komati-ites in the Eastern Goldfields (Kalgoorlie Terrane). (A) eHf mapshowing the isotopic architecture at the time of the ∼2.7 Gaplume emplacement, with the approximate extent of theplume head (red) and tail (yellow) shown for scale; (B) iso-topic cross-section (B–B′) documenting the changing eHf ofthe crust from east to west (circles represent median; squaresrepresent individual analyses) together with the occurrenceand MgO content (Table S4) of ultramafic–mafic magmatism;and (C) interpreted lithospheric architecture based on thechanging isotopic properties of the crust. The white ellipsesrepresent the types of magma available in a particular area andthe dashed lines show the approximate limits of their sourceregions. TiO2 vs. Al2O3 data (9) are shown for komatiites ofthe Eastern Goldfields, demonstrating the eastward dilutionand removal of Barberton-type melts. The location of thecontinent core and continent edge are shown based on theLu-Hf dataset. The eruption of komatiite would likely havebeen facilitated by plume-related extension at this interface.The dashed red lines shown in C account for the potentialvariation in lithospheric architecture within the Lake Johnstonblock based on the Lu-Hf data. External data used to constructthese diagrams are the same as for Fig. 5. Note that the plume-tail material moves above the plume head, despite impactingthe lithosphere later, as it is hotter, more buoyant, and sub-sequently emplaced at higher flux (15).

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Continents at Macquarie University in Sydney, Australia. These data werethen processed and plotted as time-slice contour maps using ArcGIS (Figs. 2–4 and Fig. S5). For the complete methodology we refer the reader to theSupporting Information.

ACKNOWLEDGMENTS. Adam Wilson and Alex Clarke-Hale are thanked forfield support. This project was funded by Australian Research Council(ARC) Linkage Grants LP0776780 and LP100100647 with BHP BillitonNickel West, Norilsk Nickel, St Barbara, and the Geological Survey ofWestern Australia (GSWA). The GSWA is acknowledged for sample pro-vision and technical advice. C.L.K., S.S.R., and M.P.D. publish with per-mission of the Executive Director of the Geological Survey of Western

Australia. S.J.B.’s contribution is supported by the Commonwealth Sci-entific and Industrial Research Organization (CSIRO) Minerals Down Un-der National Research Flagship. The Lu-Hf analytical data were obtainedusing instrumentation funded by Department of Education Science andTraining (DEST) Systemic Infrastructure grants, ARC Linkage Infrastructure,Equipment and Facilities (LIEF), National Collaborative Research Infra-structure Strategy (NCRIS), industry partners, and Macquarie University.The U-Pb zircon geochronology was performed on the sensitive high-resolution ion microprobes at the John de Laeter Centre of Mass Spectrom-etry (Curtin University). This is contribution 456 from the ARC Centre ofExcellence for Core to Crust Fluid Systems (CCFS) and 939 from the Centrefor the Geochemical Evolution and Metallogeny of Continents (GEMOC)Key Centre.

1. Herzberg C, Condie K, Korenaga J (2010) Thermal history of the Earth and its pet-rological expression. Earth Planet Sci Lett 292(1–2):79–88.

2. Herzberg C (1992) Depth and degree of melting of komatiites. J Geophys Res 97(B4):4521–4540.

3. Herzberg C, et al. (2007) Temperatures in ambient mantle and plumes: Constraintsfrom basalts, picrites, and komatiites. Geochem Geophys Geosystems 8(2).

4. Vacquier V (1998) A theory of the origin of the Earth’s internal heat. Tectonophysics291(1–4):1–7.

5. Arndt NT, Barnes SJ, Lesher CM (2008) Komatiite (Cambridge Univ Press, Cambridge).6. McDonough WF, Ireland TR (1993) Intraplate origin of komatiites inferred from trace

elements in glass inclusions. Nature 365(6445):432–434.7. Grove TL, Parman SW (2004) Thermal evolution of the Earth as recorded by komati-

ites. Earth Planet Sci Lett 219(3–4):173–187.8. Hill RET, Barnes SJ, Gole MJ, Dowling SE (1995) The volcanology of komatiites as

deduced from field relationships in the Norseman-Wiluna greenstone belt, WesternAustralia. Lithos 34(1-3):159–188.

9. Barnes SJ (2006) Komatiites: Petrology, volcanology, metamorphism and geochemistry.Soc Econ Geol Spec Publ 13:13–49.

10. Barnes SJ, Fiorentini ML (2012) Komatiite magmas and sulfide nickel deposits: Acomparison of variably endowed Archean terranes. Econ Geol 107(5):755–780.

11. Prokoph A, Ernst RE, Buchan KL (2004) Time‐series analysis of large igneous provinces:3500 Ma to present. J Geol 112(1):1–22.

12. Shimizu K, Nakamura E, Maruyama S (2005) The geochemistry of ultramafic to maficvolcanics from the Belingwe Greenstone Belt, Zimbabwe: Magmatism in an Archeancontinental large igneous province. J Petrol 46(11):2367–2394.

13. Nisbet EG, Cheadle MJ, Arndt NT, Bickle MJ (1993) Constraining the potential tem-perature of the Archaean mantle: A review of the evidence from komatiites. Lithos30(3-4):291–307.

14. Blichert-Toft J, Arndt NT (1999) Hf isotope compositions of komatiites. Earth PlanetSci Lett 171(3):439–451.

15. Campbell IH, Griffiths RW, Hill RI (1989) Melting in an Archaean mantle plume: Headsit’s basalts, tails it’s komatiites. Nature 339(6227):697–699.

16. Maier WD, et al. (2009) Progressive mixing of meteoritic veneer into the early Earth’sdeep mantle. Nature 460(7255):620–623.

17. Perring CS, Barnes SJ, Hill RET (1996) Geochemistry of komatiites from Forrestania,Southern Cross Province, Western Australia: Evidence for crustal contamination.Lithos 37(2-3):181–197.

18. Thebaud N, Barnes SJ (2012) Geochemistry of komatiites in the Southern Cross Belt,Youanmi Terrane, Western Australia. Aust J Earth Sci 59(5):695–706.

19. Heggie GJ, Fiorentini ML, Barnes SJ, Barley ME (2012) Maggie Hays Ni Deposit: Part 2.Nickel mineralization and the spatial distribution of PGE ore-forming signatures inthe Maggie Hays Ni System, Lake Johnston Greenstone Belt, Western Australia. EconGeol 107(5):817–833.

20. Compston W, Williams IS, Campbell IH, Gresham JJ (1986) Zircon xenocrysts from theKambalda volcanics: Age constraints and direct evidence for older continental crustbelow the Kambalda-Norseman greenstones. Earth Planet Sci Lett 76(3-4):299–311.

21. Mole DR, et al. (2012) Spatio-temporal constraints on lithospheric development in thesouthwest-central Yilgarn Craton, Western Australia. Aust J Earth Sci 59:625–656.

22. Lesher CM, Arndt NT (1995) REE and Nd isotope geochemistry, petrogenesis andvolcanic evolution of contaminated komatiites at Kambalda, Western Australia.Lithos 34(1-3):127–157.

23. Nelson DR (1997) Evolution of the Archaean granite-greenstone terranes of theEastern Goldfields, Western Australia: SHRIMP U-Pb zircon constraints. PrecambrianRes 83(1-3):57–81.

24. Chen SF, Riganti A, Wyche S, Greenfield JE, Nelson DR (2003) Lithostratigraphy andtectonic evolution of contrasting greenstone successions in the central Yilgarn Cra-ton, Western Australia. Precambrian Res 127(1-3):249–266.

25. Hawkesworth CJ, et al. (2010) The generation and evolution of the continental crust.J Geol Soc London 167(2):229–248.

26. Belousova EA, et al. (2010) The growth of the continental crust: Constraints fromzircon Hf-isotope data. Lithos 119(3-4):457–466.

27. Champion DC, Cassidy KF (2007) An overview of the Yilgarn Craton and its crustalevolution. Proceedings of Geoconferences (WA) Inc.: Kalgoorlie ’07 Conference, edsBierlein FP, Knox-Robinson CM (Geoscience Australia, Canberra, Australia), pp 8–13.

28. Mole DR, et al. (2013) Crustal evolution, intra-cratonic architecture and the metal-logeny of an Archaean craton. Ore Deposits in an Evolving Earth, eds Jenkin GRT,et al. (Geological Society of London, London), Vol 393, 10.1144/SP393.8.

29. Nash BP, Perkins ME, Christensen JN, Lee D-C, Halliday AN (2006) The Yellowstonehotspot in space and time: Nd and Hf isotopes in silicic magmas. Earth Planet Sci Lett247(1-2):143–156.

30. Ormerod DS, Hawkesworth CJ, Rogers NW, Leeman WP, Menzies MA (1988) Tectonicand magmatic transitions in the Western Great Basin, USA. Nature 333(6171):349–353.

31. Pierce KL, Morgan LA (2009) Is the track of the Yellowstone hotspot driven by a deepmantle plume? Review of volcanism, faulting, and uplift in light of new data.J Volcanol Geotherm Res 188(1-3):1–25.

32. Hanan BB, Shervais JW, Vetter SK (2008) Yellowstone plume–continental lithosphereinteraction beneath the Snake River Plain. Geology 36(1):51–54.

33. Barnes SJ (2006) Komatiite-hosted nickel sulfide deposits: Geology, geochemistry, andgenesis. Soc Econ Geol Spec Publ 13:51–97.

34. Begg GC, et al. (2010) Lithospheric, cratonic, and geodynamic setting of Ni-Cu-PGEsulfide deposits. Econ Geol 105(6):1057–1070.

35. Sleep NH (1997) Lateral flow and ponding of starting plume material. J Geophys Res102(B5):10001–10012.

36. Witt WK (1998) Geology and mineral resources of the Ravensthorpe and Cocanarup1:100 000 sheets. (Geological Survey of Western Australia, Perth, Australia), GeologicalSurvey of Western Australia Report 54.

37. Robin-Popieul CC, et al. (2012) A new model for Barberton komatiites: Deep criticalmelting with high melt retention. J Petrol 53(11):2191–2229.

38. Dentith MC, et al. (2013) A magnetotelluric traverse across the southern YilgarnCraton. (Geological Survey of Western Australia, Perth, Australia), Geological Surveyof Western Australia Report 121, p 43.

39. Pawley MJ, et al. (2012) Adding pieces to the puzzle: Episodic crustal growth anda new terrane in the northeast Yilgarn Craton, Western Australia. Aust J Earth Sci59(5):603–623.

40. Cassidy KF, et al. (2006) A revised geological framework for the Yilgarn Craton,Western Australia. Geological Survey of Western Australia - Record 2006/8:8.

41. Boyd FR, Gurney JJ, Richardson SH (1985) Evidence for a 150-200-km thick Archaeanlithosphere from diamond inclusion thermobarometry. Nature 315(6018):387–389.

42. Artemieva IM, Mooney WD (2001) Thermal thickness and evolution of Precambrianlithosphere: A global study. J Geophys Res 106(B8):16387–16414.

43. Begg GC, et al. (2009) The lithospheric architecture of Africa: Seismic tomography,mantle petrology, and tectonic evolution. Geosphere 5(1):23–50.

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