Formation of Early Archean Granite-Greenstone Terranes From

Chemical Geology 551 (2020) 119757 Contents lists available at ScienceDirect Chemical Geology journal homepage: www.elsevier.com/locate/chemgeo Formation of early Archean Granite-Greenstone Terranes from a globally chondritic mantle: Insights from igneous rocks of the Pilbara Craton, T Western Australia ⁎ Andreas Peterssona,b, , Anthony I.S. Kempa, Chris M. Graya, Martin J. Whitehouseb a School of Earth Sciences, The University of Western Australia, Crawley, Australia b Swedish Museum of Natural History, Box 50 007, SE-104 05 Stockholm, Sweden ARTICLE INFO ABSTRACT Editor: Balz Kamber The continental crust grows via juvenile additions from the mantle. However, the timing of initial continent fi Keywords: stabilisation and the rate of subsequent continental growth during the rst billion years of Earth history is widely Pilbara Craton debated, in part due to uncertainty over the composition of the mantle source of new crust. Well-preserved Chondritic mantle Archean granite-greenstone terranes, as present within the Pilbara Craton (Western Australia), provide insights Granite-greenstone belts into the sources of felsic magmas and the processes of continental growth and evolution in the distant geological Archean past at the regional scale. Here, we present zircon U-Pb, O and Hf isotope data from ancient gneissic and granitic Zircon rocks of the Pilbara Craton, to decipher magma sources and the timing and processes of craton growth. There is U-Pb, Lu-Hf, O-isotopes no evidence for depleted mantle compositions, and the simplest interpretation is that the crust of the Pilbara Crustal growth Craton was generated from mantle with a chondritic Hf isotope composition. Our results indicate crustal addition at ~3.59 Ga, represented by emplacement of gabbroic to anorthositic rocks. We suggest that the formation of these igneous rocks, and the foundering of the complementary residues, triggered extensive melting of hot, upwelling mantle, leading to the subsequent accumulation of the > 12 km thick greenstone belt eruptive se- quences from 3.53 Ga, with emplacement of coeval felsic magmas at depth. This process shaped the initial crustal configuration of the proto-craton, which subsequently underwent gravitationally driven overturn and reworking to generate stable, cratonic continental crust with the distinctive dome and keel architecture. The zircon Hf and O isotope signatures of the Pilbara igneous rocks from ~3.59–3.4 Ga do not support remelting of an ancient (> 3.8 Ga) basement, and reinforce the overwhelmingly chondritic to near-chondritic zircon Hf isotope composition of Eoarchean meta-igneous rocks from a number of different Archean cratons. A corollary of this remarkable global consistency is that a significant volume of the mantle maintained a chondritic composition for the Lu-Hf system from the formation of the Earth into the Paleoarchean (up to 3.6–3.5 Ga), as would be the case if stabilised volumes of felsic continental crust prior to 3.5 Ga were relatively small. One implication is that the common assumption of a linear evolution of depleted mantle from 4.5 Ga to the present day is in- appropriate for determining the timing and volume of continental crust extraction in the Archean. The nearly identical early evolution of the Pilbara and Kaapvaal cratons suggests a common process to generate Archean granite-greenstone terranes that does not require extensive reworking of ancient crust, but rather involves juvenile crustal addition above persistent zones of upwelling, chondritic mantle. 1. Introduction Belousova et al., 2010; Dhuime et al., 2012). In calculating the growth rate of continental crust, such models typically adopt the conventional Due to the miniscule amount of preserved Hadean to Paleoarchean view (e.g., Hofmann, 1988) that the continental crust and incompatible rocks, models for the generation and evolution of continental crust element depleted mantle reservoirs are complementary, with the im- during the first billion years of Earth history emphasise long-lived plicit assumption that the extent of mantle depletion, as registered by radiogenic isotope systems such as Sm-Nd (Bennett et al., 1993; Nd and Hf isotope compositions, can be used to constrain the mass of Bowring and Housh, 1995) and Lu-Hf (e.g. Vervoort et al., 1996; continental crust that was extracted and stabilised through time. Thus, ⁎ Corresponding author at: School of Earth Sciences, The University of Western Australia, Crawley, Australia. E-mail address: [email protected] (A. Petersson). https://doi.org/10.1016/j.chemgeo.2020.119757 Received 12 May 2020; Received in revised form 12 June 2020; Accepted 14 June 2020 Available online 22 June 2020 0009-2541/ © 2020 Elsevier B.V. All rights reserved. A. Petersson, et al. Chemical Geology 551 (2020) 119757 continental growth curves derived from large compilations of detrital been repeatedly proposed that the East Pilbara Terrane developed on an zircon U-Pb and Hf isotope data infer that 30–50% of the present even older, perhaps ≥3.8 Ga, continental substrate (Green et al., 2000; continental volume was stabilised prior to 3.5 Ga (Belousova et al., Van Kranendonk et al., 2007; Tessalina et al., 2010; Gardiner et al., 2010; Dhuime et al., 2012), an outcome that aligns with conclusions 2017; Wiemer et al., 2018). Critically, the evidence used to argue for based on other isotopic approaches (e.g. Armstrong, 1991; Bowring and this ancient basement is based on whole rock Sm-Nd model ages that Housh, 1995; Pujol et al., 2013; McCoy-West et al., 2019). assume crust separation from a strongly depleted mantle reservoir However, as pointed out by Kamber (2015), continental growth (Hamilton, 1981; Jahn et al., 1981; Gruau et al., 1987; Bickle et al., models based on detrital zircon U-Pb and Hf isotope data assume that 1989, 1993; Smithies et al., 2003; Smithies et al., 2007; Van the mass of the depleted mantle has remained constant and that the Hf Kranendonk et al., 2007; Tessalina et al., 2010), variations in zircon Lu- isotope evolution of the depleted mantle was linear, from chondritic at Hf isotope compositions (Gardiner et al., 2017), and modelling of trace ~4.5 Ga to strongly radiogenic at the present day, as represented by the element abundances in the oldest eruptive rocks (Green et al., 2000). upper mantle sampled by modern mid-ocean ridge basalts. If the mass Direct evidence for an Eoarchean substrate includes: (1) ~3.66–3.58 Ga of depleted mantle changed through time, then the radiogenic isotope gneiss enclaves within younger, ~3.42–3.24 Ga monzogranite and signatures of some Archean rocks, if primary, could indicate derivation granodiorite in the Warrawagine Granitic Complex (Kemp et al., 2015); from small, transient, highly depleted mantle domains (e.g., Bennett (2) pre-3.6 Ga zircon cores in ~3.46 Ga and younger felsic igneous et al., 1993), rather than reflect the existence of a global, convecting rocks (Thorpe et al., 1992; Kemp et al., 2015; Sheppard et al., 2017); mantle reservoir that was depleted by voluminous prior crust extraction and (3) detrital zircon grains found across the Pilbara Craton that (Bédard, 2018). Several studies highlight that a linear isotope evolution predate deposition of their respective sedimentary successions by up to of depleted mantle from 4.5 Ga to the present day is not supported by 300 million years (Van Kranendonk et al., 2007; Hickman et al., 2010; the growing Hf isotope datasets from well-preserved igneous rocks, and Kemp et al., 2015). These lines of evidence are consistent with that the depletion history of the early Archean mantle is not well Eoarchean crust predating the East Pilbara Terrane, however a base- constrained (Kemp et al., 2015; Vervoort and Kemp, 2016; Fisher and ment component that is older than 3.8 Ga has not been confirmed. More Vervoort, 2018). Small pockets of chondritic mantle may even have recently, based on Hf isotopic signatures of inherited zircon crystals in a persisted through to the present day (Woodhead et al., 2019). rhyolite, Petersson et al. (2019b) suggest a small, ~3.75 Ga felsic The above models for large volumes of ancient continental crust crustal nucleus to the Pilbara Craton, rather than a widespread felsic must also be reconciled with the paucity (< 1%) of > 3.5 Ga rocks ≥3.8 Ga ‘proto’-crust. Models for formation of the Pilbara Craton preserved on Earth today. It is important to recognise that the present therefore vary markedly regarding the timing of initial continental distribution of ancient crust reflects preservation biases and is not a crustal growth, ranging from Hadean (Tessalina et al., 2010) to ~3.6 Ga reliable proxy for the volumes of crust that were actually generated. (Kemp et al., 2015; Petersson et al., 2019a), for the most part based on However, if large continental volumes were indeed stabilised by 3.5 Ga, whether the upper mantle is assumed to have been depleted or chon- the question remains as to why early Archean continental materials, or dritic in composition. the geochemical signals of their former existence, do not feature more To address the controversy about the age of the putative continental prominently in the extant geological record. It has been suggested that, substrate for the Pilbara Craton, and the implications for global crust- globally, the low number of retrieved > 3.5 Ga detrital or inherited mantle evolution models, we report the results of a study designed to zircons is also inconsistent with numbers that might be expected if large identify and characterise the oldest igneous components of the Pilbara stabilised volumes of pre-3.5 Ga felsic continental crust were reworked Craton. These older, generally gneissic and multi-component rocks in and eroded through time (Stevenson and Patchett, 1990; Nutman, the granitic complexes have not received the same level of attention as 2001; Condie et al., 2011; Rollinson, 2017).

Load more