The Cosmos greenstone succession, Agnew-Wiluna greenstone belt, Yilgarn Craton, Western Australia: Geochemistry of an enriched Neoarchaean volcanic arc succession
The Cosmos greenstone succession, Agnew-Wiluna greenstone belt, Yilgarn Craton, Western Australia: Geochemistry of an enriched Neoarchaean volcanic arc succession
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DOI：
10.1016/j.lithos.2014.06.013
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发表时间：
2014-09-15
期刊：
影响因子：
3.5
通讯作者：
Hastie, A. R.
中科院分区：
文献类型：
--
作者：
de Joux, A.;Thordarson, T.;Hastie, A. R.
伊尔加恩克拉通新太古代东部金田超地体(EGS)的地球动力学背景是争论的主题。一些作者提出了羽流模型，而另一些作者则主张以俯冲-吸积模型的变体来解释矿化绿岩带序列的起源。EGS最西端的Kalgoorlie地体中的长英质火山作用被认为具有英云闪长岩-奥长花岗闪长岩/英安岩(TTG/D)的地球化学相似性。宇宙绿岩系位于卡尔古利地体的阿格纽-威鲁纳绿岩带(AWB)中，含有几个科马提岩赋存的硫化镍矿床，其火山下盘由一系列成分从玄武岩安山岩到流纹岩的碎屑岩和连续岩组成。轻稀土元素(LREE)和大离子亲石元素(LILEs)相对于高场强元素(HFSE)在所有火山单元中都表现出强烈的富集性，岩石表现出强烈的正铅和负Nb异常。这些地球化学特征与现代高钾钙碱性-钾玄武岩陆弧系列十分相似。对比REE、LILE和HFSE的浓度，结合同化-分步结晶(AFC)模拟，表明下盘层序中的夹层英安质和安山质火山岩不是同源的。长英质火山岩中的晶质锆石表明，较老陆壳的某种同化作用促成了下盘火山岩序列的形成。宇宙火山序列的地球化学特征表明，母质熔体是由俯冲带地幔楔体中被俯冲地壳物质污染的富集型橄榄岩部分熔融形成的。相反，横穿火山序列的两个较年轻的长英质斑岩侵入体具有明显的TTG/D亲和力。因此，这些侵入体被认为是通过俯冲板块的部分熔融而产生的，与局部高钙花岗岩类侵入体有关。宇宙火山序列代表了卡尔古利地体所描述的第一个喷出的高钾钙碱性至钾玄武岩火山弧序列，并结合地层学的年龄测定，表明形成于2736 Ma至晚于2724 Ma的长寿火山弧环境。宇宙科马提斯镍硫化物矿床火山下盘序列的成分和地球化学亲和力与AWB内的大多数长英质火山岩以及更广泛的Kalgoorlie地体形成对比，表明该地区的整体结构比目前认为的要复杂得多。我们的结论不仅对EGS最近的构造演化模式有一定的指导意义，而且对晚太古代板块构造活动的争论也有重要意义。宇宙火山序列的弧形亲和性，含有丰富的高钾钙碱性安山岩熔岩，为新太古代板块构造的运作提供了进一步的支持。(C)2014爱思唯尔B.V.保留所有权利。
The geodynamic setting of the Neoarchaean Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton is the subject of debate. Some authors propose plume models, while others advocate variants on a subduction accretion model for the origin of mineralised greenstone belt sequences. Felsic volcanism in the Kalgoorlie Terrane, the westernmost terrane of the EGS, is considered to have a tonalite-trondhjemite-granodiorite/dacite (TTG/D) geochemical affinity. The Cosmos greenstone succession, which lies in the Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, contains several komatiite-hosted nickel sulphide deposits, the volcanic footwall to which consists of an intercalated succession of fragmental and coherent rocks ranging in composition from basaltic andesite to rhyolite. Light rare earth elements (LREEs) and large ion-lithophile elements (LILEs) are strongly enriched relative to high field strength elements (HFSEs) across all volcanic units, and the rocks display strong positive Pb and negative Nb anomalies. These geochemical characteristics resemble closely those of modern high-K calc-alkaline to shoshonite continental arc successions. Contrasting REE, LILE and HFSE concentrations, coupled with assimilation-fractional crystallisation (AFC) modelling, shows that the intercalated dacitic and andesitic volcanic rocks within the footwall succession are not co-genetic. Xenocrystic zircons within the felsic volcanic lithologies indicate that some assimilation of older continental crust contributed to the generation of the footwall volcanic sequence. The geochemical characteristics of the Cosmos volcanic succession indicate that parental melts were derived via partial melting of enriched peridotite that had been contaminated by subducted crustal material within the mantle wedge of a subduction zone. In contrast, two younger felsic porphyry intrusions, which cross-cut the volcanic succession, have a distinct TTG/D affinity. Therefore, these intrusions are considered to be generated via partial melting of a subducting slab and are related to local high-Ca granitoid intrusions. The Cosmos volcanic succession represents the first extrusive high-K calc-alkaline to shoshonitic volcanic arc sequence described in the Kalgoorlie Terrane and, coupled with age dating of the stratigraphy, is indicative of formation in a long-lived volcanic arc setting active from 2736 Ma to later than 2724 Ma. The composition and geochemical affinity of the volcanic footwall succession to the Cosmos komatiite-hosted nickel-sulphide deposits contrasts with the majority of felsic volcanic rocks within the AWB and also the wider Kalgoorlie Terrane, suggesting that the overall architecture of this region is more complex than is currently thought. Our conclusions not only have consequences for recent models of the tectonic evolution of the EGS but also contribute to the debate on the operation of plate tectonics during the late Archaean in general. The arc affinity of the Cosmos volcanic succession, containing abundant high-K calc-alkaline andesite lavas, provides further support for the operation of plate tectonics in the Neoarchaean. (C) 2014 Elsevier B.V. All rights reserved.