Geochemical and isotopic constraints on the tectonic and crustal evolution of the Shackleton Range, East Antarctica, and correlation with other Gondwana crustal segments
Geochemical and isotopic constraints on the tectonic and crustal evolution of the Shackleton Range, East Antarctica, and correlation with other Gondwana crustal segments
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DOI：
10.1016/j.precamres.2010.03.005
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发表时间：
2010-06
影响因子：
3.8
通讯作者：
T. Will;H. Frimmel;A. Zeh;P. Roux;E. Schmädicke
中科院分区：
文献类型：
--
作者：
T. Will;H. Frimmel;A. Zeh;P. Roux;E. Schmädicke
在东南极洲的沙克尔顿山脉，已经发现了三个不同的、空间上分离的地壳地体：南地体、东地体和北地体。新的岩石地球化学和同位素（Rb-Sr、Sm-Nd、Pb-Pb全岩和Lu-Hf锆石）资料首次揭示了这些地体中关键单元的起源和演化。来自南地体的镁铁质片麻岩为其原岩的板块内起源提供了地球化学证据，可能是弧后起源。在约1850Ma，羽状远端脊起源于早期海洋盆地，是这些岩石就位地点的有利解释，这些岩石与一些海洋岛屿玄武岩一起，随后被合并为一个增生大陆弧/超俯冲带构造环境。约1710 ~ 1680ma，岩浆下地壳部分熔融导致南地体高温麻粒岩相变质。镁铁质和长英质片麻岩的特征是同位素贫化、正Nd和Hf首字母，模式年龄在2100 ~ 2000Ma之间。它们可以被解释为在古元古代末期形成的年轻的地壳附加物。这些年轻的岩石出现在一个狭窄的，约150公里长的东西向带，推断出与一个大型古元古代增生造山系统有关的缝合。南地体包含许多与澳南极莫森大陆相似的特征，并且可能是其向东南极洲的最远延伸。东地体的特征是在约1060Ma的晚中元古代造山运动中形成的陆相火山弧背景下形成的变质玄武岩。随后，在600Ma泛非碰撞构造中，岩石经历了高温变质作用。同位素贫化锆石的Hf模型年龄为1600 ~ 1400ma，与幼年变花岗岩的Nd模型年龄相同。这些岩石很可能是在~ 600Ma时与印度-南极大陆块体和西冈瓦纳大陆块体合并有关的缝合线。东地体被解释为南极洲东部泛非莫桑比克/莫德带的最南端延伸，根据Hf同位素数据，它也可能与南极洲西部的Ellsworth-Whitmore山脉块体和非洲南部的Namaqua-Natal省有关。地球化学证据表明，北地体基性片麻岩的大部分原岩是在板块内环境下形成的洋岛玄武岩。随后，这些岩石被合并到俯冲带环境中，最后在泛非碰撞构造期间被吸积到大陆边缘。那里的长硅片麻岩提供了板块内和火山弧/碰撞起源的证据。花岗岩类侵位发生在约530Ma，高温高压变质作用发生在510-500Ma。多数样品的Hf和Nd首字母富集和古元古代模式年龄表明，泛非造山运动期间，北地体地壳中没有添加幼体物质，但一定发生了老地壳的再循环或不同年龄地壳成分的混合。同位素亏缺的基性片麻岩在空间上与榴辉岩相辉石岩相关，产生了中元古代晚期Nd的模式年龄。这些岩石出现在一个狭窄的、至少100公里长的东西向带中，该带将碱性海洋岛屿变质玄武岩和板内变质玄武岩与北部地体的火山弧变质玄武岩和火山弧/同碰撞变质玄武岩分开。这条带子被解释为追踪…
Three distinct, spatially separated crustal terranes have been recognised in the Shackleton Range, East Antarctica: the Southern, Eastern and Northern Terranes. First insights into the origin and evolution of critical units from these terranes could be gained from new lithogeochemical and isotope (Rb–Sr, Sm–Nd, Pb–Pb whole rock and Lu–Hf zircon) data. Mafic gneisses from the Southern Terrane provide geochemical evidence for a within-plate, probably back-arc origin of their protoliths. A plume-distal ridge origin in an incipient ocean basin is the favoured interpretation for the emplacement site of these rocks at c. 1850Ma, which, together with a few ocean island basalts, were subsequently incorporated into an accretionary continental arc/supra-subduction zone tectonic setting. Magmatic underplating resulted in partial melting of the lower crust, which caused high-temperature granulite-facies metamorphism in the Southern Terrane at c. 1710–1680Ma. Mafic and felsic gneisses there are characterised by isotopically depleted, positive Nd and Hf initials and model ages between 2100 and 2000Ma. They may be explained as juvenile additions to the crust towards the end of the Palaeoproterozoic. These juvenile rocks occur in a narrow, c. 150km long E-W trending belt, inferred to trace a suture that is associated with a large Palaeoproterozoic accretionary orogenic system. The Southern Terrane contains many features that are similar to the Australo-Antarctic Mawson Continent and may be its furthermost extension into East Antarctica. The Eastern Terrane is characterised by metagranitoids that formed in a continental volcanic arc setting during a late Mesoproterozoic orogeny at c. 1060Ma. Subsequently, the rocks experienced high-temperature metamorphism during Pan-African collisional tectonics at 600Ma. Isotopically depleted zircon grains yielded Hf model ages of 1600–1400Ma, which are identical to Nd model ages obtained from juvenile metagranitoids. Most likely, these rocks trace the suture related to the amalgamation of the Indo-Antarctic and West Gondwana continental blocks at ∼600Ma. The Eastern Terrane is interpreted as the southernmost extension of the Pan-African Mozambique/Maud Belt in East Antarctica and, based on Hf isotope data, may also represent a link to the Ellsworth-Whitmore Mountains block in West Antarctica and the Namaqua-Natal Province of southern Africa. Geochemical evidence indicates that the majority of the protoliths of the mafic gneisses in the Northern Terrane formed as oceanic island basalts in a within-plate setting. Subsequently the rocks were incorporated into a subduction zone environment and, finally, accreted to a continental margin during Pan-African collisional tectonics. Felsic gneisses there provide evidence for a within-plate and volcanic arc/collisional origin. Emplacement of granitoids occurred at c. 530Ma and high-temperature, high-pressure metamorphism took place at 510–500Ma. Enriched Hf and Nd initials and Palaeoproterozoic model ages for most samples indicate that no juvenile material was added to the crust of the Northern Terrane during the Pan-African Orogeny but recycling of older crust or mixing of crustal components of different age must have occurred. Isotopically depleted mafic gneisses, which are spatially associated with eclogite-facies pyroxenites, yielded late Mesoproterozoic Nd model ages. These rocks occur in a narrow, at least 100km long, E-W trending belt that separates alkaline ocean island metabasalts and within-plate metagranitoids from volcanic arc metabasalts and volcanic arc/syn-collisional metagranitoids in the Northern Terrane. This belt is interpreted to trace the …