Continental arc magmatism in a Mesoproterozoic convergent margin: Petrological and geochemical constraints from the magmatic suite of Kondapalle along the eastern margin of the Indian plate
Continental arc magmatism in a Mesoproterozoic convergent margin: Petrological and geochemical constraints from the magmatic suite of Kondapalle along the eastern margin of the Indian plate
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DOI：
10.1016/j.tecto.2011.06.025
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发表时间：
2011-09
期刊：
影响因子：
2.9
通讯作者：
C. Rao;M. Santosh
中科院分区：
文献类型：
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作者：
C. Rao;M. Santosh
Kondapalle的岩浆岩套代表了一个中元古代（~约。1634 Ma）岩浆弧侵位于东高止山脉带（EGB）南段。在这里，我们提出了新的地质，矿物学和地球化学数据的各种岩性单位在这个复杂的，包括斜长岩，辉长岩和辉石。主要矿物成分为斜长石（An 98 -57）、角闪石（XMg 0.93 -0.52）、斜方辉石（XMg 0.94 -0.51）、单斜辉石（XMg 0.93 -0.63）和铬铁矿（XMg 0.20 -50）。在Kondapalle岩套中，斜方辉石中几乎不含斜长石，斜方辉石结晶早而丰富，形成的是辉长岩而不是辉长岩或橄榄石辉长岩，这些都与弧堆晶岩的特征有关。铬尖晶石和单斜辉石的化学成分也显示出弧堆晶的趋势。斜长石中钙长石含量与橄榄石中Mg#的变化证明了与弧有关的岩浆源。岩石显示低丰度的不相容的微量元素（Ba，Rb，K和Zr）的值相比，通常观察到的俯冲相关的岩浆弧。在微量元素N-MORB标准化图解中，各岩石单元均显示Nb-Ta-Ti-Zr槽，反映了弧岩浆的特征。我们解释的Kondapalle岩石代表的根区的深侵蚀岩浆弧建造在中元古代与俯冲的海洋岩石圈在一个长期的收敛边缘。我们确定，中元古代俯冲沿着印度板块东缘产生了广泛的弧增生杂岩与挤压高P-T变质造山带在碰撞的最后阶段。俯冲-增生过程也得到了最近发现的中元古代蛇绿混杂岩的支持，标志着从古元古代哥伦比亚超大陆的解体到新元古代Rodinia超大陆的组装。
The magmatic suite at Kondapalle represents a Mesoproterozoic (~ca. 1634Ma) magmatic arc emplaced in the southern sector of the Eastern Ghats Belt (EGB). Here we present new geological, mineralogical and geochemical data on the various lithological units in this complex including anorthosites, gabbronorites and pyroxenites. The major mineral constituents in these rocks are plagioclase (An98–57), amphibole (XMg0.93–0.52), orthopyroxene (XMg0.94–0.51), clinopyroxene (XMg0.93–0.63) and chromite (XMg0.20–50). The near-absence of plagioclase in the orthopyroxenites, early and abundant crystallization of orthopyroxene, and formation of gabbronorites rather than gabbro or olivine gabbro in the Kondapalle suite are correlated with the features of arc cumulates. The chemistry of chromian spinel and clinopyroxene also displays the trend for arc cumulates. The variations in the anorthite content of plagioclase vs. the Mg# of olivine attest to an arc-related magma source. The rocks display low abundance of incompatible trace elements (Ba, Rb, K and Zr) comparable to the values typically observed in subduction-related magmatic arcs. In trace element N-MORB normalized diagrams, all the rock units show Nb–Ta–Ti–Zr troughs reflecting the features characteristic of arc magmas. We interpret the Kondapalle rocks to represent the root zone of a deeply eroded magmatic arc built during the Mesoproterozoic associated with the subduction of an oceanic lithosphere in a long-lived convergent margin. We identify that the Mesoproterozoic subduction along the eastern margin of the Indian plate generated a wide arc-accretionary complex with an extruded high P–T metamorphic orogen during the final stage of collision. The subduction–accretion process is also supported by recent findings of Mesoproterozoic ophiolite mélanges from this zone, marking the history from the break-up of the Paleoproterozoic Columbia supercontinent to the assembly of the Neoproterozoic Rodinia supercontinent.