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首页> 外文期刊>Journal of geodynamics >The Manamedu Complex: Geochemical constraints on Neoproterozoic suprasubduction zone ophiolite formation within the Gondwana suture in southern India
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The Manamedu Complex: Geochemical constraints on Neoproterozoic suprasubduction zone ophiolite formation within the Gondwana suture in southern India

机译：Manamedu复合体：印度南部冈瓦纳缝合线内新元古代超俯冲带蛇绿岩形成的地球化学约束

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摘要

Ophiolites provide important clues on the role of subduction and have been widely investigated to reconstruct the history of development and closure of ocean basins in the geological past. The Manamedu Complex within the Palghat-Cauvery Suture Zone in southern India comprises metamorphosed equivalents of the following lithological units: (1) an ultramafic group comprising dominantly of pyroxenite and highly altered dunite, locally preserving cumulate textures; (2) a gabbroic suite consisting of gab-bro, gabbro norite, and anorthosite; (3) sheeted mafic dykes of amphibolite to meta-andesite categories, (4) plagiogranite veins and pools; and (5) a thin layer of ferruginous cherts. Cr vs. Y, V vs. Cr, Ti vs. Zr, TiO_2-MnO-P_2O_5 and Fe_2O_3-Na_2O + K_2O-Mg0 plots of the gabbros and mafic dyke assemblages show that these are related to island arc tholeiite (IAT) group with tholeiitic to calcalkaline signatures. Chondrite normalized REE patterns of mafic dykes do not show any pronounced fractionation and display slight positive Eu anomalies. The normalized MORB plots of the mafic dykes show depletion of HFSE (negative Nb, Ti, Ta, Hf anomalies) and enrichment of LFSE (positive K, Ba, Rb, Th). The petrological and geochemical characteristics of the major lithological units in Manamedu Complex suggest that these rocks represent the remnants of an oceanic crust, developed from mantle-derived arc magmas probably within a suprasubduction zone tectonic setting. From the geological set up and our field observations, we infer that these rocks were obducted on to the continental margin with the closure of an ocean basin during the Neoproterozoic. The Manamedu Complex may represent the remnants of the Mozambique Ocean crust developed during Rodinia breakup and which was destroyed during the amalgamation of the Gondwana supercontinent in the Latest Neoproterozoic-Cambrian.
机译：蛇绿岩提供了俯冲作用的重要线索，并已被广泛研究以重建地质过去海洋盆地的发展和封闭的历史。印度南部Palghat-Cauvery缝合带内的Manamedu复合体包括以下岩性单元的变质等价物：（1）一个超镁铁质群，主要由辉石岩和高度蚀变的辉光岩组成，局部保留堆积的纹理； （2）辉长岩组，由辉长岩，辉长岩和钙长石组成； （3）角质岩成片的镁铁质岩脉至安山岩类；（4）斜长花岗岩脉和水池； （5）薄薄的一层铁质硅质cher石。辉长岩和镁铁矿岩组合的Cr vs. Y，V vs. Cr，Ti vs. Zr，TiO_2-MnO-P_2O_5和Fe_2O_3-Na_2O + K_2O-Mg0图表明，这些与岛弧型辉绿岩（IAT）组有关钙碱性的特征。铁镁质岩脉的球粒陨石归一化REE模式未显示任何明显的分馏，并且显示出轻微的正Eu异常。磁化堤的归一化MORB图显示了HFSE的耗竭（负Nb，Ti，Ta，Hf异常）和LFSE的富集（正K，Ba，Rb，Th）。 Manamedu Complex中主要岩性单元的岩石学和地球化学特征表明，这些岩石代表了洋壳的残留物，这些洋壳可能是由超俯冲带构造环境中的地幔源弧岩浆形成的。从地质背景和我们的野外观察，我们可以推断，这些岩石是在新元古代以来随着海盆的封闭而被带到大陆边缘的。 Manamedu复合体可能代表了在Rodinia破裂期间形成的莫桑比克洋壳的残余，该壳在最新新元古代-寒武纪的冈瓦纳超大陆合并中被破坏了。

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