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首页> 外文期刊>Journal of geodynamics >High pressure metamorphism of mafic granulites from the Chotanagpur Granite Gneiss Complex, India: Evidence for collisional tectonics during assembly of Rodinia
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High pressure metamorphism of mafic granulites from the Chotanagpur Granite Gneiss Complex, India: Evidence for collisional tectonics during assembly of Rodinia

机译：印度Chotanagpur花岗岩片麻岩复合体的镁铁质花岗岩的高压变质作用：罗迪尼亚组装过程中碰撞构造的证据

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In the north-eastern part of the Chotanagpur Granite Gneiss Complex (CGGC), India, mafic granulite occurs as enclaves within the (similar to)1450 Ma old felsic rocks. The mafic granulite and the host felsic rock develop a pervasive planar fabric defined by minerals that are characteristics of high pressure (HP) granulite facies metamorphism. The earliest discernable mineral assemblage in the mafic granulites comprises amphibole + clinopyroxene + plagioclase + quartz + ilmenite, preserved as inclusions within garnet porphyroblasts as a record of early M-0 stage. Subsequently, the assemblage garnet + clinopyroxene + plagioclase + rutile + quartz developed during the peak metamorphic stage (M-i) defining the pervasive fabric. Quantitative geothermobarometry and intersection of isopleths in a phase diagram (pseudosection) that was numerically computed for a representative bulk composition of the mafic granulites, yield 12 +/- 1 kbar and 800 +/- 50 degrees C for the M-i stage. Subsequent changes in physical conditions in response to tectonic evolution of the complex developed two distinct sets of mineral assemblages (M-ii and M-iii). Firstly, garnet clinopyroxene + quartz broke down to symplectic aggregates of orthopyroxene + plagioclase under static conditions (M-ii stage). Afterwards, the anhydrous minerals, which developed during the M-0.ii stages, were variably replaced by amphibole-bearing assemblages (M-iii stage). Geothermobarometric estimates and the stability of different assemblages that developed during Mo-Mill stages, define a clockwise (CW) P-T path with an inferred geothermal gradient of (similar to)20 degrees C/km during the culmination of HP M-i metamorphism. The reconstructed CW P-T path and the inferred geothermal gradient are consistent with a continent-continent collisional tectonic setting. Integrating all the existing information, it is considered that a large part, if not the whole, of the CGGC behaved as a coherent lower plate during the globally extensive convergent margin orogenesis at the time of Rodinia supercontinant formation.
机译：在印度的Chotanagpur花岗岩片麻岩复合体（CGGC）的东北部，镁铁质花岗石作为围岩出现在（类似于）1450 Ma老的长英质岩石中。镁铁质花岗石和基质长英质岩石形成了一种由矿物定义的普遍的平面织物，这些矿物是高压（HP）花岗石相变质的特征。镁铁质花岗石中最早可辨别的矿物组合包括闪石+斜辉石+斜长石+石英+钛铁矿，保留在石榴石成矿细胞中，作为M-0早期的记录。随后，在高峰变质阶段（M-i）定义了无处不在的织物，组合石榴石+斜ino石+斜长石+金红石+石英。定量地热压法和相图（伪截面）中的等值交点是通过数学计算得出的黑铁质花岗石的代表性本体组成，在M-i阶段产量为12 +/- 1 kbar和800 +/- 50℃。随后，随着复杂构造演化，物理条件发生了变化，形成了两组不同的矿物组合（M-ii和M-iii）。首先，石榴石的斜辉石+石英在静态条件下（M-ii级）分解为邻辉石+斜长石的辛聚集体。之后，在M-0.ii阶段产生的无水矿物被含角闪石的组合（M-iii阶段）可变地代替。地热气压估算和在Mo-Mill阶段形成的不同组合的稳定性定义了顺时针（CW）P-T路径，并推断出HP M-i变质的顶峰时地热梯度为（近似）20°C / km。重建的CW P-T路径和推断的地热梯度与大陆-大陆碰撞构造环境一致。综合所有现有信息，可以认为，在罗丹尼亚超大陆形成时，全球范围广泛的汇聚边缘造山作用中，CGCG的大部分（如果不是全部）表现为连贯的下盘。

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