Abstract

The paper presents data acquired on epigenetic processes in rocks of the Meso- to Neoarchean greenstone complex of the Bundelkhand Craton of the Indian Shield. The study was focused on felsic and mafic metavolcanic and mafic–ultramafic rocks of the Central Bundelkhand Greenstone Complex (CBGC). The rocks contain metamorphic mineral assemblages produced during an earlier high-temperature [Grt–Prg–Pl; Cpx–Prg–Pl; Cpx–Grt–Pl; Cpx–Prg (± Ksp, Qz, Mag)] and later retrograde [Grt–Pl–Hbl; Grt–Chl–(Hbl–Act); Grt–(Zo–Czo)–(Hbl–Act); Grt–Chl–Pl (± Ksp, Qz, Mag, Ms)] episodes of metamorphism. The retrograde metamorphism was associated with the origin of zoned Ep and Qz–Ep (±Grt, Act) veins, patches, stripes, and small bodies of epidosites and actinolites. The mineral assemblages of the final episodes of the rock transformations contain prehnite and pumpellyite (Prh–Pmp–Alb; Prh–Pmp–Grs; Pmp–Grs–Alb; Prh–Cc–Act; and Prh–Grs–Cc). The composition of the garnet and amphibole was determined to broadly vary (Alm–Sps to Grs and Prg–Ts to Act and Cum, Gru, respectively). The garnet is contrastingly zoned (comprises three zones), with the boundaries of the zones marking drastic changes in the crystallization parameters (episodes of transformations). The identified sequence of the epigenetic events was as follows: amphibolite-facies metamorphism under elevated pressures (580–680°C at 7.2–10 kbar), with a clockwise P-T-t path and retrogression to the greenschist facies → Ca(Mn) metasomatism → metamorphism to the prehnite–pumpellyite facies. The metamorphic evolution of the CBGC rocks in the Bundelkhand Craton is in good agreement with the geodynamic model of cratonic crustal growth, with Archean subduction–accretion processes and Paleoproterozoic intraplate rifting.

中文翻译：

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印度地盾中央邦德尔坎德绿岩杂岩变质作用：矿物成分、共生作用和 P-T 路径

摘要

本文介绍了在印度地盾邦德尔坎德克拉通的中至新太古代绿岩复合体的岩石中获得的表观遗传过程数据。该研究的重点是中央邦德坎德绿岩杂岩体 (CBGC) 的长英质和镁铁质变质火山以及镁铁质-超镁铁质岩石。岩石包含在早期高温下产生的变质矿物组合 [ Grt-Prg-Pl; Cpx-Prg-Pl; Cpx-Grt-Pl; Cpx–Prg (± Ksp, Qz, Mag )] 和后来逆行 [ Grt–Pl–Hbl; Grt-Chl-（Hbl-Act）；Grt– ( Zo–Czo ) – ( Hbl–Act ); Grt–Chl–Pl (± Ksp, Qz, Mag, Ms)] 变质的情节。逆行变质作用与分区Ep和Qz – Ep (± Grt, Act ) 脉、斑块、条纹以及绿帘石和阳起石的小体的起源有关。岩石转变最后阶段的矿物组合包含葡萄石和抽水镁石（Prh–Pmp–Alb；Prh–Pmp–Grs；Pmp–Grs–Alb；Prh–Cc–Act；和Prh–Grs–Cc）。石榴石和闪石的成分被确定为广泛变化（Alm-Sps到Grs和Prg-Ts到Act和Cum，Gru， 分别）。石榴石呈对比分区（包括三个区域），区域的边界标志着结晶参数的剧烈变化（转变阶段）。表观遗传事件的确定序列如下：角闪岩相变质作用在高压下（580-680°C，7.2-10 kbar），顺时针方向P - T - t路径和退化到绿片岩相 → Ca(Mn ) 交代作用 → 变质作用为早发岩-菱镁矿相。Bundelkhand 克拉通 CBGC 岩石的变质演化与克拉通地壳生长的地球动力学模型、太古代俯冲-增生过程和古元古代板内裂谷的地球动力学模型非常吻合。