Coronae between olivine and plagioclase are a common replacement texture in mafic rocks by magmatic and metamorphic processes. Mafic dykes from Palghat Cauvery Shear Zone (PCSZ) of the granulite terrane of southern India display such multilayer coronae between olivine (Ol) and plagioclase (Pl), composed of orthopyroxene-magnetite (OM) and amphibole (Prg). Deformation twins, kinking, bending and fractures in plagioclase laths suggest that the rock underwent post-emplacement deformation. However, amphibole in the plagioclase fractures and preservation of delicate coronae texture indicate that the replacement texture grew in a static condition. Field occurrence and textural relations suggest that the coronae developed in two stages: (1) Stage-I: Ol → OM, followed by (2) Stage-II: OM + Pl = Prg during rehydration of the granulite host rock. Balanced chemical reactions and formation of hydrous amphibole at the expense of anhydrous reactants during Stage-II demonstrates that replacement of earlier minerals occurred in a fluid-present open system. Results from the pseudosection and the μMgO–μCaO phase diagram, suggest fluid played a crucial role in the transition from Stage-I to Stage-II corona at a P-T condition of ~650 ± 50 °C and 5.5–6 kbar. The multilayer coronae is likely to have resulted from late Neoproterozoic thermal metamorphism of granulite terrane of southern India during Pan-African orogeny.

中文翻译：

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印度南部帕尔加特高维剪切带镁铁质岩脉橄榄石-斜长石接触两阶段日冕形成过程的见解

橄榄石和斜长石之间的日冕是岩浆和变质过程中基性岩中常见的置换结构。来自印度南部麻粒岩地体 Palghat Cauvery 剪切带 (PCSZ) 的基性岩脉在橄榄石 (Ol) 和斜长石 (Pl) 之间显示出这种多层日冕，由斜辉石-磁铁矿 (OM) 和角闪石 (Prg) 组成。斜长石板条中的变形孪晶、扭结、弯曲和断裂表明岩石经历了进位后变形。然而，斜长石断裂中的角闪石和精致的日冕纹理的保存表明替代纹理在静态条件下生长。场发生和结构关系表明日冕发展分为两个阶段：（1）阶段-I：Ol → OM，然后是（2）阶段-II：在麻粒岩母岩再水化过程中，OM + Pl = Prg。在第二阶段以无水反应物为代价的平衡化学反应和含水闪石的形成表明，早期矿物的替代发生在有流体的开放系统中。假截面和 μMgO-μCaO 相图的结果表明，在~650 ± 50 °C 和 5.5-6 kbar 的 PT 条件下，流体在从第一阶段到第二阶段电晕的过渡中起着至关重要的作用。多层日冕很可能是泛非造山运动期间印度南部麻粒岩地体晚新元古代热变质作用的结果。表明在~650 ± 50 °C 和 5.5-6 kbar 的 PT 条件下，流体在从第一阶段到第二阶段电晕的过渡中发挥了关键作用。多层日冕很可能是泛非造山运动期间印度南部麻粒岩地体晚新元古代热变质作用的结果。表明在~650 ± 50 °C 和 5.5-6 kbar 的 PT 条件下，流体在从第一阶段到第二阶段电晕的过渡中发挥了关键作用。多层日冕很可能是泛非造山运动期间印度南部麻粒岩地体晚新元古代热变质作用的结果。