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首页> 外文期刊>Journal of Asian earth sciences >Progressive or continual exsolution in pyroxenes: an indicator of polybaric igneous crystallization for the Perinthatta anorthositic gabbro, northern Kerala, southwestern India
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Progressive or continual exsolution in pyroxenes: an indicator of polybaric igneous crystallization for the Perinthatta anorthositic gabbro, northern Kerala, southwestern India

机译：在辉石中进行的或连续的放出：印度西南部喀拉拉邦Perinthatta食源性辉长岩的多气压火成岩结晶的指示

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Clinopyroxene and orthopyroxene from the Perinthatta anorthositic gabbro in southwestern India exhibit exsolution intergrowths of pyroxenes (occurring in five stages involving pigeonite, orthopyroxene and/or augite) and Fe-Ti oxides. The thicker irregular pyroxene lamellae appear to be the result of heterogeneous nucleation, indicating that this was the first unmixing process to begin. This was followed by homogeneous nucleation of regularly spaced, quite uniform pyroxene lamellae and defect-free fine pyroxene platelets between early-formed exsolution lamellae, suggesting progressive or continual nature of exsolution during slow cooling. Pyroxene thermometric calculations indicate that subcalcic augite and pigeonite equilibrated at ～935℃, with the different lamellar generations formed between ～914 and ～748℃. Pre-metamorphic anorthositic gabbro crystallization is considered to have taken place at deep crustal levels (～30 km; ～9-10 kbar) and later emplacement at shallower crustal levels (～15 km; ～5-6 kbar) suggesting polybaric conditions. The apparent difference between the pressure of crystallization and the emplacement of the Perinthatta anorthositic gabbro supports the common Proterozoic anorthosite petrogenetic model, involving initial crystallization at depth, followed by intrusion as a crystal-rich mush. Following emplacement, the igneous assemblage was affected by granulite facies metamorphism on cooling, as indicated by smaller granulite minerals along grain boundaries and the partial re-equilibration of exsolved phases.
机译：来自印度西南部Perinthatta钙长石辉长岩的斜生辉石和邻辉石表现出辉石的共生共生（发生在五个阶段，包括鸽石，原辉石和/或辉长岩）和Fe-Ti氧化物。较厚的不规则辉石薄片似乎是异质成核的结果，表明这是开始的第一个分解过程。随后是规则排列的，相当均匀的辉石薄片和早期形成的析出薄片之间的无缺陷的细辉石血小板的均匀成核，这表明缓慢冷却过程中析出的进行性或连续性。辉石的热力学计算表明，亚钙钙长铁和贝尼石在〜935℃达到平衡，在〜914 ～～ 748℃之间形成了不同的层状世代。认为变质前的无定形辉闪石结晶发生在深地壳水平（〜30 km；〜9-10 kbar），后来在较浅的地壳水平（〜15 km；〜5-6 kbar）发生，表明多气压条件。结晶压力与Perinthatta钙长石辉石的位置之间的表观差异支持常见的元古代钙长石斜成岩模式，涉及深度的初始结晶，然后侵入为富含晶体的糊状物。安置后，火成岩组合受冷却时粒状相变质的影响，如沿晶界的较小粒状矿物和溶解相的部分重新平衡所表明。

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