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首页> 外文期刊>Journal of Metamorphic Geology >Formation of clinopyroxene plus spinel and amphibole plus spinel symplectites in coronitic gabbros from the Sierra de San Luis (Argentina): a key to post-magmatic evolution
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Formation of clinopyroxene plus spinel and amphibole plus spinel symplectites in coronitic gabbros from the Sierra de San Luis (Argentina): a key to post-magmatic evolution

机译：塞拉利昂圣路易斯山脉（阿根廷）的冠状辉长岩中的斜辉石加尖晶石，尖晶石和闪石加上尖晶石的共沸物的形成：岩浆后演化的关键

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摘要

The El Arenal metagabbros preserve coronitic shells of orthopyroxene +/- Fe-oxide around olivine, as well as three different types of symplectite consisting of amphibole + spinel, clinopyroxene + spinel and, more rarely, orthopyroxene + spinel. The textural features of the metagabbros can be explained by the breakdown of the olivine + plagioclase pair, producing orthopyroxene coronas and clinopyroxene + spinel symplectites, followed by the formation of amphibole + spinel symplectites, reflecting a decrease in temperature and, possibly, an increase in water activity with respect to the previous stage. The metagabbros underwent a complex P-T history consisting of an igneous stage followed by cooling in granulite, amphibolite and greenschist facies conditions. Although the P-T conditions of emplacement of the igneous protolith are still doubtful, the magmatic assemblage suggests that igneous crystallization occurred at a pressure lower than 6 kbar and at 900-1100 degrees C. Granulitic P-T conditions have been estimated at about 900 degrees C and 7-8 kbar combining conventional thermobarometry and pseudosection analysis. Pseudosection calculation has also shown that the formation of the amphibole + spinel symplectite could have been favoured by an increase in water activity during the amphibolite stage, as the temperature of formation of this symplectite strongly depends on aH(2)O (< 740 degrees C for aH(2)O = 0.5; < 790 degrees C for aH(2)O = 1). Furthermore, but not pervasive, re-equilibration under greenschist facies P-T conditions is documented by retrograde epidote and chlorite. The resulting counterclockwise P-T path consists of progressive, nearly isobaric cooling from the igneous stage down to the granulite, amphibolite and greenschist stage.
机译：El Arenal metagabbros保留了橄榄石周围的邻苯二酚+/-铁氧化物的皮质壳，以及由闪石+尖晶石，斜辉石+尖晶石，以及少部分的邻苯二酚+尖晶石组成的三种不同类型的共生石。变质岩的质地特征可以通过橄榄石+斜长石对的破裂，产生邻苯二茂铁电晕和斜向吡咯+尖晶石的共生体，随后形成闪石+尖晶石的共生体来解释，这反映了温度的降低以及可能的增加。相对于上一阶段的水活度。变石经历了复杂的PT历史，包括火成岩阶段，然后在花岗石，闪石和绿片岩相条件下冷却。尽管火成岩原石的PT条件仍然令人怀疑，但岩浆组合表明火成岩结晶发生在低于6 kbar的压力和900-1100摄氏度的条件下。据估计，粒状PT的条件约为900摄氏度和7摄氏度。 -8 kbar结合了常规热压法和伪截面分析。伪截面计算还表明，在闪石阶段水活性的增加可能有利于闪石+尖晶石复合物的形成，因为该复合物的形成温度强烈取决于aH（2）O（<740摄氏度对于aH（2）O = 0.5; <790摄氏度对于aH（2）O = 1）。此外，逆向性附子和亚氯酸盐记录了绿化相P-T条件下的重新平衡，但不是普遍的。产生的逆时针P-T路径包括从火成岩阶段到花岗石，闪石和绿片岩阶段的渐进，近等压冷却。

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