东喜马拉雅构造结石榴角闪岩变质作用P-T-t轨迹:相平衡模拟与锆石年代学
发布时间：2019-04-26 01:17
【摘要】：东喜马拉雅构造结南迦巴瓦杂岩由多种类型的高级变质岩组成,包括片岩、片麻岩、大理岩、石榴角闪岩和基性麻粒岩。石榴角闪岩呈透镜状产出在片麻岩中,可见不连续分布的规模不等的浅色体。石榴角闪岩由石榴石、角闪石、黑云母、斜长石、石英、金红石、钛铁矿和榍石组成,石榴石变斑晶可见由浅色矿物组成的"白眼圈"。岩相学、矿物化学和相平衡模拟表明石榴角闪岩经历了一条顺时针型的P-T演化轨迹,可划分为两个阶段:(Ⅰ)升温升压的进变质阶段,由石榴石和斜长石斑晶记录,峰期矿物组合为石榴石+角闪石+黑云母+斜长石+石英+金红石+钛铁矿。运用石榴石变斑晶边部和斜长石变斑晶边部成分在视剖面图上的投点确定出峰期温压条件为~11.5kbar、790℃,达到了高压麻粒岩相条件,并经历了部分熔融,产生至少9%的熔体;(Ⅱ)降温降压的退变质阶段,由石榴石边部"白眼圈"冠状体记录。运用平均温压法计算冠状体中黑云母+斜长石+角闪石+石榴石组合的形成温压条件为~7kbar、~750℃。该阶段金红石消失,熔体结晶,并与早期矿物发生回反应。在石榴石角闪岩的锆石中获得了从29.2Ma到10.2Ma的连续变质年龄。由于锆石通常在熔体结晶过程中生长,因此确定该组年龄代表石榴石角闪岩退变质年龄。本文和以前的研究结果表明,南迦巴瓦杂岩中的高温和中温麻粒岩相亚单元具有相似的降温降压P-T轨迹,但高温单元具有较高的变质压力条件,表明其俯冲到了更大的深度。
[Abstract]:The Nanjiabahua complex of the eastern Himalayan tectonic complex consists of various types of high-grade metamorphic rocks, including schist, gneiss, marble, pomegranate amphibolite and basic granulite. Pomegranate hornblende occurs in gneisses in lenticular form with discontinuously distributed light-colored bodies of varying sizes. Garnet amphibolite is composed of garnet, amphibolite, biotite, plagioclase, quartz, rutile, ilmenite and sphene. Petrographic, mineral chemistry and phase equilibrium simulations show that pomegranate hornblende has undergone an isochronous pin-type evolution track of Pxt, which can be divided into two stages: (I) the progressive metamorphism stage of rising temperature and pressure, recorded by garnet and plagioclase porphyry. The peak mineral assemblage is garnet hornblende biotite plagioclase quartz rutile ilmenite. Using the input points of garnet porphyry edge and plagioclase porphyry edge on the view profile, the peak temperature and pressure conditions are determined to be ~ 11.5kbar, 790 鈩，
本文编号：2465627
[Abstract]:The Nanjiabahua complex of the eastern Himalayan tectonic complex consists of various types of high-grade metamorphic rocks, including schist, gneiss, marble, pomegranate amphibolite and basic granulite. Pomegranate hornblende occurs in gneisses in lenticular form with discontinuously distributed light-colored bodies of varying sizes. Garnet amphibolite is composed of garnet, amphibolite, biotite, plagioclase, quartz, rutile, ilmenite and sphene. Petrographic, mineral chemistry and phase equilibrium simulations show that pomegranate hornblende has undergone an isochronous pin-type evolution track of Pxt, which can be divided into two stages: (I) the progressive metamorphism stage of rising temperature and pressure, recorded by garnet and plagioclase porphyry. The peak mineral assemblage is garnet hornblende biotite plagioclase quartz rutile ilmenite. Using the input points of garnet porphyry edge and plagioclase porphyry edge on the view profile, the peak temperature and pressure conditions are determined to be ~ 11.5kbar, 790 鈩，
本文编号：2465627
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