秦岭造山带武关杂岩石榴黑云片岩的变质作用P-T轨迹与构造意义

发布时间：2018-04-01 03:37

  本文选题：石榴石成分环带　切入点：相平衡模拟　出处：《岩石学报》2017年08期

【摘要】：秦岭造山带是华北板块与华南板块长期汇聚的产物。该造山带以商南-丹凤缝合带为界分为早古生代的北秦岭造山带和晚古生代-中生代的南秦岭造山带。武关杂岩位于南秦岭造山带的北缘,被认为是一套形成于弧前盆地的杂岩,原岩沉积时代为泥盆纪-早石炭纪,经历了晚石炭纪变质作用。本文对武关杂岩的石榴黑云片岩进行了岩石学研究。该岩石主要由斜长石、石榴石、黑云母和石英组成,含少量白云母、金红石和钛铁矿。变斑晶石榴石具有明显的生长成分环带,其核部以MgO含量增加和MnO降低为特征,幔部FeO含量逐渐增加,MgO、CaO和MnO逐渐减少,而在边部CaO明显升高,MgO、FeO和MnO含量不同程度降低。相平衡模拟和温压计计算结果表明,石榴黑云片岩具有复杂的顺时针P-T轨迹,早期进变质阶段(M1)为升温升压过程,峰期条件为~695℃和~8.3kbar,变质矿物组合为石榴石(核)和所含的黑云母、斜长石、石英及钛铁矿包裹体;中期退变质阶段(M2)是降温降压过程,达到~615℃和~6.2kbar变质条件,变质矿物组合是石榴石(幔)和包含的黑云母、斜长石、石英、白云母和钛铁矿包裹体;晚期是以近等温升压为特征的进变质过程(M3),达到~620℃和~9.1kbar条件,变质矿物组合为石榴石(边)和基质矿物黑云母、斜长石、石英、白云母和金红石。M1和M2阶段的构造了一个"发夹状"的顺时针P-T轨迹,为俯冲带变质作用典型特征,表明岩石经历了早期俯冲和后来的折返过程。而以显著增压为特征的晚期进变质作用(M3)很可能表明岩石经历了又一期俯冲作用。因此,本研究表明武关杂岩中的石榴黑云片岩很可能处于俯冲通道之中,经历了多旋回俯冲与折返过程。
[Abstract]:The Qinling orogenic belt is the product of the convergence of North China plate and South China plate for a long time. The orogenic belt is divided into early Paleozoic North Qinling orogenic belt and late Paleozoic Mesozoic South Qinling orogenic belt. Wuguan is divided into early Paleozoic North Qinling orogenic belt and late Paleozoic Mesozoic South Qinling orogenic belt. The complex is located in the northern margin of the South Qinling orogenic belt. It is considered to be a set of complex rocks formed in the forearc basin. The sedimentary age of the original rocks was Devonian to early Carboniferous. It has undergone late Carboniferous metamorphism. The petrological study of the garnet biotite schist of Wuguan complex is carried out. The rock is mainly composed of plagioclase, garnet, biotite and quartz, and contains a small amount of Muscovite, which is mainly composed of plagioclase, garnet, biotite and quartz. Rutile and ilmenite. Metamorphic garnet is characterized by increasing MgO content and decreasing MnO content, and increasing FeO content and decreasing MnO content in the mantle. The results of phase equilibrium simulation and thermobarometer calculation show that the pomegranate black cloud schist has a complex clockwise P-T trajectory, and the early progressive metamorphic stage (M1) is a warming and increasing pressure process. The peak condition is 695 鈩，

本文编号：1693816