东南极赖于尔群基性麻粒岩变质作用与同位素年代学研究

Based on an integrated study of field investigation, isotopic geochronology and metamorphic petrology on mafic granulites from the Rauer Group, East Antarctica, the following questions will be resolved in the present project: (1) the peak metamorphic conditions, P-T paths and metamorphic ages of mafic granulites associated with ultrahigh temperature (UHT) metapelites, and (2) the peak metamorphic conditions, P-T paths and metamorphic ages of mafic granulites associated with the “normal” granulite facies rocks. Coupled with a geological comparation with the adjacent areas, the scope and metamorphic ages of the UHT metamorphism in the Rauer Group will be revealed. Moreover, this research will provide new constraints on the metamorphic grade, scope and nature of two-stage high-grade metamorphic events in the Rauer Group and have potential significance for understanding the nature of Grenvillian and Pan-African high-grade metamorphic events in the Prydz Bay region.

通过对东南极赖于尔群基性麻粒岩的野外地质考察、高精度同位素年代学和变质岩石学研究来揭示：（1）与超高温变泥质岩伴生的基性麻粒岩峰期变质条件、P-T演化和变质时代；（2）与“正常”麻粒岩相岩石伴生的基性麻粒岩的峰期变质条件、P-T演化和变质时代。结合区域对比研究，查明赖于尔群超高温变质作用的影响范围和变质时代，两期变质的变质程度、影响范围及其构造意义。这项工作对于深化理解普里兹湾地区格林维尔期和泛非期构造热事件的性质具有重要的科学意义。

东南极赖于尔群超高温变质作用的影响范围和构造意义是不清楚的。本项目针对赖于尔群不同地质体中的基性麻粒岩开展了岩相学观察、矿物化学分析、锆石U-Pb定年和P-T条件估算等综合研究工作。传统温压计、相平衡模拟和REE温度计等不同P-T计算结果表明，赖于尔群太古代和中元古代地质体中的基性麻粒岩均经历超高温变质作用，峰期变质条件为930-1030 °C/~12kbar。结合前人已发现的超高温点位，我们认为整个赖于尔群岛可能均受到超高温变质作用的影响。太古宙地体中基性麻粒岩发育两种特征的退变反应结构，指示一个多阶段的演化历史。运用传统温压计和相平衡模拟对不同变质期次的P-T条件进行了估算，得到了一个顺时针的P-T演化轨迹，早期退变质表现为超高温条件下的近等温降压过程，晚期阶段表现为降温降压。这一顺时针的P-T轨迹与东冈瓦纳陆块已发现的泛非期超高温变质地体的P-T轨迹相类似。结合锆石U-Pb定年结果和赖于尔群已发表的年龄数据，我们认为赖于尔群太古宙地体中超高温基性麻粒岩顺时针P-T演化轨迹与冈瓦纳大陆的最终拼合有关。