东南极茹尔群岛梅瑟半岛富铁铝副片麻岩超高温变质作用:相平衡模拟与锆石U-Pb年龄

Ultrahigh-temperature metamorphism of Fe-Al-rich paragneisses in the Mather Peninsula,Rauer Group,East Antarctica:Phase equilibuim modeling and zircon U-Pb ages

东南极梅瑟半岛出露大量的副片麻岩。本文以岩相学和矿物化学为基础,结合相平衡模拟、地质温度计及年代学分析方法对费拉副片麻岩中的含尖晶石榴夕线石片麻岩和梅瑟副片麻岩中的含堇青石榴夕线石片麻岩进行综合研究,结果显示片麻岩经历了超高温(UHT)麻粒岩相变质作用。两个样品峰期前阶段(M1)进变质条件为600~650℃和0.63~0.85GPa;峰期UHT阶段(M2)变质条件为930~1000℃和0.9~1GPa;峰期后变质重结晶阶段(M3)变质条件为610~780℃和0.3~0.39GPa。三个不同阶段的变质条件定义了一致的顺时针的P-T演化轨迹。锆石U-Pb年龄分析结果表明两个片麻岩样品的超高温变质和相关的深熔作用发生在990~920Ma期间的早新元古代格林威尔期,而流体改造与变质重结晶作用发生在~510Ma的早古生代泛非期。结合区域地质特征,超高温变质作用发生的构造背景可能与以放射性元素衰变为热源的大型热碰撞造山带相关。

Abundant paragneisses are exposed in Mather Peninsula,East Antarctica.In this paper,based on petrography and mineral chemistry,combined with phase equilibrium modeling,geothermometer and chronological analysis methods,the spinel-bearing garnet-sillimanite gneiss in Filla paragneiss and cordierite-bearing garnet-sillimanite gneiss in Mather paragneiss are comprehensively studied.The results show that the gneisses have experienced ultra-high temperature(UHT)granulite facies metamorphism.In the pre-peak stage(M1)of two samples,the prograde metamorphic conditions are 600~650℃and 0.63~0.85GPa;in the peak UHT stage(M2),the metamorphic conditions are 930~1000℃and 0.9~1GPa;and in the post-peak stage(M3),the recrystallization metamorphic conditions are 610~780℃and 0.3~0.39GPa.The metamorphic conditions of three different stages define a consistent clockwise P-T evolution path.The zircon U-Pb age analysis results show that the UHT metamorphism and related anatexis of the two gneiss samples occurred in the Early Neoproterozoic Grenvillian at 990~920Ma,while the fluid transformation and metamorphic recrystallization occurred in the Early Paleozoic Pan-African at~510Ma.In combination with regional geological characteristics,the tectonic background of UHT metamorphism may be related to the large hot collision orogen with radioactive element decay as the heat source.