东南极拉斯曼丘陵镁铁质麻粒岩的地球化学特征及其中压变质作用

GEOCHEMICAL CHARACTERISTICS AND MEDIUM PRESSURE GRANULITE FACIES METAMOPHISM OF MAFIC GRANULITE ROCKS FROM THE LARSEMANN HILLS,EAST ANTARCTICA

在东南极普里兹湾拉斯曼丘陵地区变泥质岩和长英质片麻岩中，定向分布着透镜状、扁豆状和香肠状镁铁质、超镁铁质麻粒岩。这些岩石主量元素、微量元素和稀土元素地球化学特征显示其原岩化学成分具镁铁质堆晶岩特征，并可能代表岩墙的构造作用残留体。在米洛半岛发现石榴子石周围有斜方辉石和斜长石的反应边，斜方辉石和斜长石由下述反应形成：石榴子石＋石英→斜方辉石＋斜长石。这个反应为减压反应，应用地质温压计确定其温度和压力分别为７４７±４８°Ｃ和６．３±０．５ｋｂａｒ，本文首次应用石榴子石－斜方辉石－斜长石－石英组合确立本区早期中压麻粒岩相事件的存在。

Oriented distributed mafic granulite lenses,pods and boudins occur in metapelitic and leucogneiss in the Larsemann Hills,Prydz Bay,East Antarctica. The geochemical characteristic of the rocks imply that they are chemically similar to mafic cumulate.They probably represent remnants of mafic dykes. In the Mirror peninsula orthopyroxene plagioclase symplectites aroud garnet in mafic granulite is discovered ,orthopyroxene and plagioclase form by the reaction garnet+quartz→plagioclase+orthopyroxene Average pressure calculation on the assemblage indicates the prevailing conditions were 6.3±0.5kbar at 747±48°C.It is the first pressure estimate in the light of the equilibrium assemblage garnet orthopyroxene plagioclase quartz.An earlier medium pressure granulite facies event in the Larsemann Hills is confirmed.