豫南高压镁铁质麻粒岩的初步研究

PRELIMINARY STUDY OF HIGH PRESSURE MAFIC GRANULITES IN SOUTHERN HENAN PROVINCE

位于桐柏大别山造山带北缘桐柏信阳地段的豫南高压镁铁质麻粒岩块体主要由石榴角闪二辉麻粒岩类组成。其岩相学和矿物学特征表明它们曾经历过温度Ｔ／Ｋ＞１２６１．１５±５０，压力ｐ≥２．０ＧＰａ，２．０ＧＰａ～１．６ＧＰａ和Ｔ／Ｋ＞９７３．１５ｐ＝１．４ＧＰａ等多阶段近等温减压变质作用，有着似大陆碰撞造山带的很陡的顺时针ｐ－Ｔ轨迹。它们形成于地壳增厚深埋和隆升减薄过程中，而终至抬升折反剥露地表的动力学。

Recently,a high pressure mafic granulites block has discovered along the northern borderland of the Tongbai Dabie orogenic belt.It is located in Tongbai Xinyang area of Henan province.The granulite block consists mainly of garnet hornblende two pyroxene granulites. It is proved by mineral chemistry and petrographical studies that the block has involved in polymetamorphism of near isothermal decompression.That is to say,the changes of the temperature and pressure are >1 213.15 K and >2.0 GPa,>1 123.15 K and 2.0￣1.6 GPa,and >973.15 K and 1.4 GPa,respectively,during the polymetamorphism. The p T paths with a steep slope of the block is clockwise type.So it is similar to that of the continental collision orogenic belt.It is suggest that the granulite block was formed in the process of crust thickening,where as uplift and exposion of the block were related to the thrusting and detachement at the botton of crust.