辽东-吉南地区早元古代两种类型变质作用及其构造意义

Two Types of Early Proterozoic Metamorphism andIts Tectonic Significance in Eastern Liaoningand Southern Jilin Areas

辽宁东部和吉林南部的早元古代变质岩系可划归两个性质不同的变质地体。辽北地体包括北辽河群和老岭群，其中常见有石榴石、十字石、蓝晶石等特征变质矿物，属于典型的中压变质作用，并具有大陆碰撞带的顺时针ＰＴｔ轨迹，峰期阶段的变质条件达到低角闪岩相，它们和推覆构造所产生的构造增压作用有密切关系。辽南地体包括南辽河群和集安群，其中常见有石榴石、十字石、红柱石、堇青石、夕线石等特征变质矿物，属于典型的低压变质作用，并具有大陆边缘岩浆增生带的逆时针ＰＴｔ轨迹，峰期阶段的变质条件达到高角闪岩相，它们和大量片麻状花岗岩侵位所引起的岩浆增温作用有密切关系。研究结果表明北辽河群和南辽河群、老岭群和集安群不是同一个裂陷槽内的“同时异相”关系或“上下叠置”关系，而是两个变质地体的变质岩系在早元古代晚期经构造作用拼贴在一起。

Early Proterozoic metamorphic rock series exposed in eastern Liaoning and southern Jilin areas can be divided into two different metamorphic terranes, Liaobei terrane and Liaonan terrane determined by this study respectively. Liaobei terrane includes metamorphic rock series of Beiliaohe group and Laoling group in which the metamorphic index minerals such as garnet, staurolite and kaynite, develop commonly. All of them indicate that the metamorphism is of medium pressure one and has clockwise PTt path of continental collision belt. The conditions of peak metamorphism belong to low amphibolite facies. The characteristics of metamorphic PTt path is related to the tectonic thickness by napping. Liaonan terrane includes metamorphic rock series of Nanliaohe group and Jian group. The metamorphic rock series contain commonly metamorphic minerals such as garnet, staurolite, andalusite, cordierite and sillimanite which indicate a typical lowpressure metamorphism. The metamorphic PTt path is of an anticlockwise developing one in magmatic accretion belt of the continental margin. The conditions of peak metamorphism belong to high amphibolite facies. Metamorphic conditions are related to emplacement of a large amount of gneissic granite which caused the temperature increase. The results obtained indicate that the relationships between Beiliaohe and Nanliaohe groups, Laoling and Jian groups are considered to be two metamorphic terranes being put together by tectonism taking place in late stage of early Proterozoic and not to be out of phase formed in one fault basin or overlap of old and young metastratigraphies.