辽西地区中元古代变质岩系的初步研究

PRELIMINARY STUDY ON THE MID PROTEROZOIC METAMORPHIC ROCKS IN WEST PART OF LIAONING PROVINCE

辽西地区中元古代变质表壳岩包括石英岩、千枚岩 -片岩、大理岩及细粒长英质片麻岩和少量阳起石片岩 ,为中酸性火山活动及钙碱性玄武岩活动之后的海进型沉积旋回 ,显示出一套较为连续的火山 -沉积系列。变质深成岩以斜长花岗质片麻岩为主体。根据同位素测年、微古植物化石分析及与地层的接触关系等 ,厘定它们为中元古代产物。在中元古代该区经历了大陆边缘岛弧的形成。

The metamorphic supracrustal rocks in the western part of Liaoning province include quartzite, phyllite-schist, marble, fine-grained felsic gneiss and a small proportion of actinolite schist. It is a sedimentary cycle of marine transgression after subalkalic basaltic activity and intermediate-acid volcanic eruption. The marble yields a Rb-Sr whole rock isochron age of 1036 Ma, which is intruded by the metamorphic plutonic rocks (plagiogranitic gneiss) dated 1155 Ma. The Rb-Sr isochron ages, palaeontology and contact relation with the Archean strata, indicate the supracrustal rocks are in an age of Mid Proterozoic. The tectonic setting revealed by the petrochemical features may comprehend an island arc occurriing in the northern continental margin of North China during Mid Proterozoic.