关于冀北“单塔子群”解体的商榷

THE DISINTEGRATION OF THE "DANTAZI GROUP" IN NORTHERN HUBEI——A DISCUSSION

冀北太古界“单塔子群”由下而上包括燕窝铺组、白庙组、风凰咀组及刘营组。但经过近几年的研究工作发现“单塔子群”的上部和下部在原岩建造,变质程度,混合岩化强度,构造式样及方向,同位素年龄等方面都存在着明显的差异,这些差异实际是反映着它们的生成时间,古地理环境以及所经受的构造-热事件的不同。据此,将“单塔子群”的上部(凤凰咀组、刘营组)解体出上,归属为下元古界红旗子群。

It has been found in recent studies that the protoliths of the lower part (the Yanwopu Formation and the Baimiao Formation) of the 'Dantazi Group' are oceanic tholeiite intermediate-basic volcanic rocks and tuffs with argillo-arenaceous rocks and siliceous-ferrugious rocks. The metamorphism attains higher amphibolite-facies grade. The deformation is dominated by NE-trending brachy-folds. They have an isotopic age of 2450±20Ma. On the other hand, the protoliths of its upper part (the Fenghuangzui Formation and Liuying Formation) are island-arc tholeiite with argillo-arenaceous-calcareous sediments and very thick argilo-arenaceous sediments. The metamorphism only attains the higher greenschist-facies grade and in a few cases the lower amphibolite-facies grade. The deformation is characterized by the E-W-trending tight linear folds. The isotopic age is 2332Ma. The above-mentioned differences obviously reflect that the paleogeo-grphical environments in which they were formed and the tectono-ther-mal events that hey underwent were quite different. To sum up, the 'Datazi Group' is the product of different stages of crustal evolution. According to this, it may be disintegrated into two parts: the lower part is called the late Archean Dantaze Group, and the upper part is assigned to the early Proterozoic Hongqiyingzi Group.