川西滇东地区前寒武系地层中白云母b0值的初步研究

在川西滇东地区的前寒武系变泥质岩地层中采了263个样品并测了其白云母b₀值,结果表明:渡口运动时发生低压高温的变质作用;川滇运动时在河口组及相应地层发育区发生中压变质作用,向两侧变质压力降低;晋宁运动挤压幕第Ⅰ期形变时发生低压变质作用,第Ⅱ期形变时发生中-高压变质作用,第Ⅲ期形变和澄江运动时发生中压变质作用。基于这一工作探讨了白云母b₀值研究在进行地层对比和构造分析中的积极作用。

AN APPROACH TO b_0 VALUES OF MUSCOVITE FROM PRECAMBRIAN STRATA, WEST SICHUAN AND EAST YUNNAN

263 samples have been measured from the Precambrian strata of western Sichuan and eastern Yunnan (except Kunyang group). The b0, values of muscovite show: metamorphism of Dukou movement (about 2.45 B. Y. ago) was of low pressure, and Chuandian movement (about 1.93 B. Y. ago) of low-medium pressure (with the range of b0 values as wide as that of Cale-donides in Scotland Highland). The first stage of deformation of jinning cycle (about 1.05 B. Y. ago) is of low pressure (average muscovite b0 = 8.998 A), and the second stage (the main folding episode) of Jinning cycle (about 0.9B. Y. ago) is of high pressure (b0 = 9.045A), while the third stage (about 0.8 B. Y. ago) is of medium pressure (b0= 9.010A). Chengjiang movement (about 0.7B. Y. ago) is of medium pressure too (b0 = 9.013A). It demonstrates that the Precambrian metamorphism is very complicated. In addition to Barrovian zone, it might be of low pressure and high temperature during Archean; and high pressure metamorphism could occure since Late Proterozoic.Two improtant clues have been found in the study: (1) Every lowgrade metamorphic suite of stratum seperated bu unconformities possesses its peculiar muscovite b0 value in wide area. (2) The isobar map of Chuandian movement has been worked out based on 131 muscovite b0 values, which might be well correspondent to the regional structural pattern.