南天山榆树沟高压麻粒岩地体多期变质定年研究

Geochronology for the multiple-stage metamorphism of high-pressure terrane of granulite fades from Yushugou area, south Tianshan.

通过详细的矿物学及岩石学研究,特别是对角闪石的系统研究,确定榆树沟麻粒岩地体至少经历过高压麻粒岩相、中压麻粒岩相、角闪岩相和绿片岩相四期变质作用的改造。总结了各期变质作用的期次和特点。在此基础上,采用^(40)Ar-^(39)Ar同位素定年获得368.2±4.8Ma坪年龄和360±10Ma等时线年龄。采用Sm-Nd同位素矿物等时线定年获得Gra+Pl+Ⅰlm+全岩的等时线年龄为310±5Ma。结合已发表的定年结果综合分析认为,前者可代表榆树沟地体峰期变质-高压麻粒岩相变质作用年龄;后者为峰期后经受中压麻粒岩相变质变形的叠加改造年龄。讨论了多期变质作用中同位素的均一化和封闭温度问题。

A detailed investigation of mineralogy and petrology on amphiboles demonstrates that the granulite terrane of Yushugou underwent a four-stage metamorphism, i.e., high-pressure granulite facies, medium-pressure granulite facies, amphibolite facies and greenschist facies. The sequence and the features of the metamorphism in each stage are concluded in the paper. The Ar-40-Ar-39 dating obtains a plateau age of 368. 2 +/- 4. 8Ma and an isochron age of 360 +/- 10Ma. The Sm-Nd mineral-rock isotopic dating gets an isochron age of 310 +/- 5Ma by using Gra + PI + Ilm + whole rock assemblage. Based on the dating results in this paper and literatures, the Ar-40-Ar-39 age is probably the peak-stage age of high-pressure granulite facies of Yushugou terrane while the Sm-Nd age is a retrograde age of medium-pressure granulite facies. The homogenization and block temperatures of isotopes in the multiple-stage metamorphism are also mentioned in the paper.