川西沙坝麻粒岩的Sm-Nd和Rb-Sr同位素年龄及其地质意义

Sm-Nd and Rb-Sr Isotopic Ages of Shaba Granulite from Western Sichuan Province and Their Geological Significance

首次测定扬子板块西缘古老的结晶基底岩石沙坝麻粒岩Sm Nd矿物等时线年龄为 114 0± 110Ma ,代表中元古代末期麻粒岩相变质作用时代。Rb -Sr矿物等时线年龄为 2 18± 11Ma ,可能为晚古生代至早中生代基性岩浆侵入的热扰动改造年龄。其亏损地幔模式年龄TDM 为115 8Ma ,表明沙坝麻粒岩的原岩在成岩之后不久即经受麻粒岩相变质作用。根据上述年龄以及紫苏辉石中Nd同位素封闭温度和40 Ar/ 3 9Ar年龄等资料的计算表明 。

Using the Sm Nd and Rb Sr mineral isochron methods, we have dated the Shaba granulite, which is one of the oldest basement rocks in the western margin of the Yangtze Plate. The Sm Nd mineral isochron of 1140±110Ma represented the time of granulite facies metamorphism during the later Middle Proterozoic era, when the Grenville age Orogeny was developing around the world. The Rb-Sr mineral isochron of 218±11Ma might be a thermal event age disturbed by the Late Permian-Triassic intrusion mass of stratified gabbro. Its depleted mantle Nd model age of 1158Ma and ε Nd =5.5 showed that protolith of the Shaba granulite was experienced rapid granulite facies metamorphism after petrogenesis of the protolith. Based on above mentioned dating results and the closure temperatures of Nd isotope in hypersthene and 40 Ar / 39 Ar age of hypersthene, the authors suggest that the lower crustal rocks in western margin of Yangtze Plate, including Shaba granulite, were slowly uplifted after 1140Ma.