扬子西缘造山带基底麻粒岩的成因与形成过程

Granulites are the oldest rocks in the Panzhihua-Xichang (Pan-Xi) geological structure belt with north-south strike, western margin of Yangtze Block. We have completed the whole rock determination of major, trace and rare-earth elements in the granulites; electronic micro-probe analyzation of minerals in the rocks, Sm-Nd and Rb-Sr isotopic measurements of the minerals and whole rocks; 40Ar/39Ar dating and fission track (FT) dating of the granulites etc.. Primitive rocks of granulite were intermediate-basic volcanic rocks in ancient orogenic belt. Nd model age (TDM) = 1158 Ma, the metamorphic age of granulite facies (e.g. Sm-Nd mineral isochron age) is 1128 +/- 120 Ma, these ages mean that the process from magmatic differentiation to granulite facies metamorphism was finished in short periods. The periods were concordant with assembly times of Rodinia Supercontinent (1300-1000 Ma). The granulites were slowly uplifted from lower crust to middle-upper crust settings with a cooling ratio of 1.8℃/Ma, as well as the rocks were widely developed in metamorphism of amphibolite facies in the periods from 977 Ma to 825 Ma. The times of retrogressive metamorphism were in the same times of brocken up Rodinia Supercontinent (1000-700 Ma).. The crustal movement of Pan-Xi geological structure belt was in the stable stages with very slow uplift, that cooling ratios were (0.4-0.7)℃/Ma from Sinian to middle Mesozoic (825-143 Ma). The exhumation of crustal rocks was rapidly developed in Cenozoic, their cooling ratios were from (0.9-2.0)℃/Ma up to (4.1-7.8)℃/Ma. Rapid exhumation and block movement of crustal rocks in the Pan-Xi orogenic belt were caused by the uplift movement of Qinghai-Tibet Plateau, the later was developed by subduction between India and Euroasia Plates and the Himalaya movement of orogeny.. In addition, we had expansively studied an international correlation project on geochemistry of noble gas isotopes in mantle megacrystal minerals from Nushan and Yingfengling, eastern China, that was completed by some scientists both of Chinese and Japanese in Osaka University 2002. The project was supported by NSFC partly. The mantle fluid in megacrystal minerals are characterized by the MOBR type He of 3He/4He = 8+/-1 Ra (Ra=1.39 x 10-6), and by 40Ar/36Ar = 313-909, the Ar isotopic mixture between air and depleted mantle. Dynamic mechanism of the contamination was developed by subduction of oceanic plate with seawater and sediments dissolved some air.. We published two articles about metagranites in Dabieshan ultra-high pressure metamorphic belt in the three years..

扬子地块西缘造山带中出露的麻粒岩，代表了扬子地块晚元古代以前的结晶基底。它的形成和演化反映了扬子西缘造山作用的全过程，对研究整个扬子地块的演变历程有着十分重要的意义。本项目试图通过岩石学、矿物学与同位素定年、微量元素地球化学、热力学模拟相结合的方法，对麻粒岩进行研究，从而揭示整个造山带的抬升及剥露历史。