西南天山前寒武纪基底时代和特征:锆石U-Pb年龄和Nd-Sr同位素组成

Precambrian basement age and characteristics of Southwestern Tianshan: Zircon U Pb geochronology and Nd Sr isotopic compositions.

采用锆石 U- Pb定年方法 ,精确测定了西南天山木扎尔特群花岗片麻岩的结晶锆石年龄为 ( 70 7± 13) Ma( MSWD= 0 .33)。元素地球化学特征和低的 εNd( t)值 ( - 4.4～ - 7.1)、高的初始 Sr比值 ( 0 .70 76～ 0 .70 96 )表明花岗片麻岩的岩浆物质来自成熟度很高的基底陆壳物质 ,结晶锆石的年龄代表了基底岩石重熔生成花岗质岩浆的时代。 Nd模式年龄结果表明木扎尔特群基底岩石具有 1.7～ 1.

The Southwestern Tianshan basement Muzhaerte Group comprises a amphibolite facies metamorphic suite domainted by granitoid orthogneiss in the south slope of Haerke Mount. U Pb zircon dating on the granitoid orthogneiss yields the following new results: 707±13Ma(MSWD=0.33), which is the age of granitic magma emplacement. These orthogneisses have high ASI value(1.1<ASI<1.3), high LILE and LREE contents and high initial 87 Sr/ 86 Sr ratio values( 0.7076 ~0.7096) and very low ε Nd ( t )= -4.4 ~ -7.1. The granitoid orthogneiss was derived from ancient basement rocks with higher maturity, which have long evolution history before the partial melting. The granitic magma is interpreted as a product of partial melting of basement rocks, which coincide with major thermal events at Jinninggian orogeny. Nd model ages of gneisses about 1.7~1.9Ga provide a close estimate of the average age of the basement.