天山中段海西中期花岗岩的成岩特征

THE FEATURES OF THE MIDDLE HERCYNIAN GRANITOID ROCKS IN THE SECTION OF TIANSHAN MOUNTIANS

天山中段海西中期花岗岩分布广泛,规模不大,以小岩基、岩株状侵入体为主,侵入于泥盆系和下石炭统之中。岩石类型以黑云母花岗岩为主,侵入活动明显受区域构造控制,岩相简单,岩浆期后蚀变作用微弱。通过对本期花岗岩的岩石学、矿物学、岩石化学和地球化学等诸方面的研究,对岩石的成因类型和结晶条件进行了探讨。海西中期花岗岩主要具有I型花岗岩特征,岩石的成岩温度范围为677～750℃,水压为 20×10~7～32 × 10~7Pa。

The study area is located in the middle section of Tianshan mountains. The middle Hercynian granitoids are the products of relatively late ma-gmatic activities in the Tianshan folded zone. The granites intrude both the Devonian and the low Carboniferous and are distribuded under the control of regional structures. Three periods of magmatic activities have been recognized on the basis of the intrusive relationships. Granodiorite, granite and b-feldspar granite formed respectively during the first, second and third periods, but the granite is the main part of all the granitoid rocks. The analysis and caculation of the petrochemical and chemical compositions of biotite and plagioclase reveal that graniteforming physicochemical condition is chara-terized by the following parameters. T = 677-745℃, fo2 = 10-10-10-11Pa, fH2o = 20.72×107-22×107Pa, PH2o = 2 × 108-3.2 × 108Pa.According to the petrological and mineralogical features, the petrochemical characteristics and the REE distribution patterns, the graninoid rocks in the area should be grouped into the I-type granite.