中天山喀拉塔格一带麻粒岩包体的发现及其地质意义

The Discovery of Granulite Xenoliths in the Kalatage area,Central Tianshan Block and Its Geological Significance

为探讨中天山地块前寒武纪结晶基底组成及时代,进而制约天山造山早期地壳演化及构造归属,在野外调查基础上,结合岩石学、矿物学、矿物化学等手段,对新疆东部喀拉塔格地区(中天山地块东段)新发现的下地壳代表性岩石-麻粒岩进行了系统研究。结果表明,麻粒岩主要矿物组合为紫苏辉石+堇青石+黑云母+石英+斜长石;麻粒岩相变质发生于1899±32Ma(MSWD=2.4,error bars=2δ),原岩应形成于2354±23Ma(MSWD=1.2,error bars=2δ)。该麻粒岩为目前中天山地块有确切年龄依据的最老地质体,证实了中天山地块存在古元古代结晶基底并经历了古元古代晚期高温变质,为中天山地块基底组成与时代、与周缘地块对比研究提供了重要信息。

In order to discuss the diagenesis and forming age of the Precambrian basement of the Central Tianshan block,and further to understand the crustal evolution and tectonic attribution of the Tianshan orogenic belt,a comprehensive study on petrology,mineralogy,geochemistry,and isotopic geochronolgy of the granulite,a representative of lower crust,newly discovered in the Kalatage area,Eastern Xinjiang（ Central Tianshan block） has been carried out in this paper on the basis of detailed field investigation. Result show that the granulite is manly composed of hypersthene,cordierite,biotite,quartz,and plagioclase,with accessory minerals of rutile,apatite,and zircon,and the granular crystalloblastic texture. It is believed that the granulite is likely formed in 1899±32 Ma（ MSWD = 2. 4,error bars = 2δ） through the metamorphism of its 2354±23 Ma（ MSWD = 1. 2,error bars = 2δ） aged protolith. Therefore,it is suggested that the granulite,which is the oldest rock with U-Pb dating age in the Central Tianshan block,could be formed in late stage of Early Proterozoic through high temperature metamorphism of the Early Proterozoic basement. This has provided important information for researches on the formation and forming age of the basement of the Central Tianshan block,and for comparison study on its surrounding blocks.