天山东段中天山隆起带前寒武纪变质岩系时代及演化——据U-Pb年代学研究

U-Pb AGE AND EVOLUTION OF PRECAMBRIAN METAMORPHIC ROCKS OF MIDDLE TIANSHAN UPLIFT ZONE, EASTERN TIANSHAN, CHINA

中天山变质岩系时代是长期有争议的问题。本文以天山东段为研究区,首次对该区变质岩及岩浆岩进行系统的U-Ph年代学研究,得到如下结论:1.星星峡群的时代上限为1400Ma;2.天湖群的时代上限大于660Ma;3.区内有前加里东期(1200—960Ma)、加里东期(500—400Ma)、海西期(350—230 Ma)及燕山期的岩浆岩。用U-Pb三阶段模式讨论,认为它们属同一系列不同演化阶段的产物。

Geological age of the metamorphic rocks of Middle Tianshan has been in debate for a long time,. In this study zircons were collected from 9 metamorphic rocks and 8 mag-matic rocks. According to colour, grain size and efectro-magnetism, the zircons were di-vided into) 35 groups and determined by U-Pb dating respectively. This practice has provided useful information for age data interpretation. By using U-Pb three stage mo-del and U-Pb concordant plot, the data were calculated and good results obtained. The following conclusions have been reached: 1) 1400 Ma is recommented as the upper age limit for the Xingxingxia Group. 2) The upper limit c|f Tianhu Group is probably older than 660 Ma 3) Magmatic rocks of Precambrian (1200-960 Ma), Caledonian (500-400 Ma), Hercynian (350-230 Ma) and Yenshanian have been distinguished in this area. As indicated by the U-Pb three stage model,all of them axe regarded to be produced at various evolutional stages from a common source.