辽西东南部中生代花岗岩时代

Emplacement ages of the Mesozoic granites in southeastern part of the Western Liaoning Province.

辽西东南部是华北地台中生代花岗质岩浆作用较为发育的地区,并产有著名的杨家杖子钼矿床。但关于该区花岗岩的形成时代,一直缺乏深入的研究。本文通过细致的野外考察和系统采样,对该区不同类型的花岗质岩石进行了锆石U- Pb同位素测年。结果显示,该区的碱厂-杨家杖子岩体主体形成于180～190 Ma,部分岩石形成于150～160 Ma左右。东部海棠山-医巫闾山岩体主要形成于150～170 Ma左右。因此,该区的中生代花岗质岩浆作用主要发生在侏罗纪,而白垩纪花岗质岩浆作用相对较弱。同时。这些年代学资料还反映,区内的杨家杖子钼矿形成于中侏罗世,其东部的瓦子峪变质核杂岩形成于早白垩世。对比整个燕辽地区中生代岩浆作用的年代资料发现,该区中生代花岗岩且有自东向西逐渐年轻的趋势,且与火山作用的年代学格架有所不同。岩石中含有的捕获的古老锆石还表明,区内的早前寒武纪岩浆作用主要发生在25和18．5亿年左右。

The southeast part of the Western Liaoning Province （Liaoxi） is one of the important areas in the North China Craton in which the Mesozoic granitic magmatism was intensively developed. The well-known Yangjiazhangzi Mo deposit is located in this area. However, the emplacement ages of these granites are not well constrained. Based on the intensive field investigation and systematic sampling, zircon U-Pb isotopic analyses were conducted for various rock types in this area. The obtained U-Pb geochronological data indicate that the Jianchang-Yangjiazhangzi batholiths were emplaced mainly 180 - 190 Ma with some part formed in 150-160 Ma. The Haitangshan-Yiwulvshan batholiths in the eastern part were emplaced in 150-170 Ma. Therefore, it is concluded that the Jurassic is the main period of the granitic magmatism in area, whereas the Cretaceous granitic magmatism is limited. These data also suggested that the Yangjiazhangzi Mo deposit was formed in the Middle Jurassic, and the Waziyu metamorphic core complex was developed in the early Cretaceous. Comprehensive data compilations of the igneous rocks in the Yanshan-Liaoxi area display that the ages of the granites are not comparable to those of the volcanic rocks. However, a westward youngling trend was found for the Mesozoic granitic magmatism in the Yanshan-western Liaoning area. The inherited zircons indicate that the Early Precambrian magmatisms were developed mainly in the 2.5 and 1.85 Ga.