辽西凌源地区水泉沟组辉石安山岩锆石SHRIMPU-Pb定年及其意义

SHRIMP U-Pb dating for zircons from pyroxene andesite of Shuiquangou Formation in western Liaoning province and its tectonic significance.

水泉沟组分布在辽西凌源地区,不整合覆盖早中生代第一期推覆构造系统,其上又被稍晚形成的燕山早期推覆构造所掩覆。水泉沟组辉石安山岩锆石SHRIMPU-Pb测年结果为230.4Ma±3.1Ma。测试结果表明:①辽西水泉沟组时代为晚三叠世;②燕山地区晚三叠世安山质火山岩很可能代表一种拉张的构造环境;③燕山地区早中生代早期挤压逆冲构造发育于早中三叠世,即燕山地区印支阶段早期为挤压逆冲,晚期为伸展构造。

The Shuiquangou Formation, located in the Lingyuan area of western Liaoning, lays unconformably over the first thrust system formed during the Early Mesozoic and is covered by a early Yanshanian thrust. The SHRIMP age of zircons from pyroxene andesite of Shuiquangou Formation is 230.4 Ma±3.1 Ma. The result shows that the age of Shuiquangou Formation is the Late Triassic; the lithosphere in western Liaoning is in a stretching setting during the Late Triassic and the thrusting of the early Early Mesozoic in Yanshan mountains was occurred in the Early and Middle Triassic. It suggests that the early stage of Indochina movement is thrusting and the late is extension.