秦岭杂岩牛角山花岗质片麻岩体锆石U-Pb同位素年龄及其地质意义

ZIRCON UPb AGE OF THE NIUJIAOSHAN GRANITOID GNEISSES IN THE QINLING COMPLEX OF THE QINLING OROGENIC BELT—WITH A DISCUSSION OF ITS GEOLOGICAL SIGNIFICANCE

秦岭杂岩中发育的花岗质片麻岩体是目前秦岭造山带核部所识别的最古老的花岗质深成岩体。选取６组粒径晶形好、无磁性锆石进行ＵＰｂ同位素年龄测定，结果是（９５９±３．６）Ｍａ。这一成果对进一步认识该区晋宁期岩浆活动、构造背景及区域变形时代等具有一定意义。

Geological characteristics of the Niujiaoshan granitoid gneisses in the Qinling core complex indicate that they are the oldest granitoid plutons recognized in the complex and can be viewd as pre or syntectonic plutons in the Jinning movement. Six groups of zircons with a good crystal form and little magnetism have been selected and dated as 959±3.6 Ma by UPb dating. This age has important implications for understanding the granitic magmatism in the Jinning movement, tectonic setting and age of regional deformations.