鄂西黄陵花岗岩基同位素年龄谱

Isotopic age spectrum of the Huangling granitic batholith,western Hubei

采用Isoplot程序重新计算了鄂西黄陵花岗岩基主要岩套的Rb -Sr等时线年龄和锆石U -Pb一致曲线年龄 ,测定了各种类型脉岩的侵入年龄 ,最后获得该岩基岩浆活动的年龄谱是 :主体太平溪英云闪长岩岩套和黄陵庙花岗闪长岩岩套的侵位年龄分别是 (833± 2 9)Ma和 (819± 7)Ma ,大老岭石英二长花岗岩岩套是 (786± 5 4 )Ma ,脉岩套侵入年龄从花岗闪长斑岩的 813Ma开始 ,到770Ma的辉绿岩和 772Ma的石英脉侵入 ,整个岩基抬升作用完成 ,岩浆活动基本结束。在印支期(2 17± 7)Ma时 ,岩基上NNW和NNE向大断裂发生了强烈的再次活动。Nd ,Sr同位素证据表明 ,除大老岭岩套外 ,其他三个岩套的岩浆演化是连续的 ,这些岩浆起源于晋宁期扬子板块北缘发生的大洋板块消减作用。

The Rb Sr isochron ages and zircon U Pb concordant ages for main rock suites of the Huangling granitic batholith have been recalculated with the Isoplot program (Ludwig,1994),and the intrusive ages have been measured of variant kinds of dikes in the batholith. A age spectrum of magmatic activity have been obtained: the emplacement ages of the Taipingxi tonalite,Huanglingmiao granodiorite and Dalaoling quartz adamellite suites are (833±29 )Ma,(819±7) Ma and (786±54) Ma,respectively;the emplacement ages of granodiorite porphyry,diabase and quartz veines are 813 Ma,770 Ma and 772 Ma,which shows the end of magmatism and elevation of the batholith. Whole rock ε Nd ( t ) and ε Sr ( t ) values of the Huangling granitoid batholith indicate a continuous magmatic evolution series except for the Dalaoling suites and the magma might be derived from the subduction occurred beneath northern Yangtze plate during Jinningian.