燕山中段盘山花岗岩体锆石SHRIMP U-Pb年龄测定及其构造意义

SHRIMP U-Pb dating of zircon from Panshan granitoid pluton in Yanshan orogenic belt and its tectonic implications

位于燕山陆内造山带中段南缘的蓟县盘山花岗岩体由狼家峪、官庄、东罗庄和小盘山4个侵入单元组成,并发育侵入期后含斑石英二长岩脉,发育环绕岩体分布的周缘向斜并侵蚀早期东西向蓟县断裂。对前3个侵入单元及岩体西侧围岩中的顺层侵入的含斑石英二长岩脉等4件样品的锆石U-Pb(SHRIMP)定年结果为,年龄值界于203-207Ma,表明盘山花岗岩体侵位于三叠纪末期。这个年龄结果进一步限定了燕山陆内造山带东西向褶皱、逆冲/逆掩断层系统形成时代的上限,显示其形成时代为印支期。

Panshan granitoid pluton situated in the southern margin of middle segment of Yanshan intracontinental orogenic belt consists of four intrusive units （Langjiayu, Guanzhuang, Dongluozhuang, Xiaopanshan） and porphyritic quartz-monzonite veins. The Panshan pluton is surrounded by an arc-shape syncline. The earlier EW-trending Jixian thrust fault is cut by the intrusive body. Three units of the pluton and a porphyritic quartz-monzonite vein have been dated by SHRIMP U-Pb of zircon. Their ages are between 203Ma and 207Ma, 205Ma in average. It shows that the pluton was emplaceed at the end of the Late Triassic. The age indicates an upper limit that EW-trending folds, EW-trending thrust and nappe structures in Yanshan intracontinental orogenic belt have been taken place. That means the regional EW-trending fold-thrusting deformations in the Yanshan area were formed in Indosinian movement period.