辽西台里黑云母二长花岗岩地球化学特征及锆石U-Pb年代学

Geochemical Characteristics and Zircon U-Pb Geochronology of the Biotite Adamellite in Taili Area,Western Liaoning Province

辽西台里地区花岗质岩石主要由花岗质片麻岩、斑状花岗质片麻岩和黑云母二长花岗岩等组成，这些花岗质岩石均曾被视为新太古代花岗岩。根据各类花岗质岩石的产状序次关系确定，块状/片麻状黑云母二长花岗岩呈岩脉或岩枝状侵入太古宙花岗质片麻岩和斑状花岗质片麻岩中，分别出露于研究区南北两侧。地球化学研究表明，黑云母二长花岗岩属于准铝质弱过铝质的 I 型花岗岩，显示火山弧花岗岩的特点。黑云母二长花岗岩中锆石组成复杂，大量继承性锆石和新生锆石共存。新生锆石岩浆结晶特征明显，内部发育振荡生长环带，并具较高的 Th/U 值（0．15～1．70）。两个样品的新生锆石 U- Pb 定年结果（加权平均年龄）分别为（153．7±2．0）Ma 和（153．7±4．7）Ma。研究表明，黑云母二长花岗岩为源自下地壳中基性火成岩的晚侏罗世花岗质侵入岩，其构造背景与古太平洋板块向亚洲大陆下俯冲作用有关。

The granitoid rocks in Taili area,western Liaoning Province,are mainly composed of granitic gneiss, porphyritic granitic gneiss and biotite adamellite, and were once regarded as the Neoarchean granite.According to the occurrence sequence of various types of granitic rocks,the authors consider that the massive/gneissic biotite adamellite,located in south and north sides of the study region, intruded into granitic gneiss and porphyritic granitic gneiss as the apophysis or dike. Geochemical characteristics indicate that the biotite adamellite belongs to metaluminous-weakly peraluminous I-type granite, and shows volcanic arc granite characteristics. Zircons in the biotite adamellite are of complex origin.A large number of inherited zircons coexist with neonatal zircons. Neonatal zircons with obvious characteristics of magmatic crystallization are characterized by oscillating growth zonation and high Th/U values （0.15 1.70）.Weighted average ages of two samples by LA-ICP-MS zircon U-Pb are （153.7±2.0）Ma and （153.7±4.7）Ma,respectively.The results show that the biotite adamellite belongs to the Late Jurassic granitoid plutons with source rock as meso-basic volcanic rocks of the lower crust.The origin of the biotite adamellite is tectonically linked to the subduction of the paleo-Pacific plate to the Asian continent.