皖南歙县花岗闪长岩构造变形、年代学及其地质意义

The structural deformation and chronology of the Shexian granodiorite in southern Anhui Province, and their geological significance

位于江南造山带北缘的歙县地区,有大量的花岗质岩体出露.本文对歙县花岗闪长岩体进行了构造变形分析和LA-ICP-MS锆石U-Pb测年.构造变形特征显示该地区花岗闪长岩曾遭受深层次韧性变形,其中广泛发育的波状消光、动态重结晶颗粒、旋转残斑、云母鱼等是矿物受应力作用发生韧性变形的指示,花岗闪长岩中石英和长石的变形行为指示韧性变形温度为500℃~580℃.对歙县地区花岗闪长岩测年,获得加权平均年龄为822.8±9.5 Ma(MSWD=0.55,n=23),代表岩体的侵位年龄.综合前人研究资料,我们认为景德镇—歙县构造带内的岩石韧性变形时代应该在770 Ma左右,其可能反映了扬子板块与华夏板块最终碰撞拼合.

Shexian area is located at northern margin of the Jiangnan orogenic belt. There are a lot of granite outcroppings in this area. The structural deformation and LA-ICP-MS zircon U-Pb dating were carried out for the Shexian granodiorite. Structural deformation characteristic shows that the Shexian granodiorite suffered ductile deformation at deep level. Ductile deformation indicators such as undulatory extinction, dynamic recrystallization grain, rotated porphyroblast, mica fish are widely developed in deformed granodiorite. Deformation behaviors of quartz and feldspar indicated the deformation temperature of Shexian granodiorite is between 500 ℃ and 580 ℃. The LA-ICP-MS zircon U-Pb of the Shexian granodiorite giving a weighted mean age of 822.8±9.5 Ma(MSWD = 0.55, n = 23), which represents the emplacement age of Shexian granodiorite. Combination previous research data, it is believed that the ductile deformation event took place at ca.770 Ma, which may reflect the final collision and amalgamation between the Yangtze plate and the Cathaysia plate.