辽宁丹东地区侏罗纪花岗岩的变形时代:^(40)Ar/^(39)Ar年代学制约

Deformation age of Jurassic granites in the Dandong area, eastern China: ^(40)Ar/^(39)Ar geochronological constraints.

辽东半岛出露大量片麻状花岗岩,其锆石U-Pb年龄为180～157Ma,该套岩石的最大特点表现在岩石明显经历了早期上盘向NW推覆和后期近EW向伸展作用的韧性改造,然而其变形时代却一直未得到确定。本文以丹东市西南部黑沟二云母二长花岗岩岩体为例,通过激光^(40)Ar/^(39)Ar年代学研究探讨该岩体的变形时代。激光^(40)Ar/^(39)Ar定年结果表明,黑沟岩体经历的早期推覆、挤压事件发生在～143Ma,而后期地壳伸展作用则发生在121～113Ma,并且该区在早白垩纪期间经历了快速冷却、抬升过程。从而表明在晚侏罗纪-早白垩纪期间(143～113Ma)辽东半岛经历了区域构造体制变革。结合前人大地构造研究成果,本文认为辽东半岛晚侏罗纪-早白垩纪NW向推覆、挤压事件是古太平洋板块向欧亚大陆俯冲作用的结果,而晚期(早白垩纪)的地壳伸展事件是古太平洋板块俯冲作用的转向和变速、华北东部岩石圈较薄以及挤压后地壳松弛等综合作用的结果。

Gneissic two-mica monzogranites are widespread in the southern Liaodong Peninsula, eastern China. The SHRIMP zircon U-Pb dating indicates that their emplacement ages are between 180～157 Ma. The must remarkable characteristics of these granites are that these granites had experienced two stages of ductile deformation, i.e., the early NW-trending compression and later EW-trending extension. However, the deformation ages are still not constrained. In this paper we present UV laser ablation ^(40)Ar/^(39)Ar data of K-bearing minerals from the Heigou pluton, which is located at the southwestern of Dandong City, to study its deformation age and cooling history. Our resuhs show that the Heigou pluton was deformed at ～143 Ma and ～121 Ma, respectively, during crustal compression and extension and subsequently cooled and exhumated from 121 Ma to 113 Ma. This indicates that the tectonic transition happened during 143～113 Ma in the Liaodong Peninsula. Considering the regional tectonics, we present that the NW-trending compression was related to the subduction of Paleo-Pacific Plate beneath the Eurasia continent during Late Jurassic to Early Cretaceous, while the EW-trending extension was the result of the direction and speed transformation of the subduction of Paleo-Pacific Plate, lithospheric thinning and relaxation of compression.