华北克拉通东部地块中生代变形的关键时限及其对构造的制约——以胶辽地区为例

Key geochronology of Mesozoic deformation in the eastern block of the North China Craton and its constraints on regional tectonics:a case of Jiaodong and Liaodong Peninsula

胶辽地块是华北克拉通东部地块的重要组成,处于北倾的大别-苏鲁构造带的上盘。过去近十年来提出的几个关于东北亚构造演化的重要构造模型涉及到了胶辽地块。本文主要利用我们在辽东半岛南部地区获得的SHRIMP U-Pb锆石定年结果,结合华北克拉通东部野外地质调查的野外第一手资料、我们获得的渤海湾盆地中的中生代构造资料以及其它研究人员的SHRIMP定年资料,系统建立华北克拉通东部地块中生代的构造变形过程,并讨论相关构造模型或构造问题。最近SHRIMP定年研究发现,胶辽地块中古元古代地质体经历了～160 Ma的重熔事件。CL和BSE图象显示,在辽南新太古宙地块附近丹东花岗岩体的两个样品LJ023和LJ030中发现一些167～157Ma的自形岩浆锆石和围绕年龄大约为2100 Ma核部锆石的岩浆型锆石环带。这次重熔事件很可能为华北克拉通的下地壳原地重熔。丹东岩体呈NE走向排列,经历了强烈的近水平韧性剪切变形和随后NNE走向的褶皱变形。本文以丹东地区为例,准确确定了这些变形的年龄。根据辽东半岛东西向剪切带中白云母K-Ar和^(40)Ar/^(39)Ar年龄,第一幕变形界定在195～193 Ma之间。根据野外侵入体与变形叶理之间的关系,丹东花岗岩遭受的第二幕变形发生于153～145Ma之间。第三幕变形,也即为NNE向走滑作用。

The Jiao-Liao massif is an important part of the Eastern Block of the north China Craton and located on the hanging wall of the north-dipping Dabie-Sulu suture zone. Several important tectonic models about tectonic evolution of the eastern Asia were proposed in the last decade and related closely to the Jiao-Liao massif. This paper combined our SHRIMP U-Pb zircon ages of the Dandong Granite in the Southern Liaoning Province, China, with our wide firsthand fieldworks in the east of North China Craton, our oilfield works in the Bohai Bay Basin and other recent SHRIMP dating, to summarize Mesozoic tectonic reactivation and evolutionary processes of the Eastern Block. In this study we identify an about 160 Ma partial melting of Paleoproterozoic plutons in the Jiao-Liao massif. Some magmatic, euhedral single zircons or magmatic zircon rimes around ca. 2100 Ma cores in the Dandong Granites near the Liaonan Neoarchaean terrane, are first recognized by the CL and BSE images and identified that the latest partial melting event happened at 167 similar to 157 Ma. This partial melting is most likely derived from in-situ remelting of ancient lower continental crust, mostly of North China Craton. The Dandong plutons are aligned in the NE direction and suffered intensively from the subhorizontal ductile thrust-related shearing and the subsequent NNE-trending folding. In the Dandong area, the precise timing of deformations was solved in this paper. The first deformation is identified to be from 195 to 193 Ma according to the K-Ar and Ar-40/Ar-39 ages of muscovites in the E-W trending shear zones of Liaodong peninsula. Based on the field relationship between the plutons and deformation foliations, a range from 153 to 145 Ma is defined as the duration of the second deformation time remained in the Dandong Granites. The NNE strike-slip faulting, i. e. the third deformation, must be constrained in a range from 135 Ma to 95 Ma. This deduced result is most similar to a range from the Ar-40/Ar-39 age of 128 - 132 Ma of initial sinistral strike-slipping of the Tan-Lu fault in the Anhui province to the biotite cooling age of 100 +/- 2.3 Ma of the Yilan-Yitong segment of the Tanlu fault in the Jilin province. These faults are transtensive to control some pull-apart basins. However, during the third deformation, some metamorphic core complexes in the eastern China often took place in the overlapping area between the large-scale sinistral faults. It is well correlated to NW-directed subduction of the Paleo-Pacific Plate at 180 - 145 Ma. Our SHRIMP data also indicate that the Liaodong basement and Early Mesozoic magmatism are exactly similar to the Jiaodong basement and Mesozoic magmatism. Therefore, Early Mesozoic evolution in the Liaodong area, similar to that in the Jiaodong area, is also related closely to the Sulu Orogen in the Early Mesozoic and tightly to the Pacific subduction in the entire Mesozoic.