渤海蓬莱9-1中生代花岗岩体岩石地球化学特征及其区域构造意义

Geochemistry of Mesozoic granite from Penglai 9-1 Oilfield of Bohai Sea and its regional tectonic significance

蓬莱9-1花岗岩体是渤海海域首次发现的中生代花岗岩,鉴于渤海海域在华北克拉通中的重要构造位置,该花岗岩的形成时代和成因机制的研究对区域构造研究具有重大意义。锆石LA-ICP-MS U-Pb定年结果表明该花岗岩体形成于中侏罗世160~165Ma。花岗岩属于高钾钙碱性系列,为准铝质-过铝质花岗岩;富Al_2O_3(14.84%~17.19%)和Sr(485×10^(-6)~909×10^(-6)),贫Y(0.66×10^(-6)~1.39×10^(-6))和Yb(小于2.0×10^(-6)),无铕的负异常,多数样品表现为铕的弱正异常,表现出C-型埃达克岩特征。表明渤海地区在160~165Ma期间处于挤压地壳增厚环境下,以地壳减薄为标志的克拉通破坏过程彼时尚未发生,其区域动力学环境可能仍处于华北板块-华南板块碰撞拼接的影响范围内。

The Penglai 9-1 granite is discovered for the first time in the Bohai Sea. The study on its geochronology and petrogenesis is important for understanding the regional tectonics due to the significant location of the Bohai Sea within the North China Craton. The zircon LA-ICP-MS age of the Penglai 9-1 granite is 160 - 165 Ma. This granite is a metaluminous to peraluminous granite and belongs to the high-K calc-alkaline series; it is characterized by enrichment of Al_2O_3（ 14. 84% - 17. 19%）,and Sr（ 485 × 10-（- 6）- 909 × 10-（- 6））,and depletion of Y（ 0. 66 × 10-（- 6）- 1. 39 × 10-（- 6）） and Yb（ 2. 0 × 10-（- 6））; it has no negative Eu abnormality; instead,most of samples show weak positive Eu abnormality. Such geochemistry show the Penglai 9-1 granite belongs to C-type adakite. The characteristics of this granite imply that the Bohai region was under a compressional and crustal thickening environment during 160 -165Ma,and the craton destruction did not occur during this time,and the regional dynamics probably still controlled by the collision of North and South China blocks.