胶东半岛中生代侵入岩浆活动序列及其构造制约

Geochronological Sequence of Mesozoic Intrusive Magmatism in Jiaodong Peninsula and Its Tectonic Constraints

胶东半岛是我国东部中生代花岗质岩石较为发育的地区。通过对该区中生代侵入岩体高精度年代学数据资料分析,建立了区内中生代花岗质岩石3个显著不同的演化序列:晚三叠世(225～205Ma)幔源型花岗岩、晚侏罗世(160～150Ma)地壳重熔型花岗岩和早白垩世(130～105Ma)壳幔混合型花岗岩。通过与辽东和鲁西–徐淮地区中生代岩浆活动年代学格架的对比分析,探讨了华北东部地区中生代岩石圈构造演化和深部地球动力学过程。指出胶辽地区晚侏罗世(160～150Ma)地壳重熔型花岗岩记录了华北东部一次重要的岩石圈地壳增厚事件,其区域动力学背景可能与古太平洋板块低角度向亚洲大陆俯冲作用密切相关。正是这次增厚作用导致了早白垩世时期岩石圈拆沉减薄和大规模伸展型花岗质岩浆活动。岩石圈地壳增厚和减薄作用过程主导了中国东部中生代陆内构造应力体制的转换和岩浆活动序列。

Jiaodong Peninsula, located in the North China Craton east of the Tanlu fault zone, is one of the most important areas of Mesozoic intrusive rocks population. A geochronological sequence of Mesozoic intrusive rocks has been established through a detailed study of high-resolution isotopic ages of intrusive plutons in this area. Three periods with different magmatisms are distinctive： the Late Triassic mantle-derived granites aged 225-205 Ma, the Late Jurassic crustal-derived S-type granites aged 160-150 Ma, and the Early Cretaceous crust-mantle mixed sourced granites aged 130-105 Ma. A comparison of geochronological framework of the Mesozoic intrusive rocks with those outcropped in Liaodong and Luxi-Xuhuai areas provides key information to constrain tectonic evolution of North China. It points out that the Late Jurassic crustal-derived S-type granites in Jiao-Liao area record an important crustal thickening event, which is considered to be geodynamically related to fiat subduction of the Pacific plate beneath the Asia continent. This was followed by lithospheric delamination and attenuation during the Early Cretaceous, which resulted in widespread crust-mantle mixed sourced granitoid magmatism in East China. Crustal thickening and thinning are considered to be main cause for changes in Mesozoic tectonic regime and sequential evolution of magmatism in East China.