辽东-胶东半岛三叠纪镁铁质岩浆岩:记录从洋壳俯冲到大陆碰撞的构造转换

Tectonic Transition from Oceanic Subduction to Continental Collision:Geochemical Evidences from Triassic Mafic Igneous Rocks in the Liaodong and Jiaodong Peninsulas

大陆碰撞造山带中出露的镁铁质岩浆岩,特别是形成于洋陆转换和大陆碰撞关键时期的镁铁质岩浆岩,对理解从大洋俯冲到大陆碰撞化学地球动力学过程的转变,以及发展板块构造理论具有重要意义。本文通过对苏鲁造山带和华北东南缘(胶东和辽东地区)三叠纪镁铁质岩浆岩同位素年代学和地球化学的系统总结,概括出从大洋俯冲到大陆碰撞过程中古洋壳和大陆地壳物质再循环的岩石地球化学记录。早-中三叠世洋岛型镁铁质岩浆岩属于同碰撞岩浆岩,具有洋岛型微量元素特征和弱富集的放射成因同位素组成,记录了先前俯冲古特提斯洋壳来源的熔体与上覆地幔楔橄榄岩的相互作用;晚三叠世岛弧型镁铁质岩浆岩属于同折返岩浆岩,具有弧型微量元素特征和相对富集的放射成因同位素组成,记录了随后俯冲的华南陆壳来源的熔体与上覆华北岩石圈地幔之间的相互作用。因此,辽东-胶东半岛三叠纪镁铁质岩浆岩记录了大陆俯冲带不同类型的壳幔相互作用及其形成的化学动力学过程。

The mafic igneous rocks,outcropped in the orogenic belt of continental collision,especially those formed during the critical periods of ocean-continent transition and continental collision,are of great significance for understanding the transformation of chemical geodynamic process from oceanic subduction to continental collision,and developing the plate tectonics theory.This study presents a systematic review on geochronology and geochemistry of mafic igneous rocks from the Sulu orogen and the southeastern margin of the North China Block(mainly the Liaodong and Jiaodong peninsulas),and a summary of the petrogeochemical records of the material recycling of ancient oceanic crust and continental crust in the transition process from oceanic subduction to continental collision.The early-middle Triassic mafic igneous rocks are the products of syn-collisional magmatism,with characteristics of OIB-like trace element composition and weakly enriched radiogenic isotope compositions.They recorded the intereaction between the melt derived from previously subducted paleo-Tethyan oceanic crust and peridotite of the overlying mantle wedge.The late Triassic mafic igneous rocks belong to the products of syn-exhumation magmatism during the continental collision,with characteristics of arc-like trace element compositions and relatively enriched radiogenic isotope compositions.They recorded the intereaction of the overlying ancient lithospheric mantle of the North China Block with felsic melts derived from subsequently subducted continental crust of the South China Block.Therefore,the Triassic mafic igneous rocks in the Liaodong and Jiaodong peninsulas have recorded different types of crust-mantle interaction and accompanied chemical geodynamics processes in the continental subduction zone.