华北地台和秦岭—大别—苏鲁造山带的中生代花岗岩与深部地球动力学过程

近年来的研究证实 ,华北地台和大别—苏鲁造山带的中生代花岗岩与同时代的镁铁质超镁铁质岩有类似的Sr、Nd同位素特点 ,许多花岗岩和火山岩还具有类似埃达克岩的地球化学性质。在此基础上 ,根据现已积累的大量Sr、Nd同位素资料 ,从整个华北地台岩石圈的角度论证了中生代岩石圈地幔富集的性质、富集地幔发生的时代及其形成机制 ,进而探讨了岩浆活动的动力学机制 ,指出本区岩石圈富集地幔的形成是在Pangea超大陆裂解时岩石圈大规模拆沉减薄 ,被拆沉的太古宙古老地壳重循环进入地幔改变了地幔成分所致 ,说明超大陆裂解、岩石圈大规模拆沉减薄和富集地幔形成之间有密切的成因联系 ,超大陆裂解伴随着大陆地壳生长和消亡 (重循环 )的大体平衡。结合全球地震层析资料 ,进一步探讨了由俯冲大洋残片转化的下地壳同古老克拉通地壳物质在花岗岩源区中的重要意义。

MESOZOIC GRANITOIDS FROM NORTH CHINA BLOCK AND QINLING-DABIE-SULU OROGENIC BELT AND THEIR DEEP DYNAMIC PROCESS

Recent studies suggest that the Mesozoic granitoids and the contemporary mafic and ultra-mafic rocks from the North China block and Dabie-Sulu orogenic belt have the similar Sr, Nd isotopic characteristics, and many of the granitoids and volcanic rocks exhibit some features of adakites. Based on these studies and the collected Sr, Nd isotope data, and from the viewpoint of the whole North China lithosphere, we have discussed the nature of the EMI-type enriched mantle, the time and the mechanism of the formation of the enriched mantle, and have further discussed the dynamic mechanism of the magmatism. We suggest that the enriched mantle was caused by the Archean crust-mantle recycling in the setting of a breakup of the Pangea supercontinent, which made the mantle composition changed. Integrating with the data of the global seismic tomography, we have also discussed the significance of lower crust transferred from subducted oceanic relics, and the old craton substance for the source of the granitoids.