黑龙江省东北部街津口—抚远地区花岗闪长斑岩的锆石U-Pb定年及其地质意义

Zircon U-Pb Dating of the Granodiorite-Porphyries in Jiejinkou-Fuyuan Area,Northeastern Heilongjiang Province and Its Geological Significance

报导了黑龙江省东北部街津口-抚远地区花岗闪长斑岩中的锆石LA—ICP—MSU—Pb定年结果，以限定该区花岗闪长斑岩的形成时代及其构造属性。花岗闪长斑岩中的锆石多呈自形一半自形晶，振荡环带发育，Th／u值主要为0．31～1．23，指示其岩浆成因。对岩浆锆石的定年结果表明，这些花岗闪长斑岩均形成于晚白垩世（90．2～94．8Ma），而非前人认为的晚印支期。结合研究区及其邻区同时代火成岩的组合特征和古太平洋板块的构造演化历史，认为黑龙江省东北部街津口一抚远地区晚白垩世花岗闪长斑岩形成于古太平洋板块向东亚大陆俯冲的构造背景，该期岩浆事件标志着古太平洋板块正向俯冲作用的开始。

We report zircon U- Pb dating of the granodiorite-porphyries in Jiejinkou- Fuyuan area, northeastern Heilongjiang Province, with the aim of constraining formation time and tectonic setting of these granodiorite-porphyries. Most of the zircons from these granodiorite-porphyries are euhedral- subhedral in shape, display fine-scale oscillatory growth zoning, and have Th/U values of 0.31 - 1.23, indicating a magmatic origin. The dating results indicate that these granodiorite-porphyries formed in the Late Cretaceous （90.2 - 94.8 Ma） rather than previously believed Late Indo-Chinese epoch. Combined with the coeval igneous rock associations in the study area and adjacent areas and the subduction history of the Paleo-Pacific plate, we conclude that the Late Cretaceous granodiorite-porphyries in Jiejinkou - Fuyuan area, northeastern Heilongjiang Province occurred in the tectonic setting of the subduction of the Paleo-Pacific plate beneath the East Asia continent, and this magmatic event would mark the beginning of orthogonal subduction of the Paleo-Pacific plate.