浙东南晚中生代花岗岩的锆石U-Pb年代学、地球化学及其地质意义

浙东南地区（江绍断裂带东南）是位于华南东北部濒太平洋的沿海地区，是理解古太平洋板块俯冲作用的重要地区。本次研究选取岩坦、梁弄、新铺3个典型的岩体进行岩相学、锆石年代学和地球化学研究，并结合前人对该地区花岗岩体的研究结果，探讨古太平洋板块俯冲与岩浆活动之间的关系。LA-ICP-MS锆石U-Pb定年结果显示：新铺花岗岩的年龄为(145.8±1.4) Ma，表明浙东南地区晚侏罗世仍存在岩浆活动的记录；梁弄花岗岩和岩坦花岗岩的形成时代分别为（106.2±1.4）和（94.7±1.4） Ma，代表早白垩世晚期典型的岩浆活动。地球化学特征上，3个岩体均富SiO₂、Al₂O₃，具有高的A/CNK，属高钾钙碱性花岗岩；稀土元素球粒陨石标准化分布型式图中具显著的负Ｅu异常，稀土元素总量偏低；微量元素原始地幔标准化分布型式图中富集Rb、Cs、U、Th、Pb，亏损Ba、Sr、Nb、Ti，为典型的壳源型花岗岩。结合已有的资料，本次研究表明,新铺花岗岩形成在由侏罗纪挤压向白垩纪伸展转变的构造背景下，梁弄花岗岩和岩坦花岗岩形成在岩石圈减薄的伸展构造背景下，它们形成均受到了古太平洋板块俯冲作用的影响。

Zircon U-Pb Geochronology,Geochemistry of Late-Mesozoic Granite in Southeastern (SE) Zhejiang Province and Its Tectonic Implication

The southeastern (SE) Zhejiang (southeast side of the Jiangshan-shaoxing fault) situated in coastal area of the Pacific Ocean, is an important area to understand the subduction of the Paleo-Pacific plate. Yantan, Xinpu and Liangnong plutons in SE Zhejiang are chosen for petrography, zircon geochronology and geochemistry study.  Combined with previous research results of the granite in this area,the authors discuss the relationship between the subduction of the Paleo-Pacific plate and magmatism. LA-ICP-MS zircon U-Pb dating results show that the Xinpu granite has an crystallization age of (145.8±1.4) Ma, and emplaced in the first stage of Early Cretaceous in SE Zhejiang Province, and the Liangnong granodiorite and Yantan syenogranite, with emplacement ages of (106.2 ± 1.4) and (94.7 ±1.4) Ma, respectively, were resulted from the Late Cretaceous magmatism. Late Mesozoic granites are charactered by such geochemical characteristics as enrichment of SiO₂, Al₂O₃, and high ratio of A/CNK, which indicates the granite belongs to the high-K calc-alkaline granite. In the primitive mantle-normalized distribution patterns, these granitic rocks are enriched in Rb, Cs，U,Th, Pb, and depleted in Ba,Sr, Nb, Ti. Their REE patterns are highly fractionated, strongly negative Eu anomalies and low total REE, which is corcandant with those of the crust-derived granite. The authors also conclude that the Xinpu granite (ca.145.8 ± 1.4 Ma) formed in the tectonic setting shifting from compression in the Late Jurassic to extension in Cretaceous, and Liangnong granite (ca. 106.2 ± 1.4 Ma) and Yantan granite (ca. 94.7 ± 1.4 Ma) are formed in the extensional dynamic setting which are all influenced by subduction of the Paleo-Pacific plate.