Abstract:

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.

Key words: southeastern Zhejiang, Late-Mesozoic, granite, LA-ICP-MS, geochemistry, Paleo-Pacific plate