Petrogenesis of Late Mesozoic Volcanic and Monzonitic Intrusive Rocks in Shantouzheng, Zhejiang

二长质岩石是探索深部物质组成、演化和动力学机制的理想对象，本文对浙江山头郑地区二长质侵入岩和伴生的外围火山岩开展研究，以揭示这些火山岩和侵入岩的成因联系，并为中国东南部晚中生代构造–岩浆作用机制提供制约。LA-ICP-MS锆石U-Pb年代学分析结果显示，外围流纹岩形成于139.32 ± 0.88 Ma而石英二长岩侵入体形成于105.4 ± 1.1 Ma，分别属于早白垩世早期和晚期岩浆活动产物，二者没有直接的成因联系。锆石Lu-Hf同位素组成和全岩Mg#值等信息显示，流纹岩和石英二长岩均主要来自古老地壳基底的重熔，但有不同程度的亏损幔源物质加入，其中参与形成石英二长岩的幔源物质贡献比例更高。亏损地幔物质贡献比例的升高，反映早白垩世古太平洋板块俯冲导致上覆岩石圈伸展程度增强，板片由低角度俯冲转变为高角度俯冲。Monzonitic rocks are ideal to explore the composition, evolution and dynamics of deep materials within Earth. In this paper, monzonitic intrusion and associated peripheral volcanic rocks in the Shantouzheng area, Zhejiang Province are studied to reveal the genetic relationship between volcanic and intrusive rocks, and to provide constraints for the Late Mesozoic tectono-magmatic evolution history in SE China. LA-ICP-MS zircon U-Pb dating results show that the rhyolites were formed at 139.32 ± 0.88 Ma and the intrusive quartz monzonite was formed at 105.4 ± 1.1 Ma, which belong to the early and late episodes of Early Cretaceous magmatic activities respectively, and there is no direct genetic relationship between the two. Zircon Lu-Hf isotope compositions and Mg# values of the studied samples indicate that both rhyolites and quartz monzonites are mainly derived from remelting of ancient crustal basement, but there is obvious input of mantle materials, and the input proportion to form the quartz monzonite is higher. The increase in the contribution ratio of depleted mantle materials reflects that the overlying lithosphere extensional environment of the Early Cretaceous subduction system was enhanced, and the subducting paleo-Pacific plate changed from low angle subduction to high angle subduction.