浙东晚中生代壳幔相互作用的新例证——新昌儒岙辉绿岩-花岗岩复合岩体的年代学与地球化学

A new case of diabase-granite composite intrusions has been foundin Xinchang Ru'ao, eastern Zhejiang. The diabase is mainly composed of plagioclase (An = 45 ∼ 55,50% ∼ 60%), augite (20% ∼ 30%) and homblende (10% ∼ 15% and shows whole rock ⁴⁰Ar/ ³⁹Ar age of 109.1 ± 2.8Ma. The granite is composed of quartz (25% ∼ 30%), perthite (50% ∼ 60%), plagioclase (An = 20 ± 10% ∼ 15%) and minority ofbiotite (< 5%). The crystallization age of the granite determined by zircon SHIRIMP method is 129 - 109Ma. The upper age limit of the granite is similar to that of diabase, which elucidate that both diabase and granite were contemporary solidified. Geochemically, they share same calc alkaline series. Both diabase and granite are enriched in LREE, LILE(e. g. K, Rb and Ba) but depleted in HFS elements (e. g. Ta, Nb, Zr and Hf) having similar REE patterns and trace element spide-diagrams. They have limited ranges of I_Sr values from 0. 7074 to 0. 7079 and ε_Nd (t) values from - 3.5 to - 4.4, implying trace elements and isotopic compositions were homogenized between them. The overall elemental and Sr-Nd isotopic characteristics of the diabase-granite composite intrusions are similar to that of basalt-rhyolite composite lava flows of eastern Zhejiang and are consistent with that of the late Mesozoic composite igneous rocks in SE-Fujian. It is proposed that the diabase magma was derived from partial melting of sub-continental lithospheric mantle which could have been induced by subduction processes. Its underplating and interaction with deep crust produced the granite magma. Therefore, this research provides a new case of crust-mantle interaction in the southeastern coast of China.