关键词: 中侏罗世, 地球化学, 伸展背景, 玄武安山岩, 东南沿海

Abstract:  Among the Mesozoic volcanic rocks along the southeast coast of China, Middle Jurassic rocks are seldom reported, yet they hold significant importance for understanding Mesozoic magmatic activities and tectonic evolution in this region. The Shaowu basaltic andesite, exposed in the southeast of the Jiangshao fault zone, provides an ideal opportunity for study. This paper systematically presents petrological, zircon UPb geochronological, LuHf isotopic, wholerock geochemistry and SmNd isotopic analyses of the basaltic andesite, indicating an eruption age of (161.0±2.0) Ma. The isotopic data shows that all samples are characterized by εHf(t) values ranging from -14.33 to -10.41 and low εNd(t) values between -9.2-8.4. The geochemical results shows high w(Al2O3)  and w(Na2O) contents, along with low levels of w(MgO) and w(TFe2O3) etc. The total rare earth elements (REE) content is low, with chondritenormalized REE patterns showing LREE enrichment and weak Eu negative anomalies. Furthermore, large ion lithophile elements such as Rb, Ba and K are enriched, while the high field strength elements such as Nb, Ta, Ti and P are relatively depleted. The geochemical and petrological characteristics of the basaltic andesite imply that it originated from partial melting of a metasomatic mantle wedge, underwent certain crystallization differentiation, and formed in an intraplate tectonic environment. Based on previous studies on regional tectonicmagmatic activities, it is proposed that Pacific subducted plate retreat and tearing, resulting in encroachment of mantlederived magma and the replacement of ancient crustderived rocks, occurred amidst local extension within the broader compressional background of the southeastern coast of China during the Middle Jurassic.

Key words: Middle Jurassic, geochemical, extensional setting, basaltic andesite, southeast coast of China