Geochemical characteristics of Yanshanian high-Mg intermediate-acid intrusive rocks in eastern Anhui and their dynamic significance

Abstract：Early Cretaceous intermediate-acid intrusive rocks in eastern Anhui are composed of a quartz diorite, quartz monzodiorite, granodiorite and monzogranite association, belonging to the high-K calc-alkaline series. They are characterized by higher Al2O3, Sr, Sr/Y and La/Yb ratios enrichment in LREE and LILE, depletion in HREE, Y and Yb, weak Eu negative or positive anomalies, higher (87Sr/86Sr)i and lower εNd (t). Compared with most adakitic rocks in eastern China, these rocks have higher Mg# values, MgO and Cr and Ni contents. Our study suggests that：(1) intermediate-acid intrusive rocks in eastern Anhui might be derived from partial melting of the delaminated lower continent crust and its subsequent interaction with mantle peridotite during the rise of the magma, leaving garnet as a residual phase; and (2) the area of eastern Anhui experienced a crustal thickening process controlled by compressional structure of the Tethyan tectonic domain in the early Yanshanian, and, large-scale sinistral strike-slip movement of the Tanlu fault influenced by Pacific tectonic domain in the Early Cretaceous was the main factor responsible for delamination of the lower crust. Intermediate-acid intrusive rocks in eastern Anhui are petrological records of transition from the Tethyan tectonic regime to Pacific tectonic regime during the Mesozoic.