Abstract:

Taimushan and Gushan are located in the southeast coastal areas of Fujian. Petrology and petrography studies have shown that Taimushan and Gushan granites belong to aluminous A-type granitoids and alkaline A-type granitoids respectively. Zircon LA-ICP-MS U-Pb dating results indicate that the granites in two regions, whose diagenetic ages were (96.6±1.6) Ma (MSWD=0.65) and(99.4±2.3) Ma (MSWD=0.49) respectively, formed in the earlier of Late Cretaceous. Based on granites of the two regions, we focused on the difference of two types of A-type granites in the eastern coast of China in terms of the petrology, petrography, geochemistry and discrimination diagrams. On the whole,  the AKI values, TFeO/MgO ratio, 10⁴×Ga/Al and (Zr+Nb+Ce+Y) values of the alkaline A-type granites  are higher than those of aluminous A-type granites of the same region, but also there is a range of overlap in above chemical indicators, and the traditional A-type granite discrimination diagrams are not thoroughly applicable to the strong differentiation aluminous A-type granite. Geochemistry shows that the granites in two regions should have a similar source, namely magma originated from the partial melting of crustal material and the process of diagenesis have some mantle material involved in. However, alkaline A-type granites in Gushan region may have more mantle material involved in, showing some characteristics of mantle-derived magmatic origin. Integrated with geochemistry, field geology, regional background and geochronology reveal that petrogenesis of the granites of two regions is closely related to the angle of the subduction of PaleoPacific Plate to the Eurasian Plate, and their tectonic environment belongs to a back-arc tensional tectonic environment.

Key words: alkaline A-type granite, aluminous A-type granite, petrogenesis, Taimushan, Gushan, eastern coast of China