Late Cretaceous tectono-magmatism of southeast China: Evidence from Qushandao Granite in the eastern Zhejiang province

Abstract

The Qushandao Granite, mainly composed of alkali-feldspar granite, is situated in the eastern Zhejiang province of coastal southeast China. In this paper, we present whole-rock geochemistry, zircon U–Pb geochronology, and Hf isotopes to constrain the age, magma sources, and geodynamic setting of the Qushandao Granite. LA-ICP-MS zircon U–Pb dating results revealed that the Qushandao Granite was emplaced in the Late Cretaceous (101–98 Ma). Geochemically, the Qushandao Granite exhibits relatively high silica and alkali contents, metaluminous to weakly peraluminous (A/CNK = 0.98–1.02), and low abundances of phosphorus, titanium, magnesium, and calcium. It is also characterized by enrichment in Rb, K, Th, and depletion in Nb, Ta, P, Ti, and Sr with moderately to weakly negative europium anomalies (Eu/Eu* = 0.71–0.87). Furthermore, the Qushandao Granite displays lower FeO^T/MgO, 10⁴ × Ga/Al, and Zr + Nb + Ce + Y values relative to typical A-type granites. Therefore, we classify the Qushandao Granite as calc-alkaline I-type granite based on a synthesis of geological and geochemical characteristics. The Qushandao Granite shows variable zircon Hf isotopic compositions (ε_Hf(t) = −7.6 to +2.3) and T_DM2 model ages of 1.40–0.83 Ga with a mean value of 1.17 Ga. We argue that the Qushandao Granite was most likely generated by mixing of mantle-derived mafic magma and crust-derived felsic magma in the lower crust, and that it was formed during post-collisional extension in the Late Cretaceous, related to the gradually increasing subduction angle of the Paleo-Pacific plate.