Multiple sources of Cretaceous granitoids in northeastern Fujian, coastal area of southeastern China

Abstract

The major elemental and oxygen isotopic features of Cretaceous granitoids in the coastal area of southeastern China cannot be adequately explained by existing Sr-Nd isotopic models of two-component crust-mantle mixing. In this paper, we report the whole-rock elemental, and Sr-, Nd-, and Hf-isotopes, and the zircon U-Pb age and Hf-O isotopic compositions for the Puqian, Danyang, Qingliangshan, Nanyu, and Qishan plutons in northeastern Fujian of this area to further investigate their petrogenesis. The examined rocks included pyroxene diorite, monzodiorite, granodioritic enclave, monzogranite and alkali-feldspar granite. Zircon U-Pb dating gave crystallization ages of 115 Ma for the Puqian monzogranite and granodioritic enclave, 97–109 Ma for the Danyang monzogranite, 99 Ma for the Nanyu pyroxene diorite, 97 Ma for the Qishan alkali-feldspar granite, and 97–103 Ma for the Qingliangshan alkali-feldspar granite. Our new Sr-Nd-Hf-O isotopic and petrogenetic studies of these granitoids showed that, aside from the ancient crustal component (δ18O = 7.5‰, εHf(t) = −10) and the mantle-derived magma (δ18O = 5.3‰, εHf(t) = 2), a separate juvenile low δ18O crustal source (δ18O = 4.2‰, εHf(t) = 2) must be involved. Since the emplacement of the diorite-monzodiorite-granodiorite-monzogranite suite and the A-type granite was coeval with pull-apart basins and bimodal volcanic rocks, the Cretaceous granitoids in northeastern Fujian, coastal area of southeastern China, were emplaced in an extensional setting, possibly due to the backarc extension and the changing drifting direction of the paleo-Pacific plate.