Constraints of combined Sr-Nd-Pb-Hf-O isotopic systematics on the petrogenesis of peralkaline, metaluminous and peraluminous granitoids in the Permian Emeishan large igneous province, SW China

In addition to voluminous high-Ti and low-Ti basalts, plutonic complexes composed of gabbroic and A-type granitoid units are well preserved in the ∼260 Ma Emeishan large igneous province (ELIP) of the Yangtze Block, SW China. The genetic relationship between these gabbroic rocks and granitoids is important to understand the diversity of igneous rocks of LIPs and magma generation and evolution related to mantle plumes. We present whole-rock elemental and Sr-Nd-Pb isotopic compositions and zircon HfO isotopes of granitoids from the well-known Panzhihua, Baima and Hongge igneous complexes of the ELIP. The granitoid units of these complexes are composed of variable proportions of syenites and granites. Some of these granitoids have depleted and others have enriched SrNd isotopic compositions. The isotopically depleted granitoids have low 87Sr/86Sr(t) (0.704331 to 0.706279) and positive εNd(t) (0.14 to 2.96) values and are peralkaline to metaluminous in composition with low Al2O3/(CaO + Na2O + K2O) (< ∼0.95) and low K2O/Na2O (0.19 to 1.07). They have similar SrNd isotopic compositions and fractional crystallization trends in terms of major and trace elements with coexisting gabbros, diorites and high-Ti basalts. These features indicate that these granitoids were probably produced by fractional crystallization of the high-Ti basaltic melts. Furthermore, their OIB-like Zr/Hf, Yb/Ta and Y/Nb ratios, low δ18O values (4.06 to 5.38‰) of zircons and low (206Pb/204Pb)t ratios (16.08 to 18.87) clearly indicate that they were formed from magmas derived from partial melting of the mantle plume with variable amounts of high temperature-altered oceanic crust. On the other hand, the isotopically enriched granitoids have high 87Sr/86Sr(t) (0.705124 to 0.709713), low εNd(t) (−2.09 to −4.56) and high (206Pb/204Pb)t (18.34 to 19.00) ratios and are metaluminous to peraluminous in composition with high Al2O3/(CaO + Na2O + K2O) (> ∼0.95) and high K2O/Na2O (1.5 to 1.98). A compositional gap between these rocks and the spatially associated basalts, and the deviation from the fractionation trend in Harker diagram indicate that these granitoids were not products of fractionation of basaltic melts. In addition, εHf(t) (−4.01 to 1.69) and δ18O (4.82 to 7.43‰) values of zircons are consistent with their derivation from partial melting of juvenile lower crust together with Yangtze ancient crust. Our study highlights the importance of the interaction of mantle plume with subducted slab, juvenile lower crust and ancient crust in the generation of diverse igneous rocks of the LIPs.