Geochronology, geochemistry and petrogenesis of early Cretaceous Yaocun A-type granite in the Lower Yangtze region

The Yaocun pluton in Southern Anhui Province, lithologically consisting mainly of medium-to coarse-grained syenogranite in its centre and fine-grained porphyritic syenogranite on its margin, is outcropped around the northeastern Jiangnan orogeny of the Lower Yangtze region. This paper reports detailed study results of its the LA-ICP-MS zircon U-Pb dating, major elements, trace elements, whole-rock Nd isotopic compositions and zircon Hf isotopic compositions. LA-ICP-MS zircon U-Pb ages show that the Yaocun pluton, as the product of magmatic activity in the late Yanshanian period, was emplaced at 127.6±1.4Ma. The studies of petrography and geochemistry of this rock indicate that it is A-type granite, and is characterized by rich silica, high iron, high zircon saturation temperatures, enrichment of Rb, Th, U, K and Pb, depletion of Ba, Nb, Sr and Ti, and significant negative Eu anomalies (Eu/Eu^*=0.22-0.46). Its ε_Nd(t) and ε_Hf(t) values range from -6.2 to -5.7 and from -13.9 to -5.0 respectively, and the calculated two-stage model ages (T_DM2) of Nd and Hf isotopes from 1439 Ma to 1532 Ma and from 1508 Ma to 2062 Ma respectively. Combined with the results of regional geological research, it is suggested that the Yaocun pluton might be formed by the Mesoproterozoic crust remelting under extension-tension environment after the subduction of the Paleo-Pacific plate during the Early Cretaceous.