A hybrid origin for the Qianshan A-type granite,northeast China:Geochemical and Sr-Nd-Hf isotopic evidence
作者单位：Department of Applied GeologyCurtin University of Technology
会议名称：《中国科学院地质与地球物理研究所2006学术年会》
会议日期：2007年
学科分类：070902[理学-地球化学] 0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学]
关 键 词：A-type granite magma mixing Sr-Nd isotopes mafic microgranular enclaves zircon Hf isotopes
摘 要：Major and trace element,whole rock Sr and Nd isotope and zircon Hf isotope data are reported for a suite of A-type granites and mafic microgranuiar enclaves from the Early Cretaceous(126±2 Ma) Qianshan pluton,Liaodong Peninsula,east China,with the aim of investigating the sources and petrogenesis of A-type *** Qianshan pluton includes hornblende alkali-feldspar granite,graphic biotite granite and mafic microgranuiar *** hornblende alkali-feldspar granites have high SiO2,Fe2O3T/MgO,K2O+Na2O,Rb,Zr and LREE contents and low Ba and Sr concentrations with strongly negative Eu *** high Rb/Sr(87Rb/86Sr = 16.76-24.15) and initial 87Sr/86Sr ratios(0.7215 to 0.7283),negativeεNd(t) values(-14.1 to -16.5) and zircon eHf(t) values(-18.9 to -11.5) indicate they were mainly derived from a crustal source,but with involvement of highεNd(t) and eHf(t) *** biotite granites have similar geochemical features and Sr-Nd-Hf isotopic compositions to enclaves, indicating they were the result of crystal fractionation of evolved mafic magmas,but with involvement of lowεNd(t) andεHf(t) *** mafic enclaves have an igneous texture and contain acicular apatite,suggesting quenching of mafic magmas that have co-mingled with the host *** have low initial 87Sr/86Sr ratios(0.7097-0.7148),negativeεNd(t)(-14.5 to -11.9) and zirconεHf(t)(-17.1 to -6.9) values,and are enriched in LILEs and LREEs and depleted in *** coupled with the high MgO(Mg# up to 54),this indicates derivation from an enriched lithospheric mantle source,but contaminated by crustal materials. Geochemical and Sr-,Nd- and zircon Hf-isotopic compositions rule-out simple crystal-liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks. Instead,magma mixing of mantle-derived mafic and crustal-derived magmas,coupled with crystal fractionation,is compatible with the *** example shows that at least some A-type granites formed thr