Zircon U-Pb age and petrogenesis of the Lushigou high Ba-Sr quartz-monzonite in East Junggar,Xinjiang,and its geological significance
ZHAO Jian-xin;TONG Ying;MENG Gui-xiang;WANG Tao;ZHANG Zhao-chong;ZHANG Jian-jun;Institute of Geology,Chinese Academy of Geological Sciences;No.912 Geological Surveying Party,Jiangxi Bureau of Geology and Mineral Exploration and Development;Institute of Mineral Resources,Chinese Academy of Geological Sciences;China University of Geosciences;
The Liishigou pluton is located in the Qiongheba ore concentration area in East Junggar. This pluton intruded into the host rock of the Lushigou copper deposit. LA-ICP-MS U-Pb dating of zircons from this pluton yielded an early Carboniferous age of 354 ± 1 Ma. The main rock type of the pluton is quartz-monzonite with many mafic-ultral mafic enclaves inside. These quartz-monzonites have high SiO_2(62.31%~65.31%), Al_2O_3(15.44%~16.29%),CaO(3.71%~4.89%) and K_2O(2.85%~3.54%) contents,exhibiting high-K calcalkaline and metaluminous characteristics(A/CNK=0.93~0.99,A/NK=1.68~1.96),and belonging to I-type granite. The total REE values of them are low(90.82×10~(-6)~111.36×10~(-6)) with relative enrichment of LREE and Eu negative anomaly(δEu=0.68~0.87). The primitive mantle normalized trace element patterns are characterized by the enrichment of the LILE(K, Rb, Ba, Sr) and depletion of the HFSE(Nb, Ta, P, Ti). The quartz-monzonite has high Ba(758×10~(-6)~1113×10~(-6)),Sr(401.8×10~(-6)~512.5×10~(-6)) values with high(La/Yb)_N, Sr/Y ratios, distinct Nb, Ta and Ti depletion, and are comprehensively called high Ba-Sr granitoid.These characters indicate that the Liishigou pluton was probably formed by the magma-mixing of the mantle-derived mafic magma and crustal partial melting magma during the tectonic transition period from subduction to post-orogenic setting in the late Paleozoic.