Zircon U-Pb Geochronology and Geochemical Characteristics of the Volcanic Host Rocks from the Tongyu VHMS Copper Deposit in the Western North Qinling Orogen and Their Geological Significance  

作　　者：XIONG Xiao ZHU Laimin LI Ben ZHANG Guowei GONG Hujun ZHENG Jun JIANG Hang 

机构地区：[1]State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University [2]Centre for Exploration Targeting,ARC Centre of Excellence for Core to Crust Fluid Systems(CCFS),School of Earth and Environment,The University of Western Australia

出　　处：《Acta Geologica Sinica(English Edition)》2015年第6期1926-1946,共21页地质学报（英文版）

基　　金：jointly supported by the National Natural Science Foundation of China(Grant Nos.41272092,41421002 and 41072068);Program for Changjiang Scholars and Innovative Research Team in University(Grant IRT1281);Natural Science Basic Research Program of Shaanxi Province,China(Grant No.2013JZ013);Graduate Innovation Funds of Northwest University,China(Grant No.YZZ12006)

摘　　要：Precise in situ zircon U-Pb dating and Lu-Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr-Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE（e.g. Th, U, Pb and La） and depletion of HFSE（e.g. Nb, Ta, Ti, Zr and Hf）. Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr（0.703457 to 0.708218） and εNd（t）（-2 to 5.8） indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd（t） diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf（t） values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores（2616±39 Ma and 12Precise in situ zircon U-Pb dating and Lu-Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr-Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE（e.g. Th, U, Pb and La） and depletion of HFSE（e.g. Nb, Ta, Ti, Zr and Hf）. Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr（0.703457 to 0.708218） and εNd（t）（-2 to 5.8） indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd（t） diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf（t） values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores（2616±39 Ma and 12

关 键 词：VHMS-type copper deposit volcanic host rocks zircon U-Pb dating Lu-Hf and Sr-Ndisotope island arc environment 

分 类 号：P618.41[天文地球—矿床学] P597.3[天文地球—地质学]