Permian Tectonic Evolution in Southwestern Khanka Massif:Evidence from Zircon U-Pb Chronology,Hf isotope and Geochemistry of Gabbro and Diorite  

作　　者：CAO Huahua XU Wenliang PEI Fuping ZHANG Xingzhou 

机构地区：[1]College of Earth Sciences, Jilin University, Changehun, Jilin 130061, China

出　　处：《Acta Geologica Sinica(English Edition)》2011年第6期1390-1402,共13页地质学报（英文版）

基　　金：supported by the Natural Science Foundation of China(Grant: 1212321013019,1212010070301,40672038 and 40872049)

摘　　要：Laser ablation-inductively coupled plasma mass spectrometry （LA-ICP-MS） zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.26-1.22）, implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian （282-2 Ma） and in the Late Permian （255-3 Ma）, respectively. In addition, the captured zircons with the weighted mean age of 279-4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element （REE） abundances, fiat REE pattern, weak positive Eu anomalies （JEu）, and depletion in high field strength elements （HFSEs, Nb, Ta, and Ti）, similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from ＋7.63 to ＋14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs （Nb, Ta, and Ti）, similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from ＋11.22 to ＋14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneatLaser ablation-inductively coupled plasma mass spectrometry （LA-ICP-MS） zircon U-Pb dating and geochemical data for the Permian gabbros and diorites in the Hunchun area are presented to constrain the regional tectonic evolution in the study area. Zircons from gabbro and diorite are euhedral-subhedral in shape and display fine-scale oscillatory zoning as well as high Th/U ratios （0.26-1.22）, implying their magmatic origin. The dating results indicate that the gabbro and diorite formed in the Early Permian （282-2 Ma） and in the Late Permian （255-3 Ma）, respectively. In addition, the captured zircons with the weighted mean age of 279-4 Ma are also found in the diorite, consistent with the formation age of the gabbro within uncertainty. The gabbros belong chemically to low-K tholeiitic series, and are characterized by low rare earth element （REE） abundances, fiat REE pattern, weak positive Eu anomalies （JEu）, and depletion in high field strength elements （HFSEs, Nb, Ta, and Ti）, similar to the high-aluminum basalts from island arc setting. Initial Hf isotopic ratios of zircons from the gabbro range from ＋7.63 to ＋14.6, suggesting that its primary magma could be mainly derived from partial melting of a depleted lithospheric mantle. The diorites belong to middle K calc-alkaline series. Compared with the gabbros, the diorites have higher REE abundance, weak negative Eu anomalies, and more depletion in HFSEs （Nb, Ta, and Ti）, similar chemically to the volcanic rocks from an active continental margin setting. Initial Hf isotopic ratios and Hf two-stage model ages of zircons from the diorite range from ＋11.22 to ＋14.17 and from 424 to 692 Ma, respectively, suggesting that its primary magma could be mainly derived from partial melting of the Early Paleozoic and/or Neoproterozoic accretted lower crust. Taken together, it is suggested that geochemical variations from the Early Permian gabbros to the Late Permian diorites reveal that the subduction of the Paleo-Asian oceanic plate beneat

关 键 词：Khanka Massif the Paleo-Asian ocean arc-continent collision Permian magmatism GEOCHEMISTRY 

分 类 号：P597[天文地球—地球化学] P597.2[天文地球—地质学]