摘要
U–Pb analysis of zircons from igneous rocks in the Elashan Mountain, easternmost segment of the East Kunlun Orogen yielded 252–232 Ma. Geochemically, these rocks are mainly high in SiO_2, K_2O and K_2O＋Na_2O contents, low in P_2O_5 and TiO_2 contents, depleted in Ba, Sr, P, Ti and enriched in U, Hf, Zr, showing features of I–type granite. The zircon εHf（t） values of the Early Triassic Jiamuge＇er rhyolite porphyry（252±3 Ma） are positive（＋1.6 to ＋12.1）, suggesting a juvenile crustal source mixing with little old crustal component, and the zircon εHf（t） values of the Middle Triassic Manzhang＇gang granodiorite（244±3 Ma） and Dehailong diorite（237±3 Ma） are predominately negative（-8.4 to ＋1.0）, indicating an older crustal source. In comparison, the zircon εHf（t） values of the Late Triassic syenogranites from Suigen＇ergang（234±2Ma）, Ge＇ermugang（233±2 Ma） and Yue＇ergen（232±3 Ma） plutons vary from-3.8 to ＋5.0, suggesting a crust-mantle mixing source. From Early–Middle Triassic（252–237 Ma） to Late Triassic（234–232 Ma）, the geochemical characteristics of these rocks show the change from a subduction–collision setting to a post-collision or within-plate setting. By comparing of these new age data with 77 zircon U–Pb ages of igneous rocks of the eastern part of East Kunlun orogen from published literatures, we conclude that the igneous rocks of Elashan Mountain and these of the eastern part of East Kunlun Orogen belong to one magmatic belt. All these data indicate that the Triassic magmatic events of the eastern part of East Kunlun Orogen can be divided into three stages： 252–238 Ma, 238–226 Ma and 226–212 Ma. Statistically, the average εHf（t） values of the threestage igneous rocks show a tendency, from the old to young, from-0.75±0.25 to lower-2.65±0.52 and then to-1.22±0.25, respectively, which reveal the change of their sources. These characteristics can be explained as a crust-mantle mixing source generated in
U–Pb analysis of zircons from igneous rocks in the Elashan Mountain, easternmost segment of the East Kunlun Orogen yielded 252–232 Ma. Geochemically, these rocks are mainly high in SiO_2, K_2O and K_2O＋Na_2O contents, low in P_2O_5 and TiO_2 contents, depleted in Ba, Sr, P, Ti and enriched in U, Hf, Zr, showing features of I–type granite. The zircon εHf（t） values of the Early Triassic Jiamuge＇er rhyolite porphyry（252±3 Ma） are positive（＋1.6 to ＋12.1）, suggesting a juvenile crustal source mixing with little old crustal component, and the zircon εHf（t） values of the Middle Triassic Manzhang＇gang granodiorite（244±3 Ma） and Dehailong diorite（237±3 Ma） are predominately negative（-8.4 to ＋1.0）, indicating an older crustal source. In comparison, the zircon εHf（t） values of the Late Triassic syenogranites from Suigen＇ergang（234±2Ma）, Ge＇ermugang（233±2 Ma） and Yue＇ergen（232±3 Ma） plutons vary from-3.8 to ＋5.0, suggesting a crust-mantle mixing source. From Early–Middle Triassic（252–237 Ma） to Late Triassic（234–232 Ma）, the geochemical characteristics of these rocks show the change from a subduction–collision setting to a post-collision or within-plate setting. By comparing of these new age data with 77 zircon U–Pb ages of igneous rocks of the eastern part of East Kunlun orogen from published literatures, we conclude that the igneous rocks of Elashan Mountain and these of the eastern part of East Kunlun Orogen belong to one magmatic belt. All these data indicate that the Triassic magmatic events of the eastern part of East Kunlun Orogen can be divided into three stages： 252–238 Ma, 238–226 Ma and 226–212 Ma. Statistically, the average εHf（t） values of the threestage igneous rocks show a tendency, from the old to young, from-0.75±0.25 to lower-2.65±0.52 and then to-1.22±0.25, respectively, which reveal the change of their sources. These characteristics can be explained as a crust-mantle mixing source generated in
基金
supported by China Geological Survey(Nos.12120113094000,1212010811033 and 12120113093600)
National Natural Science Foundation of China(Nos.41172062 and 41572052)
