By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late ...By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late Early Cretaceous. Geochemically,the volcanic rocks are relatively enriched in large-ion lithophile elements( Rb,K,and Th) and depleted in high field strength elements( Nb,Ta,and Ti),and rich in light rare earth elements,and depleted in heavy rare earth elements. The fact indicates that the main body of the volcanic rocks in the Qushenla Formation was derived from the partial melting of lower crust. The lithological assemblages are characterized by continental high-K calc-alkaline and shoshonitic series,suggesting that the southward-subducting oceanic slab in southern Bangong Lake had break off and that the Bangong Lake-Nujiang Ocean had closed before 107 Ma. The main dynamic mechanisms for the genesis of this set of intermediate-acidic volcanic rocks were upwelling of the asthenosphere and partial melting of the lower crust caused by slab break-off.展开更多
The Daqing Mountains area comprises a typical occurrence of the Khondalite Belt in the Western Block of the North China Craton (NCC). In this area, both early and late Paleoproterozoic metasedimentary rocks have been ...The Daqing Mountains area comprises a typical occurrence of the Khondalite Belt in the Western Block of the North China Craton (NCC). In this area, both early and late Paleoproterozoic metasedimentary rocks have been identified in what was originally called the Upper Wula Mountains "Subgroup". Six metasedimentary rock samples yielded SHRIMP U-Pb zircon ages of 2.56-2.04 Ga for detrital and 1.96-1.83 Ga for metamorphic zircons. Based on these data and previously published results, the following conclusions can be drawn: 1) The source region for the late Paleoproterozoic detrital sedimentary rocks is mainly 2.55 2.4 and 2.2 2.04 Ga in age, consistent with the early Precambrian geological history identified widely in the basement of the NCC. 2) The majority of sedimentary rocks of the khondalite series were deposited between 2.04 and 1.95 Ga, and then in a protracted period (1.96 and 1.83 Ga) underwent a complex history of amphibolite to granulite-facies metamorphism.展开更多
基金Supported by project of National Natural Science Foundation of China(No.41172056)
文摘By using petrological,isotope chronological,and geochemical methods,the authors studied the volcanic rocks in the studied area,mainly including dacites and trachytes. The results show that they formed during the late Early Cretaceous. Geochemically,the volcanic rocks are relatively enriched in large-ion lithophile elements( Rb,K,and Th) and depleted in high field strength elements( Nb,Ta,and Ti),and rich in light rare earth elements,and depleted in heavy rare earth elements. The fact indicates that the main body of the volcanic rocks in the Qushenla Formation was derived from the partial melting of lower crust. The lithological assemblages are characterized by continental high-K calc-alkaline and shoshonitic series,suggesting that the southward-subducting oceanic slab in southern Bangong Lake had break off and that the Bangong Lake-Nujiang Ocean had closed before 107 Ma. The main dynamic mechanisms for the genesis of this set of intermediate-acidic volcanic rocks were upwelling of the asthenosphere and partial melting of the lower crust caused by slab break-off.
基金supported by National Natural Science Foundation of China (Grant No.41002062)Scientific Research Program of the Ministry of Science and Technology of China (Grant No. J0901)the Key Program of the Land and Resource Ministry of China (Grant Nos. 1212011120151,1212010811033, 1212010711815)
文摘The Daqing Mountains area comprises a typical occurrence of the Khondalite Belt in the Western Block of the North China Craton (NCC). In this area, both early and late Paleoproterozoic metasedimentary rocks have been identified in what was originally called the Upper Wula Mountains "Subgroup". Six metasedimentary rock samples yielded SHRIMP U-Pb zircon ages of 2.56-2.04 Ga for detrital and 1.96-1.83 Ga for metamorphic zircons. Based on these data and previously published results, the following conclusions can be drawn: 1) The source region for the late Paleoproterozoic detrital sedimentary rocks is mainly 2.55 2.4 and 2.2 2.04 Ga in age, consistent with the early Precambrian geological history identified widely in the basement of the NCC. 2) The majority of sedimentary rocks of the khondalite series were deposited between 2.04 and 1.95 Ga, and then in a protracted period (1.96 and 1.83 Ga) underwent a complex history of amphibolite to granulite-facies metamorphism.
