Paleoproterozoic evolution of the eastern Alxa Block,westernmost North China:Evidence from in situ zircon U-Pb dating and Hf-0 isotopes
作者单位：State Key Laboratory of Lithospheric EvolutionInstitute of Geology and GeophysicsChinese Academy of Sciences Graduate School of Chinese Academy of Sciences State Key Laboratory of Geological Processes and Mineral Resources.China University of Geosciences
会议名称：《中国科学院地质与地球物理研究所2012年度（第12届）学术年会》
会议日期：2013年
学科分类：070902[理学-地球化学] 0709[理学-地质学] 07[理学]
基 金：financially supported by the NSFC(grant No.40730315) the research grant of the State Key Laboratory of Geological Processes and Mineral Resources(grant No.GPMR201105)
关 键 词：North China Craton Alxa Block Paleoproterozoic U-Pb zircon age Zircon Hf-O isotopes
摘 要：The Alxa Block is the westernmost part of the North China Craton(NCC).In the past,it has been considered to be part of the Archean ***,formation and evolution of this block remain poorly understood,and this has hampered a broader understanding of the *** this study we analyzed the in situ zircon U-Pb age and Hf-0 isotopes for the two oldest rock units in the eastern Alxa Block,namely the Bayanwulashan and Diebusige *** Bayanwulashan Complex consists mainly of metamorphic rocks with mafic and felsic *** U-Pb zircon dating results indicate that the primary magmatic ages of the mafic and felsic igneous rocks are ca.2.34 Ga and ca.2.32-2.30 Ga,respectively,and both sets of rocks were overprinted by two metamorphic events at ca.1.89 Ga and ca.1.79 *** and zircon Hf-0 isotopic data suggest that the ca.2.34 Ga amphibolites within the Bayanwulashan Complex are characteristically high in TiO(up to 3.2%),Zr(up to 394 ppm) and Ti/V(30),resembling the basaltic rocks formed within continental *** ca.2.32-2.30 Ga felsic rocks were generated by remelting of dominant meta-igneous rocks that have zircon Hf model ages of 2.92-2.81 *** Diebusige Complex is composed of amphibolites,mafic gneisses and *** was intruded by granites dated at ca.1.97-1.98 Ga,and subjected to high grade metamorphic events at ca.1,89 Ga and ca.1.79 ***-examination of U-Pb ages for detrital and metamorphic zircons indicate that the depositional ages of protoliths of the Diebusige paragneisses may be considered to be between ca.2.45 and 2.0 *** U-Pb zircon age data do not support the existence of exposed Archean rocks in the eastern Alxa Block,although the possibility of Archean rocks at deeper crustal levels cannot be ruled out entirely. The eastern Alxa Block contrasts to the neighboring Yinshan Block and Khondlite Belt,as well as the Trans-North China Orogen,in terms of the timing and evolution of magmatism and ***,we conc