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《Acta Petrologica Sinica》 2015-10
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Geochronology of the Paleoproterozoic khondalite rocks from the Wulashan-Daqingshan area,the Khondalite Belt

CAI Jia;LIU FuLai;LIU PingHua;WANG Fang;SHI JianRong;Institute of Geology,Chinese Academy of Geological Sciences;  
The khondalite rocks are cropped out in the Wulashan-Daqingshan area,central segment of the Khondalite Belt,which are important to illustrating the metamorphic and tectonic evolution of the Precambrian basement rocks. The studied khondalite rocks consist of cordierite-garnet-biotite gneiss,sillimanite-cordierite-garnet gneiss,hypersthene-garnet-biotite gneiss,and garret-bearing quartzofeldspathic rock,showing distinct decompressional textures after petrographic observations. Cathodoluminescent images show that zircons contained in the Wulashan-Daqingshan khondalite rocks mostly are detrital and metamorphic zircons. Detrital zircons reveal oscillatory zoning with igneous origin,and the metamorphic zircons occur either as single grains or overgrowth rims surrounding detrital zircon cores which are homogeneous and low in Th / U ratio. LA-ICP-MS U-Pb analyses on magmatic-type detrital zircons yield three distinct age populations of 2400 ~ 2500 Ma,~ 2300 Ma and 2000 ~ 2100 Ma,suggesting that the sedimentary protoliths of the khondalite rocks in the Wulashan-Daqingshan area have been deposited at some time after ~ 2000 Ma. Analyses of LA-ICP-MS U-Pb dating for metamorphic zircons indicate that the metamorphic zircons of the khondalite rocks range in 1850 ~ 1950 Ma yielding two age groups,with one at ~ 1950 Ma and the other at ~ 1860 Ma. These new zircon ages in combination with metamorphic and tectonic considerations,indicate that the Wulashan-Daqingshan Paleoproterozoic granulite-facies metamorphic event involving in the subduction and collision followed by post-collisional extension and subsequent exhumation between the Yinshan block to the north and the Ordos block to the south to form the Khondalite Belt in the Western Block of the North China Craton. Moreover,~ 1950 Ma is considered the timing of the collision between the Yinshan and the Ordos blocks to form the Western Block,whereas ~ 1860 Ma should be the timing of exhumation stage.
【Fund】: 国家自然科学重点基金项目(41430210);; 科技部973项目(2012CB416603);; 中国地质调查局地质大调查项目(12120114061901;12120114021401)联合资助
【CateGory Index】: P588.345;P597.3
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