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Geochemical Characteristics of the Calc-Silicate Rocks in Khondalite Series in Daqingshan Area,Inner Mongolia

XU Zhong-yuan~(1),LIU Zheng-hong~(1),HU Feng-xiang~(2),YANG Zhen-sheng~1(1.College of Earth Sciences,Jilin University,Changchun130061,China;2.Inner Mongolia Institute of Geological Survey,Hohhot010020,China)  
In the khondalite series in Daqingshan area,Inner Mongolia,Di gneiss association is a independent litho-stratigraphic unit characteristic of calc-silicate rocks overlying a GaBi gneiss association and being overlain by a marble association.Characterized by generally containing diopside,sphene,scapolite and apatite,the unit is composed of diopside gneisses(DG) and diopside-feldspar granulitite(DFG),feldspar-diopside granulitite(FDG),diopsidite(DD) and diopside marble(DM).The association is rich in Ca,Sr,Na and depleted in Cr,Ni,Co,Sc,suggesting the presence of chemical sediments in the unit.Moreover,the negative correlation of CaO and positive of Al_2O_3 with SiO_2 reflect an increasing abundance of clastic rocks and a decreasing trend in chemical sediments from DM via DD,FDG to DFG and DG.The characteristics of major,trace and rare earth elements suggest a protolith association of(iron-rich) dolomitic pelite,calcareous mudstone and greywacke intercalated by pelitic limestone and marlite,calcareous-bearing arkose,which was deposited in the setting of dry,intertidal or laguna with insufficient supply of the terrigenous detrital material.Their similarity to GaBi gneiss in geochemistry,especially in REE,when chemical sediments are considered separately,reflects that they probably shared a mutual provenance to GaBi gneiss.The Di gneiss association,GaBi gneiss association and marble association make up a sedimentary cycle from clastic via clastic mixed by chemical to chemical sediment,a sedimentary feature characteristic of Mid-Proteroroic Changcheng Group,hence supporting the view that the khondalte series was deposited within an intracratonic basin.
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