Petrogeochemical characteristics and source analysis of sandstone rocks in the lower section of Kuche Formation in Qiulitage area
Qiulitage area is situated in the south margin of the Kuche Depression,Tarim Basin,Xinjiang.The lower section of the Upper Neozoic Series'Kuche Formation serves as a significant ore-bearing layer.However,there remains a deficiency in source analysis for Qiulitage area.The sandstone samples from the lower section of Kuche Formation,exhibiting well-developed mineralization clues,are systematically collect-ed from west to east for subsequent petrographic and petrogeochemical analysis.The research result indi-cates that the formation primarily consists of the conglomerate,sandy conglomerate,pebbled sandstone,coarse sandstone,siltstone and mudstone.The rounded shape is predominantly subangular and subcircular with the characteristics indicative of the proximal sedimentation.There is a gradual increase in cuttings con-tent while the quartz and feldspar components decrease,resulting in a finer grain size.The rock geochemical analysis reveals a progressive reduction in SiO2,Al2O3,K2O,Na2O and FeO contents from west to the east.Additionally,there is relative enrichment of the light rare earth elements and depletion of the heavy rare earth elements observed along with an evident negative Eu anomaly of the sandstone.In summary,the clastic components of the sandstone in the lower section of Kuche Formation in Qiulitage area exhibit signifi-cant lateral variations and generally display a"coarse in the west and fine in the east"pattern.The source is primarily composed of the medium-acid granite,followed by sedimentary rocks and volcanic rocks,with their respective contributions gradually decreasing from west to the east.The original rocks are predominantly formed within a passive continental margin tectonic setting.The South Tianshan Mountain serves as the pri-mary source area for erosion in the northwest area of the study region,and provides the material sources,u-ranium sources,and favorable geochemical condition.
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