秋里塔格地区库车组下段砂岩岩石地球化学特征及物源分析

Petrogeochemical characteristics and source analysis of sandstone rocks in the lower section of Kuche Formation in Qiulitage area

秋里塔格地区位于新疆塔里木盆地库车坳陷南缘,上新统库车组下段为其重要的赋矿层位,然而对其物源分析的研究仍较为薄弱。文章自西向东选取区内已发现较好矿化线索不同地段的库车组下段砂岩样品,进行岩石岩相学及岩石地球化学分析,结合现有地质资料,探讨该区域物源补给特征及规律。研究结果表明,该地层主要由砾岩、砂砾岩、含砾砂岩、粗砂岩、粉砂岩以及泥岩等组成,磨圆以次棱角-次圆状为主,具有近源沉积特征,西起喀拉玉儿滚东至盐水沟,岩屑含量逐渐增多,石英及长石组分减少,粒度逐渐变细。岩石地球化学分析结果显示,砂岩自西向东具有SiO_(2)、Al_(2)O_(3)、K_(2)O、Na_(2)O以及FeO等含量逐渐降低,轻稀土相对富集、重稀土相对亏损以及具有明显的Eu负异常等特征。综上所述,秋里塔格库车组下段砂岩的碎屑组分在横向上变化较为明显,总体而言具有“西粗东细”的特征,物源主要为中酸性花岗岩,沉积岩及火山岩次之,且对各地段的物源贡献自西向东逐渐减小;原岩主要形成于被动大陆边缘构造背景;南天山为研究区北西侧主要蚀源区,提供物源、铀源及有利地球化学环境。

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 collected from west to east for subsequent petrographic and petrogeochemical analysis.The research result indicates 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 content while the quartz and feldspar components decrease,resulting in a finer grain size.The rock geochemical analysis reveals a progressive reduction in SiO_(2),Al_(2)O_(3),K_(2)O,Na_(2)O 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 significant 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 primary source area for erosion in the northwest area of the study region,and provides the material sources,uranium sources,and favorable geochemical condition.