塔里木盆地库车坳陷东部上三叠统—中侏罗统物源特征及其地质意义

根据砂岩岩石薄片、石英阴极发光和重矿物组合分析,结合沉积构造及地震解释成果,对塔里木盆地库车坳陷东部上三叠统—中侏罗统物源体系及其演化进行详细分析,确定了物源方向及母岩性质。结果表明:塔里木盆地库车坳陷东部上三叠统—中侏罗统物源主要来自北部南天山造山带物源区,以岩浆岩和变质岩母岩为主,兼有少量沉积岩物源的影响。其中,塔里奇克组砂岩中陆源碎屑岩岩屑含量较高,阴极发光条件下不发光石英含量较高,重矿物组合具有高锆石、白钛矿和磁铁矿含量以及低石榴子石含量的特征,母岩可能为上奥陶统—上三叠统早期沉积;阿合组及阳霞组砂岩中岩浆岩岩屑含量升高,重矿物组合以较高的石榴子石含量为特征,阴极发光条件下石英主要为蓝紫色及棕褐色发光,其母岩主要来自二叠系及其下伏地层;克孜勒努尔组及恰克马克组砂岩中变质岩岩屑含量明显升高,石榴子石含量极高,阴极发光条件下棕褐色发光石英含量增多,表明变质岩母岩的影响增强。晚三叠世—中侏罗世,研究区物源区母岩演化具有明显规律性,即晚三叠世受较多沉积岩母岩影响,早侏罗世岩浆岩母岩供给增多,中侏罗世以变质岩母岩为主。晚三叠世,库车坳陷东部南天山造山带大幅抬升,导致大量变质岩母岩卷入造山带遭受剥蚀;早—中侏罗世,南天山造山带中段构造活动具有东西分段的特点,吐格尔明30团剖面以东早侏罗世砂岩率先具有高石榴子石含量的特点,而西部地区中侏罗世砂岩才大量出现石榴子石,表明南天山造山带中段的虎拉山及额尔宾山在早侏罗世隆升-剥蚀强烈,而哈尔克山在中侏罗世才进入强烈抬升期。

Provenance Characteristics of Upper Triassic-Middle Jurassic in the Eastern Kuqa Depression of Tarim Basin,China and Their Geological Significance

Based on the analysis results of thin sections,cathodoluminescence of quartz and heavy mineral assemblages,combined with sedimentary structures and seismic reflection characteristics,the provenance direction,parent rocks and evolution characteristics of Upper Triassic-Middle Jurassic in the eastern Kuqa depression of Tarim Basin were studied.The results show that the provenance of Upper Triassic-Middle Jurassic in the eastern Kuqa depression of Tarim Basin is mainly from South Tianshan orogenic belt in the north,and the parent rocks are mainly magmatic and metamorphic with a few sedimentary.Among them,there is a higher content of terrigenous clastic lithic and quartz without luminescence in the sandstone of Taliqike Formation,and the heavy mineral assemblages are characterized by higher contents of zircon,leucosphenite and magnetite,and lower contents of garnet,indicating that the parent rocks may be early deposition of Upper Ordovician-Upper Triassic;the contents of magmatic rock lithic in the sandstone of Ahe Formation and Yangxia Formation increase,the heavy minerals are characterized by higher contents of garnet,and quartz mainly gives off blue-purple and tan light under the condition of cathodoluminescence,indicating that the parent rocks of Ahe Formation and Yangxia Formation mainly come from Permian and its underlied sediments;the contents of metamorphic rock lithic and quartz with tan luminescent in the sandstone of Kezilenu'er Formation and Qiakemake Formation increase obviously,and the content of garnet is extremely high,indicating that the influence of metamorphic parent rock is enhanced.The evolution of parent rocks in the provenance area of Late Triassic-Middle Jurassic has obvious regularity.The parent rocks are mainly sedimentary in Late Triassic,and the contents of magmatic parent rocks increase in Early Jurassic,and finally,it is characterized by metamorphic parent rocks in Middle Jurassic.In Late Triassic,the South Tianshan orogenic belt is greatly uplifted in the eastern Kuqa depression,as a result,a large number of metamorphic parent rocks are involved in the orogenic belt and denuded;in Early-Middle Jurassic,the tectonic activity in the middle section of South Tianshan orogenic belt is characterized by east and west sections,the sandstone in the eastern region firstly has high content of garnet in Early Jurassic,while the sandstone in the western region does not appear garnet abundance until Middle Jurassic.It shows that Hula and E'erbin mountains in the middle section of South Tianshan orogenic belt are uplifted and denuded strongly in Early Jurassic,but Halke mountain is uplifted consumingly in Middle Jurassic.