准噶尔盆地南缘中-新生界碎屑成份特征与构造期次

MESO-CENOZOIC TECTONIC EVENTS AND STRUCTURAL CONSTRAINTS IN THE SOUTHERN JUNGGAR BASIN: EVIDENCE FROM DETRITAL COMPOSITIONS

准噶尔盆地南缘晚侏罗世—早白垩世早期、晚白垩世及晚新生代发育的近源粗碎屑沉积显示构造活动的存在。野外剖面及镜下碎屑成份统计表明:砾岩的砾石成份、砂岩碎屑成份的物源属性主要是再旋回造山带和晚古生代的岩浆弧,但盆地南缘东段与西段的岩屑组成及物源属性存在较大的差异。其中,沉积岩岩屑在晚侏罗世—早白垩世早期、晚白垩世和晚新生代发生了相应的增加,显示盆缘沉积岩物源的隆升—剥蚀作用和构造活动的相对活跃。砂岩碎屑特征、重矿物相对含量及重矿物组合特征证明盆地南缘东、西两段的物源属性存在较大差异,特别是不稳定重矿物的增加显示晚侏罗世—早白垩世早期、晚白垩世和晚新生代为构造相对活跃的构造环境。综合中-新生界沉积碎屑特征及差异分析,准噶尔盆地南缘中-新生代盆山格局发生了3次较大的转变过程,分别对应于上述3个时期。中-新生代3次构造活动对含油气系统形成具有重要控制作用,构造活动期次与油气藏形成、调整的期次也有良好的对应关系。

The conglomerates of widespread distribution suggested active tectonisms during the Late Jurassic- Earliest Cretaceous, Late Cretaceous and Late Cenozoic. The framework grains of the Jurassic-Cenozoic sandstones and conglomerates in the southern Junggar Basin generally showed low detrital maturity, which mainly resulted from tectonic activities and orogenesis of the provenance area, namely, the ancestral Tianshan. The supplied provenance consisted of provenances of metamorphic rocks, acidic volcanics and sedimentary rocks attributed to recycled orogen, magmatic-arc and arc orogenic sandstone types. The detrital compositions suggested some differences in provenance between the western segment and the eastern segment of the southern Junggar Basin, which showed different sandstone types and tectonic attributes, especially the relative increasing of sedimentary rock detritus suggesting the uplifting and denudation of sedimentary rocks along southern margin of the basin. Different heavy mineral assemblages and unstable heavy minerals during the Late Jurassic-Earliest Cretaceous, Late Cretaceous and Late Cenozoic, indicated tectonic activities during these three stages. The characteristics of sedimentary systems and petrology proved that the basin-orogen pattern changed three times corresponding to the three stages mentioned-above, respectively. The formation of petroleum systems were controlled by the three tectonic events, matching with the multi-phase hydrocarbon accumulation and adjustment events in pool forming.