新疆库鲁克塔格南华系砂岩碎屑组成对其物源及盆地演化的指示

Changes of Detrital Composition of Sandstones from the Nanhua System,Quruqtagh Area: Implications on their provenance and the evolution of basin

库鲁克塔格南华系记录了塔里木北缘同期的火山—沉积事件和蚀源区物质组成及演化的信息。该区不同剖面内南华系各组砂岩碎屑组分的统计分析显示,贝义西组砂岩在不同剖面内组成差异显著:西山口剖面以岩屑砂岩为主,且岩屑为火山岩岩屑与沉积岩岩屑,物源为再旋回地层,而依格孜塔格剖面以长石砂岩和岩屑长石砂岩为主,岩屑主要为变质岩岩屑,物源为下伏古元古代高级变质岩。砂岩碎屑组成在剖面上垂向的变化表明贝义西组沉积期与照壁山组沉积期间(725 Ma±)存在一个沉积转型事件,导致贝义西组之上的照壁山组、阿勒通沟组及特瑞艾肯组砂岩组成在不同区域趋于一致,转变为代表基底隆起—过渡大陆区物源的典型"长石砂岩"。南华系砂岩碎屑组成与大陆裂谷盆地沉积砂岩相似,且物源区存在由前裂谷地层—过渡裂谷肩部—切割裂谷肩部—克拉通内部的连续演化过程,是库满凹陷早期裂解的岩相学记录。

The Nanhua System in Quruqtagh area could record a synchronous volcanic-sedimentary events along the northern margin of the Tarim craton. The characteristics of the detrital components of Nanhua System sandstones from various sections indicate that sandstones from Bayisi Formation in different section have different detrital components.In Xishankou section,litharenites are the key components,in which the rock fragments are volcanic rocks and sedimentary rocks,obviously,indicating a recycled sedimentary provenance. Whereas,in Yigezitage section,the key components are arkoses and lithic arkoses,and the rock fragments are metamorphic rocks while there are lots of mineral inclusions in quartz,which all indicate a metamorphic provenance. Vertical variation of sandstone＇s detrital components recorded a transform event between the boundary of Bayisi Formation and Zhaobishan Formation（ 725 Ma±）,which causes Zhaobihsan,Altungol and Tereeken Formation have a uniform sandstone component. Converted to a typical arkose composition those represent a basement uplift-transitional continental provenance. The detrital component of Nanhua System sandstones and temporal-spatial variation demonstrates a continental rift setting of Nanhua System at Quruqtagh area. Meanwhile,it also shows a successive provenance evolution from pre-rift sedimentary successions to transitional rift-shoulder to dissected rift-shoulder to transitional continental and craton interior. Consequently,the petrography of sandstones in Quruqtagh area records the early breakup of Quruqtagh-Mangar aulacogen.