鄂尔多斯盆地二叠纪石盒子组沉积期南部沉积边界探讨

Discussion on the Southern Boundary of the Permian Shihezi Formation in the Ordos Basin

为了确定石盒子组沉积期鄂尔多斯盆地的南部边界,在大量野外露头观测及实验测试基础上,通过岩石学对比及物源综合分析,对鄂尔多斯盆地南缘和北秦岭地区石盒子组物源区的构造属性进行了研究,并对物源区进行了分析与对比。研究结果表明:所研究两个地区的石盒子组的岩屑组成相似,均以浅变质岩、花岗岩为主,含少量构造岩;砂岩碎屑成分相似,都与来源于再循环造山带源区中的碰撞造山带与前陆隆起物源区相关;并且在SiO2/Al2O3-K2O/Na2O和K2O/Na2O-SiO2及Zr-Th,La-Th-Sc,Th-Sc-Zr/10构造环境判别图解中两研究区物源区的构造环境基本一致,F1-F2判别图显示物源区一致,并且稀土元素配分模式相似。北秦岭元古界的变质岩、岩浆岩及其以南地区的再循环造山带中的低级变质的沉积岩可能为鄂尔多斯盆地南缘和北秦岭地区石盒子组砂岩碎屑的主要风化母岩。结合构造环境分析认为,在石盒子组沉积期,鄂尔多斯盆地的南部边界可能已经越过洛南断裂,达到北秦岭及其更南的区域。

The aim of this paper is to discuss the original southern boundary of the Permian Shihezi Formation in the Ordos Basin. Based on field observation and laboratory works, through petrological and provenance analyses, this paper discusses its provenance and tectonic affinity of the Shihezi Formation in southern Ordos Basin and North Qinling. The results suggest that rock lithics of the Shihezi Formation from both areas are similar and is characterized by epimetamorphic rock and granite, with few tectonite; the detrital mode compositions are similar and both are associated with collisional orogenic belt and foreland uplift provenance; In SiOJA1203-K20/Na20 and K20/Na20-SiO2, Zr-Th, La-Th-Sc, and Th-Sc-Zr/10 diagrams, both areas show the same tectonic background. F1-F2 distinguish diagram shows the consistent provenance of these two areas. They also have similar REE distribution patterns. Therefore, metamorphic rock and magmatic rock in Proterozoic of North Qinling as well as the low grade metamorphic rocks of recycled orogen to its southern area may most probably the potential sources for the Shihezi Formation in southern Ordos Basin and North Qinling. It is inferred that the south border of the Ordos Basin had crossed Luonan tectonic belt and maybe reached to North Qinling.