关键词: 鄂尔多斯盆地南部, 晚三叠世, 物源分析, 重矿物, REE配分模式

Abstract:

       The source  rocks of  the Late Triassic  in  the southern Ordos basin are mainly  the Archaean highly metamorphosed schists and gneisses, and the Sinian to Paleozoic shallow marine clastic rocks and carbonates. Affected by different sources, the light and heavy mineral assemblages have different features in various areas of a sedimentation system. In the western Zhenyuan-Jingchuan area, quartz content of sandstone  is  relatively high, and  the  lithic debris  is mainly  the sedimentary  rocks. To  the
southeast, in the Tongchuan-Yaoxian area, feldspar and debris of igneous and metamorphic rocks are gradually increased. In the
southern region of  the basin,  the heavy mineral assemblage  is of zircon +  tourmaline + garnet  type, controlled by sedimentation
channel net. There are mainly  four distribution areas  in heavy mineral association:  the Huanxian-Zhenyuan-Jingchuan area in  the west  is characterized by garnet + zircon +  tourmaline +  leucoxene assemblage;  the Changwu-Ningxian area  in  the south is characterized by zircon +  tourmaline +  leucoxene + garnet assemblage;  the Huangling-Tongchuan area  in  the southeast  is
characterized by garnet + zircon + leucoxene assemblage; and the Fuxian-Yan^,an area in the northeast is characterized by garnet
+ zircon + magnetite assemblage. They respectively correspond  to their own ancestral rivers and sedimentary diffusion areas. In
the Fuxian-Yan^,an area,  the REE patterns and geochemical characteristics of  theYanchang Formation are nearly similar withthe Archean and Early Proterozoic metamorphic rocks  to  the northeast of  the basin. In  the Zhenyuan-Jingchuan area,  the REE
patterns of  the Yanchang Formation sandstones are nearly similar  to  the metamorphic  rocks  to  the southwest of  the basin. This is certainly genetically  related. Consequently,  it can be  inferred  that  the structural evolution process of  the southwestern and northeastern areas of the basin was different.

Key words: southern Ordos basin, Late Triassic, provenance analysis, heavy minerals, REE pattern