Abstract:

The source rocks of the southwestern Ordos Basin were the mesometamorphic,  magmatic active and migmatizational complex metamorphic rocks of Archaean and the metavolcanite-sediment rocks of the Lower Proterozoic.The tectonic character had steady-active dualism.In different source distributing regions, there were quite differences between the characters of light minerals and those of the heavy ones.The quartz was brown metamorphosed rocks, and the feldspar was mainly alkalescent feldspar, the source rock of which was the quartz sandstone, quartz schist, quartz rocks and granite or granitic gneiss of the Taihua Group, the Qinling Group and the Kuanping Group.After being analysed synthetically, the study area had three source regions.The constituent of clastic debris and heavy minerals had clearly different characters in the southern and northern source distributing regions.In the period of member 8 of Xiashihezi Formation, the western region of Qingtongxia-Guyuan rupture began to upheave, and the western sediment provenance began to supply the old sediment gradually, where volcano movements once existed.In the southern or southwestern source near the source regions, the sandstone was thick and the reservoir  properties were better, which were quite different from the Haiyuan source.What's more, the sandstone was consistent with that of Longxi ancient land.The feldspar-dissolved-pores especially developed in Shanxi Formation and existed in the secondary dissolved pores belts, which was the best exploring target plot.

Key words: the southwestern Ordos Basin, the Early Permian, light minerals, heavy minerals, REE pattern