鄂尔多斯盆地延长组长7沉积期物源分析及母岩类型研究

通过对鄂尔多斯盆地延长组长7砂岩的类型、轻重矿物特征、重矿物聚类分析及泥岩的地化特征研究，并结合盆地周边源区露头剖面的岩性组合资料，讨论了长7沉积期的物源方向，恢复各源区母岩性质。经研究表明:鄂尔多斯盆地长7沉积期存在五个方向物源，东北、西南为主要的物源方向，西北、南部作为次要物源方向；其中东北源区母岩以中基性岩浆岩、高级变质岩为主，西南源区母岩以白云岩、浅变质岩为主，西北源区母岩以沉积岩为主，浅变质岩次之，南部源区母岩以含灰岩、碎屑岩为主，浅变质岩次之；另外经讨论证实西部存在局限的物源供给区，母岩主要为白云岩。

Provenance and Parent-rock Types of Member 7 of Yanchang Formation (Triassic), Ordos Basin

The research shows that there are 5 directions of provenances existed in Chang 7 period of Ordos Basin, that the northeast and southwest are main provenances, northwest, south and west as the secondary provenances. The lithological characteristics of parent rock from synthetic analyzing the light and heavy mineral characteristics and debris feature are inferred. Meanwhile, combining with the method of recovering relationship among heavy minerals reveals the feature of  parent rocks.
  According to the research, the basic magmatic rock and the high grade metamorphic rock are main part in the rocks of the northeast area; The sedimentary rock and the low grade metamorphic rock are main part of the rock in the southwest area; The low grade metamorphic rock, dolomite rock and sedimentary rock are main part in the rocks of northwest area; The sedimentary rock and the low grade metamorphic rock are main part in the rocks of north area; The sedimentary rock is main part in the rocks of west area. The REE pattern is similar to upper crust and the geochemical diagrams of Hf La/Th, La/Sc Co/Th and REE La/Yb indicate that the mudstones come from felsic rock area with less bedrock and andesite. (Gd/Yb)N>2 shows that the provenance of northeast should be from Archean strata, and (Gd/Yb)N<2 shows that the provenance of other areas should be from the strata above Archean.
  On this basis, by arranging the lithology of bedrock in the margin of Ordos Basin, it recovers that granulite facies metamorphite series are outcropped in the northeast area. The degree of metamorphism can be greenschist facies to amphibolite facies of low medium pressure type in the southwest area. The metamorphism has reached granulite facies to amphibolite facies and greenschist facies in the bedrock of northwest area. While greenschist facies to amphibolite facies of low pressure is the important metamorphism in the south area, and granulite facies on local area.
  Conclusion demonstrated that the parent rock can correspond to the bedrock in the northeast area, southwest area and west area. The high grade metamorphic bedrock is developed in the northwest area and south area which were not found at the parent  rock in these deposition areas. Therefore, it was inferred that the old bedrock in these areas has not uplifted at Chang 7 period, and not providing source to basin.