兰坪盆地新生代碎屑岩地球化学特征及其对物源制约

Geochemistry of Cenozoic detrital rocks and its constraints on provenance in Lanping Basin.

兰坪盆地的新生代地层,包括勐野井组、等黑组、宝相寺组、金丝厂组和三营组等,岩性有砂岩、泥岩和砾岩。由于盆地内部断层纵横,新生代地层的横向对比比较困难,研究揭示新生代地层的物源对于恢复盆地的岩相古地理环境、探讨盆地演化与构造演化的关系等具有重要地质意义。根据砂岩、泥岩和砾岩胶结物的La/Th、La/Yb、Cr/Th、K/Rb、K/Th、Zr/Hf、Th/Sc、U/Th比值以及δCe和δEu等地球化学参数并结合沉积相的研究成果,可以看出兰坪盆地新生代沉积物存在三种物源组分:即深源卤水、基性-超基性岩和长英质岩石。金顶地区存在长英质岩石、基性-超基性岩和深源卤水三种物源混合的现象,啦井地区则存在长英质岩石、基性-超基性岩物源的混合。河湖相碎屑岩的Cr/Co比值可以指示物源区的距离远近,这个比值越小则物源区距离越大。

The Cenozoic strata developing in Lanping Basin, comprising Mengyejing, Denghei, Baoxiangsi, Jinsichang and Sanying Formations, are composed of sandstones, mudstone and conglomerate. Because of the vertically and horizontally faults in the basin, there is some difficulty in comparing Cenozoic strata in Lanping Basin. There is important implication that investigate the provenance of source rocks of the Cenozoic strata, renew the sedimentary facies and paleogeography, discuss the relation between evolvement of basin and tectonic evolvement. Based on petrochemical analysis of the sandstones, mudstone and conglomerate cenment, according to the research results about La/Th, La/Yb, Cr/Th, K/Rb, K/Th, Zr/Hf, Th/Sc, U/Th, δCe and δEu etc. Combined with the data of sedimentary facies, it is refered that there are three provenance of source rocks in Cenozoic detrital rocks of Lanping basin： deep brine, basic-ultrabasic rocks, and felsic rocks. The primary materials of Cenozoic detrital rocks in Jinding area shoud come from the mixing of the felsic rocks, basic-uhrabasic rocks and deep brine. The primary materials of Cenozoic detrital rocks in Lajing area shoud come from the mixing of the felsic rocks and basic-uhrabasic rocks. It is refered in this article that the Cr/Co ratio of river-lake facies detrital rocks can show the distance of source rocks area, the ratio is more small, the source rocks area is more large.