Petrology and Provenance Analysis of Hanjiagou Conglomerates in the Northern Margin of West Qinling

On the basis of field observations of the Pliocene conglomerates of Hanjiagou in the northern margin of west Qinling, this paper carried out the research on the sedimentary characteristics and provenance.The results show that Hanjiagou conglomerate is mainly composed offine gravel.The components are mainly sandstone and limestone, others aregranite and quartzite.The poor roundness of gravels is the result of the combined action of lithology, hydrodynamic conditions and transportation distance.The proluvial conglomerates and alluvial conglomerates occured alternately.The grain size presents a reverse cycle, which reveals the progradational development of the fan. The flat surface indicates a south-to-north direction of paleocurrent.The provenance is 30-50km away in the south and southwest of the mountain areas. The sandstone gravels mainly come from Dacaotan group of Devonian System, east of Minxian county.Limestone gravels are mainly from the Permian Daguanshan formation.Granitegranodiorite gravels may come from Jiaochangba-Luchuba granodiorite monzogranite in south Zhangxian.The conglomerates is the product of the continuous northeastern extension of Pliocene Tibetan Plateau, transported by rivers from south to north in dry climate and deposited in the middle of the root of alluvial fan.