Geochemistry and Provenance of the Upper Devonian Shaliushui Formation in Jingyuan County, Gansu Province

Key words: 
• Shaliushui Formation /
• sedimentary geochemistry /
• provenance /
• Gansu province /
• the North Qilian Orogenic Belt

Abstract: Sedimentary geochemistry of detrital rocks from the upper Devonian Shaliushui Formation in Jingyuan, Gansu suggest that sandstone contain higher SiO2 and plagioclase content than mudstone; Mudstone, however, occupy higher femic mineral and mineral Kbearing than sandstone. All samples are depleted in Nb, Ta and Sr elements. Some of sandstones are enriched with Zr and Hf elements, with strong negative Eu anomalies, and others are depleted in Zr and Hf without negative Eu anomalies. All mudstones display enrichment of Ni and Cr elements, with strong negative Eu anomalies. Characteristics of samples from the Shaliushui Formation show that rocks in the source consist of the basic and acidic rocks with ancient sediments recycled from passive continental margin. And source underwent middle intense chemical weathering (CIA: 74~81). Tectonic setting discriminations suggest that rocks in the source were mainly formed in the continental arc and active continental margin, with minor the oceanic arc and passive continental margin. Evidences combining tectonic discriminations and comparisons with potential provenances revealed that sediments in the Shaliushui Formation were derived mainly from the North Qilian Continental arc and the Central Qilian Block, with minor the North Qilian subducted complex and North China Plate. Integrated in the sedimentary evolution from the upper Ordovician to Lower and Middle Devonian and igneous rocks, the North Qilian Orogenic Belt completed the transfer from compression to extension during the Late Devonian, which indicate that the upper Devonian Shaliushui Formation is the sedimentary record of this process.