Geochemical characteristics of Wusu mud volca-noes in Xinjiang and their mud sources

The mud volcano results from magmatic eruption formed by geological fluid activity. The formation of mud volcano re-quires three conditions, i.e., mud source, mud migration channel and water supply. Geochemical data of 8 samples from Wusu mud volcanoes are characterized by enrichment of LREEs relative to HREEs. Chondrite standard abnormal δEu values are 0.760~0.805, (La/Yb)_N is 5.47, and Ce/La is 2.22. The mud is enriched in large ion stone elements (LILE) such as Ba and Rb, whereas the high field strength elements (HFSE) Nb, Ta are strongly depleted. Sr/Ba ratios (0.33~1.01) suggest a lower paleo-salinity, Ce/La (2.22), Ce_anom (-0.007), and V/(V+Ni) (0.78) ratios indicate that the source rocks were formed in a reducing environment. REE and trace el-ements analyse show that the source rocks of Wusu mud volcanoes were derived from lower Jurassic Dadaowan Formation and San-gonghe Formation, suggesting a river swamp-semi-deep lake sedimentary facies of coal-bearing strata which represent a kind of weak reducing environment. The mud volcano geochemical data and stratigraphic section of Wusu imply that the maximum depth of mud source strata is about 7~8km.