Geochemical Characteristics and Sedimentary Environments of Siliceous Rocks and Siliceous Mudstone——Case Study of Bayingou Ophiolitic Mélange in Xianjiang

The flaggy cherts and argillite in the ophiolitic melange of Bayingou have a SiO2 content of 55.37%-91.19%,a high Al2O3 content between 3.07%-17.66%,and a TiO2 content of 0.12%-0.8%,having a good positive correlation between Al2O3 and TiO2,suggesting that they have a relatively high percentage of terrigenous muddy sediments. Moreover,they have typical NASC-normalized flat REE patterns without any visible Ce negative anomaly; and the Eu has an obvious right-hand dipping pattern. All these indicate a REE distribution pattern similar to that of deposited cherts and argillite found in continental margins. In addition,they have a Ce/Ce* ratio of 1.03-1.45,a (La/Ce)N of 0.62-0.92,a V/Y of 032-8.87,and a Th/U of 2.99-6.45,showing that the cherts and argillite are formed in continental margin settings into which the continental material can be easily transported. Therefore,the Bayingou ophiolite was formed in a transitional environment of continental rift to oceanic rift based on our study.