Geochemical characteristics and provenance of meta-mud siltstones from the Danfeng ophiolite mélange in eastern Qinling, central China

The Danfeng ophiolites outcrop in Guojiagou area east of Danfeng County, eastern Qinling. Being an important part of the ophiolites, the mud siltstones are closely associated with cherts, which have been metamorphosed to hornblende quart schists with minor biotite quart schists. They are featured by high CaO, MgO, MnO, Sr, Ba and low K2O/Al2O3 ratios, moderate LREE enrichment and slight Eu anomalies, geochemically similar to those of sedimentary rocks occurred in island-arc areas in an active continental margin. Furthermore, hornblende quartz schists have high Co/Th and low La/Sc, Th/Sc ratios, while biotite quartz schists have relatively low Co/Th and high La/Sc, Th/Sc ratios, indicating that they mainly derived from basic materials with limited granite material supply. Based on the fact that the siliceous rocks associated with meta-mud siltstones are formed during Ordovician to Silurian, this sedimentary set should be formed in a fore-arc basin of an active continental margin during early island-arc of north Qinling in early Paleozoic.