Geochemical characteristics of clastic rocks from Ruyang Group, western He'nan Province, and its indication to depositional environment and tectonic setting

The Mesoproterzoic Ruyang Group along the south margin of North China Craton(NCC) have been attracted much attention, resulting in an increasing number of achievements about chronology and sedimentology.In this paper, we trace the provenance of the clastic sedimentary rock of the Ruyang Group by geochemistry perspective, and reconstruct the palaeogeography and tectonic setting, which provide valuable details to describe the structure of the Meso-Neoproterozoic strata in the southern margin of NCC.The analytical results of major and trace elements contents of the Yunmengshan and Baicaoping Formations suggest that: ①Compared with Baicaoping Formation, Yunmengshan Formation shows higher SiO₂ contents, lower Fe₂O₃, MgO, CaO and K₂O contents, the obvious depletion of transition trace elements and high field strength elements, indicating relatively higher maturity.All samples show steep descending REE patterns with enriched LREE, flat HREE and obvious fractionation of LREE and HREE, moderately negative Eu anomalies(δEu=0.60~0.85) and weakly negative Ce abnormity(δCe=0.80~0.96), which are similar with those of upper continental crust.②According to trace element content and ratios (V/Cr, Ni/Co, U/Th Sr/Ba, Th/U Sr/Cu, Rb/Sr ratios and Ce, Eu anomaly) of the Yunmengshan and Baicaoping Formations, it is inferred that they are littoral and neritic deposit, and oxidation sedimentary environment, while the palaeoclimate experienced aridity-washy-aridity change.③The tectonic setting discrimination diagrams and the abundance of rare earth elements imply that the clastic rocks of the Yunmengshan and Baicaoping formations developed on passive continental margin.The island arc attribute of some points was inherited from the provenance protolith and influenced by the structure setting when the protolith was deposited.Combined with sedimentary and chronostratigraphic results, this series of passive continental margin littoral and neritic clastic deposits can serve as a record of North China Craton breakup from 1.8 to 1.6 Ga and a geological response to the initial breakup of the Columbia supercontinent.