The geochemical characteristics and tectonic significance of metasedimentary rocks in Sinian-Cambrian Xunwu rock group, southern Jiangxi Province

Metasedimentary rocks in Sinian-Cambrian Xunwu rock group of southern Jiangxi Province show obvious variation of SiO₂ values. Except for one sample with a relatively lower concentration, the average SiO₂ content is 63.01%. These rocks show comparatively high K₂O, Al₂O₃ and (TFeO+MgO) values and low Na₂O and CaO values. Compared with the concentrations of compatible trace elements, they are very close to values of Archaean Australian Shales (PASS), but their values are dramatically higher than values of the upper crust, and are consistent with the characteristics of high (TFeO+MgO) values, indicating that a certain amount of intermediate-basic components existed in the source region. Total REE concentrations are higher than those of the upper crust and PAAS. Nevertheless, , the chondrite-normalized REE patterns exhibit a slanting rightward shape with enriched LREE, flat HREE, obvious negative Eu anomalies and less obvious negative Ce anomalies, similar to features of the typical upper crust and PAAS. Based on the geochemical characteristics, the protolith should be terrigenous clastic rocks with intermediate maturity, and the provenance was mainly dominated by reconstructed felsic and granitic sediments from the upper crust, with partly contributed by certain amounts of intermediate-basic components. Immobile elements like high field-strength elements and rare earth elements reveal that the sedimentary environment was bathyal to abyssal and the tectonic background was the passive continental margin with rift systems. The results obtained by the authors shed some light on the tectonic attributes of southern China in Early Paleozoic from the perspective of sedimentary geochemistry.