Provenance and tectonic setting of the Gudongjing Group in Beishan Orogen

The clastic sedimentary rocks in an accretionary orogenic belt may preserve key evidence for understanding the architecture of orogenic belts and even the crustal evolution. The clastic sedimentary rocks of the Gudongjing Group in the middle of the Beishan Orogen is considered to be a set of stable sedimentary caprocks of the Precambrian, and it is also an important basis for the existence of micro-continents in the Beishan Orogen. In this paper, statistics on clastic particle grain sizes and heavy mineral compositions, the whole rock geochemical composition analyses, detrital zircon U-Pb dating, and Hf isotope testing are carried out on the clastic rocks of the Gudongjing Group to reveal their prevenances and tectonic settings. The clastic components of the rocks are mainly composed of quartz, feldspar and rock fragments which are mainly siliceous rock fragments together with a certain amount of volcanic ones. Heavy mineral analysis reveals they mainly consist of limonite, zircon, ilmenite and spinet, followed by hornblende, tourmaline and pyroxene, which indicates the contribution of the accretionary complex materials and ophiolites to their provenance. The whole rock major element compositions are characterized by high contents of silicon, aluminum and alkali, while low in manganese. The contents of the inert elements, such as REE, Cr, Co, Sc, Th, etc., show characteristics of a felsic source area. The youngest detrital zircon age obtained in this study is 443. 9 +/- 13 Ma, indicating that the maximum deposition age of the Gudongjing Group is Late Ordovician. The age of detrital zircons is highly concentrated around 470Ma, and the corresponding zircon epsilon(Hf) (t) values are mostly positive, indicating a large number of new crustal materials have developed in their provenance area. Based on the comparative analysis, it is suggested that these clastic rocks are possiblely formed in a slope basin on the top of an accretionary wedge. The results support the point that the Beishan orogenic belt is the product of a continuous accretion of a Paleozoic orogenic belt.