| Abstract:The Xing'an-Mongolian Orogenic Belt(XMOB) is an important part of the Central Asian Orogenic Belt(CAOB), and the Early Paleozoic tectonic evolution is one of the research hot spots in recent years, especially the collocation relationship and the basement properties between the Erguna Massif and the Xing'an Arc Basin had been debated for a long time. In this paper, we take the shallow metamorphic clastic rocks of the Jixianggou Formation, which are exposed in the Alihe area, the eastern section of the XMOB, as the research object. the provenance and tectonic significance of the Jixianggou Formation are discussed by using the methods of petrology, geochemistry and LA-ICP-MS zircon U-Pb isotope chronology. The research results show that the weighted average of the age from the youngest zircons of Hb170241, a metamorphosed conglomerate-bearing quartz sandstone sample taken from the vicinity of the Xilingti, is 406±4 Ma, with a main peak age of 462 Ma, and, the youngest single-grained zircon age of Hb170253, a metamorphosed sandstone sample taken from the vicinity of the Gaxian ophiolite-tectonic mélange zone, is 427±4 Ma, with a main peak age of 466 Ma. It is comparable to the main peak age of detrital zircons from the Jixianggou Formation in the region.The SiO2 content of 2 metamorphic feldspar quartz conglomeratic sandstone samples is 88.43%～90.39%, the SiO2/Al2O3 values are 14.24～16.86. While 7 samples of metamorphic feldspar quartz sandstone have lower SiO2 contents(63.83%～69.68%), with an average of 66.95%, and SiO2/Al2O3 values are 3.99～5.26. Trace elements show that the shallow metamorphic clastic rocks of Jixianggou Formation are depleted in high field strength elements(Nb, Ta), relatively enriched of large ion lithophile elements(Rb, Ba) and high field strength elements(Th, U).According to the comprehensive analysis, the sedimentary age of the Jixianggou Formation in the Alihe area is not earlier than 406 Ma, but the time span may be from the Cambrian to the Early Devonian. The metamorphic clastic rocks of the Jixianggou Formation mainly formed from the feldspathic rock source area with low maturity and complex composition in the Erguna block, there may be material contribution from the island arc of Duobaoshan. The formation process of the Jixianggou Formation recorded the sedimentary evolution of the Huma-Hailar back-arc basin. |
