Yan-Long Zhang

Lower Cretaceous alkali feldspar granites in the central part of the Great Xing’an Range, northeastern China: chronology, geochemistry and tectonic implications

The Mingshui–Jilasitai–Suolun area, located in the central part of the Great Xing’an Range, is characterized by large volumes of alkali feldspar granites. However, the formation time and tectonic setting of these rocks remains controversial owing to a lack of precise geochronological and detailed geochemical data. In this paper, we report new SIMS U–Pb zircon ages and mineralogical, petrographical and geochemical data for Lower Cretaceous alkali feldspar granites from the Mingshui–Jilasitai–Suolun area. The SIMS zircon dating results indicate that these granites formed at 133.6–135.9 Ma. The mineralogical, petrographical and geochemical data show that these granitic rocks belong to highly fractionated I-type granites. Combined with the regional geology data, we propose that the formation of the Lower Cretaceous alkali feldspar granitic rocks was related to an extension induced by delamination of the lithosphere that arose from subduction of the Palaeo-Pacific plate.

Age assignment and geological significance of the “Budate Group” in the Hailar Basin

Age and nature of the Budate Group in the Hailar Basin are of great significance in studying the evolution of the Hailar Basin and the Xing’an-Mongolian Orogenic Belt (XMOB). Zircon U-Pb ages of eight volcanic rocks from the Budate Group and two basement granites in the Hailar Basin were reported in this study. The dating results indicated that the formation of these volcanic rocks was consistent with the emplacement of Late Paleozoic basement granite in age (356–290 Ma), i.e., Early Carboniferous to Early Permian rather than Early Mesozoic. Combined with regional geology, it was concluded that the Budate Group is the component of the basement of the Hailar Basin, and these volcanic rocks were formed at an active continental margin, which is related to the closure of the Hegen Mountains suture zone. The captured Neoproterozoic zircons (814–873 Ma) were probably derived from the Neoproterozoic basement materials in the Ergun Block, implying the close genetic relationships between the Ergun Block (including the Hailar Basin) and the Siberian Block.