Emplacement age of the postorogenic A-type granites in Northwestern Lesser Xing’an Ranges, and its relationship to the eastward extension of Suolushan-Hegenshan-Zhalaite collisional suture zone

Abstract

A great amount of alkali-feldspar and alkaline granites have been found around Nenjiang, Northwest Lesser Xing’an Ranges, but their forming ages have been a controversial subject due to the lack of reliable geological and isotopic geochronological evidence. The zircon U-Pb isotopic dating results conducted in this note indicate that these granites emplaced at 260–290 Ma, coeval with the late stage of Late Paleozoic. Studies of mineralogy, petrology and geochemistry show that they are post-orogenic A-type granites, and consist of the northeastern extension of huge belt of Late Paleozoic A-type granite along North Xinjiang-Southeast Mongolia-Central Inner Mongolia. Therefore, we can determine that the Suolunshan-Hegenshan-Zhalaite collisional suture zone extends northeastward to Heihe with the collision age of Carboniferous.