Late Carboniferous mafic to felsic intrusive rocks in the central Great Xing'an Range, NE China: petrogenesis and tectonic implications

The timing of the amalgamation of the Xing'an and Songliao-Xilinhot blocks in the eastern Central Asian Orogenic Belt has long been the subject of debate. To explore this question, we studied a suite of late Carboniferous mafic to felsic intrusive rocks in the central Great Xing'an Range, NE China. These rocks yielded late Carboniferous zircon U-Pb isotopic ages of 320-300 Ma. The felsic monzogranites and granodiorites are strongly peraluminous with high A/CNK ratios (>= 1.1), and they have signatures transitional between I- and S-type granites. Their geochemical characteristics suggest a magmatic source in a heterogeneous juvenile crust that included both clay-rich pelitic material and metabasalt. On the other hand, the intermediate biotite granodiorites have characteristics that suggest a dual magmatic source involving both mantle material and crustal contributions. The mafic gabbros were derived from the partial melting of mantle materials including both spinel and garnet lherzolite. The upwelling of the asthenospheric mantle contributed greatly to the formation of these magmas, with the upwelling as a result of the delamination of dense lithosphere and/or previously trapped mafic slabs. The petrology, geochemical signatures, field characteristics, and rock associations of the late Carboniferous mafic to felsic intrusive rocks imply that they formed in a post-collisional extensional tectonic setting that developed after the amalgamation of the Xing'an and Songliao-Xilinhot blocks and closure of the Nenjiang Ocean between them. Considering that the tectonic setting during the early Carboniferous was one of regional subduction, our data constrain the amalgamation of the Xing'an and Songliao-Xilinhot blocks and the closure of the Nenjiang Ocean to the early late Carboniferous.