A late-Carboniferous to early early-Permian subduction–accretion complex in Daqing pasture, southeastern Inner Mongolia: Evidence of northward subduction beneath the Siberian paleoplate southern margin

Abstract

A subduction–accretion complex is identified from previously defined late-Carboniferous and early-Permian strata in Daqing pasture, southern Xiwuqi, Inner Mongolia. The subduction–accretion complex is composed of a matrix of siltstone and exotic blocks of bioclastic limestone, pillow basalt, foliated basalt, chert and asbestos. The pillow basalt possesses the geochemical characteristics of mid-ocean ridge basalt (N-MORB), whereas the foliated basalt displays the geochemical characteristics of island arc basalt (IAB), indicating that these basalts are of different origins. U–Pb (zircon) dating indicates that the foliated basalt formed in the late-Carboniferous (314.5 to 318.4Ma) and the bioclastic limestone formed in the early early-Permian. Combined with regional geological data, the subduction–accretion complex and coeval calc-alkaline granitic belt to the north constitute the essential elements of the late-Carboniferous to early early-Permian subduction zone on the southern margin of the Siberian paleoplate. The zircon εHf(t) values of the foliated basalt are positive (+14.4 to +23.9), suggesting that this basalt originated directly from depleted mantle. The temporal–spatial distribution of the subduction–accretion complex and ophiolite belts in southeastern Inner Mongolia indicates that there was significant lateral crustal growth on the southern margin of the Siberian paleoplate in the late Paleozoic.