Subduction between the Jiamusi and Songliao blocks: Geochronological and geochemical constraints from granitoids within the Zhangguangcailing orogen, northeastern China

Abstract

Bulk-rock major and trace element, Sr-Nd isotopic, and zircon U-Pb-Hf isotopic data are reported for Jurassic igneous rocks from a north-south traverse through the Zhangguangcailing orogen, which formed by the subduction of an ocean and final collision between the Jiamusi and Songliao blocks in northeastern China. These results provide new insights into tectonic processes involving the subduction and collision to form the Zhangguangcailing orogen and final amalgamation of the Jiamusi and Songliao blocks. Our new results, together with data from the literature, indicate that the Jurassic granitoid rocks in the Zhangguangcailing orogen were emplaced in the period from ca. 191 to 163 Ma, with a magmatic flare-up ca. 180 Ma accompanied by mafic magmatism. These granitoid rocks are metaluminous and I-type in composition, and enriched in K, Rb, Th, and U, and depleted in Ba, Nb, Ta, Sr, P, and Ti, with constant initial 87Sr/86Sr (0.704338-0.705349), and positive εNd(t) (+1.6 to +3.1) and zircon εHf(t) (+0.83 to +10.51) values. These geochemical features indicate that the Jurassic I-type granitoid rocks were probably generated as a consequence of variable degrees of interaction between continental crust and mantle-derived melts, which resulted from the subduction of oceanic lithosphere (Heilongjiang ocean), and led to an active continental margin during Early to Middle Jurassic time.