Spatial-temporal distribution and geochemistry of highly evolved Mesozoic granites in Great Xing’an Range, NE China: Discriminant criteria and geological significance

Highly evolved granite is an important sign of the mature continent crust and closely associated with deposits of rare metals. In this work, the authors undertake systematically zircon U-Pb ages and whole rock elemental data for highly evolved granitic intrusions from the Great Xing’an Range (GXR), NE China, to elucidate their discriminant criteria, spatial-temporal distribution, differentiation and geodynamic mechanism. Geochemical data of these highly evolved granites suggest that high w(SiO₂) (>70%) and differentiation index (DI>88) could be quantified indicators, while strong Eu depletion, high TE_1,3, low ΣREE and low Zr/Hf, Nb/Ta, K/Rb could only be qualitative indicators. Zircon U-Pb ages suggest that the highly evolved granites in the GXR were mainly formed in Late Mesozoic, which can be divided into two major stages: Late Jurassic–early Early Cretaceous (162–136 Ma, peak at 138 Ma), and late Early Cretaceous (136–106 Ma, peak at 126 Ma). The highly evolved granites are mainly distributed in the central-southern GXR, and display a weakly trend of getting younger from northwest to southeast, meanwhile indicating the metallogenic potential of rare metals within the central GXR. The spatial-temporal distribution, combined with regional geological data, indicates the highly evolved Mesozoic granites in the GXR were emplaced in an extensional environment, of which the Late Jurassic–early Early Cretaceous extension was related to the closure of the Mongol–Okhotsk Ocean and roll-back of the Paleo-Pacific Plate, while the late Early Cretaceous extension was mainly related to the roll-back of the Paleo-Pacific Plate.