The Geochronological And Geochemical Research Of Granites In Sandaowanzi, Heilongjiang Province

Heilongjiang province, Heihe city, Sandaowanzi country is known for its typical low-sulfidation gold-telluride-bearing epithermal deposit. However, the study of igneous rocks developed in this region is rare to see. This paper exert a detail research to Paleozoic-Mesozoic granites in this region by the means of petrography, geochenmical data, zircon U-Pb ages and Hf isotopes analysis. The dating outcome shows that 13 samples can be divided into 3 period: late Devonian, early Jurassic and early Cretaceous, respectively. All the samples are calc-alkaline metaluminous to aluminous. Sandaowanzi samples all belong to I-type granites, except three late Devonian granites(SDQ1402, SDQ1403, SDQ1404) show high fractional feature with fractional crystallization of feldspar, plagioclase, zircon, and sphene. In addition, two late Devonian granites(SDQ1402, SDQ1407) show the affinity of adakitic rocks with high Sr contents, low Y and Yb contents and high Sr/Y, La/Yb ratio. The adakites are considered as the product of partial melting of thicken crust in garnet-amphibole phase. The εHf(t) of late Devonian granites are 5.5-12.8 with the depleted mantle age of 554-1018 Ma. The εHf(t) of early Jurassic granites are 5.2-7.0 with the depleted mantle age of 554-1018 Ma. The εHf(t) of early Cretaceous granites are 4.8-8.8 with the depleted mantle age of 616-875 Ma, all these sample show the young material feature of magma sources, which is consistent with early study. About the tectonic model, this paper suggest that late Devonian granites are formed in the late period of oceanic crust subduction before the collision between Xingan terrane and Songliao terrane, the early Jurassic granites are formed during the early stage of Paleo-Pacific subduction, while the early Cretaceous granites are formed under the background of plate roleback. From early Jurassic to early Cretaceous, the east part of Heilongjiang province experience the transformation between compression setting of oceanic plate subduction and stretch background of palte roleback and delimination.