Geochemical Characteristics And Age Assignment Of Paleozoic Granites In Northern Baihuapai Farm Of Da Xing'an Moutain

According to the comagmatic evolution theory and the contact relation in the field, the Paleozoic granites from the northern Baihuapai are divided into four mapping units, which include, from the old to young, the fine-medium grain granodiorite, fine-medium grain monzogranite, fine-medium grain syenogranite, fine-medium grain alkali feldspar granite. The geochemical characteristics indicate that these granites can be assigned to slightly alkaline peraluminous and aluminous supersaturation high potassium calc-alkaline I-type granites. LA-ICP-MS zircon U-Pb age data demonstrate that the granites from Huma arc-basin system of the northern Baihuapai were emplaced in the late Carboniferous-early Permian, represented by 294.4±1.5 Ma monzogranite, 311±1 Ma and 302±1 Ma syenogranites, and 289.7±2.2 Ma alkali feldspar granite. Combined with previous results and the bedrock record compiling, the granodiorites have the same REE pattern as these dating samples, which were emplaced during the late Carboniferous-early Permian. Geochemically, all the granitic rock samples show similar REE patterns that are enriched in LREE and depleted in HREE, with a negative Eu anomaly. The primitive mantle-normalized trace element spider diagrams indicate that these granites are characterized by obvious negative Nb anomaly, similar to that of the island arc calc-alkaline magma, and overall elements show a downward trend. In the five group discrimination diagrams for tectonic environment of Maniarr, most granite samples fall into the POG field. In the Nb-Y and Rb-(Yb+Ta) diagrams, the granite samples mainly plot in the volcanic arc granites–syn-collision granites and volcanic arc granites fields, respectively, which suggest that these intrusive rocks belong to the post-orogenic granites, and developed in an active continental margin setting as a result of the collision between the Paleo-Asian oceanic fragments and Huma back-arc basin during the late Carboniferous-early Permian. Meanwhile, petrochemical and geochemical characteristics analysis shown that along with the large-scale orogenic movement formed an intermediate-acid rock assemblage in the Great Xing'an Range during the late Carboniferous-early Permian, which probably related to the gradually shrink and closed of the Paleo-Asian Ocean. Due to the subduction of the Paleo-Asian oceanic plate beneath the Erguna and Songnen blocks, with the deepening subduction of the oceanic crust cause delamination of subducted slab and mantle upwelling.