关键词: 晚泥盆世, 锆石UPb年龄, 地球化学, A型花岗岩, 花岗斑岩, 黑龙江多宝山地区

Abstract: The Duobaoshan area, situated within the contact zone between the Xing’an and Songnen blocks in the eastern part of Xing’anMongolia orogenic belt, holds significant importance in the study the tectonic evolution of NenjiangHeihe Ocean, which is the north branch of PaleoAsian Ocean. In this paper, we present a detailed investigation of petrology, geochronology and geochemistry of the granite porphyries exposed in the western Duobaoshan area with the aims to identify their geochronology and petrogenesis, and further to reveal the tectonicmagmatic evolution associated with the NenjiangHeihe Ocean. The investigated granite porphyries are flesh red, with multi porphyry structure and massive structure. Their phenocrysts predominantly comprise potassium feldspar, quartz and a small amount of plagioclase. The matrix is mainly composed of felsic minerals with microcrystalline structure and minor biotites. The LAICPMS UPb zircon age suggest the granite porphyry formed at Late Devonian (365.1 ± 2.6 Ma). Moreover, the granite porphyries are geochemically characterized by high SiO2 and K2O contents, along with low CaO, MgO and Al2O3 compositions, and high TFeO/MgO and Rb/Sr ratios. They are enriched in Rb, Th, Zr and Hf, and depleted in Sr, Ba, Eu, Ti, P, with swallowlike REE patterns and negative Eu anomalies, showing the characteristics of Atype granite. Distinguished from highly differentiated Itype and Stype granites, they display a high Zr/Hf ratio, Na2O, TFeO content and relatively low P2O5, Rb content. The low MgO, and Cr contents and Mg# values, together with their characteristic trace element ratios, indicated the predominant crustal source contribution. Based on the regional geology and the geochemical characteristics of the studied rocks, we concluded that the granite porphyry is an A1 subtype granite, which has the geochemical characteristics of both volcanic arc and intraplate granite. Furthermore, we infer that the granite porphyry should be formed in the local extensional environment during the northward subduction of NenjiangHeihe Ocean.

Key words:  , Late Devonian, zircon UPb age, geochemistry, Atype granite, granite porphyry, the Duobaoshan area, Heilongjiang Province