| Abstract:The Qianshao Forest Farm in the Upper Heilongjiang Basin is located on the northern margin of the Erguna micro-block in the eastern part of the Xingmeng orogenic belt. It is separated from the Siberia ancient land by the Mongolia-Okhotsk suture zone in the north. To the east, the Tayuan-Xiguitu fault is adjacent to the Xing'an block. In this paper, a systematic study of zircon chronology, major and trace elements and isotopic geochemistry of biotite monzogranites from Qianshao Forest Farm in the Upper Heilongjiang Basin. This provides a theoretical basis for exploring the collision mechanism between the Erguna micro-block and its adjacent blocks in the Early Paleozoic. The crystallization age of biotite monzogranite in the study area was 458.4± 2.4Ma (MSWD=0.022) by using LA-ICP-MS zircon U-Pb isotope measurement. The formation age of the rock mass is determined to be the Early Paleozoic and the Middle-Late Ordovician. The zircon Hf isotope ?Hf(t) values range from -4.64 to 1.84. Most of the zircons are under the chondrite evolution line, and the two-stage model ages (tDM2) range from 715 to 1126Ma. Rock mass geochemistry shows that the rock is rich in silicon, aluminum, alkali and so on. The rare earth partition curve shows a right-sloping characteristic of relative enrichment of light rare earth (LREE) and relative depletion of heavy rare earth (HREE). And the rocks are relatively enriched in large ion lithophile elements Rb, K and high field strength elements Th, U, Zr, Hf, relatively depleted in large ion lithophile elements Ba, Sr and high field strength elements Nb, Ta, P, Ti. The identification map of petrogenetic types shows that the biotite monzogranite in Qianshao Forest Farm has the characteristics of A-type granite. The characteristics of rock Hf isotope and trace elements show that the magma originates from the melting of the ancient crust in the Meso-Neoproterozoic, and there are a few mantle-derived materials and the melting of newly formed crustal materials. The elemental characteristics suggest that the rocks were formed in the extensional tectonic setting after the collision between the Erguna massif and Siberia. Combined with previous studies on the formation background of Early Paleozoic granites in the Erguna Block, it is believed that the formation mechanisms of Early Paleozoic granites in the northern and northeastern margins of the Erguna Block are different. The former was formed under the background of the collision and splicing of the Erguna block with the ancient Siberia and Mongolia-Tuva blocks. The latter is mainly formed under the background of collision and extension of Erguna and Xing'an blocks. |
