Zircon U-Pb ages, geochemical characteristics and tectonic implications of the Early Paleozoic granites in Huolongmen area, Heilongjiang Province

Abstract：Huolongmen area in Heilongjiang Province is tectonically located between the Xing'an block and Songnen block along eastern Xingmeng oregenic belt. Early Paleozoic granites comprising monzodiorite and quartz monzodiorite are distributed in this area. The zircon SHRIMP U-Pb ages of two samples from monzodiorite are （440.6±5.8）Ma and （471.3±8.7）Ma, respectively, indicating that the monzodiorite was generated in Middle-Late Ordovician. Major element analyses show high Na, Al, Mg and Ca content and medium-high K content. Trace element studies demonstrate the enrichment of K, Ba, Rb and depletion of Nb, Ta, P, Ti. The samples are enriched in LREE and depleted in HREE with pronounced Eu anomalies, suggesting a high degree of fractionation. In the R1-R2 structural setting discrimination diagram and Rb-Yb+Nb versus Rb-Yb+Ta discrimination diagram, most early Paleozoic granites fall in the post-orogenic zone and the volcanic arc granite zone, respectively, suggesting that the Xing'an block probably shifted northward, and then experienced collage, collision and suturing with Erguena block during Late Paleozoic.