Geochemical Characteristics of Early Silurian Granite from Biaoshan Area in Beishan, Inner Mongolia and Their Tectonic Implications

1:50000 geological mapping (Regional geology and mineral resources survey project)indicate that the Early Silurian intrusion in Biaoshan area are dominated by granodiorite, adamellite and syenite granite from early to late in the order.This episode of intrusion is characterized by calc-alkalic rocks, which were interpreted as quasi aluminum rock with evidence of positive SiO₂-K₂O relationship.Rare earth chondrite standardized distribution of these three types of rocks are shown as europium negative anomaly (with δEu value of 0.60~1.06,0.44~0.81,0.12~0.39, respectively).Standardization of the primitive mantle spider diagram shows relatively enrichment of medium incompatible element (La, Ce, Sm, Hf, Zr)and strong incompatible element (Rb, Th, U), while they have relatively deficient of high field strength elements (Nb, Ta, P, Ti). Granodiorite, adamellite and syenite granite have yielded the zircon LA-ICP-MS ages of (444±12)Ma, (441.2±1.8)Ma and (441.1±3.3)Ma respectively, which represent Early Silurian emplacement.Combined with previous studies, the geochemical data suggests that these Early Silurian intrusions had emplaced in the island arc tectonic setting.Regionally, strong northward subduction has been occurred along the Hongliuhe-Yueyashan-Xichangjng area in the Early Silurian, leading to the emplacement of these intrusions, which formed the early Paleozoic magmatic arc.