内蒙古北山地区标山一带早志留世花岗岩地球化学特征及构造意义

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

通过内蒙古标山一带区域地质矿产调查,查明该区早志留世侵入岩由早到晚依次为花岗闪长岩、二长花岗岩和正长花岗岩。该期侵入体为钙碱性岩系,准铝质岩石,SiO_2、K_2O具正相关变化特征。三者球粒陨石标准化稀土配分曲线均具Eu负异常(δEu值分别为0.60～1.06,0.44～0.81,0.12～0.39)。原始地幔标准化蛛网图显示中等不相容元素La、Ce、Sm、Hf、Zr及强不相容元素Rb、Th、U相对富集,高场强元素Nb、Ta、P、Ti相对亏损。在花岗闪长岩、二长花岗岩、正长花岗岩中获得LA-ICP-MS锆石U-Pb同位素年龄值分别为(444±12)Ma、(441.2±1.8)Ma、(441.1±3.3)Ma,代表该期侵入体就位时代为早志留世。综合前人及本次项目研究成果可见,标山一带早志留世侵入岩就位于岛弧的构造环境。区域上早志留世古亚洲洋壳沿红柳河—月牙山—洗肠井一线向北强烈俯冲,导致本区早志留世深成岩侵位,形成石头井-化石山早古生代岩浆弧。

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- Kz O relationship. Rare earth chondrite standardized distribution of these three types of rocks are shown as europium negative anomaly （with ;Eu 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 respecttvety, wmcn rep; y 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 suhduction 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.