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北山地区园包山一带晚石炭世早期花岗岩地球化学特征及年代学研究
Geochemical characteristics and chronology of early Late Carboniferous granites in Yuanbaoshan area, Beishan region
投稿时间:2018-07-07  
中文关键词:北山北部  晚石炭世花岗岩  岛弧  埃达克岩
英文关键词:northern Beishan  granites of early Late Carboniferous  island arc  adakite
基金项目:内蒙古自治区地质勘查基金(NMKD2014-11)
作者单位
李杰 河北省区域地质调查院, 河北 廊坊 065000 
田颖 河北省区域地质调查院, 河北 廊坊 065000 
班长勇 河北省区域地质调查院, 河北 廊坊 065000 
冯翼鹏 河北省区域地质调查院, 河北 廊坊 065000 
陈圆圆 河北省区域地质调查院, 河北 廊坊 065000 
李金和 河北省区域地质调查院, 河北 廊坊 065000 
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中文摘要:
      园包山晚古生代花岗岩位于内蒙古额济纳旗园包山一带,其岩体特征对红石山蛇绿岩带属性及北山北带的构造演化的重建具有重要意义。通过LA-ICP-MS锆石U-Pb同位素测年,确定园包山复式岩基中花岗闪长岩、二长花岗岩、奥长花岗岩的年龄分别为317.1±3.1、314.8±2.7和313.7±2.3 Ma,均属晚石炭世。岩石地球化学分析表明,园包山花岗岩高硅(SiO2=67.77%~73.00%)、富钠(K2O/Na2O<1),A/CNK=0.95~1.13,属偏铝到弱过铝质,富集大离子亲石元素(Rb、Ba、Th、K),亏损高场强元素(Ta、Nb、P、Ti),具有中等强度的负铕异常(δEu=0.46~0.65),呈现出岛弧环境的岩石地球化学特征。其中奥长花岗岩与花岗闪长岩、二长花岗岩又有所不同,岩石样品富硅,具非常弱的负铕异常(δEu=0.81~0.99),高Sr/Y和La/Yb,在Sr/Y-Y图上落入埃达克岩区域。上述特征差异暗示两者具有不同的源区。综合区域地质资料来看,晚石炭世早期研究区南侧红石山洋向北俯冲启动了这次大规模构造岩浆活动,形成了具岛弧性质的园包山花岗岩复式岩基,其中具埃达克质特征的奥长花岗岩来源于俯冲的洋板块的部分熔融,暗示红石山洋可能属较为年轻的热洋壳。
英文摘要:
      The Yuanbaoshan Late Carboniferous granite is located in the Yuanbaoshan area, Ejin Banner, Inner Mongolia. Its rock mass characteristics are of great significance for the study of the properties of the Hongshishan ophiolite belt and the reconstruction of the tectonic evolution of the northern Beishan region. LA-ICP-MS zircon U-Pb isotopic dating shows that the ages of granodiorite, monzonitic granite, and trondhjemite in the Yuanbaoshan composite batholith are 317.1+3.1 Ma, 314.8+2.7 Ma and 313.7+2.3 Ma respectively, suggesting Late Carboniferous. The petrogeochemical analysis shows that the granites of the Yuanbaoshan composite batholith have high silicon (SiO2=67.77%~73.00%), and rich sodium (K2O/Na2O<1) with A/CNK being 0.95~1.13, belonging to partially aluminous to weakly peraluminous,with the enrichment of LILEs (Rb, Ba, Th, K), depletion of HFSEs (Ta, Nb, P, Ti) and medium strength negative europium anomaly (δEu=0.46~0.65), similar to the petrogeochemical characteristics of island arc environment. The trondhjemite is different from the granodiorite and monozonitic granite; it is rich in silicon, has very weak negative europium anomaly (δEu=0.81~0.99), high Sr/ Y and La/Yb ratios, and falls into the adakite area on the Sr/Y-Y diagram. These differences suggest that they have different source characteristics. According to the regional geological data, the subduction of the Hongshishan oceanic plate under the study area during the early Late Carboniferous initiated large-scale magmatic activity and formed the Yuanbaoshan granite composite batholith with island arc affinity. The plagioclase granite with adakite-like characteristics originated from partial melting of the subductional oceanic plate, implying that the Hongshishan Ocean might have had a relatively young hot oceanic crust during the early Late Carboniferous period.
李杰,田颖,班长勇,冯翼鹏,陈圆圆,李金和,2019,北山地区园包山一带晚石炭世早期花岗岩地球化学特征及年代学研究[J].岩石矿物学杂志,38(2):160~172.
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