内蒙古杜拉尔桥地区奥陶系多宝山组地球化学特征及其地质意义

Geochemical characteristics and geological significance of the Ordovician Duobaoshan Formation located in Dula'er Bridge in Inner Mongolia

本文对内蒙古塔源-头道桥拼合带西南段南东侧杜拉尔桥地区分布的奥陶系多宝山组进行了系统的岩石学、地球化学研究。该组主要岩性为变质安山岩、变质玄武安山岩、变质砂岩、板岩、千枚岩、结晶灰岩、变质沉凝灰岩等。其与上覆奥陶纪裸河组呈整合接触,局部与泥盆纪泥鳅河组呈断层接触,并被中生代火山岩不整合覆盖。其安山岩类岩石的地球化学特征表现出Al2O3>CaO+K2O+Na2O,属于过铝型;并具钙碱性岛弧火山岩性质。其微量元素特征、稀土元素特征均表现出源区有来自消减带物质的加入的钙碱系列火山岩特征。其源区为流体交代的楔形地幔,并受到了地壳物质的混染性质。通过变质玄武安山岩LA-ICP-MS U-Pb定年,确定其岩浆活动时代为463±5.9 Ma。通过结合区域大地构造背景资料分析认为该组火山岩属于古亚洲洋板块向北西俯冲形成的扎兰屯-多宝山成熟岛弧带的产物。

A systematic study of petrology and geochemistry of Ordovician Duobaoshan Formation,which located in the southeast side of the Dula’er Bridge,southwest section of split-belt of the Tayuan-Toudao bridge in Inner Mongolia is carried out.Its lithology mainly contains metamorphic andesite,metamorphic basaltic andesite,metamorphic sandstone,slate,phyllite,crystalline limestone and metamorphic tuff.It is in conformable with overlying strata of Ordovician Luohe Formation,in partial contact with the Devonian loach formation,and is covered by the unconformity of Mesozoic volcanic rocks.The geochemistry characteristics of its andesite rocks show that it is Peraluminous,on account of Al2O3>CaO+K2O+Na2O.And it has the character of calc-alkaline island arc volcanic rock.The Microelement and the Rare earth element show their characteristics that there are calc-alkali series rock features added from subduction zone material.Its source area is the wedged mantle of fluid metasomatism and is affected by the mixed properties of crustal.Through the dating of metamorphic basaltic LA-ICP-MS U-Pb of the age of magmatic activity,it is defined as463±5.9Ma.Accoeding to the analysis of regional geotectonic background data,the volcanic rock of this group is the product of mature island arc,which was formed when the ancient Asian oceanic plate subducted to the northwest,named Zhalantun-Duobaoshan.