内蒙古北部温都尔庙群北带沉积环境及构造意义

乌拉特中旗以北的中蒙边境地区和苏尼特左旗以南地区的温都尔庙群北带是可以互相对比的。它们由成分成熟度高的细碎屑夹钙质、泥质沉积物和特殊的硅铁质沉积组成,缺乏代表强水动力条件的沉积构造,因而代表封闭、补偿条件不佳及水动力条件很弱的古环境特征。对该群火山岩的研究表明它们属拉斑系列,构造环境图解显示其碱度相当于板内玄武岩的最低范围或介于岛弧与板内玄武岩之间。上述古环境特征、火山岩特征及已有的同位素年龄证据表明温都尔庙群北带可能是中-新元古代华北板块北部的火山型被动陆缘。

SEDIMENTARY ENVIRONMENT AND TECTONIC SIGNIFICANCE OF THE NORTH BELT OF THE ONDOR SUM GROUP IN INNER MONGOLIA

The Ondor Sum Group is characterized by ferrian metamorphic series and can be divided into the north and south belts by its geographic distribution in north Inner Mongolia.The south belt is exposed in Suniteyouqi and the north belt can be divided into the east and west segments.The east segment is located in the south of Sunitezuoqi and the west segment in the north of Wulatezhongqi.In this paper sedimentary environment and tectonic significance of the north belt are discussed on the basis of sedimentary compositions and intercalated basalt chemical analyses.The north belt of the Ondor Sum Group consists of sericite chloritequartz schists,with interbeded thin marbles,quartzites,ferrian quartzites,iron ore layers and basalts.No sedimentary structures that provide littoral facies or abyssal turbidite facies with a strong energy can be observed from the relict sedimentary sequences.These provide the evidence for argillaceous,calcareous and siliceous riched sedimentary environment,which indicates a half closed marginal sea with distal materials.Chemical analyses suggest that the intercalated basalts belong to tholeiite series and are characterized by a transitional type between within plate basalt and island basalt.These data indicate that there was a passive volcanic continental margin on the northern margin of the North China plate during the middlelate Proterozoic.