内蒙古中部晚石炭世—早二叠世古地磁新数据及其地质意义

对采自内蒙古苏尼特左旗白音乌拉乡晚石炭世—早二叠世宝力高庙组和敖汉旗安庆沟乡晚石炭世酒局子组的凝灰岩和凝灰质砂岩开展了古地磁学研究。宝力高庙组和酒局子组样品退磁特征表明,高温剩磁分量均以赤铁矿为主要载磁矿物,可能携带了岩石形成时期的特征剩磁分量。层面校正后2个组平均特征剩磁分量分别为:D=159.3°,I=-33.1°,α95=8.7°;D=328.8°,I=31.3°,α95=5.7°。这反映了内蒙古中部晚石炭世—早二叠世位于北纬17°—18°N。将所获得的古地磁结果与已发表的相邻地区古地磁数据进行比较,并结合古生物、古气候等地质数据,推测晚石炭世—早二叠世时内蒙古中部与华北地块关系密切,距离较近,而远离西伯利亚地块,内蒙古中部晚石炭世—早二叠世时可能是华北地块的组成部分。

New Upper Carboniferous-Lower Permian Paleomagnetic Results from the Central Inner Mongolia and Their Geological Implications

Tuff and tuffaceous sandstone for the paleomagnetic studywere collected from the Upper Carboni-ferous-Early Permian Baoligaomiao Formation and the Upper Carboni-ferous Jiujuzi Formation located at the Bai-yinwula Country,Sonid Zuoqi,and Anqinggou Country,Aohan Qi,respectively.The demagnetization characteristics of the Baoligaomiao and Jiujuzi Formation samples indicated that the remanent magnetization components at high temperature was predominantly carried by hematite as the main magnetic minerals,which probably carried the characteristic remanence component during the periods of rock formation.The mean remanent magnetization after the bedding correction is D=159.3°,I=-33.1°,α95 =8.7°,for the Upper Carboniferous-Lower Permian Baoligaomiao Formation,and D=328.8°,I=31.3°,α95=5.7°,for the Upper Carboniferous Jiujuzi Formation,which indicated that the central Inner Mongolia located at a paleolatitude position of 17°-18°N during the Upper Carboniferous-Early Permian.Comparing the two new paleomagnetic data with previous published paleomagnetic results from adjacent regions,combined with the paleobiological and paleoclimatic data,a conclusion was inferred that the central Inner Mongolia was closely related with or even was a part of North China block,that is the central Inner Mongolia was near to the North China block and far from Siberian block during Late Carboniferous and Early Permian.