摘要
本文选取内蒙古二连浩特东北部本巴图地区,通过对石炭-二叠纪沉积典型地层的剖面测制、锆石U-Pb年代学及Hf同位素分析,查明其充填层序、沉积环境及物质来源,并进一步探讨了兴蒙造山带晚古生代伸展构造的演化过程。来自石炭-二叠纪地层的3个凝灰岩样品中最年轻峰值年龄分别为298Ma、302Ma、303Ma,表明其形成时代为303～298Ma,即晚石炭世-早二叠世,应归属格根敖包组。沉积环境研究揭示石炭-二叠纪沉积地层发育两个从前三角洲相到三角洲前缘相的旋回,其沉积速率估算结果与伸展构造背景下的裂谷盆地沉积速率相似。锆石Hf同位素特征分析表明,从约400Ma到约300Ma,其演化趋势具有新生地壳明显增多的特点,揭示从早中古生代年轻造山带形成到晚古生代伸展作用发生过程中的变化。结合区域地质研究,晚古生代北造山带的沉积演化和伸展作用过程可分为四个阶段:第一阶段为磨拉斯盆地形成,以盆地南缘泥鳅河组为代表;第二阶段为贺根山伸展带发育阶段,形成超基性-基性-酸性的岩浆组合;第三阶段为稳定的陆表海环境,以晚石炭世本巴图和阿木山组的碎屑岩-碳酸盐岩组合为代表;第四阶段是晚石炭世-早二叠世的第二次伸展,发育格根敖包组火山-沉积岩系组成的三角洲沉积,具有陆内裂谷盆地性质。
The extensi0nal tectonic regime of Xing＇an-Mongolia Orogenic Belt（ XMOB） take place in Late Paleozoic. In other words,XMOB transferred from Early Paleozoic subduction and collisional orogen to strongly extensional regime after the end of Early Paleozoic. This process formed the special tectonics regime,magmatism（ e. g.,bimodal igneous rocks,A-type granites） and sedimentary basins（ e. g.,Middle-Late Devonian molasses basin,Carboniferous continental and epeiric sea basin,Early-Middle Permian continental rift basin） in Central Inner Mongolia,NE China. In this study,sedimentary facies analysis,zircon U-Pb dating and Hf isotopes analysis were combined to indicate the sedimentary sequences,environment and provenance of the CarboniferousPermian sedimentary basin and further reveal the Late Paleozoic evolutionary history of the XMOB. Our new LA-MC-ICP-MS zircon UPb dating shows that the minimum ages of magmatic zircons from three tuff samples at the bottom of the basin were 298 Ma,302 Ma and303 Ma,respectively,implying that the Benbatu basin was formed during 303 - 298 Ma,i. e.,Late Carboniferous-Early Permian.According to the regional stratigraphic division,we suggest the formation should be a part of the Gegenaobao Formation. The estimated sedimentary rate is similar to that of the extensional rift basin. Additionally,zircon εHf（ t） and tDM2 of tuff samples in CarboniferousPermian sedimentary basin are ranging from 3. 06 - ＋ 14. 13,and 461 - 1486 Ma,respectively. These data suggest the origin from depleted mantle or juvenile crust. By contrast,the captured zircons,show lower εHf（ t） values（-4. 83 - ＋ 3. 63） and ancient tDM2（ 1490 - 2298 Ma）,implying the major contribution of relatively ancient materials in the source. In the south of basin,the detrital zircon εHf（ t） and tDM2 for the sandstone（ 404 - 462 Ma） in the Niqiuhe Formation are-4. 83 - ＋ 3. 63 and 1490 - 2298 Ma,respectively. They share the same Hf isotope characteristics with the coeval captured zircons in the above tuff samples,indicating the Carboniferous-Permian volcanic-sedimentary rocks in the basin were most likely originated on the Devonian basement（ i. e.,Niqiuhe Formation）. Furthermore,the increase of zircon εHf（ t） values with the ages ranging from - 400 Ma to 300 Ma,suggest the increasing involvement of juvenile crust in Late Paleozoic,which was probably caused by the progressively extensional process. Taken together with the previously regional researches,we can conclude that the continuous extension occurred in the XMOB during the Late Paleozoic,and the evolutionary history can be as least divided into four stages： 1） the formation of Niuqiuhe molasse formation; 2） the generation of Erenhot-Hegenshan basin along the northern part of the XMOB in the Carboniferous,formed a series of ultramafic-mafic and felsic igneous rocks; 3） the Late Carboniferous Erenhot-Hegenshan basin developed calstic and carbonate rocks in Benbatu and Amushan formations,which represented stable littoral and neritic marine environment; 4） the Late Carboniferous-Early Permian rift valley basin formed and deposed massive black mudstone-sandstonegravel stripe sandstone.
作者
张焱杰
徐备
田英杰
王志伟
ZHANG YanJie;XU Bei;TIAN YingJie;WANG ZhiWei(Key Laboratory of Regional Geology and Mineralization,Hebei GEO University,Shijiazhuang 050031,China;College of Resources,Hebei GEO University,Shijiazhuang 050031,China)
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2018年第10期3083-3100,共18页
Acta Petrologica Sinica
基金
科技部国家重点研发计划(2017YFC0601302)
国家自然科学基金项目(41672214)联合资助
关键词
火山沉积盆地
二连浩特东北部
伸展构造
兴蒙造山带
Volcanic-sedimentary basin
Northeastern Erenhot
Extensional setting
Xing＇an-Mongolia Orogenic Belt （XMOB）
