内蒙古早二叠世构造古地理的再造  

Early Permian tectono-palaeogeographic reconstruction of Inner Mongolia,China

作　　者：邵济安[1] 唐克东[2] 何国琦[1] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室、地球与空间科学学院,北京100871 [2]沈阳地质矿产研究所,沈阳110034

出　　处：《岩石学报》2014年第7期1858-1866,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41172196)资助

摘　　要：针对近年来关于内蒙古中部早二叠世古亚洲洋存在和向南北两侧大陆俯冲的观点,本文通过构造古地理图的编制,结合早二叠世沉积岩相、古地理、生物组合、陆源碎屑以及烃源岩的讨论,认为中亚陆块和华北克拉通之间晚古生代存在的是陆壳基底之上发育的陆表海和裂陷槽,而不是大开大合的大洋。我们的研究揭示了该区的演化过程。早二叠世早期伴有强烈火山喷发的沉积作用受到三条近东西向分布的同沉积裂陷槽的控制,由北向南,其滨-浅海相的沉积-火山岩厚度分别>8000m;>5000m和2900m,显示基底为不稳定的裂陷槽。沉积作用受到深断层控制的观点得到本区深部地球物理探测资料的佐证。早二叠世早期沉积岩以粗碎屑岩为主,其中成熟度低的硬砂岩、长石砂岩分布广泛。此外,从陆源碎屑的组分和来源可见,蚀源区具有新生陆壳的组成,近源沉积物具有快速堆积的特征。早二叠世晚期沉积岩为夹有灰岩透镜体的炭质粉砂岩、板岩。由于海相暗色泥岩有机质丰度的提高,形成分布于前三角洲,浅海,半深海的烃源岩(R0值=1.01%~3.67%)。上述沉积组合反映了陆壳成熟度不断提高,构造活动性减小,陆表海逐渐萎缩的特征。本区早二叠世的古生物以腕足类、珊瑚、、苔藓类为主,这一生物组合形成于滨-浅海环境,其中珊瑚大多生活在低潮线以下温暖清澈的水域——几米至50米的滨-浅海区。植物化石及碎片的存在反映海陆交互相的环境。早二叠世晚期本区生物已经混生,主要以北极区生物为主,以Spiriferella为代表的腕足动物群到处可见,但也混有暖水型的分子,如Richtofenia,Enteletes等。生物混生现象暗示早二叠世之前板块已经拼合,不存在深海洋盆。根据毛登地区哲斯组放射虫和菊石、螺、双壳类及植物化石共生的事实,作者认为放射虫可以生活在不同深度的水体中,不能In contrast of the recently promoted view of point that there was a Paleo-Asian Ocean plate subducting towards the continents on its north and south sides in the Early Permian, the present authors prefer a different understanding. Through compilation of a tectono-palaeogeographic map of the concerned area based on all the facts about the sedimentary petrography, palaeogeography, biologic association, detrital materials of terrigenous origin, and hydrocarbon source rock in the Early Permian, it seems to the authors that what existed between the Central Asian massif and the North China Craton was a Late Paleozoic epicontinental sea and rift instead of a large-scale ocean experiencing spreading and closure. Our studies reveal the actual evolution of the concerned area in the Early Permian. In the early stage, the sedimentary process accompanying strong eruption of basic-acidic volcanic rocks is controlled by three syn-sedimentary rifts with near EW strike, with the thicknesses of sedimentary rocks of the littoral-shallow marine facies and volcanic rocks being 〉 8000m, 〉 5000m, and 2900m separately from north to south. The view point of sedimentation being controlled by deep faults is supported by the deep geophysical data. The sedimental rocks of the early stage are mainly consisted of coarse elastic rocks in which the greywackes and arkoses with lower maturity are distributed widely. Besides, the denudation areas are composed of neogenic continental crusts and the proximal sediments are characterized by quick-accumulation, as seen from compositions and origins of the terrigenous detrital materials. In the later stage, the sedimentary rocks appear as grey blocks of carbonaceous siltstone and slates interlaced with limestone lenses, in which the dark marine mudstones with increased organic abundance form hydrocarbon source rocks （R0 = 1.01% -3.67% ）in prodeltas, shallow seas, and bathyal regions. The resulted sedimentary association reflect processes in which maturity of the continental ernst become increased

关 键 词：早二叠世 构造古地理 陆表海 裂陷槽 古亚洲洋 

分 类 号：P531[天文地球—古生物学与地层学] P534.46[天文地球—地质学]