二连盆地基底特征及演化新认识

前人认为二连盆地是在海西期“宽对接、软碰撞”褶皱基底上发育的中、新生代盆地，其基底年代为海西期；针对蒙南地区的归属问题研究较少，对于该区是否属于二连盆地并不明确，仅认为蒙南地区（温都尔庙隆起）是二连盆地南部的隆起造山带，并未从基底特征、构造演化等方面分析蒙南地区与盆地的关系。为此，基于地质、地球物理资料，运用重磁电特征对比、层序地层旋回对比等方法分析了二连盆地基底特征、基底演化过程、构造演化差异性，得到以下认识： ①二连盆地基底演化经历加里东期洋盆发育（阶段Ⅰ）、海西期蒙南地区隆起（阶段Ⅱ）、海西期古亚洲洋兴—蒙海槽开始发育至最终闭合（阶段Ⅲ）、印支早期盆地统一基底形成（阶段Ⅳ）、晚印支—燕山期统一盆地发育阶段（阶段Ⅴ）、喜山期的开阔内陆盆地（阶段Ⅵ）等6个阶段，其中关键阶段为Ⅱ、Ⅴ及Ⅵ。②二连盆地基底具有过渡特征，盆地北部、中部和南部基底分别发育于早海西期、晚海西—印支期以及加里东期三个不同时期，具有不同特点。③二连盆地基底演化以联合基底和统一盆地形成过程为特征，蒙南地区经历了泥盆纪—二叠纪（海西期）、新生代以来（喜山期）两期隆起；晚三叠世—白垩纪（晚印支—燕山期）在统一基底隆起上形成统一盆地。④蒙南地区和二连盆地的基底特征和盆地演化过程具有相似性，说明在地史期间蒙南地区应属于二连盆地的一部分。

New understandings of the basement characteristics and evolution process of Erlian Basin

Formers thought Erlian Basin was a Mesozoic-Cenozoic basin developed on a fold basement by wide docking and soft collision during Hercynian period.But they did not specify whether Mengnan Area(namely,Ondor Sum Uplift) belongs to Erlian Basin and only regard it as uplift orogenic belt located in south of the Erlian Basin without analyzing their relationships through basement characteristics and tectonic evolutions.Based on geological and geophysical data,a research of the basement evolution process and tectonic evolution of Erlian Basin is carried out with gravity-magnetic-electric features and sequence stratigraphic cycle correlations.The following understandings are obtained:①The basement evolution of the Erlian Basin experienced six stages including oceanic basin development in Caledonian Period(Stage Ⅰ),Mengnan area uplifted during Hercynian Period(Stage Ⅱ),Paleo-Asian ocean-Xing-Meng trough initially developed to finally closed during Hercynian Period(Stage Ⅲ),unified basement formed during early Indosinian Period(Stage Ⅳ),unified basin development during late Indosinian to Yanshanian Period(Stage Ⅴ),and open inland basin development during Himalayan Period(Stage Ⅵ); among which,Ⅱ,Ⅴ,and Ⅵ are key stages; ②The basement of Erlian Basin is characterized by transitional feature,and its north,middle,and south parts were developed respectively in Early Hercynian,Late Hercynian to Indosinian,and Caledonian with distinct features; ③The basement evolution of the Erlian Basin was characterized by unified basement and unified basin,Mengnan area experienced two uplifting periods including Devonian-Permian(Hercynian) and Cenozoic(Himalayan),and formed unified basin during Late Triassic-Cretaceous(Late Indosinian to Yanshanian) on the unified basement uplift; ④The basement characteristics and basin evolution process of Mengnan area and Erlian Basin are similar,which indicates that Mengnan area is a part of Erlian Basin during geological historical period.