莫尔道嘎地区叠加褶皱特征及其构造意义——覆盖—半覆盖区的构造研究

Characteristics of superposed folds and its tectonic significance in the Moerdaoga district: structural analysis on the complexly deformed terrains with poor outcrop conditions

莫尔道嘎地区位于额尔古纳地块的中北部,属构造面貌出露不完整的褶皱叠加变形区。通过多种方法获取了点上的构造(褶皱)要素、信息资料,构建了褶皱构造的几何形态和几何学解释,开展了(褶皱)构造剖析和综合分析等研究工作。在浅变质的新元古代佳疙瘩组中厘定出3组褶皱构造。第一组(近东西向)褶皱(F1)为露头尺度的同斜紧闭剪切小b型褶皱;第二组(北北西向)褶皱(F2)成紧密线状纵弯褶皱,构成一系列区域上的复式向斜和复式背斜构造;第三组(北东东—北西西向)纵弯褶皱(F3)为中常—开阔褶皱。区域上,第三组褶皱(F3)大角度斜跨在第二组褶皱(F2)之上,形成几何学上类似Ramsy的两类叠加,表明区域构造背景已由前中生代的多块体的碰撞、拼贴环境转换为中新生代板内变形阶段。

The Moerdaoga study area is located in central - northern part of Eerguna block. It is fold - superposition deformation district with uncompletely tectonic outcrop due to thick cover. Based on the local structural data and information derived from multiple geological methods, the paper tries to build the completely geometry and geometric interpretation of folded structure. The integrated techniques of structural analyses support development of the multi - phases deformational history with at least three folding phases of deformation affecting the Neoproterozoic Jiageda formation as followings ： （ 1 ） Nearly EW - trending isoelinal type B minor folds （ F1 ） formed by shear folding ; （2） NNW - trending tight linear buckle folds （ F2）, formed the main structures of the study area characterized with the anticlinorium or syclinorium; （3） NEE -NWW trending middle open buckle folds （F3）. Regionally, the presence of the Ramsay＇ s Type 2 （Ramsay et al, 1987 ） interference patterns produced by the overprint of the NEE -NWW -trending folds （F3） on NNW - trending ones （F＇2） at a large angle. This may be relative to the transition of the regional tectonic environment from pre - Meso- zoic amalgamation of micro - continental blocks to Middle - Cenozoic intraplate deformation mechanism.