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    西秦岭造山带东段航磁特征及断裂构造格架

    Aeromagnetic characteristics and fracture structure framework of the eastern part of the western Qinling orogen

    • 摘要: 本文基于最新高精度1:5万航磁资料,详细分析了西秦岭造山带东段航磁特征和地质成因,辅以重力资料,新推断或修正了断裂平面位置,探讨了断裂控矿作用和若干典型断裂的地质意义。研究表明,古生界泥盆系、石炭系、二叠系、中生界三叠系碳酸盐岩-沉积碎屑岩是形成平稳负磁背景的主要原因;广泛发育的各类侵入岩,是形成复杂变化、形态各异的叠加异常的主要原因。NWW-EW向、NNE-NE向以及NW向深、大断裂共同构成了全区"南北分带,东西分块"的基本构造格架。NWW-EW向深、大断裂是最早形成的主干断裂,航磁上以不同面貌磁场分界线或醒目的磁场梯度带为特征,属华北、扬子两大板块在新元古代-三叠纪分别沿商丹、勉略缝合带南北向俯冲碰撞的产物,构成了本区一级构造单元的分界线,尤其对泥盆系多金属成矿起决定性控制作用;NNE-NE向深、大断裂应是秦岭强烈陆内造山阶段(晚三叠世-新生代)垂向加积增生作用的产物,对NWW-EW向、NW向断裂具有明显的切割、牵引或阻挡作用,航磁上以连续性较好的线性梯度带或磁场扭转变异带为特征,是区内次级构造单元的界限,对深部矿源物质的运移亦起到一定的疏导作用。

       

      Abstract: According to the latest high-precision 1:50000 aeromagnetic data, the authors analyzed the aeromagnetic characteristics and geological origin of the eastern section of the western Qinling orogenic belt in detail based on gravity data, inferred newly and corrected the fracture plane position, and discussed the geological significance of ore-controlling role of fractures and some typical faults. The research shows that the main factor of forming gentle negative magnetic background seems to be Paleozoic Devonian, Carboniferous, Permian, and Mesozoic Triassic carbonate rocks-sedimentary clastic rocks, whereas all kinds of widespread intrusive rocks are the main factor for complex changes and different patterns of superimposed anomaly. The whole area's basic structural framework is formed by NWW-EW trending, NNE-NE trending and NW trending deep and major faults. The deep NWW-EW trending fault was the earliest formed main fault; its aeromagnetic features seem to be the boundaries of different magnetic fields or striking magnetic gradient belts, resulting from the NS-trending subduction and collision of North China and Yangtze plate in Neoproterozoic-Triassic along Shangdan, Mianxian, Lueyang suture zone and forming a boundary of the primary tectonic units in this region. In particular, it played a decisive role in controlling polymetallic mineralization in Devonian. The NNENE trending deep and major faults might have been the product of strong intracontinental orogenic stage of Qinling Mountain in Late Triassic -Cenozoic by the vertical accretion hyperplasia action and exerted obvious cutting, traction or blocking effects on the NWW-EW and NW faults, with the continuous linear aeromagnetic gradient characterized by good torsional or magnetic field change. They served as the limit of secondary tectonic unit in the region, and played a guiding role in the migration of deep ore source materials.

       

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