云南地区地壳磁异常与地质构造

根据美国地球物理数据中心的地磁场模型(NGDC-720),研究云南地区地壳磁异常的空间变化,包括磁异常及其梯度的分布、磁异常随高度的衰减、不同波长成分对总体磁异常的贡献.比较磁异常与重力异常、大地热流、地震活动等地球物理信息的异同特征,探讨地壳磁异常与地质构造的关系.研究结果表明:丽江—小金河、红河断裂带以西的三江、滇西造山带的异常较弱,菱形地块的异常相对较强.研究区域的地壳磁异常主要是弱磁性基底背景下叠加的浅源磁性体产生.卫星磁异常显示滇中坳陷区具有清晰的偶极场特征.沿红河断裂带分布的正负磁异常带与断裂构造走向一致.围限菱形地块的丽江—小金河断裂、红河断裂、康定—奕良—水城断裂和弥勒—师宗—水城断裂带是磁异常的强弱过渡带.强烈地震发生的地点、大地热流值高的地区,地壳磁异常为负值或相对较弱.

Crustal magnetic anomalies and geological structure in the Yunnan region

Based on the geomagnetic field model (NGDC-720) established by the U.S. National Geophysical Data Center, the spatial variations of crustal magnetic anomalies in the Yunnan region were studied, including the distribution of magnetic anomalies and their gradients, attenuation of magnetic anomalies with altitude, and the contributions of components with different wavelengths to overall magnetic anomalies. The magnetic anomalies were compared with other geophysical data such as gravity anomalies, terrestrial heat flow, and seismic activities to reveal similarities and differences and relationships between crustal magnetic anomalies and geological structure. The research results show that the magnetic anomalies are relatively weak in the Sanjiang (Three Rivers) and western Yunnan orogenic belts west of the Lijiang-Xiaojinhe, and Red River fault zones, and relatively strong in the rhombic block. The crustal magnetic anomalies in the study region were mainly generated by the shallow magnetic bodies superposed on the background of weak magnetism basement. The satellite magnetic anomalies show that the central Yunnan depression area has clear dipole field characteristics. The positive and negative magnetic anomaly zones distributed along the Red River fault zonet have consistent strikes with that of the faults. The Lijiang-Xiaojinhe fault, the Red River fault, the Kangding-Yiliang-Shuicheng fault and the Mile-Shizong-Shuicheng fault zones surrounding the rhombic block are transition belts between strong and weak magnetic anomalies. The places with active seismicity and the areas with high terrestrial heat flow values have negative or relatively weak crustal magnetic anomalies.