川滇地区地壳磁异常特征与地壳构造关系研究

Based on the higher-degree geomagnetic model constructed from marine, ground, aero，and satellite survey data, the characters of the spatial distribution of the crustal anomaly in Sichuan-Yunnan area and its decay with altitude are investigated. The regional and local anomaly fields are acquired by two-dimensional wavelets decomposition. The spatial power spectra of the anomalies is given, and the contributions of different wavelength bands to the total anomalies are discussed. The Curie isothermal surface within the lithosphere is calculated from the aforementioned anomalies and then compared with geophysical fields such as the seismic-wave velocity anomaly, the gravity anomaly, and the lithospheric thermal structure. Relationship between the magnetic basement variation and the crustal layer structure is revealed. Correlation between the anomaly and the geological structure is studied, including the correspondence between the transitional zones from strong to weak anomalies and the faults, the anomaly features of the orogenic belt, the basin and the fracture zone, as well as the physical relation between the Honghe Fault and the stripped anomaly there. The result of our research proposal provides a quantitative basis for study of geological and lithospheric structures, for exploration of underground resources, and for prevention of earthquake disaster. It also has profound scientific implication for understanding the continental geodynamic process, the continent-to-continent collision, and the geological evolution in this region.

根据海、陆、空、天磁测资料建立的高阶地磁场模型，研究川滇地区地壳磁异常的空间分布和高度衰减特征。对磁异常进行二维小波分解，得到区域异常场和局地异常场。给出磁异常的空间能谱，探讨不同波长成分对总体磁异常的贡献。由上述磁异常计算岩石圈居里等温面，并与地震波速度异常、重力异常和岩石圈热结构等地球物理场相比较，揭示磁性基底起伏与地壳层状结构的联系。研究磁异常与地质构造的关系，其中包括磁异常强弱过渡带与断裂带的对应关系，造山带、盆地和破碎带的磁异常特点，红河断裂带与该区条带状磁异常的物理联系。本项目的研究结果可以为该区域地质构造和岩石圈结构研究、地下资源探测、地震灾害研究等提供地壳磁异常分布的定量依据，对认识该地区的大陆动力学过程、陆-陆碰撞和地质演化研究有重要科学意义。

根据海、陆、空、天磁测资料建立的高阶地磁场模型，研究川滇地区地壳磁异常的空间分布和随高度衰减的特征。对磁异常进行二维小波分解，得到区域异常场和局地异常场。由上述磁异常计算岩石圈居里等温面，并与地震波速度异常、重力异常和岩石圈热结构等地球物理场相比较，揭示磁性基底起伏与地壳层状结构的联系。研究结果表明构造稳定的四川盆地分布着强正磁异常；龙门山地区分布着较强的负磁异常带，川西北、滇西造山带为负磁异常或弱磁异常；滇中地块磁异常为团状和带状分布，正负异常交错出现，磁异常衰减快，异常源较浅。沿金沙江—红河断裂分布有清晰的正负磁异常成条带，并一直向东南延伸至越南北部。龙门山断裂带、丽江—小金河断裂带、红河断裂带是地壳磁场强弱或正负异常的过渡带。滇中地块东部磁异常以康定-奕良-水城断裂和弥勒-师宗-水城断裂为界。磁异常与地壳密度、地震波速度异常有对应关系。地震波速度高、地壳密度大的地区磁异常为正，反之，磁异常为负或弱磁异常。川滇地区居里面分布在20—34km之间，隆起和凹陷区域变化分明。沿龙门山断裂带、小江断裂带、丽江-小金江断裂带附近的居里面相对较浅，隆起区为带状分布，与深大断裂带构造走向一致。川滇地区强地震主要发生在居里面隆起区域。川东地块、若尔盖地块、滇南地块等大型地块内部居里面相对较深，凹陷区域为成片分布。居里面深度与大地热流值密切相关。腾冲、丽江、大理、昆明附近的大地热流值较高，居里面相对较浅。本项目的研究结果可以为该区域地质构造和岩石圈结构研究、地下资源探测、地震灾害研究等提供地壳磁异常分布的定量依据，对认识该地区的大陆动力学过程、陆-陆碰撞和地质演化研究有重要科学意义。