最新的岩石圈磁场模型及中国磁异常特征的几点认识

介绍了最新的地球磁场模型,包括MF5,NGDC-720和WDMAM。模型MF5是由CHAMP卫星测量得来,它的球谐展开阶次为n=16~100,对应的波长段为400~2500km。模型NGDC-720和WDMAM是综合了卫星磁测、航空磁测、海洋磁测与地面磁测得到数据经过处理后得来,它们有不同的球谐阶次和分辨率。NGDC-720模型是由美国国家地球物理数据中心(The National Geophysical Data Center,NGDC)提供,它的球谐阶次从16阶到720阶,对应于由2500km到56km的波带。M.Purucker博士公布的WDMAM参考模型1是一张分辨率为3′,高度位于WGS84上方5km的磁异常图,它向上延拓后的结果与MF5中的岩石圈磁异常保持一致。作者根据国际上公布的CHAMP、NGDC-720与WDMAM Candidate1的最新数据,绘制了中国及毗邻地区的磁异常图,对中国及毗邻地区明显的大地构造,如造山带,盆地等地区的磁异常特征进行了描述和分析,塔里木、四川、松辽等盆地地区及华北平原部分地区模型中均表现为正异常,西藏高原、天山造山带等地区表现为负异常,而一些深大断裂表现为磁异常高梯度带。通过四川盆地和西藏高原地区三个模型的相互对比,我们发现模型阶次越高,它所反映的磁性体(尤其是浅部地质体)的情况越丰富,不同的是四川盆地的结果随着阶次的增高就越接近航磁结果,而西藏高原随着阶次的增高却和航磁结果差别越来越大。

The latest lithospheric magnetic models and some understanding of magnetic anomalies in China.

The paper introduces the latest improvements in mapping the magnetic field, including model MF5, NGDC-720 and WDMAM. MF5 is obtained by satellite CHAMP with spherical harmonic order n=16-100 and correspondent wavelength segment is 400-2500 km. NGDC-720 and WDMAM, combined with satellite, airborne, shipboard and ground-based magnetic data, have different spherical harmonic order and resolution. The former one is provided by the National Geophysical Data Center (NGDC) whose spherical harmonic order n=16-720 and correspondent wavelength segment is 56-2500 km. And WDMAM Candidate 1 is publicized by Dr. M. Purucker with 3-minute resolution and nominal altitude 5 km above the reference ellipsoid, which is consistent with the observations of the lithospheric magnetic field as represented by MF5 after being upward continued. The author draws the magnetic field in China and adjacent areas using the above data. The magnetic fields in Tarim, Sichuan and Songliao basins are positive, while in Tibet and Tianshan orogen are negative, and some giant great fractures are high gradient zones. Besides, some obvious magnetic anomalies such as orogenic belts and basins in China are compared and analyzed, especially the Sichuan basin and Tibet plateau. It could be figured out that the higher the order of the model the more magnetic information (especially the shallow layers) is contained, while the results from the Sichuan basin have more common with the airborne magnetic results and those from Tibet plateau are on the contrary.