论华北地区的均衡状态(一)--方法和局部补偿
ISOSTATIC STATUS IN NORTH CHINA (1)--METHOD AND LOCAL COMPENSATION
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摘要: 根据经典均衡的原理,本文重点分析了五种局部均衡补偿模式.在计算方法上利用频域三维重力场的理论公式,快速求得均衡校正值,据此计算了66个模型的均衡重力异常场,注意到对这许多不同参量的模型而言,它们的均衡异常场在形态与分布特征上基本一致,其中计入了地表和上下地壳密度差异分布的 Airy 模型具有最佳的补偿效果,它的均衡面在莫霍界面以下的上地幔中,标准深度50km.从整体上看,华北地台处于亚均衡状态,均衡异常的均值为1810-5m/s2.均衡重力异常的分布表现出明显的块体特征,正均衡异常区主要分布在东部胶辽地块和冀中平原北缘,在汾渭裂谷区存在负异常.模型对比表明,以莫霍界面作为均衡补偿面的模型是不可取的;Airy 模型比 Pratt 模型的补偿效果略好,这同地壳构造以层状为主而侧向变化有限的特征相符.有关复合补偿、均衡重力异常的基本特征和深部构造的关系等结果,将在文章的第二部分发表.
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关键词:
- 均衡重力异常;补偿;艾黎;普拉特;华北
Abstract: Follwing Airy and Pratt principles, five kinds of local compensation models are analysed with emphasis and a rapid 3-D gravity formula is utilized to calculate isostatic anomaly for sixty-six models with different parameters. It is noted that isostatic gravity maps appear nearly identical in their main patterns and features. The optimum compensation model in North China is one of modified Airy models in which the different density distribution in the surface, upper crust and lower crust are taken into account and the standard crustal thickness is 50 km. The position of complete compensation interface is located in the upper mantle. North China platform as a whole is under the sub-isostatic equilibrium status with isostatic anomaly of 1810-5 m/s2 on an average. The distribution of isostatic gravity anomaly shows an obvious blockwise pattern. Most positive anomaly areas occur over the eastern part, the Jiao-Liao block, Mt. Yan block and northern margin of Hebei-Shandong block, whereas negative area occurs in the Shanxi graben. Comparison of models indicates that the Moho discontinuity is not suitable to be taken as a compensation interface, and the compensation effects in Airy model are better than in Pratt model, which is consistent with the feature of dominantly layered structure with less lateral inhomogeneity in crust. Some results about composite compensation, the basic characteristics of isostatic gravity anomaly and deep structure will be published later in the second paper. -
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[8] Artyushkov, E. V., Rheological properties of the crust and upper mantle according to data on isostatic movements, J. Geophys. Rer., 76, 1376——1396, 1971.
[9] 顾功叙、曾融生、张忠撒,中国境内208处重力加速度测定之海陆均衡变差(一),地球物理学报,1, 101——139, 1949,
[10] 顾功叙、曾融生,中国境内208处重力加速度测点之海陆均衡变差(二),地球物理学报,2, 14——26, 1950,
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[12] 魏梦华、王启鸣、史志宏、殷秀华、刘占坡、张玉梅,中国大陆自由空气重力场的初步研究,地震地质,3,3, 47——60, 1981.
[13] 股秀华、史志宏、刘占坡、张玉梅,华北北部均衡重力异常的初步研究,地震地质,4,4, 27——34, 1982,
[14] 袁宝印、孙建中,华北新生代沉积与断块构造,华北断块区的形成与发展,221——229,科学出版社,1980,
[15] Parker, R. L., The rapid calculation of potential anomalies, Geophysics, 39, 447——455, 1973.
[16] 冯锐,中国地壳厚度及上地慢密度分布(三维重力反演结果),地震学报,7, 143—— 157, 1985,
[17] 冯锐,三维物性分布的位场计算,地球物理学报,29, 399——406, 1986,
[18] 冯锐、严惠芬、张若水,三维位场的快速反演方法及其程序设计,地质学报,60, 390——403, 1986.
[19] 冯锐、郑书真,对华北岩石圈构造的综合研究,科学通报,32,1987,
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