用压缩质面法反演重力资料以估算地壳构造

本文用压缩质面来近似二维地质体。先由地面上测得的重力数据用矩阵方法反演此压缩质面各单元的面密度,然后从面密度与体密度差的关系求得各二维质体单元的厚度,进而得到各单元的近似地壳厚度。经正演校验和反复调整结果,使计算的重力异常值与实际测量值之残差小到满足要求,从而得到较准确的地壳底部界面。 由上地幔,玄武岩层和花岗岩层的密度差异及已算出的地壳厚度,从重力异常中分解出莫霍界面和康腊界面起伏所分别引起的重力异常。将后者同样用反演地壳厚度的压缩质面法进行计算,得到康腊界面。 文中以三种假想的地壳模型和一个实测剖面为例来检验本方法,并用其他确定地壳界面方法所得到的结果相比较,表明本文提出的压缩质面法结果较好。

INVERSION OF GRAVITY DATA BY USE OF A METHOD OF“COMPRESSED MASS PLANE" TO ESTIMATE CRUSTAL STRUCTURE

This paper presents a method called the "Compressed Mass Plane" to approximate, a two-dimensional geological body. At first, the data of a gravity data is inversed, using matrix analysis to get the surface density of each element of the compressed mass plane. Then, from the relation between surface density and mass density of each element, the thickness of each two-dimensinal element can be calculated and the approximate thickness of the crust tentatively obtained. Further improvements of the estimation of the crustal thickness can be made by direct gravity computation of the crustal model thus obtained and repeated adjustments of the results in order to minimize the difference between computed and observed gravity anomalies. In that way, it may be possible to get the better depths of the lower boundary of the crust.Based on the assumed values of contrast between the "Basaltic", the "Granitic" layers and the Upper Mantle and also the above calculated crustal thickness, it is again possible to calculate the gravity anomalies coming from the undulations of the Mohorovicic and (Conrad interfaces respectively. By the same way, the inversion of the gravity anomaly of the Conrad interface, a comparatively correct position of this interface can be obtained.To test this method of gravity inversion, three hypothetic crustal models and an observed gravity profile are introduced here as examples. In comparing with other methods of determining crustal interfaces, the results of the present method of compressed mass plane seem to be better.