华北克拉通岩石圈三维密度结构

显生宙以来华北克拉通岩石圈遭到破坏,这一现象的科学问题已受到世界地学家广泛关注.本文首先将地震层析成像反演得到的P波速度扰动转化为密度扰动,以此作为初始密度模型,然后利用布格重力异常反演得到了华北克拉通岩石圈高分辨三维密度结构.为了避开大型稀疏矩阵求逆计算,提高计算效率,我们将代数重构技术用于密度反演解算.反演结果表明:华北克拉通岩石圈密度在横向和纵向上均存在明显的不均匀性,密度分布形态与地表构造格局有很好的相关性;研究区地壳整体表现为低密度异常,地壳以下岩石圈部分则以高密度异常为主;鄂尔多斯块体地壳范围内以低密度异常为主,80~120 km深度上为呈南北两端集中分布的高密度异常,并分别与秦岭造山带和阴山造山带的高密度异常分布相连,这暗示了鄂尔多斯块体可能受到了来自其南北两端造山带深部动力学过程的影响;80~120 km深度上,华北克拉通东部地区呈现出显著的南北向非均匀的高密度异常,这表明遭到破坏后该地区上地幔物质分布具有强烈的南北向非均匀性.

Density structure of the lithosphere beneath North China Craton

Geoscientists all over the world paid a broad attention to the lithosphere of North China Craton(NCC),which was destructed since phanerozoic.A three dimensional P-wave velocity model obtained from seismic tomography was used to construct an initial 3D density model.Then,we got high resolution three dimensional density distributions of the lithosphere in NCC by gravity inversion using bouguer gravity anomaly.In order to improve the inversion speed,Algebraic Reconstruction Technique(ART) was applied for it can avoid the large and sparse matrix inversion of observation equations by using row iterative technique.The results indicate as follows: density distributions of lithosphere beneath North China Craton are inhomogeneous both in horizontal direction and vertical direction.And the density distribution underground is coherent with surfical tectonic.In NCC crust the density anomaly is low,while it is strongly high at 80～120 km depth.The Ordos block crust exhibit a low density distribution,and high density anomaly with big amplitude exists at 80～120 km.The high density distribution is conjoint with the high density anomalies of Qinling and Yinshan orogen in the south and north,respectively.That may indicate that Ordos block underwent the deep dynamic process from orogen in the south and north.High density anomaly is visible beneath the mid Taihang Mountain Orogen and eastern basin region at 80～120 km depth.At the same depth,remarkable high density anomalies exist beneath eastern of NCC with strong lateral heterogeneous in NS direction.It indicates that the upper mantles are inhomogeneous in NS direction beneath this region.