马尼希基海底高原重力均衡及其构造意义研究  

Gravity Isostasy and the Tectonics of Manihiki Plateau

作　　者：胡敏章[1,2] 李建成[2] 金涛勇[2] 李辉[1] 

机构地区：[1]中国地震局地震研究所地震大地测量重点实验室,湖北武汉430071 [2]武汉大学地球空间环境与大地测量教育部重点实验室,湖北武汉430079

出　　处：《武汉大学学报（信息科学版）》2014年第11期1357-1362,共6页Geomatics and Information Science of Wuhan University

基　　金：中国地震局地震研究所重点所长基金资助项目(IS201326125);国家测绘地理信息局测绘基础研究基金资助项目(13-01-01);国家自然科学基金资助项目(41204019;41304003);国家重点基础研究发展计划资助项目(2013CB733302)~~

摘　　要：采用三维导纳分析技术,联合海底地形和重力异常数据,对马尼希基海底高原重力均衡状况进行了分析研究,并结合地震学等研究成果,分析其构造意义。马尼希基海底高原海底地形与重力异常相干性在长波部分（大于100km）相对较小,说明高原地壳底部存在低密度异常,并且,根据Airy均衡分析,这种低密度异常并非完全由洋壳对海底地形的均衡调整引起,推测高原地壳底部存在由岩浆＂板垫作用＂（crustal underplating）形成的低密度异常体,即＂底部载荷＂。马尼希基海底高原短波海底地形符合Airy均衡,据此分析获得高原地区洋壳厚度为22.7km,与地震研究结果一致。岩石圈挠曲均衡分析表明,马尼希基海底高原岩石圈有效弹性厚度为2.5~5.5km,较优拟合值为3.5km,可能意味着高原形成时岩石圈年龄较小。根据顾及底部载荷的挠曲均衡模型进行分析,定量计算了底部载荷规模,约为地形载荷的30%,其体积约为9.3×105km3,平均深度为18km,是整个高原洋壳的重要组成部分,表明洋壳底部板垫作用在马尼希基海底高原形成和演化过程中产生过重要影响。Using 3D admittance analysis technology, the state of gravity isostasy on Manihiki Plateau was studied with its gravity anomalies and bathymetry. The tectonics of the plateau was analyzed based on the isostatic results and previous research including seismic studies. The relatively low coherence observed between gravity and bathymetry at long wavelength C〉100km） may indicate the existence of a low density anomaly beneath the plateau crust. According to the results from airy isostatic analysis, this anomaly is not completely caused by as isostatic adjustment of the oceanic crust to the plateau topography, there must be mass loading beneath the plateau crust causing by an underplating of magma. At short wavelengths, the topography conforms to the airy model. The crust thickness of the plateau is 22.7km, consistent with the seismic research result. A lithospheric flexural isostatic analysis showed that the effective elastic thickness of lithosphere around the Manihiki plateau is 2.5- 5.5 km, with an optimal value of 3.5 kin. This small elastic thickness may means the plateau is em- placed on a young lithosphere. A flexural model takes into account the mass loading beneath the plateau and the scale of the bottom load was estimated quantitatively. It demonstrates that the mean depth of the bottom load is 18km, the magnitude is about 50% of the topography, and the volume is about 9.3× 10^5 km^3. Thus the bottom load is an important part of the plateau crust, while the underplating of bottom load plays an important role in the evolution of the plateau.

关 键 词：马尼希基海底高原 重力均衡 Airy均衡模型 挠曲均衡模型 底部载荷 

分 类 号：P312.3[天文地球—固体地球物理学]