Using GOCE satellite gravity data for the exploration of the African lithosphere
Using GOCE satellite gravity data for the exploration of the African lithosphere
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2011-08
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通讯作者：
A. Peyrefitte;M. Diament;G. Martelet;S. Bonvalot
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作者：
A. Peyrefitte;M. Diament;G. Martelet;S. Bonvalot
欧洲航天局 (ESA) 于 2009 年发射的 GOCE（重力场和稳态海洋环流探测器）卫星任务旨在以前所未有的细节（全球范围内为 1°x1°）绘制地球重力图。它提供了一类新的重力观测（梯度测量），可用于研究从区域到全球尺度的岩石圈结构和过程。非洲大陆的特点是古老的克拉通以及较新的造山带和大型盆地，这些盆地受到近期或实际的板内火山活动、裂谷或热点的影响。这种复杂的地质学证明了过去和正在进行的构造和地球动力学过程在岩石圈尺度上影响非洲板块。众所周知，这种模式可以提供多种密度对比，因此几十年来，从地面或空中勘测收集的重力数据被广泛用于研究非洲板块的地壳或岩石圈结构。我们在这里展示根据不久交付的 GOCE 数据集计算的第一幅重力图，并讨论它们在理解非洲岩石圈的主要结构模式和地球动力学过程中的用途。将前两个月 GOCE 数据推导出的模型与基于地面调查和卫星数据的 EGM2008 模型进行比较，发现非洲地区存在显着差异，这主要与地面数据分布的异构性有关。我们的目标是研究整个非洲板块的地壳重力特征，以便 1- 更好地区分地幔和地壳重力特征，2- 给地壳本身带来约束。为此，我们联合使用两个全球地震学模型：CRUST 2.0 和全球沉积物厚度数字图，实现了第一个 3D 正演模型，其中非洲地壳被离散为球棱柱。我们的模型由三个沉积地壳层和三个结晶地壳层组成，空间分辨率为 1°x1°。我们使用 Uieda 等人开发的基于球棱镜离散化的专用软件计算了模型的重力和张量分量效应。我们将这种重力效应减去了从第一个基于 GOCE 的自由空气异常得出的布格图。短波长残差证明了输入地壳地震模型的缺陷。长波长残差突出了地幔重力分量，反映了深层热/成分变化，例如非洲超羽流的影响。然后，我们将充分利用重力梯度的可用性，将其纳入反演过程中，以改善我们模型的地壳密度结构。
The GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite mission, launched by the European Space Agency (ESA) in 2009, aims to map the Earth's gravity with unprecedented detail (1°x1° at global scale). It provides a new class of gravity observations (gradiometric measurements) that can be used to investigate the lithospheric structures and processes from regional to global scales. The African continent is characterized by ancient cratons as well as more recent orogenic belts and large basins which, in place, are affected by recent to actual intraplate volcanism, rifting or hotspots. This complex geology attests for past and on-going tectonic and geodynamic processes which affect the African plate at the lithospheric scale. Such patterns are well known to provide a large variety of density contrasts, so gravity data gathered from ground or airborne surveys are extensively used since several decades to investigate the crustal or lithospheric structures of the African plate. We present here the first gravity maps computed from GOCE datasets shortly delivered and discuss their use for understanding the main structural patterns of the African lithosphere and the geodynamic processes. Comparison of the model deduced from the 2 first months GOCE data with EGM2008 model based on ground surveys and satellite data shows significant differences over Africa mainly related to the heterogeneous ground data distribution. Our aim is to investigate the crustal gravity signature of the entire African plate in order to 1- better discriminate between mantle and crustal gravity signatures and 2- bring constraints on the crust itself. For this purpose, we realized a first 3D forward model in which the African crust is discretized in spherical prisms, by jointly using two global seismological models: CRUST 2.0 and the global digital map of sediment thickness. Our model consists of three sedimentary and three crystalline crust layers and has a spatial resolution of 1°x1°. We computed the gravity and tensor component effects of our model using a dedicated software based on a discretization into spherical prisms developed by Uieda et al. We substracted this gravity effect to a Bouguer map that we derived from the first GOCE-based free air anomalies. Short wavelength residuals attest for shortcomings in the input crustal seismological model. Long wavelength residuals highlight mantellic gravity components which reflect deep thermal/compositional variations, such as the effect of the African Superplume. Then, we will take full advantage of the availability of the gravity gradients by incorporating them in the inversion process to improve the crustal density structure of our model.