Abstract
AbstractGeophysical data acquisition in oceanic domains is challenging, implying measurements with low and/or nonhomogeneous spatial resolution. The evolution of satellite gravimetry and altimetry techniques allows testing 3‐D density models of the lithosphere, taking advantage of the high spatial resolution and homogeneous coverage of satellites. However, it is not trivial to discretise the source of the gravity field at different depths. Here, we propose a new method for inferring tectonic boundaries at the crustal level. As a novelty, instead of modeling the gravity anomalies and assuming a flat Earth approximation, we model the vertical gravity gradients (VGG) in spherical coordinates, which are especially sensitive to density contrasts in the upper layers of the Earth. To validate the methodology, the complex oceanic domain of the Caribbean region is studied, which includes different crustal domains with a tectonic history since Late Jurassic time. After defining a lithospheric starting model constrained by up‐to‐date geophysical data sets, we tested several a‐priory density distributions and selected the model with the minimum misfits with respect to the VGG calculated from the EIGEN‐6C4 data set. Additionally, the density of the crystalline crust was inferred by inverting the VGG field. Our methodology enabled us not only to refine, confirm, and/or propose tectonic boundaries in the study area but also to identify a new anomalous buoyant body, located in the South Lesser Antilles subduction zone, and high‐density bodies along the Greater, Lesser, and Leeward Antilles forearcs.
Highlights
The oceanic lithosphere, which includes the upper mantle, the crystalline crust and overlying sediments, is one of the least known features on outer Earth
The main goal of this study is to explore the additional information that satellite derived vertical gravity gradients (VGG) provide about the structure of the oceanic crust in the Caribbean domain, considering that the usefulness of these gradients is not widely recognized, and that they are especially sensitive to density contrast in the upper layers of the Earth
The lithospheric starting model included the thicknesses of four layers, namely from the uppermost to the lowermost: (1) seawater, derived as the difference between sea level and the General Bathymetric Chart of the Oceans (GEBCO; Weatherall et al, 2015); (2) sediments, published in the NOAA Total Sediment Thickness data set (Whittaker et al, 2013); (3) crustal thickness, computed as the difference between the top of the crystalline crust and Moho depth from the GEMMA model (Reguzzoni & Sampietro, 2015); and (4) the mantle, which was subdivided into eight layers using the SL2013sv S‐wave velocity model (Schaeffer & Lebedev, 2013), from the Moho down to 200‐km depth
Summary
The oceanic lithosphere, which includes the upper mantle, the crystalline crust and overlying sediments, is one of the least known features on outer Earth. Combined data sets of satellite gravity, altimetry, and terrestrial measurements make it possible to develop and test 3‐D lithospheric models with homogeneous coverage and high spatial resolution (Götze & Pail, 2018), which depends on the limitations of the gravity data source: terrestrial measurements over continents and altimetry over the oceans. These lithospheric models, need to be tested against independent data sources to restrict the multiple options of densities, sizes, shapes and depths of bodies, which can reproduce similar gravity signals (Lowrie, 2007; Maystrenko et al, 2013)
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