Three‐dimensional estimation of elastic thickness under the Louisville Ridge

Abstract

Abstract. A three-dimensional approach to estimating elastic thickness is presented which uses dense satellite altimetry and sparse ship bathymetry. This technique is applied to the Louisville Ridge system to study the tectonic history of the region. The inversion is performed as both a firstorder approximation and a nonlinear relationship between gravity and topography based on Parker's [1973] equation. While the higher-order effect on the gravity anomaly is nearly zero for most of the region, the magnitude is significant over the summits of the ridge. Nevertheless, the inclusion of the nonlinear terms has only a minor influence on the elastic thickness estimate within each region, lowering the value by -1-2 km compared with the linear result. The incorrect assumption of two dimensionality for circular features exhibits a marked effect on the gravitational anomaly, resulting in false sidelobe structure of nearly 20 mGal for large seamounts. Our elastic thickness estimates are compared with the contradictory values obtained in previous studies by Cazenave and Dominh [ 1984] and Watts et al. [1988]. We find an increasing elastic thickness along the chain from southeast to northwest, with a discontinuity along the Wishbone scarp. The jump in elastic thickness values northwest of the scarp appears to be an indication of an age discontinuity caused by an extinct spreading center north of the ridge.

Three-dimensional admittance analysis of lithospheric elastic thickness over the Louisville Ridge

“…T e is then recovered by minimizing the differences between the ship soundings and the predicted bathymetry. The results of Lyons et al (2000) tend to agree with those of Cazenave and Dominh (1984) with respect to trend, showing increasing values from southeast to northwest.…”

“…Most of the absolute differences are less than 10 km, with a mean of -1.6 km and a standard deviation of 4.5 km. Along the Louisville Ridge, T e of the lithosphere was estimated by Cazenave and Dominh (1984), Watts et al (1988), and Lyons et al (2000). For comparison, the MWAT method is used here to calculate T e of regions A-L of Lyons et al (2000).…”

“…According to Cazenave and Dominh (1984), T e increased from southeast to northwest, while Watts et al (1988) found the opposite trend. Lyons et al (2000) tried to reconcile these results and introduced a 3D ''bathymetry-predicting'' method to estimate T e . In this method, the bathymetry around a seamount is predicted using high-resolution gravity anomalies derived from Geosat altimetric data for different T e .…”

“…The effective elastic thickness of the lithosphere (T e ) is a fundamental parameter that is sensitive to the tectonic settings of a submarine feature. There have been few attempts at calculating the T e beneath features over the Louisville Ridge (Cazenave and Dominh 1984;Watts et al 1988;Lyons et al 2000)-probably because it has been surveyed by few ships, and high-accuracy depth and gravity data are sparse.…”

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“…Another important difference between the Louisville and HawaiianEmperor Seamount Trails may be the age of the underlying seafloor at the time of volcano formation. It has been assumed that all Louisville volcanoes generally erupted onto seafloor that was ~40-50 Ma (Lonsdale, 1988;Watts et al, 1988;Lyons et al, 2000). This assumption includes the older (northwestern) portion of the Louisville Seamount Trail that formed close to the Osbourn Trough paleospreading center, which ceased its activity between 115 and 121 Ma (Downey et al, 2007).…”