Reappraisal of effective elastic thickness in the south-west Indian Ocean, and its possible implications

Deshraj Trivedi Deshraj Trivedi,Debashish Sengupta Debashish Sengupta,Rajesh R Nair Rajesh R Nair,Tanmay K Maji Tanmay K Maji

doi:10.4401/ag-5171

Deshraj Trivedi Deshraj Trivedi, Debashish Sengupta Debashish Sengupta + Show 2 more

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https://doi.org/10.4401/ag-5171

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Abstract

<p>The bathymetry of the south-west Indian Ocean is dominated by three mid-oceanic ridge systems: the Chagos–Laccadives Ridge, the Central Indian Ridge, and the Mascarene Plateau. Although there have been a number of geophysical and geological investigations over the region, the genesis of these morphological features is still contradictory. Most of the estimations of effective elastic thickness in this region have been carried out in the spectral domain, either by transfer function analysis or by free-air admittance analysis. As these investigations were along some one-dimensional profiles or discrete blocks, spatial variation of the effective elastic thickness was not achieved. Here, we reappraise the estimation of effective elastic thickness in the south-west Indian Ocean by performing the computation in the spatial domain using flexure inversion. During this process, we also estimate the Moho depth throughout the region by two independent processes: gravity inversion, and flexural inversion. The Te values (effective elastic thickness) are estimated in the spatial domain, which match well with the results in the spectral domain obtained with the free-air admittance method. In addition, there is spatial variation of the Te values over the area analyzed. Our estimated Te values are low (1-6 km) along the Chagos-Laccadives ridge, implying its proximity to a spreading ridge at the time of creation. The Te values along the Mascarene Plateau show spatial variation with a seafloor age from north (Te, ca. 4 km) to south (Te, ca. 20 km). These findings substantiate earlier data and suggest that Réunion was created due to intraplate volcanism.</p>

Highlights

The south-west part of the Indian Ocean is an amalgam of complex geological features that include, for example, oceanic ridges, seamounts, rifted margins, and hotspots
Along the Mascarene Plateau we obtained a variation of the Te values from south (Réunion, 20 km) to north (Seychelles, 4 km)
The elastic thickness values obtained in our analysis show considerable variations along the Chagos–Laccadives Ridge (CLR) and the Mascarene Plateau (Figure 4d)

Summary

Introduction

The south-west part of the Indian Ocean is an amalgam of complex geological features that include, for example, oceanic ridges, seamounts, rifted margins, and hotspots. Among these different tectonic elements, three active midoceanic ridge systems dominate the topography: the Chagos–Laccadives Ridge (CLR), the Central Indian Ridge (CIR), and the Mascarene Plateau (Figure 1). The CIR is a part of the global Mid-Oceanic Ridge system that extends southwards from the Carlsberg Ridge at 2 ̊N, to the Rodriguez Triple Junction at 25 ̊S, in the Indian Ocean The third of these prominent aseismic ridges, the Mascarene Plateau, is one of the most prominent shallow submarine plateaus in the south-west Indian Ocean. The Mascarene Plateau lies to the north and north-east of Madagascar, starting from the Seychelles in the north, and extending through the Saya de Malha Bank and Nazareth Bank down to Réunion in the south

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