Basement structures over Rio Grande Rise from gravity inversion

Abstract

The basement depth in the Rio Grande Rise (RGR), South Atlantic, is estimated from combining gravity data obtained from satellite altimetry, marine surveys, bathymetry, sediment thickness and crustal thickness information. We formulate a crustal model of the region by inverse gravity modeling. The effect of the sediment layer is evaluated using the global sediment thickness model of National Oceanic and Atmospheric Administration (NOAA) and fitting the sediment compaction model to observed density values from Deep Sea Drilling Project (DSDP) reports. The Global Relief Model ETOPO1 and constraining data from seismic interpretation on crustal thickness are integrated in the inversion process. The modeled Moho depth values vary between 6 and 27 km over the area, being thicker under the RGR and also in the direction of São Paulo Plateau. The inversion for the gravity-equivalent basement topography is applied to gravity residual data, which is free from the gravity effect of sediments and from the gravity effect of the estimated Moho interface. We find several short-wavelengths structures not present in the bathymetry data. Our model shows a rift crossing the entire Rio Grande Rise deeper than previously presented in literature, with depths up to 5 km in the East Rio Grande Rise (ERGR) and deeper in the West Rio Grande Rise (WRGR), reaching 6.4 km. An interesting NS structure that goes from 34 S and extends through de São Paulo Ridge may be related to the South Atlantic Opening and could reveal an extinct spreading center.

Moho depth and equivalent elastic thickness of the lithosphere over the Vema Channel: A new evidence of an aborted ridge

“…The modeling of the Te is made by a best fit of the flexure Moho with an independent Moho. For this paper, we use the model obtained by Constantino et al (2017) and remapped for the study area ( Fig. 3).…”

“…3. Moho from Gravity inversion (Constantino et al, 2017), superposed on the basement topography. RGR e Rio Grande Rise; Seamounts and Guyots (yellow with red contours); The São Paulo Ridge (SPR) and the Vema Aborted Ridge (VAR) are also represented.…”

“…MacLeod et al (2017) compiled largescale extinct spreading centers spreads around the world and included the Vema Channel as a possible aborted ridge, although, they suggest that this information should be target for future surveys were additional data must be used to reinforce this hypothesis. Constantino et al (2017), from a combined analysis of geophysical data, estimated the basement depth for the Rio Grande Rise and interpreted a possible extinct spreading center, which we will call in this paper as the Vema Aborted Ridge (VAR) ( Fig. 2) and differs from the morphological structure named Vema Channel.…”

“…Bringing new evidences to support the Vema Channel as an oceanic extinct spreading center (Bassetto et al, 2000;P erez-Díaz and Eagles, 2014;Constantino et al, 2017;MacLeod et al, 2017), would lead us for a new understanding on the tectonic evolution of the South Atlantic, as well as improving models such as age and spreading taxes of the oceanic crust. A key issue in the understanding of the structure of the extinct ridge is the determination of the spatial variations of the flexural rigidity or equivalent elastic thickness, as it brings implications for how we describe the tectonic processes of a specific area (P erez-Gussiny e et al, 2004; Kalnins and Watts, 2009).…”

“…This work is an extension of Constantino et al (2017) and therefore, we use part of their results during our procedure: the gravity Moho enters as input data for the flexural analysis and the basement depth is used for discussion of the achieved results. We investigate the Vema Aborted Ridge in terms of rigidity of the crust.…”