Gravity Study of the Mekelle IntraCONtinental Sag (ICONS) Basin, Northern Ethiopia.

Abstract:

The Mekelle Basin in Northern Ethiopia contains ~2 km thick mixed carbonate-siliciclastic sediments thought to be deposited in an interior rift developed in response to continental fragmentation and dispersal during late Paleozoic-Mesozoic. Recent reconnaissance studies in and around the basin found geomorphic and sedimentologic characteristics similar to those of IntraCONtinental Sag basins (ICONS). We used satellite and ground gravity data to study the Mekelle basin in order to examine the possibility that it has subsurface structures characteristic of the ICONS as in the case of its surface features. Using 2D power spectrum analysis of the satellite gravity data, we estimated depth to the Moho. We further upward continued the gravity field to various heights to extract gravity signatures at the corresponding depths. Tilt derivative maps conducted on an upward continued data outlined the major structural grains. Upward continued gravity data shows circular to elliptical anomaly that is characteristics of many ICONS. We also used the ground gravity data to develop two-dimensional (2D) forward models. GOCE and WGM2012 gravity data derived Moho depths indicate about 36-42km crustal thickness at the western margins of the basin. However, towards the center and eastern margin of the basin our Moho depth estimates significantly differs from those of passive seismic studies. This shows a significant influence from the adjacent Afar depression where crustal thickness estimates of less than 20 km have been reported. Even though the Mekelle ICONS may have been formed due to mechanisms similar to those of ICONS, our study shows the basin to be significantly modified due to later tectonic processes.