APPLICATION OF GRAVITY DATA IN DETERMINATION OF THE CRUSTAL THICKNESS AND STABILITY OF PARTS OF SOUTHERNNIGERIA

Abstract

This study focuses on the application of gravity data in determination of the distance between the earth surface and moho (crustal thickness) and stability of parts of southern Nigeria. Empirical relations, Spectral analysis and 2-D gravity modelling techniques were utilised on the bouguer gravity data covering the study area. Three empirical relations relating bouguer gravity with crustal thickness were used to calculate the crustal thicknesses within the study area, the depth ranges to the major density interfaces (basement surface, Conrad and crustal thickness) were determined from the spectral analysis of the bouguer anomalies as the bouguer gravity map was divided into thirty (30) sections. The bouguer gravity anomalies were used with the available geological and geophysical information to create two-dimensional (2-D) gravity models of the earth's crut along three profiles trending in NE, SE and SW directions to obtain a correlated crustal thickness for the study area. The obtain results from these 2-D crustal models show's that the upper and lower part of the profiles has a crustal thickness of 28 km to 39 km, bouguer anomaly of the study area varies from 30 mGal to 0 mGal, 40mGal to 0 mGal and 40 mGal to 20 mGal with the three approach has an average crustal thickness ranges from 30 km to 37 km, 30.2 km to 35.6 km, 28 km to 39 km respectively. There is a good correlation in all the average crustal thicknesses obtained using the three different approaches. Based on these results, the study area is made up of high crustal thickness ranging between 28 km to 39 km. The gravity anomaly profiles were model along profile lines (A-A', B-B' and C-C') drawn in different directions and covering a distance between 230 km - 340 km with crustal thicknesses ranges from 30km to 38km in order to ascertain the crustal thickness underlying the study area. The models identified and delineate boundaries between the Upper Crust, Lower Crust and Mantle with densities of 2.7 g/cm3, 2.8 g/cm3 and 3.2 g/cm3. The crustal thicknesses obtained from the study area ranging from 30 km to 37 km, 30.2 km to 35.6 km and 28 km to 39 km and not located in any active plate boundaries (margins) which indicates the tectonic stability of the region. The result from the study area has shown that the crustal thickness and density have influence on the tectonic stability of the study region. Hence, the area is tectonically stable as it is located in a non-major fractured zones.