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Anthony J.C. Madu
Mosto K. Onuoha
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Mosto K. Onuoha
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International Journal Geology and Mining

Bouguer anomaly and free-air anomaly correlation signatures in parts of Benue and Kogi States of Nigeria

Madu Anthony Joseph Chinenyeze* and Onuoha Mosto K

*Department of Geology, Michael Okpara University of Agriculture Umudike, Abia State, Nigeria.

PTDF Professorial Chair, Department of Geology, University of Nigeria Nsukka (UNN), Enugu State, Nigeria.

Accepted 08 July, 2016.

Citation: Madu AJC, Onuoha MK (2016). Bouguer anomaly and free-air anomaly correlation signatures in parts of Benue and Kogi States of Nigeria. International Journal Geology and Mining 2(1): 030-037.

Copyright: © 2016 Madu and Onuoha. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Abstract

Topographic values in the study area range from 80m to 170m. The rock type comprises Basement Complex at the west bounded by River Niger, and sedimentary rock type in the east. Density measurements of various rocks were taken with the highest bulk density from the metamorphic schist (2.77gm/cm3), followed by igneous rock olivine gabbro (2.73gm/cm3), and sandstone (2.35gm/cm3). Results of gravity survey revealed a mean Bouguer anomaly of +12.15 mgals and a mean free air anomaly of +22.0 mgals.  Interpretation of gravity measurements revealed the existence of a fracture at Gboloko NE-SW axis, a synclinal fold axis at about 5.5km west of Gboloko (between the Staurolite Schist and Cordierite-Tourmaline schist). The Basement-Sedimentary boundary is characterized by a drop in residual Bouguer anomaly from positive to negative at about 6km east of Gboloko. The thickness of the sediments is about 0.90km at the northern part of the Basement-Sedimentary boundary, and about 2.0km in the south, thus suggesting a progressive increase in sedimentary thickness at the western edge of the Benue trough. The Free-air anomaly ‘highs’ correspond to Bouguer anomaly ‘highs’ and tied to areas of high topography and  bands of weathered, lateritized sediments. The Bouguer anomaly profiles exhibited reliable signature changes at the rock boundaries, thus a supportive tool for delineation of those border areas.      

Keywords: Free-air anomalies, Bouguer anomaly, Gravity profiles, Basement complex rocks, bulk density.