IMPROVED MAGNETIC DATA ANALYSES AND ENHANCEMENT TECHNIQUES FOR LITHOLOGICAL AND STRUCTURAL MAPPING AROUND AKURE, SOUTHWESTERN NIGERIA

Abstract

This study employs improved magnetic data analyses and enhancement techniques to map and interpret the lithological and structural features around Akure and its environs. Several forms of filtering processes were performed to improve and enhance the Total Magnetic Intensity (TMI) data and other reduced data that were later produced. The analysed results of the upward continuation to 500 m and 1 km revealed the attitudes of deepseated basement rocks and anomalous structures with regional trend of NW-SE direction, as well as depth of structures that ranged beyond 1 km. On the other hand, derivatives images revealed lineaments/faults: F1-F’1, F2- F’2, F3-F’3 (minors) and F4-F’4 trending NNE-SSW, N-S, NE-SW, minor (ENE-WSW and E-W) and NW-SE respectively. Based on magnetisation contrast, four amplitude zones were revealed on the Analytic Signal (AS) image, which include very high zone as migmatite complexes; intermediate zone as migmatite/gneiss and charnockite complexes; fairly low zone as granite-gneiss and granite complexes, and low zone as quartzite ridge/ complex. The large causative bodies delineated from the pseudo-gravity revealed density of about 0.133 g/cc in susceptibility. The total depth estimate to top of magnetic sources ranged from 53 m to 1.98 km for shallower and deeper sources respectively. This study, therefore, suggests different rock types of varying mineralogical compositions, tectonic framework and structural deformations that led to change in intensity of rocks in the study area.

Keywords

• Automatic Gain Control (AGC)
• Analytic Signal (AS)
• Pseudo-gravity
• Spectral plot
• Litho-structure
• Akure