DERIVATIVES AND ANALYTIC SIGNALS: Improved Techniques for Lithostructural Classification.

In this study, derivatives and Analytic Signal (AS) techniques were employed to reveal the nature of rocks and lithostructural relationships that exist within the basement complexes around Ekiti and Ondo States. The derivatives techniques were used to enhance theReduction to Equator Total Magnetic Intensity (RTE_TMI) data. In order to make the results from derivatives techniques worthwhile and robust, Analytic Signal (AS) technique was then applied. The results of the derivatives and analytic signals revealed seven different lithological suites, namely: migmatite (M), migmatite-gneiss (MGn), gneiss and granite (Gn/G), schist and quartzite schist (S/Qs), granitegneiss and charnockite (Gn/Ch), charnockite and granite (Ch/G), and granite (G). Five different major lineaments/faults, folds and lithological contacts were also identified. The lineaments/faults were classified as F1, F2, F3, F4 and F5 with NW-SE, NNE-SSW, NE-SW, E-W and NNW-SSE trends respectively. Folds were classified into S1, S2, S3, S4 and S5 as symmetrical, asymmetrical, recumbent, ptygmatic and drag folds respectively. While lithological contacts were classified into C1, C2, C3, C4 and C5 as sharp contact of migmatite and granite, migmatite and granite-gneiss/charnockite/granite, migmatite and gneiss/granite, migmatite and schist/quartzite schist, and migmatite and gneiss respectively. It is evident from the study that migmatites and gneisses which form the basement in the area have been highly deformed and evince many intrusives. A detailed geological map for the study area is proposed as deduced from results analyses

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

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