Basement Complex Of Southwestern Nigeria Research Articles

Combine electrical resistivity method and multi-criteria GIS-based modeling for landfill site selection in the Southwestern Nigeria

An integration of remote sensing and geophysical data was carried out in Odode-Idanre using Geographic Information System (GIS) approach with the aim of developing a landfill site selection map of the area. The area falls within the Precambrian Basement complex of southwestern Nigeria. The remote sensing involved the processing and interpretation of Landsat-7 EMT + image covering the study area and the data were used to produce the lineament, slope, drainage and land use maps of the area. The geophysical investigation involved the vertical electrical sounding (VES) technique using Schlumberger configuration with half electrode spacing (AB/2) varying from 1 to 65 m, One hundred and one (101) soundings stations were occupied within the study area. The interpretation of the VES data was used to generate the geoelectric section and determine Dar Zarrouk parameters. The results were used to generate thematic overburden and the coefficient of anisotropy maps. The geoelectric sections generally identified four geologic/geoelectric sequences that comprise topsoil, weathered layer, fractured Basement and fresh Basement. The depth to the Basement is generally less than 10 m. The multi-criteria evaluation (MCE) analysis were used to assign weights to slope, land use, drainage density, lineament density, coefficient of anisotropy and overburden thickness using the analytical hierarchy process (AHP) and this was used to produce the landfill suitability map. The area was classified into unsuitable, moderately suitable and suitable zones. The unsuitable areas cover about 21.9%, moderately suitable areas cover about 55% and the suitable areas cover about 23.1%. The suitable areas are scattered and discontinuous but predominant within the southern part of the area. For the development of waste dump site within the study area, it should be located within the southern part which was found to be suitable.

GEOLOGICAL AND LITHOLOGICAL MAPPING OF PART OF IGARRA SCHIST BELT USING INTEGRATED GEOPHYSICAL METHODS

Integrated geophysical techniques involving magnetic and radiometric data were used to investigate the subsurface geometry of Igarra schist belt in Precambrian basement complex of southwestern Nigeria which falls within the latitude range of 7° 1635.6” to 7° 1736.0’ North and longitude range of 6° 0534.1” to 6°05’44”East, with a view to interpret the geology of part of Igarra schist belt and estimate the depth to basement of magnetic source in the area. Six profiles were established with the objective of delineating the metasediments and its structural attributes, and geophysical measurements were made at 5m intervals along these profiles. The results of magnetic datasets were presented as maps and profiles of varying magnetic intensities and the causative rock types. Qualitative interpretation of the magnetic data using Reduction to pole, Analytical signal, first vertical, horizontal and tilt derivatives, upward continuation filters shows what has been interpreted as the signature of a near-vertical fault, trending along a NE-SW and NW-SE direction while radiometric datasets gave geochemical rates of U, Th and K as well as the effect of water contents on the rocks present within the study area. Qualitative and quantitative interpretation of individual magnetic anomalies and geological knowledge of the survey area yielded information on the depth of the geological features (e.g. rock contact, faults or fractures), structure and magnetic properties of rock units. 3D Euler deconvolution and Average radial spectrum were adopted to estimate the depth of the magnetic sources which ranges from – 92.895m to 73.95m; -115.45m to 57.44m and 63m to 44.1m; 88.2m to 81.9 m respectively. The Igarra schist belt has evolved different episodes of orogenies and the metasediments were formed from low grade regional metamorphism of argillaceous sediments such as shales or sediments of varying composition.

Geoelectrical exploration for groundwater in crystalline basement rocks of Gbongudu community, Ibadan, Southwestern Nigeria

Gbongudu community, Ibadan underlain by crystalline rocks of Basement Complex of Southwestern Nigeria has need for alternative water supply due to inadequacies of surface water supply and common occurrences of low yield or dry boreholes coupled with rapid development within the community. Geophysical investigation involving electrical resistivity was carried out with the aim of evaluating the groundwater potential of the community. Thirty-three (33) Vertical Electrical Soundings were acquired across the community adopting Schlumberger electrode configuration with current electrode separation (AB) varying from 2 to 200 m. The acquired field data were interpreted using partial curve matching with suitable auxiliary chart and “RESIST” resistivity sounding interpretation software was also used for iteration. The results revealed two to five geo-electric layers, namely, topsoil, clayey soil, lateritic clay, weathered layer, fractured unit and fresh basement. The weathered and the fractured units form the aquiferous zones in the area investigated. Thematic maps of geoelectric and Dar-Zarrouk parameters produced from the interpreted VES data are aquifer unit (weathered layer) thickness map, aquifer unit (weathered layer) resistivity map, overburden thickness map, basement resistivity map, basement topography map, reflection coefficient map, total longitudinal conductance map, total transverse resistance map and electrical anisotropy (coefficient of anisotropy) map. The thematic maps were combined to form a single component which gives the groundwater potential map of the study area. The groundwater potential map was used to classify the study area into poor, low and good aquifer potential zones. The study reveals that the weathered and fractured zone that occur in the southeastern part of the study area constitute the water bearing zone which can be regarded as good groundwater potential. This study has provided evidence on the hydrogeologic framework and subsurface nature of main aquifer units in the area.KEY WORDS: Groundwater exploration, RESIST, Dar-Zarrouk parameters, Electrical anisotropy, Borehole drilling.

Tectonic and structural analysis of the Migmatite–Gneiss–Quartzite complex of Ilorin area from aeromagnetic data

ABSTRACTIn an effort to have better understanding of the geologic settings and structural disposition of the Nigerian basement rocks, Ilorin area, a notably complex region within the South-western Basement Complex of Nigeria was studied using aeromagnetic data so that existing knowledge on the geology of the area can be appraised and updated. The aeromagnetic data was enhanced using various techniques which include the Total Horizontal Derivative (THD), Standard Euler Deconvolution, Tilt Derivative and Spectral Analysis. Striking features observed over the Residual Magnetic Field map were NE-SW trending anomalies aligned diagonally and running from the SW to the NE, forming a band having a width of between 16,000 and 20,000 m that coincided with the Banded Gneiss region on the geologic map; conspicuous E-W trending magnetic low whose location lies very close to the boundary between Migmatite and Banded Gneiss; and a ring-like magnetic low occurring in the south-eastern part of the residual map with no surface expression on the geologic map. Residual Magnetic Field values ranged from +157 to −202 nT. The THD map showed that the Banded Gneiss was the most deformed unit within the Migmatite–Gneiss–Quartzite complex. Major fractures coincident with Banded Gneiss boundaries appeared to be possible channels from which heat was leached in the regional system during metamorphism such that the Banded Gneiss region attained a relatively lower grade metamorphism than the Migmatite sharing boundary with it. Result from the spectral analysis showed that the magnetic basement in the eastern region was downthrown abruptly relative to that in the western portion. The abruptness was interpreted to mean that such subsidence was fault controlled. The study concluded that the presence of major fractures interfering with metamorphic processes in a regional settings may influence the grades of metamorphism that may result; that the schist region in the study area could be overlying a region of downthrown bedrock; and that the stress pattern that defined the crustal deformation pattern at the near crust in the past had changed compared to the currently dominant pattern.

DEFORMATION MECHANISMS, TIMING AND SHEAR SENSE ANALYSIS OF PART OF THE PRECAMBRIAN TERRAIN OF SOUTHWESTERN NIGERIA.

The study area is part of the polycyclic Precambrian Basement Complex of southwestern Nigeria, which comprises meta-sediments and granitoids of varying compositions. The area was primarily deformed into a large-scale sheeted structure, which was sequentially followed by developments of first and second phases of folding that interfered with each other. Brittle to semi-ductile shear deformations, initiated by an ESE-directed transport of the hanging wall of a major NE-SW trending low-angle normal fault culminated in the third phase of fold and development of widespread shear zones. Latter phases of deformation resulted in rotation of finite strain axis relative to the instantaneous strain during a non-coaxial progressive simple shear deformation. We posit that the dominant terminal mechanism of deformation in the area is the late-kinematic progressive heterogeneous simple shear during the late- to post-Pan African orogenesis.

Petrogenetic and Compositional Features of Rare Metal Pan-African Post-Collisional Pegmatites of Southwestern Nigeria; A Status Review

Abstract This research reviews the geology, petrogenesis, compositional trends and geochronology of the rare-metal pegmatite of southwestern Nigeria. The source of these pegmatites is still presently debated which have been explained as either product of highly fractionated molten material or anatexis of the local crust. However, published works of past authors have been compiled to give a detailed understanding of the formation of the mineral deposits. The basement complex of southwestern Nigeria comprises of Precambrian rocks of amphibolite, the hornblende gneiss and the granite gneisses which were formed as a result of the opening and closing of the ensialic basin with significant, extensive subduction during the Pan-African orogeny. The pegmatites in this region have shown internal zoning and a high degree of evolution from the border zone to the core zone during the crystallization and solidification of the felsic granite to pegmatite melt. The rare-metal pegmatites have distinct chemical compositions and mineralogy, containing quartz, biotite, muscovite, microcline, garnet with localized tourmaline, tantalite and columbite. These pegmatites vary significantly by their bulk-rock and mineral chemistry which indicates a more peraluminous attribute and enrichments of lithophile elements of Rb, Cs, Ta and Ba. Previous K/Ar isotopic ages (502.8±13.0 Ma and 514.5±13.2 Ma) suggest that the pegmatites are related to the post-collisional phase of intensive metasomatism. Adopted from previous studies, a five-stage conceptual model of evolution which is widely accepted have been proposed for the origin of the pegmatites.

Radiometric survey in geological mapping of basement complex area of parts of Southwestern Nigeria

Radiometric methods were used to investigate the radioactive properties of rocks in parts of southwestern Nigeria with a view to interpreting the geological structure and abundance of natural radioactive elements in the main type rocks. The airborne radiometric dataset of Ikole Sheet and ground radiometric data recorded from eight traverses in Akoko axis of the study area were processed. Results presented as maps and profiles displayed variations of high and low radioactive concentrations across the area. These maps showed moderate to very high concentrations and very low to low concentrations of the radioelements; uranium (4.5-13.0 ppm); (LLD-low limit of detection -3.0 ppm), Th (25.0-70.0 ppm); (8.5-16.0 ppm) and K (2.0-4.0 %); but the most often observed values are in the range 2.5-7.0 ppm, 22.0-30.0 ppm and 3.0-4.0% for U, Th, and K respectively. High concentrations imply that the rocks are crystalline, undeformed and are rich in feldspar and U-Th bearing minerals. While low radioactivity is attributed to varying geologic framework compositions; weathered materials or fluids formed as a result of intense metamorphism. The radiometric datasets proved valuable in delineating different rock types and serve as a complementary tool in identifying geochemical zoning of rocks in the area.ReferencesAjibade A.C. and Fitches W.R., 1988. The Nigerian Precambrian and the Pan-African Orogeny, Precambrian Geology of Nigeria, 45-53.Ajibade A.C., Woakes M. and Rahaman M.A., 1987.Proterozoic crustal development in Pan-African regime of Nigeria: In A. Croner (ed.) Proterozoic Lithospheric Evolution Geodynamics, 17, 259-231.Appleton J.D., Miles J.C.H., Green B.M.R, Larmour R., 2008. Pilot study of the application of Tellus airborne radiometric and soil geochemical data for radon mapping. Journal of Environmental Radioactivity, 99, 1687-1697.Arisekola T.M. and Ajenipa R.A., 2013. Geophysical data results preliminary application to uranium and thorium exploration. IAEA-CYTED-UNECE Workshop on UNFC-2009 at Santiago, Chile 9-12, July, 12.Bayowa O.G., Olorunfemi O.M., Akinluyi O.F. and Ademilua O.L., 2014.A Preliminary Approach to Groundwater Potential Appraisal of Ekiti State, Southwestern Nigeria. International Journal of Science and Technology (IJST), 4(3), 48-58.Bierwirth P.N., 1997. The use of airborne gamma-emission data for detecting soil properties.Proceedings of the Third International Airborne Remote Sensing Conference and Exhibition.Copenhagen, Denmark.Grasty R.L. and Multala J., 1991. A correlation technique for separating natural and man-made airborne gamma-ray spectra. In: Current Research, Part D, Geological Survey of Canada, 111-116.Grasty R.L., Minty B.R.S., 1995a. A guide to the technical specifications for airborne gamma ray surveys. Australian Geological Survey Organization, Record.Grasty R.L., Minty B.R.S., 1995b. The standardization of airborne gamma-ray surveys in Australia. Exploration Geophysics, 26, 276-283.IAEA, 1991. Airborne gamma ray spectrometer surveying, International Atomic Energy Agency, Technical Report Series, 323.IAEA, 2007.International Atomic Energy Agency. Safety Glossary, Terminology used in Nuclear Safety and Radiation Protection-2007 Edition.Jones H.A. and Hockey, 1964.The Geology of part of’ Southwestern Nigeria.Geological Survey, Nigeria bulletin, 31.Kearey P., Brooks M. and Hill I., 2002. An Introduction to Geophysical Exploration.3rd ed. Oxford: Blackwell Science, 262.Milsom J., 2003. Field Geophysics: The geological field guide series, John Milsom University College, London. Published by John Wiley and Sons Ltd. Third edition, 51-70.MontajTM Tutorial, 2004. Two - Dimensional frequency domain processing of potential field data.Nigeria Geological Survey Agency (NGSA), 2009. Geological map of Nigeria prepared by Nigeria Geological Survey Agency, 31, ShetimaMangono Crescent Utako District, Garki, Abuja, Nigeria.Omosanya K.O., Ariyo S.O., Kaigama U., Mosuro G.O., and Laniyan T.A., 2015. An outcrop evidence for polycyclic orogenies in the basement complex of Southwestern Nigeria. Journal of Geography and Geology, 7(3), 24-34.Oyawoye, M.O., 1972. The Basement Complex of Nigeria.In African Geology. T.F.J. Dessauvagie and A.J. Whiteman (Eds) Ibadan University Press, 67-99.Oyinloye A.O., 2011. Geology and Geotectonic Setting of the Basement Complex Rocks in Southwestern Nigeria: Implications on Provenance and Evolution. Earth and Environmental Sciences, 98-117. ISBN: 978-953-307-468-9.Rahaman M.A., 1981. Recent Advances in the Study of the Basement Complex of Nigeria.First Symposium on the Precambrian Geology of Nigeria, Summary.Rahaman M.A., Emofureta W.O. and Vachette M., 1983. The potassic-grades of the Igbeti area: Further evaluation of the polycyclic evolution of the Pan-African Belt in South-western Nigeria. Precambrian Resources, 22, 75-92.Woakes M., Rahaman M.A., Ajibade A.C., 1987. Some Metallogenetic Features of the Nigerian Basement. Journal of African Earth Sciences, 6(5), 655-664.

An integrated exploration technique for groundwater on a part of the basement complex of southwestern Nigeria

Akure is underlain by the basement complex rocks of southwestern Nigeria. It is faced with difficulty in the search for groundwater due to lateral discontinuity of basement lithologies. This study therefore delineates possible groundwater potential zones through the integration of remote sensing and electrical resistivity data. Landsat TM data was digitally processed and used to produce lineament, lineament density and intersection maps while hydrogeological parameters were obtained from electrical resistivity method and used in the production of overburden/fractured map. Weighted overlay method was utilized in ArcGIS ® in order to integrate the two maps so as to produce groundwater potential map of the study area. The groundwater potential map showed four major areas of groundwater potentials viz; very low, low, high and very high groundwater potential areas. An average of 0.9445litres of groundwater is discharge per second in the area i.e., approximately 3, 400litres per hour of groundwater is disharge in th area. However, a critical analysis of borehole yields show that boreholes with the poorest yields pump at a rate of between 0.2 to 0.5 l/s which is higly inadequate while very good boreholes pump at the rate of 1.14 to 2.16 l/s . Infact, most areas with good yields are cited in the southwestern portions of the study area.

Geophysical evaluation of groundwater potential in part of southwestern Basement Complex terrain of Nigeria

The geophysical assessment of groundwater in Awa-Ilaporu, near Ago Iwoye southwestern Nigeria was carried out with the aim of delineating probable areas of high groundwater potential. The area falls within the Crystalline Basement Complex of southwestern Nigeria which is predominantly underlain by banded gneiss, granite gneiss and pegmatite. The geophysical investigation involves the very low frequency electromagnetic (VLF-EM) and Vertical Electrical Sounding (VES) methods. The VLF-EM survey was at 10 m interval along eight traverses ranging between 290 and 700 m in length using ABEM WADI VLF-EM unit. The VLF-EM survey was used to delineate areas with conductive/fractured zones. Twenty-three VES surveys were carried out with the use of Campus Ohmega resistivity meter at different location and at locations areas delineated as high conductive areas by VLF-EM survey. The result of VLF-EM survey along its traverse was used in delineating high conductive/fractured zones, it is, however, in agreement with the delineation of the VES survey. The VES results showed 3–4 geoelectric layers inferred as sandy topsoil, sandy clay, clayey and fractured/fresh basement. The combination of these two methods, therefore, helped in resolving the prospecting location for the groundwater yield in the study area.

Litho-structural analysis of eastern part of Ilesha schist belt, Southwestern Nigeria

The Ilesha schist belt is an excellent example of high strain shear belt within basement complex of southwestern Nigeria which is part of the larger West African Shield. The Ilesha schist belt is characterised by metasediment-metavolcanic, migmatite-gneiss and older granite rocks and the occurrence of a Shear zone which has been traced to and correlated with the central Hoggar Neoproterozoic shear zone as part of the Trans-Saharan Belt. Although the area is interesting in terms of geologic-tectonic setting, however, detailed geological assessment and structural interpretation of features in this area is lacking due accessibility problem.For these reasons we applied principal component analysis (PCA) and band ratio (BR) techniques on Landsat 8 OLI data for lithological discrimination while for structural interpretation, filtering techniques of edge enhancement and edge detection was applied on digital elevation model (DEM) acquired by shuttle radar topographic mission (SRTM) sensor. The PCA outperform BR for discrimination between quartzite and granite which are the most exposed rock units in the area. For structural interpretation, DEM was used to generate shaded relief model and edge maps which enable detailed structural interpretation. Geologic fieldwork was further conducted to validate structures and units identified from image processing. Based image interpretation, three deformation events were identified. The first event (D1) which is majorly a ductile deformation produced foliations and folds whose axial planes trend in NNE-SSW. The second event (D2) resulted in reactivation and rotation of the D1 structures particularly the folds in the NE-SW. The third event (D3) produced a transgressive deformation starting with the ductile deformation resulting in the development of sigmoidal structures oriented in NE-SW to E-W direction and the brittle deformation occurring at later stages producing fractures oriented in the E-W to NE-SW directions.These results have important implications in terms of regional tectonics and geological mapping as well as in land-use planning and other areas such as hydrogeology or geotechnics.

Groundwater Potential and Vulnerability Assessment from Integrated Geophysical Methods, Borehole Logging, and Hydrogeological Measurement

Geophysical investigations and hydrogeological measurements were carried out in Akoko area of Ondo State, Nigeria which are characterized by rugged hills of Precambrian Basement Complex of Southwestern Nigeria comprising mainly of the Migmatite-Gneiss-Quartzite Complex of Archean-Proterozoic age. The study was aimed at evaluating the groundwater potential of the area and assess the vulnerability of the aquifers/water bearing units within the phreatic zone to contamination especially from surface activities/anthropogenetic sources. Seventy soundings were carried out along fifteen traverses where the VLF-EM measurement was also conducted. The hydrogeological measurement involved determination of static water level/vadose zone thickness from 138 wells. Also four borehole were drilled after thorough geophysical investigations in order to constrain the interpretation of the geophysical investigation. Findings show that the major water bearing units/aquifer in the area are the weathered layer (clayey in nature) and fractured basement as delinated on the geoelectric sections, borehole sections, and very low frequency electromagnetic. The combination of these aquifer units are common in Ikare and Akungba parts of the study area. The visible depth of groundwater exploitation in the area is between 10 – 40 m. The static water level is generally less than 5 m. The map of the overburden shows that Akoko area is generally made up of thin overburden thickness except at Irun, Ogbagi, Arigidi, and Oke Agbe that showed moderate overburden thickness (10 m – 20 m). The static water level measured in the study area ranged from0.75 m – 16 m, with a modal range of 1.1 – 3.0 m as they constituted for about 78 % of the area. This generally showed that the static water level was shallow across the study area, thus suggesting that the surficial aquifers/water bearing units would be highly vulnerable to anthropogenetic/surface activities which are the major sources of groundwater contamination. Clay or silt, characterized by low resistivity (1 – 100 Ω-m) and very low permeability, and impervious or semi-impervious topsoil materials (laterite and lateritic sand), characterized by high resistivity values (>400 Ω-m) constitutedthe protective layers that cappedthe vadose zones in the area. The topsoil can provide protection to a reasonable extent, but limited due to its thin thickness across the area.

Integrating aeromagnetic and Landsat™ 8 data into subsurface structural mapping of Precambrian basement complex

The integration of Aeromagnetic data and remotely sensed imagery with the intents of mapping the subsurface geological structures in part of the South-western basement complex of Nigeria was developed using the PCI Geomatica Software. 2013. The data obtained from the Nigerian Geological Survey Agency; was corrected using Regional Residual Separation of the Total Magnetic field anomalies enhanced, and International Geomagnetic Reference Field removed. The principal objective of this study is, therefore, to introduce a rapid and efficient method of subsurface structural depth estimate and structural index evaluation through the incorporation of the Euler Deconvolution technique into PCI Geomatica 2013 to prospect for subsurface geological structures. The shape and depth of burial helped to define these structures from the regional aeromagnetic map. The method enabled various structural indices to be automatically delineated for an index of between 0.5 SI and 3.0 SI at a maximum depth of 1.1 km that clearly showed the best depths estimate for all the structural indices. The results delineate two major magnetic belts in the area; the first belt shows an elongated ridge-like structure trending mostly along the NorthNortheast-SouthSouthwest and the other anomalies trends primarily in the Northeast, Northwest, Northeast-Southwest parts of the study area that could be attributed to basement complex granitic intrusions from the tectonic history of the area. The majority of the second structures showed various linear structures different from the first structure. Basically, a significant offset was delineated at the core segment of the study area, suggesting a major subsurface geological feature that controls mineralisation in this area.

Electromagnetic profiling of Owena Dam, Southwestern Nigeria, using very-low-frequency radio fields

Abstract Very low frequency (VLF) was used to assess variations in overburden composition, bedrock lithology and the concealed basement structures within the bedrock of Owena Dam in Igbara-Oke of the Precambrian Basement Complex of Southwestern Nigeria. Five VLF-electromagnetic (EM) traverses were occupied at 5 m intervals. The VLF normal and filtered real component anomalies identify major geological interfaces suspected to be faults/fractured zones. The points of crossover between the real and imaginary components delineate the fractured zones, which were identified as areas of possible seepage (piping and sloughing). The internal erosion (permeability) of soil mass eventually leads to the formation of an open conduit in the soil, which may lead to failure of the embankment/dam. The fractured zones are suspected to be present at all traverses. In total, 21 fractured zones were identified along the dam embankment, with the deepest occurrence at Traverse 5. These seepage zones cause heterogeneity in the subsurface composition, which could lead to dam failure. The result of the study suggests that VLF is an adequate method of monitoring seepages in embankment dams.

Mineralogy and Geochemistry of the Weathering Profiles above the Basement Rocks in Idi- Ayunre and Akure Districts, Southwestern Nigeria

Idi-ayunre and Akure areas are part of the basement complex of southwestern Nigeria and are predominantly consisted of gneisses, granite and migmatite with some minor quartz veins and pegmatite. These rocks have been greatly weathered to form clay, laterite and soils.Chemical analysis were carried out on basement rocks and exposed profiles. The weathering profile was subjected to X ray diffraction (XRD) analysis to determine mineralogical compositions whereas Chemical Index of Alteration (CIA) was calculated from the elemental concentrated data.Weathering of basement rocks in Idi-Ayunre and Akure districts resulted in the formation of soil layer which ranged 0-0.4m, laterite layer 1.2-2.2m, and clayey zone 3.8-6.6m. Quartz, plagioclase, microcline, and biotite were the main minerals in parent rocks. Some of the primary minerals such as biotite and K-feldspar have been weathered to form kaolinite. Quartz, kaolinite and goethite formed the dominant minerals revealed by X-ray diffraction on decomposed granite sequences. The results from chemical analysis showed that Al and Fe have been enriched in weathering profiles of banded gneiss, migmatite gneiss and porphyritic granite whilst on the other hand Ca, Mg, Mn, Na, K, Ti were reported to be depleted.. Silica was relatively stable from basement to the topsoil in the profile. The CIA generally ranged between 80 - 99The lateritic profiles over banded gneiss, granite and porphyritic granite of Idi-Ayunre and Akure areas varied with the composition of the parent rocks. The thick clayey layers could be of great economic importance for the production of ceramics wares and for constructional purposes.

Mineralogy and Geochemistry of Residual Clay Occurrences in Idi-Ayunre and Akure Areas, Southwestern Nigeria

<p class="zhengwen">Three residual clay occurrences in Idi-Ayunre, and Akure areas which belong to the Precambrian basement complex of southwestern Nigeria were investigated for their mineralogical, chemical and industrial properties. The investigation was to evaluate their industrial applications and economic importance. The clay within the weathered profiles above banded gneiss at Idi-Ayunre is whitish with red spots, whereas the clays derived from profiles above porphyritic granite and granite gneiss in Akure are grayish and brown in color respectively.</p><p class="zhengwen">The X-ray diffraction studies show that kaolinite is the dominant clay mineral, goethite, microcline, quartz, albite are the major non clay minerals in the samples. Chemical data showed that the average values of SiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, and Fe<sub>2</sub>O<sub>3</sub> were 52.3. 30.29 and 3.54 wt% respectively constituting 86.13% of the bulk compositions.</p>Evaluation of the clay thermal characteristic, firing colour, water absorption capacities and shrinkage values show that the brownish Idi-Ayunre clay, gray and brown Akure kaolinitic clays could serve as raw materials for ceramics, building bricks, and other structural wares

An outcrop evidence for polycyclic orogenies in the basement complex of Southwestern Nigeria

In this work, the tectonic history of a classic outcrop of the Migmatized-Gneiss Complex of Southwestern Nigeria was systematically investigated. The aim of this research is to investigate how the polycyclic nature of the basement complex in Southwestern Nigeria is preserved at a local or outcrop scale. Detailed geological mapping of the outcrop was done using ‘bit-a-bit’ technique in four pre-defined quadrants. Structural measurements include a detailed inventory of fold geometry, attitudes of veins, joints, and boudins. The outcrop is characterized by alternating leucosomes and melanosomes, fractures, S-C fabric and microfolds. Three metamorphic events were interpreted in the outcrop M1, M2 and M3, which are linked to deformation D1 to D3. These events suggest that the outcrop evolved through a complex interplay of compression, extension, and late stage sinistral movement. Phase I extension is coincident with the emplacement of veins, which were later compressed into ptygmatic folds. These veins were intersected by joints associated with Phase II deformation. During the third episode of extension, quartzo-feldspathic veins were emplaced normal to the orientation of earlier joint sets. The N-S, NE-SW and NW-SE trends of the structures are consistent with the polycyclic fabric of the Nigerian basement complex. This work has shown that macroscopic structures in the study area present unique evidence for the regional polycyclic history of the bedrock in Southwestern Nigeria.

Lineament studies of rocks in Omifunfun area, southwestern Nigeria: Remote sensing and petrologic observations

Omifunfun area is situated in the southern part of Ife-Ilesa Schist Belt of the basement complex of southwestern Nigeria. The study area is traversed by the Ifewara Fault Zone which divides the area into east-west with contrasting lithologies that have been variously mylonitized. To the east, is quartzite and to the west migmatite gneiss which are intruded by prophyritic granites. The objective of this study is to delineate deformation linear structures from Landsat imageries over the study area, and attempt to correlate the information with microtectonic structures and field observations with the aim of better understanding the geologic terrain. Lineaments were extracted from Landsat images covering Omifunfun area. The analysis of these lineaments indicates low density in three prominentorientations corresponding to 0000–0350 and 0600–0900 with minor northwest-southeast structures. The most prominent of these directions is the 0000–0350 which incidentally include mylonite and mineral lineations within the Ifewara Fault system. Microtectonic observations reveal analogous results with three prominent foliation directions. The dominant one strikes in the same direction with the same Ifewara mylonitic foliation. These directions correspond to two major planar surfaces S1 and S2 and were respectively produced during two episodes of deformation (D1 andD2).KEYWORDS: Ifewara Fault Zone, Lineament, Microtectonic Structures, Mylonitization, Remote Sensing

Evaluation of Resistivity Anisotropy of Parts of Ijebu Igbo, Southwestern, Nigeria Using Azimuthal Resistivity Survey (ARS) Method

This study was carried out to determine the anisotropic properties of parts of the Southwestern Basement Complex of Nigeria in Ijebu Igbo, which is underlain by migmatite gneiss and older granites.The surface water level (SWL) of 107 hand-dug wells were measured to determine the groundwater flow direction of the area. Thirty Azimuthal Resistivity Survey (ARS) were investigated along four azimuths; 0°, 45°, 90°, and 135° to determine the electrical anisotropy, the trend of fractures and their behavioural pattern with depth. The quantitative interpretation of the Radial Vertical Electrical Sounding (RVES) curves involved the use of partial curve matching, and computer iteration using WINRESIST program ...

Variability of Characteristics and Productive Potential of Some Pedons on the Basement Complex of Southwestern Nigeria

The objective of this study is to assess variability of land quality and soil characteristics of some of the pedons on the basement complex of southwestern Nigeria. Variation in soil properties and their relationship with crop production must be studied and understood to ensure sustainability of soil. Soil characteristics can vary significantly across most fields used for crop production. Interaction among the parent materials, topography, vegetation, tillage, fertilization, make variation across fields the norm rather than the exception. Some

English

  The polycyclic nature of the Migmatized gneiss basement complex of South-western Nigeria is depicted by several tectonic imprints oriented in different manner; such setting is characterized by temporal adjustment of the minimum stress field. Attitude (strike and dip), length, width, average perpendicular distance and aspect ratios were taken for foliations, joints, veins, intrusions and boudinages. These parameters were analyzed on histograms, rose diagrams and stereo nets; outcrop maps were used to elucidate the heterogeneity of the stress field. Joints are the youngest tectonic structures in the study area; they include extensional and shear types, systematic, non-systematic and orthogonal sets with dihedral angle of <90°. The boudinages occur in gneissic rocks; the veins and intrusions are metasome in the host rock and are made of quartz, feldspar and pegmatite minerals. The dominant orientation of structures are NNE-SSW for foliations, E-W, NE-SW, and NNW-SSE for joints, N-S, NNW-SSE and NNE-SSW for veins, and N-S for intrusions with dip direction of North-west and South-east for foliations and west for intrusions. Initial orientation of σ3 was east-west during the emplacement of the veins and pegmatite intrusions and then ENE-WSW for the quartz-rich intrusions. Joints oriented NE-SW commonly intersected the other structures suggesting they are juvenile and created by NW-SE oriented σ3. Subsequently, shearing of the rocks and rotation of the least stress field produced the boudinages, conjugate joints, and tension gashes. Evidence for horizontally situated σ1 is shown by few slightly folded foliations seen in specific locations. In the study area, the joints were the product of multidirectional minimum stress which was dominantly oriented NW-SE prior to the Pan African orogeny.   Key words: Tectonic, stress, σ3, joints, veins, boudinages, Pan African.