Tectonic Settings and Petrogenesis of Pan-African S-Type Granitoids in Anka Schist Belt, NW, Nigeria

Research into geotectonic settings of the Anka schist belt was regionally carried out by (Holt, 1982) stating that there is no evidence of significant partial melting or metasomatism. This research uses chemical data of some Pan-African granitoids within the Anka schist belt to explain the tectonic setting and petrogenesis of the S-type granitoids intruding the metasediments within the Anka schist belt. Twenty-five (25) representative samples of granitoids was analyzed for major oxides and trace elements composition. Results obtained from the chemical data was used to plot various classification diagrams. The granitoids in the study area plots within the orogenic class and the use of trace element discrimination diagrams as a means of fingerprinting the tectonic environments revealed that the granitoids ranges from syn-collision to late orogenic field. The granitoids which plotted in the syn-collision field is a characteristic of chemical affinity of syn-collision peraluminous granites with highly fractionated volcanic-arc magmas.  The petrogenesis of the S-type granitoids in the study area are greywacke sourced which is largely metagreywacke and metapelitic sourced during partial melting. Keywords: Granitoids, Pan-African, S-type, Metasediments, Partial melting DOI: 10.7176/JNSR/10-2-08 Publication date: January 31st 202

Geochemistry and Petrogenesis of Gneisses Around Kafur-Yari Bori-Tsiga area within the Malumfashi Schist Belt, Northwestern Nigeria.

The gneisses around Kafur-Yari Bori-Tsiga area consist of varieties such as banded gneiss, augen gneiss and granite gneiss. This area is underlain by both igneous and metamorphic rocks; the schist and migmatite-gneiss are intruded by the Pan-African granitoids. Minerals such as microcline, plagioclase, quartz, hornblende, biotite, orthoclase forms the major components in the gneisses while garnet, zircon and sphene are the accessories minerals. Foliation in the gneisses is defined by parallel alignment of mafic and felsic minerals (bands) having a major strike range of NE-SW to N-S and lesser of E-W directions. The geochemical study revealed major oxides such as SiO2 in the range of 63.85-73.84 wt%, Al2O3 has content between 12.77-16.05 wt%, Fe2O3 is between 1.18-6.70 wt%, Na2O is between 1.93-4.78 wt% and K2O between 1.49-6.96 wt %. The concentrations of high field strength elements ( Hf, Th, U, Nb and Ta) is rather lower in the gneisses investigated and thus responsible for the small propotion of minerals like the zircon, sphene and apatite which all occurred as accessories minerals. The absence of minerals like sillimanite, kyanite, cordierite and staurolite which are typical of paragneiss confirmed an igneous protolith of the gneisses investigated. Although, geochemical variations suggest igneous precursors for the gneisses of this area, it is obvious that they were not cogenetic but derived from differing sources and depths. Keywords: “Basement Complex”, cogenetic, Malumfashi, “Older Granite

Geology and Petrographic Studies of Rocks in Anka Sheet 52, Northwestern, Nigeria

Over the years, models of evolution of the schist belts of Nigeria was proposed and classified under ensialic and ensimatic processes of formation. The study area (Anka Sheet 52) lies between latitudes 12o00′N and 12°30′N and longitudes 5°30′ E and 6°00′E and covers an area of about 3,086.76 km² (Anka Sheet 52). Field mapping and laboratory studies was considered for this study by taking every detail in the field necessary such as geologic boundaries, structures, physical appearances of rocks and orientation noted in field notebook. Structural characteristics on outcrop was also recorded with the help of photographs and sketches along with text description. Representative rock samples mostly granitoids were prepared into thin for microstructural observations to reconstruct the deformation features and mineralogical assemblages under polarized light microscope. The study area comprises of gneiss of sedimentary protolith and is the oldest rock unit forming a massive sheared and elongated ridge trending north-south for about 1800m with a porphyroblastic texture of gradual lineation of quartz and feldspar in places. Metasediments comprises of quartzite, quartz schist, pellitic schist, phyllite, hornfels and metaconglomerate accounting for more than 35 percent of the study area. Pan-African granites intruded both the gneiss and metasediments and comprises of coarse grained granites, porphyritic granites, diorite and rhyolite to accounts for about 20 percent of the study area. Field and petrological evidences indicates that the Pan-African reworking may have led to the recrystallization of the protolith rocks to form gneiss (paragneiss) resulting from partial melting signifying that metamorphism possibly reach lower amphibolite facies in part of the study area. These rocks were overlain by sedimentary rocks of Cretaceous age. Keywords: Granitoids, Protolith, Metamorphism, Porphyroblastic, Paragneiss DOI: 10.7176/JEES/10-1-06 Publication date: January 31st 202

The Application of Airborne Geophysical and Satellite Imagery Data in the Delineation of Rock Boundaries and Structural Lineaments in Anka Sheet 52, Northwestern, Nigeria

The understanding of different lithologies and geological structures is a major task of geologists for accurate geological map during geological mapping exercise. In doing so, geologist must be able to cover broad areas of the surface or subsurface of the earth through collection of reliable remote sensing data over a wide region.  The Landsat ETM+ from Global Land Cover Facility (GLCV), Shuttle Radar Thematic Mapper- Digital Elevation Model (SRTM, DEM) data from Global Mapper version 14, Airborne Magnetic and Radiometric data from Nigeria Geological Survey Agency (NGSA) was acquired and interpreted with the help of computer-image processing technology such as Oasis Montaj and ArcGIS software to process, display and represent results covering the study area (Anka sheet 52). The basis of this technology is the representation of the radiometric data in a digital raster format that contain both amplitude and spatial information.  In this format, the data was analyzed, enhanced for visual inspection and combined with other types of data to form colour composite images that clearly subdivide the Basement complex rocks into Pan-African Granites from the Metasediments and the most eye-catching feature is the basement-sedimentary contact. Also, a major NE–SW trending structural lineament referred to as the Anka Fault trends for almost 25km and other subsidiary lineaments trending NW–SE with few E–W trends. Keywords: Landsat ETM+, Magnetic, Radiometric, Structural Lineament, Satellite Imagery. DOI: 10.7176/JEES/10-1-05 Publication date: January 31st 202

Utilization of Landsat 7 ETM+ Multispectral Data and ASTER-GDEM in Geological Investigation and Alteration Mapping around Yankara-Dan Sabo-Takulawa Area within Wonaka Schist Belt, Northwestern Nigeria

The study area forms part of the Precambrian to Early Paleozoic Nigerian Basement complex. ASTER-GDEM image draped on topographical map aided 3-D perspective view of physiographic features in the area. The Landsat ETM+ remote sensing data has suitable spectral and spatial properties that aided lithological and alteration mapping. Spectral transform approaches, consisting of band ratio (BR), principal component analysis (PCA), False Color Composition (FCC), and Feature Oriented Principal Component Selection (FOPC) were utilized. Prior to image processing, the ETM+ data were also subjected to image pre-processing. The results show that BR, PCA and FCC images discriminates the granitic rocks and metasediments. Color melange including ETM+ (7/4+4/3+5/7, 3/1+5/7+4/54 and 5/7+3/2+4/5) discerned highly altered zones and iron rich minerals. Colour composite (Kauffman ratio) and FCC show vegetation preponderance mostly on metasediments. Alteration of hydroxylated-silicate rocks are distinct with PCA. Hydroxyl minerals with marked oxidization and argillization are more recognizable with FOPC (Crosta technique) than PCA techniques. Structurally, the spectral responses distinctly show symmetrical M-shape fold pattern in granitic rocks that span within the southeastern part of the area.  The area also exhibit highest lineament density. Nearly N-S lineament trend corresponding to imprints of Pan-African Orogeny predominates. Keywords: Alteration mapping, Band ratioing, Lineament density, litholog

Mineralizarion in precambrian rocks of central Nigeria: Implications for the Oban-Budu-Mandara-Gwoza complex of eastern Nigeria

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Petrology and Rare Earth Elements (REE) distribution patterns of magmatic rocks in Gboko area, lower Benue trough Nigeria: Implication for tectonic evolution

Volcanic rocks can be subdivided according to tectonic setting into oceanic, sub-oceanic, sub-continental and continental. The relationship between the magma chemistry and the tectonic settings determines the end products(rocks) by magmatic fractionation and/or progressive crustal  contamination. Attempts to explain the magmatic and tectonic evolution of the Gboko area is considered in terms of the magmatic end products and the REE distribution patterns. Volcanic and intermediate rocks such as basalts, trachyandesites, trachytes, dacites, rhyolites, nepheline syenites and quartz diorites occur within the area intermittently. The distribution of the chondrite normalized values is used to determine the effect due to magmatic fractionation and the crustal contamination. The REE distribution shows relative enrichment of the LREE compared to the chondrites and the HREE except for one of the rhyolites. The distribution patterns show similar trend for basalts, trachyandesites, dacites and quartz diorites. The trends show slight Ce, Pr, Sm, Dy and Tm negative anomalies. In the quartz diorites there is comparatively more depletion of the LREE and a significant negative anomaly of Tm. Closely similar to the trends of basalts are those of trachyte and nepheline syenite. The trachtyes and nepheline syenites have similar negative Sm, Eu, Tb, Dy, and Tm anomalies and slight positive Gd and Er anomalies as well as higher relative depletion of HREE. The rhyolites display similar trends with significant negative Eu anomaly, except in one of the rhyolite where there is relative enrichment of theHREE and a significant negative Ce anomaly. The trends of the basalts are comparable to theoleiitic basalts and their similarity with the other rocks indicates the same source magma. In theoleiitic provinces, basalts coexist with trachyandesites and rhyolites as residual products of differentiation of basic magmas as confirmed by the similar trends. The significant Ce and Eu negative anomalies in the rhyolites and quartz diorites indicate that mineral fractionation and crustal contamination has played a part

Evolution of the Niger Delta, present dynamics and the future

Evolution of the Niger Delta is closely linked to the geodynamics related to the separation of the African and South American continents and the tectonics of the formation of the Benue Trough. Tectonic activities, climate and eustasy are the major factors responsible for transgression and regression through the entrant point along the present Niger Delta area and the deposition of marine and non-marine sediments from late Aptian to Eocene. The Santonian and later Campanian to Eocene positive movements of blocks bounded by NE-SW and NW-SE trending faults along the Benue Trough and the present Niger Delta region preceded the subsidence of the Oligocene and younger Niger Delta basin along the NW-SE fault trends. From Paleocene to Eocene, the Anambra basin was filled by the transgressive Imo Shale, the regressive Ameki Formation and from Eocene to Recent the Niger Delta has been filled by Akata, Agbada and Benin Formations. At present rifting and tectonic subsidence are dormant but the basin is under a sag regime with continued deposition of Benin Formation and little changes in climate and eustasy. The present dynamics in the Niger Delta has evolved it to a near mature basin but a climate change with the resultant eustasy could destabilize the ecosystem of the region with corresponding economic consequences.Keywords: Niger Delta; Transgression; Regression; Eustasy; Evolution; Paleogeograph