Basement Complex Research Articles

EFFECT OF CALIFORNIA BEARING RATIO OF SOILS USED AS SUBGRADE MATERIALS ON THE BENIN-AKURE ROAD, NIGERIA

An investigation was carried out to assess the suitability of soils brought in for use as subgrade materials for the Benin- Sobe axis of the Benin – Akure road by testing the bearing capacity using the California Bearing Ratio (CBR)test. The road passes through four soil parent materials: - Coastal Plain Sand- CPS, Imo-Shale (IS), BendeAmaki (BA) and the False Bedded or Basement Complex (FB).Soil samples were collected from four profile pits based on the parent materials. Soil samples were also collected about 50 cm from the tarred road representing materials brought in for the subgrade. The soils were analyzed for physicochemical properties and the California Bearing Ratio. Analyses were carried out on soils collected from each section of the parent materials.Results obtained showed that there were more road failures in the Imo Shale,BendeAmeki and to a less extent in the Coastal Plains segment of the road, and least in the False Bedded parent material section.CBR for unsoaked soils showed BendeAmaki having highest values (14.6 and 16.18) for the 2.5 and 5 mm penetration test; however values were not significantly different from the other parent material sections ( p> 0.05).The Imo Shale soils were poorly drained and are seasonally floodedand had the least CBR values (4.64, 5.2 for the 2.5 and 5 mm readings for the top and bottom penetration test. Coastal Plain Sands and BendeAmeki values were not significantly different from the Imo shale but values were higher.Soaking the soil did not significantly affect the soil strength for the False Bedded segment of the road; hence the failure rate was lowest.The False Bedded had higher CBR values for the soaked test, indicating that the parent material through which the road is built had significant effect on the failure rates

1.80–1.75 Ga granite suites in the west Troms Basement Complex, northern Norway: Palaeoproterozoic magma emplacement during advancing accretionary orogeny, from field observations

The Ersfjord Granite is part of a suite of c.1.80–1.75 Ga syeno-granites in the West Troms Basement Complex, northern Norway, presumed to belong to the Transscandinavian Igneous Belt (TIB-1) in the Fennoscandian Shield. Previous data suggest the granite formed post-collisional and ascended as a batholith pluton from a source generated by delamination of mafic-intermediate lower crust. We argue that the Ersfjord Granite was emplaced initially (c. 1.80 Ga) as multiple tabular sills in an extensional setting, then as successive melt injections (c. 1.78–1.75 Ga) in an evolving Andean/Cordilleran type accretionary orogen at the waning stages of the Svecofennian orogen. Field observations indicate melt ascent initiated as successive sills (EG-I) into well-foliated Meso/Neoarchaean TTG gneisses. Some sills preserved a magmatic layering, others injected and assimilated the host rock gneisses leaving pendants of mafic gneiss/migmatite residuum in between the granite sills. The first tectonic patches of melts (EG-II) ascended into the middle/upper crust along regional shear zones and injected into ductile imbricate thrust stacks (D1 event) during NE-SW directed crustal shortening and medium grade P-T conditions, using the sills and ancestor migmatite pendants as melt pathways. Then the tabular EG-I and II granite sheets and adjacent gneisses were coaxially folded by upright macro-folds (D2 event) and steep, granitic pegmatite dyke swarms (EG-III) intruded parallel to the fold axial surface and in related D2 thrusts, at low grade metamorphic conditions. The final melt emplacement (D3 event) included granite pegmatite dykes and sills (EG-IV) along subvertical D3 fold limbs and steep strike-slip shear zones. Our provisional extension, and successive advancing accretionary orogenic emplacement model for the Ersfjord Granite may explain ascent of many other TIB-1 magmas in the Fennoscandian Shield.

Geological and geophysical transect of the Middle Tien Shan across the Naryn and Atbashi depressions

The article presents the results of integrated geological and geophysical research works dealt with detailed magnetotelluric (MT) sounding and the study of the morphology and spatial position of the sedimentary cover and basement structures along the key transect of the Middle Tien Shan crossing the Naryn and Atbashi depressions. The data on the distribution of deep electrical conductivity of the crust and upper mantle were compared with the seismic profiling data. The compilation of the results of structural-geological and geophysical studies provided the opportunity to draw 2D upper-crust geological structure, consistent with the structure of electrical conductivity of the crust to depths of about 10 km. The detailed geological cross-sections and the structural and geological data allow us to characterize the deformations of the Cenozoic sedimentary complex and Paleozoic basement surface associated with the alpine activation of the key segment of the Tien Shan. It is shown that the Cenozoic structural parageneses emerged during a relatively short-term phase of deformation and orogeny under conditions of horizontal compression and transpression, which did not manifest themselves during sagging that occurred previously.

Fractional Crystallization and Partial Melting of the Paleoproterozoic Gneisses and Pegmatite in the Giant Husab Uranium Deposit, Namibia

The giant Husab uranium deposit is located in the Paleoproterozoic Abbabis Metamorphic Complex, which was highly partially melted and metamorphosed during the Damara Orogenic Event. The timing of magma emplacement has been investigated; however, the petrogenesis is unclear. Here we reported petrology, geochemistry, and monazite U-Pb age data from biotite granitic gneisses, syeno-granite, syeno-granitic pegmatites, syeno-granitic gneiss, granitic syenite and biotite quartz monzonites of this complex. Geochemical data suggest that these Paleoproterozoic rocks show high SiO2, Al2O3, and K2O, moderate Na2O, low CaO and Fe2O3, and MgO abundance. The alkali-calcic to alkalic, peraluminous, low Fe-number, depletion in HFSE (Nb-Ta, Ti) and enrichment in LILE (e.g., Rb, Pb) characteristic correspond with I- and S-type granite. Major and trace elements are strongly fractionated with the increase of SiO2, which, together with strongly fractionated LREE patterns and high (La/Yb)N ratios of the biotite granitic gneiss and syeno-granitic gneiss, suggest that the magma was highly evolved and fractionated. Monazite U-Pb data show three metamorphic age groups of 581–535 Ma, 531–522 Ma and 518–484 Ma. The increasing trend of La/Sm and La/Yb with the increase of La, suggest these rocks most likely experienced a partial melting process during the late Palaeozoic metamorphism. We, thus, propose a fractional crystallization model for the generation of the Paleoproterozoic Abbabis Metamorphic Complex basement rock, which was metamorphosed and melted during the late Palaeozoic Damara Orogenic Event and provided the magma sources for primary uranium mineralization.

A New Insight into the Structural Framework of a Crystalline Formation and the Adjoining Sedimentary Terrain in Parts of the Precambrian Basement Complex of Nigeria

A New Insight into the Structural Framework of a Crystalline Formation and the Adjoining Sedimentary Terrain in Parts of the Precambrian Basement Complex of Nigeria

Geological and Hydrogeophysical Investigation of Angwan Zakara, Keffi Sheet 208N.E of North Central Nigeria

The geological and hydrogeophysical assessment of the groundwater prospect/potential in Angwan Zakara and its environs, Karu Local Government, Nasarawa State, North-Central, Nigeria has been carried out in this study. The study area covers 25km2.The area is underlain by the Basement Complex of the North-Central Nigeria consisting of Medium grained biotite granite, biotite gneiss, phyllite and un-mappable muscovite schist with structural features such as joints, veins, foliation, faults, and xenoliths trending NW-SE direction. Forty Nine (49) Vertical Electrical Sounding were carried out in the study area using Omega Resistivity Terrameter, GPS12 Garmix with a maximum cable spread of AB/2=100m and MN/2=5m. The results obtained from the field data were interpreted using IXID Software for quantitative analysis. True resistivity map, piezometric map, basement resistivity map and depth to basement map were prepared and interpreted using computer software for qualitative analysis (SURFER 8). From the IXID interpreted results, five (5) curve types were obtained from the acquired data namely A, H, KH, AH, and HK curve types are the dominant. The study area showed depth to basement ranges from 20-90m. That revealed good groundwater potential. The study area revealed 4-7 lithologic sequences consisting of top soil, laterite, clay, weathered/ fractured basement however the host rocks in the study area are biotite granite, quartzite and schistose-gneiss. The results obtained shows that the direction of water flows revealed five ridges R1-R5 and four depressions D1-D4 with receptacles trends of the ridges are R1 and R2:NW-SE; R3 N-S, R4 : NE-SW and R5; E-W. The geoelectric sections were produced and correlated with the geology of the study area and it was found to be in conformity with the each other. Based on this, the study area is zoned into three namely good, moderate and poor groundwater potential zones.

Mineral exploration of Iwo-Apomu Southwestern Nigeria using aeromagnetic and remote sensing

The tectonic framework, lithostructural and mineralised zones of Iwo-Apomu region of Precambrian Basement Complex rocks were investigated using integrated aeromagnetic and satellite remote datasets. Fast Fourier Transforms (FFT) performed on aeromagnetic data were: Butterworth Filter (BF), Reduction to Magnetic Equator (RTE), Regional field, Residual field, Tilt-Angle Derivative (TDR), First and Second Vertical Derivative (FVD and SVD), Tilt angle and Total horizontal derivative (TDR and TDHR), and Total Gradient Amplitude (TGA); which range from −31.97 – 123.24, −27.12 – 131.75, 1.52 – 117.90, −58.55 – 50.42, −1.35 – 1.36, −0.0712 – 0.0643, 0.0004 – 0.0102, 0.005 – 0.261 respectively. Continuations and Radially Average Power Spectrum; revealed the variations of the deep-seated basement rocks, the structures and the mineralised anomalous bodies with depth. The upward continuation maps also show that the regional trends of the mapped lithologies and lineaments/faults in the area are generally in NW-SE, E-W, and NW-SE directions. These filters defined the lithostructures, lithological boundaries, geological structures, contacts, faults, folds and mineral deposit. The results of satellite data on Principal Component Analysis (PCA), False Colour Composite (FCC) images and Band Ratio (BR) discriminated the different rock types, lithostructural boundaries and alteration zones that hosted the mineralized ore bodies which trend in NE–SW and minor NW–SE and E–W directions. The combined techniques generated showing the probable positions and trend of suspected fault/fracture, mineral deposit as well as other basement structures.

Factors controlling gully morphology on the quartzite ridges of Ibadan, Nigeria

Gullying processes on sedimentary terrains have received significant attention from researchers while such processes are often overlooked in Basement Complex areas because of their perceived resistance to denudation. In an attempt to address this deficiency, we evaluated the nature and variation in gully morphology on a Basement Complex. Three gully systems on prominent quartzite ridges of Ibadan, Southwestern Nigeria were examined: Mokola, Mapo, and Eleyele quartzite ridges. Slope angles of gullied areas were recorded along with observations on slope convexity/concavity and vegetation cover. Gully morphological characteristics of length, width, depth and depth of gully head were measured in the field, and were used to calculate width/depth ratios and gully sinuosity, shape, and volume. Gully bank soil was sampled at a depth of 0–30 cm and 23 samples were analyzed for particle size composition, pH, Electrical Conductivity (EC), Organic Matter (OM), Sodium Adsorption Ratio (SAR) and Exchangeable Sodium Percentage (ESP) using standard laboratory techniques. These parameters showed considerable variation within and between sites. The mainly reddish indurated layer of the channel beds was predominantly composed of sandy clay and gully banks exhibited significant evidence of piping and tunneling. Our study showed that SAR (r = 0.794) and ESP (r = 0.867) were positively correlated with gully cross-sectional area, and SAR and ESP show positive relationships with total gully volume (an indicator of soil loss) ofr = 0.661 andr = 0.758 respectively. The relationship between gully volume and maximum depth reveals a Durbin-Watson value of 2.67 where R°2 = 0.826. The dominant factors of gully development on the ridges were identified as topography (slope shape and angle), soil properties (SAR and ESP), and land use/ human activities (urban growth). This study has identified the need to quantify the impact of lineaments on gully morphology dynamics on Basement Complex terrains.

Geophysical Evaluation of Central Nigeria Earth Tremor Activities using High Resolution Airborne Magnetic Data

The aim of this study is to investigate the actual causes of earth tremors in Central Nigeria using geophysical technique. Since 1933 till date (over 88 years), small to moderate magnitude earthquakes have either been observed or instrumentally recorded in Nigeria. However, the specific causes of the intra plate earthquakes in Nigeria is still not well known. In this study therefore, a high-resolution aeromagnetic data analysis was performed to evaluate the various theories proposed as the causes of tremor activity in central Nigeria with a view to ascertaining the actual causes of earthquakes in the West African country that lies on a stable crust. The total magnetic intensity data acquired from the Nigerian Geological Survey Agency (NGSA) in the Central Basement complex of Nigeria, was processed and filtered using the tilt derivative, lineament analysis, and advanced Analytic Signal- Hilbert Solution filter. To define the trends of both major and minor structure, a lineament plot was extracted and plotted. The analysis revealed a dominant NE-SW and NW-SE trending structure that is distributed throughout the study area. The regional North Atlantic Romanche fault system, which extends from the offshore (Niger Delta) into the continental crust, was mapped and is thought to extend from Gwagwalada in the study area's south, through Gwarinpa and Mpape, to Kwoi, and beyond Kafanchan.Findings from our study have indicated that, areas prone to Earth tremors are linked to the Romanche fault by numerous NE-SW and NW-SE faults that act as conduits for seismic energy that causes tremor. Using lineament density analysis, tremor active areas have been interpreted to be highly deformed; thus, seismic energy induced into the environment would result in tremors. This study demonstrates that the regional North Atlantic Romanche fault system is the primary source of seismic energy that causes the earth tremors in central Nigeria.

Geology and Geoelectrical Appraisal of Panda and its Environs parts of Gitata Sheet 187NE North-Central Nigeria

Geological mapping and Geophysical investigations were carried out in Panda and its environs, with the aim of studying the geology (rock types and their structural features; joints & fractures) and its groundwater potentials. The area is underlain by the Basement Complex rocks of the North Central Nigeria consisting of porphyritic granodiorite, migmatized-gneiss and mica schist. The structural features associated with rocks in the study area include; exfoliation, joints, fault, pegmatitic and quartz veins. Twenty eight (28) Vertical Electrical Sounding (VES) were carried out away from cultural interferences. Interpreted data shows a dominance of KH and H type curve. The quantitative and qualitative interpretations revealed weathered and fractured basement. Iso-resistivity of the true aquifer, depth to basement, basement resistivity and, piezometric maps were delineated. Out of the twenty eight VES,only areas within the center of the study area (Kuban SE, Tanga North, Panda market, Jababe, Idur West, Idur and MusheJaba) have been delineated as the most viable locations for good water potentials due to the resistivity value of the rock materials (fractured and weathered basement) around those areas (50Ωm - 200Ωm) and some of the structural features (fractures, joints and faults) which serves as secondary reservoir for groundwater on account of their low resistivity values due to the high conductivity of groundwater that occupies the voids and fissures of the rock. The potential for groundwater in the study area are moderate at AngwanKwaro, AngwanMaje, and Chandap North, Kukuri area where depth to basement is shallow and occupied by fresh basement rocks (porphyritic granodiorite). While the least expected yield lies in AngwanPaa North and GidanSarki North. The two types of aquifer in the study area are weathered basement and fractured basement. This study will serve as guide for groundwater exploration and development in the study area.

Physiochemical Analysis of Water from Some Selected Boreholes and Hand dug wells in Kaltungo, Gombe State, Northeast, Nigeria

The occurrence, storage, and distribution of groundwater in the Precambrian basement complex are influenced by different geological factors. Groundwater is never chemically pure; dissolution of substances takes place in the course of its percolation through the rocks leading to its acquisition of some of their chemical constituents. The purpose of the investigation is to determine the suitability of groundwater for domestic and industrial usage. Four samples were collected from boreholes and six from hand dug wells. Samples were analyzed chemically by using the DR/2010 Spectrophotometer and Digital Titrator while physical parameters where determine using the pH meter, and TDS meter. Hydraulic conductivity and transmissivity results range from 4.24 m/day to 72.63 m/day and 23.84 m2/day to 964.0 m2/day. The geochemical result obtained from the analysis of 10 water samples in the study area with an average values pH 6.82. Temp. 310C, colour (TCU) 1.00, Turbidity 1.2, Conductivity 174.5TDS 87.7 mg/l, which revealed that the water physical parameters are below the WHO permissible value. Total Hardness 161.7mg/l, Ca2+ 64.3mg/l Na+ 68.8mg/l, NO3+ 0.1 mg/l Fe2+ 0.04 mg/l CO3 96.4 mg/l Sulphate 47 mg/l Cl- 96 mg/l and F- 0.3 mg/l. Results obtained of the water analysis reveals that the concentration of Total Hardness and F- in some parts of the study area are above the permissible standard for drinking water WHO Standard. Therefore, the water in the affected part of the study area should be subjected to proper treatment. The groundwater flow direction is from higher surface elevation to lower surface elevation.

Modeling the Interface Between the Social Geosystem and the Environment

Abstract. This article deals with the context of a new rationality in modeling due to the climate agenda and the introduction of ESG-type principles. We studied a geosystem with homogeneous ecosystems that have a similar geological basement, relief mesoforms, and industrial-territorial complexes. They function in a unified institutional climate. In this case, the focus was on the mesoscale of the systems. The institutional order was based on the relationship between private and general institutions, and organizational features of regions. The Dixit-Stiglitz monopolistic competition model was used to account for financial performance and utility in an equilibrium industry with high nature intensity. What was new was the introduction of the concept of social brands associated with ecosystem services and used simultaneously to account for the utility and customization of the new economic order, as well as the introduction of a social discount rate (a discount factor). Social brands create a certain ‘green’ meaningful context in relation to natural capital and acting brands through social platforms. Thus, the society, through the mechanism of social brands, is offered a new format of interactions in which the structure of social brands becomes a priority in relation to the productive structure of the economy.
 Keywords: climate agenda, natural and social geosystems, utility, social discount, social brand

Assessment of a New Dam Site for Water Supply Potential in Bauchi Metropolis, Nigeria

The maximum yield of 90,000 m3 /day from the existing Gubi dam in Bauchi will barely meet the water demand beyond 2030 at an average water use of 100 litres per capita/day. For higher water demand of up to 250 litres per capita/day expected in an urban centre, the existing dam capacity is inadequate, and the demand should grow to 253,102 m3/day by 2037. This is the rationale for this study, which showed the feasibility of a new dam through technical reviews and analysis of topography, hydrology of the site, field and laboratory investigations, computer analyses and designs. Hydrologic simulation of rainfall-runoff processes for 57 years of rainfall data using the Soil Conservation Service (SCS) method gave an annual runoff volume of 59 Mm3 on a stream in Miri, which can be harnessed to assure adequate water supply in the metropolis. This will require the construction of a 25 m high embankment dam. Topographic survey and analysis indicated that the proposed site has good water retention capability. Although net flow adjustment analysis showed a high evaporation loss of up to 13.5 Mm3 annually, seepage loss is expected to be small in view of the underlying basement complex rock formation.

Application of 2d Electrical Resistivity Imaging for Mineral Ore Exploration Within a Basement Complex Formation

A geophysical survey using electrical resistivity was carried out in Gbede community within latitude (8˚17’37.7”N-8˚17’49.8’’N) and longitude (4˚20’45.9’’E - 4˚20’58.8’’E) area of Oyo State southwestern Nigeria. The survey was to determine the location and the lateral extent of the suspected Iron Ore deposited in the area using 2D resistivity imaging.using a resistivity meter, Wenner array configuration and electrode spacing ranging from 5 – 25 m was implored in the survey. Five (5) electrical profiles each with 120 m long were conducted within the area. The RES2DINVsoftware was used on the data acquired for processing and inversion. The result of resistivity imaging revealed the lateral continuity of mineral ore deposit within the first layer(top soil) with resistivity values ranging from 395 Ωm to 6619 Ωm at a mean depth of 13m. These values of resistivity suggest the presence of mineral ore in the form of magnetite and hematite which all constituted over 69% of iron in the study area.

Application of geophysical method to delineate Kaolin deposit at Kankara, Northwestern Nigeria

Area around Kankara Local Government Area of Katsina State, which lies within the Northern Nigerian Basement complex, is considered as one of the most prospective regions for Kaolin mineralization in Nigeria. A geophysical survey involving aeromagnetic and electrical resistivity survey was employed to delineate the fault and features that may be related to the mineralization. The aeromagnetic map results which included the first and second vertical derivatives and analytical signal map, revealed that a continuous linear feature trends Northwest to Southeast direction and Northeast to Southwest direction with a few traces along East-West and North-South. The electrical resistivity tomography was taken at a mining site along which the fault line passes through. It revealed that the Kaolin mineral lies within the overburden and weathered layer, with depth approximately 10-15m, extending from East -West.

Interpretation of gravity data of Hadejia and its environs using tilt angle derivative method

Tilt angle derivative method was applied to satellite gravity data of Hadejia and surrounding for subsurface delineation. The study area falls in the contact region between Chad sedimentary formation and the crystalline basement complex in the Northeastern Jigawa state and Northwestern Yobe state of Nigeria which lies between latitude 80N - 140N and longitude 110E -130E. Satellite gravity data of the area was obtained from Bureau Gravimetrique International (BGI). The Bouguer correction was already applied on the data and the Bouguer graph was plotted using surfer software. Low gravity anomalies are detected in the dominant part of the map with its minimum value appearing in the south-eastern and north-eastern part of the map. The low anomalies are probably due to existence of thick sedimentary sections in these parts of the study area. Edges and Depth of the source of anomaly were also derived from the tilt angle. The tilt angle ranges between -3.5 degrees to 3.5 degrees with edges(boundary) at zero. This describes the edges/boundaries between the two formations. The method also revealed that the area has a depth ranging between 2km to 18km. The sedimentary areas were identified and isolated. Those areas with low anomaly and high depths are sufficient for hydrocarbon accumulation.

Evolution of the 3.65–2.58 Ga Mairi Gneiss Complex, Brazil: Implications for growth of the continental crust in the São Francisco Craton

The composition and formation of the Earth’s primitive continental crust and mantle differentiation are key issues to understand and reconstruct the geodynamic terrestrial evolution, especially during the Archean. However, the scarcity of exposure to these rocks, the complexity of lithological relationships, and the high degree of superimposed deformation, especially with long-lived magmatism, make it difficult to study ancient rocks. Despite this complexity, exposures of the Archean Mairi Gneiss Complex basement unit in the São Francisco Craton offer important information about the evolution of South America’s primitive crust. Therefore, here we present field relationships, LA-ICP-SFMS zircon U-Pb ages, and LA-ICP-MCMS Lu-Hf isotope data for the recently identified Eoarchean to Neoarchean gneisses of the Mairi Complex. The Complex is composed of massive and banded gneisses with mafic members ranging from dioritic to tonalitic, and felsic members ranging from TTG (Tonalite-Trondhjemite-Granodiorite) to granitic composition. Our new data point to several magmatic episodes in the formation of the Mairi Gneiss Complex: Eoarchean (ca. 3.65–3.60 Ga), early Paleoarchean (ca. 3.55–3.52 Ga), middle-late Paleoarchean (ca. 3.49–3.33 Ga) and Neoarchean (ca. 2.74–2.58 Ga), with no records of Mesoarchean rocks. Lu-Hf data unveiled a progressive evolution of mantle differentiation and crustal recycling over time. In the Eoarchean, rocks are probably formed by the interaction between the pre-existing crust and juvenile contribution from chondritic to weakly depleted mantle sources, whereas mantle depletion played a role in the Paleoarchean, followed by greater differentiation of the crust with thickening and recycling in the middle–late Paleoarchean. A different stage of crustal growth and recycling dominated the Neoarchean, probably owing to the thickening of the continental crust by collision, continental arc growth, and mantle differentiation.

Thermal history along the Araçuaí Orogen and São Francisco Craton border, eastern Brazilian continental margin, based on low-temperature thermochronologic data

Passive margins form in response to rifting affecting a continental area. Rifting evolution is dependent on structural and rheological inheritance, generally controlling differential denudation, and deposition. The Brazilian continental margin developed over a complex basement, composed of the orogenic lithosphere of the Brasiliano-Pan-African orogenic belts (e.g., the Araçuaí Orogen), and the cratonic lithosphere of the São Francisco Craton. In this work, we focus on the transitional zone between the warm and cold lithosphere of the northern segment of the Araçuaí Orogen to the São Francisco Craton. This study provides the first suite of two low-temperature thermochronometers, i.e., zircon and apatite (UTh)/He, for the region. Using this approach, we examine the main cooling events, the geodynamic forces acting upon the lithosphere, the denudation rates affecting this region since West Gondwana amalgamation, and the correlation between thermochronology and structural inheritance. Our results indicate that ZHe corrected ages range from 483.1 ± 38.6 to 93.8 ± 7.5 Ma and eU concentrations vary from 10.91 to 632.51 mg/g. AHe corrected ages span from 129.9 ± 7.79 to 32.7 ± 1.96 Ma and eU concentrations range from 5.6 to 62.8 mg/g. Both ZHe and AHe ages display a positive correlation with eU concentration. Based on this dataset, we identify three cooling episodes, constrained from Lower Devonian to Carboniferous, Triassic/Jurassic to the present day, and Late Cretaceous/Paleocene to the present day. Additionally, two reheating episodes are constrained from Middle Jurassic to Early Cretaceous and from Late Cretaceous to Paleocene. Furthermore, we analyzed lineament directions in the orogenic, cratonic, and Cenozoic sedimentary cover domains to understand how structural inheritance affects the thermochronological record. Our observations reveal that reactivation of the Brasiliano NW-SE inherited structures during continental breakup up until the Paleocene possibly kept the AHe system open, resulting in the youngest AHe ages of our data set.

Radiogeochemistry, uranium migration, and radiogenic heat of the granite gneisses in parts of the southwestern Basement Complex of Nigeria

The radiogeochemistry of granite gneisses in Akunu-Akoko (AK) and Ayere (AY) areas of the southwestern Basement Complex of Nigeria was studied using gamma-ray spectrometry, and geostatistical analysis and modeling. This study was aimed at determining the concentrations of radionuclides (K, U, and Th) in these rocks, as well as alteration scenarios, nature and rates of uranium migration (UM), levels of radiological hazards, and rate of radiogenic heat production (RHP). The interquartile (lowest Q1 < highest Q2 < highest Q3) elemental concentrations for 40K, 238U, and 232Th were 0.23 < 3.75<4.06%; 1.00 < 4.20<5.40 ppm; and 4.10 < 16.10<30.20 ppm, respectively, within the minimum and maximum limits of BDL (below detection limit) to 5.23%, BDL–9.70 ppm, and 0.40–60.20 ppm. The average activity concentrations of 40K, 238U, and 232Th with values of 629.28, 38.58, and 49.96 Bqkg−1, respectively, were above their crustal averages in the order of AK3<AK2<AK3<AY3<AY1<AY2. Variability in K-eU-eTh content and alteration in the rocks were affirmed by radioelement ratios and F-parameter. The high radionuclide concentrations may be attributed to high levels of radioactive materials, as well as trace and rare earth elements. Low radionuclide concentration in rocks is due to weathering, metamorphism, and 12–86% outward UM. The absorbed dose rate (ADR) average of 75.09 nGyh−1 was within the allowable range, with regression R-squared (R2) prediction values of 25–92% from the radionuclides. The average radium activity was below the permissible limit of 370 Bqkg−1, and the annual effective doses, hazard indices, gamma activity, and activity utilization index were all far below the safe limit of 1 mSvy−1. However, gonad equivalent and excess lifetime cancer risk were above their permissible limits. RHP average of 1.89 μWm−3 above the crustal range of 0.8–1.2 μWm−3 will considerably contribute to the heat flux in the areas. Based on the prediction accuracy of the R2 results, 36–86% of RHP rates in the rocks are achievable from the radionuclides.

Geochemical composition of dykes along the Cameroon Line (CL): Petrogenesis and similarities with the Central Atlantic Magmatic Province

We report whole-rock geochemistry and Sr–Nd–Pb isotopic compositions of mafic dykes intruded in the Precambrian granito-gneissic basement complex, exposed at Nyos, Batibo, Dschang and Foumban on the Cameroon Line. The dykes are alkaline (Batibo), transitional (Foumban), and subalkaline (Nyos, Batibo and Dschang) with SiO2 of 45–54 wt% and MgO of 2–9 wt%, similar to dykes reported in other areas of the Cameroon Line (CL) and the Central Atlantic Magmatic Province (CAMP). The abundances of rare earth elements (REE) and the Primitive Mantle normalised patterns for the Nyos, Batibo and Dschang dykes are similar to those of MORB, indicating that the dykes formed at shallower depths by a higher degree of partial melting relative to the Foumban dykes and the alkaline lavas of the CL. The transitional basaltic dykes with steeper REE patterns have their sources at deeper levels in the lithospheric mantle, possibly the garnet-spinel transition zone and were generated by a lower degree partial melting of the lithospheric and plume components. The Nyos and Batibo subalkaline dykes show similar isotopic compositions with a spectrum extending from depleted (DMM-like) to enriched (EM1-like) mantle, indicating the similarity in their source components. The Dschang dykes show distinct isotopic characteristics with relatively unradiogenic Nd-Pb isotope compositions compared to the Batibo and Nyos dykes. The Foumban transitional dykes with characteristic wide ranges in Sr-Nd-Pb isotopic compositions reveal varying contributions from enriched mantle components (EM1 and EM2) in addition to its plume signature similar to those of CL lavas. The Nyos and Batibo dykes alongside other dykes on the CL have low TiO2 abundances (<2 wt%), negative PM-normalised Nb-anomalies, and moderately to strongly enriched REE patterns, and isotopic composition that overlaps with those of CAMP, suggesting a similar lithospheric origin.