Petrographic evidence for regional burial metamorphism of the sedimentary rocks in the Lower Benue rift

Obiora, Smart C.; Umeji, A. C.

doi:10.1016/j.jafrearsci.2004.01.001

Cited by 52 publications

(21 citation statements)

References 19 publications

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“…Calc-alkaline rocks, which are the typical rocks of subduction zones (continental margin and island arcs), have not been found. The predominance of slaty cleavages over schistose foliations in the regionally metamorphosed sedimentary rocks in the Lower Benue rift (Obiora and Umeji, 2004) is in favour of the absence of penetrative compressive stress which is commonly associated with subduction zones. However, the deformation of the sedimentary rocks in the basin into a series of anticlinorium and synclinorium and identification of the pyroclastic rocks in the area of study as andesites had led some workers to propose a compressional (subduction) rather than an extensional tectonic setting for the Benue Trough (Farrington, 1952;Burke et al, 1971Burke et al, , 1972.…”

Section: Tectonic Settingmentioning

confidence: 99%

“…This suggests that the rocks are associated with compressional tectonism. Indications that this origin does not hold for the igneous suite of the Benue rift started emerging since the past two and half decades from petrographic and geochemical data on these rocks showing a predominantly alkaline character associated with an extensional, within-plate setting (Benkhelil, 1986;Maluski et al, 1995;Obiora and Umeji, 1995, 2004Obiora, 2002;Obiora and Ugwuonah, 2008). Although there are, at present, considerable geochemical data on the igneous rocks in the Benue rift, and most of the data do not contain trace-and rare-earth elements (REE) which are considered more reliable for tectonomagmatic classification and other aspects of petrogenetic studies.…”

Section: Introductionmentioning

confidence: 99%

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Tectonomagmatic origin of some volcanic and sub-volcanic rocks from the Lower Benue rift, Nigeria

Obiora

Charan

2011

Chin. J. Geochem.

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Petrological and geochemical studies on some volcanic and sub-volcanic rocks from the Lower Benue rift indicate that they are basalts, basaltic and doleritic sills, trachybasalt and trachyte which generally belong to the alkali basalt series. The alkaline affinity is clearly evident in both their normative and modal mineral compositions, as well as their chemical compositions. The generally high fractionation indices [(La/Yb) N ] are 7.06 to 17.65 for the basaltic rocks and 23.59 to 135. 35 for the trachytic rocks, against low values commonly seen in subalkaline (tholeiitic) series, with strong enrichments in the incompatible elements. All this strongly supports their alkaline affinity. The basaltic rocks are generally fine-grained and porphyritic, consisting of phenocrysts of clinopyroxene and olivine in the groundmass of the same minerals together with plagioclase. The clinopyroxene is either diopside or clinoenstatite. The trachyte consists of oligoclase, orthoclase, biotite, quartz and exhibits typical trachytic, flow structure. The basaltic and doleritic sills are commonly altered, with calcite and epidote as common alteration products. This alteration, which is reflected in the erratic behaviour of K 2 O, MnO and P 2 O 5 on Harker variation diagrams, high values of LOI, strong depletions in the more mobile LILE (Rb, K, Ba and Sr) and high Th/Ta ratios, is attributed to the effects of an aqueous fluid phase and crustal contamination. On the whole, the mineralogical, as well as major-, trace-elements and REE data suggest that the rocks are co-genetic and most likely derived from differentiation of an alkali olivine-basalt magma, generating through variable low degrees of partial melting of probably an enriched lithospheric (upper) mantle following an asthenospheric uplift (mantle plume or intumescence) with HIMU signatures in a within-plate continental rift tectonic setting. This corroborates earlier results obtained for the intrusive rocks in the region.

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Section: Tectonic Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Tectonomagmatic origin of some volcanic and sub-volcanic rocks from the Lower Benue rift, Nigeria

Obiora

Charan

2011

Chin. J. Geochem.

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“…Increase in PI denotes loss in strength, and plastic soils decrease in load bearing capacity as moisture increases (Emesiobi 2002). Obiora and Umeji (2004) observed the dominance of expansive minerals such as smectite>illite>kaolinite in the Abakaliki shale, Ezeaku and Awgu Formations. The volume changes due to humidity variations can result in either swelling or shrinking.…”

Section: Geotechnical Techniquesmentioning

confidence: 92%

“…Results obtained from the area with cracked buildings (problematic zone) will be compared with that from the noncracked area (non-problematic zone). Some authors like Manasseh and Olufemi (2004), Obiora and Umeji (2004), and Uduji et al (1996) have studied the mineralogical and geotechnical properties of this locality, but the novelty of this research work is to integrate some geotechnical and geophysical techniques in assessing the building collapse phenomenon because it gives a better understanding of the problem and hence solution can be proffered.…”

Section: Introductionmentioning

confidence: 99%

Integrating geotechnical and geophysical techniques in assessing frequent building collapse in Akpugo, Nkanu West L.G.A., Enugu State, Nigeria

et al. 2015

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Over the years, the people of Akpugo community in Nkanu West L.G.A., Enugu State, South-East Nigeria have suffered from frequent building collapse without knowing the cause. This study integrates geotechnical and geophysical techniques to evaluate possible factors responsible for this anomaly. Areas with cracked and non-cracked buildings were studied to assess the geotechnical properties of the soils. Samples were taken at different locations and subjected to x-ray diffraction analysis, grain size analysis, specific gravity, Atterberg limits, permeability, compaction, and triaxial tests. Electrical resistivity method was also used to delineate the geo-electrical layers and to image the lateral variations of the subsurface. Results revealed that problematic zone (areas with cracked buildings) has lower permeability (4.018-7.016× 10 −7 m/s), lower angle of shearing resistance (10-14°), and medium to high plasticity index (25.1-38.33), while the nonproblematic zone (areas without cracked buildings) has higher permeability (1.55-1.925×10 −6 m/s), higher angle of shearing resistance (15-18°), and low plasticity index (18.1-19.4). The x-ray diffraction results of the problematic zone revealed a significant amount of smectite which has a very high swelling and shrinkage potential. The presence of substantial quantity of smectite in the soils of the problematic zone may be a strong factor in the structural problems. The electrical resistivity profiling delineated the boundary between the problematic zone and non-problematic zone and showed that the problematic zone has lower resistivity values (2-25Ωm) while the nonproblematic zone has higher resistivity values (20-170Ωm).

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“…The sedimentary rocks of the Lower Benue Trough are the hosts of various igneous rocks (Obiora and Umeji, 2004 …”

Section: Geologymentioning

confidence: 99%

Geophysical investigation of the effects of sewage in the soil at university of Nigeria, Nsukka, Enugu State, Nigeria

Awalla¹

2014

Int. J. Phys. Sci.

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Geophysical investigation was carried out to detect the spread of sewage effluent and to locate the sources and delineate migration paths and the extent of leachate plume. The study was to find out the geological formations that are the most conductive layers in the sewage site for the free flow of the contaminants. Soil tests showed that hydraulic conductivity, bulk density and water retention were variable in sewage soil, but consistent in soil unaffected by sewage. In sewage soil, maize crops performance, organic matter, total nitrogen exchangeability, cations exchange capacity and sodium were significantly enhanced than in non-sewage soil. In sewage soil, electrical conductivity (EC), zinc (Zn), lead (Pb), copper (Cu), Cadmium (Cd), salt concentration and other saline properties, total faecal coliform and microbial activities were high. Twelve vertical electrical soundings (VES) points with Omega Terrameter were used in the Schlumberger Array configuration which the geoelectrical section from the resistivity data revealed seven subsurface layers. Three low resistivity zones were detected as correspondent zones to the plumes. The comparative evaluation of the 3-D stack model of the resistivity of layers with respect to depth suggested that these three low resistivity layers were contaminated, especially as the depth to water table is more than 100m. The flow direction of the contaminant plume is northwest to southwest as indicated by stack model of the low resistivity layers. Generally, the contaminant plume is a threat to ecosystem and a great health problem to people living around the sewage site.

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Petrographic evidence for regional burial metamorphism of the sedimentary rocks in the Lower Benue rift

Cited by 52 publications

References 19 publications

Tectonomagmatic origin of some volcanic and sub-volcanic rocks from the Lower Benue rift, Nigeria

Tectonomagmatic origin of some volcanic and sub-volcanic rocks from the Lower Benue rift, Nigeria

Integrating geotechnical and geophysical techniques in assessing frequent building collapse in Akpugo, Nkanu West L.G.A., Enugu State, Nigeria

Geophysical investigation of the effects of sewage in the soil at university of Nigeria, Nsukka, Enugu State, Nigeria

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