Preliminary results of the upper mantle conductivity structure in Nigeria

Oni, Ebun; Alabi, A. O.

doi:10.1016/0031-9201(72)90089-1

Cited by 13 publications

(8 citation statements)

References 5 publications

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“…However, a marked difference in lithospheric mantle depth was observed between the mobile belt and the craton. While Ritz (1984) used on the order of 20 MT sites, Oni and Alabi (1972) in Nigeria concluded that 3 MT sites were insufficient to obtain reliable models of the subsurface and subsequent tectonic interpretation. Nevertheless, Oni and Agunloye (1976) already developed a 3D forward model in an attempt to explain the results of their three MT sites in Nigeria.…”

Section: Pioneering Em Work In Africamentioning

confidence: 99%

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Weckmann

2011

Surv Geophys

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The African continent inherits a long history of continental accretion and breakup. The stage of "making" a continent goes back to the Archean, when the first continental masses formed cratons which mostly remained stable ever since. Subsequent collision of weaker continental masses was followed by several extension and compression episodes that resulted in the formation of supercontinents. After the assemblage of Gondwana, a period of predominantly "breaking" , i.e. the breakup of supercontinents, took over. The modern day African continent exhibits different types of margins; continental rifting occurs side by side with recent collision. Since the late 1960's Magnetotelluric (MT) experiments have played an important role in studies of the electrical conductivity structure of Africa. The early results significantly shaped the MT community's understanding of continental scale conductivity belts and basic characteristics of cratons and mobile belts on both crustal and lithospheric mantle scale for some decades. Modern MT studies in Africa have generally supported earlier results with high resistivities observed on cratons and low resistivities observed across mobile belts. Advances in instrumentation, data processing and interpretation resulted in higher resolution images of the lithosphere which in consequence induce an improved understanding of tectonic processes and geological prerequisites for the occurrence of natural resources. The high electrical conductivity of mobile belts and their relation to reactivated fault and detachment zones were often interpreted to characterize mobile belts as tectonic weak zones, which can accommodate stress and constitute zones along which continents can break. Recent breaking of the African continent can be studied on land across the East African rift; however, the lack of amphibian MT experiments across today's margins does not allow for good resolution of remnants of continental break-up processes. Naturally, the regions and the focus of the MT studies in Africa are diverse, but they all contribute to the story of making and breaking a continent.

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Section: Pioneering Em Work In Africamentioning

confidence: 99%

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Weckmann

2011

Surv Geophys

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“…Oni & Alabi (1972), using the geomagnetic depth sounding (GDS) method, inferred that a layer of increased conductivity at Ibadan, Kotangora and Zaria in Nigeria lies between 55 and 75km depth. Their interpretation of the data from the observation sites took into account a sinusoidal spatial source field above a stratified earth model.…”

Section: Introductionmentioning

confidence: 99%

Analysis of geomagnetic variations in south-western Nigeria

Ogunade

1995

Geophysical Journal International

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S U M M A R YGeomagnetic variations, observed a t 11 sites in south-western Nigeria, have been analysed t o derive interstation transfer functions with the site at Ile-Ife as reference station. T h e study involves frequencies from 1 t o 6 c.p.h. T h e reference station Ile-Ife is 160 km northward of the continental slope off the Nigerian coastline and 400 km southward of the dip equator. T h e analysis has been carried out separately with selected data sections of a few hours length during daytime and during the night. Thus expressed linear relations between field components are in the case of day events of dual implication: (1) for the source field structure of the equatorial electrojet, (2) for internal conductivity conditions, including the coast effect from the Bight of Benin. Conductivity anomalies are the sole cause for an observed spatial variability of night events. A 2-D thin-sheet conductivity model has been derived taking both the source and the coast effect into consideration. This model provides a reasonably good fit between observed and computed transfer functions during day a n d night.

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“…FORBUSH and CASAVERDE (1961), ONWUMECHILI and OGBUEHI (1967), SHUMAN (1970), DUHAU and ROMANELLI (1979), ONI and ALABI (1972), CAIN andSWEENEY (1972), andONWUMECHILI (1981 a, b), AGU (1981a, b, 1983) reported the presence of internal currents associated with the electrojet.…”

Section: Introductionmentioning

confidence: 99%

“…ONI and ALABI (1972) analysed data obtained from Ibadan, Zaria and Kontagora and showed that the average depth of the layer of increased conductivity in the upper mantle at the three stations is within the range 55-75km. Further ONI and AGUNLOYE (1976) carried out a geomagnetic depth sounding survey of Ibadan, Okitipupa and Igbanke from which they concluded that half space high conducting material of the mantle most probably lies with a horizontal top at a depth of 80km in Nigeria.…”

Section: Introductionmentioning

confidence: 99%

A profile study of geomagnetic variations in the Nigerian equatorial electrojet region.

Ezema¹,

Onwumechili²

1984

J. geomagn. geoelec

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strong non-uniform source field of the jet for day effects to make a sounding of average electrical conductivity as a function of depth. Results obtained from the analysis of data show consistency with FoRBUSH and CASAVERDOE (1961) and with ONWUMECHILI and OGBUEHI (1967). A model based on the observed Sq shows that the depth of penetration is about 600 km while a model based on the day time fast fluctuations shows that at periods of about one hour the depth of penetration lies between 400km and 600km.

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Preliminary results of the upper mantle conductivity structure in Nigeria

Cited by 13 publications

References 5 publications

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Making and Breaking of a Continent: Following the Scent of Geodynamic Imprints on the African Continent Using Electromagnetics

Analysis of geomagnetic variations in south-western Nigeria

A profile study of geomagnetic variations in the Nigerian equatorial electrojet region.

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