A case for upward continuation as a standard separation filter for potential‐field maps

Jacobsen, Bo Holm

doi:10.1190/1.1442378

Cited by 370 publications

(177 citation statements)

References 11 publications

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“…It has a maximum at the altitude h 0 , corresponding to the optimal altitude of upward continuation of the Bouguer in the region. As such, the upward of the Bouguer to the altitude h 0 serves to eliminate the gravity related effect of the sources located beyond the altitude h 0 /2 which is the depth whose anomalies constitute a residual field [25].…”

Section: Methodsmentioning

confidence: 99%

Geophysical Signature Location in the South-West of Chad: Structural Implications

Benoit¹,

Nouayou²,

Victor³

et al. 2017

J Geol Geophys

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IntroductionChad corresponds to the mobile zone formed during the PanAfrican orogenesis that occurred at Proterozoic between 830 and 665Ma [1]. This mobile zone is bounded to the south by the Congo Craton, to the West by the West African Craton and to the NorthEast by the metacraton of the Sahara. It appears that the whole of the Precambrian formations were marked by a strong imprint during the Pan-African events.These Precambrian formations identified in Chad are distributed between the Tibesti massifs in the north, Ouaddaï in the east, Yadé (Mbaibokoum) in the south and the Mayo-kebbi in the South-west. They cover 15 to 20% of the surface of the national territory [2].The secondary formations appear in the Erdis basin (Cretaceous Nubian sandstone) and the Mayo-Kebbi (Lower Cretaceous and Middle Cretaceous) basin. They also constitute the filling of several pits in Southern Chad (Lake Chad, Bousso, Doba, Salamat). They are sandstones of the intercalary continental and those of the Cretaceous with lagoon and marine features. The Pala-Lame basin located in Mayo-Kebbi, in the Southwest of Chad near the border with Cameroon, is part of the Yadé massif, a large outcrop of the Precambrian basement which extends to Cameroon, the Republic of Central Africa, Congo and Gabon, and includes the Congo Craton [3].The region consists essentially of a large granite batholith (MayoKebbi batholith), containing septa of metamorphites and two strips of volcano-sedimentary metamorphic epikeal formations similar to the greenstone belts [3,4]. The whole is intersected by a series of intrusive and vein rocks, ranging from alkaline granite to ultrabasic rocks.Although the results of the various works cited above provided useful information over the study area, none of them proposed the cartography of the lineaments therein in a precise way. The latter is the objective of the present study. The Bouguer anomaly map of the study area has strong contrasts (gradients) that indicate discontinuities such as faults and flexures. In order to study these discontinuities, we conducted an analysis based on the horizontal gradient of the vertical derivative coupled with upward continuation and Euler's deconvolution. These approaches that have been successfully used in AbstractA Study is conducted in South-West of Chad with the goal of underlining the different lineaments of the region, which are entirely or partially hidden by the sedimentary cover. Different gravity data processing techniques including horizontal gradient of vertical derivative coupled with upward continuation and Euler's de-convolution are used. These methods revealed a number of lineaments describing gravity density discontinuities whose directions are N-S, NE-SW, ENE-WSW, and WNW-ESE at NNW-SSE. However, the predominant direction for major lineaments is WNW-ESE. The major lineaments associated to the faults are: F1, F2, F3, F6, F7, F8, F9, F10, F14, F21, F22, F23, F24 and F28. Euler's solutions indicate depths up to 9.2 km for the anomaly sources. Such lineaments are very usefu...

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Section: Methodsmentioning

confidence: 99%

Geophysical Signature Location in the South-West of Chad: Structural Implications

Benoit¹,

Nouayou²,

Victor³

et al. 2017

J Geol Geophys

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“…Spectral analysis is a technique widely used in gravity analysis to design filters that make it possible to obtain regional trends and eliminate short wavelength signals produced by shallow sources. Upward continuation is one of the most effective filtering techniques for potential field maps in the frequency domain (Jacobsen, 1987;Blakely, 1995). This transformation attenuates anomalies with respect to wavelength; the shorter the wavelength, the greater the attenuation.…”

Section: Methodsmentioning

confidence: 99%

Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications.

Granja-Bruña

Vegas²,

Domingo

et al. 2015

Journal of Iberian Geology

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(M.A.S.D.); amunoz@ucm.es (A.M.M.); ssainz-maza@fomento.es (S.S.M.A)Received: 12 January 2015 / Accepted: 5 July 2015 / Available online: 20 July 2015 AbstractThe origin of the intraplate volcanism in the Calatrava Volcanic Province (CVP) is controversial. On the basis of its geochemical signature, it has been ascribed to an "aborted" rift, implying lithospheric thinning. However, the volcanism occurred during the generalized Cenozoic NW−SE-oriented compressive tectonic regime. On the other hand, on the basis of evidence for its deep-seated origin, it has been linked to the existence of a baby-plume detached from an active megaplume below the Canary-Azores Islands and the western Mediterranean. In order to understand better the aforementioned geodynamic scenarios for the origin of the CVP, we address here the study of the lithosphere in the CVP and its vicinity by means of gravity analysis and 2+1/2D modeling. Gravity modeling results do not support the rifting model adopted for the intraplate volcanism occurred in the CVP because the crust shows a quasi-constant thickness. Density models suggest the existence of a sub-crustal, anomalous low-density block that could be underplated magmatic material at the base of the crust, suggesting that only a minor part of it intruded up into the crust and erupted. The localized magmatism of the CVP can be related to the combination of two factors: active, the gentle folding of the Iberian lithosphere and associated uplifting of the Variscan basement due to the NW-directed transmission of compressive stresses in the upper plate yielded by the subduction/collision in the south Iberian margin. The formation of the lithospheric folding in the Calatrava region results in a decrease of the pressure beneath the swell of the antiform that is likely to bring about basaltic magmatism below the swell; and one passive, the existence of a Variscan right-lateral shear band, which yields a weakened crust that facilitates the ascent of the magmatic materials. The relatively small volume, but large extension, of the volcanic outcrops could be associated with the preferential ascent of the magmas along the weakened crust of this NW−SE-trending Variscan shear band.Keywords: Calatrava, intraplate volcanism, gravity modeling, lithosphere structure, upward continuation Resumen El origen del volcanismo intraplaca en la Provincia Volcánica de Calatrava (CVP) es controvertido. En base a su signatura geoquímica se ha atribuido a la formación de un rift "abortado", implicando un adelgazamiento litosférico. Sin embargo, el volcanismo se desarrolló durante un régimen tectónico compresivo orientado NW-SE que fue generalizado en la región de Calatrava durante el Cenozoico. Por otro lado, en base a las evidencias de su origen profundo, se le ha relacionado con la existencia de una mini-pluma desconectada de una mega-pluma activa debajo de los archipiélagos de Canarias y Azores, y en el Mediterráneo occidental. Con el propósito de contribuir a la discriminación entre los escenarios geodinámicos mencionados...

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“…This depth is fixed by optimum upward continuation height h 0 . Indeed, on the basis of a model of basement made up of an assembly of thin layers, [44] showed that the power spectrum of regional and residual fields can be expressed in the form of:…”

Section: Estimation Methods Of the Investigation Depthmentioning

confidence: 99%

Evidence for the Upwelling of Mafic Bodies into the Upper Crust beneath the N40-50&#176;E Branch of the Pan-African Central Cameroon Shear Zone from Gravity Studies

Yap¹,

Nouayou²,

Tchato³

et al. 2018

OJG

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The existence of mafic bodies at mid crustal level beneath the Pan-African Central Cameroon Shear Zone is still a matter of debate. To provide additional constrains on this issue, the crust of the west region of Cameroon has been investigated using gravity data. Analyses of these data show N40-50˚E oriented iso-anomal contours in the Bafoussam area, interpreted as the N40-50˚E branch of the Central Cameroon Shear Zone. In addition, spectral analysis and 2.5D gravity modeling reveal intrusions of mafic bodies at depth between 3.2 and 14.2 km under N40-50˚E aligned volcanic centers, namely Mt Bambouto and Mt Mbapit. The above observations suggest a structurally controlled emplacement of the mafic bodies. In the light of the recent geophysical data, the interaction between the NE-ward channel flow operating at the bottom of the lithosphere or the asthenosphere upwelling and the Cameroon Shear Zone could better explain the magma upwelling in the upper crust. This result is the novelty of the present work.

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A case for upward continuation as a standard separation filter for potential‐field maps

Cited by 370 publications

References 11 publications

Geophysical Signature Location in the South-West of Chad: Structural Implications

Geophysical Signature Location in the South-West of Chad: Structural Implications

Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications.

Evidence for the Upwelling of Mafic Bodies into the Upper Crust beneath the N40-50&#176;E Branch of the Pan-African Central Cameroon Shear Zone from Gravity Studies

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A case for upward continuation as a standard separation filter for potential‐field maps

Cited by 370 publications

References 11 publications

Geophysical Signature Location in the South-West of Chad: Structural Implications

Geophysical Signature Location in the South-West of Chad: Structural Implications

Gravity modeling of the lithosphere in the Calatrava Volcanic Province (Spain): geodynamic implications.

Evidence for the Upwelling of Mafic Bodies into the Upper Crust beneath the N40-50&amp;#176;E Branch of the Pan-African Central Cameroon Shear Zone from Gravity Studies

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Evidence for the Upwelling of Mafic Bodies into the Upper Crust beneath the N40-50°E Branch of the Pan-African Central Cameroon Shear Zone from Gravity Studies