The Bangui Magnetic Anomaly in Central Africa in the Light of New Geological Evidence

Кочемасов, Г. Г.; Chuprov, A.

doi:10.1080/00206819009465765

Cited by 6 publications

(3 citation statements)

References 13 publications

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“…The anomaly has a crustal origin and is strongly related to the tectonic evolution and Precambrian history of the Saharan metacraton and Congo Craton, as also revealed by the satellite magnetometer data and reported in previous studies [25][26][27]. Geologically, it is located in the region of the deposited highly metamorphosed Precambrian rocks and has a Precambrian basement with large masses of magmatic rocks [28]. The formation of the anomaly is related to the bending of the lithosphere.…”

Section: Study Areasupporting

confidence: 73%

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

Lemenkova

Debeir

2023

Minerals

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The interactions between the geophysical processes and geodynamics of the lithosphere play a crucial role in the geologic structure of the Earth’s crust. The Bangui magnetic anomaly is a notable feature in the lithospheric structure of the Central African Republic (CAR) resulting from a complex tectonic evolution. This study reports on the coherence in the geophysical data and magnetic anomaly field analysed from a series of maps. The data used here include raster grids on free-air altimetric gravity, magnetic EMAG2 maps, geoid EGM2008 model and topographic SRTM/ETOPO1 relief. The data were processed to analyse the correspondence between the geophysical and geologic setting in the CAR region. Histogram equalization of the topographic grids was implemented by partition of the raster grids into equal-area patches of data ranged by the segments with relative highs and lows of the relief. The original data were compared with the equalized, normalized and quadratic models. The scripts used for cartographic data processing are presented and commented. The consistency and equalization of topography, gravity and geoid data were based using GMT modules ‘grdfft’ and ‘grdhisteq’ modules. Using GMT scripts for mapping the geophysical and gravity data over CAR shows an advanced approach to multi-source data visualization to reveal the relationships in the geophysical and topographic processes in central Africa. The results highlighted the correlation between the distribution of rocks with high magnetism in the central part of the Bangui anomaly, and distribution of granites, greenstone belts, and metamorphosed basalts as rock exposure. The correspondence between the negative Bouguer anomaly (<−80 mGal), low geoid values (<−12 m) and the extent of the magnetic anomaly with extreme negative values ranging from −1000 to −200 nT is identified. The integration of the multi-source data provides new insights into the analysis of crustal thicknesses and the average density of the Earth in CAR, as well as the magnitude of the magnetic fields with notable deviations caused by the magnetic flux density in the Bangui area related to the distribution of mineral resources in CAR.

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Section: Study Areasupporting

confidence: 73%

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

Lemenkova

Debeir

2023

Minerals

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“…Therefore, one needs to use heat flow measurements such as those recently compiled for the United States interior by the Geothermal Laboratory at Southern Methodist University (Blackwell et al, 2011). (Kochemasov and Chuprov, 1990;Hemant and Maus, 2005b). These domains may constitute and Wyoming (e.g., Smith and Griffin, 2005;Facer et al, 2009).…”

Section: Geotherms -mentioning

confidence: 99%

Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior

et al. 2014

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The interpretation of satellite magnetic information (Magsat, Oersted, CHAMP, Swarm) requires understanding the mineralogy of crustal and mantle sources. Also, spectral analysis of magnetic data over forearcs and cratons calls for upper mantle contribution. The prospect of such a contribution contradicts the view that the mantle is too hot and too weakly magnetic to influence magnetic anomalies. Here we examine the rock magnetic properties of fresh mantle xenoliths from four settings across the United States: phlogopite-spinel dunites from the Bearpaw Mountains, Montana, and lherzolites/harzburgites from San Carlos, Arizona; Kilbourne Hole, New Mexico; and Knippa, Texas. Paleomagnetic results show single-component natural remanent magnetizations (NRM), which, combined with optical and secondary electron microscopy support the lack of post-*Manuscript Click here to download Manuscript: TECTO9071R.docx Click here to view linked References TECTO9071R-4/13 eruption alteration and absence of host-rock contamination. The NRM carriers include magnetite at Bearpaw Mountain and San Carlos, and pyrrhotite at Kilbourne Hole and Knippa. These four areas show continental crust of distinct thicknesses and various geotherms. The potential mantle contribution to magnetic anomalies is forward modeled using crustal thickness, current geotherm and average magnetic properties of xenoliths. The San Carlos and Kilbourne Hole mantle, situated near the Rio Grande Rift is too hot and too weakly magnetic to contribute to anomalies. The sulfide-dominated assemblage at Knippa does not support magnetization at mantle depths. In contrast, the Bearpaw Mountains combine a relatively cold geotherm (craton) and abundance of magnetite formed at mantle depth. This cratonic mantle, metasomatised by fluids from the Farallon plate, may contribute to long wavelength magnetic anomalies.

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“…In several cold geotherm areas, such as the Amsaga belt in the West Africa Craton or the Bangui region in the Central Africa Craton, magnetization may extend into the lithospheric mantle (Kochemasov and Chuprov, 1990;. Overall, mantle contributions to magnetic anomalies, at least in some regions, are acknowledged to be likely (e.g., Thébault et al, 2010;Purucker and Clark, 2011).…”

Section: Reason 1 Mantle Contribution To Lwma Deduced From Satellitementioning

confidence: 99%

Eight good reasons why the uppermost mantle could be magnetic

et al. 2014

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Wasilewski et al. (1979) concluded that no magnetic remanence existed in the uppermost mantle and that even if present, such sources would be at temperatures too high to contribute to long wavelength magnetic anomalies (LWMA). However, new collections of unaltered mantle xenoliths indicate that the uppermost mantle could contain ferromagnetic minerals. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 2/39This is most easily explained as a thermoremanent magnetization acquired by pre-existing ferromagnetic minerals as xenoliths cool rapidly at the Earth's surface from magmatic temperatures, acquired during ascent. 7. Modern experimental data suggest that the wüstite-magnetite oxygen buffer and the fayalite-magnetite-quartz oxygen buffer extend several tens of km within the uppermost mantle. 8. The magnetic properties of mantle xenoliths vary consistently across tectonic settings. In conclusion, the model of a uniformly non-magnetic mantle should be revisited.

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The Bangui Magnetic Anomaly in Central Africa in the Light of New Geological Evidence

Cited by 6 publications

References 13 publications

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

Coherence of Bangui Magnetic Anomaly with Topographic and Gravity Contrasts across Central African Republic

Craton vs. rift uppermost mantle contributions to magnetic anomalies in the United States interior

Eight good reasons why the uppermost mantle could be magnetic

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