2024-03-28T18:29:35Zhttps://www.tdx.cat/oai/requestoai:www.tdx.cat:10803/4006172017-08-31T14:58:22Zcom_10803_1col_10803_70
nam a 5i 4500
Geodinàmica
Geodinámica
Geodynamics
Cratons
Cratones
Àfrica
África
Africa
The lithospheric structure of Africa: Mapping crustal and lithospheric thickness using geoid and elevation constraints together with a thermal analysis
[Barcelona] :
Universitat de Barcelona,
2017
Accés lliure
http://hdl.handle.net/10803/400617
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Globig, Jan,
autor
1 recurs en línia (200 pàgines)
Tesi
Doctorat
Universitat de Barcelona. Departament de Geodinàmica i Geofísica
2016
Universitat de Barcelona. Departament de Geodinàmica i Geofísica
Tesis i dissertacions electròniques
Fernàndez Ortiga, Manel,
supervisor acadèmic
Torné Escasany, Montserrat,
supervisor acadèmic
TDX
The African continent preserves a >3.7 Ga long geological record, which comprises stabilization of oldest crust in the Archean, late Proterozoic joining of first cratonic units that lead to the formation of Gondwana and later the supercontinent Pangea, and post-breakup Mesozoic and Cenozoic continental rifting with transition to active oceanic spreading in the Afar and Red Sea region. Today, most of Africa’s basement consists of Archean cratons and blocks flanked by Proterozoic mobile belts and is considered to be tectonically stable, as it largely escaped tectonothermal deformation since the late-Precambrian Pan-African orogeny. Yet, Africa is affected by a number of active processes, many of them as young as the Cenozoic Era, including widespread hotspot volcanism, active rifting in East Africa, large-scale doming in eastern and sub-equatorial Africa and intracratonic subsidence in the Congo. The link between old Precambrian stable basement and recent tectonic activity makes Africa an ideal laboratory to study the role of the crustal and lithospheric mantle structure on the observed deformation within the continent.
The main goal of this thesis is to provide new crustal and lithospheric thickness maps of the African mainland based on integrated modelling of elevation and geoid data and thermal analysis. The approach assumes local isostasy, thermal steady-state, and linear density increase with depth in the crust and temperature-dependent density in the lithospheric mantle. The obtained results are constrained by a new comprehensive compilation of seismic Moho-depth data consisting of 551 data points from active and passive source seismic experiments, and by published tomography models relative to lithosphere thickness.
The calculated crustal thickness map shows a north-south bimodal distribution with higher thickness values in the cratonic domains of southern Africa (38 - 44 km) relative to those beneath northern Africa (33 - 39 km). The most striking result is the crustal thinning (28 - 30 km thickness) imaged along the Mesozoic West and Central African Rift Systems. The crustal model shows noticeable differences when compared to previous global and continent-scale models, especially for regions to the north of the equator. After excluding the Afar plume region, where the modeling assumptions are not fulfilled, the model shows the best fit with the available seismic data (76.3% fitting; RMSE=4.3 km). The new crustal thickness map correlates better with geological structures and tectonic provinces as well as gravity anomalies, and shows a higher spatial resolution.
The resulting lithospheric thickness map shows large spatial variability (90 to 230 km), with thicker lithosphere related to cratonic domains and shallower LAB related to Mesozoic and Cenozoic rifting domains, which is in good agreement with seismic tomography models. Though the crustal and lithosphere thickness maps show similar regional patterns, major differences are found in the Atlas Mountains, the West African Rift System, and the intracratonic basins, i.e., the Taoudeni and Congo Basin, indicating strong strain partitioning most probably due to intra-lithospheric decoupling along the crust-mantle boundary. The effects of lateral variations in crustal density as well as the non-isostatic contribution to elevation in the Afar plume region, was estimated to be ~1.8 km, and are also discussed.
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