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Long-term topographic evolution of the African plate, causes and consequences for surrounding lithospheric plates

Mansour, Sherif Elshahat Elsayed

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Abstract

The African lithospheric continent has an extended history over 3.8 Ga and is tectonically active since more than 2.9 Ga. Ever since the topography of that continent was changing under influences of a series of endogenic (tectonic) and exogenic (surface) processes. Generally the earth’s topography has major influences on the planet, examples include but are not limited to species distribution, forest succession, erosion, sedimentation, fluvial systems and climate. The topographic changes are accompanied by rock exhumations in either way of endogenic forces or as response to exogenic processes. These exhumation events could be traced by low temperature thermochronology (LTT) techniques. The LTT techniques date the rock passing through a certain isotherm (closure temperature) and are used to quantify the cooling rates. The closure temperature is function of the applied LTT technique and mineral type. Combining these cooling ages and LTT data with the time-temperature (t-T) modelling enables visualizing and quantifying the rock movement through the upper crust. Therefore, these combinations were used to compare and reconstruct the topographic changes in key areas dominated by various geologic environments as response to different magnitudes from multiple landscaping processes in the African continent. Furthermore, the ability of LTT to answer difficult questions related to landscaping processes (e.g., landslide detection and quantifying and the endogenic-exogenic processes relationship) was also tested. Comparing and reconstructing rift flanks uplifted areas (the Albertine Rift; the Rwenzori Mountains and the Gulf of Suez; the Samra Mountain area) on an old craton revealed a relatively long cycle of life. The non-uniform uplift through fault-bounded blocks was the dominant mechanism of response for all the induced far-field continental scale tectonics and surface processes. Only a uniform uplift was demonstrative during the rifting event. The thermochronological record of the Samra area has started earlier with the East African Orogeny (EAO) plutonism and accretion. Afterwards, both areas (the Rwenzoris and the Samra) were affected by the post orogenic erosional event. Shortly after, each area of them was affected differentially by a series of far-field tectonic events. Then, the rift started to activate affecting the whole areas with corresponding uplift. While the Gulf of Suez was nearly deactivated by the movement along the Dead Sea transform fault at mid-Miocene. The movement along the footwall of Bwamba fault caused additional uplift to the Rwenzoris at the Pliocene. On the other hand, comparing and reconstructing volcanic islands (Fuerteventura and La Gomera; Canary Islands) on passive margin revealed a relatively short cycle of life. That cycle started by emerging, followed by formation of the shield stage with adding a huge amount of magmatic materials forming a highly topographic island (Fuerteventura; ~20 Ma, La Gomera; ~10 Ma). Afterwards, the topography destruction starts with landsliding (Fuerteventura; ≤20 Ma, La Gomera; ~7 Ma) when suitable topographic and climatic conditions, among others, were dominated. Then the volcanic island experience other cycle, starting with constructing high topography by feeding with new magmatic materials till the hot spot related magmatic activities transfer to other regions. That activity shift was recorded by a lateral movement of the Canary plume materials beneath northwest Africa to west the Mediterranean Sea produced a track of intraplate volcanism through its course. Furthermore, LTT techniques were able to detect, differentiate, and quantify different landscaping events (including landslides) with various magnitudes in different geologic environments. - In rifted regions; the Rwenzori Mountains have experienced 4 rapid cooling/exhumation events. 1) the Silurian-Devonian (420- 390 Ma) event associated with ~3.5 (1.5) km of rock uplift as response to the post Pan-African orogeny deep erosional event. 2) The Triassic (240-220 Ma) event that caused ~3.0 km of rock uplift associated with rapid cooling and a major erosional event at the end of the Karoo sedimentary regime. 3) The Eocene- Miocene (52-10 Ma) event resulted in an average rock uplift of ~3.0 (0.2) km, the Early Eocene tectonic events were associated with India drifting afterwards the Eastern Rift activity was started. 4) The Pliocene-Pleistocene event (3-2.5 Ma) caused ~≤2.0 km of rock uplift along the footwall of Bwamba fault. The last two exhumation events with ~5 km of corresponding rock uplift produced the exceptionally high Rwenzori Mountains in the EARS extensional regime as a rift flank within two stages. The latter movement caused the tilt uplifting in the western flank of the mountains. While, the Samra Mountain area has experienced 5 rapid cooling/exhumation events. 1) The Neoproterozoic (775-640 Ma) event caused ~5.8 (0.1) km of rock uplift as a response to the accretion and plutonism during the EAO. 2) The Cambrian-Devonian (507-457 Ma) event causing ~5.6 (0.2) km of rock uplift as response to the post-EAO erosional event. 3) The Carboniferous-Permian (390-230 Ma) event resulted in ~4.2 (1.6) km of rock uplift as response to the Hercynian tectonic event. 4) The Jurassic-Cretaceous (170-70 Ma) event resulted in ~2.9 (0.5) km of rock uplift as a response to the Gondwana breakup. 5) The Oligocene-Miocene (27-22 Ma) event causing rock uplift of ~1.3 (0.3) km as response to the rift initiation. Additional reheating event was reported in the time span extending between the uplift associated with the Gulf of Suez and the prior cooling event causing an average subsidence of ~0.6 (0.3) km. - The Albertine rift flanks uplift is double the Gulf of Suez related flanks uplift which suggests an additional heat component during the Albertine rift formation. That heat component resulted from being the corresponding mantle plume directly beneath the EARS and more than 2000 Km away from the Gulf of Suez (Afar plume). - In volcanic islands; Fuerteventura Island has experienced two rapid cooling/exhumation events; one has started ~20 Ma with ~2.7 (0.5) km of corresponding rock uplift that caused the onset of the Fuerteventura landslide. The other has been initiated ~7 Ma with ~2.3 (0.2) km of corresponding rock uplift forming the doming stage on the western part of Fuerteventura ~5 Ma. Finally, these domes were eroded to nowadays surfaces. La Gomera Island also has experienced two rapid cooling/exhumation events; the first event has started between ~10 and 7 Ma with corresponding ~2.7 (0.2) km of rock uplift causing the onset of the La Gomera landslide. The second rapid cooling event occurred by ~4 Ma resulting in ~2 km of rock uplift. Finally, this topography was eroded to reduce elevation to nowadays surfaces

Item Type: Dissertation
Supervisor: Glasmacher, apl. Prof. Dr. Ulrich A.
Date of thesis defense: 18 December 2015
Date Deposited: 18 Jan 2016 07:59
Date: 2016
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Dekanat der Fakultät für Chemie und Geowissenschaften
Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Fakultät für Chemie und Geowissenschaften > Institute of Geography
Fakultät für Chemie und Geowissenschaften > Institut für Geowissenschaften
The Faculty of Physics and Astronomy > Institute of Physics
The Faculty of Physics and Astronomy > Institute of Environmental Physics
The Faculty of Physics and Astronomy > Kirchhoff Institute for Physics
Subjects: 500 Natural sciences and mathematics
530 Physics
550 Earth sciences
560 Paleontology Paleozoology
900 Geography and history
Controlled Keywords: Low-temperature thermochronology; Long-term landscape evolution; Canary Islands; Landslide Dating; East African Rift System; Albertine Rift; Rwenzori Mountains; Gulf of Suez; ; Arabian-Nubian Shield; Rift initiation; Rift Flanks Uplift; zircon; apatite; f
Uncontrolled Keywords: Low-temperature thermochronology; Long-term landscape evolution; Canary Islands; Landslide Dating; East African Rift System; Albertine Rift; Rwenzori Mountains; Gulf of Suez; ; Arabian-Nubian Shield; Rift initiation; Rift Flanks Uplift; zircon; apatite; fission-track; (U-Th-Sm)/He; t-T Modelling
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