Abstract
A fundamental mechanism of some continental rifting processes appears to be the transmission of thermal energy into the lithosphere by asthenospheric upwelling (the ‘active’ mechanism of Sengör and Burke1), for which the East African rift system is a classic example. The abundance and variety of magma types of predominantly alkaline affinities in the East Rift which derive from the thermal perturbation suggest that studies of igneous petrogenesis may offer a method of investigating the physical as well as the chemical conditions of the upwelling. Systematic variations in the temporal–spatial–compositional relations of igneous rocks associated with rifts are becoming well documented for several different rifts2–13, and it is generally observed that the degree of silica-saturation of lavas within these rifts increases with time, while incompatible element contents decrease. Furthermore, at any given instant, lavas erupted within the rifts are less silica-undersaturated than lavas erupted outside the rift. These observations are consistent with decreasing depths of origin of magmas with time as would be predicted for magmagenesis associated with an upwelling source region. Here, by deducing the physical conditions of origin of various magmatic products associated with a thermotectonic event in East Africa, the rate of upwelling is calculated and compared with the results of a simple thermal model of lithospheric thinning.
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Wendlandt, R., Morgan, P. Lithospheric thinning associated with rifting in East Africa. Nature 298, 734–736 (1982). https://doi.org/10.1038/298734a0
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DOI: https://doi.org/10.1038/298734a0
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