Geology & Geophysics Department Seminar: Friday, 9/18/20, 12pm, Zoom

Title: Igneous Ring Complexes and the African Plate

Speaker: Dr. Mohamed G. Abdelsalam

Professor of Geology, Oklahoma State University; Editor-in-Chief, Journal of African Earth Sciences.

https://geology.okstate.edu/bios/421-dr-mohamed-abdelsalam

Abstract: The African lithosphere was intruded by alkaline igneous complexes, often forming igneous ring complexes, throughout much of its geological history (from the Paleoproterozoic (2,000 Ma) to the Oligocene (25 Ma)) more than any other continent. These intrusions have significantly contributed to the growth of the upper continental crust of the continent. They are found in clusters, aligned along Paleoproterozoic – Neoproterozoic orogenic belts between cratons and metacraton of Africa. Their tectonic evolution is linked to the propagation of continental rifts and their enrichment in CO2 suggests the presence of significant amount of C02 in the lithosphere and asthenosphere. When found deformed, they are taken to define the location of ancient suture zones. Because of their emplacement near the surface (hypabyssal intrusions), their age can be used to estimate the age of the surrounding paleo-surfaces. Because of their enrichment in CO2, it is thought that their eruption and emplacement have contributed significantly to CO2 release into the atmosphere throughout the Earth’s geological history. Regardless of their importance, little effort has been spent to implement modern geophysical techniques to advance our understanding of the tectonic setting and lithospheric structure of igneous ring complexes in Africa. This work presents three examples of using aeromagnetic, radiometric, and satellite gravity data for studying igneous ring complexes in Africa. The first example shows the use of aeromagnetic, airborne radiometric, and satellite gravity data for mapping the near-surface structure of the Paleoproterozoic Singo Granite in Uganda and revealing it as a nested igneous ring complex formed through the migrating collapsing calderas. The second example highlights the use of aeromagnetic and satellite gravity data to examine the tectonic setting of the Neoproterozoic Chingale Igneous Ring Complex in Malawi and documenting it as marking the location of a Neoproterozoic suture zone. The third example outlines the use of the same geophysical data for lithospheric imaging of the Cretaceous Chilwa Alkaline Province in Malawi showing its formation as due to lithospheric stretching that led to decompression melting with the ascending melt partially accreted below the crust to form mafic magmatic under-plated body.