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Structures and mechanisms of dyke emplacement at a volcanic rifted margin – AMS, microfabric analyses and geochronology of mafic dyke swarms from NW Namibia

Principal Investigators: Dr. Reinhard O. Greiling, Dr. Robert TrumbullGreilingRundeI

Mafic dyke swarms provide a record of the orientation, mechanism, and timing of crustal extension. The composition of emplaced magmas gives access to information on mantle and crustal input to melting and magma evolution. This project will incorporate both aspects in a study of the largest mafic dyke swarm in Namibia. The planned work will build on extensive existing geochemical datasets and will concentrate on aspects of timing and mechanisms of magma emplacement. Quantitative ages of dyke emplacement will be provided by a program of Ar-Ar dating. Field work and sampling will be guided by previous remote sensing, field and geochemical studies of mafic dykes in the Henties Bay-Outjo dyke swarm from coastal and inland NW Namibia. It will comprise structural work on dykes and host rocks in order to assess potential reactivation of older structures. For the structural and tectonic aspects of dyke emplacement, the main focus is application of the AMS (anisotropy of magnetic susceptibility) method, backed up by careful magnetomineralogy, to determine the degree and orientation of flow fabric in the dykes and thus understand the dynamics of magma flow and intrusion within the continental crust during continental rifting. Post-intrusion tilting of dykes is to be tested by palaeomagnetic work. AMS will also be applied to test for postintrusion structural overprints. These fabric studies will be complemented by microstructural work. It is expected that the project will provide important new information on the timing and the interrelationships of extensional tectonics and magma emplacement during continental break-up and evolution of the volcanic continental margin