Van Breugel Master's Thesis

Large Igneous Provinces (LIPs) form as a result of either mantle plumes, rifting, or subduction, with plume origins being favored in most cases. Each geodynamic setting provides geochemical and geochronological spatial patterns, which can be used to distinguish them. Detailed spatial context has not been considered for combinations of isotope and lithogeochemical data associated with most LIPs. Therefore, the Karoo & Ferrar and Parana-Etendeka LIPs are used to test this theory. Jurassic break-up of SW Gondwana and formation of the associated Karoo and Ferrar LIPs provide a useful test case because of the amount of data available and their known spatial context. Ages range from 183 Ma to 172 Ma. While the age range is close to 11 million years (m.y.), U-Pb ages correspond to a range from 183-179 Ma. Younger Ar-Ar dates coincide with the U-Pb ages, raising the possibility that Ar-Ar dates represent closure ages rather than igneous crystallization ages. Whole-rock lithochemistry illustrates distinct variable spatial patterns logically linked to a triple junction between Africa and Antarctica for the Karoo magmatism while coeval Ferrar activity is situated parallel to the original subduction margin of Gondwana. Extensive study on the Parana-Etendeka LIP associated with the Cretaceous break-up of South America and Africa provides a similar test case as the Jurassic Karoo & Ferrar LIPs, based on the amount of data available and their known spatial context. Geochronologically, Ar-Ar dates range from 137 Ma to 125 Ma with U-Pb ages set around 135-133 Ma. With an Ar-Ar age range of 12 m.y. coinciding with the U-Pb ages, Ar-Ar dates potentially represent cooling/closure ages rather than igneous crystallization ages. Whole-rock lithogeochemistry illustrates spatially distinct variations which differ from dyke swarm patterns linked to a triple junction between Africa and South America. Difference between initially assumed and newly assumed plume centers presents the idea that Parana-Etendeka magmatism is coeval to Atlantic rifting, rather than a direct cause of rifting. Comparison of these sets of LIPs provides similar results in identification of volcanic origins and magmatism. Presence of a continued heat source, most likely caused from plume-induced magmatism, suggests Ar-Ar dates represent cooling/closure ages. Other LIP test cases present effective use of whole-rock and isotope geochemical proxies in magmatic classification