Source and petrogenetic evolution of tholeiitic gabbros associated with flood-basalt magmatism and continental breakup

• Applicant: Privatdozent Dr. Jörg Pfänder
• Subject Area: Mineralogy, Petrology and Geochemistry ; Geology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549312552

The planned project aims to reconstruct the origin and petrogenetic and thermal evolution and emplacement of tholeiitic gabbros, which are the predominant rock type of a Cretaceous (~132 Ma) magmatic ring complex in western Namibia (Messum complex). According to published studies and supported by positive gravity and magnetic anomalies, this complex with a diameter of ~18 km is regarded as an important remnant of a magma supply system that might have feeded the Etendeka flood basalt eruptions prior to and during the breakup of Gondwana and the opening of the South Atlantic. Reconstructing the magmatic evolution, emplacement and cooling history of this complex, and the origin and volume of parental magmas is thus crucial in understanding advective heat and mass transfer from the asthenospheric mantle to the lithosphere, which in turn affects the lithospheric strength and thus may support continental breakup. Based on existing literature and own reconnaissance work, it seems that the various types of gabbros are genetically related to each other and to the hosting southern Etendeka flood basalts and latites. These relationships, however, are mostly based on field observations and few petrochemical data, and will be tested in detail in the course of this study by means of EPMA and SEM based automated mineralogy as well as whole-rock major, trace element and Nd-Sr-Hf isotope studies. Crustal assimilation and fractional crystallization have played an important role during the evolution of many Etendeka lavas, and it is likely that at least some of the gabbros of the Messum complex are cumulate residual counterparts to some of these lavas. The acquired data will allow a refinement of existing petrogenetic models that estimate relative contributions from different asthenospheric (Tristan-Gough plume and upper depleted mantle) and lithospheric mantle sources to explain the geochemical record of the gabbros and Etendeka lavas. The project will complement a recently approved proposal of a long standing cooperation partner (JU 326/16-1), who aims to decipher the petrogenetic relationships between the different types of alkaline intrusive rocks (theralites, quartz and nepheline syenites) of the same complex. The combined results of both projects will support a more sophisticated petrogenetic model to explain the highly diverse rock record of this magmatic ring complex, their relationships and its thermal evolution.

• DFG Programme: Research Grants