Deep-time multi-mineral thermochronology of the Bushveld Igneous Complex – constraints for the upper crustal evolution of the northern Kaapvaal Craton

• Applicant: Dr. Mathias Hueck
• Subject Area: Geology ; Mineralogy, Petrology and Geochemistry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542908113

Despite its prominence as one of the most studied igneous complexes in the world, information about the last 2 billion years of thermal evolution at temperatures below 300°C of the Bushveld Igneous Complex (BIC) is still very limited. Recent research has demonstrated that the thermal history of the cratonic upper crust is commonly not monotonous, but episodically triggered by different geological events, such as: (1) burial & exhumation of sedimentary basins; (2) increases of the geothermal gradient due to intraplate magmatism or changes in the basal heat flow; (3) structural responses to far-field tectonic drives; or (4) large-scale, climate-induced erosion. These events are often not evident from the geological record after hundreds of millions to billions of years of accumulated erosion. The aim of this study is to reconstruct the ca. 2,000 Myr-long upper-crust geological evolution of the BIC after its rapid emplacement and cooling below ca. 300°C in the Archean Kaapvaal Craton. As such, it represents a shift from traditional apatite and zircon thermochronology focusing on geologically young regions towards a more thorough understanding of the <300°C thermal history of old cratonic regions. This will be achieved by recovering detailed thermal histories based on the systematic application of (U-Th)/He and fission-track dating of a large range of minerals with different closure temperatures (zircon, apatite, titanite, rutile, garnet, baddeleyite, magnetite) and varying contents of radioactive elements. The analyses will further be complemented by state-of the art techniques such as in-situ (U-Th)/He dating and Raman spectroscopy mapping, allowing for a single-crystal estimate of the mineral’s thermal sensitivity. The combination and cross-calibration of several thermochronometers will lead to (1) a much-improved understanding of geological processes and evolution of cratonic regions and (2) expand the toolbox for unravelling thermally complex and lithologically diverse regions. The study area is ideally suited for reconstructing its deep-time thermal history in the upper crust, as it combines: (1) a large area with equivalent history of very rapid (few Myr) post-emplacement cooling to ca. 300°C; (2) very good field exposure; (3) an impressive mineralogical variation at outcrop scale (including minerals with varying content of radioactive elements); (4) a wealth of accumulated research in the area; and (5) very long thermal evolution at mid- to low-temperature conditions.

• DFG Programme: Research Grants
• Co-Investigator: Professorin Dr. Annika Dziggel