Impact structures: Effect of post-shock thermal conditions on mineral magnetism

• Applicant: Privatdozentin Dr. Agnes Kontny
• Subject Area: Palaeontology ; Mineralogy, Petrology and Geochemistry ; Geophysics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432762445

Large impact structures on Earth like the Chicxulub in Mexico are characterized by magnetic highs but the magneto-mineralogical origin is still poorly constrained and impact-generated melt versus hydrothermal activity models are discussed. Shock features along with thermally activated processes are the most important driving forces for the creation or destruction of magnetic minerals causing magnetic anomaly signals over impact structures. The main goal of this research project is the investigation and characterization of heat treatment on shocked magnetite and pyrrhotite, the two main magnetic minerals in crustal rocks of the Earth. For this purpose, we plan to study rock magnetic properties and microstructural features from experimentally shocked and afterwards annealed material and compare it to magnetic minerals from impacted rocks. For comparison, the IODP-ICDP drill core M0077A from the Chicxulub impact crater and from the Nördlingen 1973 drill core are selected, because both structures show inner craters with impact-related magnetic anomalies. The difference is the size and it is hypothesized for the 200 km diameter Chicxulub that a long-living hydrothermal system was active, but not for the 25 km diameter Nördlingen impact structure. Temperature dependent magnetic susceptibility along with a series of microscopic (reflected light, scanning electron microscopy, magnetic force microscopy, transmission electron microscopy), x-ray diffraction techniques and magnetization experiments at room temperature and low-temperature will be used to characterize shocked and annealed samples. An understanding of the magnetic and microstructural features due to heating of shocked material and their distinction from new magnetic mineral formations are likely a key to explain magnetic anomaly pattern over large impact craters on Earth and other planetary bodies. Therefore, this proposal aims on the discrimination of different secondary processes leading to enhancement or destruction of magnetic signals over large impact structures.

• DFG Programme: Research Grants