Magnetic properties and microfabrics of shocked minerals and their influence on the magnetic anomalies in the Ries, Vredefort and Manicouagan impact structures

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Impact-cratering subjects target rocks quasi-instantaneously to extremely high stresses, strain rates and temperatures that permanently modify the minerals within them. These shock effects bear heavily on the magnetic properties of ferrimagnetic minerals within impact structures, which in turn leads them to possess distinct magnetic field anomalies. However, the impact-related modifications of the magnetic minerals and their remanent magnetizations in the target rocks remain poorly understood. We therefore propose an integrated rock fabric and magneto-mineralogy study to understand the origin of the magnetic anomalies at three complex impact structures: Ries (Germany), Vredefort (South Africa) and Manicouagan (Canada). The chosen impact structures differ in diameter by an order of magnitude, offering a wide range in pressure and temperature conditions. They contain well-exposed outcrops of shocked crystalline basement and/or impact breccias with crystalline components that experienced a wide range of shock and post-shock conditions. Moreover, these impact structures possess magnetic anomalies whose origins are wholly or partially linked to shock processes. We have experience working in each of these structures and are familiar with their magnetic characteristics. The proposed integrated, field and laboratory-based, petrological, microstructural, paleomagnetic and rock magnetic analyses aim at a better understanding how shock metamorphism influences the magnetic remanence of shocked target rocks and how particular P-T conditions act to create magnetic field anomalies in impact structures. The following key questions will be addressed: (1) Can we equate shock effects in opaque ferrimagnets with established indicators of shock stages from non-opaque phases (e.g., PDFs in quartz)? (2) How are magnetic minerals affected/modified by the rapidly changing pressure and temperature conditions during shock loading and post-shock unloading? (3) Do specific microstructures arising from particular shock pressure and/or temperature conditions translate into specific responses in the remanent magnetization and magnetic properties of the ferrimagnets? (4) How does shock-induced remanent magnetization influence magnetic field anomalies including the case of shock demagnetization? Correlating shock effects to specific processes, P-T conditions and magnetic properties of the rocks is essential for the interpretation of magnetic anomalies in impact structures, which are among the most common morphologic features in our solar system.