High pressure phases in ophiolites - products of electrical discharges?

• Applicant: Professor Dr. Christian Gerhard Ballhaus
• Subject Area: Mineralogy, Petrology and Geochemistry ; Palaeontology
• Term: from 2017 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 335612051

In recent times, high pressure minerals have been discovered in lithologies of ophiolite complexes. The high pressure phases noted include diamond, coesite, pseudomorphs of coesite after stishovite, and high pressure polymorphs of TiO2. They are intimately intergrown with highly reduced phases like moissanite SiC, Si-Fe alloys, metallic Ti, Ti carbides, and nitrides. Taken at face value, these unusual mineral assemblages have the potential to question well established models for the genesis and emplacement history of ophiolite complexes. It is proposed here that these assemblages neither reflect the tectonic history of the rocks nor their redox state. Novel experimental techniques will be employed to test if high pressure phases and highly reduced minerals can be stabilized locally by electric discharges. When a lightning bolt hits a rock, temperatures suffice to stabilize plasmas which, upon cooling, may precipitate compounds that are seemingly highly reduced but do not reflect reducing conditions during their formation. If lithologies do not disintegrate upon impact of a thunderbolt, thermal expansion can generate pressures sufficiently high that coesite, stishovite, and diamond may be stabilized. Positive results would have important implications: (1) high pressure phases do not necessarily reflect the tectonic history of the lithologies, and (2) nominally highly reduced phases like SiC or Si-Fe-Ti alloys may not monitor their redox histories.

• DFG Programme: Research Grants