Wed 19th July @ noon, Rm 312.222

Abstract:

During hyper-velocity meteorite impacts, minerals may deform in unique manners, known as shock metamorphism. The two most commonly used U – Pb geochronometers, the accessory minerals zircon and monazite, respond in distinct ways to shock, including developing mechanical twins, various crystal-plastic deformation features and in the case of zircon may undergo a solid state transformation to high pressure polymorph reidite. Shock deformation can affect the U – Pb systematics of zircon and monazite to varying degrees. This presentation will focus on a coupled microstructural and geochronological study of shocked zircon and monazite grains from the 2020 Ma Vredefort Dome in South Africa, the 259 Ma Araguainha impact structure in Brazil and the nominally Proterozoic Yarrabubba impact structure in Western Australia.

Results of this study help to quantify diagnostic shock features in zircon and monazite and constrain impact-age resetting in various microstructural domains. Furthermore, these results highlight the importance of combing microstructural studies (EBSD) with in situ analyses (e.g. SHRIMP, LA-ICP-MS) of shocked zircon and monazite to best determine the timing of shock deformation. Finally, these results demonstrate the efficacy of monazite to date impact events, especially from ancient structures within terranes which have subsequently experienced complicated and protracted geologic histories or are deeply eroded.

Short bio:

Timmons recently completed his PhD at Curtin in early 2017. Since that time he has worked as a research associate in the Department of Applied Geology studying rocks from Western Australia to Norway. Prior to moving to Western Australia he completed an MSc at the University of Puerto Rico Mayagüez, which sparked his initial interest in shock deformation of accessory phases and the geologic record of impact cratering.