BALancing Craton thickness by self-cOmpression, graiN size evolution and viscous anisotropY

Projektbeschreibung

Kratone: Die dynamischen Veränderungen ihrer durchschnittlichen Stabilität nachvollziehen

Kratone, die stabilen Kerngebiete der Kontinente, bestehen aus altem kristallinem Gestein. In einigen Kratonen in Kanada und Grönland wurde Kontinentalgestein gefunden, das etwa 4 Milliarden Jahre alt ist. Die Dicke der Kratone von 200 bis 300 km ist größtenteils mit nur geringer interner Verformung bis heute erhalten geblieben, anders als bei anderen Teilen der Lithosphäre (den zwei oberen Schichten der Erde). Dennoch weisen die meisten Kratone teilweisen Verfall auf. Mit Unterstützung der Marie-Skłodowska-Curie-Maßnahmen wird im Projekt Balcony die Hypothese untersucht, dass ein kürzlich entdeckter Mechanismus zur Selbstkompression dazu führt, dass sie langsam, aber stetig nachwachsen. Mit zeitabhängigen numerischen Modellen können die Mechanismen der Ausdünnung und Verdickung geprüft werden.

Ziel

Cratons, the oldest lithosphere on Earth, have survived for more than 3 billion years due to their neutral buoyancy, high viscosity, and thickness. The geologic record shows that, in the presence of external agents (e.g. mantle plume eruptions), most cratons have experienced partial destruction (e.g. Slave craton). Yet, cratons have retained their 200-300 km thickness more or less to the present-day. We hypothesize that a newly-identified self-compressive mechanism causes them to slowly but continuously regrow with time, promoting re-cratonization. Convective self-compression results from the diversion of mantle flow beneath thick and viscous cratonic roots, and is clearly observed and analysed in our recent numerical models. There may be temporary periods of imbalance if craton destruction is relatively new and self-compression has not had enough time to act (e.g. North China craton). Over time, self-compressive thickening may be balanced by increased shearing at the base of cratons due viscous anisotropy and grain size-dependent weakening. In this MSCA project BALCONY, I will use numerical models of cratons sitting above a convecting mantle to investigate how craton thickness may be maintained for billion years by the self-compression mechanism, despite destabilizing events and continuous erosion from below.
My objectives are to develop time-dependent numerical models to investigate (1) the effect of self-compression on craton re-thickening, (2) the importance of viscous anisotropy and grain size evolution for craton thinning, and finally (3) the balance between thickening and thinning, which ultimately determines the long-term thickness of cratons.
The project is a perfect overlap between the research interests of the supervisors (Clint Conrad, Agnes Kiraly at the Universtiy of Oslo) and myself. We are all interested in understanding lithosphere dynamics and have previous experience modelling craton stability, viscous anisotropy and grain size evolution.