Research in the petrology group
Early Earth evolution
Our understanding of processes that modify the outermost shell of today’s Earth are rooted within plate tectonic theory, in which movement of this layer, i.e. the lithosphere, is dominantly horizontal. However, the transition from an initial global magma ocean to largely rigid plates necessary for plate tectonics is poorly constrained. Without clear evidence for how and when plate tectonics initiated on Earth, interactions between the solid Earth and the early atmosphere and hydrosphere remain equivocal and largely qualitative. There are two contrasting end-member models for Earth’s earliest tectonic regimes: dominantly horizontal proto-plate tectonics where one plate subducts under another vs. vertical tectonics where the crust is recycled through gravitational “dripping”. Multiple lines of evidence support proto-plate tectonics after ~3.2-3.0 Ga, whereas most studies of the Paleoarchean Barberton and Pilbara greenstone belts (3.5-3.2 Ga) advocate vertical tectonics. In contrast, studies of the Eoarchean Isua supracrustal belt (ISB) of West Greenland (~3.8-3.6 Ga) argue that plate tectonics sensu stricto had already commenced. Our research of the ISB revealed that the latter interpretation is not unequivocal and further in-depth studies are needed to pinpoint the emergence of plate tectonics as we know it today. Consequently, the timing when modern-day tectonics commenced is still to be determined.
Life and death of chemical reaction fronts
In the geosphere, fluid-mediated mineral reactions are of pivotal importance in governing the redistribution of elements and isotopes. Incomplete elemental redistribution is preserved in the rock record in the form of geochemical reaction fronts, the boundaries between reacted and unreacted material. Such fronts control geochemical exchange between the hydrosphere and the geosphere, the formation of mineral deposits, and migration of aqueous fluids and melt in the lithosphere. Associated mineralogical changes can dramatically change the physicochemical properties of Earth materials affecting their flow properties (rheology), strength, porosity and permeability. Key features of such systems are a) reaction induced creation of porosity increasing permeability and further focusing of fluid into the zone of reaction; hence this results in a positive feedback between reaction, fluid ingress and further reaction, and b) recrystallization of mineral phases releasing potentially economic elements into the fluid.