Structural Geology and Geochronology

REGIONAL AND PROCESS-ORIENTED STUDIES

The general approach is to map well-exposed deformed and metamorphosed areas in order to constrain the structural, metamorphic and tectonic histories of those areas. This work often leads to the rise or solution of fundamental problems in structural geology and geochronology. Areas of interest are the New England Appalachians (see above), southwest Greenland, the northern Superior Province Boundary Zone and the Monashee Complex.

ARCHAEN GEOLOGY OF SOUTHWEST GREENLAND

Archaean terrains are important areas for geological research, because they allow us to study early Earth processes. Because the temperature and composition of the rocks were different from what they are today, Archaean plate tectonics may have been significantly different from modern plate tectonics. The mechanism, and even the existence, of Archaean plate tectonics is currently a highly debated topic. An excellent exposure of part of the Archean Nain craton exists in the Nuuk area of southern West Greenland. It is composed of at least six Archaean terranes. All terranes have different ages, compositions and early histories. The geological histories of various terranes and subterranes, and the nature of the terrane boundaries and timing of their formation, are studied in order to obtain a better understanding of Archaean crust forming processes in the context of plate tectonic theory. The current research area is the relatively unexplored southeastern Nuuk region. The regional extent of certain terranes and location of terrane boundaries is uncertain, and the tectonic history of the area is largely unknown. Research involves detailed mapping of relevant parts of the southeastern Nuuk region combined with (micro)structural analysis, 40Ar/39Ar and U/Pb geochronology in order to identify the terranes and their boundaries, and to reveal the tectonic history of the area. Field work is conducted during the summer months. Geochronology is performed at other institutions in collaboration with these institutions.

THE NORTHERN SUPERIOR PROVINCE BOUNDARY ZONE, MANITOBA,CANADA

The northern Superior Province Boundary Zone separates the Archaean Superior Province to the southeast from the Paleoproterozoic Trans-Hudson Orogen to the northwest. The Superior Province Boundary Zone comprises various geological domains bounded by various shear zones. Detailed mapping of the shear zones constrained the movement direction and sense along these shear zones, and the movement between the Superior Province and the Trans-Hudson Orogen. However, the question arose how exactly the movement between the Superior Province and the Trans-Hudson Orogen is accommodated by the various shear zones, and possibly the domains between the shear zones (strain partitioning). Another related more general question is how structures such as folds, foliations and lineations develop during various types of progressive deformation. Results from mathematical modeling are compared to results from the field. The questions above form part of the currently ongoing research. U/Pb and 40Ar/39Ar geochronology methods are used to constrain the timing of deformation along the shear zones and older deformation within the domains. This is a challenge, because the samples have commonly experienced multiple deformation events. In addition to conventional U/Pb and 40Ar/ 39Ar dating of mineral separates, in situ U/Pb methods (Electron Microprobe Monazite Analysis; Sensitive High-Resolution Ion Microprobe) and in situ 40Ar/39Ar geochronology are used in collaboration with other laboratories in order to solve these problems. In situ methods allow for dating of minerals in thin section, so that their structural and metamorphic context is known. Furthermore, various age domains within one mineral can be dated and various geological events can be separated. This type of research is not only interesting from a regional perspective, but also contributes towards fundamental knowledge. Because in situ U/Pb and 40Ar/39Ar geochronology methods are currently still being developed and improved, using these methods can also contribute towards the knowledge of the possibilities and limitations of these methods.

MONASHEE COMPLEX, SOUTHEASTERN BRITISH COLUMBIA, CANADA