| Summary: | Precambrian cratons are continent cores archiving the oldest crustal histories on Earth. The crystalline basement of cratons is typically characterized by complex arrays of multiple fracture and fault generations hosting minerals formed by fluids flowing through fracture networks. Disentangling absolute chronologies of the various fracturing, faulting and fluid flow events have to date been difficult given the micro-scale mineral intergrowths and zonations, inhibiting conventional dating techniques. In the general lack of age constraints, deformation and mineralization mechanisms cannot be attributed to specific tectonic regimes, hampering reconstruction of local and regional events of fluid flow and mineral precipitation, and ultimately of the geological evolution of cratons. This thesis presents diverse studies utilizing the radiogenic decay of fracture, fault and shear zone mineral assemblages sampled from the crystalline basement of the Fennoscandian Shield, aiming at detecting episodic fracturing reactivation, mineralization and microbial processes throughout the craton history. The analytical procedures involve, foremost, Rb-Sr geochronology, along with U-Pb and (U-Th)/He geochronology, stable isotope and trace element geochemistry, fluid inclusion thermometry and biomarkers. The in situ age determinations enabled 1) linking of greisen and distal veins to magmatic and post-magmatic fluid circulation, 2) slickenfibre growth to distinct faulting episodes, and 3) mineral precipitation in fractures, veins and shear zones to regionally extending deformation events across the Fennoscandian Shield. In addition, dating of mineralization related to deep fracture-hosted microbial life constrained the timing of such activity at several sites. The precipitation episodes stretch from Paleoproterozoic to Jurassic times with overgrowth generations separated in time by up to one billion years in single veins and even within individual crystals. The findings of the thesis demonstrate that the methodological protocol has ...
|
|---|