Tectono-magmatic control on vertical dip slip basement faulting: An example from the Fennoscandian Shield |
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Authors: | M Heeremans H Stel P van der Beek A Lankreijer |
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Institution: | lnstitufe of Earth Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Nefherlands |
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Abstract: | Vertical dip-slip basement faults play an important role in the evolution and structuring of the Earth's crust. The Proterozoic anorogenic rapakivi-anorthosite setting of the Fennoscandian Shield in southern Finland exhibits a widespread pattern of vertical dip-slip basement faults that are deeply eroded. The Porkkala-Mantsala (PM)-fault, located c. 30 km W of Helsinki is part of a system of crustal lineaments that closely follows the outcrop pattern of Mid-Late Proterozoic anorogenic crustal elements, such as basic dyke swarms, the outline of rapakivi granites and remnants of sediment-filled grabens. These lineaments are formed by low-grade dip-slip faults that overprint Svecofennian shear zones. Structural analysis of the PM-fault supports an interpretation in terms of reactivation of a high-grade ductile wrench zone. Successive stages of brittle deformation visible in as well the PM-fault and the Obbnäs granite demonstrate that brittle deformation in the PM-fault is coeval with the intrusion of the anorogenic Obbnäs rapakivi granite. Based on the spatial and temporal relationship of anorogenic magmatism and block faulting, a genetic relationship is proposed. |
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