Baklia Fault Zone – a regional strike slip zone splitting Prins Karls Foreland (Svalbard)

Abstract

Prins Karls Foreland (PKF) is a westernmost island of Svalbard Archipelago belonging to the Southwestern Basement Province. The island consists of low-metamorphic facies metasediments, probably Neoproterozoic, divided into two parts, northern and southern. Both parts are characterized by similar geological structures but different stratigraphy. New discoveries presented here result from joint, Norwegian Polar Institute and AGH-Kraków expeditions in 2013 and 2014. For the first time thorough characteristics of the location and character of a strike-slip fault splitting PKF (the Baklia Fault Zone) is presented here.

To date, one succession has been distinguished in the litostratigraphy of PKF’s basement. The northern part of the island consist of two groups: the Scotiafjellet Group and Grampianfjella Group (Dallmann et al. 2015). They comprise low-metamorphic metasediments (chlorite zone of greenschist facies), mostly slates, metapsamites and carbonates. Stratigraphic units of the southern part represent slightly higher, biotite metamorphic zone, and have been considered conformably underlying Scotiafjellet Group. The uppermost Peachflya Group and Geikiebreen Group (mostly phyllites with metavolcanics and carbonates) are in thrust contact with underlying Ferrierpiggen Group, comprising schistose diamictites (Harland et al. 1979, Harland et al. 1993).

This complexes have undergone the Caledonian metamorphism followed by D₁ deformation producing SE directed folding and thrusts. D₂ deformation was coaxial, but not coplanar with D₁. D₂ deformation occurred probably in Mid-Kenozoic and resulted in refolding and thrusting, followed by dextral shearing in the central area of the island. D₃ deformation is connected with transtensional formation of the Forlandsundet Graben along NNW-SSE faults finishing the West Spitsbergen Orogeny (WSO) (Manby 1986).

Distinct difference in the stratigraphy of southern and northern parts of PKF is apparent. The presence of the fault dividing the island was indicated before (Hjelle et al. 1979), but no single fault has been recognized during detailed mapping later on (Harland et al. 1979; Morris 1982; Manby 1986; Morris 1989).

Fieldwork conducted by the authors in the area of Selvågen led to the discovery of the a major fault zone (the Baklia Fault Zone - BFZ) dividing PKF into two terrains. The BKF have N-S trend from Haukebukta in the west coast, through the slopes of Alasdairhorne (where it trapped a few hundred meter long slab of the Ferrierpiggen Group rocks), to the southern Scotiadalen. Approaching Selvågen, the fault zone bends slightly to the NNE-SSW. The zone is filled with breccias and mixture of different lithologies with slabs of rocks derived from both limbs of the fault zone. The width of the zone measures approximately 100 to 250 meters. To the east, it is accompanied by at least three narrow subparallel faults. The age of the BFZ is unknown. A brittle character of deformation may suggest that it is of Tertiary age. En échelon normal faults with a drop to the north which associate BFZ may be considered as a Riedel shears R₁ formed at the beginning of a strike-slip movement. Structural measurements on slickensides as kinematic indicators revealed that normal faulting was associated with both, dextral and sinistral shear (not simultaneous). A main movement connected with dextral shearing occurred probably earlier, during late stages of the early Tertiary crustal shortening. The extended width of the fault zone and the presence of a mixture of rock material from both terranes suggest the significant lateral displacement that might reach tens of kilometers. The BFZ cuts through the boundary faults of the Forlandsundet Graben displacing them sinistrally by approximately one kilometer. This suggests that sinistral movement was probably associated with rejuvenation of the fault during late stages or after the Forlandsundet Graben formation.

There are several regional implications of BFZ. The stratigraphic relationship of southern and northern teranes is unclear. The presence of BFZ at the boundary of the Scotiafjellet and Peachflya Group does not exclude their stratigraphic succession but makes it impossible to define. The field observations suggest that BFY may be Tertiary of age. It has similar tectonic style and orientation to other strike slip zones present along western Svalbard coast. Strong tectonic deformation suggests displacement of the northern terrain of PKF by tens of kilometers. Even though southern terrain can be directly correlated with Oscar II Land, more research is needed to correlate of more exotic northern terrain of PKF with the basement rocks in the southern parts of Spitsbergen. Ongoing research towards dating and detail structural characterization of this regional fault zone will allow for reconstruction of pre-Tertiary position of this part of Archipelago.

References

Dallmann W.K., 2015 (Ed.): Geoscience Atlas of Svalbard. (Norwegian Polar Institute, Report 148) Tromsø.

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Hjelle, A., Ohta, Y., & Winsnes, T. S., 1979. Hecla Hoek rocks of Oscar II Land and Prins Karls Forland, Svalbard. Norsk Polarinstitutt Skrifter, 167, 145-169.

Manby, G. M., 1986. Mid-Palaeozoic metamorphism and polyphase deformation of the Forland Complex, Svalbard. Geological Magazine, 123(06), 651-663.

Morris, A., 1982. Low grade (greenschist facies) metamorphism in southern Prins Karls Forland, Svalbard. Polar Research, 1982(2), 17-56.

Morris, A., 1989. Distributed, right‐lateral strike‐slip in Prins Karls Forland, western Svalbard. Polar research, 7(1), 79-82.