Double-folding and thrust-front geometries associated with the Timanian and Caledonian orogenies in the Varanger Peninsula, Finnmark, North Norway

Abstract

On Varanger Peninsula, the roughly NW–SE-trending Trollfjorden–Komagelva Fault Zone separates Neoproterozoic successions that accumulated in a shallow-marine platformal domain to the SW of the fault from deep-marine basinal to deltaic sediments to the NE. In Ediacaran time the fault scarp acted as a buttress in a period of basinal inversion during the top-to-the-SW, contractional Timanian orogeny. During the subsequent, top-to-the-SE to -ESE, polyphase Caledonian orogenesis the fault acted as a dextral strike-slip megafracture and lateral ramp. In the northeastern terrane, Timanian and Caledonian fold interference has produced several examples of double-folding and intersecting cleavages. In the southwestern terrane, the Lower Allochthon Gaissa Thrust Belt overlies the Parautochthon, below which a 45 km long deformation front has been mapped. Tectonic shortening within this frontal zone varies from top-to-the-SSE in the west to top-to-the-ESE in the east. Imbricate thrust sheets disrupt the succession in the northeastern terrane, below which a floor décollement is speculated to emerge as a frontal fault along a prominent footwall of the precursor fault that acted on the seabed in outermost Varangerfjorden. By use of potential field data, the Caledonian structures on Varanger can be followed to the north into the Barents Sea where the nappe pile in the pre-Carboniferous basement reaches a thickness of several kilometres. Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts