Tectonic evolution of the west Spitsbergen fold belt

Abstract

Abstract The west Spitsbergen fold belt has a complex tectonic history which is recorded in a thick, nearly complete upper Proterozoic-Phanerozoic layered sequence. Work since 1977 near Bellsund allows recognition of the main deformational events in that segment of the fold belt. The strata are grouped informally into the metamorphosed Hecla Hoek (HH) sequence (Proterozoic) and the Van Keulenfjorden (VK) sequence (Carboniferous-Cretaceous), separated by a pronounced unconformity. The HH is divided into the Antoniabreen succession, the Chamberlindalen succession, and the Kapp Lyell tillite; the first two consist of diverse clastic and carbonate rocks, along with some volcanic rocks. The VK is a platform sequence of shallow marine and terrestrial sedimentary rocks. These layered rocks are intruded by a few Mesozoic dolerite sills and dikes. Subhorizontal Paleogene sedimentary rocks are preserved in a small graben. Both layered sequences have undergone strong deformation. Structures (mainly Caledonian age) in the HH can be grouped as phase 1 (small isoclinal folds, subhorizontal axial planar foliation, ridge-groove lineation in the foliation, and large recumbent folds), phase 2 (tight to isoclinal folds, axial planar foliation), and younger (weak folds and foliations, kink bands, crinkles). Structures (mainly Tertiary age) in the VK include faults (thrust, reverse, down-to-the-east bedding-plane normal, other normal); folds (symmetric, asymmetric, overturned, recumbent, isoclinal); and foliation (in some tightly folded Triassic shales). Six deformational events can be identified here, each described below in terms of age, intensity, and kinematic pattern: • D1 - Vendian or early Paleozoic; very strong; NNW-SSE shortening?, NNW transport? • D2 - Early Paleozoic (pre-Carboniferous); strong; NE-SW shortening, NE vergence. • D3 - Middle (?) Carboniferous; moderate; unclear (limited exposure). • D4 - Early Cretaceous (?); weak; extension, direction unclear. • D5 - Early (?) Tertiary; very strong locally; uplift in W, ENE-WSW shortening, ENE translation. • D6 - Middle (?) Tertiary; moderate; NE-SW extension.