A transpressional origin for the West Spitsbergen fold-and-thrust belt: Insight from analog modeling

摘要

The West Spitsbergen fold-and-thrust belt formed along the transform plate boundary between Greenland and the western Barents Sea during Paleocene-Eocene breakup in the northern North Atlantic. Approximately 20-40 km margin-perpendicular shortening accumulated in the belt has been attributed to transpression and strain partitioning in a restraining bend but also to head-on collision. We have applied scaled analog tectonic modeling to test the former hypothesis. A pack of brittle quartz sand with a shallow thin layer of silicon putty was deformed by transpression at a 15° convergence angle by movement of a basal plate. The kinematics was quantified by means of digital particle image velocimetry. The result was a doubly vergent transpressional wedge, consisting of a steeply tapered retrowedge and a strongly internally deformed steeply tapered prowedge separated by a central strike-slip zone and an adjacent low-taper thin-skinned fold-and-thrust belt. The doubly vergent wedge evolved through several kinematic phases. Three main stages were identified, namely, (1) initial distributed deformation, (2) development of an oblique doubly vergent wedge with progressive evolution of local strain partitioning along the marginal shear zones, and, finally, (3) a stage of full strain partitioning between a central strike-slip zone and reverse displacement along marginal shear zones, with folding and thrusting in a thin-skinned belt on the proside. The analog model convincingly reproduced the geometry and the kinematic evolution of the West Spitsbergen fold-and-thrust belt, supporting the hypothesis of its formation by strain partitioning in transpression with a small angle of convergence and significant lateral displacement.