Kinematics of Tertiary deformation in the basement-involved fold-thrust complex, western Nordenskiøld Land, Svalbard: tectonic implications based on fault-slip data analysis

Abstract

Kinematic analysis based on the interpretation of small-scale fault and fold data supports a kinematic evolution history involving heterogeneous crustal shortening and uplift, and subsequent extension (collapse) for the major, west coast fold-thrust complex in western Nordenskiøld Land, Svalbard. This deformation can be divided into three main kinematic events. Stage 1 represents an early, distinctive, NNE-SSW-oriented contractional episode that generated layer parallel and low-angle thrusts and internal folds. Stage 1 structures (population 1) are arranged in an apparent en-échelon geometry and oblique direction relative to the major NNE-SSW-trending fold-thrust complex of stage 2 affinity. Stage 2 structures include ENE-verging chevron folds and steeply WSW-dipping thrusts and duplexes, that evolved during a progressive WSW-ENE-oriented contractional episode. Initial (pre-fold) stratal shortening (stage 2a) was followed by a continuous buildup of the fold-thrust complex and general crustal thickening (syn-fold, stage 2b), until a supercritical height/thickness was reached (post-fold, stage 2c). At this stage a change in the stress field caused failure of the fold-thrust complex, and continued NE-SW-directed shortening was accommodated as vertical strike-slip faults (population 2c). Late W-E-to WSW-ENE-directed extension, the stage 3 episode, was probably related to collapse of the overthickened stage 2 fold-thrust complex. The detailed reconstruction of kinematic events in western Nordenskiøld Land supports initial breakup of the Greenland-Svalbard area in Early Paleocene (?) times during dextral, NNE-SSW-directed transpression (stage 1). The major deformational episode (stage 2), probably of mid-Paleocene to Eocene age, was characterized by progressive WSW-ENE-directed shortening and was related to decoupled deformation where broad zones of convergent strain were linked to narrow strike-slip zones. This strain partitioning is considered to have begun when the Hornsund Fault Zone widened into and reactivated the basin-bounding faults of the Carboniferous St. Jonsfjorden Trough. The latest kinematic episode (stage 3) is likely of Eocene age, and may be ascribed to extensional collapse in the hinterland of the western Spitsbergen orogenic wedge within a regional, dextral transpressive setting.