KINEMATICS OF TERTIARY DEFORMATION IN THE BASEMENT-INVOLVED FOLD-THRUST COMPLEX, WESTERN NORDENSKIOLD-LAND, SVALBARD - TECTONIC IMPLICATIONS BASED ON FAULT-SLIP DATA-ANALYSIS

Kinematic analysis based on the interpretation of small-scale fault an d fold data supports a kinematic evolution history involving heterogen eous crustal shortening and uplift, and subsequent extension (collapse ) for the major, west coast fold-thrust complex in western Nordenskiol d Land, Svalbard. This deformation can be divided into three main kine matic events. Stage 1 represents an early, distinctive, NNE-SSW-orient ed contractional episode that generated layer parallel and low-angle t hrusts and internal folds. Stage 1 structures (population 1) are arran ged in an apparent en-echelon 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-EN E-oriented contractional episode. Initial (pre-fold) stratal shortenin g (stage 2a) was followed by a continuous buildup of the fold-thrust c omplex and general crustal thickening (syn-fold, stage 2b), until a su percritical height/thickness was reached (post-fold, stage 2c). At thi s stage a change in the stress field caused failure of the ford-thrust complex, and continued NE-SW-directed shortening was accommodated as vertical strike-slip faults (population 2c). Late W-E-to WSW-ENE-direc ted extension, the stage 3 episode, was probably related to collapse o f the overthickened stage 2 fold-thrust complex. The detailed reconstr uction of kinematic events in western Nordenskiold Land supports initi al breakup of the Greenland-Svalbard area in Early Paleocene (?) times during dextral, NNE-SSW-directed transpression (stage I). The major d eformational episode (stage 2), probably of mid-Paleocene to Eocene ag e, was characterized by progressive WSW-ENE-directed shortening and wa s related to decoupled deformation where broad zones of convergent str ain 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. Jon sfjorden Trough. The latest kinematic episode (stage 3) is likely of E ocene age, and may be ascribed to extensional collapse in the hinterla nd of the western Spitsbergen orogenic wedge within a regional, dextra l transpressive setting.