ANALYSIS OF FAULT POPULATIONS IN WESTERN SPITSBERGEN - IMPLICATIONS FOR DEFORMATION PARTITIONING ALONG TRANSFORM MARGINS

Mesoscale faults, expressed in the Paleogene Central basin and Cretace ous basement along the West Spitsbergen orogenic belt, are used to def ine the history of continental deformation associated with the develop ment of the transform system that accompanied the opening of the Euras ian basin and the Norwegian-Greenland Sea. A fundamental change in the orientation of faults from dominantly north-south in the basal part o f the basin to northeast striking in the upper units broadly correlate s with a major shift in plate motion during late Paleocene-early Eocen e time. The two main populations of faults are interpreted as extensio n fractures that were variably reactivated as shear fractures and form ed in response to north-south compression followed by northeast-southw est compression. Paleostress stratigraphy, or the analysis of striated faults measured in successive stratigraphic units of the Central basi n, corroborates this interpretation and allows a time sequence of pale ostress tensors to be defined. Results show that a Late Cretaceous-ear ly Paleocene north-south compression, consistent with plate motion, wa s followed by three relatively short-lived and regionally limited faul ting events leading up to a change in plate motion during late Paleoce ne time (post-Chron 25). Major transpressive tectonism followed, produ cting northeast-trending fractures that were reactivated as dextral an d sinistral faults defining a prolate-shape paleostress ellipsoid with a horizontal sigma1. This regionally reproducible tensor, consistent with the prediction of dextral transpression along the paleotransform, was probably initiated at approximately the Paleocene-Eocene boundary . Finally, a post-early Eocene deformation, pervasively recorded in th e study area by an oblate shape paleostress ellipsoid with horizontal sigma3, is tentatively correlated with the dextral transtension that c haracterized the post-Chron 13 opening of the Norwegian-Greenland Sea and Eurasian basin. This study offers documentation of deformation par titioning during the evolution of a transform margin. The Late Cretace ous-earliest Paleocene compression associated with the prototransform did not involve substantial partitioning, and a north-south maximum pr incipal stress pervaded the continental crust away from the transform. In contrast, the late Paleocene-Eocene transpression reflects total p artitioning of deformation along the evolved, mature transform margin. Oblique plate motion was presumably partitioned into a strikeslip zon e(s) offhshore, whereas the onshore Central basin recorded only the or thogonal component of oblique convergence and divergence, a pattern si milar to modern orogenic belts developed in zones of oblique plate mot ion.