The Structural Development of the Vestbakken Volcanic Province, Western Barents Sea. Relation Between Faults and Folds

• Main Author: Giannenas, Panagiotis Athanasios
• Format: Master Thesis
• Language: English
• Published: 2018
• Subjects: Faults and Folds; Inversion structures; Vestbakken Volcanic Province; Western Barents Sea; Barents Sea; Greenland; Knipovich Ridge; Vestbakken; Greenland Sea; Iceland
• Online Access: http://hdl.handle.net/10852/64543; http://urn.nb.no/URN:NBN:no-66933

An eastward (releasing) bend in the Eocene dextral Barents Shear Margin gave rise to the formation of the Vestbakken Volcanic Province. The area has been affected by complex tectonics and both extensional and contractional structures are observed. This thesis focuses on the analysis of structural styles in this area and their relation to the regional tectonic setting. Faults and folds are interpreted from 2D seismic reflection data calibrated by well data. The structural analysis is based on interpreted key seismic profiles and constructed structural maps, time maps and special maps which focus on the geometric and spatial relations of faults and folds. The area is divided into structurally homogenous subareas. Two half-grabens, two domal areas, a gently dipping slope area and an uplifted footwall block area have been defined. The study reveals the existence of two partially inverted master faults, several branch faults with anastomosing character and many isolated secondary faults, a few reverse faults and thrust faults and 18 folds. The dominant strike of structural features in the Vestbakken Volcanic Province is NE-SW. Exceptions include the N-S striking eastern boundary fault, which defines the boundary between Vestbakken Volcanic Province and Stappen High to the east. Faults primarily dip towards NW. Structural analysis of faults revealed chiefly planar fault plane geometries that locally are interpreted to be slightly modified through later deformation. Three extensional events have been identified: (i) a late Paleocene-early Eocene event which is related to the continental break-up in the Norwegian-Greenland Sea, (ii) an early Oligocene event attributed to the plate reorganization (34 Ma) affecting mainly NW-SE striking faults and (iii) an extensional Pliocene event. Evidence of volcanic activity is observed in the 2D seismic data accompanying the first two events. Analysis of folds revealed specific structural styles: (a) upright to steeply inclined close to open anticlines with snakehead (head on) geometries buttressed against pre-existing normal faults and (b) upright or steeply inclined gentle to open synclines that are interpreted as partly inverted synclinal depocenters. Folds are principally observed to be fault-related, where regionally expressed anticlines are developed in the upper stratigraphic sections, in the hanging wall fault blocks of pre-existing extensional master faults, typically affecting middle Eocene – lower Miocene strata. The folds trend parallel to, and are focused along these faults. Folds are mainly interpreted as buckle folds and deformation was controlled by the geometry of the faults, which acted as buttresses accommodating shortening. Fault-bend folds and fault propagation folds are observed locally. Onlap configuration and pinch-out geometries reveal that the phase of tectonic inversion (which caused folding, reverse faulting and reverse reactivation of extensional faults) commenced in early Miocene times under top-to-SE contraction prior to the onset of Pliocene. The event is suggested to be primarily related to the development of the Knipovich Ridge in the NW which caused SE-directed stress through ridge-push. A SE-directed tectonic transport direction is consistent with geometric observations such as slightly steeper forelimbs compared to backlimbs, axial plane inclinations, strike and dip of fault planes that have undergone flexural rotation, thrust faults that ramp-up to the SE and forethrusting. Apart from ridge-push other processes involved may include lithospheric thinning, gravitational stresses by the elevated Iceland margin and plume-enhanced spreading.