Late Cretaceous-Paleocene extension on the Vøring Volcanic Margin

Abstract

High-quality seismic data document a Maastrichtian-Paleocene rift episode on the Voring margin lasting for ∼20 m.y. prior to continental breakup. The rift structures are well imaged in the Fenris Graben and Gjallar Ridge region in the western Voring Basin, and are characterized by low-angle detachment faults with variable fault geometries from south to north. The structural restoration has facilitated the division of pre- and syn-rift sediments across the extensional terrain, which is subsequently used to evaluate mode and mechanism for the lithospheric deformation. Extension estimates based on the structural restoration, subsidence analysis and crustal thickness evaluations yield stretching factors ranging between 1.5 to 2.3 across the main fault zone just landward of the early Tertiary flood basalts. The structural restoration also shows that a middle crustal dome structure, observed beneath the low-angle faults, can be explained by extensional unroofing. Thus, the dome structure may represent a possible metamorphic core complex. Calculations of the effects on vertical motion, assuming uniform and two-layer differential stretching models combined with the arrival of the Iceland mantle plume during rifting, indicate that the uniform extension model may account for both observed early rift subsidence and subsequent late rift uplift and erosion. Although the differential model can not be excluded, it implies early rift uplift which is not compatible with our seismic interpretation. The direct and indirect effects of the Iceland mantle plume may have caused as much as 1.2 km of late rift uplift. Comparison of the volcanic Voring margin and the non-volcanic West Iberian margin shows similarities in terms of structural style as well as in mode and distribution of extension.