No abstract

On the Vøring Margin offshore mid‐Norway, Paleogene continental breakup was characterized by the extrusion of large volumes of flood basalts erupted in different depositional environments. The transition from subaerial to submarine emplacement environment is marked by the formation of the Vøring Escarpment which records the early encroachment of flood basalt into the basin and the buildup of a lava delta system. The increased availability of new and reprocessed high‐quality seismic data allows a more detailed characterization of the along‐strike and across‐strike continuity and variability of the different volcanic seismic facies units. Detailed seismic interpretation shows that the ~350 km long NE‐SW trending Vøring Escarpment is a prominent feature along the Vøring Margin with a height ranging between 200 and 1600 m. Structurally, the Vøring Escarpment is segmented along strike into five segments (E1–E5) with different controlling factors leading to variation in accommodation space. Relative sea level change and magma supply are the major controlling factors for segments E2 and E4 which are characterized by a well‐developed lava delta system and significant escarpment height. Tectonic movements along the Jan Mayen Fracture Zone resulted in second‐order segmentation of the E1 segment into pseudoescarpments with a very thin lava delta system and limited escarpment height. Segments E3 and E5, situated along the flanks of Cretaceous/Paleocene highs, are controlled by the structural highs, which were possibly reactivated during breakup time. Our mapping results provide crucial information about the paleogeography and yield important information regarding the paleo–water depth and depocenter locations prior to and during the breakup of the Vøring Margin.

Seismic reflection data along volcanic passive margins frequently provide imaging of strong and laterally continuous reflections in the middle and lower crust. We have completed a detailed 2‐D seismic interpretation of the deep crustal structure of the Vøring Margin, offshore mid‐Norway, where high‐quality seismic data allow the identification of high‐amplitude reflections, locally referred to as the T‐Reflection. Using a dense seismic grid, we have mapped the geometry of the T‐Reflection in order to compare it with filtered Bouguer gravity anomalies and seismic refraction data. The T‐Reflection is identified between 7 and 10 s. Sometimes it consists of one single smooth reflection. However, it is frequently associated with a set of rough multiple reflections displaying discontinuous segments with varying geometries, amplitudes, and contact relationships. The T‐Reflection seems to be connected to deep sill networks and is locally identified at the continuation of basement high structures or terminates over fractures and faults. The T‐Reflection presents a low magnetic signal. The spatial correlation between the filtered positive Bouguer gravity anomalies and the deep dome‐shaped reflections indicates that the latter represent a high‐impedance boundary contrast associated with a high‐density and high‐velocity body. In ~50% of the outer Vøring Margin, the depth of the mapped T‐Reflection is found to correspond to the depth of the top of the Lower Crustal Body (LCB), which is characterized by high P wave velocities (>7 km/s). We present a tectonic scenario, where a large part of the deep crustal structure is composed of preserved upper continental crustal blocks and middle to lower crustal lenses of inherited high‐grade metamorphic rocks. Deep intrusions into the faulted crustal blocks are responsible for the rough character of the T‐Reflection, whereas intrusions into the ductile lower crust and detachment faults are likely responsible for its smoother character. Deep magma intrusions can be responsible for regional metamorphic processes leading to an increasing velocity of the lower crust to more than 7 km/s. The result is a heterogeneous LCB that likely represents a complex mixture of pre‐ to syn‐breakup mafic and ultramafic rocks (cumulates and sills) and old metamorphic rocks such as granulites and eclogites. An increasing degree of melting toward the breakup axis is responsible for an increasing proportion of cumulates and sill intrusions in the lower crust.