Revised chronostratigraphy of the Faroe Islands Basalt Group and the British Palaeogene Igneous Province : implications for Selandan-Thanetian palynofloral assemblages and correlation with the Faroe-Shetland Basin

The chronostratigraphy of the Faroe Islands Basalt Group, and thereby the entire North Atlantic Igneous Province, presents a long-standing controversy among government, industry and academic stakeholders with activities in the Faroe-Shetland region. The application of biostratigraphy, magnetostratigraphy, radio-isotopic dating and seismic analysis have all failed to agree on the absolute age span of the volcanic province. The lack of an externally consistent chronostratigraphic framework pose a risk to the hydrocarbon prospectivity in the economically important Faroe-Shetland Basin. This report provides a review of the onshore geology of the Faroe Islands Basalt Group and the British Palaeogene Igneous Province, and the contrasting age models for the emplacement of the North Atlantic Igneous Province are described in detail. New high-precision U/Pb zircon age determinations and palynological analyses of key stratigraphic sections from the Faroe Islands, Inner Hebrides and Northern Ireland are given. Available magnetostratigraphic, biostratigraphic and radio-isotopic age-constraining data from the literature and this study are assessed. It is demonstrated in detail how previous biostratigraphic interpretations, that constrain the collective pre- to syn-breakup eruptive products of the NAIP to the late Thanetian – early Ypresian (T40-T45), are fundamentally flawed. These interpretations have strongly influenced chronostratigraphic correlations between volcanically-saturated onshore basins and volcanically-starved offshore basins, and the portrayal of interaction between sedimentary and volcanic depositional processes in the Faroe-Shetland region. A consistent multidisciplinary age model for the protracted emplacement of the NAIP is presented, including absolute numerical age constraints and assessment of palynofloral assemblages from two key onshore occurrences of the Staffa Flora. The report also highlight the identification of remaining outstanding problems regarding the absolute chronostratigraphy for Palaeocene to early Eocene formations and sequences of the Faroe-Shetland Basin

Gradual caldera collapse at Bárdarbunga volcano, Iceland, regulated by lateral magma outflow

Large volcanic eruptions on Earth commonly occur with a collapse of the roof of a crustal magma reservoir, forming a caldera. Only a few such collapses occur per century, and the lack of detailed observations has obscured insight into the mechanical interplay between collapse and eruption.We usemultiparameter geophysical and geochemical data to show that the 110-squarekilometer and 65-meter-deep collapse of Bárdarbunga caldera in 2014-2015 was initiated through withdrawal of magma, and lateral migration through a 48-kilometers-long dike, from a 12-kilometers deep reservoir. Interaction between the pressure exerted by the subsiding reservoir roof and the physical properties of the subsurface flow path explain the gradual, nearexponential decline of both collapse rate and the intensity of the 180-day-long eruption.</p

Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland

Abstract The active rift zones in Iceland provide unique insight into the geodynamic processes of divergent plate boundaries. The geodynamics of Iceland are studied intensively, particularly, by geophysical methods sensitive to active and/or visible structures such as earthquake seismic and Synthetic Aperture Radar observations or aerial photographs. However, older and less active structures, that may exert a strong control on the presently active geodynamics, are often buried beneath recent volcanic or sedimentary deposits and are—due to their passive mode—overseen by the typical geophysical investigations. Aeromagnetic surveys provide spatial information about subsurface magnetization contrasts relating to both active and inactive structures. However, the aeromagnetic data in Iceland were collected in the 1970-80s and are relevant only to large-scale regional rift studies. With the availability of reliable drones and light-weight atomic scalar sensors, high-quality drone magnetic surveys can provide an unprecedented spatial resolution of both active and passive structures of rift systems as compared to conventional airborne surveys. Here, we present the results of a drone-towed magnetic scalar field and scalar gradiometry study of the north-northeast trending Bárðarbunga spreading center to the north of the Vatnajökull ice cap, Iceland. Our results provide new information about the structural complexity of rift zones with evidence of densely-spaced, conjugate and oblique faults throughout the area. Evidence is shown of a hitherto unknown and prominent east-northeast trending fault structure that coincides with the northern tip of the main eruption edifice of the 1797 and 2014-15 Holuhraun volcanic events. We suggest that this pre-existing structure controlled the locus of vertical magma migration during the two Holuhraun events

Pre-existing structural control on the recent Holuhraun eruptions along the Bárðarbunga spreading center, Iceland

The active rift zones in Iceland provide unique insight into the geodynamic processes of divergent plate boundaries. The geodynamics of Iceland are studied intensively, particularly, by geophysical methods sensitive to active and/or visible structures such as earthquake seismic and Synthetic Aperture Radar observations or aerial photographs. However, older and less active structures, that may exert a strong control on the presently active geodynamics, are often buried beneath recent volcanic or sedimentary deposits and are-due to their passive mode-overseen by the typical geophysical investigations. Aeromagnetic surveys provide spatial information about subsurface magnetization contrasts relating to both active and inactive structures. However, the aeromagnetic data in Iceland were collected in the 1970-80s and are relevant only to large-scale regional rift studies. With the availability of reliable drones and light-weight atomic scalar sensors, high-quality drone magnetic surveys can provide an unprecedented spatial resolution of both active and passive structures of rift systems as compared to conventional airborne surveys. Here, we present the results of a drone-towed magnetic scalar field and scalar gradiometry study of the north-northeast trending Bárðarbunga spreading center to the north of the Vatnajökull ice cap, Iceland. Our results provide new information about the structural complexity of rift zones with evidence of densely-spaced, conjugate and oblique faults throughout the area. Evidence is shown of a hitherto unknown and prominent east-northeast trending fault structure that coincides with the northern tip of the main eruption edifice of the 1797 and 2014-15 Holuhraun volcanic events. We suggest that this pre-existing structure controlled the locus of vertical magma migration during the two Holuhraun events.</p