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The opening of the northeast Atlantic, starting around 56 My ago, was associated with the emplacement of the North Atlantic Igneous Province, including the deposition of voluminous extrusive basaltic successions and intrusion of magma into the surrounding sedimentary basins. The mid-Norwegian Margin is a global type example of such a volcanic rifted margin and is well suited for scientific drilling with its thin sediment cover and good data coverage. During International Ocean Discovery Program Expedition 396, 21 boreholes were drilled at 10 sites in five different geological settings on the mid-Norwegian Margin. The boreholes sampled a wide variety of igneous and sedimentary settings ranging from lava flow fields to hydrothermal vent complexes, along with thick successions of Upper Paleocene and Lower Eocene strata. A comprehensive suite of wireline logs was collected in eight boreholes. These data provide new constraints for geodynamic models to explain the rapid emplacement of large igneous provinces and will also allow us to test the hypothesis that the Paleocene–Eocene Thermal Maximum (PETM) was caused by hydrothermal release of carbon in response to magmatic intrusions and/or flood basalt eruption. Successful drilling and high core recovery of target intervals at all nine primary sites and one additional alternate site will allow us to achieve these goals during postcruise work. Expedition 396 highlights include (1) drilling and coring a unique, multihole transect across a supra-sill hydrothermal system and crater that was filled in during the PETM, (2) drilling and coring all the major lithofacies at each of the component parts of a volcanic rifted margin from terrestrial to deep marine, and (3) acquiring excellent petrophysical data and imaging support for core analyses of complex and diverse volcanic and volcaniclastic intervals across the terrestrial to marine transition. 

Abstract While basaltic volcanism is dominant during rifting and continental breakup, felsic magmatism may be a significant component of some rift margins. During International Ocean Discovery Program (IODP) Expedition 396 on the continental margin of Norway, a graphite‐garnet‐cordierite bearing dacitic unit (the Mimir dacite) was recovered in two holes within early Eocene sediments on Mimir High (Site U1570), a marginal high on the Vøring Transform Margin. Here, we present a comprehensive textural, petrological, and geochemical study of the Mimir dacite in order to assess its origin and discuss the geodynamic implications. The major mineral phases (garnet, cordierite, quartz, plagioclase, alkali feldspar) are hosted in a fresh rhyolitic, vesicular, glassy matrix that is locally mingled with sediments. The major element chemistry of garnet and cordierite, the presence of zircon inclusions with inherited cores, and thermobarometric calculations all support an upper crustal metapelitic origin. While most magma‐rich margin models favor crustal anatexis in the lower crust, thermobarometric calculations performed here show that the Mimir dacite was produced at upper‐crustal depths (<5 kbar, 18 km depth) and high temperature (750–800°C) with up to 3 wt% water content. In situ U‐Pb analyses on zircon inclusions give a magmatic crystallization age of 54.6 ± 1.1 Ma, consistent with emplacement that post‐dates the Paleocene‐Eocene Thermal Maximum. Our results suggest that the opening of the Northeast Atlantic was associated with a phase of low‐pressure, high‐temperature crustal anatexis preceding the main phase of magmatism. 

The opening of the North Atlantic about 56 My ago was associated with the emplacement of the North Atlantic Igneous Province, including the deposition of voluminous extrusive basaltic successions and intrusion of magma into the surrounding sedimentary basins. The mid-Norwegian Margin is a global type example of such volcanic rifted margins and is well suited for scientific drilling with its thin sediment cover and good data coverage. During International Ocean Discovery Program Expedition 396, 21 boreholes were drilled at 10 sites in five different geological settings on this volcanic margin. The boreholes sampled a multitude of igneous and sedimentary settings ranging from lava flow fields to hydrothermal vent complexes, along with thick successions of upper Paleocene and lower Eocene strata. A comprehensive suite of wireline logs was collected in eight boreholes. The main goals of the expedition were to provide constraints for geodynamic models to test different hypotheses that can explain the rapid emplacement of large igneous provinces and the hypothesis that the associated Paleocene/Eocene Thermal Maximum was caused by hydrothermal release of carbon in response to magmatic intrusions. Successful drilling, combined with high core recovery of target intervals of all nine primary sites and one additional alternate site, should allow us to achieve these goals during postcruise work. 

Volcanic passive margins are an end-member of continental rifted margins and are believed to originate from the breakup of a continent under the influence of a mantle plume. In spite of 40 y of research into this phenomenon, it is still unknown how excess magmatism is produced and what controls its surprisingly short duration. Expedition 396 will revisit the mid-Norwegian margin 36 y after Ocean Drilling Program Leg 104. It will provide the necessary observations to parameterize comprehensive 3-D numerical models. These will allow us to identify the relative importance of different tectonomagmatic processes. Furthermore, drilling will test the predictions of volcanic seismic facies models and elucidate the role of breakup volcanism in rapid global warming. Secondary objectives relate to the onset of the meridional overturning circulation in the North Atlantic Gateway and the potential to use the breakup basalt province to store carbon dioxide on industrial scales. To this end, Expedition 396 will attempt to drill nine boreholes on the Vøring and Møre margins. They will target the breakup volcanic successions as well as the overlying postrift sediments and the underlying synrift sediments. In conjunction with the wealth of reflection seismic data collected by the hydrocarbon industry during the past 40 y, the new borehole information will provide an unprecedented picture of the formation of a large igneous province during the opening of an ocean basin.