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The Silfari Volcano: Recently Discovered Ladinian‐Carnian Triassic Volcanism Offshore Mid‐Norway Characterized by the 6307/1‐1S Borehole.

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Title: The Silfari Volcano: Recently Discovered Ladinian‐Carnian Triassic Volcanism Offshore Mid‐Norway Characterized by the 6307/1‐1S Borehole.
Authors: Millett, John M.1,2,3 (AUTHOR) john.millett@vber.no, Thomas, Steve4 (AUTHOR), Planke, Sverre1,2 (AUTHOR), Callegaro, Sara5,6 (AUTHOR), Augland, Lars E.2 (AUTHOR), Jerram, Dougal A.5,7 (AUTHOR), Charnock, Michael8 (AUTHOR), Polonio, Israel4 (AUTHOR), Svensen, Henrik2 (AUTHOR), Sandvik, Sara E.9 (AUTHOR)
Source: Basin Research. May2026, Vol. 38 Issue 3, p1-28. 28p.
Subject Terms: *Volcanoes, *Triassic Period, *Hydrothermal deposits, *Uranium-lead dating, *Alkalic igneous rocks, *Mesozoic Era, *Physiographic provinces
Geographic Terms: Norway
Abstract: Borehole 6307/1‐1S was drilled in the Froan Basin offshore mid‐Norway in 2018. The bottom of the well penetrated the upper c. 650 m of a seismically imaged mound revealing a previously unknown volcano‐sedimentary sequence, here termed the Silfari Volcano. Borehole analyses reveal four volcanic packages (V1‐V4), dominated by deeply altered extrusive lava flows and subsidiary pyroclastic units interlayered with (S1‐S3) and then capped by (S4) four prominent terrestrial volcaniclastic sedimentary intervals. Petrological analyses of core and sidewall core samples reveal a strongly alkaline series of basic‐intermediate to evolved igneous rocks ranging from foidites, through tephri‐phonolites to phonolites. Sheet intrusions and cored hydrothermal baryte‐calcite‐fluorite veins with very low δ34SVCDT (9.9‰–11.8‰) subsequently cut the sequence. The vein formation is provisionally attributed to mixing of shallow Ba‐enriched waters with saline and sulphate‐rich brines ultimately derived from sub‐volcanic magma‐evaporite interactions with an interpreted potential Permian Zechstein sequence below the well penetration. Calcite δ13C and δ18O (mean −2.10‰ δ13CVPDB and −14.79‰ δ18OVPDB, respectively) support a modified seawater component in the vein‐forming fluids. High precision U–Pb TIMS age dating on zircons extracted from the lowermost V1 (238.02 ± 0.13 Ma) and uppermost V4 (234.96 ± 0.47 Ma) volcanic packages bracket the activity of the Silfari Volcano across c. 3 Myr spanning the Ladinian‐Carnian boundary of the Middle‐Upper Triassic conformable with biostratigraphic results from overlying sediments. Magmatic zircons from within the V3 package reveal a date of 183.11 ± 0.12 Ma, indicating that a previously undocumented Early Jurassic intrusive magmatic event influenced the area. The Silfari Volcano shares some chemical affinities with the Skagerrak Centred Large Igneous Province (SCLIP) and the Oslo Rift; however, it is located several 100 km north of the nearest SCLIP deposits and post‐dates the youngest robustly dated volcanism by several million years. The identification of Triassic volcanism has significant implications for understanding the tectono‐magmatic history of the NE Atlantic margins. Highlights: Triassic Silfari Volcano and associated magmatism discovered offshore mid‐Norway.Core‐log‐seismic characterization of alkaline volcano‐sedimentary sequence.Geochemistry reveals a highly alkaline volcanic sequence cut by later hydrothermal baryte‐calcite‐fluorite veins recovered in core.High precision U–Pb age dating of volcanic zircons ranges from 238.02 ± 0.13 Ma to 234.96 ± 0.47 Ma spanning 3 Myr eruptive historyJurassic intrusive event at 183.11 ± 0.12 Ma identified from U–Pb age dating [ABSTRACT FROM AUTHOR]
Database: Energy & Power Source
Description
Abstract:Borehole 6307/1‐1S was drilled in the Froan Basin offshore mid‐Norway in 2018. The bottom of the well penetrated the upper c. 650 m of a seismically imaged mound revealing a previously unknown volcano‐sedimentary sequence, here termed the Silfari Volcano. Borehole analyses reveal four volcanic packages (V1‐V4), dominated by deeply altered extrusive lava flows and subsidiary pyroclastic units interlayered with (S1‐S3) and then capped by (S4) four prominent terrestrial volcaniclastic sedimentary intervals. Petrological analyses of core and sidewall core samples reveal a strongly alkaline series of basic‐intermediate to evolved igneous rocks ranging from foidites, through tephri‐phonolites to phonolites. Sheet intrusions and cored hydrothermal baryte‐calcite‐fluorite veins with very low δ34SVCDT (9.9‰–11.8‰) subsequently cut the sequence. The vein formation is provisionally attributed to mixing of shallow Ba‐enriched waters with saline and sulphate‐rich brines ultimately derived from sub‐volcanic magma‐evaporite interactions with an interpreted potential Permian Zechstein sequence below the well penetration. Calcite δ13C and δ18O (mean −2.10‰ δ13CVPDB and −14.79‰ δ18OVPDB, respectively) support a modified seawater component in the vein‐forming fluids. High precision U–Pb TIMS age dating on zircons extracted from the lowermost V1 (238.02 ± 0.13 Ma) and uppermost V4 (234.96 ± 0.47 Ma) volcanic packages bracket the activity of the Silfari Volcano across c. 3 Myr spanning the Ladinian‐Carnian boundary of the Middle‐Upper Triassic conformable with biostratigraphic results from overlying sediments. Magmatic zircons from within the V3 package reveal a date of 183.11 ± 0.12 Ma, indicating that a previously undocumented Early Jurassic intrusive magmatic event influenced the area. The Silfari Volcano shares some chemical affinities with the Skagerrak Centred Large Igneous Province (SCLIP) and the Oslo Rift; however, it is located several 100 km north of the nearest SCLIP deposits and post‐dates the youngest robustly dated volcanism by several million years. The identification of Triassic volcanism has significant implications for understanding the tectono‐magmatic history of the NE Atlantic margins. Highlights: Triassic Silfari Volcano and associated magmatism discovered offshore mid‐Norway.Core‐log‐seismic characterization of alkaline volcano‐sedimentary sequence.Geochemistry reveals a highly alkaline volcanic sequence cut by later hydrothermal baryte‐calcite‐fluorite veins recovered in core.High precision U–Pb age dating of volcanic zircons ranges from 238.02 ± 0.13 Ma to 234.96 ± 0.47 Ma spanning 3 Myr eruptive historyJurassic intrusive event at 183.11 ± 0.12 Ma identified from U–Pb age dating [ABSTRACT FROM AUTHOR]
ISSN:0950091X
DOI:10.1111/bre.70120