Evidence for Low‐Pressure Crustal Anatexis During the Northeast Atlantic Break‐Up

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: A. M. Morris, S. Lambart, M. A. Stearns, J. R. Bowman, M. T. Jones, G. Mohn, G. Andrews, J. Millett, C. Tegner, S. Chatterjee, J. Frieling, P. Guo, D. W. Jolley, E. H. Cunningham, C. Berndt, S. Planke, C. A. Alvarez Zarikian, P. Betlem, H. Brinkhuis, M. Christopoulou, E. Ferré, I. Y. Filina, D. T. Harper, J. Longman, R. P. Scherer, N. Varela, W. Xu, S. L. Yager, A. Agarwal, V. J. Clementi
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2024
• Subjects: crustal anatexis; Mimir High; IODP Site U1570; continental break‐up; NAIP; Geophysics. Cosmic physics; QC801-809; Geology; QE1-996.5; Northeast Atlantic
• Online Access: https://doi.org/10.1029/2023GC011413; https://doaj.org/article/747e4d671ffe4ce3af2b5c83e9fea98a

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.