Variations in Volcanism and Tectonics Along the Hotspot‐Influenced Reykjanes Ridge. (25th April 2023)

• Record Type: Journal Article
• Authors: Le Saout, M.; Pałgan, D.; Devey, C. W.; Lux, T. S.; Petersen, S.; Thorhallsson, D.; Tomkowicz, A.; Brix, S.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 24:Number 4(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-04-25
• Subjects: mid‐ocean ridge -- volcanism -- tectonic activity -- plume‐ridge interaction -- Reykjanes Ridge; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2022GC010788
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Mapping and sampling four sections of the slow‐spreading Reykjanes Ridge provide insight into how tectonic and volcanic activity varies with distance from the Iceland plume. The studied areas are characterized by significant variations in water depth, lava chemistry, crustal thickness, thermal structure, and ridge morphology. For each study area, fault pattern and dimension, tectonic strain, seamount morphology, and density are inferred from 15 m‐resolution bathymetry. These observations are combined with geochemical analysis from glass samples and sediment thickness estimations along Remotely Operated Vehicle‐dive videos. They reveal that (a) tectonic and volcanic activity along the Reykjanes Ridge, do not systematically vary with distance from the plume center. (b) The tectonic geometry appears directly related to the deepening of the brittle/ductile transition and the maximum change in tectonic strain related to the rapid change in crustal thickness and the transition between axial‐high and axial valley (∼59.5°N). (c) Across‐axis variations in the fault density and sediment thickness provide similar widths for the neo‐volcanic zone except in regions of increased seamount emplacement. (d) The variations in seamount density (especially strong for flat‐topped seamounts) are not related to the distance from the plume but appear to be correlated with the interaction between the V‐shape ridges (VSR) flanking the ridge and the ridge axis. These observations are more compatible with the buoyant upwelling melting instability hypothesis for VSR formation and suggest that buoyant melting instabilities create many small magma batches which by‐pass the normal subaxial magmatic plumbing system, erupting over a wider‐than‐normal area. Plain Language Summary: Volcanic eruptions and faults growth are two important geologic processes taking place along seafloor spreading centers. Their variations in space and time are displayed in the morphology of the spreading centers. Investigating these morphological variations is key to understanding the deeper processes of the oceanic crust formation. South of Iceland, the Reykjanes Ridge is the location of increased volcanism due to the interaction between the mid‐ocean ridge and the Iceland hotspot. Using high‐resolution seafloor topographic data, chemical analyses of volcanic rock, and videos of the seafloor from a remotely operated vehicle, we investigated how volcanism and faulting change along the ridge. The increase in fault dimensions (height, length) with distance from the plume center is probably the result of the crust and mantle becoming cooler and stiffer and thus able to support larger faults. Fault density and thickness of the sediment covering the lava flows near the ridge axis are used to delimit the region of young volcanism. Seamounts often emplaced beyond that region. A peak in seamount abundance near 60°N suggests that the thick crust here is generated from numerous small batches of magma possibly resulting from a migrating instability in the melt production process beneath the axis. Key Points: The distance from the plume center is not the only factor controlling tectonic and volcanic activity along the Reykjanes Ridge Fault dimensions are primarily controlled by the variation of crustal thermal structure with distance from the hotspot Flat‐topped seamount abundances peak where a V‐shaped ridge intersects the axis, consistent with a buoyant upwelling melting instability