Constraints on the Timing and Lower Crustal Accretion at the Schulz Massif, Mohns Ridge, Arctic Mid Ocean Ridges

Constraints on the Timing and Lower Crustal Accretion at the Schulz Massif, Mohns Ridge, Arctic Mid Ocean Ridges

The ultraslow‐spreading Mohns Ridge is a key supersegment of the Arctic Mid‐Ocean system, where it represents a boundary between the Jan Mayen hotspot in the south and the highly anomalous Knipovich Ridge to the north. Understanding the timing and mode of Plio‐Pleistocene seafloor spreading along th...

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2024-04, Vol.25 (4), p.n/a
Main Authors: Bjerga, A., Stubseid, H. H., Pedersen, L. E. R., Corfu, F., Whitehouse, M., Pedersen, R. B.
Format: Article
Language:eng
Subjects:
Accretion
Arctic Ocean
Crustal accretion
Crustal structure
crystal size distribution
gabbro
Geochemistry
Geochronology
Geochronometry
Magma
mid‐ocean ridge
Ocean floor
Oceanic crust
Oceans
Olivine
Peridotite
Petrography
Petrology
Pleistocene
Ridges
Seafloor spreading
symmetric seafloor spreading
tectonic window
ultraslow spreading ridge
Zircon
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Summary:The ultraslow‐spreading Mohns Ridge is a key supersegment of the Arctic Mid‐Ocean system, where it represents a boundary between the Jan Mayen hotspot in the south and the highly anomalous Knipovich Ridge to the north. Understanding the timing and mode of Plio‐Pleistocene seafloor spreading along this ridge segment is critical for establishing the recent geodynamic evolution of the Norwegian‐Greenland Sea. To investigate magmatic accretion at this ultraslow spreading ridge, we collected samples from the Schulz Massif, which is located off‐axis at 73.4°N and exposes gabbroic intrusives and mantle peridotite. The petrology and petrography of these samples indicate that the exposed crustal section underwent multiple episodes of magmatism, which are characterized by distinct crystal sizes and geochemistry. To calibrate the age of the seafloor, we combined high‐resolution and high‐precision single zircon U‐Pb geochronology. Our data suggest that seafloor spreading has been nearly symmetrical for the last ∼4.6 Myr with a time‐averaged half‐spreading rate of ∼7.4 mm yr−1. Crystal size analysis of olivine in porphyric intrusions suggests that the crustal section was fed crystal‐laden melts with recurrence rates predicted to stabilize fault‐dominated seafloor spreading. Our combined geochronological and crystal size approach gives a critical perspective on the mode of seafloor spreading in the Mohns Ridge and allows insights into accretionary mechanisms and crustal structures during symmetric seafloor spreading. Key Points We investigated a unique suite of lower crustal rocks recovered from a tectonic window off‐axis of the ultraslow‐spreading Mohns Ridge Zircon U‐Pb geochronology suggests 4.6 Myr of nearly symmetrical seafloor spreading at a time‐averaged half‐spreading rate of ∼7.4 mm yr−1 Small‐scale magmatic injections were important for crustal construction
ISSN:1525-2027
1525-2027