Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges

Elkins L, Sims KW, Prytulak J, Blichert-Toft J, Elliott T, Blusztajn J, Fretzdorff S, Reagan M, Haase K, Humphris S, Schilling JG (2014)

Publication Status: Published

Publication Type: Journal article, Original article

Publication year: 2014

Journal

Geochimica Et Cosmochimica Acta Meteoritical Society

Publisher: Meteoritical Society

Book Volume: 127

Pages Range: 140-170

DOI: 10.1016/j.gca.2013.11.031

Abstract

We present new U-Th-Ra-Pb, U-Pa, and Nd, Sr, Hf, and Pb isotope data for the slow- to ultraslow-spreading Mohns, Knipovich, and Gakkel Ridges. Combined with previous work, our data from the Arctic Ridges cover the full range of axial depths from the deep northernmost Gakkel Ridge shallowing upwards to the Knipovich, Mohns, and Kolbeinsey Ridges north of Iceland. Age-constrained samples from the Mohns and Knipovich Ridges have (Th/U) activity ratios ranging from 1.165 to 1.30 and 1.101 to 1.225, respectively. The high Th excesses of Kolbeinsey, Mohns, and Knipovich mid-ocean ridge basalts (MORB) are erupted from ridges producing relatively thin (Mohns, Knipovich) to thick (Kolbeinsey) oceanic crust with evidence for sources ranging from mostly peridotite (Kolbeinsey) to eclogite-rich mantle (Mohns, Knipovich). Age-constrained lavas from 85°E on the Gakkel Ridge, on the other hand, overlie little to no crust and range from small (~5%) Th excesses to small U excesses (~5%). The strong negative correlation between (Th/U) values vs. axial ridge depth among Arctic ridge basalts is controlled not only by solidus depth influence on U-Th disequilibria, but also by variations in mantle source lithology and depth to the base of the lithosphere, which is expected to vary at ultra-slow spreading ridges. Small Pa excesses (65% excess) in age-constrained basalts support the presence of eclogite in the mantle source for this region. Conversely, the ultraslow-spreading Gakkel Ridge basalts are homogeneous, with Sr, Nd, and Hf radiogenic isotopic signatures indicative of a long time-averaged depleted mantle source. The Gakkel samples have minimum (Ra/Th) ratios ranging from 3.07 to 3.65±3%, which lie along and extend the global negative correlation between Ra and Th excesses observed in MORB. The new Th-Ra data support a model for global MORB production in which deep melts record interaction with shallower materials. This scenario requires either mixing with shallow-derived melts, or melt-rock reaction with shallower rocks in the lithosphere or crust. © 2013 Elsevier Ltd.

Authors with CRIS profile

Karsten Haase Lehrstuhl für Endogene Geodynamik

Involved external institutions

Bryn Mawr College US United States (USA) (US) Woods Hole Oceanographic Institute US United States (USA) (US) Imperial College London / The Imperial College of Science, Technology and Medicine GB United Kingdom (GB) Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon and Université Claude Bernard Lyon FR France (FR) Bristol Isotope Group, University of Bristol GB United Kingdom (GB) University of Iowa US United States (USA) (US) University of Rhode Island US United States (USA) (US) Forschungszentrum Jülich / Research Centre Jülich (FZJ) DE Germany (DE)

How to cite

APA:

Elkins, L., Sims, K.W., Prytulak, J., Blichert-Toft, J., Elliott, T., Blusztajn, J.,... Schilling, J.-G. (2014). Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges. Geochimica Et Cosmochimica Acta, 127, 140-170. https://dx.doi.org/10.1016/j.gca.2013.11.031

MLA:

Elkins, Lynne, et al. "Melt generation beneath Arctic Ridges: Implications from U decay series disequilibria in the Mohns, Knipovich, and Gakkel Ridges." Geochimica Et Cosmochimica Acta 127 (2014): 140-170.

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