Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using U-238, Th-230, and Pa-231 excesses

Elkins, L; Sims, K; Prytulak, J; Elliott, T; Mattielli, N; Blichert-Toft, J; Blusztajn, J; Dunbar, N; Devey, C; Mertz, D; Schilling, J; Murrell, M

Journal article

Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using U-238, Th-230, and Pa-231 excesses

Abstract:: To examine the petrogenesis and sources of basalts from the Kolbeinsey Ridge, one of the shallowest locations along the global ridge system, we present new measurements of Nd, Sr, Hf, and Pb isotopes and U-series disequilibria on 32 axial basalts. Young Kolbeinsey basalts (full-spreading rate=1.8cm/yr; 67°05'-70°26'N) display (230Th/238U)<1 and (230Th/238U)>1 with (230Th/238U) from 0.95 to 1.30 and have low U (11.3-65.6ppb) and Th (33.0ppb-2.40ppm) concentrations. Except for characteristic isotopic enrichment near the Jan Mayen region, the otherwise depleted Kolbeinsey basalts (e.g. 87Sr/86Sr=0.70272-0.70301, εNd=8.4-10.5, εHf=15.4-19.6 (La/Yb)N=0.28-0.84) encompass a narrow range of (230Th/232Th) (1.20-1.32) over a large range in (238U/232Th) (0.94-1.32), producing a horizontal array on a (230Th/232Th) vs. (238U/232Th) diagram and a large variation in (230Th/238U). However, the (230Th/238U) of the Kolbeinsey Ridge basalts (0.96-1.30) are inversely correlated with (234U/238U) (1.001-1.031). Samples with low (230Th/238U) and elevated (234U/238U) reflect alteration by seawater or seawater-derived materials. The unaltered Kolbeinsey lavas with equilibrium 234U/238U have high (230Th/238U) values (≥1.2), which are consistent with melting in the presence of garnet. This is in keeping with the thick crust and anomalously shallow axial depth for the Kolbeinsey Ridge, which is thought to be the product of large degrees of melting in a long melt column. A time-dependent, dynamic melting scenario involving a long, slowly upwelling melting column that initiates well within the garnet peridotite stability zone can, in general, reproduce the (230Th/238U) and (231Pa/235U) ratios in uncontaminated Kolbeinsey lavas, but low (231Pa/235U) ratios in Eggvin Bank samples suggest eclogite involvement in the source for that ridge segment. © 2011 Elsevier Ltd.

Publication status:: Published

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APA Style

Elkins, L., Sims, K., Prytulak, J., Elliott, T., Mattielli, N., Blichert-Toft, J., Blusztajn, J., Dunbar, N., Devey, C., Mertz, D., Schilling, J., & Murrell, M. (2011). Understanding melt generation beneath the slow-spreading Kolbeinsey Ridge using U-238, Th-230, and Pa-231 excesses. GEOCHIMICA ET COSMOCHIMICA ACTA, 75(21), 6300–6329.

MLA Style

Elkins, L, et al. “Understanding Melt Generation beneath the Slow-Spreading Kolbeinsey Ridge Using U-238, Th-230, and Pa-231 Excesses.” GEOCHIMICA ET COSMOCHIMICA ACTA, vol. 75, no. 21, 2011, pp. 6300–29.

Chicago Style

Elkins, L, K Sims, J Prytulak, et al. 2011. “Understanding Melt Generation beneath the Slow-Spreading Kolbeinsey Ridge Using U-238, Th-230, and Pa-231 Excesses.” GEOCHIMICA ET COSMOCHIMICA ACTA 75 (21): 6300–6329.
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