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

6533b85efe1ef96bd12bff87

RESEARCH PRODUCT

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

Julie Prytulak Julie Prytulak Colin W. Devey Janne Blichert-toft J.-g. Schilling Kenneth W.w. Sims Kenneth W.w. Sims L. J. Elkins L. J. Elkins Nelia W. Dunbar Nadine Mattielli Michael T. Murrell Jerzy S. Blusztajn Tim Elliott Dieter F. Mertz

subject

NORWEGIAN-GREENLAND SEA U-SERIES DISEQUILIBRIA 010504 meteorology & atmospheric sciences [SDE.MCG]Environmental Sciences/Global Changes MID-ATLANTIC RIDGE Geochemistry [SDU.STU]Sciences of the Universe [physics]/Earth Sciences HETEROGENEOUS ICELAND PLUME Mid-Atlantic Ridge 010502 geochemistry & geophysics 01 natural sciences [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry Geochemistry and Petrology JUAN-DE-FUCA ComputingMilieux_MISCELLANEOUS TH-PA-RA 0105 earth and related environmental sciences Petrogenesis ND-PB ISOTOPE Peridotite Basalt UPWELLING RATES BENEATH [ SDU.STU ] Sciences of the Universe [physics]/Earth Sciences Crust TRACE-ELEMENT EVIDENCE [ SDU.STU.GC ] Sciences of the Universe [physics]/Earth Sciences/Geochemistry EAST PACIFIC RISE [ SDE.MCG ] Environmental Sciences/Global Changes 13. Climate action Ridge (meteorology)Upwelling Eclogite Geology

description

International audience; 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 = 1.8 cm/yr; 67 degrees 05'-70 degrees 26'N) display ((230)Th/(238)U) 1 with ((230)Th/(238)U) from 0.95 to 1.30 and have low U (11.3-65.6 ppb) and Th (33.0 ppb-2.40 ppm) concentrations. Except for characteristic isotopic enrichment near the Jan Mayen region, the otherwise depleted Kolbeinsey basalts (e. g. (87)Sr/(86)Sr = 0.70272-0.70301, epsilon(Nd) = 8.4-10.5, epsilon(Hf) = 15.4-19.6 (La/Yb)(N) = 0.28-0.84) encompass a narrow range of ((230)Th/(232)Th) (1.20-1.32) over a large range in ((238)U/(232)Th) (0.94-1.32), producing a horizontal array on a ((230)Th/(232)Th) vs. ((238)U/(232)Th) diagram and a large variation in ((230)Th/(238)U). However, the ((230)Th/(238)U) of the Kolbeinsey Ridge basalts (0.96-1.30) are inversely correlated with ((234)U/(238)U) (1.001-1.031). Samples with low ((230)Th/(238)U) and elevated ((234)U/(238)U) reflect alteration by seawater or seawater-derived materials. The unaltered Kolbeinsey lavas with equilibrium (234)U/(238)U have high ((230)Th/(238)U) 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 ((230)Th/(238)U) and ((231)Pa/(235)U) ratios in uncontaminated Kolbeinsey lavas, but low ((231)Pa/(235)U) ratios in Eggvin Bank samples suggest eclogite involvement in the source for that ridge segment

year	journal	country	edition	language
2011-11-01	Geochimica et Cosmochimica Acta

https://doi.org/10.1016/j.gca.2011.08.020