The isotopic (He, Ne, Sr, Nd, Hf, Pb) signature in the Indian Mantle over 8.8 Ma

Type Article
Date 2020-09
Language English
Author(s) Paquet Marine1, Hamelin Cédric2, Moreira Manuel3, Cannat Mathilde1
Affiliation(s) 1 : Equipe de Géosciences Marines, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, UMR7154 CNRS, 1, rue Jussieu, 75238 Paris cedex 05, France
2 : Earth Science department, University of Bergen, Allegaten 41, 5007 Bergen, Norway
3 : Observatoire des Sciences de l'Univers, Université d'Orléans, UMS3116, 1A, rue de la Férollerie, CS 20066, 45071 Orléans cedex 2, France
Source Chemical Geology (0009-2541) (Elsevier BV), 2020-09 , Vol. 550 , P. 119741 (12p.)
DOI 10.1016/j.chemgeo.2020.119741
WOS© Times Cited 1
Keyword(s) Mid-Ocean Ridge Basalts, Mantle heterogeneity, Noble gases, Isotope geochemistry, Melt/mantle interactions
Abstract

The eastern Southwest Indian Ridge, between 61° and 67°E, has a very low melt supply and comprises several corridors of nearly amagmatic spreading that expose mantle-derived serpentinized peridotite. More volcanically active ridge portions separate these corridors. He, Ne, Pb, Nd, Hf and Sr isotopes were analyzed in basalt glasses dredged on two types of seafloor: volcanic and ultramafic. Basalts dredged in ultramafic seafloor on-axis tend to be slightly more depleted for heavy radiogenic isotopes and show slightly higher 3He/4He isotope ratios than basalts dredged in volcanic seafloor, with no systematic difference in neon isotope ratios. We propose that both types of basalts are derived from the same mantle source, but that the basalts dredged on ultramafic seafloor are more affected by melt/mantle reactions, which slightly modify their isotopic signatures. Our dataset also includes a few basalts, dredged on off-axis ultramafic seafloor, that range in age between 2.6 and 8.8 Ma. These few and widely-spaced off-axis samples, erupted at the ridge axis, are a rare opportunity to capture the potential geochemical variability of the mantle source in an ultramafic seafloor corridor over 8.8 Ma. This temporal variability appears to be minor compared to the overall range of isotopic variability of the on-axis lavas from the 61°-67°E region.

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Fig. S1. Comparison of (a) 87Sr/86Sr ratios and (b) (La/Sm)n in function of the age of the samples. Same symbols as in Fig. 2. 189 KB Open access
Table S1. Compilation of major (wt%), trace (ppm) and isotopic (Hf, Nd, Sr, Pb, He, Ne) compositions for volcanic and ultramafic seafloor basalts from the 61°-67°E region of the Southwest Indian Ridge 119 KB Open access
Table S2. Two-sample Kolmogorov-Smirnov test for Pb, Nd and He isotope ratios. 25 KB Open access
Publisher's official version 50 7 MB Open access
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