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Title: The effect of primary versus secondary processes on the volatile content of MORB glasses: An example from the equatorial Mid‐Atlantic Ridge (5°N–3°S)

Abstract

We report microanalysis of volatile and trace element compositions, as well as Fe3+/ΣFe ratios, from 45 basaltic glasses from cruise RC2806 along the equatorial Mid–Atlantic Ridge. The along–strike variations in volatiles result from the complex geodynamical setting of the area, including numerous transform faults, variations in ridge depth, melting degree, and source composition. The strongest gradient is centered on 1.7°N and encompasses an increase of H2O, Cl, and F contents as well as high F/Zr ratio spatially coincident with radiogenic isotope anomalies. We interpret these variations as source enrichment due to the influence of the nearby high–μ–type Sierra Leone plume. South of the St. Paul fracture zone, H2O and F contents, as well as H2O/Ce and F/Zr ratios, decrease progressively. This gradient in volatiles is consistent with progressive dilution of an enriched component in a heterogeneous mantle due to the progressive increase in the degree of melting. These two large–scale gradients are interrupted by small–scale anomalies in volatile contents attributed to (1) low–degree melts preferentially sampling enriched heterogeneities near transform faults and (2) local assimilation of hydrothermal fluids in four samples from dredge 16D. Finally, 20 RC2806 samples described as “popping rocks” during collection do not show any difference inmore » volatile content dissolved in the glass or in vesicularity when compared to the RC2806 “nonpopping” samples. Our observations lead us to question the interpretation of the CO2 content in the highly vesicular 2πD43 “popping rock” as being representative of the CO2 content of undegassed mid–ocean ridge basalt.« less

Authors:
 [1];  [2];  [3];  [3];  [4]
  1. Department of Terrestrial MagnetismCarnegie Institution of Washington Washington District of Colombia USA, National Museum of Natural HistorySmithsonian Institution Washington District of Columbia USA
  2. National Museum of Natural HistorySmithsonian Institution Washington District of Columbia USA
  3. Graduate School of OceanographyUniversity of Rhode Island, Narragansett Bay Campus Narragansett Rhode Island USA
  4. Department of Terrestrial MagnetismCarnegie Institution of Washington Washington District of Colombia USA
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1240462
Alternate Identifier(s):
OSTI ID: 1229450; OSTI ID: 1240464
Report Number(s):
BNL-111526-2015-JA
Journal ID: ISSN 2169-9313
Grant/Contract Number:  
SC00112704; AC02‐98CH10886; FG02‐92ER14244
Resource Type:
Journal Article: Published Article
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Name: Journal of Geophysical Research. Solid Earth Journal Volume: 120 Journal Issue: 1; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; volatile elements; Mid‐Atlantic Ridge; basalt; MORB; magmatic processes; geochemistry

Citation Formats

Le Voyer, Marion, Cottrell, Elizabeth, Kelley, Katherine A., Brounce, Maryjo, and Hauri, Erik H. The effect of primary versus secondary processes on the volatile content of MORB glasses: An example from the equatorial Mid‐Atlantic Ridge (5°N–3°S). United States: N. p., 2015. Web. doi:10.1002/2014JB011160.
Le Voyer, Marion, Cottrell, Elizabeth, Kelley, Katherine A., Brounce, Maryjo, & Hauri, Erik H. The effect of primary versus secondary processes on the volatile content of MORB glasses: An example from the equatorial Mid‐Atlantic Ridge (5°N–3°S). United States. https://doi.org/10.1002/2014JB011160
Le Voyer, Marion, Cottrell, Elizabeth, Kelley, Katherine A., Brounce, Maryjo, and Hauri, Erik H. 2015. "The effect of primary versus secondary processes on the volatile content of MORB glasses: An example from the equatorial Mid‐Atlantic Ridge (5°N–3°S)". United States. https://doi.org/10.1002/2014JB011160.
@article{osti_1240462,
title = {The effect of primary versus secondary processes on the volatile content of MORB glasses: An example from the equatorial Mid‐Atlantic Ridge (5°N–3°S)},
author = {Le Voyer, Marion and Cottrell, Elizabeth and Kelley, Katherine A. and Brounce, Maryjo and Hauri, Erik H.},
abstractNote = {We report microanalysis of volatile and trace element compositions, as well as Fe3+/ΣFe ratios, from 45 basaltic glasses from cruise RC2806 along the equatorial Mid–Atlantic Ridge. The along–strike variations in volatiles result from the complex geodynamical setting of the area, including numerous transform faults, variations in ridge depth, melting degree, and source composition. The strongest gradient is centered on 1.7°N and encompasses an increase of H2O, Cl, and F contents as well as high F/Zr ratio spatially coincident with radiogenic isotope anomalies. We interpret these variations as source enrichment due to the influence of the nearby high–μ–type Sierra Leone plume. South of the St. Paul fracture zone, H2O and F contents, as well as H2O/Ce and F/Zr ratios, decrease progressively. This gradient in volatiles is consistent with progressive dilution of an enriched component in a heterogeneous mantle due to the progressive increase in the degree of melting. These two large–scale gradients are interrupted by small–scale anomalies in volatile contents attributed to (1) low–degree melts preferentially sampling enriched heterogeneities near transform faults and (2) local assimilation of hydrothermal fluids in four samples from dredge 16D. Finally, 20 RC2806 samples described as “popping rocks” during collection do not show any difference in volatile content dissolved in the glass or in vesicularity when compared to the RC2806 “nonpopping” samples. Our observations lead us to question the interpretation of the CO2 content in the highly vesicular 2πD43 “popping rock” as being representative of the CO2 content of undegassed mid–ocean ridge basalt.},
doi = {10.1002/2014JB011160},
url = {https://www.osti.gov/biblio/1240462}, journal = {Journal of Geophysical Research. Solid Earth},
issn = {2169-9313},
number = 1,
volume = 120,
place = {United States},
year = {Wed Jan 14 00:00:00 EST 2015},
month = {Wed Jan 14 00:00:00 EST 2015}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at https://doi.org/10.1002/2014JB011160

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Cited by: 55 works
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