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Title: First-order major element variation in basalt glasses from the Mid-Atlantic ridge : 29/sup 0/N to 73/sup 0/N

Abstract

Basaltic glasses from 29/sup 0/N to 73/sup 0/N on the Mid-Atlantic Ridge define two geographic and compositional groups that are characterized by different major element concentrations, phase assemblages and partition coefficients. Group A glasses occur on the ridge segment north of Gibbs Fracture Zone, from 54/sup 0/N, along the Reykjanes Ridge, the western volcanic zone of Iceland and Kolbeinsey Ridge, up to 70/sup 0/N. Similar glasses occur also on the ridge from 29/sup 0/N to 34/sup 0/N. Group A is characterized by pronounced alumina depletion and iron-enrichment trends, lower silica and alkalis and higher iron and high CaO/Al/sub 2/O/sub 3/. Clinopyroxene is only present in the more evolved group A glasses (Mg-value<58). Olivine-glass partition coefficients for Mg and Fe are systematically lower in group A than group B (Schilling and Sigurdsson, 1979), reflecting effects of melt composition on structure of the liquids. Group B glasses define the ridge segment north of 35/sup 0/N over the Azores platform and up to Gibbs F. Z., at 53/sup 0/N. They are also present on the Mohns Ridge north of the Jan Mayen F. Z. at 71/sup 0/N and at least as far north as 73/sup 0/. Group B glasses are characterized by highermore » silica and alkalis, low iron and lack of alumina depletion and iron-enrichment trends. They contain calcic clinopyroxene (Cpx) throughout the compositional range, whereas the sub-calcic augite is absent. The major-element variation within each group can be modeled quantitatively by fractional crystallization involving the phenocryst phases. The range of glass compositions in the two groups forms two distinct but parallel cotectic trends within the basalt tetrahedron, which are believed to define the quaternary univariant line 01-P1-Cpx-Liq along which the magmas evolved during fractionation at low to intermediate pressure.« less

Authors:
Publication Date:
Research Org.:
Graduate School of Oceanography, University of Rhode Island, Kingston, Rhode Island 02881
OSTI Identifier:
5636555
Resource Type:
Journal Article
Journal Name:
J. Geophys. Res.; (United States)
Additional Journal Information:
Journal Volume: 86:B10
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; BASALT; CHEMICAL COMPOSITION; MID-ATLANTIC RIDGE; GEOCHEMISTRY; FRACTIONATION; GLASS; MAGMA; MELTING; PETROCHEMISTRY; PETROGRAPHY; CHEMISTRY; IGNEOUS ROCKS; PHASE TRANSFORMATIONS; ROCKS; SEPARATION PROCESSES; VOLCANIC ROCKS; 580400* - Geochemistry- (-1989)

Citation Formats

Sigurdsson, H. First-order major element variation in basalt glasses from the Mid-Atlantic ridge : 29/sup 0/N to 73/sup 0/N. United States: N. p., 1981. Web. doi:10.1029/JB086iB10p09483.
Sigurdsson, H. First-order major element variation in basalt glasses from the Mid-Atlantic ridge : 29/sup 0/N to 73/sup 0/N. United States. https://doi.org/10.1029/JB086iB10p09483
Sigurdsson, H. 1981. "First-order major element variation in basalt glasses from the Mid-Atlantic ridge : 29/sup 0/N to 73/sup 0/N". United States. https://doi.org/10.1029/JB086iB10p09483.
@article{osti_5636555,
title = {First-order major element variation in basalt glasses from the Mid-Atlantic ridge : 29/sup 0/N to 73/sup 0/N},
author = {Sigurdsson, H},
abstractNote = {Basaltic glasses from 29/sup 0/N to 73/sup 0/N on the Mid-Atlantic Ridge define two geographic and compositional groups that are characterized by different major element concentrations, phase assemblages and partition coefficients. Group A glasses occur on the ridge segment north of Gibbs Fracture Zone, from 54/sup 0/N, along the Reykjanes Ridge, the western volcanic zone of Iceland and Kolbeinsey Ridge, up to 70/sup 0/N. Similar glasses occur also on the ridge from 29/sup 0/N to 34/sup 0/N. Group A is characterized by pronounced alumina depletion and iron-enrichment trends, lower silica and alkalis and higher iron and high CaO/Al/sub 2/O/sub 3/. Clinopyroxene is only present in the more evolved group A glasses (Mg-value<58). Olivine-glass partition coefficients for Mg and Fe are systematically lower in group A than group B (Schilling and Sigurdsson, 1979), reflecting effects of melt composition on structure of the liquids. Group B glasses define the ridge segment north of 35/sup 0/N over the Azores platform and up to Gibbs F. Z., at 53/sup 0/N. They are also present on the Mohns Ridge north of the Jan Mayen F. Z. at 71/sup 0/N and at least as far north as 73/sup 0/. Group B glasses are characterized by higher silica and alkalis, low iron and lack of alumina depletion and iron-enrichment trends. They contain calcic clinopyroxene (Cpx) throughout the compositional range, whereas the sub-calcic augite is absent. The major-element variation within each group can be modeled quantitatively by fractional crystallization involving the phenocryst phases. The range of glass compositions in the two groups forms two distinct but parallel cotectic trends within the basalt tetrahedron, which are believed to define the quaternary univariant line 01-P1-Cpx-Liq along which the magmas evolved during fractionation at low to intermediate pressure.},
doi = {10.1029/JB086iB10p09483},
url = {https://www.osti.gov/biblio/5636555}, journal = {J. Geophys. Res.; (United States)},
number = ,
volume = 86:B10,
place = {United States},
year = {Sat Oct 10 00:00:00 EDT 1981},
month = {Sat Oct 10 00:00:00 EDT 1981}
}