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Title: Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity

Abstract

A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95/sup 0/ W and 85/sup 0/ W on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However, the P/sub 2/O/sub 5//K/sub 2/O ratio averages 0.83 at 95/sup 0/W and 1.66 at 85/sup 0/W and implies distinct mantle source compositions for the two areas. These source regions also have different rare earth element (REE) abundance patterns, with (La/Sm)/sub EF/ = 0.67 at 95/sup 0/W and 0.46 at 85/sup 0/W. The sequence of fractional lavas differs for the two areas and indicates earlier fractionation of apatite and titanomagnetite in the lavas from 95/sup 0/W. Incompatible trace element abundances in 26 samples are used to infer that the range of Fe-Ti-rich basalt from 85/sup 0/W represents 19 to 35% residual liquid following crystal fractionation of a mineral assemblage of plagioclase, clinopyroxene, and lesser olivine. Most samples from 85/sup 0/W can be related to a common parental magma that contained approximately 9 wt %FeO*, 1 wt % TiO/sub 2/, and had an Mg number (Mg/sup 3/ =more » 100 Mg/(Mg+Fe/sup 2 +/)) of about 65. Although the samples from 95/sup 0/W cannot all be derived from a common parental magma, the inferred parental magmas may have been derived by varying degrees of partial melting of a common source. The fractionation sequence consists of two parts: an initial iron enrichment trend followed by a silica enrichment trend. The most iron rich lavas represent about 32% residual liquid derived by crystal fractionation of plagioclase, clinopyroxene, and lesser olivine from a parental magma with an Mg number of about 66. The silicic enrichment trend results from crystallization of titanomagnetite and some apatite.« less

Authors:
; ; ;
Publication Date:
OSTI Identifier:
5757130
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; LAVA; CHEMICAL COMPOSITION; MAGMA; OCEANIC CRUST; GEOCHEMISTRY; EARTH MANTLE; FRACTIONATION; GEOLOGIC HISTORY; MELTING; PACIFIC OCEAN; SEA-FLOOR SPREADING; VOLCANIC ROCKS; CHEMISTRY; EARTH CRUST; IGNEOUS ROCKS; PHASE TRANSFORMATIONS; ROCKS; SEAS; SEPARATION PROCESSES; SURFACE WATERS; 580400* - Geochemistry- (-1989)

Citation Formats

Clague, D A, Frey, F A, Thompson, G, and Rindge, S. Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity. United States: N. p., 1981. Web. doi:10.1029/JB086iB10p09469.
Clague, D A, Frey, F A, Thompson, G, & Rindge, S. Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity. United States. https://doi.org/10.1029/JB086iB10p09469
Clague, D A, Frey, F A, Thompson, G, and Rindge, S. 1981. "Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity". United States. https://doi.org/10.1029/JB086iB10p09469.
@article{osti_5757130,
title = {Minor and trace element geochemistry of volcanic rocks dredged from the Galapagos spreading center: Role of crystal fractionation and mantle heterogeneity},
author = {Clague, D A and Frey, F A and Thompson, G and Rindge, S},
abstractNote = {A wide range of rock types (abyssal tholeiite, Fe-Ti-rich basalt, andesite, and rhyodacite) were dredged from near 95/sup 0/ W and 85/sup 0/ W on the Galapagos spreading center. Computer modeling of major element compositions has shown that these rocks could be derived from common parental magmas by successive degrees of fractional crystallization. However, the P/sub 2/O/sub 5//K/sub 2/O ratio averages 0.83 at 95/sup 0/W and 1.66 at 85/sup 0/W and implies distinct mantle source compositions for the two areas. These source regions also have different rare earth element (REE) abundance patterns, with (La/Sm)/sub EF/ = 0.67 at 95/sup 0/W and 0.46 at 85/sup 0/W. The sequence of fractional lavas differs for the two areas and indicates earlier fractionation of apatite and titanomagnetite in the lavas from 95/sup 0/W. Incompatible trace element abundances in 26 samples are used to infer that the range of Fe-Ti-rich basalt from 85/sup 0/W represents 19 to 35% residual liquid following crystal fractionation of a mineral assemblage of plagioclase, clinopyroxene, and lesser olivine. Most samples from 85/sup 0/W can be related to a common parental magma that contained approximately 9 wt %FeO*, 1 wt % TiO/sub 2/, and had an Mg number (Mg/sup 3/ = 100 Mg/(Mg+Fe/sup 2 +/)) of about 65. Although the samples from 95/sup 0/W cannot all be derived from a common parental magma, the inferred parental magmas may have been derived by varying degrees of partial melting of a common source. The fractionation sequence consists of two parts: an initial iron enrichment trend followed by a silica enrichment trend. The most iron rich lavas represent about 32% residual liquid derived by crystal fractionation of plagioclase, clinopyroxene, and lesser olivine from a parental magma with an Mg number of about 66. The silicic enrichment trend results from crystallization of titanomagnetite and some apatite.},
doi = {10.1029/JB086iB10p09469},
url = {https://www.osti.gov/biblio/5757130}, 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}
}