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

Journal Article · Sat Oct 10 04:00:00 EDT 1981 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB086iB10p09469· OSTI ID:5757130

Clague, D A; Frey, F A; Thompson, G; Rindge, S

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.

• OSTI ID: 5757130
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 86:B10; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580400* -- Geochemistry-- (-1989)
CHEMICAL COMPOSITION
CHEMISTRY
EARTH CRUST
EARTH MANTLE
FRACTIONATION
GEOCHEMISTRY
GEOLOGIC HISTORY
IGNEOUS ROCKS
LAVA
MAGMA
MELTING
OCEANIC CRUST
PACIFIC OCEAN
PHASE TRANSFORMATIONS
ROCKS
SEA-FLOOR SPREADING
SEAS
SEPARATION PROCESSES
SURFACE WATERS
VOLCANIC ROCKS