Evolution of high-Ca, high-Sr C-series basalts from Grenada, Lesser Antilles; the effects of intra-crustal contamination

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doi: 10.1144/gsjgs.141.3.0427
Authors:Thirlwall, M. F.; Graham, A. M.
Author Affiliations:Primary:
Univ. Leeds, Dep. Earth Sci., Leeds, United Kingdom
Other:
Britoil, United Kingdom
Volume Title:Journal of the Geological Society of London
Source:Journal of the Geological Society of London, Vol.141(Part 3), p.427-445. Publisher: Geological Society of London, London, United Kingdom. ISSN: 0016-7649
Publication Date:1984
Note:In English. 37 refs.Subduction-related magmatism; illus. incl. 4 tables
Summary:Basaltic lavas from Grenada may be divided into two series on the basis of CaO-MgO relations; the C-series corresponds roughly with the ankaramites or high-Sr series of earlier literature (they have a higher CaO value at a given MgO compared with the M-series and are strongly augite-phyric). Compositional variation within the C-series (16 analyses for major and trace elements) is dominated by fractional crystallization of augite and plagioclase but this was accompanied by assimilation of sedimentary material from the island-arc crust. The assimilation-fractional crystallization process is illustrated by an increase in 206Pb/204Pb from 18.6 to 19.4 with fractionation and correlated increases in Nd/Sr, Zr/Sm and Rb/Ba. The most primitive members of the C-series can not be generated from M-series near-primary basalts but show evidence for an origin by olivine fractionation from high-Mg basalts not seen at the surface. These appear to have been derived from a source similar to that of MORB, but enriched in 87Sr and other hydrophile elements by dehydration of subducted lithosphere, and in REE and radiogenic Pb by a small component of subducted sediment. [R.A.H.]
Subjects:Alkali metals; Alkaline earth metals; Andesites; Ankaramite; Augite; Basanite; Calcium; Chain silicates; Clinopyroxene; Crust; Fractional crystallization; Genesis; Geochemistry; Igneous rocks; Isotopes; Lead; Major elements; Metals; Nd-144/Nd-143; Neodymium; Nesosilicates; Orthosilicates; Pb-206/Pb-204; Petrology; Pyroxene group; Radioactive isotopes; Rare earths; Rubidium; Silicates; Sr-87/Sr-86; Stable isotopes; Strontium; Ultramafic composition; Volcanic rocks; Zircon; Zircon group; Zirconium; Antilles; Caribbean region; Grenada; Lesser Antilles; West Indies; Nd/Sr; Northern Domes; Plagioclase group; Ratios; Rb/Ba; Zr/Sm
Coordinates:N120500 N120500 W0614000 W0614000
Abstract Numbers:84M/2950
Record ID:1985081096
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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