Smith, Terence Edward, Thirlwall, Matthew, Holm, Paul Eric and Harris, Michael John (2004) Petrogenesis of orthopyroxene- and amphibole-bearing andesites, Mustique, Grenadine Islands, Lesser Antilles Arc: isotope, trace element and physical constraints. Island Arc, 13 (1).
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On the island of Mustique, fresh and propylitized olivine ()clinopyroxene basalt, plagioclase () clinopyroxene () orthopyroxene and plagioclase () clinopyroxeneamphibole andesite lavas and minor intrusions are interbedded with Oligocene pyroclastic and epiclastic rocks. Chemical data show that two isotopically identical, but chemically different, suites of lava are present: (i) the OPXS (87Sr/86Sr 0.70403 - 70454; 143Nd/144Nd 0.512952 ()0.512986; d18Ocpx 5.49 and 5.61), comprising basalts and orthopyroxene-bearing andesites; and (ii) the AMPHS (87Sr/86Sr 0.70401 -513037; d18Ocpx 5.54), made up of basalts and amphibole-bearing andesites. The OPXS has higher contents of TiO2, P2O5, light rare earth elements, Sm, Pb, Th, U, Zr, Y and Nb, and higher La/Yb ratios than the AMPHS. The isotopic data suggest that both suites formed from melts derived from the same subduction-modified depleted mantle source as the volcanic rocks of nearby St Vincent and Bequia, and the northern islands of the Lesser Antilles Arc. The immobile trace element contents, and La/Yb ratios, of the OPXS are indicative of ~10% partial melting of the source, whereas those of the AMPHS are indicative of ~25% partial melting. The within-suite chemical variation of the OPXS is consistent with ~45% fractional crystallization of its intratelluric mineral assemblages, and that of the AMPHS is consistent with the removal of ~65% of its intratelluric assemblages. Experimental evidence suggests that both suites of basalt crystallized at pressures <8 kbar from melts containing 1 -2 wt% water. After extensive fractional crystallization, the andesites crystallized at pressures between approximately 5 and 2 kbar. The OPXS magmas appear to have lost more of their water content than the AMPHS magmas. Thus, the OPXS andesites formed from melts with an estimated water content of 2 - 3 wt%, whereas the AMPHS andesites formed from melts containing at least 4.5 wt% water.
This is a Published version This version's date is: 2004 This item is peer reviewed
https://repository.royalholloway.ac.uk/items/0c0e6236-7dd7-b48b-5fbe-685f3a343785/1/
Deposited by () on 23-Dec-2009 in Royal Holloway Research Online.Last modified on 23-Dec-2009
This is an electronic version of an article published in The Island Arc, Volume 13: Issue 1, pp.73-94, (C) 2004 Blackwell Publishing.
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