Publication Date:
2014-11-05
Description:
Olivine-hosted melt inclusions from both Fernandina and Santiago islands in the Galapagos Archipelago have compositions indicating that plagioclase played an important role in the magmatic evolution of these volcanic islands. The major and trace element chemistry of the Santiago melt inclusions indicates simple plagioclase assimilation. In contrast, Fernandina inclusions have compositions for which the plagioclase appears to be present only as a ‘ghost’ trace element signature (i.e. ‘ghost plagioclase’ signature). Two competing hypotheses have been proposed to explain this unique signature: (1) incorporation of an ancient recycled plagioclase-rich cumulate into the mantle; (2) shallow-level interaction between melts and plagioclase-rich cumulates in the present-day lower oceanic crust. Here we present new Pb isotope measurements for olivine-hosted melt inclusions from Fernandina and Santiago islands to distinguish between the two models. The new Pb isotope data are within the range previously reported for whole-rock basalts from those islands. Melting and mixing models involving ancient (~0·5–1 Ga) recycled plagioclase-rich cumulates cannot reproduce the observed trace element and Pb isotopic characteristics of the Fernandina melt inclusions with a ghost plagioclase signature. Shallow-level diffusive interactions between basalt and present-day plagioclase-rich cumulates provide the simplest explanation for the observed trace element compositions and Pb isotope ratios of melt inclusions from Fernandina and Santiago islands.
Print ISSN:
0022-3530
Electronic ISSN:
1460-2415
Topics:
Geosciences
