GOLDSCHMIDTCONFERENCE TOULOUSE 1998 Using glass inclusions to investigate a heterogeneous mantle: An example from N- and EMORB-like lavas from Baffin Island

The study of glass inclusions in early-crystallized phenocrysts in basalts offers a means for investi-gating primitive melt compositions.(e.g. Sobolev and Shimizu, 1993; Nielsen et al. 1995). Glass inclusions may sample melt compositions not available as erupted magmas, most of which probably represent mixtures of a range of melts (largely homogenized in magma chambers and conduits). In particular, where mixing of melts derived from sources of different composition has occurred, glass inclusions can potentially provide information on endmember compositions unavailable from the study of erupted lavas alone. Results and discussion We have analysed olivine-hosted (Fo84-Fo92) glass inclusions from a suite of picritic rocks from Baffin Island, Canada, erupted during the opening of the Davis Strait at- 58 Ma (Francis, 1985). Major element compositions of-200 glass inclusions were measured by electron microprobe and REE abun-dances were measured in a subset of these inclusions by ion microprobe. Our results are also compared to major element and REE data for matrix glasses from the same samples reported by Robillard et al. (1992). The Baffin Island picrites occur as two stratigraphi-cally interbedded, but geochemically distinct, lava types: (i) NMORB-like lavas, that have matrix glasses with depleted LREE ([La/Sm]N ~ 0.6-0.7) and low KzO/TiO2 (< 0.08); and (ii) EMORB-Iike lavas that have matrix glasses with enriched LREE ([LaJSm]N ~ 1.1-1.2) and higher KzO/TiO2 (> 0.08) (RobiUard et al., 1992). Sr and Nd isotopic analysis of these matrix glasses were also performed as part of this study and show that E- and NMORB-Iike samples are also isotopieally distinct: NMORB-lik