HR: 0800h
AN: V31C-1446    [Abstracts]
TI: Melt Inclusions in Primitive Olivines from Padloping Island, Baffin Bay
AU: * Smit, Y
EM: y.smit@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans OPGC Universite Blaise Pascal, 5 Rue Kessler, Clermont-Ferrand, 63038 France
AU: Schiano, P
EM: p.schiano@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans OPGC Universite Blaise Pascal, 5 Rue Kessler, Clermont-Ferrand, 63038 France
AU: Faure, F
EM: f.faure@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans OPGC Universite Blaise Pascal, 5 Rue Kessler, Clermont-Ferrand, 63038 France
AB: Tertiary picrites from Padloping Island, Baffin Bay, are thought to be the result of early activity of the Iceland Plume. The olivines found in these lavas are primitive to very primitive with Fo-content ranging from 88 to 93. However, they are not in equilibrium with the liquid, suggesting that they have been derived from earlier cumulates. Therefore, by obtaining the composition of the melt inclusions in these olivines we might be able to gain some insight in the composition of, possibly primary, mantle derived melts. We have optically evaluated a large set of olivines and it is clear that they all contain primary inclusions ranging in size from $\sim$10 to $\sim$100 micron in diameter. The inclusions are randomly distributed and not related to any fractures. They contain glass, included spinel minerals, daughter minerals and volatiles, suggesting relatively slow cooling after entrapment. Electron microprobe analysis of daughter minerals has suggested a primitive composition for the initial trapped liquid, which has evolved into a residual Si-rich liquid after the growth of Al-rich clinopyroxene. In order to analyse the original trapped melt homogenisation experiments have been carried out under ambient pressure using a heating stage under controlled fO$_{2}$ conditions (purified He atmosphere). These experiments suggest that our liquidus temperature could be as high as $1350\deg$C. However, the fact that we are unable to complete our homogenisation, i.e. let the gas phase dissappear, suggests that the melt was either oversatured in CO$_{2}$-rich volatiles or that the entrapment has taken place at higher pressures than can be obtained by our experiments. Major element compositions for the homogenised inclusions have been obtained by electron microprobe. Our first results suggest that the early melts, in equilibrium with Fo 93, are low in total alkalis and range from 51 to 56 wt% SiO$_{2}$, i.e. a composition ranging from basalt to basaltic andesite. There are two mantle rocks that could generate these type of melts of which some are quartz normative. Very shallow level melting of a peridotite and melting at higher pressures of an eclogite. Further work should allow us to decide which mantle rock has contributed and to what extent.
DE: 3630 Experimental mineralogy and petrology
DE: 3640 Igneous petrology
DE: 1025 Composition of the mantle
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting