HR: 0800h
AN: V41C-1472 [Abstracts]
TI: Source and Melting Characteristics of the Reunion Plume: Constraints From Primitive Melt
Inclusions
AU: * Laubier, M
EM: M.Laubier@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, OPGC - CNRS - Universite Blaise Pascal, 5, rue Kessler,
Clermont-Ferrand, 63038
France
AU: Schiano, P
EM: P.Schaino@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, OPGC - CNRS - Universite Blaise Pascal, 5, rue Kessler,
Clermont-Ferrand, 63038
France
AU: Laporte, D
EM: D.Laporte@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, OPGC - CNRS - Universite Blaise Pascal, 5, rue Kessler,
Clermont-Ferrand, 63038
France
AU: Doucelance, R
EM: R.Doucelance@opgc.univ-bpclermont.fr
AF: Laboratoire Magmas et Volcans, OPGC - CNRS - Universite Blaise Pascal, 5, rue Kessler,
Clermont-Ferrand, 63038
France
AU: Alard, O
EM: o.alard@open.ac.uk
AF: Isotope Geochemistry Group, Department of Earth Sciences, The Open University, Walton Hall, Milton
Keynes, MK7 6AA
United Kingdom
AU: Burton, K
EM: k.w.burton@open.ac.uk
AF: Isotope Geochemistry Group, Department of Earth Sciences, The Open University, Walton Hall, Milton
Keynes, MK7 6AA
United Kingdom
AB:
The mantle plume that generated the Deccan flood basalts 65 Ma ago, the Chagos-Maldive-Laccadive Ridge and the Mascarene
Plateau is presently located below the R‚union island (Indian Ocean). To understand the long-term variations in the
geochemical dynamics of the R‚union plume, we studied lava samples from Mauritius and R‚union (Piton des Neiges and Piton de
la Fournaise volcanoes) islands, which record about 8.5 Ma of volcanic activity. Our approach consists in analyzing melt
inclusions hosted in Mg-rich olivines (Mauritius: Fo86-90; Piton des Neiges: Fo85-89; Piton de la Fournaise: Fo83-87) in
order to have access to the most primitive compositions of the Reunion hotspot magmas.
Major and trace-element concentrations of melt inclusions were determined by EMP and LA-ICP-MS. Melt inclusions display
transitional to tholeiitic compositions, a result which is in agreement with the evolution through time from alkalic to
tholeiitic of the whole rock compositions reported in previous studies (e.g., Upton and Wadsworth, 1966; Fisk et al., 1988;
AlbarŠde et al., 1997). However, contrary to what has been proposed for the evolution in whole rock compositions, the nearly
constant CaO/Al2O3 ratio in melt inclusions rules out a major control by clinopyroxene.
Trace-element compositions of melt inclusions display relatively small variations within a single sample and within the
different samples compared to whole rock data of R‚union Island. The relative depletion of heavier to lighter REE, low Lu/Hf
ratios, and elevated Sm/Yb ratios require the presence of residual garnet in the source. Trace-element variations in the melt
inclusions can be explained by models of continuous partial melting at low degrees of a homogeneous undepleted mantle
source. Two melting models can successively reproduce the melt inclusion compositions: isobaric melting at 3.5 GPa with melt
fractions ranging from 1 to 3 % and isentropic (adiabatic) melting at degrees lower than 1 % between 2.9 and 2.8 GPa.
Our results require no change in the mantle plume chemical composition over the last 8.5 Ma, and very small variations in the
degree of melting through time.
Albarede, F., Fitton, G., Luais, B., Semet, M., Kaminski, E., Upton, B.G.J., BachŠlery, P., Chemin‚e, J.-L., J. Petrol. 38,
171-201, 1997
Fisk, M.R., Upton, B.G.J., Ford, C.E., White, W.M., J. Geophys. Res. 93, 4933-4950, 1988
Upton, B.G.J. and Wadsworth, W.J., Bull. Volc. 29, 7-23, 1966
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005