HR: 1340h
AN: DI33A-1122 [Abstracts]
TI: Limestone Assimilation by Basaltic Magmas: an Experimental re-Assessment and Application to Italian Volcanoes
AU: * Gaillard, F
EM: gaillard@cnrs-orleans.fr
AF: ISTO CNRS, Institut des Sciences de la Terre d'Orléans (ISTO), UMR 6113 CNRS, 1A rue
de la Ferollerie, 45071 Orléans CEDEX 2, France, Orleans, 45071, France
AU: Iacono Marziano, G
EM: g.iacono@pa.ingv.it
AF: INGV Palermo, Istituto Nazionale di Geofisica e Vulcanologia, sezione di Palermo, via Ugo
La Malfa 153, 90146 Palermo, Italy, Palermo, 90146, Italy
AU: Pichavant, M
EM: pichavan@cnrs-orleans.fr
AF: ISTO CNRS, Institut des Sciences de la Terre d'Orléans (ISTO), UMR 6113 CNRS, 1A rue
de la Ferollerie, 45071 Orléans CEDEX 2, France, Orleans, 45071, France
AB:
Based on field observations, Daly proposed hundred years ago that limestone assimilation could generate silica
undersaturated magma. Discarded by successive studies this process is here re-assessed by an experimental
survey and is proposed as a differentiation mechanisms operating in the plumbing system of Italian Plio-
Quaternary volcanoes. The widespread presence of sedimentary limestone in their basement, the abundant high
temperature skarns in their eruptive products and their important CO2 emissions make carbonate assimilation in
the plumbing system of Italian volcanoes a central question, which, however, has been poorly addressed by
specific studies. Experimental results of Ca-Mg carbonate assimilation by hydrated mafic magmas in the range
1050-1150°C, 0.1– 500 MPa are here reported. Two types of experiments have been performed in internally
heated pressure vessels to simulate magma-carbonate interactions.
In the first type we characterized equilibrium phase diagram of basaltic system as a function of variable amount of
added carbonate (up to 20 wt percent of the total charge). In all experiments, carbonates completely breakdown
and no immiscible carbonate melts are observed. MgO and CaO are essentially incorporated in clinopyroxene
and olivine, while CO2 is partitioned between the fluid phase and the silicate glass, with a strong preference for
the fluid. The major effect of carbonate incorporation on liquidus phase equilibria is to favor the massive
crystallization of Ca-rich clinopyroxene (accompanied by leucite for some starting magma compositions) and the
consumption of the other phases crystallizing in carbonate-free conditions (olivine, plagioclase, Fe-Ti oxides).
Crystallization of pyroxene from carbonate consumes magmatic SiO2 leading to silica undersaturated residual
liquid. Such desilication trend is recognized in several magmatic series emitted in Italy strongly suggesting that
assimilation of carbonate is an important regional process.
The second type of experiments focused on the non-equilibrium interactions between carbonate and hydrated
basalts. Similarly to diffusion couple experiments, two cylinders, one of hydrated basaltic glass and one of
carbonate (either calcite or dolomite) were juxtaposed at high temperature during few hours. Magma desilication
is also observed together with clinopyroxene growth but the formation of high temperature skarn in the carbonate
end-member complicate further the mineralogical assemblage. The comparison between equilibrium and non
equilibrium interactions is proposed and allows a better interpretation of the differentiation process occurring in
the plumbing system of Italian volcanoes.
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3618 Magma chamber processes (1036)
DE: 3630 Experimental mineralogy and petrology
DE: 3660 Metamorphic petrology
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting