Limestone assimilation by basaltic magmas: an experimental re-assessment and application to Italian volcanoes

Autor: Michel Pichavant, Giada Iacono Marziano, Fabrice Gaillard
Přispěvatelé: Institut des Sciences de la Terre d'Orléans (ISTO), Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Dipartimento di Chimica e Fisica della Terra [Palermo], Università degli studi di Palermo - University of Palermo, This study has been supported by the French national agency for research, ANR JC05-42707 (Electrovolc) attributed to F. Gaillard., AGU, Bavarian Research Institute of Experimental Geochemistry and Geophysics (Bayerisches Geoinstitut), Universität Bayreuth, ANR-05-JCJC-0019,ELECTROVOLC,Mesures expérimentales des propriétés électriques et sismiques des magmas et de leur zone source(2005), POTHIER, Nathalie
Rok vydání: 2007
Předmět:
Zdroj: EOS Trans. AGU
AGU Meeting San Francisco
AGU Meeting San Francisco, Dec 2007, San Francisco, United States. 1 p
Contributions to Mineralogy and Petrology
Contributions to Mineralogy and Petrology, Springer Verlag, 2008, 155 (6), pp.719-738. ⟨10.1007/s00410-007-0267-8⟩
HAL
ISSN: 1432-0967
0010-7999
1050-1150
DOI: 10.1007/s00410-007-0267-8
Popis: International audience; 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.
Databáze: OpenAIRE
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