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Trace element and isotopic exchange during acid-basic magma interaction processes

Published online by Cambridge University Press:  03 November 2011

G. Poli
Affiliation:
Giampiero Poli and Simone Tommasini, Department of Earth Sciences, University of Perugia, Piazza Università, 06100 Perugia, Italy.
S. Tommasini
Affiliation:
Giampiero Poli and Simone Tommasini, Department of Earth Sciences, University of Perugia, Piazza Università, 06100 Perugia, Italy.
A. N. Halliday
Affiliation:
Alex N. Halliday, Department of Geological Sciences, University of Michigan, 1006 C.C. Little Building, Ann Arbor, MI 48109-1063, U.S.A.

Abstract:

Interaction processes between acid and basic magmas are widespread in the Sardinia–Corsica Batholith. The resulting hybrid magmas are extremely variable and can be broadly divided into: (i) microgranular mafic enclaves with geochemical characteristics of both magmatic liquids and cumulates; (ii) basic gabbroic complexes with internal parts mainly formed by cumulates and with interaction zones developing only in the marginal parts; and (iii) basic septa with the form of discrete, lenticular-like bodies often mechanically fragmented in the host rock. Different styles of interaction, ranging from mixing to mingling, have been related to variations in several physicochemical parameterś, such as: (i) the initial contrast in chemical composition, temperature and viscosity; (ii) the relative mass fractions and the physical state of interacting magmas; and (iii) the static versus dynamic environment of interaction.

A model is presented for the origin and history of interaction processes between basic and acid magmas based on the geochemical characteristics of hybrid magmas. Physico-chemical processes responsible for the formation of hybrid magmas can be attributed to: (i) fractional crystallisation of basic magma and contamination by acid magma; (ii) loss of the liquid phase from the evolving basic magma by filter pressing processes; (iii) mechanical mixing between basic and acid magmas; and (iv) liquid state isotopic diffusion during the attainment of thermal equilibrium.

Type
Research Article
Copyright
Copyright © Royal Society of Edinburgh 1996

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