Possible role of amphibole in the origin of andesite: some experimental and natural evidence

Article Abstract:

The basaltic andesite composition of the uppermostmantle crust results from the magmatic reaction of cooling, hydrous mafic liquid with anhydrous ferromagnesian deposits. The process does not involve thefractional crystallization of amphibole as the source of andesites. However, amphibole does take part in the equilibrium crystallization of the primary basaltic magma resulting in the formation of andesites. The continuous formation of basaltic andesites in the lithosphere and the crystallization of mafic and ultramafic deposits in the lower crust create continental arc growth.

Composition, Magmatism, Rocks, Igneous, Igneous rocks

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The influence of amphibole fractionation on the evolution of calc-alkaline andesite and dacite tephra from the central Aleutians, Alaska

Article Abstract:

An analysis of the impact of amphibole fractionation on calc-alkaline andesite and dacite tephra composition is presented. Evidence from tephra studies from the Kanaga, Adak and Great Sitkin Islands show that such fractionation and magma mixing influence their composition. Horneblende dacite tephra composition suggests the evolution of dacites in isolated magma chambers. In addition, a more complex history is observed for the mixing and fractional crystallization process.

Natural history, Fractionation, Fractional distillation, Aleutian Range

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Stability and chemical composition of pargasitic amphibole in MORB pyrolite under upper mantle conditions

Article Abstract:

A study was conducted to determine the stability field of pargasitic amphibole in mantle composite for a fixed water content. A solidus for a pargasite-bearing iherzolite was obtained at pressures below the limit of amphibole stability at 30 kbar. Results indicated cooling and decompression paths and heating events in natural peridotites that can be correlated from changes in the composition of pargasitic amphibole.

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