Evidence for excess argon during high pressure metamorphism in the Dora Maira Massif (western Alps, Italy), using an ultra-violet laser ablation microprobe (super 40)Ar-(super 39)Ar technique

Article Abstract:

The Dora Maira Massif in the western Alps in Italy undergoes high pressure eclogite/amphibolite metamorphism which results in excess argon having high (super 40)Ar-(super 39)Ar ratios, and a relation exists between apparent ages and metamorphic textures. At high pressure conditions, excess argon is formed which, after mixing with atmospheric constituents during fast cooling and retrogression, lead to high argon concentrations and (super 40)Ar/(super 39)Ar ratios. A major portion of the argon ratio is related to high closure temperature minerals or large diffusion domains in single mineral phases.

Research, Analysis, Environmental aspects, Argon, Metamorphism (Geology), Amphiboles, Western Alps

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Stable isotope geochemistry and phase equilibria of coesite-bearing whiteschists, Dora Maira Massif, western Alps

Article Abstract:

A study was conducted in Dora Maira Massif, western Alps, to determine temperatures by oxygen isotope thermometry. Accurate data about peak metamorphic pressure, temperature and fluid composition of the whiteschists enables the understanding of the metamorphic processes in the deeper crustal regimes. The intimate and enigmatic connections between the whiteschists and the hosting orthogneiss, the deprivation of the rock's iron content and the enhancement of magnesium content in the whiteschists can be determied from the metasomatism of the orthogneiss protolith by a slab-derived fluid.

Methods, Temperature measurements, Temperature measurement

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Ultra-high temperatures from oxygen isotope thermometry of a coesite-sanidine grospydite

Article Abstract:

The oxygen isotope compositions of mineral separates from a ultra-high pressure-temperature coesite-bearing grospydite are measured in order to estimate temperatures of formation. Results show that the oxygen isotope thermometric estimates are the highest measured to date due to the extremely refractory behavior of the grospydite mineral assemblage combined with a rapid cooling from ultra-high temperatures.

South Africa, Oxygen, Oxygen isotopes

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