Reaction spaces and P-T paths: from amphibole eclogite to greenschist facies in the Austroalpine domain (Oetztal Complex) |
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| Authors: | Stefano Poli |
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| Institution: | 1. Dipartimento di Scienze della Terra, Via Botticelli 23, I-20133, Milano, Italy
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| Abstract: | The transition from feldspar amphibolite to eclogite is a very wide P-T field that extends from some-where close to 5 kbar where the garnet-amphibole pair starts to appear, to 10–20 kbar at albite-out reaction, then up to 25–30 kbar where an hydrated phase such as amphibole can be stable with pyroxene and garnet. Thus the assemblage garnet (py)+ amphibole (tr)+epidote (cz)±plagioclase (ab)±clinopyroxene (di)±quartz (qz)±fluid is commonly reported in a large number of metamorphic terrains. These mineral phases are complex solid-solutions which adapt to variations in environmental conditions mainly by means of continuous reactions. The reaction space, introduced by. Thompson in 1982a, provides a very elegant and powerful tool to approach these high-variance assemblages. The reactions:
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