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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEÅž-BOLYAI
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Rezumat: Oscillatory or discontinuous zoned and sieved plagioclase, resorbed pyroxene and amphibole are important features of the magmatic minerals in volcanic environments. They are related mainly to magma mixing processes and can be successfully used to understand better magma dynamic history in shallow and intermediate magma chambers. Generally, the mafic melt mixes with felsic magmas before or during volcanic eruptions and the final products cover a large spectrum of petrographic types from andesitic to basaltic ones (e.g. Stimac & Pearce, 1992; Hattori, 1993; Kuritani, 2001).
The external zones of the plagioclase phenocrysts show equilibrium either disequilibrium between melt and the magmatic crystals. Thus, the same content of anorthite was observed in the overgrowth zone of all size groups of plagioclase phenocrysts in equilibrium conditions. On the other hand, at disequilibrium, the border of the resorbed plagioclase consisted of several distinct crystallizing centers.
The main types of the melt inclusions found both, in plagioclase and mafic minerals, are silicate melt inclusions (now glass or recrystallized glass) and globular sulphide melt inclusions as zoned and not-zoned primary cavities. Frequently, a supercritical aqueous fluid phase as vapor-rich inclusions (+/- solids) also occurs. The melt and the vapor-rich inclusions were formed as a result of interaction between phenocrysts and sulfur-undersaturated silicate magma during mixing in intermediate magma chambers at ca. 870-1200oC and 1-2 kb, and equilibrium P-T conditions, respectively. ... |
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