X-ray crystal structure refinements and microprobe analyses of pyroxenes from two spinel lherzolite xenoliths (A and B) enclosed in a camptonite dyke from Predazzo were carried out in order to evaluate similarities with analogues from Mt. Leura, Mt. Porndon and Mt. Noorat of the Newer Volcanics of Western Victoria, Australia. Mercier's (1980) geothermobarometer and Saxena's geothermometer were applied to estimates pressure and inter- and intracrystalline temperatures. The crystal chemical configurations of orthopyroxenes were consistent with a high-pressure environment and fitted a mean calculated pressure value of 15 kbar for both xenoliths. Instead the crystal chemical variations of five clinopyroxenes showed that three crystals fitted those of orthopyroxenes, whereas two of them seemed to be related to subvolcanic conditions of formations, which conflicts with the pressure value of 26 kbar obtained for them. It is reasonable to suppose that they represent overgrowths on crystals at the point of contact with the host rocks and that pressure estimates are strongly influenced by the barometric formulation used.Intercrystalline temperatures estimates obtaine using both clinopyroxene and orthopyroxene phases were in good agreement for both xenoliths. Intrarcrystalline temperature estimates were lower for clinopyroxenes than for orthopyroxenes in both cases.

PRESSURE AND TEMPERATURE ESTIMATES FROM CRYSTAL CHEMICAL STUDIES OF PYROXENES IN SPINEL LHERZOLITE XENOLITHS FROM THE PREDAZZO IGNEOUS COMPLEX, DOLOMITES REGION, NORTH ITALY

SALVIULO, GABRIELLA
1998

Abstract

X-ray crystal structure refinements and microprobe analyses of pyroxenes from two spinel lherzolite xenoliths (A and B) enclosed in a camptonite dyke from Predazzo were carried out in order to evaluate similarities with analogues from Mt. Leura, Mt. Porndon and Mt. Noorat of the Newer Volcanics of Western Victoria, Australia. Mercier's (1980) geothermobarometer and Saxena's geothermometer were applied to estimates pressure and inter- and intracrystalline temperatures. The crystal chemical configurations of orthopyroxenes were consistent with a high-pressure environment and fitted a mean calculated pressure value of 15 kbar for both xenoliths. Instead the crystal chemical variations of five clinopyroxenes showed that three crystals fitted those of orthopyroxenes, whereas two of them seemed to be related to subvolcanic conditions of formations, which conflicts with the pressure value of 26 kbar obtained for them. It is reasonable to suppose that they represent overgrowths on crystals at the point of contact with the host rocks and that pressure estimates are strongly influenced by the barometric formulation used.Intercrystalline temperatures estimates obtaine using both clinopyroxene and orthopyroxene phases were in good agreement for both xenoliths. Intrarcrystalline temperature estimates were lower for clinopyroxenes than for orthopyroxenes in both cases.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/123157
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