Chemistry of clinopyroxenes from the Lower Cretaceous alkaline volcanic rocks of the Mecsek Mountains, south Hungary.

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Abstract

These volcanic and subvolcanic alkaline rocks comprise mainly alkali basalts, trachybasalts, trachyandesites and phonolites. Representative probe analyses of 53 clinopyroxenes show that in the basic and intermediate rocks these follow the diopside-salite-ferrosalite-hedenbergite fractionation trend which is significant for the undersaturated alkaline rock suites with low silica activity. The Ti and Al content in pyroxenes of alkali basalts increases with crystallization, but the coprecipitation of the other Ti- and Al-bearing phases impoverishes the pyroxenes of trachybasalts and trachyandesites in these elements in the later stages of crystallization. The incorporation of both elements into the pyroxene structure is indicative of non-equilibrium crystallization (e.g. sector zoning). Phonolites have salite and ferrosalite xenocrysts; pyroxenes which crystallized from the phonolitic melt change their composition from hedenbergite to aegirine-hedenbergite; in some of the latter ZrO2 up to 1.9 wt.% may occur. The continuous variation of pyroxene chemistry from diopside to aegirine presents a good example of low-P fractionation in an undersaturated alkaline suite. -R.A.H.

Original languageEnglish
Pages (from-to)281-301
Number of pages21
JournalNeues Jahrbuch fur Mineralogie, Abhandlungen
Volume156
Issue number3
Publication statusPublished - 1987

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hedenbergite
Volcanic rocks
alkaline rock
Crystallization
aegirine
volcanic rock
crystallization
alkali basalt
Rocks
Alkalies
diopside
Fractionation
Cretaceous
pyroxene
mountain
Bearings (structural)
fractionation
Zoning
Coprecipitation
Silicon Dioxide

ASJC Scopus subject areas

  • Geochemistry and Petrology

Cite this

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title = "Chemistry of clinopyroxenes from the Lower Cretaceous alkaline volcanic rocks of the Mecsek Mountains, south Hungary.",
abstract = "These volcanic and subvolcanic alkaline rocks comprise mainly alkali basalts, trachybasalts, trachyandesites and phonolites. Representative probe analyses of 53 clinopyroxenes show that in the basic and intermediate rocks these follow the diopside-salite-ferrosalite-hedenbergite fractionation trend which is significant for the undersaturated alkaline rock suites with low silica activity. The Ti and Al content in pyroxenes of alkali basalts increases with crystallization, but the coprecipitation of the other Ti- and Al-bearing phases impoverishes the pyroxenes of trachybasalts and trachyandesites in these elements in the later stages of crystallization. The incorporation of both elements into the pyroxene structure is indicative of non-equilibrium crystallization (e.g. sector zoning). Phonolites have salite and ferrosalite xenocrysts; pyroxenes which crystallized from the phonolitic melt change their composition from hedenbergite to aegirine-hedenbergite; in some of the latter ZrO2 up to 1.9 wt.{\%} may occur. The continuous variation of pyroxene chemistry from diopside to aegirine presents a good example of low-P fractionation in an undersaturated alkaline suite. -R.A.H.",
author = "G. Dobosi",
year = "1987",
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volume = "156",
pages = "281--301",
journal = "Neues Jahrbuch fur Mineralogie, Abhandlungen",
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AU - Dobosi, G.

PY - 1987

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N2 - These volcanic and subvolcanic alkaline rocks comprise mainly alkali basalts, trachybasalts, trachyandesites and phonolites. Representative probe analyses of 53 clinopyroxenes show that in the basic and intermediate rocks these follow the diopside-salite-ferrosalite-hedenbergite fractionation trend which is significant for the undersaturated alkaline rock suites with low silica activity. The Ti and Al content in pyroxenes of alkali basalts increases with crystallization, but the coprecipitation of the other Ti- and Al-bearing phases impoverishes the pyroxenes of trachybasalts and trachyandesites in these elements in the later stages of crystallization. The incorporation of both elements into the pyroxene structure is indicative of non-equilibrium crystallization (e.g. sector zoning). Phonolites have salite and ferrosalite xenocrysts; pyroxenes which crystallized from the phonolitic melt change their composition from hedenbergite to aegirine-hedenbergite; in some of the latter ZrO2 up to 1.9 wt.% may occur. The continuous variation of pyroxene chemistry from diopside to aegirine presents a good example of low-P fractionation in an undersaturated alkaline suite. -R.A.H.

AB - These volcanic and subvolcanic alkaline rocks comprise mainly alkali basalts, trachybasalts, trachyandesites and phonolites. Representative probe analyses of 53 clinopyroxenes show that in the basic and intermediate rocks these follow the diopside-salite-ferrosalite-hedenbergite fractionation trend which is significant for the undersaturated alkaline rock suites with low silica activity. The Ti and Al content in pyroxenes of alkali basalts increases with crystallization, but the coprecipitation of the other Ti- and Al-bearing phases impoverishes the pyroxenes of trachybasalts and trachyandesites in these elements in the later stages of crystallization. The incorporation of both elements into the pyroxene structure is indicative of non-equilibrium crystallization (e.g. sector zoning). Phonolites have salite and ferrosalite xenocrysts; pyroxenes which crystallized from the phonolitic melt change their composition from hedenbergite to aegirine-hedenbergite; in some of the latter ZrO2 up to 1.9 wt.% may occur. The continuous variation of pyroxene chemistry from diopside to aegirine presents a good example of low-P fractionation in an undersaturated alkaline suite. -R.A.H.

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