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Microstructural and mineralogical evidence for limited involvement of magma mixing in the petrogenesis of a Hercynian high-K calc-alkaline intrusion: the Kozárovice granodiorite, Central Bohemian Pluton, Czech Republic

By
Vojtěch Janoušek
Vojtěch Janoušek
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D. R. Bowes
D. R. Bowes
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Colin J. R. Braithwaite
Colin J. R. Braithwaite
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Graeme Rogers
Graeme Rogers
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Published:
January 01, 2000

Textural and mineralogical features in the high-K calc-alkaline Kozárovice granodiorite (Hercynian Central Bohemian Pluton, Bohemian Massif) and associated small quartz monzonite masses imply that mixing between acid (granodioritic) and basic (monzonitic/ monzogabbroic) magmas was locally petrogenetically significant.

Net veining, with acicular apatite and numerous lath-shaped plagioclase crystals present in the quartz monzonite, and abundant mafic microgranular enclaves (MME) in the granodiorite, indicate that as the monzonitic magma was injected into the granodioritic magma chamber, it rapidly cooled and was partly disintegrated by the melt already present. Evidence from cathodoluminescence suggests that the two magmas exchanged early-formed plagioclase crystals. In the quartz monzonite, granodiorite-derived crystals were overgrown by narrow calcic zones, followed by broad, normally zoned sodic rims. In the granodiorite, plagioclase crystals with calcic cores overgrown by normally zoned sodic rims are interpreted as xenocrysts from the monzonite. After thermal adjustment, crystallisation of the monzonitic magma ceased relatively slowly, forming quartz and K-feldspar oikocrysts.

Although the whole-rock geochemistry of the quartz monzonite and the MME support magma mixing, major- and trace-element based modelling of the host granodiorite has previously indicated an origin dominated by assimilation and fractional crystallisation. Magma mixing therefore seems to represent a local modifying influence rather than the primary petrogenetic process.

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GSA Special Papers

The Fourth Hutton Symposium on the Origin of Granites and Related Rocks

Bernard Barbarin
Bernard Barbarin
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William Edryd Stephens
William Edryd Stephens
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Bernard Bonin
Bernard Bonin
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Jean-Luc Bouchez
Jean-Luc Bouchez
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David Barrie Clarke
David Barrie Clarke
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Michel Cuney
Michel Cuney
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Hervé Martin
Hervé Martin
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Geological Society of America
Volume
350
ISBN print:
9780813723501
Publication date:
January 01, 2000

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