Fine-grained peraluminous synkinematic leuco-monzogranites (SKG), of Cambro-Ordovician age, occur as veins and sills (up to 20-30 m thick) in the Deep Freeze Range, within the medium to high-grade metamorphics of the Wilson Terrane. Secondary fibrolite + graphite intergrowths occur in feldspars and subordinately in quartz. Four main solid and fluid inclusion populations are observed: primary mixed CO2 + H2O inclusions + Al2SiO5 +/- brines in garnet (type 1) ; early CO2-rich inclusions (+/- brines) in quartz (type 2) ; early CO2 + CH4 (up to 4 mol%) +/- H2O inclusions + graphite + fibrolite in quartz (type 3); late CH4 + CO2 + N2 inclusions and H2O inclusions in quartz (type 4). Densities of type 1 inclusions are consistent with the crystallization conditions of SKG (almost-equal-to 750-degrees-C and 3 kbar). The other types are post-magmatic: densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature (almost-equal-to 700 -550-degrees-C). Type 4 inclusions were trapped below 500-degrees-C. The SKG crystallized from a magma that was at some stage vapour-saturated; fluids were CO2-rich, possibly with immiscible brines. CO2-rich fluids (+/- brines) characterize the transition from magmatic to post-magmatic stages; progressive isobaric cooling (T< 670-degrees-C) led to a continuous decrease of f(O2), entering in the graphite stability field; at the same time, the feldspars reacted with CO2-rich fluids to give secondary fibrolite + graphite. Decrease of T and f(O2) can explain the progressive variation in the fluid composition from CO2-rich to CH4 and water dominated in a closed system (in situ evolution). The presence of N2 the late stages indicates interaction with external metamorphic fluids.

Frezzotti, M., Di Vincenzo, G., Ghezzo, C., Burke, E. (1994). Evidence of magmatic CO2-rich Fluids in Peraluminous Graphite-Bearing Leukogranites from deep Freeze Range (Northern Victoria Land, Antarctica). CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 117(2), 111-123 [10.1007/BF00286836].

Evidence of magmatic CO2-rich Fluids in Peraluminous Graphite-Bearing Leukogranites from deep Freeze Range (Northern Victoria Land, Antarctica)

Frezzotti, M;
1994

Abstract

Fine-grained peraluminous synkinematic leuco-monzogranites (SKG), of Cambro-Ordovician age, occur as veins and sills (up to 20-30 m thick) in the Deep Freeze Range, within the medium to high-grade metamorphics of the Wilson Terrane. Secondary fibrolite + graphite intergrowths occur in feldspars and subordinately in quartz. Four main solid and fluid inclusion populations are observed: primary mixed CO2 + H2O inclusions + Al2SiO5 +/- brines in garnet (type 1) ; early CO2-rich inclusions (+/- brines) in quartz (type 2) ; early CO2 + CH4 (up to 4 mol%) +/- H2O inclusions + graphite + fibrolite in quartz (type 3); late CH4 + CO2 + N2 inclusions and H2O inclusions in quartz (type 4). Densities of type 1 inclusions are consistent with the crystallization conditions of SKG (almost-equal-to 750-degrees-C and 3 kbar). The other types are post-magmatic: densities of type 2 and 3 inclusions suggest isobaric cooling at high temperature (almost-equal-to 700 -550-degrees-C). Type 4 inclusions were trapped below 500-degrees-C. The SKG crystallized from a magma that was at some stage vapour-saturated; fluids were CO2-rich, possibly with immiscible brines. CO2-rich fluids (+/- brines) characterize the transition from magmatic to post-magmatic stages; progressive isobaric cooling (T< 670-degrees-C) led to a continuous decrease of f(O2), entering in the graphite stability field; at the same time, the feldspars reacted with CO2-rich fluids to give secondary fibrolite + graphite. Decrease of T and f(O2) can explain the progressive variation in the fluid composition from CO2-rich to CH4 and water dominated in a closed system (in situ evolution). The presence of N2 the late stages indicates interaction with external metamorphic fluids.
Articolo in rivista - Articolo scientifico
Petrology, granites, Antarctica
English
111
123
13
Frezzotti, M., Di Vincenzo, G., Ghezzo, C., Burke, E. (1994). Evidence of magmatic CO2-rich Fluids in Peraluminous Graphite-Bearing Leukogranites from deep Freeze Range (Northern Victoria Land, Antarctica). CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, 117(2), 111-123 [10.1007/BF00286836].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/174648
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