Wagnerite in a cordierite-gedrite gneiss: Witness of long-term fluid-rock interaction in the continental crust (Ile d’Yeu, Armorican Massif, France)
-
Pavel Pitra
,
Philippe Boulvais
Abstract
We describe the first occurrence in the Variscan Belt of Western Europe of the relatively rare phosphate wagnerite, ideally Mg2PO4F. It occurs in albite-rich, cordierite-gedrite-bearing gneisses on the island of Ile d’Yeu, southern Armorican Massif, France. These gneisses are associated with a network of shear zones that crosscut granitoid orthogneisses of calc-alkaline affinity. Wagnerite is zoned and displays a rimward decrease of Fe/(Fe + Mg) from 0.16 to 0.08 and a concomitant increase in F. The F content ranges 0.46-1.05 apfu, but critically depends on the choice of the analytical standard. Based on phase diagrams calculated with THERMOCALC, we infer that the wagnerite-bearing orthoamphibole + cordierite + biotite + chlorite paragenesis equilibrated at ca. 550 °C, and pressures lower than 4 kbar. The presence of staurolite relics requires similar temperatures, but pressures higher than 4 kbar, implying an evolution dominated by decompression. On the basis of whole-rock chemistry and stable isotopes, we suggest that superimposed periods of metasomatic alteration throughout the metamorphic history led to the prograde stabilization of the cordierite-gedrite gneiss at the expense of the orthogneiss. This alteration involved aqueous fluids in isotopic equilibrium with local rocks and caused significant loss of Ca, K, and Si, and gain of Mg and Na. We argue that the Na-enrichment is the most significant difference between wagnerite-bearing and wagnerite-free Mg-rich, Ca-poor rocks on Ile d’Yeu. This emphasizes the possible importance of Na metasomatism for the formation of wagnerite. In light of comparisons with other wagnerite occurrences, we conclude that a long-term fluid-rock interaction, typically associated with shear-zones, may be the rule rather than the exception for the formation of wagnerite in metamorphic rocks unaffected by anatexis.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Why is amazonitic K-feldspar an earmark of NYF-type granitic pegmatites? Clues from hybrid pegmatites in Madagascar
- Metamorphosed Ordovician Fe- and Mn-rich rocks in south-central Maine: From peri-Gondwanan deposition through Acadian metamorphism
- Boralsilite, Al16B6Si2O37, and “boron-mullite:” Compositional variations and associated phases in experiment and nature
- Prograde muscovite-rich pseudomorphs as indicators of conditions during metamorphism: An example from NW Maine
- Wagnerite in a cordierite-gedrite gneiss: Witness of long-term fluid-rock interaction in the continental crust (Ile d’Yeu, Armorican Massif, France)
- Mineral chemistry of Ti-rich biotite from pegmatite and metapelitic granulites of the Kerala Khondalite Belt (southeast India): Petrology and further insight into titanium substitutions
- Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control
- Proto-polymorphs of jimthompsonite and chesterite in contact-metamorphosed serpentinites from Japan
- Silicate garnet: A micro to macroscopic (re)view
- Monazite occurrence, chemistry, and chronology in the granitoid rocks of the Lachlan Fold Belt, Australia: An electron microprobe study
- Single-crystal 40Ar/39Ar age variation in muscovite of the Gassetts Schist and associated gneiss, Vermont Appalachians
- Single-crystal X-ray studies of trioctahedral micas coexisting with dioctahedral micas in metamorphic sequences from western Maine
- Tourmaline chemistry and the IIIB site
- The octahedral sheet of metamorphic 2M1-phengites: A combined EMPA and AXANES study
- Crystal chemistry of phlogopite from Vulture-S. Michele Subsynthem volcanic rocks (Mt. Vulture, Italy) and volcanological implications
- Beneath the Stillwater Complex: Petrology and geochemistry of quartz-plagioclasecordierite (or garnet)-orthopyroxene-biotite ± spinel hornfels, Mountain View area, Montana
- Correlation between crystallization pressure and structural parameters of phengites
- The modular structure of dovyrenite, Ca6Zr[Si2O7]2(OH)4: Alternate stacking of tobermorite and rosenbuschite-like units
- Environmental parameters affect the physical properties of fast-growing magnetosomes
- In situ Raman spectroscopy measurements of MgAl2O4 spinel up to 1400 °C
- Vibrational properties of δ-AlOOH under pressure
- Mössbauer spectroscopic study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O
- Rhönite in Luna 24 pyroxenes: First find from the Moon, and implications for volatiles in planetary magmas
- New high-pressure B2 phase of FeS above 180 GPa
- Magnesium K-edge EXAFS study of bond-length behavior in synthetic pyrope-grossular garnet solid solutions
Articles in the same Issue
- Why is amazonitic K-feldspar an earmark of NYF-type granitic pegmatites? Clues from hybrid pegmatites in Madagascar
- Metamorphosed Ordovician Fe- and Mn-rich rocks in south-central Maine: From peri-Gondwanan deposition through Acadian metamorphism
- Boralsilite, Al16B6Si2O37, and “boron-mullite:” Compositional variations and associated phases in experiment and nature
- Prograde muscovite-rich pseudomorphs as indicators of conditions during metamorphism: An example from NW Maine
- Wagnerite in a cordierite-gedrite gneiss: Witness of long-term fluid-rock interaction in the continental crust (Ile d’Yeu, Armorican Massif, France)
- Mineral chemistry of Ti-rich biotite from pegmatite and metapelitic granulites of the Kerala Khondalite Belt (southeast India): Petrology and further insight into titanium substitutions
- Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control
- Proto-polymorphs of jimthompsonite and chesterite in contact-metamorphosed serpentinites from Japan
- Silicate garnet: A micro to macroscopic (re)view
- Monazite occurrence, chemistry, and chronology in the granitoid rocks of the Lachlan Fold Belt, Australia: An electron microprobe study
- Single-crystal 40Ar/39Ar age variation in muscovite of the Gassetts Schist and associated gneiss, Vermont Appalachians
- Single-crystal X-ray studies of trioctahedral micas coexisting with dioctahedral micas in metamorphic sequences from western Maine
- Tourmaline chemistry and the IIIB site
- The octahedral sheet of metamorphic 2M1-phengites: A combined EMPA and AXANES study
- Crystal chemistry of phlogopite from Vulture-S. Michele Subsynthem volcanic rocks (Mt. Vulture, Italy) and volcanological implications
- Beneath the Stillwater Complex: Petrology and geochemistry of quartz-plagioclasecordierite (or garnet)-orthopyroxene-biotite ± spinel hornfels, Mountain View area, Montana
- Correlation between crystallization pressure and structural parameters of phengites
- The modular structure of dovyrenite, Ca6Zr[Si2O7]2(OH)4: Alternate stacking of tobermorite and rosenbuschite-like units
- Environmental parameters affect the physical properties of fast-growing magnetosomes
- In situ Raman spectroscopy measurements of MgAl2O4 spinel up to 1400 °C
- Vibrational properties of δ-AlOOH under pressure
- Mössbauer spectroscopic study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O
- Rhönite in Luna 24 pyroxenes: First find from the Moon, and implications for volatiles in planetary magmas
- New high-pressure B2 phase of FeS above 180 GPa
- Magnesium K-edge EXAFS study of bond-length behavior in synthetic pyrope-grossular garnet solid solutions
