Staurolite Stability in a Part of the System Fe-Al-Si-O-H

Spinel in direct contact with quartz is newly found in the Grt Sil leucogneiss from Skallevikshalsen, Lützow Holm Complex, East Antarctica. It is included in the outermost core of the garnet porphyroblast and is characterized by low ZnO content (2.77 3.83 wt%) and very low Cr 2 O 3 content (0 0.09 wt%). Incorporation of 2.77 3.39 wt% ZnO stabilized the Spl + Qtz assemblage to lower temperatures for about 50 degrees. As a result, their coexistence can be attained around the peak P T conditions of Skallevikshalsen. The occurrence of relic staurolite, kyanite and breakdown texture of staurolite to spinel and kyanite included in the garnet core suggests that prograde stage is preserved in the garnet core and breakdown of staurolite itself was attained in the kyanite stability field. The Spl + Qtz assemblage is included at outermost part of the garnet core, suggesting that outermost core of the garnet was formed near the peak metamorphic conditions. Decrease in anorthite content of plagioclase included in the garnet core from that found in the rock matrix suggests that decompression took place during garnet formation. Attainment of these reaction sequences requires clockwise P T path as previously proposed for the Lützow Holm Complex.

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“…(2) is difficult to determine, we use the reaction line of Richardson (1968) and that in for reference (Fig. 4).…”

Section: Discussionmentioning

confidence: 99%

Timing of attainment of the spinel+quartz coexistence in garnet-sillimanite leucogneiss from Skallevikshalsen, Luetzow-Holm Complex, East Antarctica

Kawakami

Motoyoshi

2004

Journal of Mineralogical and Petrological Sciences

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“…Experimental studies of the system Al 2 Si0 5 (Richardson and others, 1969;Holdaway, 1971) and of staurolite in the system Fe-Al-Si-0-H (Richardson, 1968) suggest that the assemblage kyanite-staurolite-quartz crystallized at a temperature and pressure no lower than 530° C and 4.5 kb (A, fig. 3).…”

Section: Physical Conditions Of Metamorphismmentioning

confidence: 97%

“…3). These estimates may be too high because Richardson's (1968) curve for the formation of staurolite will be displaced toward lower temperatures by the addition of MgO to the system and by having the partial pressure of water less than that for pure water in the fluids in the rocks. The restriction that these three minerals coexist with biotite and muscovite, however, raises the estimated pressure and temperature of crystallization.…”

Section: Physical Conditions Of Metamorphismmentioning

confidence: 99%

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Geological Survey research 1972

1972

Professional Paper

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“…Coexisting garnet and staurolite from sample 7 yield temperatures of 650°C. These two reactions were modeled with available experimental (Richardson, 1968;Ganguly, 1972;Rao & Johannes, 1979;Dutrow & Holdaway, 1989) and thermodynamic (Gibbons et al, 1981;Hemingway & Robie, 1984) data (cf. Tuccillo, 1990.…”

Section: Staurolite-garnetmentioning

confidence: 99%

Thermobarometry, Geochronology and the Interpretation of P-T-t Data in the Britt Domain, Ontario Grenville Orogen, Canada

Tuccillo¹,

Mezger

Essene³

et al. 1992

Journal of Petrology

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Textural evidence, thermobarometry, and geochronology were used to constrain the pressuretemperature-time (P-T-t) history of the southern portion of the Britt domain in the Central Gneiss Belt, Ontario Grenville Province. Typical metapelitic assemblages are quartz + plagioclase+ biotite + garnet + kyanite ± alkali feldspar ± sillimanite ± rutile ± ilmenite ± staurolite ± gahnite ± muscovite. Metatonalitic assemblages have quartz + plagioclase + garnet + biotite + hornblende + rutile + ilmenite. Metagabbroic rocks contain plagioclase + garnet + clinopyroxene + biotite + ilmenite ± hornblende ± rutile± quartz. Notable textural features include overgrowths of sillimanite on kyanite and of spinel on staurolite. The spinel overgrowths can be modeled by the breakdown of staurolite via the reaction Fe-staurolite = hercynite +kyanite + quartz+ H 2 O. The decomposition of staurolite to hercynite has a steep dP/dT slope and constrains the late prograde path of a staurolite metapelite. Garnet-Al 2 SiOj-plagioclase-quartz (GASP) barometry applied to metapelitic garnets that preserve calcium zoning reveals a pressure decrease from ~ 11 to 6 kb at an assumed temperature of 700 °C. Garnet-plagioclase-ilmenite-rutile-quartz and garnet-clinopyroxene-plagioclase-quartz barometry is in good agreement with pressures obtained with the GASP barometer. Geochronologic data from garnet, allanite, and monazite in metapelitic rocks give ages that fall into two groups, ~ 1-4 Ga and 1 • 1 Ga, suggesting the presence of at least two metamorphic events in the area. It is most reasonable to assign the 1-4 Ga age to the high-pressure data and the 1-1 Ga age to the lower-pressure data. Collectively the P-T-t data indicate a complex and protracted history rather than a single cycle of burial and uplift for this part of the Grenville Province.

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Staurolite Stability in a Part of the System Fe-Al-Si-O-H

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Timing of attainment of the spinel+quartz coexistence in garnet-sillimanite leucogneiss from Skallevikshalsen, Luetzow-Holm Complex, East Antarctica

Timing of attainment of the spinel+quartz coexistence in garnet-sillimanite leucogneiss from Skallevikshalsen, Luetzow-Holm Complex, East Antarctica

Geological Survey research 1972

Thermobarometry, Geochronology and the Interpretation of P-T-t Data in the Britt Domain, Ontario Grenville Orogen, Canada

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