Original paper

Carpholite, sudoite, and chloritoid in low-grade high-pressure metapelites from Crete and the Peloponnese, Greece

Theye, Thomas; Seidel, Eberhard; Vidal, Olivier

European Journal of Mineralogy Volume 4 Number 3 (1992), p. 487 - 508

52 references

published: Jun 11, 1992
manuscript accepted: Nov 8, 1991
manuscript received: Oct 15, 1990

DOI: 10.1127/ejm/4/3/0487

BibTeX file

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Abstract In the high-pressure metamorphic Phyllite-Quartzite Unit of Crete and the Peloponnese, aluminous metasediments contain assemblages with Fe-Mg-carpholite, sudoite, chloritoid, pyrophyllite, chlorite, garnet, white mica and quartz. Variations of parageneses and mineral reactions in response to varying pressure, temperature and activity of H2O have been studied in detail. In Eastern Crete (≈ 300°C, 8 kbar), metapelites with high Mg/Fe2+ are characterized by sudoite-bearing assemblages with chlorite or pyrophyllite. In rocks with low Mg/Fe2+, chlorite + pyrophyllite occur instead, suggesting the (continuous) reaction sudoite + quartz = chlorite + pyrophyllite + H2O. Additional carpholite rarely occurs in chlorite-pyrophyllite schists, probably through the hydration reaction chlorite + pyrophyllite + H2O = carpholite + quartz. Progress of this reaction requires relatively high aH2O otherwise chlorite+pyrophyllite persist. In Central Crete (≈ 350°C, 9 kbar), the paragenesis chlorite+pyrophyllite is no longer stable and chloritoid appears as a widespread rock-forming mineral, occasionally associated with carpholite, through the reactions carpholite = chloritoid + quartz + H2O, chlorite + pyrophyllite + H2O = chloritoid + carpholite +quartz. As in Eastern Crete, reactions involving carpholite proceed only in the case of relatively high aH2O; the estimated values range between 1.0 and 0.7. This variability of a H2O is reflected in AFM diagrams by the compositional shift of the three-phase assemblages caφholite-chloritoid-pyrophyllite and carpholite-chloritoid-chlorite. At lower a H2O probably the normal case in Crete, no carpholite appears and chloritoid directly forms after chlorite + pyrophyllite = chloritoid + quartz + H2O. In this case, no minerals or parageneses diagnostic for high-P/low-T metamorphism appear. The same parageneses as in Central Crete have been observed in Western Crete (400°C, 10 kbar) and in the Peloponnese (≈ 450°C, 17 kbar), but with carpholites richer in Mg. For these rocks, AFM three-phase parageneses show fixed mineral compositions, suggesting equilibrium with a hydrous fluid phase of constant composition. The highest grade of metamorphic evolution of metapelites from the Phyllite-Quartzite Unit is reflected by the appearance of almandine-rich garnet in the Peloponnese. Considering metapelite assemblages involving quartz, carpholite, chloritoid, sudoite, chlorite and pyrophyllite, both the observed succession of AFM topologies and the calculated equilibrium curves offer possibilities for evaluating P, T and aH2O of very low to low-grade high-pressure metamorphism


Fe-Mg-carpholitesudoitechloritoidhigh-pressure metamorphismactivity of H2OPhyllite-Quartzite Unit (Greece)