• journal_title：American Mineralogist
• Contributor：Kei Sato ; M. Santosh ; Toshiaki Tsunogae
• Publisher：Mineralogical Society of America
• Date：2010-
• Format：text/html
• Language：en
• Identifier：10.2138/am.2010.3170
• journal_abbrev：American Mineralogist
• issn：0003-004X
• volume：95
• issue：1
• firstpage：177
• section：Articles

High-pressure and high-temperature phase relation on Mg_0.74Fe_0.26-staurolite composition with excess water in the system FeO-MgO-Al₂O₃-SiO₂-H₂O was experimentally determined at 12–19 kbar and 850–1050 °C, with a focus on the lower-pressure stability limit of magnesian staurolite. The experimental results show that the stability field of staurolite in the system shifts to higher temperatures as compared to that of pure-Mg staurolite. At 950 °C, the lower-pressure stability limit is located between 15 and 14 kbar. This study demonstrates that staurolite breaks down with isothermal decompression by a series of reactions at 950 °C: St → Opx + Crn + Melt and St + Opx → Spr + Melt. The Mg′ [=Mg/(Fe+Mg)] of staurolite in the former reaction is 0.7. When staurolite coexists with orthopyroxene in run products, the staurolite Mg′ is decreased to 0.6–0.5. Moderate-Mg staurolite (Mg′ = ~0.5) in natural occurrences has been reported as inclusion minerals in poikiloblastic garnets within ultrahigh-temperature (UHT) metamorphic rocks from major collisional orogenic belts in southern India and southern Africa. The experimental data presented in our study suggest the possibility that the staurolite-bearing UHT metamorphic rocks had experienced high-pressure metamorphism and/or UHT extreme metamorphism during the prograde metamorphic stage.