Record details

    Kornerupine parageneses in whiteschists and other magnesian rocks: is kornerupine + talc a high-pressure assemblage equivalent to tourmaline + ortoamphibole?
Statement of responsibility
    Edward S. Grew, Nikolaj N. Percev, Stanislav Vrána, Martin C. Yates, Charles K. Shearer, Michael Wiedenbeck
    Grew, Edward S.
    Percev, Nikolaj N.
    Shearer, Charles K.
    Vrána, Stanislav
    Wiedenbeck, Michael
    Yates, Martin C.
Source title - serial
    Contributions to mineralogy and petrology
    Vol. 131, no. 1
    p. 22-38
    5 obr., 4 fot., 7 tab., 2 s.bibl.
    Zkr. název ser.: Contr. Mineral. Petrology
Subject group
    břidlice mastková
    chemismus minerálů
    metamorfóza vysokotlaká
    podmínky P-T
Geographical name
    Evropa severní
Abstract (in english)
   Kornerupine,(Fe, Mg)(Mg,Fe,Al)9(Si,Al,B)5(O,OH,F)22, has been reported with talc in rocks from six localities worldwide, but only at Chilapila Hill in the Lufilian Arc, Zambia do textural relationships imply that kornerupine (Krn) equilibrated with talc (Tlc) during a prograde metamorphic event at T=640 C, P=13 kbar, a prograde Krn+Tlc assemblage has also been reported from Mautia Hill, Tanzania ( 13kbar). In order to estimate possible constraits on the stability range for the kornerupine + talc paragenesis in nature, we constructed a P-T diagram in the model system AlO-Al2O3-SiO2-H2O (MASH) for seven phases quartz (Qtz). B-free kornerupine sensu stricto, anthophyllite (Ath), chlorite (Chl), cordierite (Crd), kyanite (Ky), and talc. The minimum pressure for Krn+Tlc+Ky stability in MASH is close to that for Ky+Tlc stability, i.e., 6-8 kbar at T 780 C.
   However, in natural system, B2O3 and Na2O are major constituents in Krn and orthoamphibole (Oam), respectively, and dravitic tourmaline (Tur) is widespread. The critical assemblage alternative to Krn+Tlc in nature is Tur+Oam. The upper pressure limit of Tur+Ath is determined by the upper pressure for anthophyllite: 7.7-10.5 kbar at 682-794 C in the MgO-SiO2-H2O system (Cherbosky et al. 1985. Am Mineral 70:223-236), and is undoubtebly higher in the presence of Na2O, CaO, and Al2O3. At three of the six localities, talc is a retrograde phase; nonetheless, it possibly equilibrated with kornerupine on the retrograde path or during a later metamorphic event at P-T conditions appropriate for Ky+Tlc. At the sixth locality (Mulvoj, southwestern Pamir Mountains, Tajikistan). Krn is found in the same thin section a talc and kyanite and all three minerals formed during a prograde metamorphic event at T 650 C, P near 7 kbar.
   However, Krn is restricted to a lens 4 to 6 mm thick of phlogopite + anthophyllite + Tur and it does not touch either talc or kyanite. A reaction relating the Mulvoj and Chilapila Hill (Krn+Tlc+Ky+Otz+Tur) parageneses is calculated from compositions in the M
    Česká geologická služba
Contributor code
    ČGS (UNM)
Source format
Entered date
    18. 2. 2008
Import date
    8. 8. 2012