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Notes: Zusammenfassung Geologische, geomorphologische, petrologische und geophysikalische Daten, die über die 46 km im Durchmesser aufweisende Rundstruktur von ševĚtín in Südböhmen (49

Notes: Abstract Garnetiferous, perpotassic granulites associated with voluminous, felsic calc-alkaline garnet-kyanite granulites in the Blanský les massif are described as a new rock type. A K2O content near 13 wt%, Zr content ranging from 17 to 5877 ppm, primary Ca-Mg-Fe garnet (pyrope up to 33 mol %), and the absence of primary plagioclase and quartz characterize the new type of granulite. Calcium is incorporated only in garnet and apatite. Owing to the content of garnet the bulk syenitic compositions are metaaluminous to peraluminous. The perpotassic granulites are accompanied by subordinated melanocratic perpotassic granulite and alkali-feldspar melanocratic granulite containing up to 20 vol % quartz. These rock types also contain highly variable amounts of zircon. High-pressure, noneutectic partial melting of crustal rocks and crystallization under upper mantle conditions is suggested as the main process in generation of perpotassic granulites. A polyphase, ductile to brittle deformation and recrystallization in pyroxene granulite and later in amphibolite facies accompanied obduction of the granulite massif which carries numerous enclaves of pyrope peridotite. Euhedral equant zircon crystals up to 4 mm long enclosed in large garnet crystals and in the alkali feldspar matrix of perpotassic granulite represent a uniform, high-temperature population with a nearly concordant U-Pb system (Aftalion et al. 1989). The Hercynian age of this zircon indicates the role of the Hercynian anatexis of crustal rocks under upper mantle conditions in generation of granulites in the Moldanubian zone of the Bohemian massif.

Notes: Abstract 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 (P ≤ 13 kbar). In order to estimate possible constraints on the stability range for the kornerupine + talc paragenesis in nature, we constructed a P-T diagram in the model system MgO-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 the 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 (Chernosky et al. 1985, Am Mineral 70:223–236), and is undoubtedly 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 as 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 + Qtz + Tur) parageneses is calculated from compositions in the Mulvoj rock to be 0.40Tur + 2.55Ath + 1.33H2O + 0.27F = Krn + 2.16Tlc + 0.36B2O3 + 0.02Rutile + 0.19Na2O + 0.17CaO. Given the difference in metamorphic pressures estimated for Mulvoj and Chilapila Hill, Krn + Tlc is inferred to be favored by increasing pressure as well as by low Na2O and CaO contents. Some FeO, F, Fe2O3, and BeO are present in measurable amounts in at least one of the phases in the Mulvoj and Chilapila Hill whiteschists (e.g., Krn contains 0.24–0.67 wt% BeO), but the effect of these constituents is subordinate to that of Na2O, CaO and B2O3. The Krn + Tlc could be a more important assemblage in B-bearing whiteschists than has been reported to date, particularly at pressures where orthoamphibole is no longer stable.