Abstract
Complex reaction textures in coronitic metagabbros and retrograded eclogites of the KTB pilot and an adjacent drilling provide evidence for a multistage metamorphic history in the Variscan basement of the NW Bohemian Massif. The eclogites show complete metamorphic recrystallization leaving no textural or mineral relics of their igneous precursors. In contrast, textural relics of the igneous protolith are still preserved in the metagabbros where the metamorphic overprint under high pressure conditions achieved only partial replacement of the initial assemblage plagioclase + augite + amphibole (+olivine or orthopyroxene?) + ilmenite to form the eclogite facies assemblage garnet + omphacite + kyanite + zoisite + quartz+rutile. The garnets in the metagabbros occur in the typical ‘necklace’ fashion at the borders between the original plagioclase and mafic phase domains. In the same rocks, omphacite formed by a topotactic reaction mechanism replacing igneous augite as well as in smaller grains at the margins of the texturally igneous clinopyroxene where it occurs without fixed orientation with respect to the relict phase. Both eclogites and metagabbros show a partial breakdown under high pressure granulite (transitional to high pressure amphibolite) facies conditions during which omphacite broke down to vermicular symplectites of diopside + plagioclase. A later pervasive medium pressure metamorphism under amphibolite facies conditions led to the development of assemblages dominated by hornblende + plagioclase+titanite: phases prevailing in the overwhelming majority of the surrounding metabasites. Subsequent vein-associated retrogression produced minerals typical of the greenschist to zeolite facies. All metamorphic stages may be represented in a single thin section but although the overall reaction sequence is apparent, the obvious disequilibrium in the rocks makes the use of conventional geothermobarometry difficult. However, calculations made by assuming an approach to domainal equilibrium show that both the eclogite facies and early breakdown occurred above 10 kb. As the metamorphic unit hosting these particular metabasites is generally characterized by pressures below 10 kb these results have important implications for understanding the tectonometamorphic evolution of the region. The relationship between the studied rocks and other units in the NW Bohemian Massif exhibiting a multistage metamorphic evolution is discussed and possible tectonic models evaluated.
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References
Beard BL, Medaris LG, Johnson CM, Mísař Z, Jelínek E (1991) Nd and Sr isotope geochemistry of Moldanubian eclogites and garnet peridotites, Bohemian Massif, Czechoslovakia. Second Eclogite Field Symposium, Terra Abstracts (suppl to Terra Nova 3):4
Behr H-J, Engel W, Franke W (1980) Münchberger Gneismasse und Bayerischer Wald. Excursion Guide No.2, International conference on the effect of deformation on rocks, Göttingen: 1–100
Blümel P (1986) Metamorphic processes in the Variscan crust of the central segment. Freeman R, Mueller St and Giese P (eds) Third EGT Workshop: the central segment. European Science Foundation, Strasbourg:149–155
Blümel P (1990) Metamorphism along the SW margin of the Bohemian massif. In: Franke W (ed) Field guide Bohemian massif, IGCP Conference on Palacozoic orogens in central Europe, Göttingen-Giessen:65–76
Blundy JD, Holland TJB (1990) Calcic amphibole equilibria and a new amphibole-plagioclase geothermometer. Contrib Mineral Petrol 104:208–224
Boettcher AL (1970) The system CaO−Al2O3−SiO2−H2O at high pressures and temperatures. J Petrol 11:337–379
Busch K (1970) Die Eklogitvorkommen des kristallinen Grundgebirges in NE-Bayern-IV. Die Eklogite der Oberpfalz und ihr metamorpher Abbau. Neues Jahrb Mineral Abh 113:138–178
Deer WA, Howie RA, Zussman J (1978) Rock-forming minerals. Vol 2A: Single-chain silicates, 2nd edn, Longman, London
Fekert JO Jr, Newton RC, Kleppa OJ (1989) Recalibration of the garnet-anorthite-diopside-quartz (GADS) geobarometer by oxide-melt solution calorimetry of stoichiometric mineral mixes. EOS 70:1392
Essene EJ, Fyfe WS (1967) Omphacite in Californian metamorphic rocks. Contrib Mineral Petrol 15:1–23
Franz G, Thomas S, Smith DC (1986) High-pressure phengite decomposition in the Weissenstein eclogite, Münchberg Gneiss Massif, Germany. Contrib Mineral Petrol 92:71–85
Gaertner HR von, Horstig G von, Stettner G, Wurm A (1968) Guide to excursion C34, Federal Republic of Germany, Saxothuringikum in Bavaria. International Geological Congress XXIII, Prague 1968. Bundesanstalt für Bodenforschung, Hannover: 1–160
Gehlen K von, Matthes S, Okrusch M, Richter P, Röhr C, Schüssler U (1991) Ultramafische Einschaltungen in Metabasiten der KTB-Vorbohrung. KTB Report 91-1:83–95
Goldsmith JR (1982) Plagioclase stability at elevated temperatures and water pressures. Am Mineral 67:653–675
Graham CM, Powell R (1984) A garnet-hornblende geothermometer: calibration, testing and application to the Pelona Schist, Southern California. J Metamorphic Geol 2:13–31
Green DH, Ringwood AE (1967) The genesis of basaltic magmas. Contrib Mineral Petrol 15:103–190
Griffin WL, Råheim A (1973) Convergent metamorphism of eclogites and dolerites, Kristiansund area, Norway. Lithos 6:21–40
Heinrich CA (1982) Kyanite-eclogite to amphibolite facies evolution of hydrous mafic and pelitic rocks, Adula nappe, central Alps. Contrib Mineral Petrol 81:30–38
Hansen BT, Teufel S, Ahrendt H (1989) Geochromology of the Moldanubian-Saxothuringian Transition Zone, northeast Bavaria. In: Emmermann R, Wohlenberg J (eds) The German Continental Deep Drilling Program (KTB), site-selection studies in the Oberpfalz and Schwarzwald, Springer, Berlin Heidelberg New York, pp 55–66
Helz RT (1973) Phase relations of basalts in their melting range at PH 2 O=5 kb as a function of oxygen fugacity. Part I. Mafic phases. J Petrol 14:249–302
Holland TJB (1980) The reaction albite = jadeite + quartz determined experimentally in the range 600–1200°C. Am Mineral 65:129–134
Joanny V, Van Roermund H, Lardeux JM (1991) The clinopyroxene/plagioclase symplectite in retrograde eclogites: a potential geothermobarometer. Geol Rdsch 80:303–320
Jelinek E, Pačesova M, Mísař Z, Martinec P, Weiss Z (1984) Geochemistry of a dismembered metaophiolite complex, Letovice, Czechoslovakia. Trans Roy Soc Edinburgh, Earth Sci 75:37–48
Johnson CD, Carlson WD (1990) The origin of olivine-plagioclase coronas in metagabbros from the Adirondacks Mountains, New York. J Metamorphic Geol 8:697–717
Keyssner S, Massalsky T, Müller H, Röhr C, Graup G, Hacker W (1988) Tiefbohrung KTB-Oberpfalz VB, Ergebnisse der geowissenschaftlichen Bohrungsbearbeitung im KTB-Feldlabor (Windischeschenbach), Teufenbereich von 992 bis 1530 m: Geologie. KTB Report 88-6:B1–B88
Kleemann U (1991) Die P-T-t-d-Entwicklung in Grenzbereich zwischen der Zone von Erbendorf-Vohenstrauss (ZEV) und dem Moldanubikum in der Oberpfalz/NE Bayern. Doktoral Dissertation, Ruhr-Universität Bochum: 1–218
Klemd R, Matthes S, Okrusch M (1991) High-pressure relics in meta-sediments intercalated with the Weissenstein eclogite, Münchberg gneiss complex, Bavaria. Contrib Mineral Petrol 107:328–342
Kohl J, Hacker W, Röhr C, Sigmund J (1989) Geologische Strukturen in Gesteinen der KTB-Vorbohrung. KTB Report 89-3:467
Kohn MJ, Spear FS (1990) Two new geobarometers for garnet amphibolites, with application to southeastern Vermont. Am Mineral 75:89–96
Koziol AM, Newton RC (1988) Redetermination of the anorthite breakdown reaction and improvement of the plagioclase-garnet-Al2SiO5-quartz geobarometer. Am Mineral 73:216–223
Koziol AM, Newton RC (1989) Grossular activity-composition relationships in ternary garnets determined by reversed displaced-equilibrium experiments. Contrib Mineral Petrol 103:423–433
Kreuzer H, Seidel E, Schüssler U, Okrusch M, Lenz KL, Raschka H (1989) K−Ar geochronology of different tectonic units at the northwestern margin of the Bohemian massil. Tectonophysics 157:149–178
Krogh EJ (1988) The garnet-clinopyroxene Fe−Mg geothermometer—a reinterpretation of existing experimental data. Contrib Mineral Petrol 99:44–48
Leake BE (1978) Nomenclature of amphiboles. Mineral Mag 42:533–563
Matthes S, Seidel E (1977) Die Eklogitvorkommen des kristallinen Grundgebirges in NE-Bayern. X. Bestehen genetische Beziehungen zwischen Eklogit und Meta-Gabbro innerhalb des Münchberger Gneisgebietes? Neues Jahrb Mineral Abh 129:269–291
Mielke H, Blümel P, Langer K (1979) Regional low-pressure metamorphism of low and medium grade in meta-pelites and-psammites of the Fichtelgebirge area, NE Bavaria. Neues Jahrb Mineral Abh 137:83–112
Moecher DP, Essene EJ, Anovitz LM (1988) Calculation and application of clinopyroxene-garnet-plagioclase-quartz geobarometers. Contrib Mineral Petrol 100:92–106
Morimoto N (1988) Nomenclature of pyroxenes. Mineral Mag 52:535–550
Mørk MBE (1985) A gabbro to eclogite transition on Flemsøy, Sunnmøre, Western Norway. Chem Geol 50:283–310
Neumann ER (1976) Two refinements for the calculation of structural formulae for pyroxenes and amphiboles. Norsk Geol Tidsskr 56:1–6
Newton RC, Perkins D III (1982) Thermodynamic calibration of geobarometers based on the assemblages garnet-plagioclase-orthopyroxene-(clinopyroxene)-quartz. Am Mineral 67:203–222
O'Brien PJ (1989a) The petrology of retrograded eclogites of the Oberpfalz Forest, NE Bavaria, West Germany. Tectonophysics 157:195–212
O'Brien PJ (1989b) A study of retrogression in eclogites of the Oberpfalz Forest, north-east Bavaria, West Germany, and their significance in the tectonic evolution of the Bohemian Massif. In: Daly JS, Cliff RA, Yardley BWD (eds) Evolution of metamorphic belts. Geol Soc London Spec Pub 43:507–512
O'Brien PJ (1991a) High pressure metamorphism in the NW Bohemian Massif: Comparison and contrasts between the Moldanubian Zone, Münchberg Massif, ZEV, ZTT and Erzgebirge. KTB Report 91-1:1–12
O'Brien PJ (1991b) A multistage metamorphic evolution in eclogites from the Mariánské Lázně Complex, NW Bohemia, Czechoslovakia: the implications for uplift mechanisms. Terra Abstracts 3:93
O'Brien PJ (1992) Partially retrograded eclogites of the Münchberg Massif, Germany: records of a multistage Variscan uplift history in the Bohemian Massif. J Metamorphic Geol (in press)
O'Brien PJ, Carswell DA, Gebauer D (1990) Eclogite formation and distribution in the European Variscides. In: Carswell DA (ed) Eclogite facies rocks. Blackie, Glasgow, pp 204–224
O'Brien PJ, Schmidt I (1991) The multistage metamorphic evolution of a retrograded garnet websterite from the Variscan basement of the Oberpfalz, NE Bavaria, Germany. Terra Abstracts 3:94
Okrusch M (1969) Die Gneishornfelse um Steinach in der Oberpfalz. Contrib Mineral Petrol 22:32–72
Okrusch M (1971) Garnet-cordierite-biotite equilibria in the Steinach Aureolc, Bavaria. Contrib Mineral Petrol 32:1–23
Okrusch M, Matthes S, Klemd R, O'Brien PJ, Schmidt K (1991) Eclogites at the northwestern margin of the Bohemian Massif. A review. Eur J Mineral 3:707–730
Otten MT (1984) The origin of brown hornblende in the Artfjället gabbro and dolerites. Contrib Mineral Petrol 86:189–199
Otten MT, Buseck PR (1987) TEM study of the transformation of augite to sodic pyroxene in eclogitised ferrogabbro. Contrib Mineral Petrol 96:529–538
Patzak M, Okrusch M, Röhr C (1989) Metabasite der KTB-Vorbohrung: Vorläufige Ergebnisse bis 1610 m. KTB Report 89-3:67–80
Patzak M, Okrusch M, Röhr C (1991) Metabasite der KTB-Vorbohrung: Petrographie, Geochemie, Mineralchemie, Metamorphoseentwicklung. KTB Report 91-1:63–82
Pflug HD, Prössl KF (1991) Palynology in the pilot hole of the Continental Deep Drilling Program: results and implications. KTB Report 91-1:239–258
Piboule M, Coffrant D (1970) Métagabbros coronitiques dans le Rouergue et le Limousin (Massif Central français), une stade banal de l'éclogitisation. CR Acad Sci Paris 270(D), 22–24
Powell R (1985) Regression diagnostics and robust regression in geothermometer/geobarometer calibration: the garnet-clinopyroxene geothermometer revisited. J Metamorphic Geol 3:231–243
Powell R, Holland TJB (1988) An internally consistent dataset with uncertainties and correlations: 3. Applications to geobarometry, worked examples and a computer program. J Metamorphic Geol 6:173–204
Quadt A von (1990) U−Pb-zircon and Sm−Nd analyses on metabasites from the KTB pilot bore hole. KTB Report 90-4:545
Reinhardt J (1990) Metamorphism of the metapelites in the KTB drillcore: reaction sequences and thermobarometric constraints. KTB Report 90-4:535
Richardson SW, England PC (1979) Metamorphic consequences of crustal eclogite production in overthrust orogenic zones. Earth Planet Sci Lett 42:183–190
Röhr C, Kohl J, Hacker W, Keyssner S, Müller H, Sigmund J, Stroh A, Zulauf G (1990) German Continental Drilling Program (KTB) — geological survery of the pilot hole “KTB Oberpfalz VB”. KTB Report 90-8:B1–B55
Rubie DC (1990) Role of kinetics in the formation and preservation of eclogites. In: Carswell DA (ed) Eclogite facies rocks. Blackie, Glasgow, pp 111–140
Salje E (1986) Heat capacities and entropies of andalusite and sillimanite: the influence of fibrolitization on the phase diagram of the Al2SiO5 polymorphs. Am Mineral 71:1366–1371
Schmädicke E (1991) Quartz pseudomorphs after coesite in eclogites from the Saxonian Erzgebirge. Eur J Mineral 3:231–238
Schmädicke E, Okrusch M, Schmidt W (1992) Eclogite-facies rocks in the Saxonian Erzgebirge, Germany: high pressure metamorphism under contrasting conditions. Contrib Mineral Petrol 110:226–241
Schüssler U (1990) Petrographie, Geochemie und Metamorphose-Alter von Metabasiten im KTB-Zielgebiet. Geologica Bavarica 95:5–99
Sigmund J, Hacker W, Keyssner S, Kohl J, Müller H, Röhr C, Stroh A, Tapfer M (1990) Tiefbohrung KTB-Oberpfalz VB 1a und 1b, Ergebnisse der geowissenschaftlichen Bohrungsbearbeitung im KTB-Feldlabor (Windischeschenbach), Teufenbereich von 3500 bis 4000.1 m: Geologie. KTB Report 90-2:B1–B142
Stosch H-G, Lugmair GW (1990) Geochemistry and evolution of MORB-type eclogites from the Münchberg Massif, southern Germany. Earth Planet Sci Lett 99:230–249
Wayte GJ, Worden RH, Rubie DC, Droop GTR (1989) A TEM study of disequilibrium plagioclase breakdown at high pressure: the role of infiltrating fluid. Contrib Mineral Petrol 101:426–437
Weber K, Vollbrecht A (1989) The crustal structure at the KTB drill site, Oberpfalz. In: Emmermann R, Wohlenberg J (eds) The German Continental Deep Drilling Program (KTB), site-selection studies in the Oberpfalz and Schwarzwald. Springer, Berlin Heidelberg New York, pp 5–36
Wikström A (1970) Electron microprobe studies of the alteration of omphacite in eclogites from the Nordfjord area, Norway. Norsk Geol Tidsskr 50:137–155
Wimmenauer W, Klein H, Müller H, Stenger R (1989) Petrography and petrology of the KTB location Schwarzwald. In: Emmermann R, Wohlenberg J (eds) The German Continental Deep Drilling Program (KTB), site-selection studies in the Oberpfalz and Schwarzwald. Springer, Berlin Heidelberg New York, pp 243–264
Yoder HS Jr, Tilley CE (1962) Origin of basalt magmas: an experimental study of natural and synthetic rock systems. J Petrol 3:342–532
Zwart HJ (1967) The duality of orogenic belts. Geol Mijnbouw 46:283–309
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O'Brien, P.J., Röhr, C., Okrusch, M. et al. Eclogite facies relics and a multistage breakdown in metabasites of the KTB pilot hole, NE Bavaria: implications for the Variscan tectonometamorphic evolution of the NW Bohemian Massif. Contr. Mineral. and Petrol. 112, 261–278 (1992). https://doi.org/10.1007/BF00310460
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DOI: https://doi.org/10.1007/BF00310460