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J. metamorphic Geol., 2011, 29, 79–102 doi:10.1111/j.1525-1314.2010.00906.xHeat sources and trigger mechanisms of exhumation of HPgranulites in Variscan orogenic rootO. LEXA, 1 K. SCHULMANN, 2 V. JANOUŠEK, 1,3 P. ŠTÍPSKÁ, 2 A. GUY 2,4 AND M. RACEK 1,31 Institute of Petrology and Structural Geology, Faculty of Science, Charles University in Prague, Albertov 6, 128 43 Prague 2,Czech Republic (lexa@natur.cuni.cz)2 Institute de Physique de Globe, UMR 7516, École et Observatoire de Science de la Terre, Université de Strasbourg, 1 RueBlessig, Strasbourg 67084, France3 Czech Geological Survey, Klárov 3, 118 21 Prague 1, Czech Republic4 Department of Geophysics, Faculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 3, 180 00Prague 8, Czech RepublicABSTRACTThe structure of the Moldanubian domain is marked by felsic granulites of Ordovician protolith ageforming the cores of domes that are separated from mid-crustal Neoproterozoic and Palaeozoicmetasedimentary rocks that occur in synclines by a late Ordovician to Silurian metabasic unit. Reflectionand refraction seismic sections combined with gravity inversion modelling suggest the presence of a lowdensity layer at the bottom of the crust (interpreted as felsic granulite) overlain by a denser layer(interpreted as amphibolite) with layers of intermediate density at the top (interpreted as metasedimentaryrocks). It is proposed that the granulite domes surrounded by middle crustal rocks reflect transposedhorizontal layering originally similar to that preserved in the deep crust and imaged by the geophysicalsurveys. This geological and geophysical structure is considered to be a result of Vise´an gravityredistribution initiated by radioactive heating of felsic crust tectonically emplaced at the bottom of aPalaeozoic orogenic root. The radioactive layer with heat production of 4 lW m )3 correspondsgeochemically and isotopically to Ordovician felsic metaigneous rocks of the Saxothuringian domain thathave been emplaced at Moho depth under thickened crust during late Devonian–early Carboniferouscontinental subduction. Part of the continental crust continued to be subducted and produced fluids ⁄low-volume melts which directly contaminated and enriched the local lithospheric mantle by lithophileelements, most notably Cs, Rb, Li, Pb, U, Th and K. Thermal incubation of 10–15 Myr was sufficient toheat and convert the underplated felsic layer into granulites via dehydration melting and meltsegregation. The process of melt loss was responsible for the removal of radioactive elements and forswitching off the heat at the beginning of the exhumation process. At the same time, the metasomatizedunderlying mantle was heated producing characteristic ultrapotassic magmas. Gravitational instabilitywas then induced by the density contrast between the light granulites and the overlaying denser maficlower crustal layer and a viscosity drop related to thermal weakening and partial melting of the latter.Key words: crustal structure; exhumation of lower crust; heat sources; radioactive heating.Mineral abbreviations: bi, biotite; mu, muscovite; g, garnet; ky, kyanite; sill, sillimanite; cd, cordierite; pl,plagioclase; ksp, K-feldspar; liq, granitic liquid; o, omphacitic clinopyroxene; ilm, ilmenite; ru, rutile.INTRODUCTIONThe Variscan Bohemian Massif, Czech Republic, ischaracterized by the occurrence of large high-pressure(HP) granulite bodies within the central high-gradepart of the orogen. These granulite bodies are mainlycomposed of alkali feldspar-garnet-kyanite granulites,eclogites and fragments of mantle peridotites surroundedby mid-crustal rocks. The exhumation andemplacement of the whole assemblage is commonlyinterpreted in terms of two contrasting models. In thefirst model, granulite massifs are inferred to be allochthonous,representing klippen of far travelled nappesrooted in the central part of the Bohemian Massif (e.g.Franke, 2000), whereas in the second model, granulitescorrespond to eroded windows of the orogenic infrastructurethat have been vertically extruded to midcrustallevels from lower crustal depths (e.g. Sˇtı´pska´et al., 2004; Schulmann et al., 2005). The latter modelis analogous to that proposed for the Saxonian granuliteMassif by Behr (1978) and Weber (1984).The problem of exhumation of granulite lower crusthas been discussed by a number of authors in relationto Archean and Mesoproterozoic orogenic belts (e.g.Perchuk, 1989). In these terranes, the emplacement ofhot granulite lower crust has been interpreted in termsof gravity overturn driven by an inverted densityprofile (e.g. Roering et al., 1992), whereby heavy maficÓ 2010 Blackwell Publishing Ltd 79181
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Contentsviii4.7 Schulmann, Konopás
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Dedicated to my wife Markéta, daug
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Foreword 2First topic “Quantitati
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Foreword 4source and freely availab
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1. Quantitative analysis of deforma
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Chapter 2Mechanisms of lower crusta
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2. Mechanisms of lower crustal flow
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Chapter 3Quantitative analyses ofme
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3. Quantitative analyses of metamor
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Bibliography 42Culshaw, N., Beaumon
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Bibliography 44sources and trigger
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Bibliography 46Skrzypek, E., Štíp
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Journal of Structural Geology 23 20
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JOURNAL OF GEOPHYSICAL RESEARCH, VO
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DTD 5ARTICLE IN PRESSJournal of Str
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DTD 5ARTICLE IN PRESSL. Baratoux et
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Table 1Statistical values of the qu
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Page 149 and 150: Probabi l irequencyProbabi l ireque
Page 151 and 152: EXHUMATION IN LARGE HOT OROGEN 279y
Page 153 and 154: EXHUMATION IN LARGE HOT OROGEN 281N
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Page 172 and 173: Author's personal copyK. Schulmann
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Page 222 and 223: 58 J. FRANĚK ET AL.to c. 346 Ma (J
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78 J. FRANĚK ET AL.Weber, K., 1984
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650 O. LEXA ET AL.followed by moder
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652 O. LEXA ET AL.(a)(b)Fig. 3. Geo
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654 O. LEXA ET AL.(a)(b)(c)(d)Fig.
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656 O. LEXA ET AL.Table 2. Summariz
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658 O. LEXA ET AL.Table 5. Represen
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660 O. LEXA ET AL.Fig. 7. Chemical
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662 O. LEXA ET AL.Fig. 9. (a) Plot
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664 O. LEXA ET AL.onset of dynamic
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666 O. LEXA ET AL.clase thermometry
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98 L. BARATOUX ETAL.bearing rocks a
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100 L. BARATOUX ETAL.regime but und
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102 L. BARATOUX ETAL.is observed wi
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104 L. BARATOUX ETAL.only 10-20% of
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106 L. BARATOUX ET AL.Fig. 7. Drawi
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108 L. BARATOUX ET AL.Fig. 9. BSE i
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110 L. BARATOUX ETAL.r~t'-,IMdMdddd
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112 L. BARATOUX ET AL.Quantitative
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114 L. BARATOUX ETAL.o ._,
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116 L. BARATOUX ETAL.Plagioclase -
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118 L. BARATOUX ETAL.Plagioclase -
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120 L. BARATOUX ET AL.are contempor
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122 L. BARATOUX ET AL.recrystallize
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124 L. BARATOUX ETAL.KNIPE, R. J. 1
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ClickHereforFullArticleJOURNAL OF G
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B10210ZÁVADA ET AL.: EXTREME DUCTI
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30 P. HASALOVÁ ET AL.These authors
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32 P. HASALOVÁ ET AL.The onset of
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34 P. HASALOVÁ ET AL.Table 1. Repr
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36 P. HASALOVÁ ET AL.Evidence of m
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38 P. HASALOVÁ ET AL.PlQtz70% 30%B
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40 P. HASALOVÁ ET AL.(a)(b)(c)Fig.
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42 P. HASALOVÁ ET AL.Fig. 9. Grain
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44 P. HASALOVÁ ET AL.(a)(b)Fig. 11
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46 P. HASALOVÁ ET AL.steep D 1 fab
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48 P. HASALOVÁ ET AL.refractory. I
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50 P. HASALOVÁ ET AL.creep and gra
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52 P. HASALOVÁ ET AL.Lafeber, D.,
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PRECURSOR AND RHEOLOGY OF VARISCAN
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