Quantitative structural analyses and numerical modelling of ...

More documents

Recommendations

Info

274 K. SCHULMANN ET AL.orogenic root systems that arise from the polyphasenature of vertical and horizontal material and heattransfer during long-lasting orogenic events that makethese systems more difficult to unravel. The polyphaseand discontinuous character of orogeny may be due tomajor changes in plate configurations (e.g. Deweyet al., 1989) or to the existence of inherited rheologicalheterogeneities and variations in mechanical anisotropy(e.g. Burg, 1999). Therefore, detailed regionalstructural, petrological and geochronological studiesof orogenic fabrics may provide a key to decipheringthe succession, and length and time scales of processesresponsible for material and heat transfer within theselarge orogenic root systems.Classically, the Palaeozoic Variscan orogen inWestern and Central Europe (Fig. 1) is a large, hot,bivergent orogen that is interpreted to have developed50S.ArmoricanF.BrayF.Cadomian0TBBav. F.ElbeF.hercynianRhenohercynianthuringianSaxothuringianMoldanubian14 1Bruni runia48-40N50 kmMOLDANUBIANMonotonous andVaried GroupGföhl unitTEPLA-BARRANDIANProterozoicEarly Palaeozoic4WEST SUDETES52 oLUGIANPRAHA50 o 48 o12 oSAXOTHURINGIANduring prolonged convergence between Laurussia andGondwana (e.g. Ziegler, 1986; Matte et al., 1990).Traditionally, burial and exhumation of UHP and HProcks are thought to be the result of a kinematic continuumof coaxial subduction and subsequent collisionprocesses (e.g. OÕBrien & Carswell, 1993; Konopa´ sek& Schulmann, 2005), and as a consequence petrologicaland geochronological data may fit in one of the2D conceptual models discussed above.In this study, we present structural, petrological andgeochronological data acquired during the last twodecades from the eastern termination of the EuropeanVariscan front within an area of about 20 000 km 2(Figs 1 & 2). It is shown that exhumation of the orogeniclower crust occurred during two distinct periodsrelated to a major change in the configuration oflithospheric plates during the Visean. The first exhu-TEPLA-BARRANDIANELBE -ZONESaxothuringiansubductionSouth Central Bohemian Bohemian pluton plutonC retaceousBasinMOLDANUBIAN DOMAINMORAVO-SILESIANBRUNIA14 o 16 o BrnoFig. 1. Outline geological map of the Bohemian Massif with major units shown schematically (modified after Franke, 2000).Upper inset is the position of the Bohemian Massif in the framework of the European Variscides (after Edel et al., 2003). The areadiscussed in this review is marked by a rectangular box.Ó 2007 Blackwell Publishing Ltd134
EXHUMATION IN LARGE HOT OROGEN 275mation event was related to almost vertical materialtransfer, which was driven by S-E directed oceanic andcontinental (Armorican–Saxothuringian) subductiondynamics during the Devonian and Tournasian toEarly Visean (Fig. 1). Following this early evolution,during the Middle to Late Visean indentation from theeast by a promontory of the Brunia continent at a highangle to the Saxothuringian subduction directionresulted in horizontal flow and transport of theextruded orogenic lower crust over the rigid continentas a hot fold nappe.GEOTECTONIC SETTINGSuess (1912, 1926) described the geology of the easternVariscan front and divided the crystalline complexes ofthe Bohemian Massif into two parts, an internalMoldanubian–Lugian domain and an external Moravo–SilesianZone (Figs 1 & 2). Dudek (1980) completedthis subdivision and defined a Brunia continentwith the Moravo–Silesian Zone as its westerndeformed margin. The eastern segment of the Bruniacontinent is built up of unmetamorphosed to weaklymetamorphosed Neoproterozoic granites, high-gradeschists and migmatites. This basement is unconformable,covered by Lower Carboniferous foreland basinsedimentary rocks, by Devonian shallow marine sedimentaryrocks, and locally by Cambro-Ordovicianclastic, pelitic metasediment rocks and bimodal metavolcanicrocks (Franke, 2000; Hartley & Otava, 2001).The Moravo–Silesian Zone represents a NE–SWtrendingbelt of sheared and metamorphosed rocksderived from the Brunia continent. This 300 km long,30)50 km wide belt consists of three NE–SW-elongatedtectonic windows emerging through structurallyoverlying high-grade rocks of the Moldanubian–Lugian domain: a southern Thaya window; a centralSvratka window; and a northern Silesian domain(Fig. 2). Schulmann et al. (2005) identified the Moldanubian–Lugiandomain in the Bohemian Massif asthe deep orogenic root system of the Variscan orogen(Fig. 2). The Elbe zone (Fig. 2) divides rocks of theMoldanubian–Lugian domain into two: a larger highgradeMoldanubian domain to the south and a smallerhigh-grade Lugian domain to the north (Suess, 1926).The Moldanubian domain (Figs 1 & 2) has beensubdivided into three major lithotectonic units (e.g.Fuchs, 1986), namely the amphibolite facies Monotonousand Varied Groups, which together with gneissesmake up the orogenic middle crust, and the predominantlygranulite facies Gfo¨ hl Unit, which is inferred tobe the orogenic lower crust (Fig. 2). The Varied Groupoutcrops structurally above the Monotonous Group,with a contact that is commonly marked by bodies ofgranite gneiss. The Monotonous Group consists ofmigmatitic paragneisses (metagraywacke) interlayeredwith granite orthogneisses, quartzites and rare eclogites(Dudek & Fediukova´ , 1974; Petrakakis, 1997). TheVaried Group consists of a thick sequence of paragneissesinterlayered with calcsilicate rocks, marbles,quartzites, graphite schists, amphibolites and felsicmetavolcanic rocks. The Gfo¨ hl Unit is composed oflarge areas of migmatitic granite gneiss, called theGfo¨ hl gneiss, and of areas of various highly anatecticmigmatites and paragneisses that are in placesaccompanied by migmatitic amphibolites at the base.The Gfo¨ hl Unit includes numerous bodies of Ky–Kfsfelsic granulite as well as tectonic lenses of eclogite andgarnet and ⁄ or spinel peridotite.The main part of the Lugian domain is composed ofmedium- to high-grade granite gneisses and metamorphosedvolcano-sedimentary rocks with Cambro–Ordovician protolith ages (Kro¨ ner et al., 2001, andreferences therein). The granite gneisses contain boudinsof eclogite and a belt of garnet–omphacite granulite,and are considered an equivalent of the Gfo¨ hlUnit, whereas the belts of medium-grade schists ofvolcano-sedimentary origin are regarded as an equivalentof either the Monotonous or the Varied Groups(Fig. 2). An Ordovician leptyno-amphibolite lowercrustal complex (the Stare´ Město belt) occurs in theeastern part of the Lugian domain (Sˇtı´ pska´ et al.,2001).DEFINITION OF BASEMENT AND OROGENICCRUSTAL LEVELSIn this section, multiple criteria, such as the peakpressure conditions attained by individual units, thecharacter and the age of the protolith and chronologyof metamorphic zircon, are used to decipher the relativevertical position of crustal units during the LowerPalaeozoic and the Devonian. This information is thenused to propose a model for the stratification of theorogenic crust along the eastern Variscan front.The Brunia continentBased on zircon protolith ages (Fig. 3a) and 40 Ar ⁄ 39 Arcooling ages ranging from 600 to 540 Ma, granites andmigmatites forming the basement of the Brunia continentare inferred to have originated during the Pan-African orogenic events (Van Breemen et al., 1982;Fritz et al., 1996; Finger et al., 2000; Friedl et al.,2004). Tectonic imbrication of Devonian metasedimentaryrocks and basement, and metamorphism tolower greenschist facies occurred at the western marginof the Brunia continent during the Carboniferous(Francu˚ et al., 2002). In the northern Silesian domain(Fig. 2), the metamorphic pattern of nappes derivedfrom the Brunia continent shows an inverted Barrovianzonation ranging from chlorite grade in the east tokyanite ⁄ sillimanite grade in the west (Sˇtı´ pska´ &Schulmann, 1995; Schulmann & Gayer, 2000). Thewestern termination of the Moravo–Silesian Zone inthe north reached eclogite facies conditions (Fig. 4;Sˇtı´ pska´ et al., 2006), and it is likely that the western tipof the Moravo–Silesian Zone in the south has beenÓ 2007 Blackwell Publishing Ltd135
Page 3:
“It strikes me that all our knowl
Page 8 and 9:
Contentsviii4.7 Schulmann, Konopás
Page 11:
Dedicated to my wife Markéta, daug
Page 14 and 15:
Foreword 2First topic “Quantitati
Page 16 and 17:
Foreword 4source and freely availab
Page 18 and 19:
1. Quantitative analysis of deforma
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 31 and 32:
Chapter 2Mechanisms of lower crusta
Page 33 and 34:
2. Mechanisms of lower crustal flow
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Chapter 3Quantitative analyses ofme
Page 43 and 44:
3. Quantitative analyses of metamor
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51:
Page 54 and 55:
Bibliography 42Culshaw, N., Beaumon
Page 56 and 57:
Bibliography 44sources and trigger
Page 58 and 59:
Bibliography 46Skrzypek, E., Štíp
Page 61 and 62:
Journal of Structural Geology 23 20
Page 63 and 64:
J. KonopaÂsek et al. / Journal of
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
JOURNAL OF GEOPHYSICAL RESEARCH, VO
Page 83 and 84:
SCHULMANN ET AL.: STRAIN DISTRIBUTI
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95: SCHULMANN ET AL.: STRAIN DISTRIBUTI
Page 98 and 99: 5 - 2 LEXA ET AL.: COLLISION IN WES
Page 106 and 107: 5 - 10 LEXA ET AL.: COLLISION IN WE
Page 114 and 115: 156O. Lexa et al. / Journal of Stru
Page 121 and 122: DTD 5ARTICLE IN PRESSJournal of Str
Page 123 and 124: DTD 5ARTICLE IN PRESSL. Baratoux et
Page 135 and 136: Table 1Statistical values of the qu
Page 141 and 142: Table 2Summary of parameters derive
Page 145: J. metamorphic Geol., 2008, 26, 273
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
Page 155 and 156: EXHUMATION IN LARGE HOT OROGEN 283w
Page 157 and 158: EXHUMATION IN LARGE HOT OROGEN 285a
Page 159 and 160: EXHUMATION IN LARGE HOT OROGEN 287w
Page 161 and 162: EXHUMATION IN LARGE HOT OROGEN 289T
Page 163 and 164: EXHUMATION IN LARGE HOT OROGEN 291O
Page 165 and 166: EXHUMATION IN LARGE HOT OROGEN 293r
Page 167 and 168: EXHUMATION IN LARGE HOT OROGEN 295B
Page 169: EXHUMATION IN LARGE HOT OROGEN 297R
Page 172 and 173: Author's personal copyK. Schulmann
Page 193 and 194: J. metamorphic Geol., 2011, 29, 79-
Page 195 and 196: HEAT SOURCES AND EXHUMATION MECHANI
Page 197 and 198:
HEAT SOURCES AND EXHUMATION MECHANI
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
J. metamorphic Geol., 2011, 29, 53-
Page 219 and 220:
EXTRUSIONOFLOWERCRUSTINVARISCANOROG
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
J. metamorphic Geol., 2005, 23, 649
Page 245 and 246:
CONTRASTING TEXTURAL RECORD OF TWO
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Contrasting microstructures and def
Page 263 and 264:
TEXTURES OF NATURALLY DEFORMED META
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
1.0--0.9__Mg~(Mg2++Fe2+)9 Core of p
Page 275 and 276:
Page 277 and 278:
' ~'-----2~--~----TEXTURES OF NATUR
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289:
Page 292 and 293:
B10210ZÁVADA ET AL.: EXTREME DUCTI
Page 294 and 295:
Page 296 and 297:
Page 298 and 299:
Page 300 and 301:
Page 302 and 303:
Page 304 and 305:
Page 307 and 308:
ClickHereforFullArticleJOURNAL OF G
Page 309 and 310:
B10406SCHULMANN ET AL.: RHEOLOGY OF
Page 311 and 312:
Page 313 and 314:
Page 315 and 316:
Page 317 and 318:
Page 319 and 320:
Page 321 and 322:
Page 323 and 324:
Page 325 and 326:
Page 327 and 328:
J. metamorphic Geol., 2008, 26, 29-
Page 329 and 330:
ORIGIN OF FELSIC MIGMATITES 31Ó 20
Page 331 and 332:
ORIGIN OF FELSIC MIGMATITES 33durin
Page 333 and 334:
ORIGIN OF FELSIC MIGMATITES 35(a)Ty
Page 335 and 336:
ORIGIN OF FELSIC MIGMATITES 37(a)Pl
Page 337 and 338:
ORIGIN OF FELSIC MIGMATITES 39Grain
Page 339 and 340:
ORIGIN OF FELSIC MIGMATITES 41(a)(b
Page 341 and 342:
ORIGIN OF FELSIC MIGMATITES 43(a)(b
Page 343 and 344:
ORIGIN OF FELSIC MIGMATITES 45Fig.
Page 345 and 346:
ORIGIN OF FELSIC MIGMATITES 47produ
Page 347 and 348:
ORIGIN OF FELSIC MIGMATITES 49stron
Page 349 and 350:
ORIGIN OF FELSIC MIGMATITES 51Cmı
Page 351:
ORIGIN OF FELSIC MIGMATITES 53easte
Page 354 and 355:
104 J. FRANĚK ET AL.in terms of th
Page 356 and 357:
106 J. FRANĚK ET AL.Fig. 2. Struct
Page 358 and 359:
108 J. FRANĚK ET AL.(a)perthite po
Page 360 and 361:
110 J. FRANĚK ET AL.(a)(b)(c) (d)
Page 362 and 363:
112 J. FRANĚK ET AL.Table 1. Repre
Page 364 and 365:
114 J. FRANĚK ET AL.at these P-T c
Page 366 and 367:
116 J. FRANĚK ET AL.(a)(b)Fig. 10.
Page 368 and 369:
Page 370 and 371:
120 J. FRANĚK ET AL.Table 2. Quant
Page 372 and 373:
Page 374 and 375:
124 J. FRANĚK ET AL.Fig. 16. Inter
Page 376 and 377:
126 J. FRANĚK ET AL.development of
Page 378 and 379:
128 J. FRANĚK ET AL.Behrmann, J.H.
Page 380:
130 J. FRANĚK ET AL.Southern Bohem
show all

Quantitative structural analyses and numerical modelling of ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?