Orogenic Processes: Quantification and Modelling in the Variscan Belt

Contents......Page 6
Orogenic processes: quantification and modelling in the Variscan Belt......Page 8
The Palaeozoic time scale reviewed......Page 12
Table 1.......Page 13
The Late Palaeozoic relations between Gondwana and Laurussia......Page 16
Fig. 1. Palaeozoic sutures in Europe (in part after Franke et al. .........Page 18
Fig. 2. Continental dispositions in Early Devonian time (Lochkovian, 415 Ma) showing .........Page 20
Fig. 3. Continental dispositions in Late Devonian time (Frasnian, 380 Ma) showing .........Page 22
Fig. 4. Continental dispositions in Early Carboniferous time (Viséan, 350 Ma) showing .........Page 23
Fig. 5. Continental dispositions in Late Carboniferous time (Westphalian, 320 Ma). Apart .........Page 24
Palaeomagnetism and Palaeozoic palaeogeography of Gondwana and European terranes......Page 28
Fig. 2. Selected paleopole positions (Q > 3/7) for Ordovician to Permain .........Page 30
Fig. 3. Palaeogeographical reconstructions based on palaeomagnetic data. Proto-Alps and ATA based .........Page 33
Table 1. Ordoricean to Permian palaeopoles with quality factors >3/7......Page 31
The mid-European segment of the Variscides: tectonostratigraphic units, terrane boundaries and plate tectonic evolution......Page 42
Fig. 1. Structural subdivision of the European Variscides (from Franke 1992)......Page 43
Fig. 3. Allochthonous units in the Rhenish Massif and Harz Mts (after .........Page 44
Fig. 4. Palinspastic restoration of allochthonous units in the Rhenish Massif......Page 45
Fig. 5. Diagrammatic representation of tectonic relationships between the Rheno-Hercynian Belt, the .........Page 48
Fig. 6. Saxo-Thuringian Belt: diagrammatic palaeogeographic section through the Münchberg Klippe and .........Page 49
Fig. 7. Teplá-Barrandian unit: dynamic stratigraphy......Page 51
Fig. 8. Plate kinematic evolution of the mid-European Variscides......Page 54
Fig. 9. Tectonic section across the mid-European Variscides, with palaeogeographic affiliations of .........Page 57
Table 1. U-Pb zircon ages of late Silurian-early Devonian magmatic are rocks .........Page 47
The eastern termination of the Variscides: terrane correlation and kinematic evolution......Page 70
Fig. 1. Geological map of the Bohemian Massif and areas adjacent to .........Page 71
Fig. 2. Dynamic stratigraphy of the Lausitz-Izera Unit. Location of diagrammatic sections .........Page 72
Fig. 3. Dynamic stratigraphy of the South Karkonosze and Rudawy Janowickie Units, .........Page 74
Fig. 4. Dynamic stratigraphy of the Góry Sowie Block and neighbouring units .........Page 76
Fig. 5. Dynamic stratigraphy of the Fore-Sudetic Block NE of the Sudetic .........Page 78
Fig. 6. Simplified terrane map of the Bohemian Massif and areas adjacent .........Page 83
Table 1. Comparison of geological events in the West Sudetes and areas .........Page 84
The Baltica–Gondwana suture in central Europe: evidence from K–Ar ages of detrital muscovites and biogeographical data......Page 94
Fig. 1. Simplified structural map of central Europe showing the crustal units .........Page 95
Fig. 2. Stratigraphic columns of the crustal units forming the Variscan foreland .........Page 96
Fig. 3. Facies distribution and the inferred transport directions of clastic material .........Page 97
Fig. 4. K–Ar cooling ages of detrital muscovites in the Cambrian clastic .........Page 98
Fig. 5. K–Ar cooling ages of detrital muscovites in the Cambrian clastic .........Page 99
Fig. 6. K–Ar cooling ages of detrital muscovites in Devonian clastic rocks .........Page 105
Table 1. Summary of K–Ar cooling age data for detrital muscovites from .........Page 103
The Brunovistulian: Avalonian Precambrian sequence at the eastern end of the Central European Variscides?......Page 110
Fig. 1. Geology of the Brunovistulian block as far as is known .........Page 112
Fig. 2. Tentative geodynamic model for the evolution of the Brunovistulian (see .........Page 115
Fig. 3. Schematic comparison of the Cadomian–Cambrian stratigraphy in the Saxo–Thuringian, Teplá–Barrandian .........Page 116
Table 1. Compilation of the currently available zircon ages from the granitoid .........Page 113
Review of Nd isotopic data and xenocrystic and detrital zircon ages from the pre-Variscan basement in the eastern Bohemian Massif: speculations on palinspastic reconstructions......Page 120
Fig. 1. Simplified geological map of the Sudetes Mountains. Outline of map .........Page 122
Fig. 2. Geological map of the Jeseniky Mountains, Eastern Sudetes (modified after .........Page 123
Fig. 3. (a) Nd model ages (T[sub(DM)]) for samples from the Sudetes Mts, .........Page 125
Fig. 4. Histogram showing distribution of Nd modelages from the NE margin .........Page 126
Fig. 5. Histograms showing distribution of xenocrystic and detrital zircon ages for .........Page 128
Fig. 6. Orogenic events and corresponing U–Pb ages for detrital zircons of .........Page 129
Fig. 7. Model for late Neoproterozoic distribution of terranes along the northern .........Page 130
Table 1. Sm–Nd isotopic data......Page 124
From Cadomian subduction to Early Palaeozoic rifting: the evolution of Saxo-Thuringia at the margin of Gondwana in the light of single zircon geochronology and basin development (central European Variscides, Germany)......Page 138
Fig. 1. Palaeogeography of the Avalonian–Cadomian Orogenic Belt and proposed distribution of .........Page 139
Fig. 2. Location of Saxo-Thuringia. (a) Present-day distribution of peri-Gondwanan terranes as .........Page 141
Fig. 3. Generalized lithosections of low-grade peri-Gondwanan units of Saxo-Thuringia combined with .........Page 142
Fig. 4. Scanning electron photomicrographs of typical zircons of significant igneous rocks .........Page 151
Fig. 5. Geotectonic events and significance of ages of inherited and detrital .........Page 155
Fig. 7. Reconstruction of the geotectonic scenario at c. 560 Ma of .........Page 156
Fig. 8. Lithosections of Lower to Middle(?) Cambrian and Tremadoc sedimentary rocks .........Page 157
Fig. 9. Reconstruction of the geotectonic scenario during Ordovician time on the .........Page 158
Table 1. [sup(207)]Pb/ [sup( 206)]Pb single zircon evaporation ages of Cadomian to Ordovician .........Page 144
Table 2. [sup(207)]Pb/ [sup( 206)]Pb single zircon evaporation ages of detrital and inherited .........Page 148
Table 3. Average of trace element values of some Peri-Gondwanan sedimentary rocks .........Page 153
Review of geochemical variation in Lower Palaeozoic metabasites from the NE Bohemian Massif: intracratonic rifting and plume–ridge interaction......Page 162
Fig. 1. Sketch map showing the location of the main crustal blocks .........Page 164
Fig. 2. Chemical discrimination of Ordovician Sudetic metabasites into Low-Ti tholeiitic metabasalts. .........Page 167
Fig. 3. Typical chondrite-normalized REE patterns for the three magmatic series (Low-Ti .........Page 168
Fig. 4. Chondrite-normalized REE patterns showing the average and compositional range (mean .........Page 169
Fig. 5. N-MORB-normalized incompatible element patterns for the three magmatic series (Low-Ti .........Page 170
Fig. 6. Diagrams illustrating chemical variation within the Sudetic metabasite series as .........Page 171
Fig. 7. Comparison of contamination trends (increasing Th/Ta ratios:arrow) in Sudetic metabasite .........Page 172
Fig. 9. Diagrams illustrating that the range of chemical variation within Sudetic .........Page 173
Fig. 10. Chemical tectonic environment discrimination diagrams illustrating the range of variation .........Page 174
Fig. 11. Utilizing HFSE ratios indicative of source, variation in Sudeten tholeiitic .........Page 175
Fig. 12. Diagram showing the correlation between enrichment factors (La/Sm and Zr/Nb .........Page 176
Chronological constraints on the pre-Variscan evolution of the northeastern margin of the Bohemian Massif, Czech Republic......Page 182
Fig. 1. Simplified geological map of the eastern and northeastern margin of .........Page 183
Fig. 2. Sketch map showing tectonic units of the Silesian and Lugian .........Page 184
Fig. 3. Synoptic cross-section along line as indicated in Fig. 2 and .........Page 185
Fig. 4. Histograms showing distribution of radiogenic lead isotope ratios derived from .........Page 188
Fig. 5. Concordia diagrams showing analytical data for single zircons from rocks .........Page 190
Fig. 6. Concordia diagrams showing analytical data from single zircons from rocks .........Page 193
Fig. 7. Histograms (a–c) and concordia diagram (d) showing distribution of radiogenic .........Page 195
Fig. 8. (a) Position of western Sudetes with respect to recent geometry and .........Page 198
Fig. 9. Tectonic model of early Palaeozoic sequential rifting and related magmatism .........Page 200
Passive margin detachment during arc–continent collision (Central European Variscides)......Page 206
Fig. 1. (a) Summary geological map. Major thrust systems are highlighted and numbered: .........Page 209
Fig. 4. The 3D detachment geometry of basal detachment and principal thrust .........Page 211
Fig. 5. Simplified restored sections through western Rhenish Massif and Ardennes. (a) .........Page 218
Fig. 6. (a) Map of restored basin showing growth fault traces, branch lines .........Page 219
Fig. 7. P–T diagram for rocks from near basal detachment. I, Phyllite Zone .........Page 220
Fig. 8. Best-fit flexural isostatic model of early collision geometry (335–325 Ma) .........Page 222
Fig. 9. Schematic sketch of detachment and thrust-belt growth (325–305 Ma). Activated .........Page 224
Deformation, metamorphism and exhumation: quantitative models for a continental collision zone in the Variscides......Page 230
Fig. 1. Modelling concept (simplified after Willett et al.(1993)). (a) The .........Page 231
Fig. 3. Flow laws based on power-law creep parameters of upper- and .........Page 234
Fig. 4. Sketch map showing Variscan massifs in Central Europe and the .........Page 235
Fig. 5. (a) Initial tracking grid (only central part is shown). (b) Deformed .........Page 237
Fig. 6. (a) Deformed FE grid (detail of Fig. 5d). (b) Total strain .........Page 239
Fig. 7. Comparison of modelled peak metamorphic pressures (a) and temperatures (b) .........Page 240
Fig. 8. Variation of contemporaneous P–T paths for selected points now at .........Page 241
Table 1. Thermal and mechanical material parameters used in this study; whenever .........Page 232
Heat flow evolution, subsidence and erosion in the Rheno-Hercynian orogenic wedge of central Europe......Page 244
Fig. 1. Geological map of the studied areas, including locations of ID .........Page 245
Fig. 2. Generalized stratigraphic column for the northern Rhenish Massif and the .........Page 247
Fig. 3. Crustal structure (top) and stretching factor (bottom) for the syn-rift .........Page 250
Fig. 4. Burial and heat flow history and calibration data for the .........Page 252
Fig. 5. Overview of thicknesses of eroded Palaeozoic overburden (km) ( first of .........Page 254
Fig. 6. Top: finite-element models of the cross-sections along the river Rhein .........Page 255
Fig. 7. Top: the finite-element model of the eastern cross-section througt the .........Page 257
Fig. 8. Burial and heat flow histories and calibration data for the .........Page 259
Fig. 9. Result of a 2D simulation of a cross-section through the .........Page 260
Fig. 10. Comparison of simulated burial (top) and temperature (bottom) histories for .........Page 262
Fig. 11. Modelled temperature evolution for the Gedinnian sequence (see Fig. 2) .........Page 263
Table 1. Heat flow during times of maximum burial, and amount of .........Page 261
Turbidite basin and mass dynamics related to orogenic wedge growth: the Rheno-Hercynian case......Page 270
Fig. 1. (a) Highly idealized cross section through the Rheno-Hercynian Turbidite Basin (RHTB) .........Page 271
Fig. 2. Late Viséan goniatite stratigraphy of various researchers for Central Europe .........Page 273
Fig. 3. (a) The Rheno-Hercynian Turbidite Basin (RHTB) with the allochthonous (i.e. the .........Page 274
Fig. 4. (a) Conceptional interpretation of the turbidite filling pattern of the Wildungen .........Page 276
Fig. 5. Map of the eastern Rhenish Massif with major thrust systems. .........Page 277
Fig. 6. Schematized diagram of a major turbidite sequence associated with assumed .........Page 279
Fig. 7. Correlation of large-scale turbidite cycles that show the transition from .........Page 280
Fig. 8. Sequence stratigraphic interpretation of the eastern Rheno-Hercynian Turbidite Basin showing .........Page 281
Fig. 9. Time and spatial transgressive onlap of turbidite deposition as indicated .........Page 282
Fig. 10. Average sedimentation rates for the two investigated basins, the Rheno-Hercynian .........Page 283
Fig. 11. Volumes involved during mass balance calculation. Scenarios I and II: .........Page 285
Upper-plate deformation during collisional orogeny: a case study from the German Variscides (Saxo-Thuringian Zone)......Page 294
Fig. 1. Geological overview map of the Central European Variscides. showing the .........Page 295
Fig. 2. Main tectonic units of western Saxo-Thuringia and associated age data. .........Page 296
Fig. 3. (a) Section sketch of main tectonic units showing fabric relation as .........Page 298
Fig. 4. (a) Migrated reflection seismic profiles DEKORP 4N and DEKORP 3B/MVE West. .........Page 302
Fig. 5. Concordia diagram for several post-kinematic Variscan granites. (a) Alkaline, biotite–amphibole .........Page 305
Fig. 6. P–T diagram of the Vesser Unit and the Schwarzburg Anticline. .........Page 307
Fig. 7. Schematic section across the Rheno-Hercynian–Saxo-Thuringian doubly vergent orogenic wedge system. .........Page 310
Table 1. U–Pb analytical data of zircon from the post-Variscan intrusions in .........Page 304
Table 2. Formation temperatures of homogeneous garnets ( grt I ) and .........Page 308
Geophysical constraints on exhumation mechanisms of high-pressure rocks: the Saxo-Thuringian case between the Franconian Line and Elbe Zone......Page 316
Fig. 1. Map of the investigated area with location of geophysical profiles. .........Page 317
Fig. 2. Depth-migrated seismic section of profile GRANU 9502, with line drawing .........Page 318
Fig. 3. Depth-migrated seismic section of profile GRANU 9501, with line drawing .........Page 321
Fig. 4. 2D resistivity model along profile GRANU 95A. NW of the .........Page 323
Fig. 5. Resistivity model with a laterally unlimited conductor at 18-20 km .........Page 324
Table 1. Velocity-density values for the eastern Saxo-Thuringian Belt (after Müller 1995) .........Page 325
Fig. 7. Gravity model and resulting Bouguer anomaly (a) along refraction line .........Page 326
Fig. 8. Gravity model and resulting Bouguer anomaly (a) along reflection line .........Page 327
Fig. 9. Compilation of the various geophysical datasets along lines GRANU 95A .........Page 329
Fig. 10. Interpretation of the seismic reflection line GRANU 9502, crossing the .........Page 330
Fig. 11. Conceptual models of granulite emplacement that are in agreement with .........Page 332
White-mica [sup(40)]Ar/[sup(39)]Ar ages of Erzgebirge metamorphic rocks: simulating the chronological results by a model of Variscan crustal imbrication......Page 336
Fig. 2. (a) Schematic stratigraphic section of metamorphic rock units of the Erzgebirge; .........Page 338
Fig. 3. Examples of [sup(40)]Ar/[sup(39)]Ar spectra of white mica (a, b, d, .........Page 340
Fig. 4. Position of investigated rocks with white mica in the crustal .........Page 341
Fig. 5. Diagrams of model temperature evolution (models A–D) in a cool .........Page 343
Table 1. Alternative model boundaries for the calculations of temperature in the .........Page 344
Fig. 8. The calculated partial [sup(40)]Ar(rad) retentions (in per cent) from 1000 .........Page 345
Fig. 10. The calculated partial [sup(40)]Ar(rad) losses for models C (a) and .........Page 346
Exhumation of high-grade rocks in the Saxo-Thuringian Belt: geological constraints and geodynamic concepts......Page 350
Fig. 1. Geological map of the Saxo-Thuringian Belt between the SW margin .........Page 352
Fig. 2. Diagrammatic tectonic cross-section through the western part of the Saxo-Thuringian .........Page 353
Fig. 4. Simplified cross-section of the Saxonian Granulite Antiform (see Fig. 3 .........Page 355
Fig. 5. Tectonic section along seismic profile DEKORP 9502 (see Fig. 3 .........Page 356
Fig. 6. Tectonic stratigraphy of the Erzgebirge Antiform. P–T data from Schmädicke .........Page 357
Fig. 7. 3D reconstruction of the refractor and main reflector depicting the .........Page 358
Fig. 8. Timing of geological events in different parts of the Saxo-Thuringian .........Page 359
Fig. 9. Diagrammatic section across the eastern part of the Saxo-Thuringian Belt.......Page 360
Fig. 10. Geodynamic models for two phases of exhumation of HP rocks .........Page 361
Foreland-directed lower-crustal flow and its implications for the exhumation of high-pressure-high-temperature rocks......Page 368
Fig. 1. Schematic model of lower-crustal flow in response to pressure gradients .........Page 369
Fig. 2. Horizontal deviatoric stress profiles after 15 Ma taken from a .........Page 370
Fig. 4. Modelling concept......Page 371
Fig. 5. Initial FE grid (a), material distribution (b) and temperature field .........Page 374
Fig. 6. Modelling results after 12 Ma assuming 5 mm a[sup(-1)] displacement .........Page 375
Fig. 7. Modelling results after 12 Ma assuming fixed side-walls of the .........Page 376
Fig. 8. Orientation of the least principal stress axis σ[sub(3)] in the......Page 377
Fig. 9. Pressure–temperature–time (P–T–t) describing the exhumation history of the granulites in .........Page 378
Table 1. Material parameters used for thermal and mechanical calculations. As modelling .........Page 372
The fundamental Variscan problem: high-temperature metamorphism at different depths and high-pressure metamorphism at different temperatures......Page 382
Fig. 1. Location of the main Variscan basement blocks in Europe with .........Page 383
Fig. 2. Simplified geological map of part of the Bohemian Massif showing .........Page 384
Fig. 3. Schematic pressure-temperature evolution diagram for the metamorphic rocks of the .........Page 389
Fig. 4. A simplified subduction–collision model to explain the typical Variscan high-P .........Page 392
Syn-convergent high-temperature metamorphism and magmatism in the Variscides: a discussion of potential heat sources......Page 400
Fig. 1. Distribution of granitic to granodioritic rocks in the Variscan Orogen .........Page 401
Fig. 2. Conceptual models accounting for high-temperature metamorphism and magmatism in orogenic .........Page 405
The Variscan lower continental crust: evidence for crustal delamination from geochemical and petrophysical investigations......Page 414
Fig. 1. Seismic profile (a) of the studied part of the Variscan .........Page 416
Fig. 2. REE pattern of the Variscan mafic lower continental crustal rocks. .........Page 421
Fig. 3. REE pattern of the Variscan mafic lower continental crustal rocks .........Page 422
Fig. 4. Outer left column: distribution of principal crustal units as observed .........Page 424
Table 1. Description of rocks; sample number, rock type, location and modal .........Page 418
Table 2. Experimentally derived in situ seismic properties of the different rock .........Page 419
Table 3. Compilation of the mafic lower continental crust......Page 420
Table 4. Mass balance of the bulk continental crust......Page 423
Hybrids, magma mixing and enriched mantle melts in post-collisional Variscan granitoids: the Rastenberg pluton, Austria......Page 428
Fig. 1. Geological sketch map of the South Bohemian Batholith. (a) Regional .........Page 429
Fig. 2. Classification of the rocks of the Rastenberg Pluton in the .........Page 430
Fig. 3. Major element variations (in wt %) of the RbP rocks .........Page 433
Fig. 4. Selected trace element (in ppm) variations of the RbP rocks. .........Page 434
Fig. 5. Average continental-crust (Taylor & McLennan 1985) normalized multi-element diagram for .........Page 435
Fig. 6. Initial Pb isotope composition for leached K-feldspare samples from the .........Page 436
Fig. 7. eNd v. initial [sup(87)]Sr[sup(/86)]Sr for the RbP rocks. The rocks .........Page 439
Fig. 9. [sup(87)]Sr/[sup(86)]Sr[sup(330)] v. 1/Sr plot for the RbP rocks. Symbols as .........Page 440
Table 1. Chemical and isotopic composition of representative RbP rocks......Page 437
Geochemistry and provenance of Devono-Carboniferous volcano-sedimentary sequences from the Southern Vosges Basin and the geodynamic implications for the western Moldanubian Zone......Page 446
Fig. 1. Geological sketch map of the Variscan aspects of the Vosges .........Page 447
Fig. 2. Geological map of the Southern Vosges Basin (after Schaltegger et .........Page 448
Fig. 3. Stratigraphic sections of sedimentary sequences from the Lower, Middle and .........Page 451
Fig. 4. QFL values (plots after Dickinson & Suczek (1979)) of samples .........Page 452
Fig. 5. Geochemical variation of trace elements and element ratios from the .........Page 453
Fig. 6. Multi-element diagrams for the greywackes of the Southern Vosges Basin .........Page 454
Table 1. Major and trace element composition of Lower Unit 1 (L1) .........Page 449
Table 2. Major and trace element composition of Middle Unit 1 (M1) .........Page 450
B......Page 458
C......Page 459
F......Page 461
G......Page 462
K......Page 463
M......Page 464
P......Page 466
R......Page 467
S......Page 468
T......Page 470
V......Page 471
Z......Page 472