Rapid extensional unroofing of a granite–migmatite dome with relics of high-pressure rocks, the Podolsko complex, Bohemian Massif

2016 ◽  
Vol 154 (2) ◽  
pp. 354-380 ◽  
Author(s):  
JIŘÍ ŽÁK ◽  
JIŘÍ SLÁMA ◽  
MIROSLAV BURJAK
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Bohemian Massif ◽  
Early Carboniferous ◽  
Ultrahigh Pressure ◽  
High Grade ◽  
Variscan Belt ◽  
High Pressure Metamorphism ◽  
Variscan Orogen ◽  
Tectonothermal Event

AbstractThe Podolsko complex, Bohemian Massif, is a high-grade dome that is exposed along the suprastructure–infrastructure boundary of the Variscan orogen and records snapshots of its protracted evolution. The dome is cored by leucocratic migmatites and anatectic granites that enclose relics of high- to ultrahigh-pressure rocks and is mantled by biotite migmatites and paragneisses whose degree of anatexis decreases outwards. Our new U–Pb zircon ages indicate that the leucocratic migmatites were derived from Early Ordovician (c. 480 Ma) felsic igneous crust; the same age is inferred for melting the proto-source of the metapelitic migmatites. The relics of high- to ultrahigh-pressure rocks suggest that at least some portions of the complex witnessed an early Variscan subduction to mantle depths, followed by high-temperature anatexis and syntectonic growth of the Podolsko dome in the middle crust at c. 340–339 Ma. Subsequently, the dome exhumation was accommodated by crustal-scale extensional detachments. Similar c. 340 Ma ages have also been reported from other segments of the Variscan belt, yet the significance of this tectonothermal event remains uncertain. Here we conclude that the 340 Ma age post-dates the high-pressure metamorphism; the high temperatures required to cause the observed isotopic resetting and new growth of zircon were probably caused by heat input from the underlying mantle and, finally, the extensional unroofing of the complex requires a minimum throw of about 8–10 km. We use this as an argument for significant early Carboniferous palaeotopography in the interior of the Variscan orogen.

scholarly journals High temperature superconductivity in sulfur hydride under ultrahigh pressure: A complex superconducting phase beyond conventional BCS

2016 ◽  
Vol 2 (1) ◽  
Author(s):  
Annette Bussmann-Holder ◽  
Jürgen Köhler ◽  
M.-H. Whangbo ◽  
Antonio Bianconi ◽  
Arndt Simon
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Transition Temperature ◽  
Hydrogen Bonds ◽  
Pressure Dependence ◽  
High Temperature Superconductivity ◽  
Superconducting Phase ◽  
Ultrahigh Pressure ◽  
Phonon Modes ◽  
Interband Coupling

AbstractThe recent report of superconductivity under high pressure at the record transition temperature of Tc =203 K in pressurized H2S has been identified as conventional in view of the observation of an isotope effect upon deuteration. Here it is demonstrated that conventional theories of superconductivity in the sense of BCS or Eliashberg formalisms cannot account for the pressure dependence of the isotope coefficient. The only way out of the dilemma is a multi-band approach of superconductivity where already small interband coupling suffices to achieve the high values of Tc together with the anomalous pressure dependent isotope coefficient. In addition, it is shown that anharmonicity of the hydrogen bonds vanishes under pressure whereas anharmonic phonon modes related to sulfur are still active.

scholarly journals Carboniferous high-pressure metamorphism of Ordovician protoliths in the Argentera Massif (Italy), Southern European Variscan belt

Lithos ◽  
2010 ◽  
Vol 116 (1-2) ◽  
pp. 65-76 ◽  
Author(s):  
Daniela Rubatto ◽  
Simona Ferrando ◽  
Roberto Compagnoni ◽  
Bruno Lombardo
Keyword(s):  
High Pressure ◽  
Variscan Belt ◽  
High Pressure Metamorphism

Terranes and terrane boundaries in the Sudetes, northeast Bohemian Massif

1997 ◽  
Vol 134 (5) ◽  
pp. 717-725 ◽  
Author(s):  
Z. CYMERMAN ◽  
M. A. J. PIASECKI ◽  
R. SESTON
Keyword(s):  
High Pressure ◽  
Central Region ◽  
Bohemian Massif ◽  
Low Grade ◽  
High Grade ◽  
High Pressure Granulite ◽  
Facies Metamorphism ◽  
History Of ◽  
Ophiolitic Rocks ◽  
Southwestern Margin

In the Sudetes, seven distinct lithostratigraphic terranes exhibit a symmetric distribution. A central region of basinal/oceanic and ophiolitic rocks, the Central Sudetic terrane is bordered, respectively to the northwest and southeast, by the sialic Saxothuringian and Moldanubian terranes. These exhibit contrasting metasedimentary/metavolcanic successions and tectonic-metamorphic sequences, but both are characterized by Palaeozoic plutonism. These are in turn bordered (again respectively to the northwest and southeast) by the Lusatian and Moravian terranes, which are also sialic, but contain Cadomian granitoids and represent rifted and now widely separated fragments of Gondwana. Along the southwestern flank of the Sudetes, the Barrandian terrane, largely covered by younger sediments, extends to the southwestern margin of the Bohemian Massif. The Sowie Góry terrane forms a klippe of high grade gneisses tectonically emplaced on top of low-grade, sheared ophiolites of the Central Sudetic terrane. The Sowie Góry terrane exhibits a history of three distinct, probably multi-orogenic, regional metamorphic events: an early high-pressure granulite/eclogite metamorphism followed by medium- to low-pressure granulite, and in turn by amphibolite facies metamorphism. All the terrane boundaries are complex zones of ductile to brittle shearing, modified by later brittle movements. Some, such as the Leszczyniec shear zone, mark lines of old, pre-Variscan rift and suture zones, reactivated and overprinted during a series of Variscan ductile to brittle events of extensional shearing with related metamorphism and plutonism.

scholarly journals Lightning-induced high temperature and pressure microstructures in surface and subsurface fulgurites

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Li-Wei Kuo ◽  
Steven A. F. Smith ◽  
Chien-Chih Chen ◽  
Ching-Shun Ku ◽  
Ching-Yu Chiang ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Reference Sample ◽  
Near Surface ◽  
Landing Point ◽  
High Pressure Metamorphism ◽  
High Temperature And Pressure ◽  
Cloud To Ground Lightning ◽  
Temperature And Pressure ◽  
First Time

AbstractCloud-to-ground lightning causes both high-temperature and high-pressure metamorphism of rocks, forming rock fulgurite. We demonstrate that a range of microstructural features indicative of high temperatures and pressures can form in fulgurites at the surface and in fractures up to several meters below the surface. In comparison to a granite reference sample collected from a borehole at a depth of 138 m, microstructures in both the surface and fracture fulgurite are characterized by: (i) the presence of glass, (ii) a phase transformation in K-feldspar with the presence of exsolution lamellae of plagioclase, and (iii) high residual stresses up to 1.5 GPa. Since this is the first time that fracture-related fulgurite has been described, we also carried out a 1-D numerical model to investigate the processes by which these can form. The model shows that the electric current density in fractures up to 40 m from the landing point can be as high as that on the surface, providing an explanation for the occurrence of fracture-related fulgurites. Our work broadens the near-surface environments in which rock fulgurite has been reported, and provides a detailed description of microstructures that can be compared to those formed during other types of extreme metamorphic events.

Evidence of deformation control on the P-T record in compositionally heterogeneous shear zone during subduction-exhumation cycle

2020 ◽  
Author(s):  
Matteo Maino ◽  
Leonardo Casini ◽  
Stefania Corvò ◽  
Antonio Langone ◽  
Filippo Schenker ◽  
...  
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Subduction Zones ◽  
Equilibrium Temperature ◽  
Tectonic Stress ◽  
Heat Diffusion ◽  
Ultrahigh Pressure ◽  
Lithostatic Pressure ◽  
Lower Grade ◽  
Thermal Anomalies

<p>Pressure-temperature paths are a major tool for tectonic reconstruction as proxies of the burial and exhumation history of the rocks during subduction-exhumation phases. The mineral assemblages are commonly considered to reflect lithostatic pressure and near-equilibrium regional geothermal gradients. These axioms ground on the assumptions that the rock cannot support high differential stress in one place, and that heat diffusion in rocks is fast enough to defocus localized thermal anomalies, respectively.</p><p>The rare but systematic occurrence, in actual mountain ranges, of ultrahigh-pressure and/or high-temperature rocks within lower grade metamorphic rocks rise a major challenge for developing a consistent geodynamic model for exhumation of such deep seated rocks. Subduction zones are, in fact, efficient player driving material from the surface down into the Earth's mantle. However, the mechanisms to exhume part of this material (and particularly the denser oceanic rocks) back to the shallow crust are still highly debated.</p><p>In this contribution, we present new structural, petrological and thermochronometric data from an exhumed subduction zone - the Cima di Gagnone in the Central Alps– where small ultramafic inclusions (peridotite) preserving high temperature and high pressure record are enveloped within amphibolite-facies gneisses, defining a classical inclusion-in-matrix system. We found evidence of heterogeneous metamorphic and temperature records in both peridotite and felsic rocks, being the gneisses generally characterized by much lower pressure. However, we detect also in the matrix gneiss close to peridotite inclusions high-pressure and high-temperature remnants, which are structurally and temporally associated with those of ultramafic bodies.</p><p>The coexistence, at the outcrop scale, of such different conditions implies either extreme mechanical decoupling or extremely variable metamorphic equilibrium during Alpine subduction and exhumation. A possible alternative explanation is to consider part of the metamorphic record as due to mechanical deviations from lithostatic pressure and equilibrium temperature. We compare the observed metamorphic pattern with the outcome of numerical simulations obtained from elasto-visco-plastic 2D Finite Difference models. The evolution of rocks strength and viscosity is furthermore monitored to control the effectiveness of physical conditions simulated with the analytical dataset. Finally, we discuss a possible positive feedback of tectonic stress on the development of apparently incompatible metamorphic patterns.</p>

scholarly journals Preliminary data for melt inclusions in garnet porphyroblasts from Ograzhden metapelites, SW Bulgaria

2020 ◽  
Vol 81 (3) ◽  
pp. 84-86
Author(s):  
Lyubomira Macheva
Keyword(s):  
Raman Spectroscopy ◽  
High Pressure ◽  
Melt Inclusions ◽  
High Grade ◽  
Crystal Shape ◽  
Garnet Porphyroblasts ◽  
High Pressure Metamorphism ◽  
Micro Raman Spectroscopy ◽  
Negative Crystal ◽  
Crystallographic Orientations

Micro-inclusions in garnet porphyroblasts from high-grade Ograzhden metapelites, SW Bulgaria, have been studied by SEM and micro-Raman Spectroscopy. Micro-inclusions are presented by single grains with facetted outlines parallel to rational crystallographic orientations of the host garnet or by multiphase aggregates with negative crystal shape. Many of studied micro-inclusions can be formed by the presence of melt. The morphology of some of them suggests formation under high pressure metamorphism.

scholarly journals The Saxo-Danubian Granite Belt: magmatic response to post-collisional delamination of mantle lithosphere below the southwestern sector of the Bohemian Massif (Variscan orogen)

2009 ◽  
Vol 60 (3) ◽  
pp. 205-212 ◽  
Author(s):  
Fritz Finger ◽  
Axel Gerdes ◽  
Miloš René ◽  
Gudrun Riegler
Keyword(s):  
Bohemian Massif ◽  
Early Carboniferous ◽  
Mantle Lithosphere ◽  
Fold Belt ◽  
The South ◽  
Geochronological Data ◽  
Central European ◽  
Variscan Orogen ◽  
Saxothuringian Zone ◽  
Granite Belt

The Saxo-Danubian Granite Belt: magmatic response to post-collisional delamination of mantle lithosphere below the southwestern sector of the Bohemian Massif (Variscan orogen)On the basis of the synchronicity of geochronological data and the similarity of granite types, it is proposed that the mid-Carboniferous Fichtelgebirge/Erzgebirge Batholith in the Saxothuringian Zone of the central European Variscan Fold Belt and the South Bohemian Batholith in the Moldanubian Zone (including the intervening Oberpfalz and Bavarian Forest granite areas) belong to one coherent and cogenetic, ca. 400 km long plutonic megastructure. Unlike older (syn-collisional) plutonic structures in the Bohemian Massif, this Saxo-Danubian Granite Belt (nov. nom.) has developed discordant to the Devonian/Early Carboniferous collision-related tectonic architecture of the Bohemian Massif. It is argued that the Saxo-Danubian Granite Belt formed in response to a post-collisional detachment of lithospheric mantle below the south-western sector of the Bohemian Massif.

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