On the mechanics of basin formation in the Pannonian basin: Inferences from analogue and numerical modelling     

Gbor Windhoffer  Gbor Bada  Dick Nieuwland  Gza Wrum  Ferenc Horvth  Sierd Cloetingh 《Tectonophysics》2005,410(1-4):389-415

We present the results of a thrust fault reactivation study that has been carried out using analogue (sandbox) and numerical modelling techniques. The basement of the Pannonian basin is built up of Cretaceous nappe piles. Reactivation of these compressional structures and connected weakness zones is one of the prime agents governing Miocene formation and Quaternary deformation of the basin system. However, reactivation on thrust fault planes (average dip of ca. 30°) in normal or transtensional stress regimes is a problematic process in terms of rock mechanics. The aim of the investigation was to analyse how the different stress regimes (extension or strike-slip), and the geometrical as well as the mechanical parameters (dip and strike of the faults, frictional coefficients) effect the reactivation potential of pre-existing faults.

Results of analogue modelling predict that thrust fault reactivation under pure extension is possible for fault dip angle larger than 45° with normal friction value (sand on sand) of the fault plane. By making the fault plane weaker, reactivation is possible down to 35° dip angle. These values are confirmed by the results of numerical modelling. Reactivation in transtensional manner can occur in a broad range of fault dip angle (from 35° to 20°) and strike angle (from 30° to 5° with respect to the direction of compression) when keeping the maximum horizontal stress magnitude approximately three times bigger than the vertical or the minimum horizontal stress values.

Our research focussed on two selected study areas in the Pannonian basin system: the Danube basin and the Derecske trough in its western and eastern part, respectively. Their Miocene tectonic evolution and their fault reactivation pattern show considerable differences. The dominance of pure extension in the Danube basin vs. strike-slip faulting (transtension) in the Derecske trough is interpreted as a consequence of their different geodynamic position in the evolving Pannonian basin system. In addition, orientation of the pre-existing thrust fault systems with respect to the Early to Middle Miocene paleostress fields had a major influence on reactivation kinematics.

As part of the collapsing east Alpine orogen, the area of the Danube basin was characterised by elevated topography and increased crustal thickness during the onset of rifting in the Pannonian basin. Consequently, an excess of gravitational potential energy resulted in extension (σ_v > σ_H) during Early Miocene basin formation. By the time topography and related crustal thickness variation relaxed (Middle Miocene), the stress field had rotated and the minimum horizontal stress axes (σ_h) became perpendicular to the main strike of the thrusts. The high topography and the rotation of σ_h could induce nearly pure extension (dip-slip faulting) along the pre-existing low-angle thrusts. On the contrary, the Derecske trough was situated near the Carpathian subduction belt, with lower crustal thickness and no pronounced topography. This resulted in much lower σ_v value than in the Danube basin. Moreover, the proximity of the retreating subduction slab provided low values of σ_h and the oblique orientation of the paleostress fields with respect to the master faults of the trough. This led to the dominance of strike-slip faulting in combination with extension and basin subsidence (transtension).  相似文献   

Genesis of carbonate aggregates in lamprophyres from the northeastern Transdanubian Central Range, Hungary: Magmatic or hydrothermal origin?     

T. Azbej  C. Szabó  R. J. Bodnar  G. Dobosi 《Mineralogy and Petrology》2006,88(3-4):479-497

Summary Carbonate aggregates in Late Cretaceous lamprophyre dikes of the northeastern Transdanubian Central Range (TCR) in Northwest Hungary have been classified into three genetic groups. Type-I dolomite + calcite ± magnesite aggregates have petrographic and geochemical features similar to ocelli described by other workers. Fluid inclusions in Type-I aggregates homogenize between 77 and 204 °C and are of hydrothermal origin. Type-II aggregates are characterized by a polygonal shape and are mostly dolomite. Based on their shape and primary fluid inclusions which homogenize between 95 and 172 °C, these carbonate aggregates are interpreted to fill vugs produced by the dissolution of olivine phenocrysts. Type-III carbonate aggregates show an irregular to polygonal shape and distinct compositional zonation and contain secondary aqueous fluid inclusions. Homogenization temperatures of fluid inclusions are below 104 °C, and zonation patterns suggest partial recrystallization. These carbonate aggregates are most likely xenoliths and xenocrysts from the wall rocks of the lamprophyre melt conduits.  相似文献   

Petrology of a new basalt occurrence in Hungary     

Dr. A. Embey-Isztin  G. Dobosi  Dr. G. Noske-Fazekas  E. Árva-Sós 《Mineralogy and Petrology》1989,40(3):183-196

Summary A new occurrence of basalt (minimum K/Ar age 57.9 ± 2.2 m.y.) is reported from Budaliget, near Budapest. Major and minor element concentrations show that the basalts are alkaline and potassic in nature ranging from olivine tholeiite to moderately undersaturated basanite. High mg-values and concentrations of Ni and Cr indicate that some of the samples may represent primary compositions. High pressure accidental xenoliths, xenocrysts and cognate megacrysts are frequent and the chemical zoning patterns of olivine and pyroxene phenocrysts indicate a complex evolution and polibaric conditions for the crystallization. The discovery of the new basalt occurrence is important from a geodynamical point of view: prior to the last two major geodynamical events (Plio-Pleistocene rifting with associated alkali basaltic volcanism and collision of microplates with associated Miocene calk-alkaline volcanism) the continental lithosphere below NE Transdanubia may have experienced another rifting period in the Paleocene or Upper Cretaceous.With 7 Figures  相似文献   

Lower crustal granulite xenoliths from the Pannonian Basin,Hungary. Part 1: mineral chemistry,thermobarometry and petrology   总被引：1，自引：0，他引：1  

Antal Embey-Isztin  Hilary Downes  Pamela D. Kempton  Gábor Dobosi  Matthew Thirlwall 《Contributions to Mineralogy and Petrology》2003,144(6):652-670

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Changes in the structure and direction of expanding commodity transport on the Danube     

Gábor Korompai 《Geoforum》1971,2(2):63-74

Self-propelling boats gain increasing importance on European waterways compared with push boats on the Mississippi and on the Volga. Danubian navigation, though growing, appears still to be rather under-developed due to the still insufficient management of the river, the economic setbacks caused by two World Wars, and the unsatisfying linkage of the Danube with other navigation systems. The construction of the Rhine-Main-Danube-Canal, of the Iron Gates dam, and other measures, however, justify rather optimistic prospects. Along with the development of container boats as well as with improving trade relations and general economic growth of the Danubian countries, navigation on the Danube will experience an exceptional growth during the years to come, providing a focus position to Hungary.  相似文献   

On the onset of thermal metastabilities in the solar core     

Attila?GrandpierreEmail author  G’bor?’goston 《Astrophysics and Space Science》2005,298(4):537-552

For infinitesimal, homologous perturbations, stability analysis has found the solar radiative interior thermally stable. It is considered for the first time here whether stability is preserved when finite amplitude nonhomologous perturbations are present. We argue that local heated regions may develop in the solar core due to magnetic instabilities. Simple numerical estimations are derived for the timescales of the decay of these events and, when heated bubbles are generated that rise towards the surface, of their rising motion. These estimations suggest that the solar core is in a metastable state. For more detailed analysis, we developed a numerical code to solve the differential equation system. Our calculations determined the conditions of metastability and the evolution of timescales. We obtained two principal results. One of them shows that small amplitude heating events (with energy surplus Q_o < 10²⁶ ergs) contribute to subtle but long-lifetime heat waves and give the solar interior a persistently oscillating character. Interestingly, the slow decay of heat waves may make their accumulation possible and so their overlapping may contribute to the development of an intermittent, individual, local process of bubble generation, which may also be generated directly by stronger (Q_o > 10²⁶ ergs) heating events. Our second principal result is that for heated regions with ΔT/T ≥ 10⁻⁴ and radius 10⁵–10⁶cm, the generated bubbles may travel distances larger than their linear size. We point out to some possible observable consequences of the obtained results.  相似文献   

Intraplate volcanism influenced by distal subduction tectonics at Jeju Island,Republic of Korea     

Marco Brenna  Shane J. Cronin  Gábor Kereszturi  Young Kwan Sohn  Ian E. M. Smith  Jan Wijbrans 《Bulletin of Volcanology》2015,77(1):1-16

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How do species and data characteristics affect species distribution models and when to use environmental filtering?     

Lukáš Gábor  Vojtěch Barták  Vincent Lecours 《International journal of geographical information science》2020,34(8):1567-1584

ABSTRACT

Species distribution models (SDMs) are widely used in ecology and conservation. However, their performance is known to be affected by a variety of factors related to species occurrence characteristics. In this study, we used a virtual species approach to overcome the difficulties associated with testing of combined effects of those factors on performance of presence-only SDMs when using real data. We focused on the individual and combined roles of factors related to response variable (i.e. sample size, sampling bias, environmental filtering, species prevalence, and species response to environmental gradients). Results suggest that environmental filtering is not necessarily helpful and should not be performed blindly, without evidence of bias in species occurrences. The more gradual the species response to environmental gradients is, the greater is the model sensitivity to an inappropriate use of environmental filtering, although this sensitivity decreases with higher species prevalence. Results show that SDMs are affected to the greatest degree by the species response to environmental gradients, species prevalence, and sample size. Models’ accuracy decreased with sample size below 300 presences. Furthermore, a high level of interactions among individual factors was observed. Ignoring the combined effects of factors may lead to misleading outcomes and conclusions.  相似文献   

A Discrete Random Model Describing Bedrock Profile Abrasion     

András A. Sipos  Gábor Domokos  Andrew Wilson  Niels Hovius 《Mathematical Geosciences》2011,43(5):583-591

We use a simple, collision-based, discrete, random abrasion model to compute the profiles for the stoss faces in a bedrock abrasion process. The model is the discrete equivalent of the generalized version of a classical, collision based model of abrasion. Three control parameters (which describe the average size of the colliding objects, the expected direction of the impacts and the average volume removed from the body due to one collision) are sufficient for realistic predictions.  相似文献   

Trace element abundances in garnets and clinopyroxenes from diamondites – a signature of carbonatitic fluids     

G. Dobosi  G. Kurat 《Mineralogy and Petrology》2002,76(1-2):21-38

Summary ?Silicates intergrown with diamonds from 10 diamondites (polycrystalline diamonds, framesites) have been analysed for trace element contents by laser ablation ICP-MS. The diamondites are fine- (< 100 μm) to coarse-grained (> 1 mm) rocks with abundant pores and cavities. The walls of the open cavities are covered by euhedral diamond crystals. Silicates (commonly garnets) are mostly interstitial or occupy the space in cavities and often contain inclusions of euhedral diamonds. Four diamondites contain lilac “peridotitic” garnets with low CaO contents (3.6–5.7 wt%), high Mg-numbers (0.83–0.84) and high Cr₂O₃ contents (3.9–6.4 wt%). Occasionally, they are accompanied by Cr-diopside. “Peridotitic” garnets have heavy rare earth element-enriched and light rare earth element-depleted chondrite-normalised patterns, occasionally with a small hump at Eu and Sm. The remaining six diamondites contain orange coloured “eclogitic” garnets with low Cr₂O₃ contents (< 1 wt%). “Eclogitic” garnets can be divided into two subgroups: E-I garnets have high Mg-numbers (0.84–0.85, as high as those of the “peridotitic” garnets) and higher Cr₂O₃ and TiO₂ and lower heavy rare earth element contents than the E-II garnets. The chondrite-normalised trace element patterns of the two subgroups of “eclogitic” garnets are similar to each other, all are depleted in light rare earth elements with respect to the heavy rare earth elements and show significant positive anomalies of Zr and Hf. “Eclogitic” garnets are more depleted in highly incompatible elements (light rare earth elements, Nb and Ta) than the “peridotitic” garnets. Diamondites and their silicates very likely crystallised from a fluid phase. The trace element contents of the hypothetical fluids in equilibrium with the “peridotitic” garnets are similar to the trace element contents of kimberlitic and carbonatitic liquids. Thus, crystallisation of these diamondites from a highly alkaline liquid in the presence of carbonates can be suggested. Hypothetical melts in equilibrium with “eclogitic” garnets are highly magnesian but depleted in light rare earth elements and other highly incompatible elements relative to the typical kimberlitic, lamproitic or carbonatitic liquids. This is an unexpected result because eclogites are richer in trace elements than peridotites and fluids in equilibrium with these rocks should reflect this. The different trace element contents of fluids which precipitated, beside diamonds, “peridotitic” and “eclogitic” garnets, respectively, therefore, must be the result of differences in the properties of these fluids rather then of different source rocks, as was already suspected by Kurat and Dobosi (2000). Received October 27, 2000; revised version accepted December 29, 2001  相似文献