bluuebunny/crossref_metadata_2025_split huggingface dataset:
Exhumation of high‐pressure rocks: a review of concepts and processes
Authors: Platt J.P. 
Published: July 2007

The exhumation of high‐pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures, or the transport of the metamorphic rocks through the overburden. Exhumation cannot be achieved simply by thrusting or strike‐slip faulting. It may be caused by erosion of shortened and thickened crust, but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km. One or more of the following additional mechanisms may be involved.1 Corner flow of low‐viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock, and may explain some occurrences of high‐pressure tectonic blocks in mélange. This process does not, however, appear to be adequate to explain the exhumation of regional high‐pressure terrains.2 Buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings. This is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle, but cannot explain the emplacement of coherent tracts of high‐density metamorphic rock into shallow crustal levels. Some high‐pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low‐density mud or serpentinite.3 Extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high‐pressure terrains. Extension may occur in the upper part of an accretionary wedge thickened by underplating; or it may affect the whole lithosphere in a region of intracontinental convergence, if surface elevation has been increased by the removal of a lithospheric root. In the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain.
Temperature logs in deep wells—a useful tool for past climatic reconstruction
Authors: Cermak V. , Kukkonen I.T. , Safanda J. 
Published: July 2007

According to the theory of heat conduction in a semi‐infinite body, temperature changes at the surface propagate into the subsurface with the amplitude attenuation and time delay that increase with depth. Temperature changes on the earth's surface, reflecting the past climatic history, can thus be evaluated by analysing the curvature they have caused in the present temperature‐depth distribution. As a rule, temperature profiles to depths of 200–300 m record surface temperature trends accurately over the last two centuries or so; deeper holes may reveal climate history farther back but with decreasing resolution.We present several synthetic temperature‐depth profiles to demonstrate the expected signature of past surface temperature changes in the subsurface, the analysis of which may help better identify the climate of the past. Examples of extracted climate recollections from holes in North America and Europe are discussed. While inconspicuous underground records may correspond to the postglacial warming 8–11 kyr ago, reasonably well‐documented borehole logging data have confirmed climate excursions in the past millenium, namely the Little Climate Optimum and the Little Ice Age. Traces of recent warming are generally common in many temperature records, evidencing the temperature rise by 1–2 K over the past 100 years.
Salt insertions in sedimentary sequences: impacts on temperature and thermal maturation with depth
Authors: Zhao K. , Lerche I. 
Published: July 2007

Due to the contrast in thermal conductivity between salt and typical sedimentary formations the presence of salt in various shapes in the sub‐surface can have a significant impact on the sub‐surface temperature distribution and thermal maturation of source rocks.Using a thermal indicator tomography 1‐D modelling system, which deals with salt insertion, the thermal and excess maturity anomalies caused solely by the presence of a salt layer are investigated. Two cases, salt ‘plug’ and ‘lens’, illuminate the different patterns of vitrinite reflectance variation with depth that would be recorded by borehole sampling. Salt can be inserted either as a primary depositional layer or by secondary intrusion at depth.The effects of salt are more dominant on the subsalt layers because: 1 salt insertion changes the burial paths of subsalt sediments. Thus the compaction‐driven fluid flow of subsalt sediments, and also basement subsidence, are altered;2 iso‐temperature lines are modified by the presence of the salt and the variation depends on the thickness of the salt layer.The model was also designed to estimate the time of salt insertion and the variation of salt thickness in an inverse sense using present day data on temperature with depth and measured thermal indicators. An investigation is given of the degree to which inverse procedures resolve parameters associated with salt insertion. The sensitivity of those parameters is also discussed.
Tertiary tectonic evolution along the Arne‐Elin Trend in the Danish Central Trough
Authors: Clausen Ole Rønø , Korstgård John A. 
Published: July 2007

Tertiary sequence boundaries are mapped on reflection seismic sections in the northern part of the Danish Central Trough, North Sea. The geometry of the sequence boundaries and the isopach maps of the sequences are used as indicators of differential subsidence.The Tertiary tectonic evolution is subdivided into: (i) Late Palaeocene and Early Oligocene episodes of inversion along the NNW–SSE striking Arne–Elin Trend (ii) Early Oligocene to Pliocene episodes of differential subsidence across pre‐Tertiary fault trends.The observed differential subsidence and inversion is related to pre‐Tertiary faults and fault trends, and dating of the sequences shows that the tectonic phases were contemporaneous with tectonic events in NW Europe. It is suggested that the differential subsidence‐inversion is controlled by reactivation of pre‐Tertiary faults/fault‐trends by block movements due to an interaction of the Alpine collision and the opening of the Atlantic.
Fractal damage mechanics of geomaterials
Authors: Chelidze Tamaz 
Published: July 2007

Recent progress in a new field of mechanics of diluted solids is reviewed ‐ the fractal mechanics of geomaterials. It has become clear that the mechanics of geomaterials should take into consideration the influence of the fracture delocalization process on fundamental fracture characteristics such as the strength, the fractal dimension of a network of cracks, the surface energy of fracture and the elastic properties of fragmented media.The percolation model of fracture proposed by this author in 1979, in accordance with experimental data, treats the destruction process as a sequence of nucleation and coalescence of microcracks caused by their interaction. This approach enables the mathematical description of the entire process of fracturing. Many aspects of the fracture of heterogeneous solids ‐ the magnitude‐frequency distribution of seismic activity and acoustic emission, the high‐surface energy of fracture in composite materials and rocks, the geometrical peculiarities of a crack network, the appearance of forerunners of mechanical collapse, and the intermittency of the fracture process in the time domain ‐ find quantitative explanation in the percolation model. The process of determining the elasticity of fractured media, which is the object of the elastic percolation theory, also reveals some unusual features that can affect the process of geophysical interpretation. For example, the elastic modulus M and the velocity of elastic waves v become scale‐dependent in the fractal regime. It is shown that the fractal dimension of the elastic modulus of a depleted solid differs significantly for ‘refilled’ and ‘hollow’ voids.Several implications of fractal mechanics for seismology are considered, namely the generalized form of the magnitude‐frequency relationship, the phenomenon of anomalous tensosensitivity, the scale‐dependence of the elastic moduli of massively faulted rocks and the possibility of apparent seismic boundaries.
Precession‐punctuated growth of a late Miocene submarine‐fan lobe on Gavdos (Greece)
Authors: Postma G. , Hilgen F. J. , Zachariasse W. J. 
Published: July 2007

Sedimentary cycles in an upper Miocene succession of hemipelagic sediments (marls) and laminites (sapropels) were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity. Individual marl‐laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr. The lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences. The turbidite sequences occur within or substitute entirely the laminite beds, so that turbidite deposition is similarly precession punctuated.The turbidite facies is characteristic for small, prograding fan lobes fed by small‐volume turbidites. The abundant plant remains, the local palaeogeographic setting and the association with laminites (related to wet climate) suggest a river‐fed submarine fan‐lobe, where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run‐off. The onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief. Sea‐level changes seem least important for the triggering of turbidites, which is in contrast with current beliefs.
Seismic response of classical monuments‐a numerical perspective developed at the Temple of Apollo in Bassae, Greece
Authors: Papastamatiou Dimitri , Psycharis Loannis 
Published: July 2007

We report on the initial phase of assessing numerically the seismic vulnerability of sections of the Temple of Apollo in Bassae, in the W. Peloponnesus, Greece. The site is exposed to large subduction earthquakes and to smaller local extensional events. In this phase the only link with the seismotectonic environment is the selection of representative recorded accelerograms for numerical analysis.The analysis confirms the highly non‐linear nature of the response of megalithic structures relying for their stability on the friction and cohesion between the constituent blocks. Intact sections of the Temple showed substantial resistance to strong ground motions due to their capacity to absorb energy with large relative movements of the building blocks that do not impair the stability of the structure. However, imperfections typical of the present condition of the monument, namely deterioration of the building stones and of the foundation material, substantially reduce the stability threshold.Powerful numerical tools are available to assist rational schemes for the protection of ancient structures and to subject archaeological hypotheses to numerical tests. This analysis quantifies the effects of weaknesses of the structure and allows testing the effectiveness of strengthening procedures. In the archaeological context there is a strong interaction with the ongoing geodynamic processes.
Large cold anomalies in the deep mantle and mantle instability in the Cretaceous
Authors: Yuen D.A. , Čadek O.P. , Boehler R. , Moser J. , Matyska C. 
Published: July 2007

ABSTRACTTwo large cold masses in the deep mantle have been delineated by using long‐wavelength seismic tomographic models in conjunction with mineralogical experimental data at high pressure. These cold anomalies are found under the western Pacific and the Americas with temperatures more than 1000 degrees below the ambient mantle temperature. These strong cold anomalies existing in the lower mantle today would suggest that there might have existed not too long ago a substantial temperature jump across a thermal boundary layer between the upper and lower mantle. Numerical simulations in an axisymmetric spherical‐shell model incorporating the two major phase transitions have shown that very large pools of cold material with temperatures of around 1500 K can be flushed down to the core–mantle boundary during this tumultuous gravitational instability. A correlation is found between the current locations of these very cold masses and regions of past subduction since the Cretaceous. Correlation analysis shows that the slab mass‐flux into the lower mantle does not behave in a steady‐state fashion. These findings may support the idea of a strong gravitational instability with origins in the transition zone, as suggested by numerical models of mantle convection.
Lithological influences on the fractal dimension of coastal morphology: the volcanic islands of Vulcano. Stromboli and Alicudi in the Southern Tyrrhenian Sea
Authors: Leonardi Sabrina , Mulargia Francesco , Rossi Pier Maria Luigi 
Published: July 2007

ABSTRACTFractal geometry is an important concept for describing geological morphologies, providing not only a qualitative description, but also a basis for quantitative comparisons. The goal of the present study is to identify some of the geological factors which affect the fractal dimension of coastlines. In particular, a tentative classification is presented of the lithological factors influencing the coastlines of recently formed Italian volcanic islands ‐ Vulcano, Stromboli and Alicudi ‐ located in the Southern Tyrrhenian Basin.
Types of crust beneath the Ligurian Sea
Authors: Pasquale V. , Verdoya M. , Chiozzi P. 
Published: July 2007

ABSTRACTThe structural setting beneath the Ligurian Sea resuJts from several tectonic events reflected in the nature of the crust. The central‐western sector, called the Ligurian basin, is part of the northwestern Mediterranean. It is a marginal basin that was generated in Oligocene‐Miocene time by subduction of the Adriatic plate beneath the European plate and by the eastward drift of the Corsica‐Sardinia block. The eastern sector belongs to the Tyrrhenian basin system and is characterized by extensional activity which since Tortonian time superimposed an earlier compressional regime. Our effort has been addressed in particular towards simplifying the complex nature of the crust of the Ligurian basin by modelling its genesis using uniform extension and sea‐floor depth variation with age. In the rift stage of the basin's evolution, the initial subsidence reaches the isostatic equilibrium level of the asthenosphere by a thinning factor of 3.15. The additional passive process, corresponding to the cooling of the lithosphere since 21 Ma, leads to a total tectonic subsidence of 3.4 km, representing the boundary of the extended continental crust. For values up to 4.1 km a transitional‐type crust is expected, whereas for higher tectonic subsidence values a typical oceanic crust should exist. After setting these constraints, the boundaries of the different crust types have been drawn based on total tectonic subsidence observations deduced from bathymetry and post‐rift sediment thickness. Although there is a general agreement with the previous reconstructions deduced from other experimental data, the oceanic realm has wider extent and more complex shape. The northernmost part of this realm shows crust of sub‐oceanic type altemating basement highs with lower subsidence values. The observed surface heat flux is consistent with the predicted geothermal held in the Alpine‐Provençal continental margin and in the oceanic domain. However, a characteristic thermal asymmetry is clearly visible astride the basin, due to the enhanced heat flux of the Corsica margin. Even if the uniform extension model accounts well at a regional level for the present basement depth, a remarkable tectonic subsidence excess has been found in the Alpine‐Provençal continental margin. This evidence agrees with the reprise in compression of the margin; the direction of the greatest principal stress is N120°E on average.
The use of correspondence analysis and principal component analysis as a tool for deducing metamorphic mineral crystallization in Mn‐rich lithologies
Authors: Jiménez‐Millán J. , Jiménez‐Espinosa R. , Velilla N. , Chica‐Olmo M. 
Published: July 2007

ABSTRACTPrincipal component analysis (PCA) and correspondence analysis (CA) have been used to identify several critical mineral crystallization factors during metamorphism of Mn‐rich lithologies from the Iberian Massif, Spain. Three types of variables have been considered in the system: mineralogical variables, bulk composition variables and one physical variable (oxygen fugacity). PCA was applied to the compositional variables to obtain four components, which were used as new compositional variables. These, together with the mineralogical and physical variables, were treated in the CA. The plot of the variables on the factor 1‐factor 2 plane reveals that tephroite crystallization is controlled by a compositional variable representing low values of ratio Si/(Mn+Fe) in the rocks. Moreover, it is possible to deduce from this plot the importance of high oxygen fugacity conditions for the crystallization of piemontite. The third factor shows that the crystallization of spessartine does not require very restrictive physical‐chemical conditions.
New injection experiments in non‐Newtonian fluids
Authors: Hallot E. , Auvray B. , de Bremond d'Ars J. , Martin H. , Davy Ph. 
Published: July 2007

ABSTRACTIn order to identify the dominant non‐Newtonian effects which occur during the injection of a new Newtonian magma through a partially crystallized magma chamber, we have performed some preliminary analogue experiments which enable us to point out several features induced by the non‐Newtonian properties of the host fluid during injection processes. These experiments were performed in a three‐dimensional device and involve complex non‐Newtonian fluids—clay suspensions in which rheological properties such as bulk strength, yield strength and rheofluidification exponent may vary. Forced injection takes place through a slot which in the case of a Newtonian host fluid is the geometry that provides planar structures. Depending both on the density contrast and on the rheological contrast between the injected dyed water and the host fluid three kind of structures were observed: (1) permanent plumes when the injected water is lighter than the suspension exhibiting rheological properties close to Newtonian fluids; (2) pseudo‐fountains and spreading at the bottom of the tank with a destabilizing density contrast and in high yield strength/more viscous suspensions; (3) fountains with a slightly stablizing density contrast. The implications for magma chamber evolution are briefly discussed. In particular it seems that homogeneous non‐Newtonian media inhibit the formation of planar structures and partially crystallized magma may induce the spreading of the new magma at the bottom or at the top of the chamber regardless of the density contrast between the magmas.
The Roer Valley Graben earthquake of 13 April 1992 and its seismotectonic setting
Authors: Camelbeeck Thierry , van Eck Torild 
Published: July 2007

ABSTRACTA moderately sized pure, normal dip‐slip earthquake occurred in the Roer Valley Graben (RVG) near Roermond, The Netherlands on 13 April 1992 at 1h 20m UTC. This contribution presents an overview of the locations, fault‐plane solutions and magnitudes obtained for the mainshock and the aftershocks by the different scientific groups involved in their analysis. The observed maximum intensity of VII is compared with that of other earthquakes in the region to illustrate the relatively low level of damage caused by the mainshock.Using SH and Lg waves recorded at seven local and regional broadband stations, we determine a seismic moment of 1.4 × 1017 Nm, a static stress drop of 9.7 MPa and an average displacement of 33 cm over a rupture surface of approximately 11 km2.The seismotectonics of the region extending from the RVG to the city of Liège including the western part of the Rhenish Massif (WRM) and the eastern part of the Brabant Massif (EBM) is analysed based on the Roermond earthquake studies and data collected since 1985 by the Belgian seismic network. The geographical distribution of focal mechanism reveals four different seismotectonic regimes in this area. From stress tensor inversion we find that s̀3 coincides with the minimum horizontal stress component in the RVG, the WRM and possibly in the EBM, while in the Liège region s̀3 is approximately vertical. The minimum horizontal stress component shows a 30° rotation to the north in the WRM and the Liège region and possibly 50° in the EBM when compared with the minimum horizontal stress component in the RVG.
The Roermond earthquake of 13 April 1992, the Netherlands: geological aspects
Authors: Trifonov Vladimir G. , Klerkx Jean , Theunissen Karel 
Published: July 2007

ABSTRACTThe epicentre of the Roermond earthquake is located near the western boundary fault of the Roer valley trough, one of the deepest and the most active in the Quaternary part of the Lower Rhine graben. The Late Pleistocene and Holocene activity of the trough is manifested by offsets of the main (Mindel) and the lower (Riss and Late Pleistocene) terraces along the boundary faults.Surface fractures have been observed in an area of more than 50 km2: 2.5–3.5 km to the north of the town of Roermond, at 0.8 km to the south of the village of Herkenbosch and in the southeastern part of the village of Montfort. Three types of ruptures were differentiated: scarps up to 50 cm high along open fractures near the Maas River; open fractures (continued by scarps in some places) and open fractures with a liquefaction of the Quaternary alluvium sands. The last type is predominant. The location of the ruptures depends on the landscape and water‐table of the region. While they could be produced solely by hydraulic shock during the earthquake (increased by the wet spring season), the majority of the ruptures strike N50°W ± 10°, i.e. parallel to the main trough faults, or N55°E ± 10°, along ‘neotectonic lines’, parallel to the Maas valley and deduced from space imagery. Thus, the ruptures could be the secondary surficial effect of the earthquake, linked indirectly with the active tectonics of the region.
The Cretaceous–Tertiary boundary in southern low‐latitude regions: preliminary study in Pernambuco, northeastern Brazil
Authors: Albertão Gilberto A. , Koutsoukos Eduardo A.M. , Regali Marília P.S. , Attrep Moses , Martins Paulo P. 
Published: July 2007

ABSTRACTA preliminary integrated study of a Cretaceous‐Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non‐graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea‐level lowstand, the former possibly generated by the K/T boundary Yucatán impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm‐thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock‐metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite‐like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact‐derived material has not been found in the uppermost Cretaceous beds.