bluuebunny/crossref_metadata_2025_split huggingface dataset:
Subsidence, deformation, thermal and mechanical evolution of the Mesozoic South Alpine rifted margin: an analogue for Atlantic-type margins
Authors: Bertotti Giovanni 
Published: April 2008

Abstract

The geological record of the currently exposed South Alpine transect of the Mesozoic passive continental margin provides information on the evolution of Atlantic-type margins. Before the onset of rifting, in Mid-Triassic to Carnian time, strong subsidence affected the central parts of the Southern Alps, in the Lombardian basin. No major fault is documented for this time span. Thermal conditions were strongly perturbed. Continental rifting began in Norian times, and until the beginning of the Liassic period was characterized by overall subsidence of the Lombardian basin with rates up to 200 mm ka
−1
. The strong subsidence is a result of continuing extension and of generalized crustal cooling. Subsidence rates were still important in Liassic times, although lower than in Late Triassic time. At the end of the Liassic period, the site of extension shifted towards the west, where crustal break-up eventually took place in Mid-Jurassic times. Previously poorly documented features such as the very strong subsidence in the initial rifting stages, the changing geometry and mechanics of normal faults are here associated with the thermal interactions between pre-existing thermal anomalies and rifting.
The Steinmann Trinity revisited: mantle exhumation and magmatism along an ocean-continent transition: the Platta nappe, eastern Switzerland
Authors: Desmurs Laurent , Manatschal Gianreto , Bernoulli Daniel 
Published: April 2008

Abstract
The close association of serpentinites, basalts and radiolarites, later known as the Steinmann Trinity, was clearly described by Steinmann from the south Pennine Arosa zone and its southern prolongation, the Platta nappe of the eastern Swiss Alps. This classical ‘ophiolite’ is distinctly different from typical fast-spreading ridge associations and can be compared with the transitional crust occurring along non-volcanic passive continental margins in present-day oceans. It includes serpentinized peridotites that we interpret as subcontinental mantle rocks, which were exhumed along low-angle detachment faults and locally overlain by extensional allochthons of continental crust, minor gabbroic intrusions, tholeiitic pillow lavas and flows and a succession of oceanic sediments. The serpentinized peridotites record deformation at falling temperatures during extension leading to final exposure of the mantle rocks at the sea floor and their inclusion in tectono-sedimentary breccias (ophicalcites). Field relationships, and mineral-chemical and radiometric data show that the gabbros intruded already serpentinized mantle rocks at shallow depth 161 Ma ago. They are Mg gabbros, Fe gabbros and Fe-Ti gabbros, cut by dioritic pegmatoid veins and albitite dykes, which originated by differentiation from the same parental magma. All gabbros show the same metamorphic evolution, i.e. intrusion at relatively low pressure, oceanic hydration at elevated temperature and a subsequent static oceanic alteration. The pillow lavas stratigraphically overlie the exhumed mantle rocks and the tectono-sedimentary breccias related to the exhumation of both mantle rocks and gabbros. However, both gabbros and pillow basalts are characterized by εNd values typical for an asthenospheric mid-ocean ridge-type source of the melts. They may be the products of a steady process that combined extensional deformation with magma generation and emplacement. They appear to document the onset of sea-floor spreading across an exhumed subcontinental mantle during the earliest phases of a slow-spreading ridge.
Evolution of the Aveiro Cretaceous aquifer (NW Portugal) during the Late Pleistocene and present day: evidence from chemical and isotopic data
Authors: Condesso De Melo M. T. , Carreira Paquete P. M. M. , Marques Da Silva M. A. 
Published: April 2008

Abstract

A combined hydrogeological, geochemical and isotopic investigation was performed in the Aveiro Cretaceous coastal aquifer in order to investigate the rock-water interaction and the evolution of palaeowaters. The results indicate an aquifer with well-defined freshwater (<50 mg l
−1
Cl
−
throughout most of the aquifer as far as the coastline and with very slow chemical kinetics for the water-rock interactions. The low mineralization may be explained by the mainly siliciclastic composition of the aquifer sediments, while calcite dissolution and cation exchange were also considered to be involved in the groundwater chemical evolution. This interpretation is in agreement with lithology and facies changes, and was validated by the PHREEQC-2 modelling results. Radiocarbon ages indicate a smooth gradient across the aquifer, implying continuous flow during the late Pleistocene and Holocene. Noble gas ratios indicate that the mean annual air temperatures were lower by 5–6°C at the last glacial maximum (LGM). In contrast to most areas with continental palaeowaters, the environmental isotopes indicate enrichment (0.8–1.0%. in
18
O), interpreted as reflecting the composition of the oceans at the time of the LGM at this maritime site, as well as the constancy of the air mass circulations over the period to the present day. An outlet for the aquifer is inferred offshore to account for the observed geochemical data, with the possibility that freshwater could still also be found offshore.
Before the hills in order stood: the beginning of the geology of time in England
Authors: Fuller John G. C. M. 
Published: April 2008

Abstract
That order should govern the nature of the world is an idea not confined to England, though the history of science in this country demonstrates again and again that a conception of Divine Order lay at its heart. To people of earlier days, want of order implied confusion, displacement, derangement, time out of joint, even the presence of malevolent power — ‘when the planets in evil mixture to disorder wander’. The divine scheme revealed by scripture was a frame and support for Earth science. It told an indisputable story of an ordered beginning, a diluvial reordering, and a future end in dissolution. It was a story backed by secular law, and no thinking person could have been unaware of it. Yet ‘when’ and ‘how’ were legitimate questions, answered in detail by hexaemeron writers. It is an educational curiosity in England that a particular Biblical chronology drawn up in 1650 accompanied scriptures printed for use in schools until 1885 — a matter of consequence to the history of all geological thought in this country.
Jean-André de Luc and nature’s chronology
Authors: Rudwick Martin J. S. 
Published: April 2008

Abstract
Jean-André de Luc (or Deluc) (1727–1817), who first proposed the term ‘geology’ almost in its modern sense, was one of the most prominent geologists of his time. His ‘theory of the Earth’, published in several versions between 1778 and 1809, divided geohistory in binary manner into two distinct phases. The fossiliferous strata had been formed during a prehuman ‘ancient history’ of immense but unquantifiable duration. Then the present continents had emerged above sea-level in a sudden physical ‘revolution’, at the start of the Earth’s ‘modern history’ of human occupation. De Luc argued that the rates of ‘actual causes’ or observable processes (erosion, deposition, volcanic activity, etc.) provided ‘natural chronometers’ that proved that the ‘modern’ world was only a few millennia in age; and he identified the natural revolution at its start as none other than the Flood recorded in Genesis. So ‘nature’s chronology’ could be constructed from natural evidence, to match the well-established historical science of chronology based on textual evidence from ancient cultures. De Luc’s natural chronology was restricted to the recent past, but it provided a template for later geologists to develop a geochronology extending into the depths of geohistory. The historical importance of de Luc’s work has only been obscured by the myth of intrinsic conflict between science and religion.
Current issues and new developments in deformation mechanisms, rheology and tectonics
Authors: De Meer S. , Drury M. R. , De Bresser J. H. P. , Pennock G. M. 
Published: April 2008

Abstract
We present a selective overview of current issues and outstanding problems in the field of deformation mechanisms, rheology and tectonics. A large part of present-day research activities can be grouped into four broad themes. First, the effect of fluids on deformation is the subject of many field and laboratory studies. Fundamental aspects of grain boundary structure and the diffusive properties of fluid-filled grain contacts are currently being investigated, applying modern techniques of light photomicrography, electrical conductivity measurement and Fourier Transform Infrared (FTIR) microanalysis. Second, the interpretation of microstructures and textures is a topic of continuous attention. An improved understanding of the evolution of recrystallization microstructures, boundary misorientations and crystallographic preferred orientations has resulted from the systematic application of new, quantitative analysis and modelling techniques. Third, investigation of the rheology of crust and mantle minerals remains an essential scientific goal. There is a focus on improving the accuracy of flow laws, in order to extrapolate these to nature. Aspects of strain and phase changes are now being taken into account. Fourth, crust and lithosphere tectonics form a subject of research focused on large-scale problems, where the use of analogue models has been particularly successful. However, there still exists a major lack of understanding regarding the microphysical basis of crust- and lithosphere-scale localization of deformation.
In situ
experimental study of roughness development at a stressed solid/fluid interface
Authors: Brok Bas Den , Morel Jacques , Zahid Mohsine 
Published: April 2008

Abstract

Theory and experiments have demonstrated that the initially flat surface of an elastically strained solid is morphologically unstable. The elastic strain energy of a rough, corrugated surface is lower than that of a flat one. Hence, stress forces the surface into a rough structure, but the associated increase in surface energy counteracts this roughening. In this way an equilibrium surface roughness consisting of μm-scale grooves and ridges can develop if the solid is transported, e.g. by diffusion through an aqueous solution, from sites of high stress to sites of low stress. We report
in situ
experimental observations of the surface of elastically strained potassium (K-) alum single crystals held in K-alum solution. The observations confirm earlier reports of the development of stress-induced μm-scale grooves on the surface of this material. The
in situ
observations show, however, that the stress-induced surface morphology is not a static, but a dynamic structure. The grooves are mobile, and may for example propagate or increase or decrease in length. They may move upwards, downwards, or remain where they are. Others rotate and undulate. It is suggested that if stress is high enough, grain boundaries in (wet) rocks could posses a similar structure of channels, continuously changing position and orientation, in line with the so-called ‘dynamically stable’ island-channel grain boundary structure that is essential to several pressure solution models.
Quantitative texture analysis of glaucophanite deformed under eclogite facies conditions (Sesia-Lanzo Zone, Western Alps): comparison between X-ray and neutron diffraction analysis
Authors: Zucali M. , Chateigner D. , Dugnani M. , Lutterotti L. , Ouladdiaf B. 
Published: April 2008

Abstract

X-ray and neutron diffraction techniques have been applied to quantitative texture analysis of a glaucophanite from the Sesia-Lanzo Zone (Western Italian Alps), naturally deformed under eclogite facies conditions. The comparison has been carried out in order to reveal the limits and problems of texture analysis related to strongly deformed polymineralic. Different methods of measuring and computing the orientation distribution function from diffraction data have been tested, in particular X-rays, direct peak integration, and neutron diffraction using Rietveld-texture analysis. Due to grain-size problems and heterogeneity of individual amphibole minerals, neutron radiation is shown to be the best probe for characterizing the whole rock: being more penetrative than conventional X-rays, a larger volume of the mineral aggregate is sampled, giving better statistics. However, results obtained by summing the corresponding individual spectra of at least three X-ray diffraction experiments on parallel slabs of the same specimen also give statistically valid, semiquantitative results that reproduce the overall textures. The quantitative texture analysis shows the strong texture of the two generations of amphiboles (AmpI and AmpII), which are mainly characterized by [001]*-directions at an angle of about 10° to the mineral lineation and by (
hk0
) planes describing girdles around the lineation. The texture is comparable to those described in the literature for amphibole deformed under different temperature and pressure conditions, and the pronounced asymmetry of the [001]* directions with respect to the mineral lineation is consistent with a non-coaxial component that occurs during the deformation.
Non-linear feedback loops in the rheology of cooling-crystallizing felsic magma and heating-melting felsic rock
Authors: Burg Jean-Pierre , Vigneresse Jean-Louis 
Published: April 2008

Abstract
At least six major parameters control the rheology of partially molten systems: melt content, rate of melt production, reaction to strain of the solid component, reaction to strain of the molten component, temperature and chemical composition of the source rocks. We examine their interactions to understand the rheology of partly molten rocks and partly crystallized magmas. In particular, this paper focuses on the rheology in the transitional domains between two pairs of thresholds that bracket a transitional regime between solid state and fluid behaviour during melting and crystallization, respectively. We review related information and point out non-linear effects that develop during heating of melting rocks and cooling of crystallizing magmas. Owing to the non-linear interactions, positive or negative feedback loops accelerate or damp the system. Melt in migmatite experiences shear-softening which, along with strain partitioning, facilitates melt segregation. Conversely, the increasing number of rigid crystals during cooling increases the suspension viscosity (shear hardening), which soon inhibits magma movement. These effects reinforce the asymmetry between solid-to-melt and melt-to-solid transitions. They severely contradict the concept of one rheological critical melt percentage valid for both melting and crystallization transitions. Fabric acquisition competes with nucleation and crystal growth, thus leading to hysteresis of the stress-strain rate curves. Implications for field observations include horizontal magma segregation, magma extraction and successive magma intrusions.
Do calcite rocks obey the power-law creep equation?
Authors: Renner Jörg , Evans Brian 
Published: April 2008

Abstract

The power-law creep equation,
ε̇
∞

σ
n

exp(−
Q/RT
), is commonly used to relate strain rate,
ε̇
, stress,
σ
, and temperature,
T
, for thermally activated dislocation creep in rocks. When triaxial deformation experiments on marble and limestone samples are performed at temperatures of 400–1050°C, to strains <0.2, and with strain rates between 10
−3
and 10
−7
s
−1
, the variations in strength among different rocks at nominally identical conditions are much larger than the experimental uncertainty. During dislocation creep, the strengths of various limestones and marbles decrease with increasing grain size, similar to the Hall-Petch effect in metals. The stress sensitivity of strain rate,
n
′ =
∂
ln
ε̇
/
∂
ln
σ
, and the temperature sensitivity of strain rate,
Q
′ = −
R
∂
ln
ε̇
/
∂
(1/
T
), differ greatly for the various calcite aggregates. There is a systematic dependence of
n
′ and
Q
′ on stress, grain size, and perhaps, temperature, and there is no interval in stress where
n
′ is constant. Thus, the steady-state power-law equation is an inadequate description of dislocation creep in calcite rocks. To improve the constitutive law, it may be necessary to include at least one additional state variable that scales with grain size.
The influence of dynamic recrystallization on the grain size distribution and rheological behaviour of Carrara marble deformed in axial compression
Authors: Ter Heege J. H. , De Bresser J. H. P. , Spiers C. J. 
Published: April 2008

Abstract

Strain localization and associated rheological weakening are often attributed to grain size reduction resulting from dynamic recrystallization. Most studies investigating rheological changes due to dynamic recrystallization regard recrystallized grain size as a single value that is uniquely related to stress during steady-state deformation. However, rock materials invariably exhibit a grain size distribution with distribution parameters that may be altered by dynamic recrystallization during transient deformation, affecting the rheological behaviour. This study aims to investigate the effect of deformation conditions on the evolution of grain size distribution and rheological behaviour during dynamic recrystallization in the approach to steady state. To study this, we have deformed Carrara marble to natural strains of 0.15–0.90 in axial compression at temperatures of 700–990°C, stresses of 15–65 MPa, strain rates of 3.0 × 10
−6
–4.9 × 10
−4
s
−1
and a confining pressure of 150 or 300 MPa, and analysed the grain size distribution of each sample. The results show that during dynamic recrystallization, grain size distributions evolve by a competition between grain growth and grain size reduction. The relative importance of grain-size-sensitive creep increases as the average grain size is reduced with strain. Minor weakening is observed, which is probably insufficient to cause strain localization in nature.
GPR survey of a Holocene aeolian/fluvial/lacustrine succession, Lauder Sandhills, Manitoba, Canada
Authors: Havholm K. G. , Bergstrom N. D. , Jol H. M. , Running G. L. 
Published: April 2008

Abstract
A stream cut-bank at Flintstone Hill, Lauder Sandhills, Glacial Lake Hind Basin, southwestern Manitoba, exposes an extensive Holocene sedimentary sequence. Ground penetrating radar (GPR) is used to determine lateral continuity of four major stratigraphic units (wetland complex, Mid-Holocene aeolian dune, sandsheet/fluvial, Late Holocene aeolian dune) and to image primary sedimentary features within the dune strata. Depth of GPR signal penetration is only about 5 m. Signal attenuation is attributed to the presence of primarily pedogenic silts/clays and carbonate- and iron sesquioxide-rich horizons within the sandier units. Nevertheless, the stratigraphic units are shown by GPR, and confirmed by core data, to be laterally continuous within the survey area. Finer-scale dune strata are not well displayed in the aeolian units. Signal attenuation above the Mid-Holocene unit and relatively high iron sesquioxide concentrations within the unit limit imaging of well-preserved dune foreset strata. In the Late Holocene unit, depositional strata are poorly preserved and GPR primarily images soil A-horizons formed on surfaces of temporary stabilization within the dune sediment.
Monitoring sediment infilling at the Ship Creek Reservoir, Fort Richardson, Alaska, using GPR
Authors: Hunter Lewis E. , Ferrick Michael G. , Collins Charles M. 
Published: April 2008

Abstract

The Ship Creek Reservoir serves as the municipal water supply for Fort Richardson, Elmendorf Air Force Base, and Anchorage, the largest city in Alaska. The reservoir is located at the base of a ∼4.8 km-long canyon along the flanks of the Chugach Mountains, where it is fed by a 234 km
2
unglaciated drainage basin. High sediment production within the watershed results in rapid infilling of the reservoir and a need for periodic dredging. During March 2001, we conducted a ground penetrating radar (GPR) survey of the reservoir to document the current state of sedimentation and to evaluate sediment trap designs. These data are presented here as a case study in which the utility of GPR for evaluating sediment infilling in a shallow reservoir is evaluated

The survey was conducted from a 45 cm-thick ice cover in the lower reservoir that thinned to about 6 cm at a distance of 220 m above the dam. A total of 49 radar profiles were collected from the ice cover and an additional 10 profiles were collected on a gravel bar in the upper parts of the reservoir. Water depth near the dam was about 6 m and sediment in that reach forms a blanket deposit. More hummocky and asymmetric bed topography was found away from the dam, apparently controlled by palaeochannel geometry and bedrock sills. GPR profiles collected on the gravel bar document a sedimentary wedge that thickens downvalley and toward the southern edge of the reservoir, apparently the palaeothalweg of Ship Creek. Transverse profiles across the bar indicate that an average of about 2 m of sediment can be removed across this reach, with 3 m or more being available adjacent to the active channel. This survey indicates that infilling of the entire reservoir had reached a level approaching that of the pre-1995 dredging. Analysis of sediment-yield data and basin geometry showed that a weir built across the reservoir approximately 215 m from the dam would produce a trap capable of storing 60% to 70% of that currently held in the reservoir. Sediment trapped within this portion can be excavated using standard machinery, providing a more cost-effective alternative to periodic dredging.
Radar reflections from sedimentary structures in the vadose zone
Authors: Van Dam Remke L. , Van Den Berg Elmer H. , Schaap Marcel G. , Broekema Lucas H. , Schlager Wolfgang 
Published: April 2008

Abstract
Ground penetrating radar (GPR) is a suitable technique for imaging sedimentary structures in the vadose zone because small texture-related capillary-pressure variations lead to changes in water content and electromagnetic properties. To study exactly how GPR reflections are generated by sedimentary structures, GPR profiles of an aeolian sedimentary succession are combined with measurements of textural, electromagnetic and water-retention characteristics from a trench. Time domain reflectometry indicates that small variations in texture in the high-angle dune sediment are associated with changes in water content. Synthetic modelling shows that these changes cause clear GPR reflections. In an experimental approach to estimate the radar response of structures below the wave resolution, i.e. features smaller than λ/4, variations in grain-size distribution and porosity in a thin section were used to reconstruct water-retention curves and impedance models of the thinly layered sediment. Synthetic radar records calculated from the impedance models show that reflections from the studied subcentimetre-scale structures are composites of interfering signals. Although these low-amplitude interfering signals will commonly be overprinted by more prominent reflections, they may cause reflection patterns that change with frequency and do not represent primary bedding.