bluuebunny/crossref_metadata_2025_split huggingface dataset:
Permeability of rock samples from the Kola and KTB superdeep boreholes at high
P-T
parameters as related to the problem of underground disposal of radioactive waste
Authors: Zharikov A. V. , Malkovsky V. I. , Shmonov V. M. , Vitovtova V. M. 
Published: April 2008

Abstract

An experimental study of the samples collected from a depth of 3.8–11.4 km in the Kola and KTB superdeep boreholes, and from the Earth’s surface at the Kola drilling site was carried out at temperatures up to 600°C and pressures up to 150 MPa. The study was focused on the estimation of
in situ
permeability of the deep-seated rocks, their palaeopermeability during metamorphic transformations, and their protective properties for HLW disposal. Permeability dependencies on pressure and temperature were obtained. An increase in confining pressure leads to a decrease in rock sample permeability. The temperature trends obtained are of different types: permeability may decrease within the entire temperature range, or it may firstly decrease, reach its minimum and then decrease. It was found that this permeability behaviour is due to rock microstructure transformations caused by the competing effects of temperature and effective pressure. A possible
in situ
permeability trend for the superdeep section was proposed. A numerical simulation of convective transport was performed in order to determine a safe depth for the HLW well repository. The estimates obtained show that HLW well repositories can be used safely at relatively shallow depths.
On the neutron absorption properties of basic and ultrabasic rocks: the significance of minor and trace elements
Authors: Harvey P. K. , Brewer T. S. 
Published: April 2008

Abstract
The neutron absorption macroscopic cross-section, Σ, is measured routinely by neutron porosity tools and, although rarely presented as a logging curve in its own right, is used indirectly for the estimation of (neutron) porosity. One of the reasons that this primary measurement is not often employed directly in petrophysical analysis is the difficulty of interpretation. In particular, little is known about the range of Σ values for common lithologies, or exactly what information the measurement is providing.
In this contribution we demonstrate that excellent estimates of Σ can be calculated, provided that the chemistry of a sample is known in sufficient detail. When applied to a range of geochemical reference materials, it becomes apparent that the minor and trace elements present may have a profound effect on the Σ value of a sample, and, in turn, on the interpretation of neutron porosity measurements. Using this approach we present Σ data for basaltic and ultrabasic rocks, and model the change in Σ with alteration.
Alteration is considered in these models as an increase in alteration minerals (which are mainly clays, but also carbonates and zeolites in basic rock alteration) and changes in the trace-element chemistry of the rocks. Of the trace elements, boron and some of the rare-earth elements are of particular importance. Modelling the variation in Σ with these mineralogical and compositional changes indicates that increases in boron are the most important of these factors in increasing Σ; this is enhanced by the alteration, particularly to clay phases, which generally accompanies an increase in boron.
These models suggest that a Σ log should be able to act as a proxy for alteration trends in basic and ultrabasic crystalline rocks, and a quantitative model for such alteration is described.
Effect of compositional variations on log responses of igneous and metamorphic rocks. II: acid and intermediate rocks
Authors: Pechnig R. , Delius H. , Bartetzko A. 
Published: April 2008

Abstract
An extensive data-set of petrophysical down-hole measurements exists for boreholes drilled into continental crystalline crust. We selected boreholes covering a range of different types of plutonic rocks and gneisses in amphibolite or high-grade metamorphic rocks. According to Serra’s concept of electrofacies, a specific set of log responses should characterize one rock type. Here, we concentrate on the detection of compositional variations between rock types. Bulk composition of the protoliths influences the mineralogical composition of the metamorphic rock, and we demonstrate how this impacts on the down-hole measurements. Integration of logging data with geochemical core data and mineralogical descriptions allows the calibration of the log responses to rock types. The relationship of the log responses with core data shows a remarkably good correlation, and diagnostic trends are detected. From the logs, potassium and neutron porosity are particularly helpful in distinguishing different types of gneisses and igneous rocks with respect to their protoliths. The proportions of amphibole/pyroxene, mica + K-feldspar and feldspar + quartz in the rocks seem to control the direction of correlation in a cross-plot, i.e. positive or negative, depending on increasing or decreasing mineral proportions. This is true for all boreholes, and a generalized classification scheme could be developed for these crystalline rocks.
Laboratory investigations for the evaluation of
in situ
geophysical measurements in a salt mine
Authors: Kulenkampff J. , Just A. , Aschmann L. , Jacobs F. 
Published: April 2008

Abstract
Problem zones in a sylvinite mine were explored by underground measurements using a set of geophysical methods (geosonar, seismics, georadar, EM methods and geoelectrics), which yield parameter sets for disturbed and undisturbed rock. Underground geo-electrical methods are most suitable for examining humidity content and structures for the transport of brines, although they have to be constrained by wave-propagation methods. Additional laboratory experiments on rock salt samples were carried out in order to provide quantitative evaluation methods. A titration method was used to determine the amount of water. This was applied simultaneously with a four-electrode resistivity measuring system for samples with very high resistivity. These measurements were made on samples at different scales, yielding relationships between water content and resistivity, as well as information about the parameter distribution in larger core samples. Together, the field and laboratory results show that geo-electrics is a suitable method for the detection and evaluation of problem zones of the geological barrier of hazardous waste repositories, and a criterion for the risk assessment based upon resistivity measurements is defined.
Deformation of metavolcanics in the Karachay Lake area, Southern Urals: petrophysical and mineral-chemical aspects
Authors: Petrov V. A. , Poluektov V. V. , Zharikov A. V. , Velichkin V. I. , Nasimov R. M. , Diaur N. I. , Terentiev V. A. , Shmonov V. M. , Vitovtova V. M. 
Published: April 2008

Abstract

This paper is the result of laboratory tests aimed at comparative assessment of the filtration, elastic and mechanical properties of metavolcanics, as well as a preliminary investigation of the nature of characteristic variations in
P–T
parameters, simulating the conditions in the vicinity of an underground storage facility for heat-generating radioactive waste. The properties have been studied in cores collected from the deepest (1200 m) hole in the metavolcanics, focusing on intervals subjected to different strain intensities. Interpretation of the data obtained suggests that the identification of the most probable pathways for fluid flow and radionuclide transport depends on estimates of the retardation characteristics of zones of disjunctive dislocation. However, the widespread occurrence of linear zones of schistosity, mylonitization and brecciation may not be a decisive negative factor in the long-term performance assessment of the underground storage facility, because these minerals, which concentrate radionuclides such as epidote, chlorite, sericite, and Fe oxyhydroxides are widely distributed in these zones. Moreover, open microfractures and pores affected by heat will be filled with neoformed minerals (epidote, chlorite, carbonate) characterized by high sorption capacity with respect to radionuclides, due to release of intergranular water, as well as carbonatization reactions. Simultaneously, the system of open macro- and microfractures that resulted from stress affecting relatively undisturbed blocks may be one of the factors dramatically reducing country rock retention capability. Therefore, the results of petrophysical and mineral-chemical investigations must be taken into account in feasibility studies of designs for the construction of underground systems for final disposal of high-level wastes and/or long-term storage of spent nuclear fuel in the PA Mayak area.
Melt rates at calving termini: a study at Glaciar León, Chilean Patagonia
Authors: Haresign Eleanor , Warren Charles R. 
Published: April 2008

Abstract

Glaciar León, a temperate, grounded outlet of the North Patagonian Icefield, terminates at an active but stable calving margin in Lago Leones. Glaciological and limnological data gathered during 2001 and 2002 are used to examine the relative contributions of calving and melting to mass loss at the terminus, and the interplay between glacier and lake processes. The calving rate of 880 m/a in a mean water depth of 65 m is high for lake-calving glaciers. Subaerial melt rates at the terminus are small compared with calving rates, but melting at the waterline facilitates calving by undercutting the subaerial calving cliff. Ice-proximal surface water temperatures of 6–7°C allow waterline melt notches to grow at rates of
c.
0.8 m/day, suggesting that melt-driven calving accounts for
c.
23% of ice loss at the terminus. The significance of melting at calving termini decreases with increasing calving speeds, but is greater than simple calculations of melt losses suggest because of the process-linkage with calving.
Actual paraglacial progradation of the coastal zone in the Kongsfjorden area, western Spitsbergen (Svalbard)
Authors: Mercier Denis , Laffly Dominique 
Published: April 2008

Abstract
This research was carried out on the Brøgger Peninsula, northwest Spitsbergen, Svalbard (79°N 12°E). In the western part of Spitsbergen, cold-based valley glaciers have retreated more than 1 km from their Little Ice Age limits, and glacial meltwater has extensively reworked glacigenic sediments on exposed glacier forelands. In such areas, a paraglacial sediment transport regime has become predominant, with runoff as the dominant process. A combination of GIS, DEM, aerial photographic and field data was employed to estimate shoreline progradation at sandur outflows. Average shoreline progradation is estimated to amount to 3 m/annum over the last 30 years, a period of uninterrupted sediment provision from the glacial runoff system.
Holocene permafrost aggradation in Svalbard
Authors: Humlum Ole 
Published: April 2008

AbstractThe distribution and dynamics of permafrost represent a complex problem, confounded by a short research history and a limited number of deep vertical temperature profiles. This lack of knowledge is pronounced for the High Arctic, where most permafrost is found and where amplified responses to various climatic forcing mechanisms are expected. Within the High Arctic, the Svalbard region displays a unique climatic sensitivity and knowledge of Holocene, and modern permafrost dynamics in this region therefore have special interest. This paper reviews knowledge on Holocene permafrost development in Svalbard and the climatic background for this. In Svalbard, modern permafrost thickness ranges from less than 100 m near the coasts to more than 500 m in the highlands. Ground ice is present as rock glaciers, as ice-cored moraines, buried glacial ice, and in pingos and ice wedges in major valleys. Svalbard is characterized by ongoing local-scale twentieth-century permafrost aggradation, even though a distinct temperature increase around 1920 introduced relatively unfavourable climatic conditions for permafrost in Svalbard. Modern permafrost aggradation is to a large extent controlled by wind, solid precipitation and avalanche activity, and exemplifies the complexity of relating climate and permafrost dynamics.
Constraining kinematic rotation axes in high-strain zones: a potential microstructural method?
Authors: Reddy Steven M. , Buchan Craig 
Published: April 2008

Abstract
The correct determination of the kinematic rotation axis in high-strain zones is essential to the study of the tectonic evolution of the Earth’s crust. However, the common assumption that the kinematic rotation axis lies orthogonal to the XZ plane of the finite strain ellipse may be invalid in the case of general shear. Orientation data obtained by electron backscatter diffraction from calcite, deformed in the high-strain Gressoney Shear Zone of the Western Alps, has been investigated using orientation maps, bulk sample crystallographic orientation and misorientation analyses, and detailed intragrain misorientation and crystallographic dispersion analysis. The results demonstrate a strong geometrical coincidence amongst (1) the bulk macroscopic kinematic rotation axis, (2) the orientation of misorientation axes associated with low-angle boundaries, and (3) rotation axes associated with crystallographic dispersion at the intragrain scale. This coincidence is interpreted to reflect a geometric control of the kinematic framework of the high-strain zone on the activity of crystal slip systems. It is proposed that this relationship may be exploited as a new microstructural tool to determine the orientation of bulk kinematic rotation axes in high-strain zones without assuming a geometric link between kinematic rotation and XZ sections. Although further testing is required, application of the approach may lead to a significant advance in our understanding of natural general shear deformation.
Crack-seal patterns: records of uncorrelated stress release variations in crustal rocks
Authors: Renard François , Andréani Muriel , Boullier Anne-Marie , Labaume Pierre 
Published: April 2008

AbstractStatistical properties of crack-seal veins are investigated with a view to assessing stress release fluctuations in crustal rocks. Crack-seal patterns correspond to sets of successive parallel fractures that are assumed to have propagated by a subcritical crack mechanism in the presence of a reactive fluid. They represent a time-sequence record of an aseismic and anelastic process of rock deformation. The statistical characteristics of several crack-seal patterns containing several hundreds of successive cracks have been studied. Samples were collected in three different areas, gold-bearing quartz veins from Abitibi in Canada, serpentine veins from the San Andreas system in California and calcite veins from the Apennine Mountains in Italy. Digitized pictures acquired from thin sections allow accurate measurement of crack-seal growth increments. All the samples show the same statistical behaviour regardless of their geological origin. The crack-seal statistical properties are described by an exponential distribution with a characteristic length scale and do not show any spatial correlation. They differ from other fracture patterns, such as earthquake data, which exhibit power-law correlations (Gutenberg-Richter relationship). Crack-seal series represent a natural fossil record of stress release variations (less than 50 bars) in the crust that show a characteristic length scale, associated with the resistance of rock to effective tension, and no correlation in time.
Single-contact pressure solution creep on calcite monocrystals
Authors: Zubtsov Sergey , Renard François , Gratier Jean-Pierre , Dysthe Dag K. , Traskine Vladimir 
Published: April 2008

Abstract

Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 °C for six weeks using ceramic indenters under stresses in the 50–200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH
4
Cl. The deformation (depth of the hole below the indenter) is measured
ex situ
at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0–100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH
4
Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate indentation rate and the dry control experiments did not show any measurable deformation. The rate of calcite indentation is found to be inversely proportional to the indenter diameter, thus indicating that the process is diffusion-controlled. The microcracks in the dissolution region under the indenter dramatically enhance the rate of calcite indentation by a significant reduction of the distance of solute transport in the trapped fluid phase. This result indicates that care should be taken in extrapolating the kinetic data of pressure solution creep from one mineral to another.
Steep extrusion of late Archaean granulites in the Northern Marginal Zone, Zimbabwe: evidence for secular change in orogenic style
Authors: Blenkinsop Thomas G. , Kisters Alexander F. M. 
Published: April 2008

Abstract

The Northern Marginal Zone (NMZ) of the Limpopo Belt in southern Zimbabwe is an essentially plutonic terrain, now consisting of granulite-gneisses, that was assembled by extensive magmatic under- and intraplating between
c.
2.7 and 2.6 Ga during late Archaean crustal shortening. In this study, we present the first evidence for regional-scale normal shear in the NMZ. Normal shear has been identified along an up to 500 m wide, steeply dipping belt of mylonites, the Mitilikwe shear zone. Geochronological and mineralogical-textural data indicate that normal shear occurred coeval with crustal shortening that was accommodated along gently dipping thrust zones. The bulk strain pattern consisted of horizontal shortening, vertical stretching, and subvertical extrusion of a crustal segment. Horizontal shortening persisted throughout the orogenic evolution in the NMZ and no features typical of gravitational collapse in modern orogens are seen. This could imply that there was never major overthickening of the crust by thrusting, which may be a characteristic feature of Archaean orogeny.
Lithospheric-scale analogue modelling of collision zones with a pre-existing weak zone
Authors: Willingshofer Ernst , Sokoutis Dimitrios , Burg Jean-Pierre 
Published: April 2008

Abstract
Lithospheric-scale analogue experiments have been conducted to investigate the influence of strength heterogeneities on the distribution and mode of crustal-scale deformation, on the resulting geometry of the deformed area, and on its topographic expression. Strength heterogeneities were incorporated by varying the strength of the crust and upper mantle analogue layers and by implementing a weak plate or part-of-a-plate between two stronger ones. Three (brittle crust/viscous crust/strong viscous upper mantle) and four (brittle crust/viscous crust/brittle upper mantle/strong viscous upper mantle) layer models were confined by a weak silicone layer on one side in order to contain but not oppose lateral extrusion. Experimental results show that relative strength contrasts between converging plates and intervening weak plates control the location and the shape of deformation sites taken as ‘collision orogens’. If the contrast is small, internal deformation of the strong plates through fore- and backthrusting occurs early in the deformation history. However, the bulk system is dominated by buckling that nucleates on the weak plate whose antiformal topography is highest; model Moho of the bordering stronger plates is deepest under these conditions. If the contrast is large, deformation remains localized within the weak plate for a larger amount of shortening and develops a root zone below a narrow deformation belt, which coincides with the locus of maximum topography. Implementing a buoyant, low-viscosity layer above the model Moho of the weak plate favours the development of asymmetric model orogens notwithstanding the initial symmetric setup. Once the asymmetry is established strain remains localized in thrust faults and ductile shear zones documenting foreland directed displacement of the model orogen. Such laterally and vertically irregular configurations have applications in continent-continent collision settings such as the Eastern Alps. First-order mechanical boundary conditions recognized from modelling to be favourable to the post early Oligocene tectonics of the Eastern Alps include: (1) subtle rather than high-strength contrasts between the Adriatic indentor and the strongly deformed region comprising Penninic and Austroalpine units to the north of it; (2) decoupling of Penninic continental upper crust from its substratum to allow for crustal-scale buckling of the Tauern Window; (3) weak mechanical behaviour of the European lower crust during collision to account for its constant thickness along the TRANSALP deep seismic transect; and (4) the direct continuation of the basal detachment underlying the fold and thrust belt in the hangingwall of the European plate with a wide ductile shear zone in the core of the orogen, which separates the European from the Adriatic plate.
Calcareous turbidity current emplacement as an initiation mechanism for substrate brecciation and deformation
Authors: Savary B. 
Published: April 2008

Abstract

The Barremian-Aptian Baronnies syncline, located in SE France, provides the opportunity to study a calcareous turbidite lobe with intercalated breccias and slumps. These features are formed
in-situ
by the emplacement of turbidity currents that distorted the underlying semi-consolidated substrate. The brecciation occurs in three stages. The first stage is represented by the penetration of calcarenitic sediment into the underlying unlithified calcisiltic sediment due to the hydraulic pressure of an overriding turbidity current. In the next stage, a pseudo-breccia forms where the brecciated clasts are still attached to the substrate. Finally, these breccia clasts are separated entirely from the seabed and locally entrained into the flow. In addition, the penetration of the flow into the underlying semi-consolidated sediment can induce destabilization, down slope movement and folding. Similar Tithonian-aged (Late Jurassic) breccias have been interpreted previously as
in-situ
wave-induced features in this region; however, this study testifies that this deformation is not diagnostic of storms but can also be induced by turbidity current deposition.

The mechanisms that induce brecciation have to be identified correctly in order to consider them within a sequence stratigraphic context. Calcareous turbidites and their associated breccias, however, are not strongly diagnostic of relative sea-level.