bluuebunny/crossref_metadata_2025_split huggingface dataset:
Marginal-marine glacial sedimentation in the late Precambrian succession of East Greenland
Authors: Moncrieff A. C. M. , Hambrey M. J. 
Published: April 2008

Abstract
The late Precambrian succession of the fjord region of East Greenland is characterized by two glacigenic formations. The lower one, the Ulvesø Formation, rests on different members of the Limestone-Dolomite ‘series’ (Eleonore Bay Group), and comprises diamictite, conglomerate, sandstone, and rhythmite, all with a high dolomite content. Few beds can be traced for more than a few hundred metres, and erosional breaks are sometimes present. Clasts are predominantly intrabasinal. A turbiditic dolomitic sandstone-mudstone succession, the Arena Formation, lies above. The upper glacigenic horizon, the Storeelv Formation, contains a similar range of facies as the Ulvesø Formation, but is less dolomitic and contains exotic gneiss, granite and volcanic clasts, as well as intrabasinal carbonates.
The Ulvesø and Storeelv formations contain facies characteristic of a low-level terrestrial to marine glacial environment, including: basal tillite, waterlain tillite, debris-flow deposits, ice proximal to distal glacimarine sediments, glaciolacustrine and glacimarine rhythmites with ice-rafted material, permafrost features, aeolian sands and evaporites.
The bulk of the glacigenic sediment appears to have been associated with an ice sheet of continental proportions, which in terms of its thermal regime was probably below the pressure melting point but sliding on its bed. Our interpretation of large parts of the succession as waterlain till implies that floating, debris-bearing ice was an important part of the system, probably in the form of outlet glaciers or ice streams, coalescing as an ice shelf in a tectonically controlled marine basin beyond an irregular coastline. Considerable current activity, both beneath the ice shelf, and sedimentation controlled by iceberg drifting in distinct lanes existed. The succession further illustrates the response of glacimarine sedimentation to ice-retreat onto land, with marked changes from facies with obvious glacial affinities to those devoid of them.
Fracture evolution in the upper ocean crust: evidence from DSDP hole 504B
Authors: Agar Susan M. 
Published: April 2008

Abstract
Detailed structural studies of ocean crust specimens from DSDP borehole 504B have been integrated with a well defined alteration history to yield fracture evolution paths during movement away from the mid-ocean ridge. Fracturing was the dominant deformation process in the upper ocean crust of 504B. A broad range of fracture types exists. The type and orientation of most early fractures were related to lithology. Late fracture orientations and intensities were less dependent on lithology and may have been more closely related to tectonic stress conditions. Prolonged deformation histories are evident in the transition zone where non-coaxial deformation overprints successive generations of dilational veins. Changes in the orientation of the local stress field between successive generations of fractures occurred between and within lithological units. This suggests the presence of numerous mechanical discontinuities in the upper ocean crust, particularly in the transition zone. Changes in fracture porosity between alteration stages were often large and, together with changes in the characteristics of fractures, would have influenced local thermal gradients. The upper ocean crust rheology would have been extremely time dependent as a result. Zones of weakness were created by clay alteration products in basalts and were located in the most permeable horizons. Movement on these zones was promoted by elevated pore-fluid pressures with major failure most likely during major upwelling associated with a hydrothermal system. Subsequent precipitation of high temperature minerals from circulating fluids may have strengthened permeable horizons causing migration of detachment surfaces to another level.
Velocity-dependent friction in a large direct shear experiment on gabbro
Authors: Cox S. J. D. 
Published: April 2008

Abstract

Velocity-stepping sliding experiments on a 0.1 m
2
interface between two gabbro blocks under 0.5–2.0 MPa normal stress have shown consistent velocity-weakening behaviour. The parameter values are in a similar range to those measured on other materials in other laboratories. However, simulation of the complete transient behaviour requires a second state-variable which has a characteristic decay distance
c.
100 × longer than the first, and with the opposite sign (velocity-strengthening). The second delayed effect is not sufficient to cancel out the short period effect, and is not expected to control the onset of unstable stick-slip sliding. These experiments extend the observed realm of velocity-weakening behaviour to larger interfaces and lower normal stresses than has been previously reported.
Reaction-enhanced formation of eclogite-facies shear zones in granulite-facies anorthosites
Authors: Klaper Eva M. 
Published: April 2008

Abstract
Infiltration of a dry granulite-facies anorthosite complex by a hydrous fluid phase under high pressure was crucial to start (a) an eclogitization process which led to the breakdown of plagioclase and the formation of either dense or hydrated minerals and (b) dynamic recrystallization of plagioclase in shear zones. Reaction products of the eclogitization process are related spatially to cracks and shear zones. The reduction in grain size during dynamic recrystallization, the foliation development in shear zones and the occurrence of new ‘soft’ and/or dense minerals changed the mechanical properties (e.g. ductility) of the rocks considerably.
The initiation of detachment and thrusting in the lower crust may be an important large scale consequence of such localized processes.
Propagation and localization of stylolites in limestones
Authors: Carrio-Schaffhauser E. , Raynaud S. , Latière H. J. , Mazerolle F. 
Published: April 2008

Abstract
Matrix investigations (X-Ray tomography, porosimetry by mercury injection, SEM analysis) around stylolites revealed major zones that represent different states in the propagation of the pressure solution structure.
Near the stylolite termination, a significant increase of porosity relative to the far-field host rock porosity and variations in the shape of matrix particles are associated with the lateral propagation of the dissolution zone in the plane of the seam. Close to the sides of the seam, this porosity enhancement zone is found again and may be responsible for vertical development of the stylolite style. Above and below the stylolite seam, the rock matrix is less porous than the reference state and this region appears to have been a site of precipitation of diffused solute. These observations imply that the enhanced porosity state around the stylolite tip is a transient one. This zone becomes a site of deposition as the stylolite tip propagates through it.
High-temperature deformation of calcite single crystals by r
+
and f
+
slip
Authors: De Bresser J. H. P. , Spiers C. J. 
Published: April 2008

Abstract

Optical quality calcite single crystals have been uniaxially compressed at constant strain rates and temperatures (
T
) in the range 3 × 10
−4
to 3 × 10
−7
s
−1
and 550–800°C respectively. The tests were performed with the compression direction parallel to [4041], i.e. parallel to the intersection of two cleavage rhombs. At strains above 1% strain, steady state flow was observed at
T
≥ 600°C. The flow stresses at these temperatures were found to be rather insensitive to strain rate, and can be empirically described by a power law creep equation with a stress exponent ranging from
c.
13 at 600°C to
c.
9.5 at 700–800°C. The active glide systems were identified by slip line analysis. The crystals were found to deform by
e
-twinning at
T
< 600°C, and by slip on a single
r
<2021> system plus a single
f
system in the so-called positive sense at
T
≥ 600°C. The effective slip direction on the active
f
-plane was of <1011> type rather than the <0221> type reported previously. The observed creep behaviour in the slip dominated regime has been compared with microphyical models. The deformation behaviour seems best explained by cross slip or glide-controlled creep models, or a combination of these.
Microstructure in hornblende of a mylonitic amphibolite
Authors: Skrotzki Werner 
Published: April 2008

Abstract
The microstructure in a dynamically recrystallized amphibolite of a deep crustal shear zone from the Ivrea Zone, NW Italy, has been investigated by conventional and high resolution transmission electron microscopy. The microstructure in the amphibole phase consists of recrystallized grains, subgrains, free dislocations and various stacking faults bounded by partial dislocations. The Burgers vectors of the dislocations are [001], [100], 1/2 <110> and very likely <101>. Dislocations with [100] Burgers vector and [001] line direction are mainly arranged in low angle tilt boundaries lying parallel to (100) planes. Faceting of these subgrain boundaries is produced by 1/2 <110> edge dislocations dissociated on (010). The free dislocations are mainly non-dissociated [001] and [100] dislocations gliding on (100) and (010) planes, respectively. It is assumed that [001] and [100] dislocations recombined to form <101> dislocations which subsequently dissociate in (010). The stacking faults extended on (010) planes either have pyroxene or sheet silicate character. They act as obstacles for dislocation motion on the main slip system (100)[001]. High resolution imaging of the dislocation cores suggests these areas consist of lower density material providing channelways for fast diffusion which may be responsible for the deformation-induced compositional changes found within amphibolite shear zones.
Albite deformation within a basal ophiolite shear zone
Authors: White Joseph Clancy 
Published: April 2008

Abstract

Albite mylonites at the base of the White Hills Peridotite ophiolite fragment at St. Anthony, Newfoundland formed during obduction at lower crustal
P - T
conditions. Optical microstructures preserve a history of intracrystalline distortion, recovery and cyclic dynamic recrystallization associated with hot-working. The crystallographic fabric is consistent with shear of the polycrystalline aggregate dominated by glide on (010) planes, as is also indicated by TEM observations. Slip systems implied by trace analysis and invisibility experiments using TEM are b = [101](010), b = [001](010) and b = 1/2[112](201). Dissociated dislocations have separations ranging from 8.3–15 nm. These separations are notably smaller than in more calcic plagioclases and indicate a relatively higher ductility for albite in the case of cross-slip controlled creep. The observed dislocation densities relate to a high stress/strain rate pulse imposed on the dominant high-temperature creep textures.
High temperature deformation of octachloropropane: dynamic grain growth and lattice reorientation
Authors: Ree Jin-Han 
Published: April 2008

Abstract
Dynamic grain growth and lattice preferred orientation development in octachloropropane polycrystals simple-sheared at 0.8 Tm using synkinematic microscopy are discussed. Both soft and hard grains are observed to grow. It is suggested that globular grains are not necessarily an indicator of coaxial deformation. Strain heterogeneity is induced by partitioning of deformation into relatively increased components of rigid-body rotation in hard grains and strain in soft grains. With dominant grain rotation, similar lattice preferred orientation to that of a single-slip model is introduced although the unlocking process is different.
Vein structure and the role of pore fluids in early wet-sediment deformation, Late Miocene volcaniclastic rocks, Miura Group, SE Japan
Authors: Pickering Kevin T. , Agar Susan M. , Prior David J. 
Published: April 2008

Abstract
The Misaki Formation, Miura peninsula, SE Honshu, Japan, comprises deep-shelf/slope volcaniclastic rocks deposited on a segment of the Izu-Bonin island arc prior to accretion about 2.5 Ma. Wet-sediment deformation structures occur as gravity-controlled slides, and sediment injections intruded into semi-lithified over-pressured sediments. Vein structures are locally abundant in the Misaki Formation, mainly as 1–10 cm wide layer-parallel zones, with individual veins about 0.1–3 cm apart. The veins are planar and up to 0.1–2.0 mm in width in their central parts. Vein structure occurs within blocks in chaotic horizons, interpreted as early sediment slides on the seafloor. The vein structures have a strike interpreted as forming parallel to the strike of the basin slope and are considered to arise from pervasive creep-related phenomena in unconsolidated sediments at shallow depths of burial. Back scattered electron (BSE) studies of the vein structure suggest high average atomic number contrasts between the infill of the vein structure and the surrounding sediments and, together with microprobe analyses, suggest that this is due to very fine disseminated pyrite. The pore-fluids involved in the vein evolution were derived from trapped sea water in which certain elements such as S, Fe and Ca were preferentially concentrated in the vein structure. Later generations of vein structure tend to have more complex geometry, are larger, show greater spacing, and appear to have a geometry that cannot be related to any regional trends.
Slickenside lineations due to ductile processes
Authors: Wilson C. J. L. , Will Thomas M. 
Published: April 2008

Abstract
Faults with features characteristic of slickensides, but with plastically deformed wallrocks, were propagated in paraffin wax in a shear environment. Flow of the bulk of the sample produced a strong foliation with fabric strengthening in localized zones that preceded the initiation of the fault. The faults contain ridge-in-groove type slickenlines that have excess-lengths with respect to the measured slip displacement on the fault plane. With progressive movement on the fault surface, these surface markings are disrupted by both ductile shear bands and brittle fractures. The slickenside lineations observed on the fault surface are produced while the material behaves in a ductile manner which does not involve brittle processes.
Convergence-related ‘dynamic spreading’ in a mid-crustal ductile thrust zone: a possible orogenic wedge model
Authors: Holdsworth Robert E. , Grant Colin J. 
Published: April 2008

Abstract
Collisional orogenic belts usually form as approximately wedge-shaped dynamic units irrespective of their bulk rheology. Quantitative models suggest that if the boundary conditions and mechanical properties of a wedge remain unchanged, it will undergo internal yielding (shortening or extension) until a stable, unchanging shape (or ‘taper’) is established. It follows that geological processes periodically leading to changes in wedge shape, or mechanical properties, will perturb the system, generating internal deformation as the wedge strives to re-establish a stable taper.

Geological applications of wedge models to upper-crustal features such as accretionary prisms and foreland thrust belts have highlighted the importance of internal, thrust-parallel shortening strains. The Caledonian, mid-crustal ductile thrust zone of Sutherland, N Scotland, displays many geometric and kinematic similarities to shallow-crustal thrust belts. In contrast to such belts, however, deformation fabric studies suggest a predominance of thrust-parallel
extension
strains which developed
synchronously
with large bulk shortening due to thrust telescoping. Using a viscous wedge model, it is suggested that the deformation occurs due to a process of
dynamic spreading
, possibly triggered by intermittent thrust-slice accretion, towards the foreland, at depth (‘underplating’) and/or strain softening in amphibolite-facies mylonite zones along the ductile thrusts. Similar deformation fabrics are recognized in many regions of ductile thrusting which suggests that a dynamic spreading model may be applicable to mid-crustal deformation regimes in collision zones worldwide.
The Precambrian, Caledonian and Variscan framework to NW Europe
Authors: Coward M. P. 
Published: April 2008

Abstract
During the Precambrian and the Palaeozoic, the tectonics of NW Europe were dominated by the sequential accretion of different terrains on to the North American Craton, e.g. old continental crust of the Scandinavian Craton, magmatic arcs of the Avalon-Brabant Massif, Pentevrian continental crust and the Brioverian magmatic arc. Terrains were locally bounded by thrust packages, by NW-SE trending strike-slip — transform faults parallel to the accretion direction, and by NE-SW trending strike-slip faults defining localized oblique collision or, more generally, boundaries to zones of lateral continental extrusion and escape. Close analogies can be made with the Tertiary Makran-Himalaya-Tibet collisional zones. The Laxfordian/Caledonian/Variscan thrusts and more importantly the large-scale strike-slip faults, imposed a complex heterogeneity to the crust which critically influenced the subsequent extension directions and the siting of basin bounding faults and tectonic inversion, from Devonian times to the present day.
The early to mid-Jurassic evolution of the northern North Sea
Authors: Richards Philip C. 
Published: April 2008

Abstract
The early to mid-Jurassic history of the northern North Sea is summarized as a complex transgressive-regressive-transgressive cycle controlled by variations in ‘long-term’ eustatic sea level rise, basin subsidence/margin uplift and sediment supply. The first of the transgressions occurred in the Hettangian when the Boreal Ocean spread southwards during a phase of fluctuating but generally increasing sea level rise. Offshore marine conditions developed in the north of the area during the Hettangian to Pliensbachian, while coastal to non-marine conditions developed around the ocean margins in the Unst Basin, the Beryl Embayment, the central Viking Graben and over parts of the Horda Platform. The coastal systems in the Beryl Embayment and central Viking Graben were drowned in the late Pliensbachian as a result of continued sea level rise. A widespread marine link was established with the Tethys Ocean to the south at this time. Sea level fall and/or basin margin uplift and erosion in the Aalenian led to the shedding of coarse clastic sediment transversely into the East Shetland Basin and the northern end of the Viking Graben. The main reservoir unit of the area, the Middle Jurassic Brent Group, formed in this way. A marine connection was maintained into the central Viking Graben area throughout the transverse progradation further north. Drowning of the progradational clastics and the start of the third major transgression began in the late Bajocian, but offshore conditions did not become fully established throughout the area until the Callovian or early Oxfordian.
Controls on Eocene submarine fan deposition in the Witch Ground Graben
Authors: Harding A. W. , Humphrey T. J. , Latham A. , Lunsford M. K. , Strider M. H. 
Published: April 2008

Abstract
The framework of Eocene sedimentation in the Witch Ground Graben is described using an integrated analysis of seismic stratigraphy, biostratigraphy, and lithofacies mapping. Primary controls on the distribution of Eocene submarine fan sands are (1) Cimmerian tectonic elements, (2) palaeotopography created by deposition of Palaeocene sediments, and (3) variations in sea level.
Subsidence and sedimentation in semi-starved half-graben: a model based on North Sea data
Authors: Barr David 
Published: April 2008

Abstract
By combining simple extensional fault-block geometries with overall tectonic subsidence curves generated by geodynamic mechanisms such as uniform lithospheric stretching, it is possible to generate forward tectono-stratigraphic models of basin evolution. Previous studies have used simplistic assumptions about sedimentation, e.g. that half-graben were filled to sea level or to the crests of their constituent fault blocks. A better appreciation of the range of possible natural geometries can be obtained by inputting subsidence and sedimentation histories derived by observation of a real sedimentary basin.
The central North Sea is a well studied basin which in general terms can be explained by a simple model of uniform lithospheric stretching in the Late Jurassic, followed by thermal subsidence to the present day. Long-period departures from this model principally reflect the waning thermal effect of Permo-Triassic rifting, but short-period complications are shown to result primarily from variations in the externally controlled sediment input rate. Periods of sediment starvation permitted a substantial increase in water depth, and subsequent rapid sediment input resulted in episodes of load-driven subsidence.
Three typical central North Sea subsidence histories have been combined with a simple model of domino faulting with a 10 km initial fault spacing. Contrasting depositional geometries, with or without the emergence of footwall islands, result from relatively subtle variations in sediment input rate within a small area which can reasonably be inferred to have had a consistent tectonic history.
Continental extension on sets of parallel faults: observational evidence and theoretical models
Authors: Westaway Rob 
Published: April 2008

Abstract

Extension of the upper-crustal brittle layer is taken up in many regions on sets of sub-parallel normal faults that have sub-parallel slip vectors and are approximately planar between the earth’s surface and
c.
10 km depth. This style of faulting accommodates different deformation senses in the underlying upper mantle lithosphere in different deforming regions.

In the western North Anatolian fault zone, southernmost Italy, Tunisia and Libya, simple shear and extensional pure shear are distributed over zones up to
c.
200 km wide and are taken up by oblique slip on faults that strike parallel to the simple shear direction. The strain rate tensor in such zones is biaxial, and although vertical vorticity is non-zero, blocks in the brittle layer do not rotate around vertical axes relative to the zone boundaries. In central Italy extension involving uniaxial extensional pure shear is taken up by normal slip on parallel faults.

In the northeastern Basin and Range province, central Greece and western Turkey, single sets of parallel faults take up extension in the interiors of deforming regions with dimensions >
c.
500 km and appear to rotate around vertical axes relative to the boundaries of the regions. Distributed simple shear, oblique to fault strike, combined with extensional pure shear may
a priori
account for this deformation sense. However, it requires faults to strike in a unique direction that depends on the ratio of rates of pure and simple shear, and to have slip vector azimuth perpendicular to the simple shear direction. With this geometry, left-lateral slip takes up clockwise rotation and right-lateral slip anticlockwise rotation around vertical axes. To take up finite extension and rotation this unique geometry must persist over time. It is unlikely that this process explains deformation of any region considered. In contrast, uniaxial extension, whether occurring on its own or combined with rotation around a vertical axis at a non-zero rate, does not require any strong geometrical constraints: fault slip vector azimuths follow the direction of extensional pure shear and the sense of any strike-slip depends on the orientation of this direction relative to fault strike. Blocks in the brittle layer generally rotate around vertical axes at the same rate as elements in the underlying plastic deformation, which may equal half the vertical vorticity in the upper mantle lithosphere. This deformation sense, which accounts for the observed deformation in these regions, minimizes local differences in horizontal velocity between the brittle layer and the underlying upper mantle lithosphere.