bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental study of grain-size sensitive flow of synthetic, hot-pressed calcite rocks
Authors: Walker A. N. , Rutter E. H. , Brodie K. H. 
Published: April 2008

Abstract
Synthetic calcite rocks of controlled grain-size were prepared by crushing large, clear calcite crystals, centrifuged to separate restricted grain-size fractions, cold-pressed and then hot-pressed to produce low-porosity polycrystals of mean grain-size covering the range 2–40 µm. These were deformed dry over the range 400–700°C, mainly at 200 MPa confining pressure, to investigate the onset with decreasing grain-size of grain-size sensitive flow.
The deformation of the fine-grained material can be described by a flow law of the form

ė
=
A
exp (−
H/RT
) σ

n

d

m

in which at low stresses (<25 MPa differential stress)
A
= 10
4.9
,
H
= 190 kJ mol
−1
,
n
= 1.7 and
m
= −1.9, when strain-rate,
ė
, is in s
−1
, stress, σ, is in MPa and grain-size,
d
is in µm. At higher stresses (25–250 MPa)
A
= 100,
H
= 190 kJ mol
−1
,
n
= 3.3 and
m
= −1.3. In the low stress regime, grains remain equidimensional during flow, a pre-existing preferred crystallographic orientation produced during cold-pressing tends to weaken and grain-boundary sliding is important. At higher stresses, a grain flattening fabric develops, the pre-existing preferred crystallographic orientation pattern is preserved, and recovery-accommodated intracrystalline plastic flow is inferred to be the dominant deformation mechanism. Grain-size sensitivity of the flow stress persists even into the intracrystalline plastic flow regime. Grain-size insensitive flow only develops at grain-sizes greater than 40 µm, as demonstrated by reference to mechanical data for the flow of Carrara and Taiwan marbles.

The flow laws which describe most of the experimental data do not extrapolate well through the lowest strain-rate data at the coarser grain-sizes. This indicates that a complete description of the flow, which can be used reliably to extrapolate to geological conditions, requires one or more of the material parameters
A, n
and
m
to be a function of one or more of stress, strain-rate and grain-size. This implies variable contributions from different deformation mechanisms as the deformation conditions change.
Estimates of the rates of microstructural changes in mylonites
Authors: Prior David J. , Knipe Robert J. , Handy Mark R. 
Published: April 2008

Abstract

Microstructures developed during dislocation creep such as the dynamically recrystallized grain-size and the subgrain-size are modified in response to increasing differential stresses and shear-strain rates adjacent to rigid minerals in mylonites. In two specimens variations in quartz subgrain-size around rigid minerals has been quantified from orientation contrast SEM images. In a deformed granite from the Pogallo ductile fault zone, quartz two-dimensional subgrain-size is reduced from background values of about 30 μm to 8 μm and then 4 μm in progressively narrower channels between rigid feldspars. In pelitic mylonites from the Alpine fault zone, New Zealand, quartz bands are wrapped around rigid garnets and the subgrain-size is reduced from background values of about 20 μm to 14 μm within 2000 μm of the garnet to 11 μm adjacent to the garnet. In both specimens examined the microstructure responds to both increases and decreases in differential stresses and coupled strain-rates. The analysis of the distribution of subgrain sizes provides information for the assessment of microstructural stability and the estimation of the rates of microstructural changes. The New Zealand specimens have good regional shear strain-rate controls and minimum subgrain boundary migration rates (during reduction in differential stresses and strain-rates) of 1.2 × 10
−9
μm s
−1
to 1.2 × 10
−11
μm s
−1
are estimated, for bulk shear strain rates of 10
−10
s
−1
and 10
12
s
−1
respectively. Palaeopiezometry coupled with rheological considerations suggests that these microstructural changes correspond to minimum differential stress-rates of 5 × 10
−9
MPa s
−1
to 5 × 10
−11
MPa s
−1
. Similar or slower regional stress-rates during fault zone evolution, will allow continuous re-equilibration of the microstructure. Thus the time at which any given microstructure is frozen in will be critically dependent upon fault zone deformation history. In the Alpine fault zone rapid uplift and high near surface temperatures combine to generate rapid stress drops as mylonitic deformation gives way to cataclastic faulting during uplift. Mylonite microstructure is frozen in during this rapid stress drop and represents the shallowest level of major crystal-plastic deformation.
Crystallographic fabrics: a selective review of their applications to research in structural geology
Authors: Law R.D. 
Published: April 2008

Abstract
In this brief introductory review the potential geological use of crystallographic fabrics is illustrated by considering selected geological problems which, given appropriate conditions, may be investigated in plastically deformed rocks using fabric analysis. Quartz and calcite are taken as the main illustrative examples. Numerical fabric simulations indicate that the imposed strain path (strain symmetry, vorticity etc.) is reflected in the relationship between the fabric pattern, kinematic framework and finite strain axes. Although these fabric patterns are sensitive to the numerical model and combination of crystallographic slip systems chosen, many of the major fabric types have been observed in experimentally and naturally deformed rocks. The fabric pattern itself may contain important information on strain symmetry, orientation of fields of extension and contraction and operative slip systems. Similarly, the angular relationship between the fabric pattern and finite strain features (foliation and lineation) may provide information on shear sense and vorticity of deformation. Spatial transitions with decreasing grain size in naturally deformed rocks, from strongly defined fabrics to a complete lack of crystallographic preferred orientation, have been interpreted as indicating a switch to deformation mechanisms involving grain boundary sliding. Potential problems associated with using the absence of a fabric as an indication of grain boundary sliding (and by inference superplastic flow) are discussed. Experimental studies indicate that geometrical relationships between intracrystalline strain features and the crystal lattice of individual grains may be used to deduce palaeo-stress directions. Results of palaeo-stress analysis techniques based on such relationships are compared.
A simulation of the temperature dependence of quartz fabrics
Authors: Jessell M. W. , Lister G. S. 
Published: April 2008

Abstract
This paper presents the predictions of a hybrid model of fabric development in quartzites that combines aspects of previous models based on lattice rotations and dynamic recrystallization. The input parameters for the model have been systematically varied in order to investigate changes in deformation fabrics due to increasing temperature, and predictions of crystallographic preferred orientations and grain shape fabrics are made. The resulting fabrics reflect the combination of both deformation processes over the range of the parameters used. The fabrics evolve continuously with progressive deformation, and produce crossed girdles, single girdles and point maxima for a single deformation geometry. The results suggest that the coupling of dynamic recrystallization with lattice rotations can actually produce a larger variation in crystallographic preferred orientations with temperature than is predicted by using a model that only considers lattice rotations. Using this model point maxima develop even though a multiple slip model has been assumed.
Practical application of entropy optimization in quantitative texture analysis
Authors: Schaeben H. , Siemes H. , Höfler S. , Will G. 
Published: April 2008

Abstract
Finite series expansion methods are applied to the texture problem of recovering an orientation density function (odf) from its pole density functions (pdf) measured in X-ray or neutron diffraction experiments, the mathematical model of entropy maximization is applied to pole figure data and numerical results are presented as well as an interpretation of their geological significance.
Deformation in an accretionary melange, Alexander Island, Antarctica
Authors: Nell P.A.R. 
Published: April 2008

Abstract
Alexander Island contains several belts of melange in a wide accretionary complex. One melange belt in the northwest of the island incorporates both oceanic and trench-fill material. It evolved by many different deformation mechanisms: dispersed independent particulate flow (IPF) and limited cataclasis at shallow levels; and diffusion mass transfer (DMT) and limited crystal plastic processes at deeper levels. Fluid pressures may have risen due to the subduction of young hot oceanic crust, which probably affected the structural evolution of the region by controlling the strength of the decollement and hence the taper of the accretionary prism.
Centrifuge modelling of thrust faulting: strain partitioning and sequence of thrusting in duplex structures
Authors: Liu Shumin , Dixon John M. 
Published: April 2008

Abstract
The kinematic evolution of fold-thrust duplex structures has been investigated by analog scale modelling using the centrifuge technique. Plasticine and silicone putty simulate rocks such as limestone and shale, respectively. Model stratigraphic units consist of microlaminations (55–250 μm thick) of these two materials, different ratios of thickness of the constituent laminae simulating different limestone/shale ratios (bulk competence). The models involve six stratigraphic units totalling 4 mm in thickness, with alternating bulk competence (low at the base, high at the surface). They were subjected to layer-parallel compression from one end, and kinematic evolution was monitored by cutting profile sections at six deformation stages.
Structural style varies with depth. The top competent unit develops upright buckle-folds which propagate from ‘hinterland’ to ‘foreland’. The middle competent unit also buckles, but the folds have pronounced foreland vergence. The bottom competent unit first develops gentle folds that propagate forwards, but the foreland-dipping limbs of these folds are soon cut by thrust faults. As shortening continues, this unit is telescoped into a classic blind duplex structure: thrust faults root in the underlying incompetent unit, ramp through the competent unit, and merge into a roof thrust in the overlying incompetent unit. The ‘wavelength’ of the duplex structure is inherited from the initial buckling instability. The duplex develops by serial nucleation of faults from hinterland to foreland as in natural thrust belts. However, all the faults remain active while the stratigraphic pile deforms as a tapered wedge.
Palinspastic reconstruction by restoration of buckle folds and fault slip shows that layer-parallel shortening accounts for approximately half of the total shortening at all structural levels. Folding and faulting account for the remainder, with folding dominating at high levels and faulting at depth. The transfer is accommodated by decollement in the incompetent units.
The models bear striking resemblance to fold-thrust structures of the Appalachian Valley and Ridge Province of West Virginia and Virginia, USA.
Vein distribution in a thrust zone: a case history from the Northern Apennines, Italy
Authors: Coli Massimo , Sani Federico 
Published: April 2008

Abstract
In the Northern Apennines the Cervarola Thrust superposes the Cervarola Unit (Early-Middle Miocene sandstones and shales) on the Marnoso Arenacea Unit (Middle-Late Miocene marly sandstones) and has the geometry of a leading imbricate fan. Each thrust sheet consists of a thick turbiditic sandstones sequence (Mt Cervarola Fm.), which grades downward into shales (Scisti Varicolore Fm.). During thrusting, the Scisti Varicolore Fm. was intensely deformed and widely affected by shear veins, filled with calcite. A regional pattern has been detected in the vein distribution: veins are concentrated some ten metres above the thrust fault, in a band a few metres thick, and can be grouped into two systems. The principal one presents two sets of veins striking in the same direction as the thrust: one set dips at a high angle to the thrust fault (High Angle Set, HAS), whereas the other one lies sub-parallel to the thrust fault (Low Angle Set, LAS). Both of these sets of veins have dip-slip slickenfibres. The secondary system comprises two other sets of veins, which lie obliquely to the thrust fault. Slickenfibres are strike-slip and trend nearly parallel to the thrusting direction and to the intersection lineation between the two sets. Vein development can be explained in the light of the fluid-dynamic studies recently developed for present-day accretionary prisms.
Tectono-stratigraphic development and hydrocarbon habitat of the Carboniferous in northern England
Authors: Fraser A. J. , Gawthorpe R. L. 
Published: April 2008

Abstract
Over 70 years of exploration in the Carboniferous of northern England has resulted in the discovery of rather modest recoverable reserves totalling 75 million barrels of oil and 27 billion cubic feet of gas. Nevertheless during this time the petroleum industry has amassed a substantial quantity of borehole and seismic information. Integrating this essentially subsurface database with information derived from outcrop studies has permitted a hitherto unachievable understanding of the Carboniferous in terms of its tectonostratigraphic development and hydrocarbon habitat.
The strong NW-SE and NE-SE structural trends developed in the northern England Carboniferous were inherited from the late Palaeozoic Caledonian orogeny. These fault trends were consistently reactivated throughout the Carboniferous in both an extensional and compressional sense. The main influence on Carboniferous basin evolution in northern England was the Variscan collision-type orogeny. The Variscan plate cycle controlled the development of syn-rift, post-rift and inversion megasequences from late Devonian to early Permian times. Sequences developed within these Carboniferous megasequences are primarily controlled by episodic rifting and periodic fault reactivation with eustatic sea-level changes providing only minor control at the subsequence level.
The late Carboniferous-early Permian culmination of the Variscan orogeny is seen to be the main trap forming event. All hydrocarbon discoveries to date display some element of Variscan inversion in their geometry. Variscan tectonics have also exerted a subtle but important control on play fairway evolution. The main source rocks (pro-delta shales) are confined to isolated, syn-rift depocentres. Syn-rift siliciclastic reservoirs are also restricted to the rifted half graben. Carbonate grainstone reservoirs rim the margins of the deeper half graben where terrigenous input has been limited. Delta top channel and mouth bar reservoirs are best developed where they axially infill remnant syn-rift bathymetry.
Mesozoic burial, ensuring hydrocarbon generation post Variscan trap formation, is, however, the main control on the present day distribution of hydrocarbons in the Carboniferous of northern England. Several key areas where Carboniferous source rocks have generated significant hydrocarbons during the Mesozoic have been identified; the East Midlands being the most significant in terms of produced hydrocarbons and perceived future potential.
The structural controls on Upper Jurassic and Lower Cretaceous reservoir sandstones in the Witch Ground Graben, UK North Sea
Authors: O’Driscoll D. , Hindle A. D. , Long D. C. 
Published: April 2008

Abstract
The Witch Ground Graben is a product of Mid- and Late Cimmerian extensional tectonism. The principal orientation of normal faulting was NNE-SSW during the Mid-Cimmerian (Bajocian to Early Kimmeridgian) and a combination of NW-SE and E-W during the Late Cimmerian (Late Kimmeridgian to Barremian). Block rotation on the dominant Late Cimmerian trends, combined with reactivation of older structural grains formed the fault block traps in the area.
Two major depositional systems form the reservoirs of the late Jurassic and early Cretaceous of the Witch Ground Graben, namely, the deltaic and shallow marine systems of the Sgiath and Piper Formations and the deeper water turbiditic sands of the Kimmeridge Clay and Valhall Formations. The transition between the systems is highly diachronous. The turbiditic sandstones are often enclosed within or onlap sealing strata, thus providing a stratigraphic element to many of the traps in the area.
A chronostratigraphic framework was established and used as the basis for understanding firstly, the timing of the tectonic episodes responsible for moulding the Witch Ground Graben and secondly, the importance of these events in determining reservoir sandstone distribution and trap development.
Tertiary structures and hydrocarbon entrapment in the Weald Basin of southern England
Authors: Butler Malcolm , Pullan Christopher P. 
Published: April 2008

Abstract
The Weald Basin of southeast England was formed by rapid subsidence associated with thermal relaxation following early Mesozoic extensional block faulting. The basin appears initially to have taken the form of an easterly extension of the Wessex Basin but became the major depocentre during the Upper Jurassic and Lower Cretaceous, with associated active faulting. These movements appear to have ceased prior to Albian times and a full Upper Cretaceous cover is believed to have been deposited in a gentle downwarp which extended far beyond the confines of the Weald and Wessex Basins. Major inversion of the Weald Basin took place in the Tertiary, with both gentle regional uplift, which in the eastern part of the basin is estimated to have exceeded 5000 feet (1525 metres), and intense local uplift along pre-existing zones of weakness, which led to the formation of compressional features such as tight folds and reverse faults. Zones of Tertiary deformation appear to have been strongly influenced by underlying, particularly Hercynian, structural trends.
Lower Jurassic source rocks reached maturity in the early Cretaceous and initial migration occurred at this time, often over long distances, into traps closed by pre-Aptian faults. Tertiary tilting and uplift led to the breaching of many of these pre-existing traps and the formation of large folded closures. A second phase of hydrocarbon migration, particularly of gas, took place at this time, with significant vertical migration along fault zones. Major reservoirs located to date occur in Middle Jurassic carbonates and Upper Jurassic sandstones, but deep burial in the basin has caused considerable destruction of primary reservoir characteristics; changes in the temperature and pressure regimes and the mobilization of fluids within the basin resulting from the Tertiary uplift caused further diagenetic changes, particularly in the carbonate reservoirs.
Exploration of the Weald Basin remains at a very early stage, with a low drilling density to date. The more recent drilling has focussed on earlier structures, but traps formed or modified during the Tertiary movements represent important exploration objectives, although general deterioration in reservoir quality towards the centre and east of the basin makes large fold closures in these areas less attractive.
Active normal faulting in central Greece: an overview
Authors: Roberts Steven , Jackson James 
Published: April 2008

Abstract
Rapid extension in central Greece is accommodated by large active normal faults that largely control the geomorphology. The faults bound graben whose asymmetry is evident in the topography, bathymetry, vertical movements of the coastline and tilting of Neogene sediments adjacent to them. Graben up to 20 km in width appear to be simple half-graben, whereas the hangingwalls in wider graben are generally broken by faults antithetic to the major bounding faults. The graben form basins up to 100 km long, but the faults bounding these basins are segmented, with individual segments no longer than about 20 km. The fault segments step en echelon or change polarity along strike of the large basins, but are not linked by simple strike-slip (‘transfer’) faults: the regions between the main fault segments appear to be pervasively deformed by numerous small faults. Drainage in central Greece is controlled by fault segmentation and footwall lithology. Where footwalls consist of Mesozoic limestone the drainage is often axial, breaking through the fault system into the main basin by flowing round the ends of fault segments or through gaps where the fault segments step. In such places, drainage directly off the fault scarps is relatively minor, and the fault segmentation controls the spacing of major fans along the basin margin. Where footwalls consist of Neogene sediments, drainage may flow directly across the fault scarp, though in such cases the catchment areas are relatively small and linear. The origin of the fault segmentation is unclear, but may be related to rotations of the fault-bounded blocks about horizontal and vertical axes.
The geometry of normal faults in a sector of the offshore Nile Delta, Egypt
Authors: Beach A. , Trayner P. 
Published: April 2008

Abstract
This paper presents an interpretation of the geometry of normal faults in part of the offshore Nile Delta. The structure is dominated by north-dipping faults that are clearly imaged on seismic reflection profiles, and affect sediments of Pliocene-Pleistocene age, together with the underlying Miocene sequences that contain potential hydrocarbon reservoir rocks. The geometrical analysis is carried out in several stages. Firstly, time slice maps of the fault pattern are produced in order to establish the overall fault geometry of the area. Secondly, for each indivdiual fault identified, structure contours on the fault surface itself are mapped. This procedure serves to highlight any complexities in the geometry of the faults, and allows potential inconsistencies in the interpretation to be identified. Thirdly, horizon interpretations and correlations are made across the faults, and these are checked for consistency by constructing maps of the magnitude of the dip slip component of displacement within the fault surface. The complete geometric analysis makes it possible to extend the results from the good data areas in the upper parts of seismic sections to the poorer quality areas lower down. In this way it is possible to derive an interpretation of the structural geometry of the Miocene reservoir sequences. The seismic reflections from the Miocene are poor and irregular, and structural interpretation and modelling reduces the uncertainty associated with the reservoir geometry. The structural interpretation is presented as a model of tilted and fault bounded blocks, with considerable horizontal separation. This provides a much clearer and more consistent picture of the reservoir geometry, and contrasts with previous interpretations that have shown a more or less continuous reservoir sequence with little structure. The geometrical interpretation should form the basis for a new hydrocarbon play in the area because it predicts the locations of footwall crests, as well as areas where reservoir is missing because of separation across faults.