bluuebunny/crossref_metadata_2025_split huggingface dataset:
Models of convective fluid flow and mineralization in south-west England
Authors: SAMS M. S. , THOMAS-BETTS A. 
Published: December 2007

Two notable features of the mineralization in SW England are the asymmetrical pattern of mineral lodes and the mineral zoning within this distribution. Despite the fact that many theories have been advanced to explain the mechanisms of mineralization qualitatively no numerical models have been produced. In this paper, the finite element technique is used to construct a very simple model which helps to explain general features of the pattern of mineralization.
The model describes the steady state convection of fluid in the environment of the Cornubian batholith. Convection is driven by the radiothermal contrast between the granite and the host rocks. Results show that the locations of upward flowing, hot fluids are determined by the three-dimensional shape of the batholith. Initially, upward flow was concentrated along the axis of the batholith and these regions correlate with high temperature mineralization. Erosion of the cover rock above the granites altered the fluid flow pattern such that the upward flow became concentrated outside the outcropping granites. These regions correlate with low temperature mineralization. A correlation also exists between kaolinization and areas of downward flowing fluid for present day levels of erosion.
Is the Welsh Borderland Fault System a terrane boundary?
Authors: WOODCOCK N. H. , GIBBONS W. 
Published: December 2007

The Welsh Borderland Fault System forms one of the most prominent tectonic lines in Southern Britain and, along with the Menai Straits and Malverns Fault Systems, is a candidate for a terrane boundry. A review of stratigraphic linkage across the system reveals significant contrasts in pre-Ashgill sequences. These contrasts occur particularly across its north-west edge, the Pontesford and Tywi Lineaments, rather than across the Church Stretton Lineament. The Ashgill event produced strike-slip dominated structure and an unconformity that expands from the Welsh Basin towards the platform. An important linkage sequence was produced by the subsequent late Ashgill to Llandovery marine transgression across the fault system. Silurian facies changes are marked but gradational, and no more than expected across a basin margin from stable to thinned crust.
Devonian (Acadian) sinistral transpression, and later Phanerozoic movements, reactivated the fault system but did not engineer major terrane amalgamation across it. This reactivation has obscured the early history of the fault system. The remaining evidence admits, though does not prove, major Ashgill or earlier transcurrent movements. Broader considerations suggest that the Welsh Borderland Fault System originated either as a Cambro-Ordovician extensional system on the south-eastern margin of the Welsh Basin or during Late Precambrian-Early Cambrian transcurrent movements occurring within Avalonia, inboard from the Menai Strait line.
Low grade metamorphism of the Manx Group, Isle of Man: a comparative study of white mica ‘crystallinity’ techniques
Authors: ROBERTS B. , MORRISON C. , HIRONS S. 
Published: December 2007

Studies have been made in two laboratories on metapelites from the Manx Group, Isle of Man, showing the distribution of white mica ‘crystallinity’, using the Kubler index (Δ°2Θ) and the Weber index
(Hb

rel

).
Two isocryst maps, which show broadly similar distributions of metamorphic grade, are illustrated and a correlation between the laboratories is presented. The mineralogy of the
<2 m
fraction in relation to ‘crystallinity’ has been determined. The distribution of metamorphic grade over central and eastern parts of the Isle of Man, as depicted by the Kubler index isocryst map, is related to subjacent granite plutons, but these contact metamorphic effects overprint an earlier, largely anchizonal, regional metamorphism. Localized, late, retrograde effects are related to low temperature hydrothermal mineralization and to cold re-working in a large fault zone.

Differences between the maps are largely in the degrees of resolution which stem directly from the different sampling intervals employed. Comparisons between the maps suggest a sampling interval of 1-2 km is adequate in regions of simpler geology; but that an interval of <1 km may be necessary in more complex regions. Well resolved maps can be produced only when the sampling interval is linked to geology.
The changes in the mineralogy of the <2 m fraction in relation to grade are closely similar to those described from Lower Palaeozoic metapelites from North Wales, although higher grades have been reached in the Manx Group with the development of biotite.
Aspects of climatic influence on the clay mineralogy and geochemistry of soils, palaeosols and clastic sedimentary rocks
Authors: CURTIS C. D. 
Published: December 2007

Climate strongly influences soil clay mineralogy and bulk chemical composition. In humid climates chemical weathering is at its most intense and virtually all ‘primary’ bedrock minerals suffer complete breakdown. They are replaced by authigenic hydrated oxides of Fe and Al together with halloysite and kaolinite in deep profiles. These minerals develop where the residence time of water in the soil is slight. Longer residence times lead to higher solute concentrations and the stabilization of smectite. Authigenic palygorskite and sepiolite may form in highly saline, alkaline soils. The stability of these precipitated minerals is problematic: they may be metastable or even unstable. All other clays found in soils are unstable, being incomplete, solid-state hydrolysis products of substrate minerals. The balance between stable, metastable and unstable minerals and the rate of profile development are both much influenced by temperature, rainfall and activities of soil biota; themselves reflecting climate.
Bedrock influence is greatest under conditions of low to moderate precipitation where unstable minerals persist. Local topography, however, also strongly influences both the rate and products of chemical weathering, quite independently of climate. On the grand scale, tectonic factors may constrain the time available for profiles to develop, hence the extent to which bedrock minerals survive or are altered. Mountain soils reflect local climate and bedrock composition much more than latitude.
The sediments delivered to major basins today do not reflect global soil distribution patterns. The bulk composition of suspended sediment entering the Indian Ocean, for example, is rather similar to that entering the Arctic Ocean. Sediment dispersal patterns can also confuse climatic signals: a problem not encountered with palaeosols. Authigenic clays formed within sedimentary basins and post-depositional (burial) alteration of both sediments and buried soil profiles must lead to interpretational ambiguities. Climatic signals are likely to survive best in bulk compositional data (although diagenetic reactions at depths in excess of about 2 km do not appear to be isochemical) and in the distribution of more stable yet climatically sensitive minerals (kaolinite as opposed to illite, chlorite).
Geochronology of appinitic and related granitic magmatism in the W Highlands of Scotland: constraints on the timing of transcurrent fault movement
Authors: ROGERS GRAEME , DUNNING GREGORY R. 
Published: December 2007

The timing of appinitic and related granitic magmatism throughout the W Highlands of Scotland has been investigated using U-Pb geochronological techniques. An appinite from the Garabal Hill/Glen Fyne complex is dated at 429 ±2 Ma (zircon) and 422 ±3 Ma (titanite); appinites from Arrochar and Rubha Mór give titanite ages of 426 ± 3 Ma and 427 ± 3 Ma respectively. The Strontian granodiorite is 425 ±3 Ma (zircon) and 423 ±3 Ma (titanite), and a pyroxene-mica diorite from Rat again gives an age of 425 ± 3 Ma. The data show the value of using titanite to date basic rocks which may lack zircon, and of using inheritance-free phases in rocks which contain mostly inherited zircon.
The narrow range of ages for this magmatism reported here contrasts with a broad smear of previously published ages, and indicates that the middle Silurian was a major period of transcurrent fault movement throughout the W Highlands. Voluminous magmatism of this age is also found in Newfoundland, highlighting the importance of this event in the wider context of the Caledonide orogen.
Comparative sequence stratigraphy and structural styles of the Slyne Trough and Hebrides Basin
Authors: TRUEBLOOD S. , MORTON N. 
Published: December 2007

The Slyne Trough to the west of Ireland is divided into three sections: North, Central and South. The South and Central sub-basins are separated by a seismic ‘dead zone’ along the line of the Clew Bay disturbance. The Central and North sub-basins are separated by a zone transferring the fault bounding the main basin from the western margin in the Central sub-basin to the eastern margin in the North sub-basin.
Five stratigraphic sequences from the Slyne Trough, which span the Rhaetian to Middle Jurassic, are recognized in the 27/13–1 well, and they are compared to the equivalent sequences in the Hebrides Basin. The Late Jurassic Hebridean sequences are expected in the deeper parts of the Central Slyne Trough. The Slyne Trough and Hebrides Basin sediments are mainly tectonically controlled, although major eustatic events in the Early Toarcian and Late Bathonian are recognized.
Sedimentology and depositional setting of the Dartmouth Group, Bigbury Bay, south Devon
Authors: SMITH SIMON A. , HUMPHREYS B. 
Published: December 2007

The Lower Devonian Dartmouth Group records some of the earliest stages in the evolution of the Variscan basins of southwest England. This thick, mudstone-dominated group has previously been interpreted as distal fluvial sediments, deposited on a coastal mudplain.
The sequence at Bigbury Bay is made up of two large-scale sedimentary cycles. The base of each cycle consists of pebbly mudstones, graded siltstones and sandstones, massive mudstones, and heterolithic sediments with sporadic phosphatic nodules. These facies were deposited in substantial lakes; they were modified by phases of syn-sedimentary deformation which generated subaqueous debris flows and turbidites. The overlying parts of the cycle, making up the bulk of the succession, consist of mudstone and thin, sheet-like, sandstones. These are fluvial and were probably deposited in mud-dominated terminal fans. Each cycle represents a phase of rapid, probably fault-controlled, subsidence followed by relative tectonic quiescence. This behaviour may reflect pulses of rifting or extension in strike-slip basins, followed by thermal relaxation.
Crustal structure of the central and southern North Sea from BIRPS deep seismic reflection profiling
Authors: BLUNDELL D. J. , HOBBS R. W. , KLEMPERER S. L. , SCOTT-ROBINSON R. , LONG R. E. , WEST T. E. , DUIN E. 
Published: December 2007

Through the generous gift of shiptime on M/V Mobil Search in June 1987, BIRPS (British Institutions Reflection Profiling Syndicate) was able to acquire nearly 1500 km of deep seismic profiles recorded to 16s TWT in a regional survey across the central and southern North Sea. Reflective lower crust beneath the southern North Sea basin gives way laterally to a zone of mid-crustal reflections within the London–Brabant platform. These mid-crustal reflectors are interpreted as due to crustal shearing, although whether related to stretching during basin formation or to some earlier event remains enigmatic. Sub-crustal, SW-dipping reflections are observed at the edge of the London–Brabant platform. Across the mid-North Sea High, N–S profiles show distinctive patterns of lower-crustal reflectivity that indicate lateral variability in structure and character on a scale of 30–50 km. These are interpreted as crustal units relating to the Iapetus suture developed during the Caledonian orogeny. They may have been modified, however, during Carboniferous basin development, or subsequently. The absence of any distinctive sub-crustal reflectors associated with the Iapetus Suture, where a Caledonian subduction zone should have existed, tends to suggest that sub-crustal reflections observed elsewhere around Britian are not subduction related but are more likely to be from younger faults or shear zones relating to lithosphere extension and basin formation.
Onshore wide-angle recording in northern England of the marine seismic source produced good quality data. The high resolution obtained has revealed details of mid-crust (PcP) and Moho (PmP) reflections, from around 18 and 30 km depth respectively, not observed before in this area. Both reflectors show events of laterally variable reflectivity that appear as bands of discontinuous reflection segments.
Modern and ancient continental hypsometries
Authors: ALGEO T. J. , WILKINSON B. H. 
Published: December 2007

Controls on coastal hypsometries of modern continents and oceanic islands may be used to estimate palaeo-continental area-elevation distributions. The most important controls on coastal hypsometry are landmass area and coastal gradient, increases in which result in steeper area-elevation distributions. Thus, any change in sea level will flood or expose a smaller fractional area of continents which are large or have steep coastal gradients than of those which are small or have gentle coastal gradients. Coastal gradients are dictated primarily by the tectonic setting and age of continental margins. While active and transform margins generally have steep coasts, mean coastal gradients for passive margins decrease exponentially with increasing margin age. Consequently, continents comprised mostly of mature passive margins are generally more ‘floodable’.
These observations are applicable to a variety of palaeo-eustatic problems. Hypsometries corrected for changes in landmass area reduce variance in flooding records between different Palaeozoic continents by more than 50%. Assuming minimum-variance superimposition of flooding curves for different Palaeozoic continents permits identification of possible hypsometric anomalies. Calculated Palaeozoic sea level maxima are between +200m and +400m with respect to present sea level, substantially lower than previous estimates to +600 m.
Modelling evolution of coastal hypsometries due to changes in length and age of passive margins suggests that hypsometry varies cyclically in response to continental rifting and collision. Coastal hypsometries are steepest during rifting events and decrease by a factor of two to three as passive margins age. Coastal hypsometries in a ‘sutured’ world are steeper than those of a 'rifted' world due to increased continent size and decreased passive margin length. Thus, sea level highstands associated with times of continent dispersal may result in part from the enhanced ‘floodability’ of rifted continents.
Hercynian transpressional tectonics at the southern margin of the Central Iberian Zone, west Spain
Authors: SANDERSON D. J. , ROBERTS S. , McGOWAN J. A. , GUMIEL P. 
Published: December 2007

The boundary between the Central Iberian and Ossa-Morena zones, in south-central Spain, occurs within the Badajoz–Cordoba shear zone. The spatial and temporal relationships of structures across the La Codosera syncline, located within the Central Iberian zone just to the north of the shear zone, demonstrate a progressive increase in strike-slip shear towards the Badajoz shear zone.
Within the region of the La Codosera syncline, Precambrian to Cambrian rocks were subject to pre-Ordovician tilting and open folding, accompanied by local faulting and veining, but no cleavage. These, together with overlying Palaeozoic rocks were subsequently affected by Hercynian ductile deformation, which produced steeply inclined folds, cleavage and faulting. Intense left-lateral shearing on the southern limb of the La Codosera syncline produced augen, shear bands, sub-horizontal stretching lineation, boudinage, variably oriented folds and steep faults, whereas the northern limb of the syncline is characterized by folding and thrusting in a transpressional regime, with limited net northward transport.
Late Hercynian faulting produced N–S and NE–SW faults which overprint the early structures and granites. These rotate to a NW-SE trend and increase in right-lateral displacement as a result of domino or bookshelf faulting which can be attributed to continued left-lateral motion along the Badajoz shear zone.
Neotectonics of western India: evidence from deformed Quaternary fluvial sequences, Mahi River, Gujarat
Authors: JAIN MAYANK , WOODCOCK NIGEL H. , TANDON SAMPAT K. 
Published: December 2007

A Quaternary fluvial sequence along the Mahi River, Gujarat, western India, shows evidence for a discrete episode of normal faulting and related surface slumping. Four mapped NW-striking faults have throws ranging from 1 m to over 3 m, and have related growth folds in synchronous sediment units. A slump sheet moved tens of metres northeastward down the 0.7° dip slope of one tilt block during displacement on its bounding fault. The exposed part of the internally folded sheet is probably one side of a lobate slump mass, several hundred metres in width.Fault activity began after deposition of a lower gravel, which regional correlations suggest is about 300 ka old. Faulting ended just before deposition of an upper gravel-sand complex dated by luminescence techniques in correlated sections at no younger than about 60 ka. The Mahi River section shows that neotectonic activity in Peninsular India, exemplified by the 1993 Killari (Latur) earthquake, has a mid- to late Pleistocene component.
Instantaneous sediment deposition rates deduced from climbing-ripple cross-lamination
Authors: Allen John Robert Lawrence 
Published: December 2007

Summary
A mathematical analysis is made showing how the geometrical properties of climbing-ripple cross-lamination, a common sedimentary structure in fluviatile and turbidity current deposits, depend on the ripple height and the prevailing rates of sediment deposition and bed load transport. This structure is very commonly found in the field in vertical association with parallel laminated sand-grade deposits. The orientation of the ripple structures and of the parting lineations and/or grain fabric associated with the parallel laminae can be accounted for only if the two kinds of deposit were formed during consecutive stages in the change of a single current. Because the hydraulic conditions attending the transition between current ripples (giving cross-lamination) and a plane bed (giving parallel laminations) are known, the sediment deposition rate at the moment of transition can be calculated, from field measurements of ripple height, angle-of-climb and sediment size. Examples of deposition rates calculated in this way are discussed from the Old Red Sandstone and the Aberystwyth Grits of Wales.
A note on the structural evolution of Alaska
Authors: Stoneley Robert 
Published: December 2007

Considerable
progress in the mapping and geological understanding of Alaska has been made in recent years through the efforts of the United States Geological Survey, petroleum companies and academic institutions. Sufficient reliable data now seem to be available to attempt, very tentatively, a synthesis of its geological history in the light of modern tectonic theories.

Distribution of major tectonic elements

A.
Southern Alaska

East central Alaska is divided fundamentally along the line of the Tintina Trough (Fig. 1), a feature which lies on approximately the same general trend as the homologous Rocky Mountain Trench of western Canada. It separates unmetamorphosed Palaeozoic and early Mesozoic miogeosynclinal rocks to the north from a series of eugeosynclinal belts to the south, and may have marked the edge of the continental platform in early Palaeozoic times. The Tintina Trough cannot be traced with certainty for more than 300 kms westwards into Alaska, and the continental margin then appears to have degenerated into a narrow welt along the Ruby Geanticline.
The Ruby Geanticline, which consists of rocks as yet poorly dated, also bounds the eugeosynclinal belts to the south: but, interposed between it and the miogeosyncline, there is now the Koyukuk Geosyncline, a middle Mesozoic feature with associated ophiolites, that was compressed during the Cretaceous. This possibly represented a deep ocean basin during the Palaeozoic and the Ruby Geanticline an island arc, analogous perhaps to the modern Bering Sea and Aleutian Arc.
The various tectonic belts of southern Alaska seem to represent a history of
Conductive faults and sealing fractures in the West Sole gas fields, southern North Sea
Authors: Barr D. 
Published: December 2007

Abstract
Understanding the distribution and geometry of sealing faults and conductive natural fractures is important at all stages of field development and infill drilling. Sealing faults or fractures reduce contacted hydrocarbon volume per well by compartmentalizing the reservoir and reduce rate by locally impairing permeability. Open fractures or conductive faults enhance well productivity and contacted volume, but cause drilling difficulties and may lead to early aquifer influx or injection water breakthrough. With their lengthy drilling and production history, the West Sole area gas fields provide a natural laboratory for the study of sealing and conductive fractures and their inter-relationships. Conductive fractures were recognized early in field life, but the poor performance of some wells indicated that fractures were not uniformly distributed. As development continued, entire field segments were found to be unfractured. Subsequent appraisal drilling identified undepleted and partially depleted compartments, demonstrating that sealing faults or fractures are also present. More recent development of the satellite fields Newsham and Hoton has confirmed the presence in a single field of both conductive and sealing fractures, although there is a general inverse spatial relationship between the two. The structural history of the reservoirs provides an explanation for this phenomenon. Faulting at high pressures and temperatures during Jurassic rifting gave rise to sealing lithified cataclasite fault rocks. Inversion to form the hydrocarbon traps took place at lower pressures and temperatures. The associated brittle deformation breached sealing faults and generated open fractures.
Fracture intensity from geomechanical models: application to the Blue Forest 3D survey, Green River Basin, Wyoming, USA
Authors: Wilkins S. J. 
Published: December 2007

Abstract
A geomechanical method is presented for the prediction of subseismic fracture intensity associated with faulting using a boundary element model conditioned from 3D seismic interpretation within the Green River Basin, Wyoming, USA. Seismic data indicate two major phases of deformation: (1) an early phase of approximately ESE‐verging contraction accommodated along a NNE–SSW striking system of basement-involved reverse faults and associated drape folds; and (2) a later phase of transtension accommodated by ENE–WSW-trending normal faults that are preferentially located in the hanging wall, above the crest of the drape fold.

The models predict different spatial patterns of fracture intensity for each phase of deformation. For D
1
, enhanced probability for shear failure develops in the upper quadrant of the footwalls along the reverse faults (i.e. forelimb) and the greatest magnitudes occur adjacent to regions with the largest component of observable dip-slip displacement along the faults. During D
2
, enhanced probability for joint and fault formation occurs along-strike of the normal faults and in a general NE trend. Seismic velocity anisotropy data support the geomechanical predictions for both phases of deformation in that the location and azimuth of large anisotropies correlate with regions of predicted enhancement in joint and fault intensity.