bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cause and effect among thrust and normal faulting, anatectic melting and exhumation in the Himalaya
Authors: England Philip , Molnar Peter 
Published: April 2008

Abstract
The transition from compression to extension in a regime of overall convergence in a narrow mountain belt requires a change with time in at least one of the following: horizontal normal stress applied to the belt by its surroundings; the distribution of shear traction on the base of the belt; the constitutive relation between stress and strain rate of material in the belt itself; the surface height of the belt. The following processes could have caused one or other of these changes in the Himalaya in Miocene time and thus could have triggered the onset of extension by normal faulting on planes parallel to thrust faults that were active at the same time. The shear stress on the thrust fault at the base of the Himalaya could have decreased, for instance because of melting on the fault plane. Alternatively, the creation of a new deeper thrust fault, and hence a new locus of convergence, could have initiated extensional faulting if the distribution of shear stress on the new thrust fault were unable to support the Himalaya above it. The Himalaya could have been weakened by an increase in pore fluid pressure, for instance owing to metamorphic dehydration reactions within the wedge. The Himalaya could have been elevated, for instance following the detachment of a tongue of mantle lithosphere from beneath it, or by the underthrusting of a lens of material beneath its base.
The apparent simultaneity of thrust and normal faulting on nearly parallel planes, of anatexis and of exhumation in the Himalaya in Miocene time can be explained if normal faulting was responsible for most of the exhumation and, through decompression melting, for anatexis. Existing data suggest that the most probable cause for Miocene normal faulting was either uplift of the Himalaya or the cessation of slip on the Main Central Thrust at the base of the orogenic wedge and the creation of a new, deeper thrust fault and a new base to the deforming Himalaya.
The emplacement of the Manaslu granite of Central Nepal: field and magnetic susceptibility constraints
Authors: Guillot S. , Pêcher A. , Rochette P. , Le Fort P. 
Published: April 2008

Abstract
This paper investigates the relationship between the emplacement of the Manaslu leucogranite and the regional deformation. Structural data are derived from field measurements and from the anisotropy of magnetic susceptibility of oriented samples. The geometrical relationship between the internal structure of the granite, north vergent folds affecting the Higher Himalayan Sedimentary Series and the E-W dextral shear-zone, separating the Higher Himalayan Crystalline Series and its sedimentary cover, indicate that in the sedimentary series, the collapse structures and E-W dextral shearing are two distinct structural features. Emplacement of the granite post-dates the collapse structures but is related to the E-W dextral shearing. A model for the Manaslu granite emplacement is proposed which requires development of extensional fracturing at 45° to the shear direction, followed by intrusion of granitic magma in successive pulses which results in lateral expansion of the pluton towards the NE.
Numerical modelling of the thermal history of the NW Himalayas, Kullu Valley, India
Authors: Grasemann Bernhard 
Published: April 2008

Abstract
This paper demonstrates two-dimensional time-dependent finite-difference modelling of Himalayan metamorphism illustrated by the Kullu-S Lahul area (Himachal Pradesh) after the collision between India and Asia and the over-thrusting of the Higher Himalayas over the Lesser Himalayas.
It is shown that a one-dimensional model with crustal thickening by a single thrust cannot satisfy the observations present in the section along the Kullu valley. A two-dimensional solution demonstrates that during thrust sheet emplacement at geologically realistic strain rates of several centimetres a year, a temperature inversion does not occur, in contrast to the inversion assumed by the one dimensional instantaneous thrust models. Therefore the variability of two other model parameters were explicitly considered. (i) There is a significant conductivity contrast between the different types of rocks. As conductivity layers function as a barrier to the transport of heat, the conductivity limit should be variable for different regions in the grid. (ii) Rocks in the Higher Himalayas record a phase of metamorphism that preceded the movements on the Main Central Thrust. This observation, together with the knowledge that rocks with different radiogenic heat production and conductivity are not uniformly distributed in the crust, emphasizes that there were considerable horizontal temperature variations across the whole region. For that reason the initial temperature profile, too, has to be adapted for a realistic model.
A study of illite crystallinity and fluid inclusions in the Kathmandu Klippe and the Main Central Thrust zone, Nepal
Authors: Morrison C. W. K. , Oliver G. J. H. 
Published: April 2008

Abstract

The Kathmandu Klippe is an outlier of the Tibetan crustal slab resting on the Main Central Thrust (MCT); it contains a 20 km thickness of Precambrian and Lower Palaeozoic metasediments and Ordovician granites folded into a large syncline. The regional metamorphism predates granite emplacement and, on the basis of illite crystallinity and index mineralogy, is lowest grade in the core of the syncline (epizone-chlorite zone) and highest on the north and south limbs (garnet zone). The distribution of metamorphic zones is ‘normal’ for a burial sequence. The klippe rests on the Benighat Slates of the Midland Formations of the Indian crustal slab. Fluid inclusion studies of the syn-MCT quartz veins in the Benighat Slates show H
2
O, CO
2
, CH
4
, Na
+
, K
+
, Cl′ fluids which were hotter than the country rocks. The MCT contact at Dolalghat does not show the effects of ‘reverse’ metamorphism expected from the Le Fort model of heat transfer from the hot klippe several kilometres down into the Midland Formations. A study of index minerals, illite crystallinity and illite b
0
indicates that the grade of regional metamorphism within the anticlinal Midland Formations varies between epizone-chlorite and garnet zone with the highest grades occurring in the core of the structure. Further to the N around Barahbise, the contact along the MCT between the Midland Formations and the Tibetan Slab is a 2 km thick zone of highly sheared Benighat Slates. The grade of metamorphism in the Benighat Slates is chlorite-epizone grade i.e. lower than either of the sequences above (kyanite zone) or below (garnet zone). The inference drawn from these relationships is that although the inverse metamorphic zonation in the base of the Tibetan Slab might be explained by cooling against the Indian Slab during the Tertiary Himalayan collision, metamorphism in the Indian plate was largely pre-collision.
The Main Boundary Thrust and propagation of deformation into the foreland fold-and-thrust belt in northern Pakistan near the Indus River
Authors: McDougall James W. , Hussain Ahmad , Yeats Robert S. 
Published: April 2008

Abstract
The Main Boundary Thrust in northwestern Pakistan is a floor thrust along which a thrust system incorporating Precambrian and Phanerozoic rocks of the Kala Chitta and Attock-Cherat Ranges was emplaced over Cenozoic strata of the northern Kohat and Potwar Plateaus. The MBT and successive thrusts toward the foreland are interpreted as low angle to flat decollement thrusts at 8–10 km depths that bound thrust sheets with large lateral dimensions. Admissible cross sections indicate over 60 km of shortening along the largely pre-Palaeocene Khairabad, Cherat, and Hissartang thrusts within the MBT allochthon. In the toe of the MBT allochthon, contraction is manifest at the surface as tight folds in largely Mesozoic and lower Tertiary strata, decoupled in the upper third of the allochthon. Displacement of the MBT is estimated at over 40 km and south of the MBT, shortening is interpreted along blind thrusts accompanied by shallow (0–3 km deep) backthrusting. The MBT allochthon was deformed prior to its low angle displacement over the northern Kohat and Potwar Plateaus, and folded and eroded during or after its emplacement. The MBT thrust front may participate in its own later deformation, but not as an emergent low angle thrust through the Quaternary.
The interaction between channel geometry, water flow, sediment transport and deposition in braided rivers
Authors: Bridge John S. 
Published: April 2008

Abstract
Models of braided-river deposition must be detailed, fully 3D, and preferably quantitative to be of use in understanding and predicting the nature of ancient deposits. In order to construct and validate adequate predictive models it is necessary to have information on: (1) variation and interaction of channel geometry, water flow and sediment transport in time and space in modern channel belts, as these control erosion and deposition, the formation and migration of channels and bars, and channel abandonment and filling; (2) 3D variation of bed geometry, texture, sedimentary structures and paleocurrents throughout modern channel-belt deposits, including the age and spatial arrangement of preserved parts of bars and channel fills; (3) long-term (more than hundreds of years) trends in channel and floodplain geometry, flow and sedimentary processes in order to understand channel-belt movements such as avulsions, and the spatial arrangement of channel-belt deposits relative to overbank deposits. Such information is rare because: (1) it is difficult to study modern braided-river geometry, flow and sedimentary processes throughout a range of the all-important high discharges; (2) detailed reconstructions of braided channel and bar geometry and movement are only available for the past half-century and cannot readily be linked to causative mechanisms; (3) 3D documentation of modern deposits below the water table (especially large scale features like lateral-accretion bedding) requires extensive coring and dating of the deposits, and geophysical profiling. As a result of this lack of information, and because of the quality of analysis and presentation of the information available, existing braided-river facies models are virtually useless as interpretive and predictive tools. The nature of the information available is critically reviewed. Using information from recent detailed field and laboratory studies of the geometry, flow and sedimentary processes in braided rivers of simple geometry, in single river bends, in channel confluences, and using some theoretical reasoning, it has been possible to construct fully 3D qualitative and quantitative models of braided river deposits. These models can be used to provide sophisticated quantitative interpretations of palaeochannel geometry, hydraulics and migration, as illustrated by comparison with some particularly well described examples of ancient braided river deposits.
Understanding braiding processes in gravel-bed rivers: progress and unsolved problems
Authors: Ferguson R. I. 
Published: April 2008

Abstract
This paper is a review, from a geomorphologist’s point of view, of recent progress in understanding the interrelationships between channel form, flow, bed texture, and bedload transport in braided gravel-bed rivers. The fundamental geomorphological units in such rivers are not bars alone but bar-pool units, usually associated with confluences and bifurcations. Braiding can develop not only by midstream deposition but by bar dissection and partial avulsion; the hydraulic conditions favouring different mechanisms deserve study. Braiding is highly dynamic, with rapid feedback between channel configuration, flow, and sediment transport. These interactions can profitably be observed in Froudescaled flume models, and can to some extent be quantified by intensive field measurements, but numerical modelling is potentially the best approach. Sediment is sorted both laterally and longitudinally within pool-bar units, but some of the possible mechanisms have not been adequately studied. The downstream fining which occurs along entire braidplains can be explained by selective transport but associated changes in bar types may not follow any single sequence.
Braiding and meandering parameters
Authors: Friend P. F. , Sinha R. 
Published: April 2008

Abstract

Modifications to standard definitions of braiding and meandering are proposed to indicate the morphology of every river channel reach quantitatively, whether it has single channel or multiple channels. Sinuosity (
P
) is defined as,
P
=
L
cmax
/
L
R
, where
L
cmax
is the length of the midline of the channel (in single-channel rivers), or the widest channel (in multi-channel rivers), and
L
R
is the overall length of the reach. Braiding is a measure of channel multiplicity and a new term ‘braid-channel ratio’ (
B
) has been defined as,
B
=
L
ctot
/
L
cmax
, where
L
ctot
is the total of the mid-channel lengths of all the channels in a reach. Another expression for the braid-channel ratio which gives the same numerical result is,
B
=
P
ctot
/
P
, where the total sinuosity,
P
ctot
=
L
ctot
/
L
R
, and
P
has been defined above. Scatter plots on braid-channel ratio/sinuosity axes show a negative correlation between these parameters, as would be expected from the above relationships. Single-channel rivers (
B
= 1) have relatively higher sinuosities and the upper limit of these is the point at which cut-off becomes highly probable. For multi-channel rivers (
B
> 1), sinuosity remains low, reflecting the limiting effect of braid bars on the development of fully developed spiral secondary flow. Data analyses showing that increases in channel slope and bankfull discharge are associated with changes from meandering to braided morphology are diverting attention from the importance of the increased availability of bed-load-grade sediment as a control.
Braided stream and flood-plain deposition in a rapidly aggrading basin: the Escanilla formation, Spanish Pyrenees
Authors: Bentham Peter A. , Talling Peter J. , Burbank Douglas W. 
Published: April 2008

Abstract
Models of braided stream deposition have largely been developed from studies of regionally degrading and laterally confined alluvial environments. Glacial outwash streams, in particular, have supplied important and widely cited descriptions of intra-channel processes. These fluvial systems are typically confined within quite narrow valleys. It is felt that such systems have low long-term preservation potential and are unlikely to be present in the geologic record in large quantities. Therefore, the study of these modern laterally confined degradational systems may not provide holistic analogs of the larger-scale alluvial architecture developed in braided river environments in the ancient. The Escanilla Formation of the Spanish Pyrenees provides a well-exposed example of an Eocene fluvial system flowing axially within the Pyrenean foreland basin. Sedimentologic study shows coarse channelized deposits of braided character wholly enclosed within large amounts of fine-grained overbank mudstones and siltstones (>40% by volume), with both being deposited coevally across the Escanilla floodplain.
A new depositional model is proposed that combines facets of existing models derived from other fluvio-morphologic systems. This consists of a laterally confined channel belt, internally preserving a braided stream character, capable of rapid vertical aggradation on short geological time-scales (about a thousand years). Avulsion processes are used to explain finer sediment deposition in interfluve settings, as well as the large-scale architectural geometries within the lower Escanilla Formation. This new model illustrates that discrete channel belt avulsion, and the preservation of thick sequences of overbank material are not exclusively characteristics of higher sinuosity fluvial systems.
Variability of late Holocene braiding in Britain
Authors: Passmore David G. , Macklin Mark G. , Brewer Paul A. , Lewin John , Rumsby Barbara T. , Newson Malcolm D. 
Published: April 2008

Abstract

Braided channel patterns are relatively rarely found in contemporary British rivers, although site studies have been undertaken for reaches in catchments ranging in size from 2.6 km
2
to 2850 km
2
in area. Systematic study of two major British rivers, the Tyne (2927 km
2
) and the Upper Severn (1000 km
2
), reveal braiding at several sites, albeit at a limited scale. An examination of historical maps and air photographs shows, however, that braiding processes have been more widely active in the eighteenth and nineteenth centuries. Episodic braiding activity is discussed for selected sites. Floodplain stratigraphy shows significant channel aggradation and transformation to braided river planforms also occurred in the late Roman period and in the thirteenth and fourteenth centuries. Possible explanations are suggested in terms of flood frequency and magnitude variations (reflecting climatic fluctuations and land-use change), alterations in sediment supply (including the impact of historic mining activities), and channelization control.
A meso-scale field investigation of channel change and floodplain characteristics in an upland braided gravel-bed river, New Zealand
Authors: Warburton J. , Davies T. R. H. , Mandl M. G. 
Published: April 2008

Abstract

Detailed data from active gravel-bed braided rivers over time periods greater than a decade is relatively sparse. The aim of this study is to establish a field site for examining channel change over an extended period (> 10 years) and determining the main mechanisms which produce the braidplain morphology. The prototype is the Ashley River, Lees Valley, New Zealand, which is 2.5 km in length, has an average braidplain width of 400 m and slope of 0.012 m m
−1
. The flow regime is dominated by low flows (average flow 3.15 m
3
s
−1
) with 2–3 winter flood events in excess of 25 m
3
s
−1
per year. Planform information on this reach dates back to the 1860s with ten sets of maps/air photographs up to the present. Since 1989 the sedimentary and morphological characteristics of the braidplain have been carefully surveyed. There is a downstream decrease in sediment size which is accompanied by a reduction in bank height at the margin of the floodplain and a decrease in cross-section bed amplitude. Certain elements in the floodplain (vegetated bars, channels with coarse lag sediments and banks with armoured bank toes) persist while other features such as unconsolidated gravel banks and fine-gravel sheets do not. Channels are migrating towards the northern edge of the braidplain with old bars becoming vegetated on the southern margin. Channel patterns change most dramatically when the flood flows reoccupy old channel segments. Observations of channel change from flood to flood indicate that, although some channel segments switch dramatically, other segments are left intact and largely unaltered. Movement of small sediment lobes affected the flow at node-points within the channel (e.g. areas of flow divergence and convergence) causes avulsion. The dominant mechanisms of channel change are avulsion and bank notching/scalloping.
Sedimentology and gravel bar morphology in an Archaean braided river sequence: the Witpan Conglomerate Member (Witwatersrand Supergroup) in the Welkom Goldfield, South Africa
Authors: Karpeta W. P. 
Published: April 2008

Abstract
The Witpan conglomerate member is the lower, thicker, more channelized of the two auriferous conglomerates that comprise the Archaean ‘A’ Reefs (Aandenk Formation, Central Rand Group, Witwatersrand Supergroup) mined in the southern part of the Welkom Goldfield, Republic of South Africa. It is interpreted as the deposit of a degrading, gravelly, braided river system with well developed topographical differentiation. Three morphological elements have been identified in the Witpan Conglomerate member, namely Major Channels, Minor Channels and Terrace areas which are comparable to Levels 1, 2 and 3 of the modern Donjek River. Nine facies are present in the Witpan Conglomerate member combined into eight facies assemblages which show differing three dimensional architecture and relationship to channels. The four conglomeratic bar facies assemblages (FA1 to FA4) are interpreted as longitudinal, diagonal, transverse and side bars respectively and are combined to form compound bars. The three quartzitic channel fill facies assemblages (FA5 to FA7) represent active, slough and abandoned channel fills. The eighth facies assemblage (FA8) forms the interchannel terrace areas.
The distribution of gold mineralization in the Witpan Conglomerate member is related to sedimentological factors including the presence of massive gravels, the accessibility of these gravels to flood water and the formation of areas of confined, convergent flow. Hence the bar facies assemblages are the richest followed by channel fill facies assemblages with the interchannel facies assemblage having generally low gold concentrations. Of the bars, diagonal bars are the most favourable for gold mineralization followed by longitudinal bars then side bars with transverse bars being the lowest.
Debris provenance mapping in braided drainage using remote sensing
Authors: Copley Victoria R. , Moore John McM. 
Published: April 2008

Abstract
The NERC Geoscience community airborne remote sensing test site near Carboneras in southeast Spain is dissected by several flash flood drainage channels. These contain a variety of clastic debris types related to diverse source rocks in the catchment basins. As part of a larger study of source rock, regolith and drainage debris relationships, the spectral reflectance characteristics of debris types in braided flash flood channels have been used to map debris dispersion with remotely sensed imagery. The study is based upon 11 channel 7.5 m pixel Airborne Thematic Mapper (ATM) imagery acquired by NERC in May 1989. The objective of the research was to achieve optimum discrimination of channel debris types and to study the integration of distinctive source rock/regolith spectral signatures caused by progressive downstream mixing during transport.
Image processing enhances small spectral variations to improve discrimination of debris types. Imagery was masked to display only channel bed pixels and maximise spectral discrimination within drainage channels. Several enhancement techniques, including principal components and hue-saturation-intensity transformations, and decorrelation and contrast stretches, were then used to emphasise spectral differences among the debris assemblages in the channel beds. One of the most successful products is a selective principal components colour composite image. The image data are presented as a debris lithology distribution map.