ALBERT

Description / Table of Contents: Geoscientists need to familiarize themselves with the characteristics of actual plate motions. A popular, current thesis relates the state of stress to the degree of coupling of the two convergent plates. Recent two-dimentional, finite element modelling has demonstrated how the stress in the overriding plate is critically dependent on wether the subduction zone is locked (i.e. high degree of coupling) or unlocked. Thus the compressional stress regime occurs in locked systems, and extensional strees in unlocked systems; a gradient from compression in the fore-arc to extension in the back-arc is said to characterize partially locked system. However, studies of the strain field in real cases (modern arc regions) clearly indicate the prevalence of subhorizontal extension orientated nearly perpendicular to the arc. Implicit in these real observations is the suggestion that stresses resulting from plate coupling are either not transmitted to the volcanic arc, or else locked subduction zones are uncommon and extension may be the normal mode of behaviour. The rationale and evidence for extension and coeval volcanism at consuming plate margins is presented. Using mainly Cenozoic case histories for oceanic and continental margin arcs, structural evidence is presented, which demonstrates that volcanism in most arc systems is contemporaneous with normal faulting and subsidence as a general case. Representive, modern geochemical data sets are provided and integrated in a petrological discussion for each case history. The western Pacific, now widely regard as a type region for the study of convergent plate margin processes, is particularly well represented. Also included is evidence from less commonly insvestigated regions, where subduction has ceased or is no longer obvious but an association with an arc is unequivocal. By these means, it is hoped that this volume contains a representative cross-section of current research on extension-related arc volcanism in broadest sense, and that it will stimulate further discussion and research into the complex tectonics and petrology of covergent plate margins.

Description / Table of Contents: C. S. Bristow and J. L. Best: Braided rivers: perspectives and problems / Geological Society, London, Special Publications, 75:1-11, doi:10.1144/GSL.SP.1993.075.01.01 --- John S. Bridge: The interaction between channel geometry, water flow, sediment transport and deposition in braided rivers / Geological Society, London, Special Publications, 75:13-71, doi:10.1144/GSL.SP.1993.075.01.02 --- R. I. Ferguson: Understanding braiding processes in gravel-bed rivers: progress and unsolved problems / Geological Society, London, Special Publications, 75:73-87, doi:10.1144/GSL.SP.1993.075.01.03 --- N. J. Clifford, J. Hardisty, J. R. French, and S. Hart: Downstream variation in bed material characteristics: a turbulence-controlled form-process feedback mechanism / Geological Society, London, Special Publications, 75:89-104, doi:10.1144/GSL.SP.1993.075.01.04 --- P. F. Friend and R. Sinha: Braiding and meandering parameters / Geological Society, London, Special Publications, 75:105-111, doi:10.1144/GSL.SP.1993.075.01.05 --- M. S. E. Robertson-Rintoul and K. S. Richards: Braided-channel pattern and palaeohydrology using an index of total sinuosity / Geological Society, London, Special Publications, 75:113-118, doi:10.1144/GSL.SP.1993.075.01.06 --- J. O. Leddy, P. J. Ashworth, and J. L. Best: Mechanisms of anabranch avulsion within gravel-bed braided rivers: observations from a scaled physical model / Geological Society, London, Special Publications, 75:119-127, doi:10.1144/GSL.SP.1993.075.01.07 --- Peter Ashmore: Anabranch confluence kinetics and sedimentation processes in gravel-braided streams / Geological Society, London, Special Publications, 75:129-146, doi:10.1144/GSL.SP.1993.075.01.08 --- Christoph Siegenthaler and Peter Huggenberger: Pleistocene Rhine gravel: deposits of a braided river system with dominant pool preservation / Geological Society, London, Special Publications, 75:147-162, doi:10.1144/GSL.SP.1993.075.01.09 --- Peter Huggenberger: Radar facies: recognition of facies patterns and heterogeneities within Pleistocene Rhine gravels, NE Switzerland / Geological Society, London, Special Publications, 75:163-176, doi:10.1144/GSL.SP.1993.075.01.10 --- Peter A. Bentham, Peter J. Talling, and Douglas W. Burbank: Braided stream and flood-plain deposition in a rapidly aggrading basin: the Escanilla formation, Spanish Pyrenees / Geological Society, London, Special Publications, 75:177-194, doi:10.1144/GSL.SP.1993.075.01.11 --- Keith Richards, Shobhit Chandra, and Peter Friend: Avulsive channel systems: characteristics and examples / Geological Society, London, Special Publications, 75:195-203, doi:10.1144/GSL.SP.1993.075.01.12 --- David G. Passmore, Mark G. Macklin, Paul A. Brewer, John Lewin, Barbara T. Rumsby, and Malcolm D. Newson: Variability of late Holocene braiding in Britain / Geological Society, London, Special Publications, 75:205-229, doi:10.1144/GSL.SP.1993.075.01.13 --- David J. Gilvear: River management and conservation issues on formerly braided river systems; the case of the River Tay, Scotland / Geological Society, London, Special Publications, 75:231-240, doi:10.1144/GSL.SP.1993.075.01.14 --- J. Warburton, T. R. H. Davies, and M. G. Mandl: A meso-scale field investigation of channel change and floodplain characteristics in an upland braided gravel-bed river, New Zealand / Geological Society, London, Special Publications, 75:241-255, doi:10.1144/GSL.SP.1993.075.01.15 --- Colin R. Thorne, Andrew P. G. Russell, and Muhammad K. Alam: Planform pattern and channel evolution of the Brahmaputra River, Bangladesh / Geological Society, London, Special Publications, 75:257-276, doi:10.1144/GSL.SP.1993.075.01.16 --- C. S. Bristow: Sedimentary structures exposed in bar tops in the Brahmaputra River, Bangladesh / Geological Society, London, Special Publications, 75:277-289, doi:10.1144/GSL.SP.1993.075.01.17 --- C. S. Bristow: Sedimentology of the Rough Rock: a Carboniferous braided river sheet sandstone in northern England / Geological Society, London, Special Publications, 75:291-304, doi:10.1144/GSL.SP.1993.075.01.18 --- Andrew D. Miall: The architecture of fluvial-deltaic sequences in the Upper Mesaverde Group (Upper Cretaceous), Book Cliffs, Utah / Geological Society, London, Special Publications, 75:305-332, doi:10.1144/GSL.SP.1993.075.01.19 --- John H. Martin: A review of braided fluvial hydrocarbon reservoirs: the petroleum engineer’s perspective / Geological Society, London, Special Publications, 75:333-367, doi:10.1144/GSL.SP.1993.075.01.20 --- W. P. Karpeta: Sedimentology and gravel bar morphology in an Archaean braided river sequence: the Witpan Conglomerate Member (Witwatersrand Supergroup) in the Welkom Goldfield, South Africa / Geological Society, London, Special Publications, 75:369-388, doi:10.1144/GSL.SP.1993.075.01.21 --- Lisa Edgington and Neil Harbury: Provenance of braided alluvial deposits of the Thari Formation, Rhodes, SE Aegean: evidence for major erosion of an ophiolite-bearing thrust sheet / Geological Society, London, Special Publications, 75:389-403, doi:10.1144/GSL.SP.1993.075.01.22 --- Victoria R. Copley and John McM. Moore: Debris provenance mapping in braided drainage using remote sensing / Geological Society, London, Special Publications, 75:405-412, doi:10.1144/GSL.SP.1993.075.01.23