bluuebunny/crossref_metadata_2025_split huggingface dataset:
Placer deposits symposium
Authors: Pitty Alistair F. 
Published: December 2007

Report of a whole-day joint meeting of the Institution of Mining and Metallurgy and the British Geomorphological Research Group held at Burlington House, 15 November 1984. The meeting was organized by Professor F. K. G. Hosking, Dr Ian Reid, Dr D. G. Sutherland and Professor M. F. Thomas, and convened by Drs Reid and Sutherland.

At this joint meeting, some 160 participants explored those areas where process geomorphology is instrumental in the identification of metalliferous palaeosediments. Water transport and reworking of debris are fundamental controls on placer concentration by mechanical processes, and chemical deepweathering of land surfaces is a feature of environments where residual enrichments are concentrated.
The initial session, chaired by K. F. G. Hosking, was an immediate reminder of the global span and regional diversity of the topic. D. G. Sutherland’s overview featured the main areas in the world of placer deposits. He examined the fundamental role of chemical deep weathering in releasing minerals from the host rock, noting the temperature and moisture conditions required. Climate is also important and controls the volume of runoff, which then determines the amount of debris moved. The climatic changes of the past, particularly during the last 2 Ma, were emphasized.
T. K. Smith’s talk featured an area of former hydraulic mining in the Sierra Nevada in the San Juan placer gold deposits. The significance of the unlikely name of his study area, the Red Dog–You Bet district, was only explained during the informal discussions, which were a conspicuous feature of
The geochemistry of early Proterozoic metavolcanic rocks hosting massive sulphide deposits in the Skellefte district, northern Sweden
Authors: Claesson L. Å. 
Published: December 2007

The Skellefte district, an early Proterozoic massive sulphide ore province in Northern Sweden, contains a well-preserved volcano-sedimentary rock association, referred to as the Skellefte Group, metamorphosed predominantly under low-grade conditions. The volcanic rocks in the lower part of the succession host the massive sulphide deposits and comprise a bimodal sequence, composed of a calc-alkaline group of felsic rocks and a tholeiitic group of mafic rocks displaying a basaltic to andesitic composition. Derivation of the felsic rocks by fractional crystallization from the mafic rocks is not supported by the geochemical data. Application of tectonic environment discriminant diagrams involving the elements Ti, Zr, Y and Cr suggests that these rocks were deposited in a volcanic arc setting.
Stratigraphically above the volcanic rocks hosting the massive sulphide deposits, there follows a sequence of metamorphosed greywackes and pelitic sediments with intercalation of primitive basaltic to ultrabasic volcanic and high-level intrusive rocks. The volcanic rocks show geochemical similarities to both Archaean basaltic komatiites and Phanerozoic boninites. The primitive nature of these rocks present difficulties in assessing their palaeotectonic setting. A volcanic arc or transition to an inter- or back-arc rift situation is suggested.
A gravity and magnetic interpretation of the structure of the Irish Midlands and its relation to ore genesis
Authors: Brown C. , Williams B. 
Published: December 2007

Regional gravity and magnetic data from the Irish Midlands have been studied in an attempt to map the structures within and beneath the Lower Carboniferous Limestones. The magnetic data suggest that the Precambrian crystalline basement is at a depth of 3–4 km and is overlain by Ordovician volcanics of varying magnetization. A Fourier analysis of the gravity field has been used to construct a residual gravity map which represents principally the gravity effect of shallow sources. These sources are probably the topographic variations of dense Ordovician volcanics beneath a less dense succession of Ordovician to Carboniferous sediments.
The residual gravity clearly shows the presence of a series of linear volcanic blocks and sedimentary troughs trending NE–SW. The major mineralized zones in the area all occur close to the margins of these troughs. This investigation indicates that the initial position of the Midland Plain was controlled by Caledonide factors, some of which modified the later subsidence which we attribute to Hercynian plate-margin processes. The genesis of the major ore-bodies is probably associated with de-watering of the shale-filled troughs, the subsequent concentration of metal-bearing fluids along the trough margins and their deposition in relatively unloaded carbonate host rocks on the up-standing blocks.
Geomorphological approaches to the study of neotectonics
Authors: DOORNKAMP J. C. 
Published: December 2007

The study of morphotectonics is concerned with the analysis of landforms whose form or origins have been affected by neotectonic activity. Traditional morphotectonic studies have been used as a basis for more refined (e.g. statistical) analyses. After the 1960s, however, there emerged new techniques and new approaches to the study of morphotectonics. These have made more precise not only the recognition of morphotectonic features, but have also improved their dating.
The time has come to integrate morphotectonic studies more fully both with the approaches used by other disciplines and with modern geomorphological theory.
Geochemical aspects of acid rain
Authors: EDMUNDS W. M. , COE K. 
Published: December 2007

A meeting on the Geochemistry of Acid Rain was held in the University of Strathclyde on 30 August 1985. It was convened by W. M. Edmunds (Institute of Hydrology, Wallingford, Oxon.) and K. Coe (University of Exeter).
The phenomenon of acid rain has been known for at least a century; one of the first records of acid rain was from Britain (Smith 1852.

Memoirs and Proceedings of the Manchester Literary and Philosophical Society
,
2
, 207–17.) Smith described acidic rainfall (with up to 38 mg 1
−
SO
2−
4
) from the industrial areas of Manchester and noted amongst other things the effects on stone buildings. General awareness of the long range international consequences as well as the widespread, as opposed to local environmental impact, of acidic deposition has grown during the last 15–20 years, mainly as a result of research in Scandinavia and North America.

There is now an extensive literature on the subject of acidic deposition and its effects, particularly in relation to the origin and fate of acidic substances in the atmosphere and their possible impact on surface waters and biota. The two most serious questions to emerge are (i) whether current levels of acidic deposition are responsible for the increase in the number of fishless streams and lakes in Scandinavia and elsewhere, and (ii) whether the presence of anthropogenic acidic substances in the atmosphere is a threat, directly or indirectly, to the productivity of European and North American forests.
Relativety little research has so far been carried out on
Oceanic fracture zones
Authors: WHITE R. S. , WILLIAMS C. A. 
Published: December 2007

Report of the William Smith meeting of the Geological Society, London held at Burlington House on 1-2 May 1985, and introduction to published papers and abstracts.

Oceanic fracture zones are one of the most conspicuous features of the ocean basins. They are formed where offsets occur in the oceanic spreading centres, and they leave scars that stretch thousands of kilometres across entire ocean basins. Through the 1960s and 7Os, oceanic fracture zones were mapped extensively by magnetic and bathymetric surveys and were used frequently in global reconstructions Only in the past 5 years or so have they been studied intensively in their own right using more and more sophisticated geophysical and geological techniques.
This conference brought together 25 speakers from around the world to present some of the huge amount of recent work on oceanic fracture zones. Perhaps the most striking feature of the meeting was that with modem high resolution geophysical tools it is at last becoming possible to narrow the gap between observations from remote measurements and those of field geologists. That does not necessarily mean that interpretations are becoming easier;rather the converse, because the closer you look the more complicated things become. But there is hope at last that soon we may be able to make geological maps of the ocean floor just as we can on land.
A great deal can be learnt about the tectonics of young oceanic features simply by looking at the bathymetry and the ‘grain’ of the seafloor. During the meeting a
Structure and seismotectonics of the Vema Fracture Zone, Atlantic Ocean
Authors: LOUDENR K. E. , WHITE R. S. , POTTS C. G. , FORSYTH D. W. 
Published: December 2007

The structure and seismo-tectonics of the Vema Fracture Zone and the adjacent regions of its transverse ridge to the south and the Mid-Atlantic Ridge spreading centre to the north is discussed, based on an analysis of seismic refraction profiles, micro-earthquake activity and gravity anomalies. Crustal structures were determined by analysis of wide angle seismic data from explosive and airgun sources recorded on arrays of ocean bottom seismometers. Micro-earthquakes were recorded by six instruments for a period of 14 days in an array to the north of the ridge-transform intersection.

Immature crust, similar to that reported by
Fowler (1976)
from the FAMOUS area, lies beneath the spreading centre. The lower crust thins and normal mantle appears as the fracture zone is approached. The thinnest crust lies beneath the northern end of the topographic deep at the fracture zone intersection. This is also the locus of current microearthquake activity at sub-bottom depths of 3–4 km, which a composite fault-plane solution suggests may originate on normal faults that parallel the trend of the local topography on the eastern wall of the median valley.

Within the central region of the fracture zone valley, the crust thickens but still retains an anomalous velocity structure. Seismic layer 3 is absent and crustal velocities are low. This is probably the consequence of attenuated crustal accretion, of faulting and cracking, and of hydrothermal alteration. The pattern of residual gravity anomalies, after correction for topography, for sediment thickness and for mantle temperature variations, is consistent with the crustal structure defined by the seismic experiments. The gravity measurements indicate that there is a broad thinning of the crust over 20–40 km in the vicinity of the fracture zone, on which are superimposed localized regions of low and high densities.
To the south of the fracture zone, the crust thickens and assumes a normal velocity structure including a mature seismic layer 3. The seismic Moho is warped upwards under the transverse ridge, suggesting a tectonic origin from buckling rather than uplift by serpentinization.
Transport and accumulation of river-derived sediment on the Washington continental shelf, USA
Authors: STERNBERG R. W. 
Published: December 2007

The combined results of many physical oceanographic, geochemical, and geological investigations provide a coherent picture of the sedimentology of the Washington continental shelf. The major source of modern sediment is the Columbia River. Sediment on the shelf is transported by bottom currents resulting from surface wind stress and gravity waves which occur as individual storm or wave events lasting one to several days, primarily during the winter months.
Field measurements of the sediment response to wind- and wave-generated bottom currents suggest that the modern sediment is transported as suspended load and disperses primarily northward parallel to the isobaths and is associated with a well-developed mid-shelf silt deposit. Smaller quantities of sediment are transported seaward over the shelf edge and into the numerous submarine canyons that incise the shelf. Analysis of available wave data suggests that thresholds of sediment motion were exceeded on the order of 22%, 16%, and 1.5% of the time annually on the inner, central, and outer shelf respectively. Bottom current measurements suggest that threshold conditions were exceeded 13% and 6% of the time annually on the inner and central shelf respectively.

Measurements of accumulation rates using
210
Pb geochronology show that about 67% of the annual sediment discharge from the Columbia River is being deposited in the mid-shelf silt deposit; 6% is being deposited over the shelf edge on the open slope, and 11% is accumulating in the four major submarine canyons.
The iron ores and associated sediments of the Chichali formation (Oxfordian to Valanginian) of the Trans-Indus Salt Range, Pakistan
Authors: HALLAM A. , MAYNARD J. B. 
Published: December 2007

A distinctive and widespread belemnite-bearing shale of the Tethyan region is well exposed in the Trans-Indus Salt Range as the Chichali Formation, where it contains two workable ironstone seams. Facies analysis indicates a pronounced deepening in the Upper Oxfordian and Kimmeridgian followed by two regressive cycles marked by a transition from glauconitic–phosphatic shales to glauconitic silts and sands and finally to winnowed and oxidized glauconitic sandy ironstones. The first cycle ends in Berriasian belemnite-rich beds; the second cycle, which has few belemnites, extends into the Valanginian, and is followed by deltaic sediments of the Lumshiwal Formation.
Comparison with other areas indicates that the source area for the clastic components was the Indian Shield to the east and south. The increased clastic supply in the Upper Jurassic–Lower Cretaceous is thought to result from tectonic uplift in this source area rather than from climatic change.

The ironstone beds are distinctive in being pelletal glauconites compared with the oolitic chamosite and goethite so typical of the Jurassic elsewhere. Enrichment of the glauconite to commercial grade was by winnowing and oxidation on the seafloor. The absence of oolitic chamosite and goethite could be related to generally deeper water and an overall Eh in the environment too high to allow iron to migrate in appreciable quantities as Fe
2+
.
Sediment exchanges across the coastal margins of NW Europe
Authors: KIRBY R. 
Published: December 2007

This contribution serves as an introduction to the ‘Coastal Margins as Sediment Traps’ thematic set.

One of the most basic questions which faces those concerned with sediment transport in the marine environment is whether the coastal margin is a net source or sink for sediment. The coastal margin is taken to mean the coast itself with its cliffs, bays and estuaries, and the immediate coastal zone stretching a few hundred metres to a few kilometres off shore. It is not clear to what extent the coasts of NW Europe have recovered from the last period of depressed sea level. Uncertainty exists as to whether sediment lost from the coastal margin is deposited in offshore sinks, whether sediment originally laid down on the continental shelves is returning to depositional sites located principally in bays and estuaries, or more particularly whether all coastal margins are subject to the same balance of processes.
The reason for this lack of knowledge is clear. The calculation of the sediment budget of an estuary is difficult. The calculation of the budget for a whole coastal sector, including the continental shelf fronting it, is even more problematical. For entire seas our capacity for reliable quantification at the present time is negligible.
A perspective on this issue can be obtained by considering the situation in a parallel discipline. Oceanographers have been studying the circulation of our shallow seas for 70–80 years, latterly with co-operative experiments using tens of simultaneously deployed, self-recording, current meters and the mathematical models
The tectonic history of Kohistan and its implications for Himalayan structure
Authors: COWARD M. P. , BUTLER R. W. H. , KHAN M. ASIF , KNIPE R. J. 
Published: December 2007

The tectonic history of Kohistan, northern Pakistan, involves two collisional events. Cleavage and folding developed at 90-100 Ma along the northern suture between the Kohistan island arc and the Asian plate. At the same time there was major folding and shearing of the lower part of the Kohistan arc, approximately 100 km south of the suture. This deformation was followed by ocean subduction south of the Kohistan arc, generating the Kohistan calc-alkaline batholith, with subsequent ocean closure during the Eocene and obduction of the Kohistan arc, together with the adjacent part of the Asian plate, over the Indian continental crust. The construction of balanced cross-sections through the imbricated upper part of the Indian continental crust, in the footwall to this southern suture indicates a minimum displacement of 470 km, requiring the western Himalayan hinterland to be underlain by a large wedge of Indian middle to lower crust. There is some shortening of the overriding Kohistan and Asian plates by thrusts and shear zones, but it is insufficient to satisfy the palaeomagnetic data; there must be major crustal shortening, involving thrusts, in the Hindu Kush and Pamirs north of Kohistan.
The post-Eocene thrust direction, which for most of Pakistan is towards 160°, is almost perpendicular to that immediately to the east in the Himalayan belt, generating complex refolded thrust patterns in the Hazara syntaxis and large scale folding and rapid uplift with associated brittle faulting and seismic activity adjacent to the Nanga Parbat syntaxis. These different thrust trends indicate that major thrust movement as well as the folds and deformation fabrics, cannot always be related to plate movement vectors, but are modified by, or develop from, complex rotations during place collision or from the gravitational spreading of a thickened crust. A regional approach is required to recognize and correctly attribute the various components in thrust displacements.
The Rb-Sr geochronological evolution of the Ras Gharib segment of the northern Nubian Shield
Authors: ABDEL-RAHMAN ABDEL-FATTAH M. , DOIG R. 
Published: December 2007

Rb-Sr whole-rock isochron ages have been determined for six igneous rock suites from the Ras Gharib. These represent all major crustal components of the northern Nubian Shield and are, from oldest to youngest: diorite-tonalite, extrusive rocks, granodiorite-adamellite and leucogranite, muscovite trondhjemite (orogenic Pan-African suites), dyke swarms and anorogenic peralkaline granites. The ages obtained are: 881 ± 58 Ma, 620 ± 16 Ma, 552 ± 7 Ma, 516 ± 7 Ma, 493 ± 7 Ma and 476 ± 2 Ma. The initial
87
Sr/
86
Sr ratios of the Pan-African suites and the dykes are in the range 0.7039 to 0.7047. The initial ratio of the anorogenic peralkaline granites is 0.7110 ±0.0012, higher than any previously reported for igneous rocks from the Egyptian belt.

The 493 ± 7 Ma age of the dyke swarms represents a younger limit for the Pan-African compression–accretion event and an upper (older) limit for an extensional tectonic regime. Linked with this is the anorogenic peralkaline granite magmatism (476 ±2 Ma), which is the last manifestation of igneous activity in this region.
The low initial ratios of the Pan-African suites provide no support for the existence of an older (Archaen) sialic continental crust in the region. The anorogenic peralkaline granite with the high initial ratio was produced by partial melting of earlier Pan-African suites. The age data are used to construct a tentative correlation scheme for shield rocks of Egypt, Sudan and Saudi Arabia.
The origin of the Upper Palaeozoic Chañaral mélange of N Chile
Authors: BELL C. M. 
Published: December 2007

The fragmented and mixed strata of the Chañaral melange extend for some 220 km from N to S in the coastal ranges of N Chile (26°20′ to 28°20′S). The mélange was produced in an accretionary wedge resulting from the NE subduction of the ancestral Pacific oceanic plate beneath the Gondwana-land margin during Carboniferous times. The mélange consists essentially of blocks of sandstone in a pelitic matrix. These sediments were deposited as deep-sea basin-plain turbidites prior to their fragmentation. Other blocks in the mélange include mafic volcanic rocks, with the geochemical characteristics of oceanic island basalts, and rare shallow-marine limestones.
Structures in the mélange suggest an origin by two distinct deformation processes involving unlithified sediments. Initial boudinage and break-up of the strata was apparently accomplished by intrastratal movement resulting from imbricate thrusting within the accretionary wedge. The second process produced cross-cutting zones of breccia which are interpreted as fluid escape conduits resulting from the high pore pressures produced during underthrusting.
Mantled gneiss antiforms and fold nappes in the Rinkian belt, West Greenland: diapiric structures or structures formed in a thrust system?
Authors: GROCOTT J. , VAN DEN EECKHOUT B. , VISSERS R. L. M. 
Published: December 2007

In Lower Proterozoic metasedimentary cover rocks of Svartenhuk Halvø, and in their reactivated Archaean basement of tonalitic gneisses, features of the structure and metamorphism are identified which are critical to the understanding of the kinematics and dynamics of the orogenic evolution of the Rinkian belt. These features are as follows: (1) a major ductile shear zone at the gneiss–sediment contact which has a normal-slip displacement and dips steeply NE away from the gneisses in its present orientation, (2) a fan in the main cleavage in the metasediments, in which cleavage steepens over a distance of 15 km from a 30° dip SW towards the contact through the vertical, finally coming to lie parallel with the contact, (3) the existence of a major synform in the sediments near the gneiss–sediment contact which is overprinted by the main cleavage, (4) the orientation and restricted distribution of later crenulation cleavage, and (5) a high temperature–low pressure metamorphic facies series, with thin metamorphic zones close to the basement, reaching anatexis at the gneiss–sediment contact.
The features which relate to the pattern of strain are compared with those to be expected: (1) as a result of the ascent of a diapiric ridge of gneiss into the cover sediments, and (2) as a result of thrusting to the NE, followed by SW-directed backthrusting. It is concluded that gneisses on Svartenhuk Halvø rose diapirically into the cover sediments. This has implications for the origin of flat lying gneiss-cored nappes in areas adjacent to Svertenhuk Halvø. These may respresent, (1) the spreading lobes of mature diapirs, or (2) diapiric antiforms amplified during a subhorizontal shear regime.