bluuebunny/crossref_metadata_2025_split huggingface dataset:
Late Cenozoic evolution of the Nankai trench-slope system: evidence from sand petrography and clay mineralogy
Authors: Underwood Michael B. , Fergusson Christopher L. 
Published: April 2008

Abstract
Submarine slope systems in subduction zones evolve in response to a combination of tectonic and sedimentary forcing. It can be difficult to determine how and when tectonic forcing affects sedimentation, especially when investigating ancient rock successions, but one of the more reliable indicators is a change in sediment composition. During Leg 190 of the Ocean Drilling Program, sandy turbidites were recovered from a Quaternary trench wedge (Nankai Trough), a Pliocene-Pleistocene slope basin, the underlying Pliocene-Miocene accretionary prism, and a Miocene turbidite facies in the Shikoku Basin. Differences in detrital provenance between the sand and clay-sized fractions indicate that turbidity currents did not follow pathways of suspended-sediment transport during the past 10 Ma. During the middle and late Miocene, the sand probably was eroded from a newly exposed accretionary complex (Shimanto Belt). In contrast, high contents of detrital smectite in Miocene mudstones (>50 wt% of the <2 μm size fraction, relative to illite, chlorite + kaolinite, and quartz) point to a strong volcanic component of suspended-sediment input (Izu-Bonin island arc). The sand in accreted Pliocene turbidites was also eroded from the Shimanto Belt and transported by transverse flow down the insular slope. The trench-wedge facies then switched to axial flow during the Quaternary, when the sand supply tapped a mixed volcanic-metasedimentary provenance in the rapidly uplifted Izu-Honshu collision zone. Progressive depletion of smectite during the Pliocene and Pleistocene (<20 wt%) points to increased movement of illite- and chlorite-rich clay toward the east and NE from sources on Kyushu and Shikoku. That shift in mud composition coincides with intensification of the North Pacific western boundary current (Kuroshio Current) at approximately 3 Ma. Overall, the depositional system in the Nankai Trough and Shikoku Basin shifted its sand sources because of regional tectonics, whereas the suspended-sediment budget was modulated by hemispheric changes in ocean-water circulation.
Erosion of canyons in continental slopes
Authors: Mitchell Neil C. 
Published: April 2008

AbstractSonar images of the Atlantic USA continental slope reveal an eroded landscape that appears remarkably similar to subaerial landscapes eroded by surface runoff. Analysis of multibeam data reveals that they are also similar in a number of quantitative aspects, such as similar scaling between channel gradient and contributing area, they show Hack’s law scaling of channel length and contributing area, and tributary channels join trunk channels at the same elevation without an intervening waterfall. In modern geomorphology, the physics of river bed erosion and rules for runoff hydrology are used to model how erosion rate varies spatially and temporally, in order to predict large-scale landscape characteristics. This paper describes attempts to adapt such an approach to submarine canyon systems eroded by sedimentary flows. The mathematical form of the erosion is studied using the vertical relief of the canyons for the net erosion depth and is compared with results deduced from long-profile concavity. The rough correspondence between the two approaches lends support to the model. It is shown how the model can be used to help interpretation of canyon morphology by relating the pattern of erosion to the pattern of hemipelagic sediment supplied to the slope and other properties.
Laramie Peak shear system, central Laramie Mountains, Wyoming, USA: regeneration of the Archean Wyoming province during Palaeoproterozoic accretion
Authors: Resor Phillip G. , Snoke Arthur W. 
Published: April 2008

Abstract
The Laramie Peak shear system (LPSS) is a 10 km-thick zone of heterogeneous general shear (non-coaxial) that records significant tectonic regeneration of middle-lower crustal rocks of the Archean Wyoming province. The shear system is related to the 1.78–1.74 Ga Medicine Bow orogeny that involved the collision of an oceanic-arc terrane (Colorado province or Green Mountain block or arc) with the rifted, southern margin of the Wyoming province. The style and character of deformation associated with the LPSS is distinctive: a strong, penetrative (mylonitic) foliation commonly containing a moderately steep, SW-plunging elongation lineation. In mylonitic quartzo-feldspathic gneisses of the Fletcher Park shear zone, shear-sense indicators indicate southside-up, and this interpretation is supported by metamorphic and geochronological studies across the LPSS. We argue that distributed general shear (non-coaxial) involving high-strain zones and multiple folding events yielded a broad, en-masse uplift (Palmer Canyon block) during the late stages of the Medicine Bow orogeny. The LPSS is thus an excellent example of how crystal-plastic strain is distributed in sialic crust during an oceanic arc-continental margin collision. As magmatism (and attendant thermal softening) did not occur in the Wyoming province during its partial subduction beneath the oceanic-arc terranes of the Colorado province, the crystal-plastic strain manifested within the Wyoming province is mechanical in nature and was concurrent with crustal thickening. Strain is localized into discrete shear zones separated by weakly deformed rocks. These high-strain zones are commonly located along contacts between differing rock types and we propose that mechanical and chemical weakening processes may have contributed to strain localization.
Rigid polygons in shear
Authors: Schmid Daniel W. 
Published: April 2008

Abstract
Clasts, inclusions and intrusions in shear are potential recorders of strain, stress, rheology and metamorphism. In order to extract the recorded information, it is essential to have analytical and numerical theories that describe the deformation mechanics of such bodies. To overcome the simplifications of the commonly employed ellipsoid-based shape approximation, a combination of Muskhelishvili-type analytical solutions and finite-element method calculations is used to study the behaviour of (quasi) rigid polygons in shear. The results confirm that the polygon rotation and the pressure perturbation outside rigid polygonal clasts are well approximated by ellipse-based theories. However, this observation does not hold for the inside of these polygons, which show strongly varying values of pressure perturbation and maximum shear stress. For example, pressure perturbations inside the polygons are usually the opposite of the neighbouring matrix values across the polygon-matrix interface. This complex behaviour is summarized in the ellipse decomposition rule that allows for the qualitative understanding of the pressure perturbation in and around a wide range of polygons in shear. Other quantities studied include maximum values of over-pressure relative to the shortening stress, and the area that undergoes overpressure with respect to the clast size. The results demonstrate that overpressure can be twice as large as the rock strength.
Strain localization conditions in porous rock using a two-yield surface constitutive model
Authors: Issen Kathleen A. , Challa Vennela 
Published: April 2008

Abstract
This work examines theoretical conditions for localized deformation in porous rock, with emphasis on two recently identified deformation structures: compaction bands and dilation bands. Field and laboratory observations report that compaction/dilation bands consist of pure compressional/dilational deformation, which form perpendicular to maximum/minimum compression. A bifurcation approach is employed, with a two-yield surface constitutive model, to develop localization conditions under axisymmetric stress states for different stress paths. The first yield surface corresponds to a dilatant, frictional-damage mechanism (brittle regime), while the yield surface cap corresponds to a compactant mechanism (ductile regime). In the transitional regime, where both mechanisms are active, this model successfully predicts compaction bands and shear bands observed in axisymmetric compression tests. Due to discontinuities in the predicted band angle for probable material parameter values, this model may explain the lack of low angle compacting shear band observations in experiments. The two-yield surface model may also be applicable for a non-traditional axisymmetric extension stress path: increasing confining pressure with constant axial compression. Conditions for dilation band formation for this stress path are significantly less restrictive than corresponding compaction band conditions, suggesting that dilation bands could be a common deformation mode for high porosity sandstone.
The Famatina complex (NW Argentina): back-docking of an island arc or terrane accretion? Early Palaeozoic geodynamics at the western Gondwana margin
Authors: Miller Hubert , Söllner Frank 
Published: April 2008

Abstract
This paper concerns sedimentary, volcanic, metamorphic and igneous rocks of the Sierra de Famatina and adjacent rock series in NW Argentina, for which the name ‘Famatina system’ has been used widely in the literature. It is suggested that this is renamed the ‘Famatina complex’, since ‘system’ is an internationally defined stratigraphical term. The Famatina complex is considered to have formed as an island arc on continental crust, represented in its diversity by metasediments and meta-volcanic rocks of the Sierra de Famatina, with a corresponding back-arc basin exposed in the medium- to high-grade metamorphic rocks of the adjacent Las Termas belt to the east. The Famatina complex was deposited in contact with the eastern Pampean complex (‘Pampia terrane’) at the western active continental margin of Gondwana in latest Proterozoic and Ordovician times. Deposition was, in part, accompanied by voluminous Ordovician magmatism of calc-alkaline composition. NNW-SSE-striking shear zones, dated previously at 402 ± 2 Ma, are interpreted as marking the final stage of collision of the island-arc/back-arc/continent complex. The dynamics of crustal block movements along the most prominent (TIPA) shear zone indicate overthrusting of the eastern Pampean series onto the western Famatina series and, hence, uplift and cooling of the eastern block must have occurred earlier than cooling of the western one. The composition of inherited components in Famatina metasediments and meta-granitoids argues for autochthonous arc-continent convergence rather than accretion of an exotic terrane.
Lithospheric mantle domains beneath Antarctica
Authors: Leat P. T. , Dean A. A. , Millar I. L. , Kelley S. P. , Vaughan A. P. M. , Riley T. R. 
Published: April 2008

AbstractThe chemistry of mafic volcanic rocks and minor intrusions erupted on continents can be used to define sub-continental asthenospheric and lithospheric mantle sources. Data have been collated from Antarctica and the Falkland Islands (adjacent in Gondwana) in order to identify lithospheric mantle sources beneath the continent. The lithosphere-derived magmas include lamproitic and some lamprophyric rocks and end-members in basaltic suites that are interpreted as mixtures of magmas from lithospheric and asthenospheric sources. The lithosphere-derived mafic rocks from Archaean to Middle Proterozoic cratonic and circumcratonic areas of East Antarctica have time-corrected εNdvalues of −20 to −3. This demands isolation of the LREE-enriched sources within pockets of stable sub-cratonic lithosphere for more than 1 Ga, consistent with the lithosphere thickness up to 250 km imaged by seismic tomography. In contrast, lithosphere-derived mafic rocks from Middle Proterozoic to Early Palaeozoic areas of West Antarctica, Victoria Land and the Falkland Islands that formed the Gondwana continental margin, have time-corrected εNdvalues of −3.6 to +3.5, implying more recent isolation from asthenosphere. In terms of mantle reservoirs, cratonic and circumcratonic areas trend toward EMI, with EMII possibly being a minor component. In contrast, Gondwana margin areas trend toward EMII, with EMI being, at most, a very minor component.
Gold mineralization within the Witwatersrand Basin, South Africa: evidence for a modified placer origin, and the role of the Vredefort impact event
Authors: Hayward C. L. , Reimold W. U. , Gibson R. L. , Robb L. J. 
Published: April 2008

Abstract
The chemical composition of gold within the Archaean metasedimentary rocks of the Witwatersrand Supergroup displays significant heterogeneity at the micro-, meso-and regional scales. A detailed electron microbeam analytical and petrological study of the main auriferous horizons in the Central Rand Group throughout the Witwatersrand Basin indicates that gold has been remobilized late in the paragenetic sequence over distances of less than centimetres. Contemporaneous chlorite formation was strongly rock-buffered. Gold mobilization occurred under fluid-poor conditions at temperatures that did not exceed 350 °C. Widespread circulation of mineralizing fluids within the Central Rand Group is not supported by the gold and chlorite chemical data. Brittle deformation that affects most of the paragenetic sequence of the Central Rand Group late in its post-depositional history is followed by sequences of mineral growth and dissolution that appear throughout the Central Rand Group and have consistent textural relationships with gold. The consistent location within the paragenetic sequence, the wide regional and stratigraphic extent of the brittle deformation, together with mineral chemical and petrological data suggest that the Vredefort Impact Event (2.02 Ga) was the cause of this late deformation, and that post-impact fluid-poor metamorphism resulted in crystallization of a significant proportion of the gold on and within mineral grains that were deformed during this event.
Fluid velocity fields in 2D heterogeneous porous media: empirical measurement and validation of numerical prediction
Authors: Cassidy Rachel , MccLoskey John , Morrow Philip 
Published: April 2008

Abstract
The scale invariance of geological material and the consequent absence of a length scale on which to base the upscaling of measurements made on geological samples represent a serious challenge to the prediction of fluid behaviour in rock at economically interesting scales. Numerical simulation is an important tool for understanding constraints in this problem and current discrete fluid models in which complex boundary conditions can be represented have the potential for testing many possible upscaling schemes. At present, however, there are no accurate empirical data on the distributions of fluid velocities in complex, scale-invariant geometries, with which to validate such models.
To address this, fluid velocity fields in complex 2D media with fractal heterogeneity were measured. Digital models of rock geometries were created and translated into physical form using electric discharge machining and stereolithography. These physical models were then enclosed between parallel sheets of glass and Perspex forming a Hele-Shaw cell which was permeated with water, doped with small neutrally buoyant spheres and pumped at accurately steady and reproducible velocities. Local velocity vectors were estimated by the analysis of sequential images captured using high-resolution video. Precision digital control systems were used to move the cell relative to the camera and repeated measurements allowed the construction of full 2D velocity fields. The accuracy of the technique was assessed by comparison between automated and manual measurements, confirming the accuracy over approaching three orders of magnitude in velocity.
The results have been compared to the output of lattice Boltzmann (LB) simulations of flow in identical geometries, showing that the correlation between simulated and measured velocity fields is strongly dependent on the viscosity used in the numerical simulation. In particular, the LB scheme used in these tests is incapable of simulating correct viscosities for complex geometries. Some important effects are shown to be strongly viscosity dependent and it is concluded that some simulations may be able to predict the behaviour of high viscosity fluids only. Nonlinear effects between fracture and matrix flow are likely to be more important in these cases.
Sustainable small-scale gold mining in Ghana: setting and strategies for sustainability
Authors: Eshun P. A. 
Published: April 2008

Abstract

In Ghana, small-scale/artisanal gold mining has been on-going for more than a century. Artisanal mining has been the support for the rural people who more often than not are forced to sacrifice their farmlands and means of livelihood for large-scale mining operations. In order to reduce the activity of small scale/artisanal during the colonial era, laws were passed to bar indigenous operators from dealing in gold ore, amalgam, bullion, retorted gold, slags, concentrates and mercury. In recent years, however, under the auspices of the German non-governmental agency,
Gesellschaft für Technische Zusammenarbeit
(GTZ) and the World Bank, the Ghana government has undertaken a number of initiatives to formalise and regulate small-scale mining operations. Unfortunately, small-scale mining activities are characterised by lack of capital and minimum use of appropriate technology in the mining and treatment of the minerals into finished products. In addition, the industry is associated with land degradation and water pollution. This paper explores possible strategies that aim to make small-scale gold mining in Ghana more sustainable (i.e. more efficient, less destructive to the environment and more meaningful to the operators and the country as a whole). The roles of stakeholders in the small-scale mining industry in Ghana are also identified. It concludes that, for sustainable small-scale mining, a pragmatic synergistic approach must be adopted by all stakeholders in the organisation, regularisation, training and support of small-scale mining operations in Ghana. Mineable lands need to be delineated, illegal operators should be organised and brought under a responsible umbrella, small-scale mining operators should be supported with funds, technology and education, and alternative livelihood programmes must be pursued in mining communities.
Approaches to sustainable minerals development in Zambia
Authors: Nyambe Imasiku A. , Kawamya Vincent M. 
Published: April 2008

Abstract

Zambia is a land-locked country occupying an area of 752 614 km
2
, with the geology dominated by Archaean to Neoproterozoic age rocks that contain significant mineral resources. Economically, the most important of these are the Neoproterozoic Katangan rocks, which yield the copper and cobalt ores exploited in the Zambian Copperbelt. Copper and Cobalt exports account for over 80% of Zambia’s foreign exchange earnings. Coal-bearing rocks of Karoo age (Permo-Carboniferous to Early Jurassic age) occur in rift valley basins such as the mid-Zambezi Valley in the south of the country. Issues such as a lack of capital investment led to privatization of the Zambian large-scale mining industry. Smaller scale gemstone mining is becoming increasingly important. For example, in 1998, the Ministry of Mines and Minerals Development granted over 200 gemstone-mining licences, 30 small-scale mining licences and prospecting permits, and over 70 artisanal mining rights for various minerals. A policy Framework Paper (1999–2001) published by the Zambian Government encourages the formalization of small-scale mining activities through the provision of licences for small-scale mining and gemstone trading, and the establishment of four regional mining bureaus for licensing and other services to the mining community. Furthermore, the Government has embarked on a Mining Sector Diver-sification Project with the support of the European Union, with the objectives of increasing export earnings through economic diversification, generating employment opportunities and contributing to poverty alleviation. In addition, the new policies and legal framework encourage private ownership of medium- and large-scale mining operations, and development of new mines. Currently, all former Government-owned mines that were under Zambia Consolidated Copper Mines Limited have been privatized. These activities are slowly generating much needed new investment to the mineral industry in Zambia. For many years, copper mining has supported the social and economic development of Zambia, accounting for around 90% of all Zambia’s foreign exchange earnings in 1991. Copper reserves are steadily declining, with total reserves remaining estimated at just over 2 billion tonnes at an average grade of 2.51% total copper. There are no recent economic mineral deposits discoveries to replace depleting copper reserves. Lead and zinc mining at Kabwe finished in 1994 due to reserve depletion. The Maamba Coal Mine in the Zambezi Valley is in need of re-equipment and modernization. Gemstone mining and marketing needs a complete overhaul. This paper reviews the major issues that have contributed to decline in sustainable development of the mineral industry in Zambia and highlights initiatives, both private and public, currently undertaken to revitalize the sector.
The emperor’s new clothes: sustainable mining?
Authors: Whitmore Andy 
Published: April 2008

Abstract
Over the last few years, the idea of ‘sustainable mining’ has, thanks to industry sponsorship, been working its way into the agenda of many international processes. There is now a push in many countries to invite in multinational mining companies with the idea that there is a ‘new, sustainable mining’ that is different from the old, bad practices of the past. Yet what has actually changed in the industry to match this shift in rhetoric? From the perspective of mine-affected communities, nothing seems to have changed. Their land is still being taken from them without giving their free, prior and informed consent, and they are suffering the same ill effects on their ways of life, health and environment. This paper will illustrate, using case studies from the Philippines and West Papua, how under this rhetoric, the mining industry ‘emperior’ has the same old naked ambitions. This paper intends to look at how ‘sustainable mining’ is perceived from the viewpoint of mines-affected communities and their supporters. Ideally a representative of such a community should be writing this, but as this was not possible, I am writing this as a member of the editorial board of Mines and Communities (MAC). (MAC is a network of organizations across the world seeking to empower mining-affected communities in their struggles against damaging proposals and projects. More information on Mines and Communities, including the members of its editorial board, can be viewed at http://www.minesandcommunities.org.) Many of the communities MAC works with are made up of indigenous (or first, aboriginal) peoples, who have been unfairly disadvantaged by mineral development on or near their land. The paper will therefore concentrate to some extent on the issues of indigenous communities.