bluuebunny/crossref_metadata_2025 huggingface dataset:
Single-contact pressure solution creep on calcite monocrystals
Authors: Zubtsov Sergey , Renard François , Gratier Jean-Pierre , Dysthe Dag K. , Traskine Vladimir
Published: April 2008

Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 °C for six weeks using ceramic indenters under stresses in the 50–200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH
4
Cl. The deformation (depth of the hole below the indenter) is measured
ex situ
at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0–100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH
4
Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calcite-saturated aqueous solution show moderate indentation rate and the dry control experiments did not show any measurable deformation. The rate of calcite indentation is found to be inversely proportional to the indenter diameter, thus indicating that the process is diffusion-controlled. The microcracks in the dissolution region under the indenter dramatically enhance the rate of calcite indentation by a significant reduction of the distance of solute transport in the trapped fluid phase. This result indicates that care should be taken in extrapolating the kinetic data of pressure solution creep from one mineral to another.
Steep extrusion of late Archaean granulites in the Northern Marginal Zone, Zimbabwe: evidence for secular change in orogenic style
Authors: Blenkinsop Thomas G. , Kisters Alexander F. M.
Published: April 2008

The Northern Marginal Zone (NMZ) of the Limpopo Belt in southern Zimbabwe is an essentially plutonic terrain, now consisting of granulite-gneisses, that was assembled by extensive magmatic under- and intraplating between
c.
2.7 and 2.6 Ga during late Archaean crustal shortening. In this study, we present the first evidence for regional-scale normal shear in the NMZ. Normal shear has been identified along an up to 500 m wide, steeply dipping belt of mylonites, the Mitilikwe shear zone. Geochronological and mineralogical-textural data indicate that normal shear occurred coeval with crustal shortening that was accommodated along gently dipping thrust zones. The bulk strain pattern consisted of horizontal shortening, vertical stretching, and subvertical extrusion of a crustal segment. Horizontal shortening persisted throughout the orogenic evolution in the NMZ and no features typical of gravitational collapse in modern orogens are seen. This could imply that there was never major overthickening of the crust by thrusting, which may be a characteristic feature of Archaean orogeny.
Lithospheric-scale analogue modelling of collision zones with a pre-existing weak zone
Authors: Willingshofer Ernst , Sokoutis Dimitrios , Burg Jean-Pierre
Published: April 2008

Lithospheric-scale analogue experiments have been conducted to investigate the influence of strength heterogeneities on the distribution and mode of crustal-scale deformation, on the resulting geometry of the deformed area, and on its topographic expression. Strength heterogeneities were incorporated by varying the strength of the crust and upper mantle analogue layers and by implementing a weak plate or part-of-a-plate between two stronger ones. Three (brittle crust/viscous crust/strong viscous upper mantle) and four (brittle crust/viscous crust/brittle upper mantle/strong viscous upper mantle) layer models were confined by a weak silicone layer on one side in order to contain but not oppose lateral extrusion. Experimental results show that relative strength contrasts between converging plates and intervening weak plates control the location and the shape of deformation sites taken as ‘collision orogens’. If the contrast is small, internal deformation of the strong plates through fore- and backthrusting occurs early in the deformation history. However, the bulk system is dominated by buckling that nucleates on the weak plate whose antiformal topography is highest; model Moho of the bordering stronger plates is deepest under these conditions. If the contrast is large, deformation remains localized within the weak plate for a larger amount of shortening and develops a root zone below a narrow deformation belt, which coincides with the locus of maximum topography. Implementing a buoyant, low-viscosity layer above the model Moho of the weak plate favours the development of asymmetric model orogens notwithstanding the initial symmetric setup. Once the asymmetry is established strain remains localized in thrust faults and ductile shear zones documenting foreland directed displacement of the model orogen. Such laterally and vertically irregular configurations have applications in continent-continent collision settings such as the Eastern Alps. First-order mechanical boundary conditions recognized from modelling to be favourable to the post early Oligocene tectonics of the Eastern Alps include: (1) subtle rather than high-strength contrasts between the Adriatic indentor and the strongly deformed region comprising Penninic and Austroalpine units to the north of it; (2) decoupling of Penninic continental upper crust from its substratum to allow for crustal-scale buckling of the Tauern Window; (3) weak mechanical behaviour of the European lower crust during collision to account for its constant thickness along the TRANSALP deep seismic transect; and (4) the direct continuation of the basal detachment underlying the fold and thrust belt in the hangingwall of the European plate with a wide ductile shear zone in the core of the orogen, which separates the European from the Adriatic plate.
Calcareous turbidity current emplacement as an initiation mechanism for substrate brecciation and deformation
Authors: Savary B.
Published: April 2008

The Barremian-Aptian Baronnies syncline, located in SE France, provides the opportunity to study a calcareous turbidite lobe with intercalated breccias and slumps. These features are formed
in-situ
by the emplacement of turbidity currents that distorted the underlying semi-consolidated substrate. The brecciation occurs in three stages. The first stage is represented by the penetration of calcarenitic sediment into the underlying unlithified calcisiltic sediment due to the hydraulic pressure of an overriding turbidity current. In the next stage, a pseudo-breccia forms where the brecciated clasts are still attached to the substrate. Finally, these breccia clasts are separated entirely from the seabed and locally entrained into the flow. In addition, the penetration of the flow into the underlying semi-consolidated sediment can induce destabilization, down slope movement and folding. Similar Tithonian-aged (Late Jurassic) breccias have been interpreted previously as
in-situ
wave-induced features in this region; however, this study testifies that this deformation is not diagnostic of storms but can also be induced by turbidity current deposition.

The mechanisms that induce brecciation have to be identified correctly in order to consider them within a sequence stratigraphic context. Calcareous turbidites and their associated breccias, however, are not strongly diagnostic of relative sea-level.
High-strain zones: laboratory perspectives on strain softening during ductile deformation
Authors: Burlini L. , Bruhn D.
Published: April 2008

Deformation in the Earth’s outer shell is mostly localized into narrow high-strain zones. Because they can have displacements up to several hundreds or thousands of kilometres, they can affect the entire lithosphere. The properties of high-strain zones control the kinematics and dynamics of our planet, and are therefore of key importance for an understanding of plate tectonics, stress accumulation and release (e.g. earthquakes), mountain building, etc.

One of the requirements of shear zone formation in ductile rocks is localized strain softening (Hobbs
et al.
1990). In this paper we review the strain softening mechanisms that were identified and proposed 25 years ago and analyse their relevance in light of recent experimental results conducted to large strains. For this purpose, some of the newer developments in experimental deformation techniques that permit high strain in torsion are summarized and recent results are reviewed. Using these results we discuss mechanisms, processes and conditions that lead to localization.
Shear strain localization from the upper mantle to the middle crust of the Kohistan Arc (Pakistan)
Authors: Burg J.-P. , Arbaret L. , Chaudhry N. M. , Dawood H. , Hussain S. , Zeilinger G.
Published: April 2008

Shear structures from mantle to middle crust levels of the Kohistan palaeo-island arc, in Pakistan, are described. Pre-Himalayan ductile shear zones show a wide variety in size and shape, and developed from gabbro subsolidus to amphibolite facies conditions. Their lithological context and geological history give insights into mechanisms that initiate shear strain localization, factors that control stabilization of deformation in shear zones and flow properties at the mantle-crust transition. Shear strain localization began within compositional gradients. Gabbros were more prone to localization into anastomosing patterns than diorites and granites, which show more homogeneous strain. Shear strain localization during cooling led to less numerous but longer and thicker shear zones. Viscous heating within shear zones resulted in melt production and segregation in deformation structures, and seems to have taken part in the plutonic history of the arc. Using Kohistan as an example, we suggest that the plutonic, lower crust of arcs is strongly affected by subhorizontal, synmagmatic shear zones, probably consistent with the bulk flow direction of the subduction zone. These features can obviously be preserved in collision orogens and may be mistaken for structures documenting the continental collision.
Geometric aspects of synkinematic granite intrusion into a ductile shear zone — an example from the Yunmengshan core complex, northern China
Authors: Passchier C. W. , Zhang J. S. , Konopásek J.
Published: April 2008

The Cretaceous Yungmengshan core complex in northern China contains a large syntectonic granodiorite batholith that intrudes a slightly older diorite intrusion. A major gently dipping ductile décollement shear zone is developed along the contact of the diorite and granodiorite. The shear zone is invaded by a large volume of granitic and pegmatite veins associated with the main granodiorite batholith during activity of the shear zone under high-grade metamorphic conditions. Progressively older veins are more strongly deformed into tight cylindrical fold structures rotated into parallelism with the lineation and foliation in the shear zone. Parallelism of veins to the foliation is partly due to this rotation, but also to foliation-parallel injection of younger syntectonic pegmatite veins. Several small-scale structures have been recognized that allow distinction of solid-state deformation of veins. Granite veins do not extend much above the ductile shear zone that seems to act as a lid and an effective depository to intruding granite veins from the underlying batholith. There was considerable volume increase in the footwall and lower part of the shear zone by vein intrusion.
Initiation of basement thrust detachments by fault-zone reaction weakening
Authors: Wibberley Christopher A. J.
Published: April 2008

This paper examines how crystalline basement thrust sheets can detach in foreland thrust belts, in terms of the deformation mechanisms and rheological evolution of the detachment fault zones. Basement thrust fault zones of the Moine Thrust Belt and the external Western Alps show relatively narrow thrust zones considering the large displacements accommodated. Microscopic examination of fault rocks from these high strain thrust zones show that syntectonic alteration of fractured feldspars to white mica of strong preferred orientation generated ultramylonites deforming by diffusion creep and other viscous deformation mechanisms, similar to documented basement thrust zones in North America. Motivated by these observations coupled with other published examinations of foreland basement thrust zones, and recent developments in crustal hydrology, a conceptual model is proposed to explain basement detachment formation and evolution. Meteoric fluid that percolated into a previously fractured upper crust is drawn into developing fault zones by dilatancy pumping during the early stages of thrust-related deformation. The generation of cataclastic fault rocks with fresh fracture surfaces by microfracturing enhances the rate of fluid-rock interaction. Syntectonic alteration causes a deformation-mechanism transition to phyllosilicate-dominated ductile fault-rock rheologies, resulting in a large ductility contrast between host rock and fault zone that inhibits growth of the zone into the wall rock and weakens the thrust. Deformation becomes focused into these weakened early thrust zones so that they become zones of high strain, preventing the development of other newer fault zones elsewhere. This model explains the detachment and continued sliding of basement thrust sheets on narrow mica-rich zones of high strain in foreland thrust belts, and suggests that reaction weakening of the basement is important in decreasing the strength of the foreland crust in orogenic wedge evolution.
The Tasmanides of eastern Australia
Authors: Glen R. A.
Published: April 2008

The Tasmanides of eastern Australia record the break-up of Rodinia, followed by the growth of orogenic belts along the eastern margin of Gondwana. Spatially, the Tasmanides comprise five orogenic belts, with an internal Permian-Triassic rift-foreland basin system. Temporally, the Tasmanides comprise three (super)cycles, each encompassing relatively long periods of sedimentation and igneous activity, terminated by short deformational events. The Neoproterozoic-earliest Ordovician Delamerian cycle began by rifting, followed by convergent margin tectonism and accretion of island-arc forearc crust and ?island arcs in the Middle-Late Cambrian. The Ordovician-Carboniferous convergent margin Lachlan supercycle consists of three separate cycles, each ending in major deformation. The Ordovician Benambran cycle includes convergent (island-arc) and transform margin activity terminated by terrane accretion in the latest Ordovician-earliest Silurian. The Silurian-Middle Devonian Tabberabberan cycle reflects development of a large back-arc basin system, marked by rift basins and granite batholiths, behind intra-oceanic arcs and an Ordovician-Early Devonian terrane that were accreted in the Middle Devonian. The Middle Devonian to Carboniferous Kanimblan cycle began by rifting, followed by continental sedimentation inboard of a major convergent margin system that forms the early part of the Late Devonian-Traissic Hunter-Bowen supercycle. This supercycle comprises a Late Devonian-Carboniferous continental arc, forearc basin and outboard accreted terranes and subduction complexes intruded by the roots of a Permian-Triassic continental margin arc. Complex deformation ended with accretion of an intra-oceanic arc in the Early Triassic. Key features of the Tasmanides are: continuity of cycles across and along its length, precluding growth by simple eastwards accretion; development of a segmented plate margin in the Late Cambrian, reflected by major rollback of the proto-Pacific plate opposite the southern part of the Tasmanides; rifting of parts of the Delamerian margin oceanwards, to form substrate to outboard parts of the Tasmanides; the presence of five major Ordovician terranes in the Lachlan Orogen; and the generation of deformations either by the accretion of arcs, the largely orogen-parallel ‘transpressive’ accretion of Ordovician turbidite terranes (in the Lachlan Orogen), or by changes in plate coupling.
New Zealand tectonostratigraphy and implications from conglomeratic rocks for the configuration of the SW Pacific margin of Gondwana
Authors: Wandres A. M. , Bradshaw J. D.
Published: April 2008

The active margin of Gondwana is presently preserved in the southwest Pacific region in the formerly continuous Gondwana fragments of Australia, Antarctica and New Zealand. The Phanerozoic tectonic history of New Zealand is interpreted in terms of progressive Pacific-ward growth by accretion of arc-trench systems and the basement rocks are described in terms of a number of volcano-sedimentary accreted terranes, suites and batholiths that intrude the terranes. The age of these basement rocks ranges from Early Cambrian to late Early Cretaceous. The origin of the magmatic and sedimentary rocks and the time of accretion of the New Zealand terranes to the Gondwana margin are important for the understanding of Phanerozoic Pacific tectonics. Geochronological research over the last decade on igneous rocks and conglomeratic units shows that the Tutoko Complex/Amundsen Province plutons are major contributors of detritus to the Pahau depositional basin and that the Antarctic sector of the Panthalassan Gondwana margin has to be (re)considered as the likely source for the Permo-Triassic Rakaia sediments. Igneous clast data have greatly improved understanding of the evolution of the New Zealand microcontinent and have put tighter constraints on its Mesozoic tectonic setting within the southwest Pacific margin of Gondwana.
Pacific subduction coeval with the Karoo mantle plume: the Early Jurasssic Subcordilleran belt of northwestern Patagonia
Authors: Rapela C. W. , Pankhurst R. J. , Fanning C. M. , Hervé F.
Published: April 2008

The Early Mesozoic magmatism of southwestern Gondwana is reviewed in the light of new U-Pb SHRIMP zircon ages (181 ± 2 Ma, 181 ± 3 Ma, 185 ± 2 Ma, and 182 ± 2 Ma) that establish an Early Jurassic age for the granites of the Subcordilleran plutonic belt in northwestern Argentine Patagonia. New geochemical and isotopic data confirm that this belt represents an early subduction-related magmatic arc along the proto-Pacific margin of Gondwana. Thus, subduction was synchronous with the initial phase of Chon Aike rhyolite volcanism ascribed to the thermal effects of the Karoo mantle plume and heralding rifting of this part of the supercontinent. Overall, there is clear evidence that successive episodes of calc-alkaline arc magmatism from Late Triassic times until establishment of the Andean Patagonian batholith in the Late Jurassic involved westerly migration and clockwise rotation of the arc. This indicates a changing geodynamic regime during Gondwana break-up and suggests differential rollback of the subducted slab, with accretion of new crustal material and/or asymmetrical ‘scissor-like’ opening of back-arc basins. This almost certainly entailed dextral displacement of continental domains in Patagonia.
Northern Victoria Land terranes, Antarctica: far-travelled or local products?
Authors: Tessensohn Franz , Henjes-Kunst Friedhelm
Published: April 2008

The early Palaeozoic Ross Orogen in northern Victoria Land, Antarctica, consists of three major fault-bounded tectonostratigraphic terranes. Their true nature, fartravelled or local part of the accretionary collage, is under discussion. The inboard Wilson terrane (WT) consists mainly of high-grade metamorphic rocks intruded by the calcalkaline magmatic arc of the Ross Orogen. The terrane nature of the WT is doubtful, as it appears more like the leading edge of the East Antarctic craton. The Bowers terrane (BT) comprises a mixed sedimentary-volcanic succession, beginning with volcanic rocks of island-arc character, followed by turbidites, mudstones, conglomerates and fossiliferous Middle Cambrian shallow-water sediments. The whole sequence is capped by a fluvial to deltaic quartizitic series several kilometres thick, with strong continental affinity. The combination of primitive forearc to back-arc volcanics at the bottom and mature continental sediments at the top poses a problem. The outer Robertson Bay terrane (RBT) is made up of a thick turbidite succession which, in one area, contains allochthonous blocks of fossiliferous Tremadocian limestones. All terrane boundaries appear to be distinct fault zones. The WT/BT boundary forms a deep-reaching continent-ocean suture associated with strongly sheared rock units, ultramafic lenses and high-pressure rocks. Coesite in eclogites of the Lanterman Range indicates a depth of burial of around 90 km. A greenschist-facies schist belt marks the BT/RBT boundary. The terranes contain evidence for subduction at an active margin setting as well as for accretion processes along major faults. The present changes of the Cambrian time-scale, such as younging of the base of the Upper Cambrian by about 30 Ma since the 1980s, allow separation of arc formation and later terrane accretion events.
Archaeocyathan limestone blocks of likely Antarctic origin in Gondwanan tillite from the Falkland Islands
Authors: Stone P. , Thomson M. R. A.
Published: April 2008

Cambrian limestone clasts containing a rich, well-preserved archaeocyathan fauna have been recovered from the late Carboniferous Fitzroy Tillite Formation of the Falkland Islands. Since neither Cambrian strata nor limestone are present anywhere in the indigenous rock succession, the clasts are regarded as exotic erratics introduced during the Permo-Carboniferous Gondwana-wide glaciation. Most recent reconstructions of Gondwana rotate the Falklands into proximity with the Eastern Cape, South Africa and the Ellsworth Mountains, Antarctica. In both of these areas, Permo-Carboniferous diamictites correlated with the Fitzroy Tillite Formation also contain rare, exotic clasts of archaeocyathan limestone. The Transantarctic Mountains seem the most likely source for all of these unusual erratics. This interpretation sustains the requirement for substantial rotation of the Falklands microplate into Gondwana reconstructions and illustrates the extent of the late Carboniferous ice sheet. Apparent differences in the tillite clast assemblages between East and West Falkland suggest variable provenance within the regional ice-flow regime.
Provenance studies of very low- to low-grade metasedimentary rocks of the Puncoviscana complex, northwest Argentina
Authors: Zimmermann Udo
Published: April 2008

A provenance study of Neoproterozoic to Lower Cambrian rocks for the entire Puncoviscana Basin was conducted, using 119 samples from 15 different outcrops. Petrographic data (Q
t
60–80, F15–35, L5–20, P/F 0.2–0.4, L
v
/L = 0) show a composition comparable to foreland-basin successions. Lithoclasts are of metamorphic and metasedimentary origin. Volcanic debris is detected only in the form of sanidine, and volcanic lithoclasts were probably decomposed to form pseudo-matrix. Framework clasts are sub-angular to sub-rounded, and the rocks are poorly sorted. Major element geochemistry shows a moderate to high Chemical Index of Alteration (56–77) and failed to provide coherent provenance and rock classification. Trace element geochemistry suggests a rhyodacitic composition overall. Rare earth element patterns are comparable to those of model upper continental crust (UCC), as are concentrations of Nb, Ta, Ti, Th-Sc and Eu/Eu* (0.45–0.87; 95% between 0.4 and 0.7); reworking signatures are not detected. The uniform mineralogical and geochemical composition reflects supra-crustal source(s) for the entire basin, including significant metamorphic rock debris. The Puncoviscana complex is interpreted as a peripheral Pampean foreland basin, fed mainly from an eastern fold-thrust belt, but includes relicts of pre- and syn-collisional magmatic activity as well. A source area of UCC composition to the west is represented by the Arequipa block.
Distinguishing biological from hydrothermal signatures via sulphur and carbon isotopes in Archaean mineralizations at 3.8 and 2.7 Ga
Authors: Grassineau N. V. , Appel P. W. U. , Fowler C. M. R. , Nisbet E. G.
Published: April 2008

Carbon and sulphur isotopes have been analysed in mineralization from two Archaean greenstone belts at 3.8 Ga and 2.7 Ga, with the aim of distinguishing between the inorganic and organic processes that occurred. Despite an obvious overprinting by metamorphism (in the early belt), or hydrothermal fluids, there are convincing differences between the values of carbon and sulphur in inorganic formations and those formed by biological processes. An attempt is made to estimate the changes that occurred in the early life activities over this 1 Ga year period. Life in the Isua Greenstone Belt (3.8 Ga) was most likely present in transitory settings, probably under high temperature conditions. This was very different from the life at 2.7 Ga in the Belingwe Greenstone Belt, indicated by ranges of 38‰ for δ
34
S and 37‰ for δ
13
C
red
. By this time, the biological sulphur and carbon cycles seem to have reached almost full operation, with the presence of well-established photosynthetic microbial mat communities.
Diamond mega-placers: southern Africa and the Kaapvaal craton in a global context
Authors: Bluck B. J. , Ward J. D. , De Wit M. C. J.
Published: April 2008

Diamond mega-placers, defined as ≥ 50 million carats at ≥ 95% gem quality, are known only from along the coast of southwestern Africa, fringing the Kaapvaal craton, where two are recognized. One is associated with the Orange-Vaal dispersal, the other, to the south, has an uncertain origin. Placers are residual when left on the craton, transient when being eroded into the exit drainage, and terminal. Terminal placers, the final depositories of diamonds, have the greatest probability of being a mega-placer. There are four main groups of controls leading to the development of a mega-placer: the craton, the drainage, the nature of the environment at the terminus and the timing.

Cratons, being buoyant, have a tendency to leak diamonds into surrounding basins; however, being incompressible they may have orogens converge onto them resulting in some lost sediment being returned as foreland basin fills. The craton size, its diamond-fertility and the retention of successive kimberlite intrusions that remain available to the final drainage, are significant to mega-placer development.

Maximum potential recovery is achieved when the drainage delivering diamonds to the mega-placer is efficient, not preceded by older major drainages and focuses the supply to a limited area of the terminal placer. There should be sufficient energy in the terminal placer regime to ensure that sediment accompanying the diamonds is removed to areas away from the placer site. All conditions should be near contemporaneous and most were satisfied in the Orange-Vaal Rivers-Kaapvaal system and mega-placers were consequently generated.
The NERC Micro to Macro Programme: implications for fluid resource management
Authors: Heffer K. J.
Published: April 2008

The Micro to Macro (μ2M) Programme has been focused on developing understanding of subsurface fluid flows within geological heterogeneities spanning wide ranges of spatial and temporal scales. This paper highlights the opportunities for industries to incorporate recent observations and emerging theories in this field towards improved fluid resource management. The background to, and objectives of, the μ2M Programme are reviewed. Selected results from the projects in the programme are discussed and, where possible, compared with evidence from industrial field data. Some conclusions and recommendations for future practice in reservoir characterization are made. For example, there is currently very little recognition of modern theories that point to the likelihood of prevailing criticality in the mechanical state of the Earth’s crust and its implication for coherent large-scale collective behaviour emerging from small-scale interactions. Also associated with criticality are long-range spatial correlations and the likelihood that flow properties change during the life of commercial developments: such changes, for example, to absolute permeability, should be looked for and analysed for spatial and temporal patterns. Allied with these features is the importance of coupled processes, principally geomechanics, fluid flow, heat flow and chemistry. Knowing that local faults and fractures play a strong role in fluid flow mechanisms in a potentially time-varying, rather than just a static, fashion, gives even more motivation for acquiring detailed information on micro- and macro-structure over a range of scales.
MOPOD: a generic model of porosity development
Authors: Bloomfield J. P. , Barker J. A.
Published: April 2008

A code, MOPOD, has been developed to investigate general relationships between simple porosity growth laws and pore growth phenomena. MOPOD has been formulated as an ‘initial value problem’ and to date, investigations have focused on a very simple porosity growth law of the form

da
i
(t)/dt

=

v
e
i

, where
e
is the aperture growth rate exponent. A range of qualitatively distinct evolved geometries have been described for porosity growth on 2D and 3D arrays of varying geometries and connectivities as a function of the exponent,
e
, of the aperture growth-rate law, and the width of the initial aperture distribution, σ

z

. At low growth-rate exponents and moderate values of σ

z

over time there is a homogenization of apertures oriented sub-parallel to the head gradient. At moderate growth-rate exponents these apertures become increasingly heterogeneous in evolved arrays, with planar heterogeneities developing sub-parallel to the head gradient for low values of σ

z

while anastomosing structures develop at higher values of σ

z

. For larger growth-rate exponents preferentially enlarged array-spanning paths develop. No self-organization phenomena have been observed because periodic or cyclic behaviour is not inherent in the simple growth laws investigated to date.
About this title
Authors: Shaw R. P.
Published: April 2008

Understanding how fluids flow through though rocks is very important in a number of fields. Almost all of the world's oil and gas are produced from underground reservoirs. Knowledge of how they got where they are, what keeps them there and how they migrate through the rock is very important in the search for new resources, as well as for maximising the extraction of as much of the contained oil/gas as possible. Similar understanding is important for managing groundwater resources and for predicting how hazardous or radioactive waste or carbon dioxide will behave if stored or disposed of underground. Unravelling the complex behaviour of fluids as they flow through rock is difficult, but important. We cannot see through rock, so we need to predict how and where fluids flow. Understanding the type of rock, its porosity, the character and pattern of fractures within it and how fluids flows through it are important. Some contributors to this volume have been trying to understand real rocks in real situations and others have been working on computer models and laboratory simulations. Put together, these approaches have yielded very useful results, many of which are discussed in this volume.
Sustainable Minerals Operations in the Developing World: introduction
Authors: Marker B. R. , Petterson M. G. , McEvoy F. , Stephenson M. H.
Published: April 2008

excerpt

Sustainable development requires an appropriate abalance between social, economic and environme ntal well-being, now and for the future. Since most minerals are non-renewalble resources, sustainability of supply can only be addressed by extracting, processing and distributing raw in the least environmentally damaging ways, using minerals wisely, and recycling as much as possible. However, there also is significant scope for inproved sustainability in terms of economic and social aspects.

Minerals are essential raw materials but high-quality deposits havem become depleted in many developed countries. These countries have increasingly turned to developing countries for supplies and it is in these that modt high-quality untapped futre prospect remain. for countries with limited export opportunities, minerals are often a mainstay of the domestic economy. However, low selling prices may reflect limited environmental regulation and low wages. This can lead to charges that the rich countries are exporting their environmental damage to, andexploiting, poorer countries. As more countries develop, the global demand for supplies of essential raw materials increases, and resources will be depleted more quickly. Therefore, sustainable minerals supply from the developing countries is an important global issue.

In this Special Report, general aspects of sustainable minerals operations in the developing world are reviewed by Petterson
et al.
, Hobbs, and Richards while the remaining papers consider specific issues in more detail. Hobbs, in particular, emphasizes the need to give proper weight each to human capital, financial capital, manufactured capital, and environmental capital in any full analysis as a context for sustainable development and effective.
The need and context for sustainable mineral development
Authors: Petterson M. G. , Marker B. R. , McEvoy F. , Stephenson M. , Falvey D. A.
Published: April 2008

A special thematic conference was organized at the Geological Society of London in November 2003, aimed at bringing together experts in minerals development in the Developing Countries. Representatives of many aspects of mineral development attended, including mining companies, governments, aid agencies, non-governmental organizations (NGOs), academics and consultants. The opening address to the conference is given in this paper. Mining is an ancient human activity developed through essential societal demand. As society and technology have developed, they have inevitably become ever-more materials hungry. This demand will remain for the foreseeable future. Many areas of the Developed World have depleted high-grade mineral deposits, and remaining resources are subject to strong environmental constraints. This increases pressure on the Developing World to generate the mineral commodities upon which society depends. Mineral resources are also a potential source of capital over which Developing Countries can have their own decision-making powers (in contrast to aid money for example). Sustainable mineral development is all about balance. Achieving the dynamic balance between supply and demand, equitable capital distribution, good financial and environmental management and governance, economics, and social stability is the challenge the world faces in the twenty-first century and beyond.
The role of minerals in sustainable human development
Authors: Richards Jeremy P.
Published: April 2008

Sustainable mineral resources development can be seen as the equitable conversion of transient mineral wealth into durable social and environmental capital. In the past, this conversion has not been efficient or equitable, with benefits accruing mainly to First World investors and consumers by externalization of social and environmental costs to local people and places. Modern industry, led by large multinational corporations, is in the process of changing its
modus operandi
to embrace ideas of corporate and social responsibility. The damage from past practices to the developing world is severe, however, and may require measures beyond voluntary or current legal instruments to reverse degenerative trends. Central among these requirements is Third World debt cancellation. However, the mining industry can also contribute by fully internalizing the costs of mineral production, and paying a fair price for the resources it extracts; these internalized costs should be reflected in higher commodity prices. This can be achieved through a combination of financial instruments and incentives, innovation, and best practice, with essential consumer buy-in through increased awareness.
Markets for industrial mineral products from mining waste
Authors: Scott Peter W. , Eyre John M. , Harrison David J. , Bloodworth Andrew J.
Published: April 2008

The composition of mining waste varies according to the nature of the mining operation and many other factors, but where the same mineral is extracted from a similar style of metalliferous or industrial mineral deposit or coal, the waste usually has similar characteristics. There are many potential sources of industrial minerals from mining waste. Waste from one mine may be a byproduct or coproduct in a mining operation elsewhere. Much technical research work on mine waste utilization, for example studies on slate waste, has included a manufacturing process. The waste is invariably an inferior material compared with an industrial mineral from a primary resource for the manufacturing process. Successful markets have not been found. Four scenarios are proposed where an industrial mineral product made from mining waste may be marketed successfully. These are a bulk product for a local market made with minimal or no processing; a low unit value product and a cost-effective alternative source of a mineral for local industry; an industrial mineral commodity traded nationally or internationally; and extraction of a high unit value rare mineral. Making an industrial mineral product from mining waste and successfully marketing it should involve minimal processing of the waste consistent with the value of the mineral product.
FarmLime: low-cost lime for small-scale farming
Authors: Mitchell Clive J.
Published: April 2008

In the less-developed parts of southern Africa, where agriculture is crucial in daily survival, agricultural lime is often difficult to obtain. This is due to the scarcity of production sites, high transport costs and inadequate support for farmers from government extension services. In Zambia there are upwards of 700 000 small-scale farmers who struggle to farm on acid soils and as a result have poor crop yields. They cannot afford to use agricultural lime, which would solve the problem, and as a result are trapped in a cycle of poverty. In an attempt to address this problem, the UK research project ‘FarmLime’, based in Zambia, investigated a means of producing affordable agricultural lime using simple, locally available technology. Dolomite suitable for agricultural lime occurs throughout Zambia, including those farming districts with acidic soils. It is estimated that small-scale production using partly manual methods could produce agricultural lime for US$25 – 30 per tonne. Demonstration crop trials were successful in demonstrating the benefits of using agricultural lime to small-scale farmers. Where the price of maize is high and the cost of lime is low, the economic benefits of its use are high. However, even if there is a demonstrable economic benefit, the use of agricultural lime will be constrained by the lack of cash in the rural economy; one potential solution to this could be bartering of crops for agricultural lime.
Climatic controls on alluvial-fan activity, Coastal Cordillera, northern Chile
Authors: Hartley Adrian J. , Mather Anne E. , Jolley Elizabeth , Turner Peter
Published: April 2008

A description of the distribution, drainage basin characteristics, surface morphology, depositional process and age of 64 alluvial fan systems from both flanks of the hyper-arid Coastal Cordillera of northern Chile between 22°15′S and 23°40′S is presented. The coastal fans on the western flank of the Coastal Cordillera are dominated by debris-flow deposits fed from steep catchments. Two drainage basin types are recognized: type A drainage basins are small (10–30 km
2
) and do not cut back beyond the main coastal watershed; and type B drainage basins are large (up to 400 km
2
) and cut inland beyond the coastal watershed. The western Central Depression fans on the eastern flank of the Coastal Cordillera are characterized by sheetflood deposition fed from relatively shallow catchments in small drainage basins (10–50 km
2
). The surface morphology, sedimentation rates, a luminescence date and regional cosmogenic radionucleide data suggest that these fans have been inactive for at least the last 230 000 years and probably for much of the Neogene.

The principal control on fan activity in the study area is climate. The Coastal Cordillera forms an orographic barrier to recent El Niño-related precipitation events that are restricted to the western flank of the Coastal Cordillera. These events did not penetrate into the Central Depression as indicated by the inactive nature of the western Central Depression fans located 25 km east of the active coastal-fan catchments. This scenario is considered to have prevailed for much of the Neogene. Climate also controls rates of weathering on alluvial-fan surfaces. The coastal fog results in rapid salt weathering of clasts on coastal fans resulting in the production of fines, but does not penetrate into the Central Depression. Fault activity is important in controlling drainage basin size. The larger (type B) drainage basins are commonly focused on active faults that cut the coastal watershed, facilitating drainage basin expansion. Source-area lithology is not important in controlling depositional processes. Fans on both sides of the cordillera have the same basaltic andesite and granodiorite source lithologies, yet coastal fans are dominated by debris-flow and western Central Depression fans by sheetflood deposition. A combination of chemical weathering and stream power related to gradient are considered to account for the differences in process.
Luminescence dating of alluvial fans in intramontane basins of NW Argentina
Authors: Robinson R. A. J. , Spencer J. Q. G. , Strecker M. R. , Richter A. , Alonso R. N.
Published: April 2008

Alluvial fans are sensitive recorders of both climatic change and tectonic activity. The ability to constrain the age of alluvial-fan sequences, individual sedimentary events and the rates of sediment accumulation are key for constraining which mechanisms most control their formation. Recent advances in optically stimulated luminescence (OSL) measurement and analysis have resulted in vast improvements in the dating technique and reliability of age determinations, particularly for OSL dating of quartz grains, and routine application to a wide variety of depositional environments is now possible. Here we apply OSL methods to date a variety of deposits within Late Pleistocene conglomeratic alluvial sequences in NW Argentina. The ages obtained range from 39 to 83 ka and were determined from debris-flow- and fluvial-dominated deposits and lacustrine sequences in intramontane basins bounded by tectonically active mountain ranges with as much as 2 km of relief. With careful choice of facies and sample collection, OSL techniques can be used to date Late Pleistocene, predominately matrix-supported, cobble-conglomerate alluvial deposits.
Factors controlling sequence development on Quaternary fluvial fans, San Joaquin Basin, California, USA
Authors: Weissmann G. S. , Bennett G. L. , Lansdale A. L.
Published: April 2008

Variable geometry and distribution of stratigraphic sequences of fluvial fans in the eastern San Joaquin Basin, California, were controlled by tectonics, through basin subsidence and basin width, and response to Quaternary climate change, related to the degree of change in sediment supply to stream discharge ratios and local base-level elevation changes. Three fluvial fans — the Kings River, Tuolumne River and Chowchilla River fans — illustrate the influence of these factors on ultimate sequence geometry. In areas with high subsidence rates (e.g. the Kings River fluvial fan) sequences are relatively thick and apices of subsequent sequences are vertically stacked. Areas with relatively low subsidence rates (e.g. the Tuolumne River fan) produced laterally stacked sequences. Rivers that experienced a significant increase in sediment supply to stream discharge ratios due to direct connection to outwash from glaciated portions of the Sierra Nevada developed high accommodation space and relatively thick sequences with deep incised valleys. Conversely, rivers that were not connected to glaciated regions (e.g. the Chowchilla River fan) and, thus, experienced a relatively minor change in sediment supply to discharge ratios during climate change events, produced thinner sequences that lack deep incised valleys. Local base-level connection to sea level, via the axial San Joaquin River, produced deeper incised valleys than those of internally drained rivers. Finally, narrow basin width allowed glacially connected fans to completely fill available accommodation space, thus producing smaller fans that lack preservation of distal, interglacial deposits. Evaluation of these controls allows prediction of sequence geometries and facies distributions for other San Joaquin Basin fans for input into future hydrogeological models.
Mid-Cretaceous turnover of saurischian dinosaur communities: evidence from the Neuquén Basin
Authors: Coria Rodolfo A. , Salgado Leonardo
Published: April 2008

Successional changes are recorded among saurischian dinosaur faunas throughout the Cretaceous of the Neuquén Basin. Both sauropod and theropod lineages present in NW Patagonia show comparable transformations and indicate that some clades did not survive the Late Turonian boundary. Similar patterns of changes are observed in other Patagonian sedimentary basins. Diplodocoid sauropods and carcharodontosaurid theropods are not yet recorded in levels younger than Turonian, while titanosaurians and abelisauroids are present before and after this period. Important floral changes during the mid-Cretaceous, mainly related to the proliferation of angiosperms, could be one element that influenced some dinosaurian associations.
Deformation transfer in viscous detachments: comparison of sandbox models to the South Pyrenean Triangle Zone
Authors: Koyi Hemin A. , Sans Maura
Published: April 2008

Results of scaled sandbox models, containing three viscous layers located at different geographic and stratigraphic levels simulating three evaporitic units in the South Pyrenean Triangle Zone, and interpreted field data are presented here to explain structural variation and kinematics in shortened areas containing multiple weak horizons acting as detachments. In the Southern Pyrenean Triangle Zone, the Beuda, Cardona and Barbastro thrust fronts have similar geometric features to those developed in the models, suggesting that they could have formed and evolved in a similar way. These deformation fronts are not always perpendicular to the regional shortening direction. Instead, their direction is governed by the initial pinch-out of the viscous horizonts. Model results show that triangle zones form when: (1) deformation is transferred to weak horizons located at higher stratigraphic levels, and (2) the deformation front reaches the pinch-out of the weak horizons. Model results also show that the rheology of the detachment horizonts controls the geometry of the deformation front. Weak detachments (Cardona Formation, and pure silicone in the models) promote folding and back-vergent structures, and thus formation of triangle zones at the deformation front, irrespective of the location of the thrust front relative to the pinch-out of the viscous detachment. However, over strong (more viscous) detachments (Barbastro and Beuda formations, and impure silicone in the models), folds that eventually evolve to thrusts are dominant. In such cases, backthrusts form only at the pinch-out of the detachment layer. In cases where no viscous detachment is present, no backthrusts form, and therefore the thrust front does not develop a triangle zone geometry. Instead, a foreland-vergent piggyback sequence of thrusts forms. Model results show that the stratigraphic level of a detachment governs size, geometry and spacing of the imbricates formed above it.