bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metamorphic evolution of the mainland Lewisian complex
Authors: Sills J. D. , Rollinson H. R. 
Published: April 2008

Summary
The equilibration conditions of early Scourian (Badcallian) granulite-facies metamorphism appear to be similar for the whole mainland Lewisian outcrop. Pyroxene and garnet assemblages equilibrated at about 7–8 kb and 750–800°C. Peak granulite facies conditions may have been slightly higher. An early high-pressure gt-cpx assemblage partially broke down to lower pressure opx + plag ± magt ± sp ± hb symplectites, indicating decompression after the peak of metamorphism. At a later stage, there was growth of a more Fe-rich garnet. Discordant trondhjemite and granite sheets, which were also metamorphosed to granulite facies, indicate very high magmatic temperatures of 890–1030°C from Fe-Ti oxides and 1000°C from hypersolvus feldspars.
The Scourian complex was extensively retrogressed during the Inverian as a result of the influx of hydrous fluids at about 600°C.
The boundary between Proterozoic and Archaean crustal blocks in central West Greenland and northern Labrador
Authors: Korstgård J. , Ryan B. , Wardle R. 
Published: April 2008

Summary
The contact between the Early Proterozoic Nagssugtoqidian Mobile Belt and the Archaean craton in West Greenland, and that between the Churchill Province and the Archaean (Nain) craton in Northern Labrador represent two cross-sections of an Early Proterozoic orogenic boundary. The Archaean cratons in both regions display the peripheral effects of Proterozoic orogenic events. The best indicators of Proterozoic effects on the Archaean cratons are the Late Archaean-Early Proterozoic dykes and the Early Proterozoic supracrustal rocks which unconformably overlie the gneisses and dykes. In Greenland the boundary zone evolution is characterized by Late Archaean (Nag. 1) transcurrent shearing, Early Proterozoic Kangâmiut dyke intrusion and subsequent (Nag. 2) ductile overthrusting. Ductile overthrusts are characteristic of the Nagssugtoqidian-Archaean boundary and attest to substantial shortening of the crust in this region. In Labrador the boundary region has been divided into several distinct zones. Although facets of its evolution are analogous to the boundary in Greenland there are several fundamental differences, the most important of which is that transcurrent movement appears to have been dominant over ductile overthrusting. These differences are provisionally related to contrasting tectonic settings of the two areas during Early Proterozoic continental collision, the Greenland segment being the frontal collision zone whilst the Labrador segment documents slightly oblique transcurrent motion.
The regional tectonic setting and possible causes of Cenozoic extension in the North American Cordillera
Authors: Coney P. J. 
Published: April 2008

SummaryTiming and tectonic setting of middle Cenozoic crustal extension in the North American Cordillera supports the concept that an overthickened crustal welt formed behind or astride the thrust belts as a result of compression during the Mesozoic to early Cenozoic. At the end of the Laramide Orogeny the gravitationally unstable welt collapsed by deep-seated crustal extension. The extension was aided by a lowering of crustal viscosity resulting from a complex pattern of volcanism and a reduction in intraplate compressive stress. As plate regimens evolved along the Pacific margin during the late Cenozoic, subduction progressively ceased as did compressive stress also. An evolving transform boundary and a massive Cordilleran-wide lithospheric uplift allowed a second phase of extension to develop across the already thinned and thermally weakened crust to form the Basin and Range Province, being active up to the present time.
Crustal extension along a rooted system of imbricate low-angle faults: Colorado River extensional corridor, California and Arizona
Authors: Howard Keith A. , John Barbara E. 
Published: April 2008

SummaryThe upper 10 to 15 km of crystalline crust in the 100-km-wide Colorado River extensional corridor of mid-Tertiary age underwent extension along an imbricate system of gently dipping normal faults. Detachment faults cut gently down-section eastward in the direction of tectonic transport from a headwall breakaway, best expressed in the Old Woman Mountains, California. Successively higher and more distal allochthons are displaced farther from the headwall, some as much as tens of kilometres. The basal fault(s) cut initially to depths of 10 to 15 km, the palaeothickness of a tilted allochthonous slab of basement rocks above the Chemehuevi-Whipple Mountains detachment fault(s). Hanging wall blocks tilt consistently toward the headwall as shown by dips of capping Tertiary strata and of originally horizontal Proterozoic diabase dykes. Block tilts and the degree of extension increase northeastward across much of the corridor. The faults are interpreted as rooting under the unbroken Hualapai Mountains and Colorado Plateau on the down-dip side of the corridor in Arizona. Slip on faults at all exposed levels of the crust was unidirectional, and totals an estimated 50 km. These data and inferences support the concept that the crust in California moved out from under Arizona along a rooted, normal-slip shear system. Brittle thinning above the sole faults affected the entire upper crust, and in places wholly removed it along the central part of the corridor. Upwarp exposed metamorphic core complexes in footwall domes.
Introduction
Authors: Jones Mervyn E. , Preston R. M. F. 
Published: April 2008

In recognition of the increasing interest in the subject of deformation of sediments and sedimentary rocks shown by Earth scientists in recent years, a major international conference with this theme was held at University College London in April 1985. This volume contains the texts of those contributions to the Conference that were submitted for publication. The collection of papers presented is not a complete record of the proceedings, as some contributors chose not to submit a manuscript. However, most important subject areas are represented, and the papers provide both a review of the present state of the art and pointers for future investigation. The articles have been grouped into three main divisions: experimental and theoretical, process orientated, and descriptive of particular areas or localities. Within those groupings there is no particular significance in the order of printing except that articles with aspects in common have been placed near to one another.
Studies of naturally deformed sedimentary rocks repeatedly indicate that much of the observed deformation resulted from processes active before the rock was lithified. An understanding of the origins of these structures cannot be established using the principles of rock mechanics and crystal physics commonly employed in ‘hard-rock’ structural geology (Rutter 1976; White 1976), the principles of the engineering discipline of soil mechanics being more appropriate. Alternatively, the post-lithification deformation of sediments is a typical rock mechanics problem and may involve an understanding of elasticity (Jaeger & Cook 1969), fracturing (Price 1966; Barton 1976), crystal plasticity (Turcotte & Schubert 1982) and diffusion based deformation mechanisms (Rutter 1976, 1983). The student of sediment deformation must therefore be conversant with all aspects of rock and soil deformation. The Conference, with its contributions by structural geologists, sedimentologists, geotechnical engineers and those conversant with specific aspects of rock and soil mechanics, provided a coverage of this very wide subject area. This is reflected in the contents of the volume.
Pressure solution-deposition creep and associated tectonic differentiation in sedimentary rocks
Authors: Gratier J. P. 
Published: April 2008

Summary
Several models of pressure solution-deposition have been established by using various hypotheses: on the rate-limiting process of the deformation (kinetics of the solid/fluid reaction or rate of mass transfer); on the driving force for mass transfer (difference in normal stress or elastic, plastic or surface energies) and on the mechanism of mass transfer (diffusion or infiltration). These creep relations have been tested experimentally and in nature. In the last case the observations show that the pressure solution-deposition process is always associated with a chemical differentiation of the rocks when these rocks are initially composed of several minerals with various mobilities under stress. The aim of this paper is to discuss the development of this chemical (and mechanical) differentiation. The first part deals with the initiation and the development of the zone of dissolution (relation between stress and dissolution, effect of the initial heterogeneities, etc.) and of the zone of crystallization (effects of the nature of the rocks, processes of deposition, etc.). The second part deals with the development of chemical differentiation during the progressive deformation. The geometry and the equilibrium composition of the differentiated layer are fixed by various factors such as: the size of the dominant heterogeneities (initial or tectonically induced), the possibilities of mass transfer, the state of stress, and the nature of the solid and that of its solution. The wavelength of some stylolites could also be imposed by these various factors.
Soft-sediment deformations from glaciodeltaic, glaciolacustrine and fluviolacustrine sediments in the Kleszczów Graben (central Poland)
Authors: Brodzikowski K. , Gotowała R. , Hałuszczak A. , Krzyszkowski D. , Van Loon A. J. 
Published: April 2008

Summary
The Kleszczów Graben, situated some 50 km south of Łódź, has a Tertiary and Quaternary infilling of up to 300–400 m. The graben is some 40 km long and a large exposure is formed by an open-cast browncoal mine. The well discernible structural pattern is due to frequent deformations, many of which are related to subsidence of the graben. The sediments within the graben are all unconsolidated and show a large variety of deformational structures with respect to both genesis and geometry. Various stages of more intense deformation can be discerned. The glaciodeltaic, glaciolacustrine and fluviolacustrine sediments in particular show frequent deformations. They are interpreted as being induced by both endogenic and exogenic agents, often during several phases that affected the same sedimentary unit.
Deformation of Scottish Quaternary sediment sequences by strong earthquake motions
Authors: Davenport Colin A. , Ringrose Philip S. 
Published: April 2008

Summary
Deformed Quaternary sand, silt, clay and peat sequences from four localities in Scotland are interpreted as seismites by the deformation history of liquefied, fluidized, slumped, and faulted units, and by comparison with seismites documented elsewhere. Two of the sequences consist of outwash sands and silts, deposited during the recession of the Devension ice cap in the region of Perth. Other deposits consist of glacial sands and interglacial peats in the Western Highlands, and glacio-lacustrine silts in the Glen Roy area; both probably deposited during the late stages of the Loch Lomond Readvance.
Careful evaluation of internal geometries and deformation sequences reveals an intimate association of ball-and-illow, fluidization, dish, load, flame and ‘fault-grading’ structures which are most satisfactorily explained by prolonged ground shaking produced by shallow earthquakes. In some cases, potential fault sources for the inferred earthquakes have been identified.
Syn-sedimentary and burial related deformation in the Middle Jurassic non-marine formations of the Yorkshire Basin
Authors: Alexander J. 
Published: April 2008

Summary
The non-marine formations of the middle Jurassic Ravenscar Group consist of channel sandstone bodies set in interbedded mudstones, silts and thin sheet sandstones. These rocks contain syn-sedimentary and burial related deformation structures.
Frequent discharge fluctuations are deduced to have enhanced inherent river bank instability and with occasional tectonic movements produced a wide range of bank collapse structures. These had a low preservation potential and are observed at various stages of erosion.
Several faults associated with channel sandstones can be related neither to tectonic activity nor to bank collapse. They may be explained as compensation structures formed during differential compaction of the sandstones and adjacent mudstones. Differential compaction structures form on a smaller scale around plant material, early diagenetic nodules and sandstone dykes.
Continued sedimentation on the alluvial plain, together with differential compaction, produces a positive topography over channel sandstones. This effect was reduced by variations in deposition rate and facies. Laterally continuous beds deposited on this topography form gentle folds that are exaggerated by differential compaction during burial.
Although most of the deformation seen in the Ravenscar Group is related to alluvial processes or sediment burial, some is connected to syn-sedimentary tectonic activity.
Aspects of veining in the Welsh Lower Palaeozoic Basin
Authors: Fitches Bill 
Published: April 2008

Summary
In the Welsh Lower Palaeozoic marginal basin, veins of diverse origin are widely distributed in space and time. The veins are categorized as pre-, syn- and post-tectonic with respect to folding and cleavage development; these sub-divisions denoting different types of veining processes. Among the pre-tectonic veins are those described as regional veins which were emplaced diachronously by hydraulic jacking and related processes due to overpressured pore fluids affecting newly lithified rocks while sedimentation continued above. Other pre-tectonic veins are those around Snowdon which were due to processes closely associated with the development of an Ordovician resurgent caldera. Syn-tectonic veins are uncommon. They include the auriferous lodes of Ogofau in south-central Wales. Post-tectonic veins are the most widespread type and are exemplified mainly by those of the Harlech and Plynlimon Domes. These late veins are attributed largely to regional extension and dewatering of the Lower Palaeozoic pile caused by the early Variscan extensional regime.
The petrochemistry of the northern part of the Chilwa alkaline province, Malawi
Authors: Woolley A. R. , Jones G. C. 
Published: April 2008

Summary
The Chilwa province of alkaline igneous rocks and carbonatites lies at the southern end of the East African rift, and is unique within the rift for its essentially intrusive nature. The province comprises numerous carbonatite centres (some with nepheline syenite and nephelinite), large complexes of nepheline syenite and syenite, and plutons of peralkaline syenite, quartz syenite and granite, together with dykes compositionally equivalent to all the major rock types. 196 rock samples from the northern half of the province have been chemically analysed and the data indicate that three rock series are present: (1) syenite-quartz syenite-granite, (2) nepheline syenite-syenite and (3) nephelinite-carbonatite-nepheline syenite. It has not proved possible to relate these series to a single parental magma, and it is concluded that three parental magmas of trachytic, phonolitic and nephelinitic-carbonatitic composition were involved.
A model is suggested for the generation of these three magmas involving production of a zoned metasomatized lithosphere wedge by lithosphere focussing. Fracturing of the crust above the growing wedge led to pressure release and to the uprise of geotherms and volatiles with consequent partial melting at different levels throughout the metasomatized wedge. The metasomatism may have reached the base of the crust and it was from this region that trachyte magmas were produced by melting of rocks similar to syenitic fenites. Phonolitic magmas were generated directly at intermediate levels, and nephelinites were generated at the base of the metasomatized lithosphere.
Tertiary alkaline magmatism in East Greenland: a review
Authors: Nielsen T. F. D. 
Published: April 2008

SummaryThe Tertiary alkaline magmatism in E Greenland is the result of the processes related to the continental break-up of the N Atlantic in the Lower Tertiary. The alkaline rocks are divided into three groups: A, inland alkaline lavas, dykes and intrusive complexes of nephelinitic parentage; B, mildly-alkaline to nephelinitic mafic lavas and dykes mostly in areas that previously experienced tholeiitic magmatism; C, salic subalkaline to alkaline dykes and intrusive complexes related to group B.All three groups are exposed over about 1000 km along the E coast of Greenland, and close to 100 intrusions have been identified, excluding the very intense dyke-swarms. The rocks of nephelinitic parentage occur inland about 100 km W of the coastal zone of most intense magmatism and are believed to constitute an alkaline ‘flank’ activity to the tholeiitic magmatism of the spreading ridge. Early tholeiites and the nephelinites are thought to be derived from the same mantle source. Both group B and group C rocks occur along the coast and along what has been called the ‘initial magmatic lineament’, which in some areas evolved to a spreading zone of intense tholeiitic magmatism. The group B rocks may have been generated in the tholeiite feeder system after the end of the tholeiitic magmatism by processes in replenished magma chambers. Interaction between the magmas in the feeder system and the Archaean crust generated the subalkaline to alkaline salic liquids of group C. The occurrences of the alkaline rocks and their relationships with one another, with the preceding tholeiitic magmatism and with the process of continental break-up are described, and petrogenetic models are presented.
Sedimentology of basin plains
Authors: Pilkey Orrin H. 
Published: April 2008

Summary
The study of 13 basin plains in the Western N Atlantic Ocean, the Caribbean Sea and the Mediterranean Sea has revealed a number of factors that control basin-plain filling. Basin plains are strongly dominated by turbidity currents which enter the basins mostly from canyon mouths. Such turbidity currents are little affected by channelization, and erosion of pre-existing turbidites is of minor importance. In order to maintain a basin plain, occasional ‘giant events’ are required, i.e. turbidity currents which flow across and cover the entire basin. The two main factors that control sand-layer geometry in basin plains are (1) the arrangement of entry points around the edge of the plain and (2) the ratio of the area of the drainage basin to the area of the basin-plain floor.
Mapping of hemipelagic versus turbiditic muds by feeding traces observed in deep-sea photographs
Authors: Huggett Q. J. 
Published: April 2008

Summary
The Madeira Abyssal Plain is composed mainly of turbiditic sediments derived from the NW African margin. Through this cover project hills covered with draped pelagic sediments. The surface layers of both sediment types are similar with respect to grain size and mineralogy. Similarly, there is no difference in the distribution of pelagic organisms living in the overlying waters. The foraging behaviour of benthic communities on each sediment type is markedly different, however, so that sediment type can be determined from this parameter alone. It is suggested that the potentially richer food supply available at depth within the turbidites has produced the differences observed.
Geochemical characteristics and provenance of late Quaternary sediments from the Madeira Abyssal Plain, N Atlantic
Authors: de Lange Gert J. , Jarvis Ian , Kuijpers Antoon 
Published: April 2008

Summary

Late Quaternary sediments of the Madeira Abyssal Plain (MAP) consist of alternations of metre-thick distal turbidites and thin (centimetre to decimetre) pelagic clays, marls and oozes. The geochemical characteristics of 29 turbidites are described using major- and trace-element data from more than 350 samples. These were obtained from two representative piston cores located in the NE and W central parts of the MAP. Three separate groups of turbidites are defined by the geochemical data: (a) organic-rich, (b) ‘volcanic’ and (c) calcareous turbidites. ‘Organic’ turbidites contain 0.3–2% organic carbon. Their sediment originated from the lower continental slope of NW Africa N of 20°N, although one turbidite may have been derived from S of this latitude. ‘Volcanic’ turbidites contain a large proportion of volcaniclastic material and are distinguished by their high TiO
2
contents (about 1.5% on a carbonate-free basis). Much of their sediment originated from the oceanic islands of the Canaries and Madeira to the E. Calcareous turbidites are composed predominantly of pelagic carbonate and are defined by high CaCO
3
values (more than 75%). Their sediment was derived from the Great Meteor-Cruiser Seamount Chain, W of the MAP.
Geochemical oxidation fronts in NE Atlantic distal turbidites and their effects in the sedimentary record
Authors: Thomson J. , Colley S. , Higgs N. C. , Hydes D. J. , Wilson T. R. S. , Sørensen J. 
Published: April 2008

Summary
Overall sediment accumulation on the abyssal plain E of Great Meteor Seamount is dominated by distal turbidite deposition. A colour contrast is seen at the tops of many individual turbidites, so that a single turbidite has two distinct colour tones. Porewater data from the uppermost turbidite are used to demonstrate that these colour contrasts are consequences of an oxidation-front phenomenon. Distributions of organic carbon, uranium, vanadium and copper are proposed as diagnostic solid-phase indicators in both active and fossil types. A generalized description of the features of such turbidites is presented.
Trace-element mobility during early diagenesis in distal turbidites: late Quaternary of the Madeira Abyssal Plain, N Atlantic
Authors: Jarvis Ian , Higgs Nigel 
Published: April 2008

Summary

Sediments deposited on the Madeira Abyssal Plain (MAP) during the late Quaternary consist of an alternating succession of distal turbidites and pelagites. Individual turbidites may be correlated over most of the northern MAP. The sediment geochemistry of the succession has been investigated in detail using material from a representative 10 m piston core. The turbidites have been divided into organic-rich (at least 0.5% C
org
) and organic-poor groups. At the time of emplacement all turbidites were characterized by homogeneous major- and trace-element distributions, although thicker beds have thin silty bases of different compositions. Organic-rich turbidites, however, have undergone considerable early post-depositional modification as a result of oxidation of labile organic matter by sea-water oxygen diffusing downwards from the sediment-water interface. The progressive advance of oxidation fronts through the turbidites has produced distinctive two-tone colourations with light-brown tops and olive-green bottoms, and has caused significant early diagenetic relocation of iron, manganese, phosphorus, cobalt, copper, nickel, uranium, vanadium and zinc. Iron is marginally enriched in formerly oxic sediments. Manganese oxyhydroxides occur as dark-brown diagenetic laminations in recently oxidized turbidite tops, but have been dissolved by anoxic conditions in older examples. Mn
2+
pore-water profiles have been preserved by the adsorption of manganese by calcite. Phosphorus, cobalt, nickel and some copper were initially complexed by the precipitation of manganese oxyhydroxides and other processes occurring at active redox boundaries. Copper was also concentrated in the reduced sediments at this time. Later migration of these elements as reduced phases has produced thin purple diagenetic laminations in both turbidities and pelagites. Uranium, vanadium and zinc were relocated into reduced sediments during early diagenesis, but were not remobilized later. The diagenetic sequence in MAP sediments contrasts strongly with established ‘steady-state’ models based on hemipelagic and pelagic environments, but may be typical of a significant proportion of recent and ancient sequences.