bluuebunny/crossref_metadata_2025 huggingface dataset:
Human cutaneous reactive hyperaemia: role of BKCachannels and sensory nerves
Authors: Lorenzo Santiago , Minson Christopher T.
Published: September 2007

Reactive hyperaemia is the increase in blood flow following arterial occlusion. The exact mechanisms mediating this response in skin are not fully understood. The purpose of this study was to investigate the individual and combined contributions of (1) sensory nerves and large‐conductance calcium activated potassium (BKCa) channels, and (2) nitric oxide (NO) and prostanoids to cutaneous reactive hyperaemia. Laser‐Doppler flowmetry was used to measure skin blood flow in a total of 18 subjects. Peak blood flow (BF) was defined as the highest blood flow value after release of the pressure cuff. Total hyperaemic response was calculated by taking the area under the curve (AUC) of the hyperaemic response minus baseline. Infusates were perfused through forearm skin using microdialysis in four sites. In the sensory nerve/BKCaprotocol: (1) EMLA®cream (EMLA, applied topically to skin surface), (2) tetraethylammonium (TEA), (3) EMLA®+ TEA (Combo), and (4) Ringer solution (Control). In the prostanoid/NO protocol: (1) ketorolac (Keto), (2)NG‐nitro‐l‐arginine methyl ester (l‐NAME), (3) Keto +l‐NAME (Combo), and (4) Ringer solution (Control). CVC was calculated as flux/mean arterial pressure and normalized to maximal flow. Hyperaemic responses in Control (1389 ± 794%CVCmaxs) were significantly greater compared to TEA, EMLA and Combo sites (TEA, 630 ± 512,P= 0.003; EMLA, 421 ± 216,P< 0.001; Combo, 201 ± 200,P< 0.001%CVCmaxs). Furthermore, AUC in Combo (Keto +l‐NAME) site was significantly greater than Control (4109 ± 2777versus1295 ± 368%CVCmaxs). These data suggest (1) sensory nerves and BKCachannels play major roles in the EDHF component of reactive hyperaemia and appear to work partly independent of each other, and (2) the COX pathway does not appear to have a vasodilatory role in cutaneous reactive hyperaemia.
Release of ATP in the central nervous system during systemic inflammation: real‐time measurement in the hypothalamus of conscious rabbits
Authors: Gourine Alexander V. , Dale Nicholas , Llaudet Enrique , Poputnikov Dmitry M. , Spyer K. Michael , Gourine Valery N.
Published: September 2007

Receptors for extracellular ATP (both ionotropic and metabotropic) are widely expressed in the CNS both in neurones and glia. ATP can modulate neuronal activity in many parts of the brain and contributes to the central nervous control of several physiological functions. Here we show that during the systemic inflammatory response the extracellular concentrations of ATP increase in the anterior hypothalamus and this has a profound effect on the development of the thermoregulatory febrile response. In conscious rabbits we measured ATP release in real time with novel amperometric biosensors and monitored a marked increase in the concentration of ATP (4.0 ± 0.7 μm) in the anterior hypothalamus in response to intravenous injection of bacterial endotoxin – lipopolysaccharide (LPS). No ATP release was observed in the posterior hypothalamus. The release of ATP coincided with the development of the initial phase of the febrile response, starting 18 ± 2 min and reaching its peak 45 ± 2 min after LPS injection. Application of the ATP receptor antagonists pyridoxal‐5′‐phosphate‐6‐azophenyl‐2′,4′‐disulphonic acid, Brilliant Blue G or periodate oxidized ATP dialdehyde to the site of ATP release in the anterior hypothalamus markedly augmented and prolonged the febrile response. These data indicate that during the development of the systemic inflammation, ATP is released in the anterior hypothalamus to limit the magnitude and duration of fever. This release may also have a profound effect on the hypothalamic control of other physiological functions in which ATP and related purines have been implicated to play modulatory roles, such as food intake, hormone secretion, cardiovascular activity and sleep.
Wasp Gene Expression Supports an Evolutionary Link Between Maternal Behavior and Eusociality
Authors: Toth Amy L. , Varala Kranthi , Newman Thomas C. , Miguez Fernando E. , Hutchison Stephen K. , Willoughby David A. , Simons Jan Fredrik , Egholm Michael , Hunt James H. , Hudson Matthew E. , Robinson Gene E.
Published: September 2007

The presence of workers that forgo reproduction and care for their siblings is a defining feature of eusociality and a major challenge for evolutionary theory. It has been proposed that worker behavior evolved from maternal care behavior. We explored this idea by studying gene expression in the primitively eusocial wasp
Polistes metricus.
Because little genomic information existed for this species, we used 454 sequencing to generate 391,157 brain complementary DNA reads, resulting in robust hits to 3017 genes from the honey bee genome, from which we identified and assayed orthologs of 32 honey bee behaviorally related genes. Wasp brain gene expression in workers was more similar to that in foundresses, which show maternal care, than to that in queens and gynes, which do not. Insulin-related genes were among the differentially regulated genes, suggesting that the evolution of eusociality involved major nutritional and reproductive pathways.
A Bright Millisecond Radio Burst of Extragalactic Origin
Authors: Lorimer D. R. , Bailes M. , McLaughlin M. A. , Narkevic D. J. , Crawford F.
Published: September 2007

Pulsar surveys offer a rare opportunity to monitor the radio sky for impulsive burst-like events with millisecond durations. We analyzed archival survey data and found a 30-jansky dispersed burst, less than 5 milliseconds in duration, located 3° from the Small Magellanic Cloud. The burst properties argue against a physical association with our Galaxy or the Small Magellanic Cloud. Current models for the free electron content in the universe imply that the burst is less than 1 gigaparsec distant. No further bursts were seen in 90 hours of additional observations, which implies that it was a singular event such as a supernova or coalescence of relativistic objects. Hundreds of similar events could occur every day and, if detected, could serve as cosmological probes.
Escherichia coli
Physiology in Luria-Bertani Broth
Authors: Sezonov Guennadi , Joseleau-Petit Danièle , D'Ari Richard
Published: September 2007

Luria-Bertani broth supports
Escherichia coli
growth to an optical density at 600 nm (OD
600
) of 7. Surprisingly, however, steady-state growth ceases at an OD
600
of 0.3, when the growth rate slows down and cell mass decreases. Growth stops for lack of a utilizable carbon source. The carbon sources for
E. coli
in Luria-Bertani broth are catabolizable amino acids, not sugars.
TIME-DELAYED FEEDBACK IN A NET OF NEURAL ELEMENTS: TRANSITION FROM OSCILLATORY TO EXCITABLE DYNAMICS
Authors: GASSEL M. , GLATT E. , KAISER F.
Published: September 2007

The influence of time-delayed feedback on the dynamics of a net of oscillatory FitzHugh-Nagumo elements is investigated. We show that the global oscillation of the net can be suppressed (amplitude death) via time-delayed feedback for properly chosen delay time and feedback strength. The result of a linear stability analysis fits very well to the simulations. In the amplitude death regime, weak additive noise can induce excitation waves (noise-induced pattern formation), a fingerprint of excitable network dynamics.
SPATIO-TEMPORAL THERMAL FLUCTUATIONS AND LOCAL SUSCEPTIBILITY IN DISORDERED POLYMERS
Authors: ISRAELOFF N. E. , CRIDER P. S. , MAJEWSKI M. E.
Published: September 2007

Spatial and temporal fluctuations of the electric polarization were imaged in polymer thin films near the glass transition using electric force microscopy. Below the glass transition the fluctuations are quasi-static and spatial fluctuations were found to quantitatively agree with predictions for thermal fluctuations. Temporal fluctuations appear near the glass transition. Images of the space-time nanoscale dynamics near the glass transition are produced and analyzed. Local, complex dielectric susceptibility was also studied, and shows that dynamics on the free-surface are faster relative to the bulk.
RENORMALIZATION GROUP APPROACH TO THE EFFECT OF NOISE AT THE BIRTH OF A STRANGE NONCHAOTIC ATTRACTOR
Authors: KUZNETSOV SERGEY P. , SATAEV IGOR R.
Published: September 2007

Scaling regularities associated with additive noise are examined in a model of the pitch-fork bifurcation map with multiplicative quasiperiodic driving (Grebogi et al., Physica D13, 261) with the golden-mean frequency ratio at the birth of a strange nonchaotic attractor (SNA). This case of the onset of SNA termed as the blowout bifurcation route was discussed in the context of realistic systems governed by non-autonomous differential equations (Yalçynkaya and Lai, Phys. Rev. Lett., 77, 5039). Our method taking into the account of noise is based on renormalization group (RG) analysis of the birth of SNA (Kuznetsov et al., Phys. Rev. E51, 1629) with application of an appropriate generalization of the approach of Crutchfield et al. (Phys. Rev. Lett., 46, 933) and Shraiman et al. (Phys. Rev. Lett., 46, 935) originally developed for the period doubling transition to chaos. A constant γ=7.4246 is evaluated that determines the scaling law regarding the intensity of noise: A decrease of the noise amplitude by this factor allows resolving one more level of the fractal-like structure associated with the characteristic time scale which is increased by a factor of [Formula: see text]. Numeric results demonstrating evidence of the expected regularities are presented, e.g. portraits of the noisy attractors in different scales.
ON THE ORIGIN OF 1/F NOISE IN MOSFETS
Authors: VANDAMME L. K. J.
Published: September 2007

Often the 1/f noise in MOSFETs is stated to be an ensemble of many RTS with different time constants. The majority of literature on 1/f noise is overlooking the contribution due to mobility fluctuations that are uncorrelated with number fluctuations. Here, we demonstrate that the so-called proofs for Δ N can also be obtained from the empirical relation. The following misunderstandings and controversial topics on the surface and bulk contributions to the low-frequency noise will be addressed: 1) 1/f and RTS noise can have different physical origins. An analysis in time domain shows that the low-frequency noise with RTS is nothing else than a superposition of a two level noise with a Lorentzian spectrum and a Gaussian noise with a pure 1/f spectrum and different bias dependency. 2) It is very unlikely that in a spectrum consisting of one strong two level RTS and a pure 1/f noise, the 1/f noise is a superposition of many RTS with different time constants. 3) The spreading in WLS I /I2 below a critical WL is not a proof for the Δ N origin. 4) The typical shape in the double log plot from sub threshold to strong inversion of S I/ I 2 versus I , is also not a proof for the Δ N origin.
AVALANCHE CORRELATION IN POWER SPECTRA WITH WIDE PEAKS
Authors: EGGENHÖFFNER ROBERTO , CELASCO EDVIGE , CELASCO MARCELLO
Published: September 2007

The occurrence of wide peaks in the frequency range spanning fifteen decades from mHz to above THz was reported in the power spectra of many natural systems. Mostly, these spectral peaks appear superimposed to the 1/f noise. Actually, two different types of spectral peaks were picked out: a first type characterized by wide peaks and high 1/f slope of the overall spectral behavior, the second one by narrow peaks spanning less than one frequency decade and low slopes. Here we highlight the role of correlation among avalanches as the main source of the wide noise peaks observed. The present theory is based on first principle statistics of elementary events clustered in time-amplitude correlated avalanches. A spectral power master equation suitable to explain peaked noise spectra arising from avalanche correlations is achieved analytically. Excellent agreement with our experiments in superconductors and many other observations in biological and natural systems are reported. Our statistical model shows that avalanche correlation gives wide peaks in the power spectrum superimposed to the 1/f behavior with high slope, a typical signature of avalanche processes.
A marine foundation problem in the Arabian Gulf
Authors: Broadhead A.
Published: September 2007

The paper describes a foundation problem associated with a tanker berth at Das Island in the Arabian Gulf. The tanker berth, to accommodate 200 000 ton tankers, was constructed in 1967 using high tensile steel tubes drilled into the sea bed to form mooring and berthing dolphins. A jack-up platform was used for the installation of these cylinders and this platform subsequently became part of the permanent installation as the central island. Site investigation borings were sunk at the locations of each dolphin and calculations of the lateral resistance of the dolphin cylinders were made. The location where the lowest lateral resistance was indicated was chosen for a full scale site pulling test. The results of this test are described in the paper together with the methods used for the installation of the mooring and berthing dolphin cylinders.
Drilling techniques in ball clays
Authors: Vincent Anthony
Published: September 2007

In the strata of the Oligocene clay basins of Devonshire, wireline increases penetration rate by a factor of at least 3. It eases the casing problem and, in conjunction with mud flush, often obviates casing. Efficient bit design improves core recovery and cuts down costs. The wireline system, efficient bit design and mud flush have reduced costs on all cored footage, including the cost of grouting and the restoration of the disturbance to agricultural land, to £4·72 per metre, or £1·55 per foot.
Geotechnical aspects of shallow sewer tunnels in urban areas
Authors: Newbery John , Davenport Colin Anthony
Published: September 2007

Geology is an important determinant affecting the construction of tunnels. This paper gives the principal characteristics of three shallow sewer tunnels constructed with segmental and flexible linings in Kent and Worcestershire, England, where their location in urban areas adds additional geotechnical constraints to those generally encountered.

Methods of construction and rates of progress are shown to be controlled by lithology, structure, ground-water, recent human activity such as mining, quarrying and waste disposal, and the response of residents to blasting techniques.

These experiences show that even such exotic problems as those arising when tunnelling at shallow depth beneath refuse tips should be anticipated by careful investigation and that conflicting interests of residents and tunnellers should be resolved by sympathetic negotiation.
A geophysical investigation of saline water in the chalk of the South Coast of England
Authors: Monkhouse R. A. , Fleet M.
Published: September 2007

The Chalk on the South Coast of England between the rivers Adur and Ouse is in hydraulic continuity with the sea. Certain pumping stations up to 3.5 km from the shoreline have shown in the past abnormal chloride ion concentrations which have been considered to be due to seawater intrusion into the aquifer. Geophysical logging of boreholes especially drilled for the purpose close to the shoreline has confirmed the presence of saline water at various horizons, and has also shown diurnal variations in salinity due to the tide and seasonal variations related to infiltration and groundwater abstraction rates.
Case histories of some effects of solution/dissolution in the Keuper rocks of the Severn Estuary region
Authors: Hawkins A. B.
Published: September 2007

The Keuper strata in the Severn Estuary region can be divided into two fades, a scree/rock fan deposit known as the Dolomitic Conglomerate and a basin facies referred to as the Keuper Marl. Both facies contain gypsum or evidence indicating that gypsum was once present. As a result of diagenetic changes, such as the release of strontium when aragonite changes to calcite, and also calcite to dolomite, in some areas the initial gypsum, anhydrite accumulation has been replaced by celestine.

Recent construction works have indicated that in parts of the area cavities occur in the Keuper rocks. Some of these cavities have caused engineering problems. Those near the top of the Keuper Marl in the Airport Road tunnel caused machine stress due to the Dosco boom attempting to deflect to the areas of nil resistance. In addition, there was some overbreak and increased grout take.

Data obtained on samples from Llandough Quarry, Cardiff are presented to support the hypothesis that where dolomitic strata combine with gypsum, dedolomitization may occur resulting in degraded, very weak mudstone. Pronounced dolomitised ‘veins’ occur in one area of the quarry; these are described and X-ray diffraction traces are presented to support dolomitization from a joint outwards.
Soil pipes and slope stability
Authors: Pierson T. C.
Published: September 2007

Experimentation with a Hele-Shaw viscous-flow analogue apparatus has supported earlier suggestions, based on field evidence, that a causal link may exist between some soil pipes and slope failure. The analogue has shown that when a pipe is blocked or is a dead-end passageway (a closed pipe), the cavity can readily fill with water during rainstorms. Pipes partially filled with standing water will generate pore pressures in the surrounding soil matrix in proportion to the hydrostatic head achieved. Long pipes parallel to the fall line of the slope have the potential, when partially filled with water, of generating soil pore-water pressures much greater than those generated by total saturation of the soil. Such pore-pressure increases could trigger landslides at sites that would otherwise be stable.
Controls of size and shape of natural armourstone
Authors: Dibb T. E. , Hughes D. W. , Poole A. B.
Published: September 2007

The sizes and shapes of armourstone blocks for rubble breakwaters are primarily determined at the quarryface, and later modification then occurs
in situ
in the breakwater environment. The principal controlling parameters in the quarry include: rock type, rock joint frequency and orientation, size and type of blasting charge and the orientation of the blast's fractionating power.

The majority of existing data on this subject has been obtained from detailed studies of quarries principally concerned with aggregate production in Britain, but extensive studies have recently been carried out on a variety of rock types in quarries that are currently producing primary armourstone for breakwater structures in the United Arab Emirates and the United Kingdom. These studies combine to permit the relative importance of the various controlling factors which operate during quarrying, transport, placement and subsequently in service to be evaluated and are reported here.

The quarry-orientated study is supplemented by detailed studies of block modification and deterioration in the several different environmental zones of breakwater structures. The principal factors controlling this shape modification are micro-fracture pattern, mineralogy and fabric, grade of weathering of the original rock, grain interlock and intergranular cement type. Changes in shape will modify the stability factors of
in situ
armour blocks and alter void ratios and slope angles, which together are perhaps the most important factors controlling the dissipation of wave energies on rubble mound breakwaters.

The importance of long-term abrasion effects should not be underestimated; to monitor these effects, damage assessments have been used to relate the shape modification to slope.
A55 Pwll Melyn Slip and remedial works: a case history
Authors: Siva Subramaniam A. , Carr R. W.
Published: September 2007

In October 1976 a 7-year old road embankment, constructed on side-long ground across a stream valley to eliminate a bend, failed after a period of exceptionally heavy rainfall. Site investigation identified slip surfaces at the weathered and softened top of the mudstone bedrock. Fluvioglacial deposits encountered beneath and up-slope of the embankment were considered the main source of the high pore-water pressures responsible for failure. The remedial measures adopted included drainage provision to prevent the future build-up of pore-water pressures beneath the reconstructed embankment. The original road, carrying the diverted traffic since the time of the slip, was supported by a temporary, rock-anchored, sheet-pile retaining wall during the excavation of slip debris and weathered bedrock.

The events leading up to the slip, the subsequent site investigations and resulting design are described, together with the construction of the remedial measures.
Microprocessors and microcomputers: a review and implications for engineering geologists
Authors: Hill John J. , Young R. Paul
Published: September 2007

The low cost of microprocessor and microcomputer technology is such that microcomputers are finding wide application in many of the geological sciences and engineering. This paper, therefore, is aimed at providing an introduction to, and brief review of, the microcomputer field. The basic terms in use are explained and the main microprocessor chips and microcomputer systems surveyed. The distinction is made between systems which use embedded microprocessors and systems which provide enhanced capabilities by software development and interfacing to a personal microcomputer. A number of applications of microcomputers in engineering geology and engineering geophysics are used to illustrate the impact and scope of the new technology.
An example of tomographic and Fourier microcomputer processing of seismic records
Authors: New B. M.
Published: September 2007

A technique for processing seismic data has been developed that provides a ‘representative velocity’ tomogram which may be interpreted in terms of the engineering properties of the subject rock mass. This transmission system is intended for use in cross-borehole surveys and has been successfully tested between sub-parallel mine roadways in a massive granite body.

The velocities of compressional waves between numerous source and transducer locations are analysed, and the interactive character of the observations is used to build a two-dimensional array of computed ‘representative velocities’ appropriate to specific areas within the intervening rock mass. Evaluation of the processed data is undertaken using site-specific and more general rock mass classification systems. The processing is carried out on a CBM Pet microcomputer and the program is readily adaptable to most field configurations. The program also allows various mapping and influence parameters to be varied and optimized to obtain the best resolution of rock mass inhomogeneities.

Fast Fourier transform routines for the calculation of the energy spectral density (and other frequency domain functions) of ground vibrations are also briefly discussed.
Microcomputer based seismic instrumentation systems
Authors: Young R. P. , Hill J. J. , Green A. D. , Haigh R. N. , Middleton R.
Published: September 2007

Developments in microprocessor technology are having considerable influence on the way engineering seismic data is collected, processed and analysed. Case studies of two seismic instrumentation systems and their applications are described.

A microcomputer enhanced engineering seismograph, Geoseis-Merlin, has been developed as a portable repackaged Apple unit with a 5 inch monitor, internal printer, bubble memory and disk drive to give on-site processing and results. The unit includes a multi-channel, 12 bit analogue to digital converter card with programmable gain amplifiers, and the system is designed to operate in the field as a self-contained, six channel, seismic processing system. Menu-driven software operations include: data capture incorporating a pre-trigger memory facility for blast monitoring, concatenation and editing of files, display of seismic time data, seismic refraction analysis of up to 24 channels, power spectral computation, display of power and attenuation spectra, spectral smoothing, and digital filtering of waveforms. The system can also be used as an interface to existing seismographs or to the radio telemetric seismic monitoring system.

A 24 channel, radio telemetric, seismic monitoring system has been developed, consisting of six portable outstations which can be positioned up to 2 km from a base station located in a Land Rover or site office. Each microcomputer controlled outstation has one air overpressure and three ground vibration channels for recording up to 16 sec of pre-and post-trigger data. Communication between each outstation recorder and base is via a UHF duplex telemetry link which is used to activate and program each outstation, to maintain synchronization and to transfer data from each recorder to the microcomputer controlled base station. Here the captured seismic event can be stored on cassette, displayed on a 5 inch monitor, or transferred to an Apple II microcomputer (Geoseis-Merlin) for processing.

The case studies outline the application of these systems in engineering geology to bedrock depth determination, rock mass characterization, and the monitoring of quarry blasting.
Discussion on ‘Locating potential borehole sites in a discordant flow regime in the Chalk aquifer at Lulworth using integrated geophysical surveys’ by J. T. F. Houston, J. C. Eastwood & T. K. P. Cosgrove
Authors: Jones C. R. C. , Beeson S.
Published: September 2007

C. R. C. J
ones
and S. B
eeson
write: Mr Houston and his co-authors are to be congratulated on a valuable paper which describes the integrated use of the Geonics EM 34 and the ABEM SAS 300 Terrameter to locate potential borehole sites. A similar procedure was developed in Kano State, Nigeria for the siting of 429 boreholes in the Basement Complex which were drilled between 1984 and 1986. Much of the experience from Kano is relevant to the discussion of the Lulworth case history:

Fractures at depths of up to 60 m can be detected by using a 40 m coil spacing in the vertical dipole orientation. In areas of interest the EM 34 traverse should comprise both horizontal and vertical dipoles in order to define the depth and nature of conductivity features more fully. The vertical dipole orientation is insensitive to near-surface variations, which include the root zone, and the need for smoothing the data is reduced. The ratio of the results for the two orientations can be incorporated directly in the site selection criteria. Traversing with a range of coil spacings is possible but slower.

The specific electrical conductance (EC) of groundwater is as important as moisture content and rock type in governing overall geoelectric properties. In Kano State where EC values ranged from 0.02 to 1.0 ms cm
−1
, interpretation of the geophysical results required that the hydrochemistry be taken into account. No details are given for the Lulworth area; could EC differences (between pore water and fissure
J. H
ouston
, J. E
astwood
& T. Cosgrove reply
Authors: Houston J. , Eastwood J. , Cosgrove T.
Published: September 2007

We thank Mr Jones and Dr Beeson for their comments. The variation in electrical conductance between pore water and fissure water would have to be large to account for the observed variations in ground conductivity. Similarly for the variations between lithostratigraphic units. There is no evidence to suggest that this is the case at Lulworth.
Magmatism during and after continental break-up
Authors: White R. S.
Published: September 2007

Magmatism accompanying continental break-up is caused primarily by decompression melting of the underlying mantle as it wells up beneath the rift. The amount of melt produced depends mainly on the temperature of the asthenospheric mantle and on the rate of rifting. Break-up above normal mantle generates only small amounts of melt, reaching a maximum of 7 km in fully oceanic crust. If extension lasts for 10 Ma or more, as on many such ‘non-volcanic’ continental margins, then still less melt is generated because the slowly upwelling mantle cools by conductive heat loss.

Break-up above abnormally hot mantle surrounding mantle plumes generates much larger melt volumes and ‘volcanic’ continental margins. The largest melt volumes occur when rifting is above a newly initiated mantle plume, with its transient high excess temperatures and flow rates. This creates flood basalt provinces. The resultant basalt may flow distances of over 1000 km, both as surface flows and as dykes and sills intruded laterally in the crust. Only about one-quarter of the melt reaches the surface, the remainder underplating or intruding the lower crust. The excess gravitational potential provided by mantle plumes assists rifting, though plumes do not always cause continental break-up.
The lower lithosphere as a major source for continental flood basalts: a re-appraisal
Authors: Menzies Martin A.
Published: September 2007

Continental flood basalt provinces (cfb) have isotopic ratios different from midocean ridge basalts, characteristics that may be due to (a) interaction of asthenospheric melts with old crust, (b) melting of enriched continental lower lithosphere, (c) upwelling of deep mantle plumes containing recycled components, (d) mixing of enriched and depleted mantle sources, or (e) combinations of these processes. It is apparent that several aspects of the chemistry of cfb are subcrustal in origin and therefore crustal contamination cannot be invoked as a generally applicable hypothesis. In addition wholesale extraction of cfb from the lower lithosphere is unlikely because the lithospheric mantle is believed to be a rather thin (< 150 km) reservoir of cold, anhydrous, granular peridotite. Dry melting of such peridotites would not produce a normal ‘basalt’ because they have already experienced a melting event. Metasomatism or enrichment processes can enhance the chemical budget of the lower lithosphere thus providing an adequate reservoir for small volume alkaline and potassic melts. However no conclusive evidence exists that such modification of the lower lithosphere is widespread enough to generate a laterally continuous, wet, enriched reservoir. It would appear that cfb require a dominant sub-lithospheric component (plume) to account for the large volumes of magma, in some cases produced over a short time period (e.g. Deccan). If so, the heterogeneity observed in mantle-derived magmas within flood basalt provinces reflects inhomogeneities within plumes rather than relatively shallow inhomogeneities in the lithosphere. The apparent concentration of depleted (
87
Sr/
86
Sr ≪ 0.7045) cfb in the northern hemisphere and enriched cfb (
87
Sr/
86
Sr ≫ 0.7045) in the southern hemisphere may be linked to the preponderance of enriched plumes in the Southern Oceans.
Consequences of plume-lithosphere interactions
Authors: Saunders A. D. , Storey M. , Kent R. W. , Norry M. J.
Published: September 2007

Splitting or thinning of lithosphere above a mantle plume can result in voluminous melt generation, leading to the formation of large igneous provinces, or LIPs. Examples of LIPs include continental flood basalt provinces and oceanic plateaus. Basaltic samples from the Ontong Java Plateau, Nauru Basin and Manihiki Plateau, which are among the largest of the LIPs, have isotopic compositions within the range of ocean island basalts. The majority of continental basalts, however, record a trace element and isotopic contribution from the lithosphere through which they have erupted. We are thus unable to reconcile the available compositional data with models which derive the isotopic and large-ion lithophile element-enriched character of continental flood basalts solely from sub-lithospheric mantle plume sources. A combination of mantle sources is indicated, with the thermal energy being supplied by voluminous melts from a plume, and the lithospheric components in continental flood basalts being inherited by contamination of plume-derived melts by low melting point hydrous and carbonated fractions in the lithosphere. Successive injection of plume-derived melts serves to heat the lithosphere, reducing its viscosity and making it susceptible to rupture if allowed by regional plate forces. Furthermore, the lithosphere, including the mechanical boundary layer, may be thinned by thermal stripping from below, allowing the plume mantle to ascend and decompress further. Such a system has the potential for positive feedback leading to rapid melt generation. While we do not exclude recent models of LIP formation which require the sudden impact of a new mantle plume, we favour a model whereby the thermal anomaly builds gradually, incubating beneath a steady-state lithospheric cap.
Asthenosphere-derived magmatism in the Rio Grande rift, western USA: implications for continental break-up
Authors: Gibson S. A. , Thompson R. N. , Leat P. T. , Dickin A. P. , Morrison M. A. , Hendry G. L. , Mitchell J. G.
Published: September 2007

Magmas that are generated at continental rift zones provide an insight into the processes operating during the early stages of continental break-up. Our detailed study of mafic volcanism along the axis of the Rio Grande rift shows that, throughout both phases (30–17 and < 13 Ma) of its evolution, magmas with compositions interpreted as melts from the asthenospheric mantle have reached the surface. This recognition of early phase (26 Ma) magmas with incompatible trace element concentrations and radiogenic isotope ratios resembling those normally associated with ocean-island basalts and small seamounts (OIB) is significant because: (1) magmas dominated by the composition of asthenosphere-derived melts are not usually thought to be characteristic of early-phase continental rifting; (2) Tertiary mafic magmatism of an age greater than late Miocene in Colorado and New Mexico was hitherto regarded as subduction-related.

Previous studies have shown that the final erupted composition of asthenosphere-derived melts is determined by the potential temperature of the convecting mantle, the amount and rate of lithosphere extension, fractional crystallization and crustal contamination. However, in the Rio Grande rift and elsewhere, such as the Basin and Range province, Eifel, NW Sardinia and the Cameroon Line, the final composition of these melts is also significantly influenced by earlier magmatic episodes. During the initial stages of asthenosphere melt generation the magma batches that first penetrate may heat a previously undisturbed segment of lithosphere and mix with strongly potassic, low temperature melt fractions. When these segments have been subsequently temporarily purged of such fusible potassic fractions the asthenosphere-derived melts can rise unimpeded through the sub-continental lithosphere.
Role of subduction-plate boundary forces during the initial stages of Gondwana break-up: evidence from the proto-Pacific margin of Antarctica
Authors: Storey B. C. , Alabaster T. , Hole M. J. , Pankhurst R. J. , Wever H. E.
Published: September 2007

In the West Antarctic sector of Gondwana, early stages of break-up are associated with the large Antarctic-Karoo-Tasman basalt province. Formation of this
within-plate
province was synchronous with active margin tectonics and development of both a proto-Pacific margin magmatic suite along the Antarctic Peninsula and the extensive Tobífera volcanic suite associated with the Rocas Verdes marginal basin system of southern South America and South Georgia.

Extension, concurrent with subduction and oceanward migration of the magmatic focus, resulted in a broad extensional province in a back-arc and intra-arc-setting. High geothermal gradients and basalt underplating caused crustal melting on the east coast of the Antarctic Peninsula and formation of bimodal basalt-rhyolite suites. Large-ion lithophile element enriched initial rifting magmas were succeeded, at least in part of the Rocas Verdes basin, by early drift magmas of transitional chemistry and then by entirely asthenospheric MORB magmas representing lithospheric rupture and sea-floor spreading.

A plate interaction model is proposed for the initial stages of Gondwana break-up relating the broad zone of mantle melting to a reduction in subduction-plate boundary forces. The change from Gondwanide compression to lithospheric extension in the Jurassic may be linked to a change from shallow to steeply dipping subduction, and to a slowing of subduction rates caused by a change in plate boundary zone parameters. A possible reduction of compressive boundary stresses may have enabled unconfined, overthickened Permo-Triassic crust to extend because of gravitational instability, thus facilitating break-up. We suggest that break-up was not plume-related, but was due to variations in the regional stress field associated with changing plate-boundary forces. The continental crust was placed under tension with substantial lithospheric thinning and decompression melting of an enriched mantle source forming the broad linear zone of within-plate magmatism. The presence of a plume beneath the Karoo province may have thermally weakened the lithosphere and induced local rifting, contributing to, but not causing the eventual separation of East and West Gondwana.
Coats Land dolerites and the generation of Antarctic continental flood basalts
Authors: Brewer T. S. , Hergt J. M. , Hawkesworth C. J. , Rex D. , Storey B. C.
Published: September 2007

On the basis of geochemical signatures, Mesozoic magmatism in Antarctica is divided into the Ferrar Magmatic Province and the Dronning Maud Land Province. The tholeiitic magmatism of the Ferrar Magmatic Province is distinguished by such features as low Ti/Y (< 200) and Zr/Y (< 5.0) ratios, negative εNd values (< −3) and relatively enriched initial
87
Sr/
86
Sr ratios (> 0.709). All of these geochemical features indicate a major contribution from the continental mantle lithosphere in the generation of these magmas. In contrast, the Dronning Maud Land magmatism has elevated trace element ratios and εNd values (Ti/Y 250–600; Zr/Y 3.0–9.0; εNd −2 to +3) and lower initial
87
Sr/
86
Sr ratios (< 0.707) relative to the Ferrar Magmatic Province. The trace element and isotopic correlations suggest that these magmas were derived by the mixing of an OIB like asthenospheric component with a continental lithosphere component. The transition between these two geochemical provinces is located in Coats Land.

In Coats Land, the Mesozoic tholeiitic magmatism is represented by doleritic sills and minor dykes which intrude Permo-Triassic sedimentary rocks. The dolerites can be subdivided into two series based on their TiO
2
contents. Series 1 dolerites (TiO
2
< 1.5%) can be further subdivided into three groups, which give Ar/Ar ages of 171±6 Ma (Group 1) and 193±7 Ma (Groups 2 and 3). It is only Group 2 magmas which have trace element and isotopic signatures akin to the Ferrar Magmatic Province. Group 1 dolerites have geochemical signatures which are transitional between the Ferrar Magmatic Province and Dronning Maud Land magma types.

The Ferrar Magmatic Province signature in Coats Land is confined to the early magmatic episode (193±7 Ma) and this appears to mark the initiation of rift related magmatism in this region. It is argued that extension was limited and that most of the melt was derived from the continental mantle lithosphere. In contrast, the younger rocks (176±5 Ma) have relatively lower initial
87
Sr/
86
Sr and higher trace element ratios relative to the Ferrar Magmatic Province, and this appears to be associated with the later stages of rifting and relatively enhanced crustal extension which allowed for the encorporation of a small asthenosphere component.
The granites of northern Patagonia and the Gastre Fault System in relation to the break-up of Gondwana
Authors: Rapela C. W. , Pankhurst R. J.
Published: September 2007

The transcurrent Gastre Fault System in central Patagonia, which is closely associated with subvolcanic granite emplacement, is recognized as a major dextral shear-zone and geological boundary. We propose its equivalence to a Late Triassic-Jurassic precursor of the Aghulas Fracture Zone, allowing dextral displacement of the Southern Patagonian Block relative to the rest of South America during the earliest rifting phase of Gondwana break-up. This model could explain some of the inferred movement of the Falkland/Malvinas Islands and alleviate geometrical problems inherent in reconstructions of the South Atlantic region. It can also explain unique geological features of southern Patagonia, such as the Upper Triassic to Lower Jurassic calc-alkaline granitoids of the North Patagonian Massif and the extensive silicic volcanism of Mid-Late Jurassic times. The magmatism is seen as a consequence of the mechanism of Gondwana disintegration and it is not necessary to invoke a relationship to deep mantle structure or plume activity.
Paraná magmatism and the opening of the South Atlantic
Authors: Hawkesworth C. J. , Gallagher K. , Kelley S. , Mantovani M. , Peate D. W. , Regelous M. , Rogers N. W.
Published: September 2007

New chemical and isotope results are presented on dyke rocks associated with the Paraná CFB, together with preliminary laser
40
Ar/
39
Ar analyses on selected Paraná basalts. Dyke rocks from the Ponta Grossa Arch are similar to the Pitanga and Paranapanema magma types in the Paraná lavas, but dykes from the Santos-Rio de Janeiro section include samples with compositions not observed in the overlying lavas. Rather their minor and trace elements are strikingly similar to basalts recently erupted on Tristan de Cunha, and thus these late stage dykes may represent the first direct evidence for the involvement of typical plume-related OIB in the Paraná province. Laser
40
Ar/
39
Ar analyses of two Gramado low Ti basalts have yielded preferred isochron ages of 132.4 ± 1.4 and 132.9 ± 2.8 Ma. These indicate a short eruption time for at least the Gramado magma type, and that magmatism took place several million years after the species extinction in the Tithonian (
c.
141 Ma).

The majority of basalts and basaltic andesites in the Paraná CFB have distinctive trace elements ratios (low Nb/La and Nb/Ba), and relatively enriched Sr, Nd, and Pb isotope compositions. Since such features are not commonly observed in oceanic basalts, and they occur in CFBs which have been screened for the effects of crustal contamination, they are typically attributed to old, incompatible element enriched source regions in the continental mantle lithosphere. In some models the minor and trace element ‘mantle lithosphere’ component was introduced in small degree melts (lamproites) added to asthenosphere derived magmas. However, such models appear to be inconsistent with the data from low Ti CFB, and they also require that the asthenosphere derived magmas have very low incompatible element contents, in marked contrast to the high Nb/La late stage dykes in the Paraná. Alternatively some CFBs may have been generated within the mantle lithosphere in the presence of small amounts of water. The results of preliminary calculations indicate that in the presence of a mantle plume up to 5 km of melt may be generated entirely from within the mechanical boundary layer, for
β
values of less than 1.2.
Magmatism and continental rifting during the opening of the South Atlantic Ocean: a consequence of Lower Cretaceous super-plume activity?
Authors: Wilson Marjorie
Published: September 2007

Two large-scale mantle plumes, whose present-day foci are close to the oceanic islands of Tristan da Cunha and St Helena, appear to have played a significant role in the initial stages of rifting between Africa and South America during the Early Cretaceous opening of the South Atlantic Ocean. They may represent the initial burst of a super-plume event which generated extensive oceanic plateaux in the Pacific and Indian oceans.

The recent volcanic products of Tristan da Cunha and St Helena have near endmember Sr-Nd-Pb isotopic characteristics (EM I and HIMU) in the spectrum of ocean basalt isotopic compositions. These isotopic signatures are recognised for more than 100 Ma in the plume-related magmatic products and therefore appear to be a long-lived feature of the plume source. The history of rifting and magmatism in West and Central Africa/NE Brazil and in southern Brazil, above the broad heads of the initial starting plumes between 145 Ma and 130 Ma, strongly suggests that there are different physical differences between the two plumes in addition to chemical ones. The St Helena plume appears to have been much weaker and cooler, with a smaller buoyancy flux. The hotter Tristan plume has generated voluminous flood basalts volcanism in the Paraná basin of Brazil and appears to be associated with continental break-up within a few million years of the plume head impinging on the base of the lithosphere. In contrast, in West and Central Africa, rifting above the St Helena plume, associated with small volumes of alkaline-transitional magmatism, spans an extended period of 30–40 Ma before break-up occurs in the Equatorial Atlantic.
New geophysical evidence for extensional tectonics on the divergent margin offshore Namibia
Authors: Light M. P. R. , Maslanyj M. P. , Banks N. L.
Published: September 2007

Over 14 000 km of high-resolution multifold seismic data together with gravity and magnetic data provide the opportunity to examine the mechanism and history of rifting on the Namibian continental margin. The region is a completely developed divergent margin containing a pre-rift megasequence of interior cratonic sag origin; two rift basin megasequences dominated by siliclastic deposition; a transitional megasequence and thermal sag megasequences dominated by overlapping progradational wedges. In the Orange Basin acid to intermediate volcanic rocks erupted at the end of the pre-rift phase in Mid- to Late Jurassic times and this was followed by regional uplift. Basaltic volcanic activity was associated with the synrift phases and widespread volcanic rocks developed during the second synrift event, related to the Tristan da Cunha-Walvis Ridge mantle plume. Regional seismic mapping indicates that rifting migrated from south to north with time. The geophysical data enable the recognition of major structural elements which include the Eastern Graben Province, the Medial Hinge Line, the Central Half Graben and the Marginal Ridge. The geometry of the rift basin is asymmetric and can be explained by a simple shear mechanism. South of Walvis Ridge extension was accommodated by movement along a major normal fault which is listric at depth. The basin depocentre represented by the Central Half Graben lies landward of this major fault and is offset from the area of thinnest crust as interpreted from the gravity data.