bluuebunny/crossref_metadata_2025 huggingface dataset:
The use of dynamic reaction cell ICP mass spectrometry to facilitate Rb-Sr age determination
Authors: Vanhaecke F. , De Wannemacker G. , Balcaen L. , Moens L.
Published: April 2008

By using a set of granitic whole rock samples, originating from the Regensburg Forest (Germany) and dated (approximately 350 Ma old) previously by means of thermal ionization mass spectrometry (TIMS), the capability of dynamic reaction cell (DRC) inductively coupled plasma mass spectrometry (ICPMS) for Rb-Sr age determination was demonstrated. With DRC-ICPMS, chemical separation of Sr from Rb during the sample pretreatment is no longer required as interference-free determination of the
87
Sr/
86
Sr isotope ratio can be accomplished by monitoring the signals of the SrF
+
adduct ions, formed as a result of the selective reaction between the Sr
+
ions extracted from the ICP and the reaction gas CH
3
F. The mass discrimination was established to depend strongly on the matrix composition. This drawback could be overcome by using the United States Geological Survey reference material G-2 as an external standard. Results obtained by DRC-ICPMS (age and initial
87
Sr/
86
Sr ratio) showed an excellent agreement with both (a) experimental values obtained by means of quadrupole-based and sector field ICPMS after isolation of Sr via cation exchange chromatography and (b) TIMS literature values. In addition, DRC-ICPMS offers a smaller combined uncertainty on the isotope ratio results as a result of (a) an improved internal isotope ratio precision (<0.1% RSD when also using Ne as an additional non-reactive collision gas) and (b) the fact that, in contrast to quadrupole-based and sector field ICPMS, no correction for the remaining overlap between the signals of
87
Sr
+
and
87
Rb
+
is required.
Melt segregation rates in migmatites: review and critique of common approaches
Authors: Kriegsman Leo M. , Nyström Annika I.
Published: April 2008

The rate of melt segregation in regional migmatite terrains can be estimated by various lines of research. Firstly, the segregation rate of a melt batch, with a volume below the melt percolation threshold, cannot exceed the melt production rate and is therefore limited by the heating rate derived from geothermometry and geochronology (method A). Other estimates come from physical models for melt percolation (method B) and from the degree of (dis)equilibrium reached between melt and source rocks (method C). The first method is restricted by the current time resolution of isotopic techniques. Results from the second and third approaches depend heavily on assumed values of melt viscosity and other parameters (B); on the correct recognition of (dis)equilibrium trace element distributions (C); and on the migmatization model used (B and C).

The validity of method C is undermined by the mathematical equivalence of trace element models for five different scenarios: (1) disequilibrium melting (with or without melt escape) followed by
in situ
crystallization of non-segregated melt; (2) equilibrium melting, followed by equilibrium crystallization and major melt escape; (3) disequilibrium melting, followed by equilibrium crystallization and minor melt escape; (4) pervasive retrograde re-equilibration; and (5) subsolidus differentiation. Hence, trace element data in support of model 1 (implying fast melt segregation rates) are equally consistent with models 2 to 4 (implying slow melt segregation rates), and even with melt-absent model 5. The level of trace element saturation reached during accessory phase dissolution into melt may not provide better answers, as it is largely controlled by textural constraints, e.g. shielding of accessories by porphyroblasts.

We conclude that the way forward is to directly couple microtextural and microgeochemical information with time constraints. This requires high-resolution (space and time) geochronology, possibly with more advanced methods than presently available.
40
Ar/
39
Ar ages in mantle xenolith phlogopites: determining the ages of multiple lithospheric mantle events and diatreme ascent rates in southern Africa and Malaita, Solomon Islands
Authors: Wartho Jo-Anne , Kelley Simon P.
Published: April 2008

Kimberlites are extraordinary natural phenomena, ascending through the Earth’s lithosphere, entraining xenoliths, to erupt at the surface within hours to days of their inception deep within the lithospheric mantle. With the realization that some Ar/Ar phlogopite grain core ages may be indicative of geological events, we have undertaken high spatial resolution Ar/Ar dating of phlogopites in xenoliths and megacrysts from Kimberley, Monastery and Letseng in southern Africa, and Malaita, in the Solomon Islands, to est whether other mantle phlogopite cores may yield meaningful ages.

Modelling of Ar diffusive loss profiles from phlogopite grain boundaries to cores provides information on both the eruption age and the duration of outgassing within the kimberlite magma, and hence yields estimates on diatreme ascent rates. The ascent durations are very similar for all of the southern African pipes studied, yielding durations of 0.9–6.9 days, assuming an average kimberlite magma temperature of 1000 °C. These can be compared to estimates from phlogopite xenoliths from Siberian diamond-bearing kimberlites yielding ascent durations of 2–15 hours (assuming the same magma temperature).
The Tertiary Grès de Ville of the Barrême Basin: feather edge equivalent to the Grès d’Annot?
Authors: Evans Martin J. , Elliott Trevor , Apps Gillian M. , Mange-Rajetzky Maria A.
Published: April 2008

The Tertiary Grès de Ville in the Barrême Basin of the French Alps is conventionally considered to be the feather edge equivalent to the Grès d’Annot to the east. Both units accumulated in a province of thrust-sheet-top basins behind the initial thrust front and were supplied from a southerly hinterland (Maures-Esterel/Corsica-Sardinia). The units are also partially coeval, with the Grès de Ville being equivalent to the youngest part of the Grès d’Annot. However, the units accumulated in structurally distinct sub-basins that were separated by a fold (the St Lions anticline) that was growing at the time of Grès de Ville deposition. The Grès de Ville accumulated close to storm wave base, whereas deposition of the Grès d’Annot was notably deeper, indicating that the Barrême Basin was structurally higher than the Grès d’Annot Basin. There is also evidence that the Grès de Ville and the Grès d’Annot were fed by separate sediment transport paths linked to different drainage basins in the hinterland. It is therefore an oversimplification to regard the Grès de Ville as a feather edge to the Grès d’Annot; instead it should be regarded as an independent element of the fill of the Barrême Basin.
Three-dimensional stratigraphic modelling of the Grès d’Annot system, Eocene-Oligocene, SE France
Authors: Euzen T. , Joseph P. , Du Fornel E. , Lesur S. , Granjeon D. , Guillocheau F.
Published: April 2008

The Eocene-Oligocene Grès d’Annot series of SE France is a well-known turbidite system for sand-rich gravity deposits. The Grès d’Annot were deposited in several parallel and tectonically controlled elongated sub-basins in the western Alps foreland setting. Regional stratigraphic correlation is used to reconstruct and simulate in three dimensions the large-scale geometry and facies distribution of the Grés d’Annot in the Annot and Trois Evêchés sub-basins. The input parameters of the model are the accommodation, the sediment supply and the transport parameters. These are estimated from the geological model and subsequently adjusted in order to fit the simulation with selected sedimentological sections. From the analysis of the three-dimensional simulated block and of the adjusted input parameter set, an interpretation is proposed in which the relative contribution of external factors controlling the stratigraphic architecture are estimated. The first-order parameters that control the large-scale stratigraphic architecture are the initial basin physiography, the basin-floor deformation and the sediment supply variations through time and space. Small-scale folding and large-scale flexuration of the substratum control the confinement of the system and the available space for sedimentation. Sediment supply and water discharge variations through time are responsible for high frequency (fourth-order) and low frequency (third-order) stratigraphic cycles. This interpretation fits well with a model of a flood-dominated fluvio-turbidite ramp system in which physical continuity exists between the fan delta and the basinal turbidites. In such a tectonically active and confined basin, third- and fourth-order stratigraphic cyclicity might respectively result from uplift-denudation cycles and climatic variations through time. Tectonic activity in the source area may also be responsible for the migration of the main feeding system.
The character and origin of thick base-of-slope sandstone units of the Peïra Cava outlier, SE France
Authors: Lee Simon E. , Amy L. A. , Talling P. J.
Published: April 2008

Many hydrocarbon reservoirs occur within confined turbidite systems in which the depositional pattern of turbidity currents has been strongly influenced by basin-floor topography. In certain settings basin-floor topography may cause the development of anomalously thick (tens of metres) sandstones that are potentially excellent reservoir units. Southern exposures of the Peïra Cava outlier (Eocene-Oligocene; Annot Sandstones) provide well-exposed outcrops of such decametre-thick sandstone bodies. These units are located close to basin margins and downstream from an inferred topographic break-in-slope. Several base-of-slope sandstone bodies are examined that illustrate a common sedimentary theme of a complex basal unit, comprising laterally pinching or inter-fingering debrite and turbidite, abruptly overlain by a single, thick normally graded turbidite deposit. One of these sandstone bodies pinches out laterally over less than several hundred metres and sits within a deep (>20 m) ‘spoon shaped’ erosional scour. The scour is similar to morphological features observed in modern base-of-slope settings recently imaged using high-resolution submarine bathymetric surveys. Several different process interpretations may explain the occurrence of such sandstone bodies including remobilization of newly deposited sediment off basinmargins and enhanced deposition due to flow across a break-in-slope. A submarine channel interpretation is not consistent with the field observations. However, these units do share a number of similar features to channels that could lead to the misinterpretation of reservoir geometry.
The Grès d’Annot in the Annot syncline: outer basin-margin onlap and associated soft-sediment deformation
Authors: PuigdefàBregas Cai , Gjelberg John , Vaksdal Monica
Published: April 2008

The Grès d’Annot onlap on the outer basin margin has been extensively studied, but a number of important issues and critical outcrops remain controversial. A new geological map of the Annot syncline is here presented, supplemented with structural and sedimentological field observations. The mapped onlap traces in Annot reveal a curved, east-concave surface, with distinct westward shift of the successive onlap lines. The inferred onlap direction at Chalufy is to the SW, the only orientation compatible with the movement of the normal fault near Cabane des Abeurons. The similarity of the onlap relations between the areas of Annot and Chalufy, together with the structural features of the Annot syncline, support the concept of a common outer basin margin, rather than of a northern confinement of the Annot turbidites. The margin-onlap setting involved a specific style of syndepositional deformation. As a large, high-density turbidity current arrived on the basin-flank slope, it rapidly decelerated, thickened and dropped its coarse load, while being simultaneously deflected away from the slope. The associated normal stress and overpressure caused sub-horizontal injection and de-lamination of the soft substrate, with the tangential strain curling up the detached substrate slice into an overturned synclinal structure. The process provides an efficient way to incorporate fragments of mudstone and thin-bedded sandstone within the still moving highly-concentrated flow, eventually constituting the chaotic intervals within ‘tri-partite’ beds as the examples observed at the Braux section.
Onlap stratal architectures in the Grès d’Annot: geometric models and controlling factors
Authors: Smith Ru , Joseph Philippe
Published: April 2008

Onlap terminations of deep-marine sandstones in the Grès d’Annot, SE France, exhibit a range of styles, from abrupt onlap to feathering ‘aggradational onlap’ geometries. These are well exhibited in the large exposure of southward onlap terminations at Montagne de Chalufy, on the southern end of the Trois Evêchés Massif (Alpes de Haute Provence). These stratal architectures are here simulated by geometrical models that are governed simply by bounding slope gradients and the ratio of coeval slope to basinal aggradation rates. In cases of no coeval deposition on bounding slopes, pure onlap results. In cases of high slope aggradation rates relative to basinal aggradation rates, a feathered geometry results with successive sandstone beds onlapping against successively younger slope drapes. The cyclicity of alternating sand-rich and sand-poor packets seen at Chalufy results in a stepped climbing trajectory of successive slope base positions, with climb angle equal to bounding slope angle when mud-poor sandy flows deposited sandstone bodies with abrupt onlap, and climbing more steeply when slope drapes are deposited. An implication of this result is that any zones of facies change and palaeocurrent swing that are related to distance from bounding slope will exhibit a comparable vertical trajectory through time. The two end member termination types can be compared with the convergent-baselapping and convergent-thinning seismic facies used in the Gulf of Mexico subsurface and elsewhere. The convergent-baselapping seismic facies may include both abrupt onlap and intervals of feathering aggradational onlap if the presence of slope drapes is not resolvable by the frequency content of the available seismic data.
Key controls on the characteristics of turbidite systems
Authors: Bouma Arnold H.
Published: April 2008

Four main controls (tectonics, climate, sedimentary characteristics and processes, and sea-level fluctuations) commonly interact with each other and do so at varying intensities. This results in a wide variety of basin types and shapes, timing of transport within the sequence stratigraphy framework, transport and depositional processes, grain size ranges, and distribution of sediment within a basin. Two major end members of turbidite systems can be recognized: coarse-grained/sand-rich and fine-grained/mud-rich. Coarse-grained fans typically belong to active margin settings. They prograde gradually into a basin and show a decrease in thickness and grain size in the downflow direction. The sediment source is near the coastline, and the turbidite basins are commonly small to medium in size. The fine-grained fans occur on passive and active margins, prograde rapidly into a basin, and deposit most of the input sand in the distal fan as oblong sheet sands. Tectonically confined basins normally have their sediment source nearby, and therefore will be filled with coarse-grained fans. Most of the open (unconfined) basins are medium to large in size, have their sediment source far from the coast, and therefore lose the coarser fractions during continental transport. Diapirically controlled basins are small- to medium-sized confined basins that have a fine-grained turbidite fill, but may not reveal the bypassing of the majority of the sand to the outer fan because of the abundance of sediment transport to the basin.
Present morphology and depositional architecture of a sandy confined submarine system: the Golo turbidite system (eastern margin of Corsica)
Authors: Gervais Anne , Savoye Bruno , Piper David J. W. , Mulder Thierry , Cremer Michel , Pichevin Laetitia
Published: April 2008

The modern sandy Golo turbidite system (500 km
2
) is located in a confined basin on the eastern margin of Corsica. The Golo turbidite system is fed by a single river, which supplies coarse sand derived from active weathering of the neighbouring mountains. The late Quaternary deposits have been imaged using a closely spaced grid of 1000 km of sparker seismic-reflection profiles (line spacing close to 1.6 km, vertical resolution of 2m). The turbidite system is composed of four non-coalescent fans that were at times active simultaneously and of two small deposits onto the slope. The resulting sedimentation pattern is characterized by stacked turbidite deposits. At a regional scale, there is a continuum of fan morphologies and geometries from south to north. The use of both seismic and sedimentary facies, together with mapped seismic geometry of sedimentary bodies, allowed definition of four architectural elements: (1) submarine valley (canyon and gully), (2) sandy channel, (3) muddy levee, and (4) sandy lobe. Some of these architectural elements can be recognized at a scale that is comparable to outcrop examples. Features such as progressive lateral migration and avulsion, or complex longitudinal evolution (progradation and retrogradation), can also be accurately described. Despite the active tectonics along the studied margin, the main variations in sedimentation appear to be controlled by eustatic changes, pre-existing seafloor topography, and sediment source characteristics. The general pattern of sedimentation is controlled by the influence of a confining slope, leading to the predominance of aggradation and to specific morphology and architecture of sedimentary bodies.
Multiple terraces within the deep incised Zaire Valley (ZaïAngo Project): are they confined levees?
Authors: Babonneau N. , Savoye B. , Cremer M. , Bez M.
Published: April 2008

Terraces have been frequently observed and described along turbidite valleys. Many interpretations have been aimed at determining the origin of these structures, including a tectonic origin, succession of infilling and incision processes, channel-wall slumps, or inner levee aggradation. The Zaire submarine valley presents a complex structure with multiple terraces bordering a deep incised meandering thalweg. The detailed analysis of the morphology, the seismic structure and the recent sedimentation (in cores) along the Zaire upper-fan valley show that terraces are inner levees confined within the incised valley. Many terraces correspond to the infilling of abandoned meanders, and aggrade by deposition of turbidite sequences due to current overflows. The major process affecting the initiation and the development of terraces inside the valley is the vertical incision of the thalweg, simultaneously with meander migration.
Basin-floor fans of the Central Tertiary Basin, Spitsbergen: relationship of basin-floor sand-bodies to prograding clinoforms in a structurally active basin
Authors: Crabaugh Jeff P. , Steel Ronald J.
Published: April 2008

Lower Eocene shelf-slope clinoforms are exposed in 1 × 10 km mountainside outcrops in the Central Tertiary Basin, Spitsbergen. Where clinoforms are sand-prone they include a deepwater sand complex. Submarine fans represent an early, basin-floor aggradational phase of clinoform growth, whereas later growth of the same clinoform involves a phase of shelf-margin accretion. Individual fans, within stacked series, can be distinguished when traced towards the slope, where a thickening wedge of mudstones separates successive fan bodies. The sand-prone parts of basin-floor fans are some 15–60 m thick and extend into the basin by up to 10–12 km. The lower levels of any fan consist of ripple- to parallel-laminated thin-bedded turbidites interbedded with some thick-bedded turbidites. This association changes irregularly upwards to a succession dominated by thick beds that are structureless and parallel-laminated. The thin-bedded facies are interpreted as turbidite sheets that formed as channel-mouth sandy lobes, sandy levees and crevasse splays. The erosively based, thick-bedded facies are interpreted as constructional channel-fill sandstones. The shallow channels fed sheet-complexes both laterally and distally. The apparent short basinward extent and longitudinal palaeocurrents for the youngest fans suggest that downslope sediment transport became longitudinally deflected by anticlinal topography once sediment reached the basin floor.
Submarine fans within small basins: examples from the Tertiary of New Zealand
Authors: Zink Christoph , Norris Richard J.
Published: April 2008

This study uses the example of two small sedimentary basins to draw lessons for the stacking patterns of submarine fan facies in restricted basins. The Te Anau and Waiau basins are located in southwest New Zealand. They developed from the Middle Eocene onwards close to and under the direct influence of the evolving Australia-Pacific plate boundary. Although never more than a few tens of kilometres wide, both basins accumulated sedimentary successions more than 6 km thick. We discuss the scale, nature and composition of submarine fans within the basins. Sediment stacking patterns are characterized by rapid lateral and vertical changes within the full range of facies predicted by most submarine fan models. Despite the small basin size, some submarine fans contain sandstone bodies of impressive thickness (50 m) and many kilometres lateral extent. Such bodies of well-sorted, highly permeable sandstone are excellent potential hydrocarbon reservoirs. The occurrence of complete Bouma sequences and well-developed couplets of clastic- and hemipelagic mudstones indicates that such features are not restricted to large-scale fans (covering thousands of square kilometres). Even in small sedimentary basins, submarine fans can develop that show an impressive range of sedimentary facies and architectural elements, commonly described only from their large-scale counterparts.
Reservoir modelling of the Hamitabat Field, Thrace Basin, Turkey: an example of a sand-rich turbidite system
Authors: Conybeare D. M. , Cannon S. , Karaoğuz O. , Uygur E.
Published: April 2008

The inter-montane, fault bounded Thrace Basin of northwestern Turkey is one of the largest Tertiary sedimentary basins in Turkey. Tertiary sedimentation within the basin comprises interbedded fine- to coarse-grained clastics from a variety of depositional environments, muddy carbonates with local reef developments, and tuff horizons. A thick pile of Quaternary alluvial deposits overlies this marine-dominated succession. Accommodation space, and hence sedimentation, has been influenced by the structural history of the basin, reflecting the active compressional setting adjacent to the North Anatolian Fault System. The Hamitabat Field, located towards the northern basin margin, is the largest developed gas field in the Thrace Basin. The trapping mechanism is by an anticlinal structure bounded to the north by a northwest-southeast striking reverse fault and to the south by a set of antithetic normal faults with a general east-west strike orientation. The main reservoir is the middle to upper Eocene Hamitabat Formation, comprising sandstones deposited by episodic gravity flow events in a shallow marine shelf to slope environment, with sediment sourced from fluvial/deltaic systems to the north and northeast. Correlation, based mainly on upward-fining cyclical successions, indicates lobate depositional geometries and topographic control on sediment dispersal (compensation). Progradational shallow marine sandstones, which infill earlier topography, overlie the turbidite succession. A three-dimensional geocellular reservoir model of the field, based on well and seismic data, has been constructed. The model has been subdivided on the basis of the stratigraphical correlation and populated with facies objects with dimensions based on analogue data. These facies have then been populated with petrophysical parameters. The model has been upscaled and simulated fluid flow through the modelled volume has been compared with the production history. This history matching provides an opportunity to assess and refine the model and to determine a strategy for future field development.
Late Carboniferous-Permian of NW Europe: an introduction to a new regional map
Authors: Heeremans Michel , Faleide Jan I. , Larsen Bjørn T.
Published: April 2008

The Carboniferous-Permian evolution of NW Europe has recently been the focus of an EC-funded Training and Mobility of Researchers (TMR) project ‘Permo-Carboniferous-Rifting in Europe’ (PCR). One of the main goals of this project was to produce a new map for this time period showing the distribution of Late Carboniferous-Early Permian (Lower Rotliegend) volcanics, dykes and sills, and the extent of the tectonic structures of the Early-Late Permian (Upper Rotliegend) sedimentary basins (better known as the Southern and Northern Permian Basins). In order to produce this map, an overview of all the available literature was made. The new map was completed based on our own interpretations from seismic and borehole data. Unpublished data were available through industrial partners associated with the PCR project.
Late Carboniferous-Permian tectonics and magmatic activity in the Skagerrak, Kattegat and the North Sea
Authors: Heeremans Michel , Faleide Jan Inge
Published: April 2008

This study focuses on Late Carboniferous-Permian tectonics and related magmatic activity in NW Europe, and specifically in the Skagerrak, Kattegat and North Sea areas. Special attention is paid to the distribution of intrusives and extrusives in relation to rift-wrench geometries. A large database consisting of seismic and well data has been assembled and analysed to constrain these objectives. The continuation of the Oslo Graben into the Skagerrak has been a starting point for this regional study. Rift structures (with characteristic half-graben geometries) and the distribution of magmatic rocks (intrusives and extrusives) were mapped using integrated analyses of seismic and potential field data. For the analysis of the Sorgenfrei-Tornquist Zone and the North Sea, seismic and well data were used. The rift structures in the Skagerrak can be linked with extensional structures in the Sorgenfrei-Tornquist Zone in which similar fault geometries have been observed. Both in the Skagerrak and in the Kattegat, lava sequences were erupted that generally parallel the underlying Lower Palaeozoic strata. This volcanic episode, therefore, pre-dates main fault movements and the development of half-grabens filled with Permian volcaniclastic material. Upper Carboniferous-Lower Permian extrusives and intrusives have also been found in wells in the Kattegat, Jutland and the North Sea (Horn and Central grabens). Especially in the latter area, the dense seismic and well coverage has allowed us to map out similar Upper Palaeozoic geometries, although the presence of salt often conceals the seismic image of the underlying strata and structures. From the results, it is assumed that the pre-Jurassic structures below large parts of the Norwegian-Danish Basin and northwards into the Stord Basin on the Horda Platform belong to the same tectonic system.
Geochemistry and mineralogy of Rotliegend metavolcanic mafic rocks from Poland: pervasive low-grade metamorphism versus parent rock signature
Authors: Dubińska Elżbieta , Bylina Paweł , Bagiński Bogusław , Kaproón Grzegorz , Kozłowski Andrzej
Published: April 2008

Permian volcanic rocks from the Gorzów Wielkopolski region (NW Poland), although pervasively altered by low-grade metamorphism, still preserve the geochemical characteristics of continental mafic volcanic rocks formed by partial melting of an enriched mantle source. The metamorphic assemblage comprises corrensite, pumpellyite, laumontite, quartz and chalcedony, albite, calcite and solid bitumen (major components). Petrological studies combined with microthermometric determinations indicate a low-pressure zeolite-greenschist-facies transitional zone metamorphic grade with a clockwise (pressure-temperature)
P-T
path: earliest event 140–210 °C and 630–760 bar; metamorphic peak 220–300 °C and 950 bar; youngest episode:
T
⩾ 130 °C and 630–760 bar.

The metamorphism of the Rotliegend volcanic rocks is generally ascribed to penetration of upwelling fluids released from clastic rocks underlying the extrusive Permian unit. However, the ubiquitous occurrence of anhydrite in the altered volcanic rocks suggests an influence of pore water from the overlying Zechstein evaporite sequence. The source of metamorphic heat can be tentatively assigned to abnormal heat flow and/or exothermic reactions during magmatic mineral alteration processes. Dating of metamorphism in neighbouring areas suggests an Upper Jurassic thermal event related to the upwelling of a mantle diapir during the initiation and early evolution of the North Atlantic rift.
Carboniferous-Permian mafic magmatism in the Variscan belt of Spain and France: implications for mantle sources
Authors: Perini G. , Cebria J. M. , Lopez-Ruiz J. , Doblas M.
Published: April 2008

Carboniferous-Permian magmatism in the Spanish Central System, Iberian Ranges, Cantabrian Chain, Pyrenees (Maladeta plutonic complex) and the French Massif Central includes a range of mafic calc-alkaline and shoshonitic rock types, as well as amphibole-bearing lamprophyres (spessartites) and minor alkaline lamprophyres (camptonites). Subalkaline basalts with intermediate characteristics between enriched mid-ocean ridge basalts (E-MORB) and the mafic calc-alkaline rocks also occur in the Pyrenees (Panticosa, Cinco Villas and La Rhune). The incompatible trace-element characteristics of the least differentiated subalkaline rocks and lamprophyres indicate that variably enriched mantle sources were involved in their genesis. High large ion lithophile element/high-field-strength element (LILE/HFSE), light rare earth element (LREE) HFSE and low Ce/Pb ratios in the calc-alkaline and shoshonitic rocks require either assimilation of crustal rocks plus fractional crystallization (AFC) of the parental mafic magmas or melting of a previously subduction-modified mantle source. In the Cantabrian Chain and the Massif Central, melting of a subduction-modified mantle source seems more likely. In the Central System, Iberian Ranges and Maladeta area the lack of any evidence for a contemporaneous subduction system suggests that AFC processes were more likely to be responsible for the crustal signature of the magmas. The alkaline camptonites from the Central System were generated from an enriched mantle source, which had lower LREE/HFSE and LILE/HFSE ratios than the source of the older calc-alkaline magmas from the same area. The incompatible trace-element patterns and ratios (e.g., Y/Nb, Zr/Nb) of the subalkaline basalts from Panticosa, Cinco Villas and La Rhune suggest that they were generated from similar parent magmas, formed by mixing of partial melts of an asthenospheric source and a crustal component.
Shear zones in the upper mantle: evidence from alpine- and ophiolite-type peridotite massifs
Authors: Dijkstra Arjan H. , Drury Martyn R. , Vissers Reinoud L. M. , Newman Julie , Van Roermund Herman L. M.
Published: April 2008

There is abundant field and microstructural evidence for localization of deformation in alpine- and ophiolite-type mantle massifs. On the basis of field relationships and microstructures we recognize two types of tectonite shear zones (medium- to coarse- and fine-grained), as well as two types of mylonitic shear zones (anhydrous and hydrous peridotite mylonites). In tectonite shear zones, softening processes responsible for localization are probably melt-related weakening in the medium to coarse tectonites and a change in limiting slip system in the fine-grained tectonites. In peridotite mylonites, the most likely cause for softening and localization is a change in dominant deformation mechanism from dislocation to grain size sensitive creep. Microstructural and petrological study of mylonite rocks reveals that reactions, either continuous net-transfer reactions (anhydrous and hydrous) or melt-rock reactions, play a key role in the formation of fine-grained material that promotes grain size sensitive creep. These reactions occur over a broad range of pressure-temperature conditions encompassing a large part of the lithospheric upper mantle. We conclude that mantle shear zones are widespread and that they reduce the (bulk) strength of the lithosphere significantly.
Insights from the Ocean Drilling Program on shear and fluid-flow at the mega-faults between actively converging plates
Authors: Maltman Alex , Vannucchi Paola
Published: April 2008

The mega-faults between actively converging plates have recently been penetrated by the Ocean Drilling Program at three plate margins: Barbados, Costa Rica and Nankai. Cores, downhole instrumentation and detailed seismic imagery provide data which may be helpful in interpreting ancient examples of shear zones. The mega-faults, developed in poorly lithified sediments, separate major lithospheric plates yet are merely tens of metres in thickness. They respond to ongoing strain by intensifying inwards rather than propagating outward splays and can grow thinner because of continuing compaction. Surprisingly, lithological influence on the localization of fault propagation seems slight, but lithology determines the deformation style within the faults. The resulting structures show asymmetric distributions within the zones but, in these flat-lying structures, tend to show a downward increase in strain. Upper margins are typically gradational whereas lower boundaries can be strikingly abrupt. The fluid-transport behaviours are complex. In some situations the horizontal flux is very diffuse but centred around the fault. Some faults can efficiently channelize fluids — for distances of tens of kilometres — while at the same curbing flow across them. The fluid transport is clearly episodic and heterogeneous. Fingers of pressured fluid migrate within the fault zone, in patterns that constantly change through time.
Geometric and kinematic analysis of a transpression terrane boundary: Minas fault system, Nova Scotia, Canada
Authors: Macinnes E. A. , White J. C.
Published: April 2008

The Minas fault system is an ENE-WSW trending transpressional boundary between the Appalachian Meguma and Avalon tectono-stratigraphic terranes of Nova Scotia, Canada. Along this boundary there is large-scale partitioning of deformation into distinct external (contractional) and internal (shear) zones. With the increase in strain from external to internal zones there is progressive localization of deformation, culminating in the discrete shear band domain. Deformation has produced materially, temporally and spatially distinct folds and faults throughout the fault system history. Ductile structures are generally composite features derived from multiple transposition of pre-existing layers. The partitioning of deformation found amongst fault rock units can in turn be associated with contrasting deformation micromechanisms. The distinctive variation in mechanical response and microstructures provides an insight into the role of localization, partitioning and distribution of deformation. Kinematic analysis has demonstrated that the Minas fault system segment examined here is a thinning deformation zone, in which strain is accommodated within progressively narrower volumes of rock. Deformation can be summarized as a broad, initially diffuse zone of triclinic transpression that has evolved, with the accumulation of finite strain, into zones of distinct structural style and variation in finite strain. It is not possible to demarcate ‘deformed shear zone’ and ‘undeformed host rocks’. Instead, the Minas fault system is described in terms of discontinuous transitions in finite strain and deformation style within a large scale movement picture.
Constraints on kinematics and strain from feldspar porphyroclast populations
Authors: Giorgis Scott , Tikoff Basil
Published: April 2008

We develop a method for constraining the kinematics and finite strain of deformation in shear zones based on a three-dimensional numerical model of the rotation populations of rigid clasts. The results of the model are characterized in terms of a fabric ellipsoid, which is directly measurable from field data. Fabric ellipsoids measured from populations of prolate clasts have anisotropies that increase steadily and plateau; the shape of the fabric ellipsoid becomes increasingly more prolate with progressive deformation. The behaviour of populations of oblate clasts is much more complex because the stability of individual oblate clasts depends on their aspect ratio and the vorticity of deformation. Populations of oblate clasts may produce fabric ellipsoids with oscillating anisotropies and shapes if their aspect ratio is low enough for a continuous rotation. For either prolate or oblate clasts, the maximum anisotropy that a fabric ellipsoid will reach is governed by the aspect ratio of the individual clasts of that population. The theoretical maximum anisotropy is achieved when all of the clasts are perfectly aligned. The shape of the fabric ellipsoid, in conjuncture with the anisotropy, can be used to constrain the vorticity and finite strain of deformation.

The numerical model suggests that there is no consistent relationship between the asymmetrical orientation of a population of rigid markers and the simple shear component of deformation. Therefore, the asymmetrical alignment of a population of porphyroclasts is not a reliable shear sense indicator. Additionally, there is no direct correlation between the fabric ellipsoid and the strain ellipsoid.

Model results are applied to shape preferred orientation data collected from a feldspar megacrystic granite in the western Idaho shear zone (USA). Three-dimensional fabric ellipsoids are calculated from two-dimensional sectional measurements of oblate-shaped, unmantled, potassium feldspar porphyroclasts. Comparison of these data with the results of the numerical model suggests that transpressional deformation had an intermediate angle of oblique convergence (30°–60°). This implies that deformation in the western Idaho shear zone was characterized by a large component of convergent motion.
Brittle-ductile shear zone evolution and fault initiation in limestones, Monte Cugnone (Lucania), southern Apennines, Italy
Authors: Mazzoli S. , Invernizzi C. , Marchegiani L. , Mattioni L. , Cello G.
Published: April 2008

The processes of brittle-ductile shear zone evolution and fault initiation by the coalescence of en echelon arrays of tensile cracks are quantitatively analysed in terms of displacement and temperature conditions at which they took place in very low-grade, well bedded micritic limestones from the southern Apennines, Italy. Three different types of structures are distinguished: (i) conjugate arrays of en echelon, calcite-filled tension gashes, showing extensional shear offsets; (ii) en echelon vein arrays showing incipient development of discontinuous shear-parallel fractures cutting through the tension gashes; and (iii) faulted vein arrays, in which vein array breaching by a continuous, discrete normal fault has occurred. Fluid inclusion microthermometry from vein calcite sampled from the different sets of structures (i) to (iii) above indicates that environmental conditions remained roughly constant during the different stages of vein array evolution and fault development, with average homogenization temperatures from primary fluid inclusions being in the range 130–140°C. Our results show how displacement accumulation and shear strain essentially control vein array evolution by rotation of en echelon tension gashes, fracture linkage and, eventually, fault nucleation, at approximately constant temperature.
Bath thermal waters: 400 years in the history of geochemistry and hydrogeology
Authors: Edmunds W. Mike
Published: April 2008

The importance of the Bath thermal springs in the development of science over some 400 years is explored. Several references to the springs from Saxon times and the Middle Ages give qualitative information of interest for the present day. The springs have drawn some of the most famous philosophers and scientists to test new theories and develop hypotheses on the nature of matter and to develop early ideas in the chemical and geological sciences. Theories on the hydrological cycle and on hydrogeology were tested and the springs have a long history as a site for discoveries in chemistry and natural radioactivity. Interest in the springs continues to the present day. Whilst our knowledge of the origin of the water, the heat, the detailed chemistry and other properties has been resolved, some questions still remain for the attention of future generations and for the application of advancing scientific methods.
The Scottish hydropathic establishments and their use of groundwater
Authors: Spence Iain , Robins Nick
Published: April 2008

Scotland today has a plentiful supply of drinking water derived from upland gathering grounds, but groundwater supplied all of its major towns and cities in the past. Pollution of many of the old groundwater sources, as well as the atmosphere, by the massive industrial boom of the mid nineteenth century in central Scptland led to the development of hydropathic establishments to dispense the ‘water cure’. Most drew on fresh and pure groundwater sources, and the establishments continued to be a popular source of medical care until the early part of the twentieth century. The groundwater sources were characterized by weak to moderate mineralization unlike the strongly mineralised waters typical of the more traditional spa resorts. A small part of the hydropathic legacy remains in use until this day
Stevenson Buchan (1907–1996): field geologist, hydrogeologist and administrator
Authors: Gray D. A. , Mather J. D.
Published: April 2008

Stevenson Buchan, a Scot educated at Aberdeen University, joined the Geological Survey of Great Britain in 1931. Assigned to the Southern District Unit he became involved in hydrogeology when he revised the 6-inch to the mile maps of Greater London. This led to the publication of a memoir on the water supply of the County of London in 1938. During the war he was involved in the search for water and coal. Appointed Head of a new Water Department when hostilities ceased he was given responsibility for overseeing the statutory obligations placed on the Survey by recent Water Acts. He developed around him a group of able colleagues creating the first groundwater research group of any size in the UK. Promoted to Assistant Director in 1960, he was very active internationally and in his role as an enabler and administrator played an important role in the development of hydrogeology in the UK.
Groundwater studies in the Institute of Geological Sciences between 1965 and 1977
Authors: Gray D. A.
Published: April 2008

Until 1965 the Water Department of the Institute of Geological Sciences had two principal functions — data collection and a national groundwater advisory service, but a limited research role. A change in the legislation then led to the loss of the advisory service but a major increase in the research role, backed by the support of successive Directors. After two years in which outstanding commitments were met and six new staff recruited, a portfolio of research projects was introduced. These were principally applied projects in the UK and overseas, but with a continuing background of fundamental studies. The most successful projects involved hydrogeochemistry; mechanisms of matrix flow in the Chalk; diffuse pollution from agriculture; point source pollution from landfills; groundwater/surface water interactions; automation of well records for publication; hydrogeological maps and the application of hydrogeology to civil engineering projects. The development of advisory work overseas was also important. The presence of the Hydrogeological Department in the Institute of Geological Sciences and its introduction of innovative techniques and ideas had a significant influence on the development of the hydrogeological community in the UK.
Conglomerates record the tectonic evolution of the Yarlung-Tsangpo suture zone in southern Tibet
Authors: Davis Aileen M. , Aitchison Jonathan C. , Badengzhu  , Hui Luo
Published: April 2008

The histories of individual conglomeratic units along the Yarlung-Tsangpo (River) suture zone in southern Tibet reflect significant phases in the Mesozoic to Cenozoic tectonic evolution of this area. Several temporally distinct conglomerate units are recognized along the suture, and their detailed examination permits analysis of the collision between India and Asia.

Upper Jurassic to Lower Cretaceous conglomerates crop out within the Sangri Group along the southern Lhasa terrane. They are dominated by limestone and andesitic volcanic cobbles derived entirely from the Lhasa terrane. These rocks have experienced amphibolite facies metamorphism, and exhibit a strong penetrative regional foliation.

Thick successions of the Palaeocene Liuqu Conglomerate crop out within the suture from Xigaze to Lhaze. They contain detritus sourced from intra-oceanic terranes associated with the suture zone, as well as clasts of Indian affinity, while Lhasa and Xigaze terrane-derived material is notably absent. These conglomerates record an early suture zone event prior to India-Asia collision.

Uppermost Oligocene to Lower Miocene ‘Gangrinboche facies’ conglomerates crop out on the southern edge of the Lhasa terrane along the length of the suture. Several correlative units within this facies exhibit broadly similar stratigraphic histories. A basal depositional contact upon an eroded Lhasa terrane surface is ubiquitous with initial clast derivation from the north. Up-section, the first arrival of coarse-grained, suture-zone and India-derived clasts, is abrupt. These southerly derived clasts predominate by the top of most sections.

An areally restricted succession of gently dipping Late Neogene ultramafic breccias unconformably overlies folded Liuqu Conglomerate near Quanggong. Other Neogene sediments are extensive west of Mount Kailas. Deposition of coarse clastic sediments is presently continuing along the length of the Yarlung Tsangpo.

Discrimination and detailed investigation of each of these units will improve our understanding of the evolution of the India-Asia collision.
Ultra-high pressure minerals in the Luobusa Ophiolite, Tibet, and their tectonic implications
Authors: Robinson Paul T. , Bai Wen-Ji , Malpas John , Yang Jing-Sui , Zhou Mei-Fu , Fang Qing-Song , Hu Xu-Feng , Cameron Stanley , Staudigel Hubert
Published: April 2008

Numerous ultra-high-pressure minerals have been recovered from podiform chromities in the Luobusa ophiolite, Tibet. Recovered minerals include diamond, moissanite, Fe-silicides, wüstite, Ni-Fe-Cr-C alloys, PGE alloys and octahedral Mg-Fe silicates. These are accompanied by a variety of native elements, including Si, Fe, Ni, Cr and graphite. All of the minerals were hand-picked from heavy-mineral separates of the chromitites and care was taken to prevent natural or anthropogenic contamination of the samples. Many of the minerals and alloys are either enclosed in, or attached to, chromite grains, leaving no doubt as to their provenance. The ophiolite formed originally at a mid-ocean ridge (MOR) spreading centre at 177±33 Ma, and was later modified by suprasubduction zone magmatism at about 126 Ma. The chromitites were formed in the suprasubduction zone environment from boninitic melts reacting with the host peridotites. The UHP minerals are believed to have been transported from the lower mantle by a plume and incorporated in the ophiolite during seafloor spreading at 176 Ma. Blocks of the mantle containing the UHP minerals were presumably picked up by the later boninitic melts, transported to shallow depth and incorporated in the chromitites during crystallization.