bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygen isotope and chemical studies on the origin of large plagiogranite bodies in northern Oman, and their relationship to the overlying massive sulphide deposits
Authors: Stakes Debra S. , Taylor Hugh P.
Published: April 2008

The extraordinarily well-preserved and well-exposed Semail ophiolite of northern Oman hosts several large plagiogranite intrusions in proximity to economic copper sulphide deposits of the Lasail mining district. A progression of isotopic, chemical and mineralogical transformations observed within the plagiogranites and high-level gabbros (HLG), and a comparison of these effects with those in the lowermost dykes of the immediately overlying sheeted dyke complex (SDC) tracks the evolution of hydrothermal fluids and the alteration of overlying dykes and pillow lavas during discharge of these fluids on the sea floor. The largest hydrothermal alteration aureoles, and the greatest extent of metamorphic veins and metasomatic replacement features, are found adjacent to the largest high-level plagiogranite bodies, beneath and adjacent to the major ore bodies in northern Oman. The ubiquitous presence of metamorphic actinolitic hornblende, sodic plagioclase, epidote and titanite in metabasalts within the high-temperature alteration zones points to the most likely mineralogical and structural controls on the development and evolution of the hydrothermal fluids. Depleted Cu contents of the adjacent crustal rocks and Cu enrichments above the plagiogranite intrusions demonstrate the redistribution of heavy metals adjacent to the complexes. Field relationships implicate the formation of both the epidosites and plagiogranites in the genesis of the ore deposits. An important process inferred from the field and geochemical data is the assimilation of previously hydrothermally altered basaltic and gabbroic country rocks by stoping into the magma chambers developed near the SDC-gabbro horizon in the ophiolite. We suggest that this process of combined assimilation-fractional crystallization, together with replenishment and recharge by injection and quenching of basaltic magma ‘pillows’ into these plagiogranite magma chambers (i.e. RAFC), plays a major role in the development of these composite intrusions.
Bioalteration recorded in ophiolitic pillow lavas
Authors: Furnes H. , Muehlenbachs K.
Published: April 2008

In this paper we summarize the present knowledge on bioalteration of basaltic glass from pillow lava rims of former oceanic crust, based on the study of four ophiolite complexes. These complexes range in age from Late Cretaceous to Mid-Proterozoic, and their metamorphic grades vary from non-metamorphosed to low greenschist- to low amphibolite-facies metamorphism. In the non-metamorphosed volcanic part of ophiolite complexes, in which undevitrified glass is still present in pillow lava rims and/or hyaloclastites, biogenerated textures are common. These textures (termed granular and tubular) are similar to those found in volcanic glass of recent to old (170 Ma)
in situ
ocean floor, and mimic microbes in terms of size and shape. In the metamorphic and completely recrystallized examples, the textural evidence of bioalteration is generally obliterated, although it may still be visible in little-deformed volcanic domains of low-grade greenschist-facies metamorphism. Where biogenerated textures are present, element mapping invariably reveals the presence of organic carbon, and sometimes nitrogen, sulphur and phosphorus. Carbon-isotope signatures (δ
13
C) in the pillow lava rims from all four investigated ophiolites show lower values than those of the adjacent crystalline parts. This phenomenon may be attributed to bio-induced fractionation of carbon isotopes during preferential bioalteration of the pillow lava glass, and may further represent a feature that seems to survive metamorphism and deformation.
Ophiolite obduction and the Samail Ophiolite: the behaviour of the underlying margin
Authors: Gray D. R. , Gregory R. T.
Published: April 2008

Samail ophiolite emplacement has become a type-example for ophiolite obduction. Despite this, problems and controversy remain with respect to the age of high-
P
metamorphism, the vergence of structures in deformed rocks beneath the ophiolite, the suprasubduction character of the ophiolite and the
P-T
conditions of the metamorphic sole. The presence of major, regional-scale NE-facing isoclinal folds and SW- and west-dipping shear zones with top-to-the-NE shear sense in Arabian margin rocks beneath the Samail Ophiolite nappe requires that the margin was not simply passively overridden during obduction of the ophiolite. The development of these folds at 72–76 Ma is at the time the ophiolite is emplaced finally onto the margin (80–70 Ma), accompanied by development of a major shear zone in Saih Hatat (the upper plate-lower plate discontinuity described by earlier workers) at
c.
82–80 Ma. Structural scenarios that incorporate these folds and shear zones include lateral escape from a rising buoyant crustal slice along the former subduction interface, back-folding (‘retrocharriage’) associated with major oceanwards-directed underthrusting, or simple underthrusting of the margin by the oceanic realm. Previous models involving craton-directed overthrusting with domal culminations related to deep-seated footwall and lateral ramps are more applicable to the Tertiary structure and Tertiary evolution of the mountain range. Oman ophiolite obduction clearly involves ocean-vergent thrusting within the continental margin platform to slope facies sequences.
Geochemical evolution of magmatism in an arc-arc collision: the Halmahera and Sangihe arcs, eastern Indonesia
Authors: Macpherson Colin G. , Forrde Emily J. , Hall Robert , Thirlwall Matthew F.
Published: April 2008

The Molucca Sea Collision Zone in eastern Indonesia is the site of an orthogonal collision between two active subduction systems. Both the Halmahera subduction zone, to the east, and the Sangihe subduction zone, to the west, have subducted oceanic lithosphere of the Molucca Sea Plate, which has now been completely consumed. Both volcanic arcs were active since the Neogene and provide a means of probing the element fluxes through the two systems. The geochemistry of Neogene and Quaternary lavas from each volcanic arc is compared to constrain changes in the mass fluxes through the systems and the processes controlling these fluxes at different times during their history. Both arcs show increased evidence for sediment recycling as the collision progressed, but for contrasting reasons. In Halmahera this may represent an increased sediment flux through the arc front, while in Sangihe it may simply reflect a greater opportunity for melting of sediment-fluxed portions of the mantle wedge. In both cases the change in arc geochemistry can be related to the evolving architecture of the particular subduction zone. The Halmahera lavas also record a temporal change in the chemistry of the mantle component that resulted from induced convection above the falling Molucca Sea Plate drawing compositionally distinct peridotite into the mantle wege.
Geochronology: linking the isotopic record with petrology and textures — an introduction
Authors: Vance Derek , Müller Wolfgang , Villa Igor M.
Published: April 2008

One of the key aims of geochronology, and the subject of the papers in this Special Publication, is the linkage of isotopic ages to petrological and textural information. A close link between the two types of information greatly improves the constraints available from geochronology on the nature and rates of lithospheric processes such as metamorphism and deformation. There have been several key advances in this area over the past 10–20 years, relating to increased precision and accuracy of isotopic ages but also, and crucially, to the spatial resolution available to geochronologists. This resolution now approaches that on which petrological, chemical and textural information is obtained. We also, in this introduction, identify the barriers that have impeded further progress, which relate both to technical issues as well as to problems of understanding. Finally we set the papers in this volume in the context of the preceding discussion and outline the key ways in which these papers point towards further progress in the future.
Effect of metamorphic reaction history on the U-Pb dating of titanite
Authors: Romer Rolf L. , Rötzler Jochen
Published: April 2008

Drill core samples of garnet-clinopyroxene granulite at Tirschheim and a reference sample at Waldheim (Saxon Granulite Massif, Germany) endured the same P-T conditions, but developed variable mineral assemblages due to differences in bulk chemistry, reaction progress, deformation and retrogression. Titanite formed during peak-metamorphic conditions of 22–24 kbar and 1020–1050 °C. Dating titanite from the various samples should yield the same age for all. The observed age variation, which exceeds the duration of the entire metamorphic cycle, originates from the contrasting preservation of isotopic inheritance during peak metamorphism and from post-peak re-equilibration. (1) Pb inheritance observed in some peak-metamorphic titanite demonstrates that geochronologically relevant elements are redistributed among remaining reactants and reaction products during prograde metamorphism and that the sequence of metamorphic reactions does not result in isotopic homogenization. Instead, metamorphic minerals inherit the radiogenic signatures of the precursor minerals and may in extreme cases approach the age of the precursor mineral. (2) Titanite that formed at peak-metamorphic conditions is characterized by high A1 contents and X
F
≈ 0.8−1. Texturally comparable titanite that re-equilibrated during cooling (reduced Al contents and X
F
) yields too young U-Pb ages. The age of such re-equilibrated titanite does not correspond to the age of the event indicated by the texture.
Evidence from Rb-Sr microsampling geochronology for the timing of Alpine deformation in the Sonnblick Dome, SE Tauern Window, Austria
Authors: Cliff R. A. , Meffan-Main S.
Published: April 2008

The Sonnblick Dome forms a large antiformal structure within the Pennine of the SE Tauern Window. The structural and metamorphic evolution of this area is relatively well constrained. However, mineral age determinations of the Alpine event within the Zentralgneis granitoid basement remain ambiguous due to a lack of isotopic equilibration during the Alpine event. In this paper we use a newly developed technique, namely Rb-Sr microsampling, in an attempt to place more reliable age constraints upon Alpine deformation. The new age determinations range between
c.
22 Ma and 28 Ma. The oldest ages are interpreted to result from shearing related to the earliest stages of dome formation while the youngest ages probably represent late fabric development during uplift of the Zentralgneis complex. A clustering of six fabric ages around 25.5 ± 0.3 Ma is thought to represent the peak of deformation activity associated with formation of the dome. These new data can be fitted into a model for the metamorphic and structural evolution of the SE Tauern Window.

In most of the rocks studied isotopic disequilibrium is apparent between and within minerals. It is clear that large feldspar augen did not attain isotopic equilibrium despite amphibolite facies metamorphism. In fact, even where chemical equilibrium was achieved isotopic homogenization did not always occur. The Rb-Sr data from white mica suggest that isotopic equilibration may occur during isochemical rotation of grains suggesting differing mechanisms for chemical and isotopic movement within grains. The data presented herein suggest that small-scale,
in-situ
sampling methods may provide the most reliable method for deformation chronology in basement gneisses.
Staircase normal fault geometry in the Grès d’Annot (SE France)
Authors: Lansigu C. , Bouroullec R.
Published: April 2008

A normal fault geometry is observed in the sediments of the Grès d’Annot Formation. The sediments are deep-water siliciclastic deposits composed of mud-rich and sand-rich successions. This seismic- to sub-seismic scale fault system is considered as a good analogue for syntectonic basin infilling. The outcropping Grès d’Annot Formation allows small- to large-scale fault analysis coupled with stratigraphic analysis. The major faults, which have throws ranging from a few metres to hundreds of metres, belong to a tilted block succession. The mud-rich and sand-rich beds thickness range from a few centimetres to tens of metres. The characterization of the fault system and the kinematic analysis carried out show strong correlation between fault geometry and lithological discontinuities. The fault geometry is largely controlled by the rheological coupling between the mud-rich and sand-rich succession. Downdip displacement of fault blocks is accommodated by layer-parallel movement. Graben structures and synthetic fault sets are related to small-scale fault steps. The fault zone characteristics are related to these fault profile heterogeneities. Kinematic analysis of this fault system provides tools for the characterization of stress field perturbation in a multi-layer system and its consequences in terms of strain localization and hydrodynamic behaviour.
Syndepositional faulting in the Grès d'Annot Formation, SE France: high-resolution kinematic analysis and stratigraphic response to growth faulting
Authors: Bouroullec Renaud , Cartwright Joe A. , Johnson Howard D. , Lansigu Christophe , Quémener Jean-Marie , Savanier Dominique
Published: April 2008

The presence of syndepositional reservoir scale faulting in the Grès d'Annot Formation adds an additional level of complexity in understanding the stratigraphic architecture of these, and potentially other, deep-water reservoir successions. A series of five synsedimentary faults have been characterized in relation to the high-resolution depositional framework of the Annot deep-water sandstone, faults that were active at the time of deposition of the Grès d'Annot, influencing both stratigraphic architecture and depositional processes. The five faults have normal throw, strike NE-SW (perpendicular to the regional palaeocurrent direction), and have maximum syndepositional throws of between 5 and 30m (sub-seismic-resolution scale). To understand the nature of the synsedimentary faulting, a high-resolution stratigraphic framework was developed from six vertical sedimentary sections measured along the 600m high cliff face, and from detailed correlations along photomosaic panels. Ten lithofacies have been identified and grouped into three different architectural elements that have been used as reference units for the high-resolution kinematic analysis. Syndepositional deformation of these architectural elements indicates that the faults had a polycyclic kinematic behaviour. In the hanging wall, abrupt pinchout of sandstone bodies and unusual local variations in sandstone texture also support the influence of faulting during deposition.
Scale effects of non-uniformity on deposition from turbidity currents with reference to the Grès d’Annot of SE France
Authors: McCaffrey W. D. , Kneller B. C.
Published: April 2008

Turbidity current non-uniformity arises when flows experience changes in slope or degree of confinement. The phenomenon may operate across a range of scales with respect to flow size, to produce a range of characteristic depositional effects. Non-uniforrnity effects at three scales can be inferred within the Grès d’Annot exposed around the town of Annot. At the basinal scale, the very presence of sedimentary deposits may reflect a non-uniformity control. At the inferred flow scale, non-uniformity effects upon facies development can be linked to particular system geometries, for example channels or scours versus sheet systems. At the smallest scale, detailed facies heterogeneity may be linked to variability in the local sea floor topography. In poorly-exposed or subsurface systems, recognition of these effects may allow the non-uniformity regime of the parental flows to be constrained and hence permit improved prediction of the first order of sedimentary architecture away from point s of control.
Patterns of geochemical variability in relation to turbidite facies in the Grès d’Annot Formation
Authors: Garcia Daniel , Joseph Philippe , Maréchal BenoÎt , Moutte Jacques
Published: April 2008

The deep marine Grès d’Annot Formation is one of the best exposed analogues to sand-rich turbidite sub-surface systems. Provenance and reservoir heterogeneities have been investigated through a geochemical study of different areas and facies in this formation. Most compositions may be described as mixtures between carbonate and three clastic end-members, i.e. clay, framework grains and a subset of the heavy minerals (zircon, Tioxide, apatite, monazite). These end-members have a nearly uniform chemistry over the studied area and a granite-dominated provenance consistent with a Corsica-Sardinia source hypothesis. This rather uniform provenance makes the Annot Formation a favourable case for exploring the relationships between facies and geochemistry. Not only do different facies differ in average composition, but chemical variations at the bed scale fingerprint the depositional mechanism: archetypal (graded) turbidites and traction-dominated (over-bank) deposits display contrasting variation trends in geochemical plots. The local-scale variation patterns and the general relationship between grain size and chemistry are tentatively integrated in a single differentiation model, providing a rationale for the use of geochemistry in provenance studies, and a possible way to characterize sedimentary facies.
The Grès d’Annot as an analogue for Brazilian Cretaceous sandstone reservoirs: comparing convergent to passive-margin confined turbidites
Authors: Moraes Marco A. S. , Blaskovski Paulo R. , Joseph Philippe
Published: April 2008

The Eocene deep-water sand-rich deposits of the Grès d’Annot of southern France have been used as outcrop analogues for offshore Cretaceous reservoirs of Campos Basin, southeastern Brazil. The analogy is chiefly based on the sand-rich, confined nature of the two systems. Such application can be questioned as the contrasting geological settings, i.e. convergent versus passive margin, could produce rather different depositional scenarios. Detailed comparison between the two systems permits, however, recognizing additional similarities, and also some differences, whose recognition is important to ensure the correct application of the Grès d’Annot as an analogue for this and other passive-margin reservoirs. Comparative analysis of channel dimensions, facies continuity, and three-dimensional expression suggests that confined sand-rich systems show many similarities in terms of critical reservoir heterogeneity, providing that palaeotopographic control was similar, regardless of the tectonic environment in which they were formed. In addition, contrasts found among sequences in the same tectonic setting suggest that other factors (such as, for example, sand/shale ratio of the sediment input) play an important role in defining reservoir architecture. These observations further suggest that, once similarities and differences are correctly understood, analogue data, even from quite different tectonic settings, may provide a powerful tool for improving subsurface reservoir models.
Turbidite systems influenced by structurally induced topography in the multi-sourced Welsh Basin
Authors: Smith Ru
Published: April 2008

The latest Ordovician and lower Silurian fill of the Welsh Basin contains a range (in terms of scale, sediment texture, stratigraphic architecture and supply configuration) of deep-water depositional systems that record the influence of basin-floor topography on sediment distribution patterns. Systems supplied from the eastern basin margin at a time of broadly rising relative sea-level are interpreted to have initially filled an inboard base of slope depression lying above a tilted basement fault block (Cerig Gwynion Grits System). An opposing slope is thought to have caused deflection of turbidity currents to run parallel with the strike of the slope. Following this fill phase, a channel-fed lobe system (Caban-Ystrad Meurig System) extended further basinwards. After flooding of the eastern basin margin, voluminous, texturally immature axial systems, supplied from the southern basin margin, developed. These systems exhibit evidence for deflection of flows to run parallel to tectonically induced slopes and probable local flow reflections in areas of obliquity between bounding slopes and incident flows. The architecture of the lateral-slope to basin-axis profile has been plausibly modelled using a geometric forward model with a low-gradient lower basin slope and basinward higher aggradation rates and sand percentage.
Spatial variability of Hurst statistics in the Castagnola Formation, Tertiary Piedmont Basin, NW ITaly: discrimination of sub-environments in a confined turbidite system
Authors: Felletti Fabrizio
Published: April 2008

The purpose of this paper is to investigate the potential of the use of the Hurst test as a statistical tool for quantifying the degree of clustering of high and low values of field measurements in vertical turbiditic sections within a small and confined tectonically mobile basin. The paper (1) documents the fact that significant clustering occurs in almost all sections, (2) shows that there are systematic spatial variations in the degree of clustering such that different parts of the basin have different Hurst statistics, (3) discusses the origin of those spatial trends, and (4) compares Hurst
H
with Chen and Hiscott’s Hurst
K
. The case study focuses on one well-exposed reservoir-scale turbiditic unit cropping out in the eastern part of the Tertiary Piedmont Basin (NW, Italy) and representing the lower portion of an Upper Oligocene-Lower Miocene turbidite system (Castagnola Formation). The sedimentological model that has been adopted is based on the description of 41 sedimentological logs (approximately 25–35 m apart) physically correlated bed by bed. Three variables were studied: thickness of sandstones and siltstones, grain size score, and sand and silt thickness percentage (i.e. the ratio of coarse division to overlying mudstones, in percent). The Hurst test has revealed the existence of common clustering for the three studied variables (only 2 of 41 logs failed to pass the test at the 10% significance level for all the studied variables). This clustering is associated with lateral and vertical facies variations in response to changes in depositional sub-environments within the Castagnola Basin. A geostatistical analysis has been performed in order to estimate the spatial distribution of the Hurst statistics within the studied area. The analysis makes possible predictions at unsampled locations.
Rheology of a two-phase material with applications to partially molten rocks, plastic deformation and saturated soils
Authors: Vigneresse J. L.
Published: April 2008

A global model is presented to account for the specific rheology of a two-phase material. Examples of observations are taken from a crystallizing magma and these are applied to a partially molten rock, plastic deformation and soil liquefaction. The general behaviour of the viscosity is drawn as a function of the strain rate and the amount of solid phase. It constitutes a 3D diagram developing a cubic surface. The cubic equation is justified by thermodynamic considerations. It results from the mixing of a Newtonian (
n
= 1) and a power law (
n
= 3) type of deformation. The diagram shows two types of rheological response. At high strain rate values, the viscosity contrast between the two phases is the lowest. The resulting
en masse
behaviour is observed during tectonic activity. It manifests itself by homogeneous transport of magma during emplacement and fabric development. An equivalent medium, with average viscosity is a good proxy. Conversely, at low strain rate values, the viscosity contrast between the two phases is the highest. The two end members behave according to their respective rheology. In between, a transitional state develops, in which instability occurs depending on the strain rate and stress conditions. In the 3D diagram it appears as a cusp shape. Rheology presents continuous jumps between the liquid-like and the solid-like rheology. They result in strain localization or phase segregation. The latter preferentially develops during magma crystallization. Deformation under a constant amount of each phase is also possible, resulting in pressure dissolution-like processes. A bifurcation in the solution plane of the equation of viscous motion causes instability. It is comparable with strain softening. A similar situation should develop when mixing Newtonian and power law rheology, for example during diffusion and dislocation creep, or water-saturated sediment deformation. Owing to the continual jumps between the two types of rheology, hysteresis or memory effect may develop. Rapid cyclic deformation may drive strain to extreme straining. The effect of simple shear seems much more effective than pure shear (compaction) to separate the weak phase from its strong matrix. The development of instabilities and continuous jumps from one rheology to the other lead to discontinuous motion of the weak phase. In a molten region, it corresponds to discontinuous bursts of magma that are extracted.
A comparison of structural data and seismic images for low-angle normal faults in the Northern Apennines (Central Italy): constraints on activity
Authors: Collettini C. , Barchi M. R.
Published: April 2008

During the past 18 Ma extensional tectonism has migrated from the Tyrrhenian sea eastward into the Northern Apennines of Italy. The extension is due in part to lowangle east-dipping normal faults, that are now exhumed in the Tyrrhenian islands and Tuscany, while additional extension is still occurring in the Apennine chain (Umbria region,
c.
200 km eastward). This tectonic framework is an example where active extensional processes affecting the Umbria region can be studied in exhumed faults that are no longer active. Here a comparison between the Zuccale Fault (ZF), cropping out in the Isle of Elba, and the Altotiberina Fault (ATF), revealed by geophysical data, seismology and seismic profiles crossing the Umbria region, provide insights into the processes affecting low-angle normal fault development and evolution.

Recorded microseismicity suggests that the ATF is presently active under a vertical σ
1
. Structural analysis of the ZF depict a comparable scenario with fluid involvement during the activity. The comparison of these two structures suggests movements with fluid involvement along gently dipping planes under a vertical σ
1
, implying that these faults are mechanically weak.
Shear deformation of pelitic rocks in a large-scale natural fault
Authors: Casciello Emilio , Cesarano M. , Cosgrove J. W.
Published: April 2008

Experimental tests on simulated clay gouges and data from shear zones developed in pelitic media at convergent plate margins provide contrasting evidence regarding the hydraulic characteristics and, in consequence, the frictional properties of sheared clays. The natural shear zone analysed in this work indicates that shear strain can induce mineralogical changes in smectite-bearing sediments that imply loss of water from the smectite minerals and their replacement with anhydrous illite minerals. The extreme localization of the illitization process and its geometric characteristics allow us to argue that the reaction is initiated by stress concentration along the shear zone and, once discrete shears develop, it is accelerated by both cataclasis and the frictional dehydration of smectites. This process would generate fresh water from within the shear zone, leading to fluid overpressure build up, and can account for the observed hydraulic circulation and salinity anomalies in modern accretionary prisms.
Contrasting styles of fluid-rock interaction within the West Fissure Zone in northern Chile
Authors: Janssen C. , Lüders V. , Hoffmann-Rothe A.
Published: April 2008

Geochemical data from three profiles crossing the West Fissure Zone in northern Chile were used to describe the chemical effects of fluids on faulting processes. The results document considerable differences of fluid-rock interactions between the profiles (A–C). Within the area of profile A and C fluid activities have neither led to intensive exchange reactions between fluids and rocks nor to notable changes in whole rock and mineral composition of fault rocks relative to their undeformed host rock. Investigations of stable isotopes (δ
13
C, δ
18
O) and fluid inclusions indicate infiltration of predominantly descending (meteoric) fluids and only subordinate involvement of ascending hydrothermal fluids. In the case of profile B, fluid-enhanced weakening mechanisms are dominant. Dissolution transfer has led to the formation of an alteration zone up to 400 m wide. Along profile B we have no indications for warm fluids derived from a deep source. Rather, a number of lines of evidence (e.g. δ
18
O and δD) show that fault rock alteration took place due to the infiltration of low temperature meteoric water. For this profile, all geochemical data indicate an open fluid system. Moreover, the chemical variations across the West Fissure Zone agree well with the structural variability observed at this traverse. The application of a variety of geochemical analyses of fault rocks shows the heterogeneity of large-scale continental fault zones.
Development of local orthorhombic fabrics within a simple-shear dominated sinistral transpression zone: the Arronches sheared gneisses (Iberian Massif, Portugal)
Authors: Pereira M. Francisco , Silva J. Brandão
Published: April 2008

The Coimbra-Cordoba shear zone (Iberian Massif), characterized by simple-shear dominated sinistral transpression, exposes several outcrops of strongly sheared peralkaline gneisses surrounded by mica schists and amphibolites. These gneisses are included in the Arronches Tectonic Unit, a thick unit of mylonitic rocks with a steep foliation and an associated gently plunging stretching lineation parallel to the fold axes. Strain partitioning is testified by widely spaced anastomosing shear bands around less-strained domains and by the existence of different shearing domains ranging from relatively ‘less-strained’ and coarse-grained mylonites to highly strained and fine-grained ultramylonites.

Three shearing domains defined by textural and structural changes resulted from progressive deformation and increasing strain, which leads to increased mylonitization of gneisses. This is revealed by the increased modal percentage of the matrix and the decreased percentage of porphyroclasts, accompanied by evolution from orthorhombic to monoclinic fabrics: Conjugate Shearing Domain (
CSD
), Intermediate Sinistral Domain (
ISD
), and Sinistral Domain (
SD
).

This contribution shows that in a simple-shear sinistral dominated transpression zone with a well-developed and widespread monoclinic fabric, it is possible to find mechanical conditions to produce local orthorhombic fabrics. In the Arronches gneisses a local strain regime exists in apparent contradiction with the bulk deformation regime.
Shear zones and metamorphic signature of subducted continental crust as tracers of the evolution of the Corsica/Northern Apennine orogenic system
Authors: Molli G. , Tribuzio R.
Published: April 2008

This paper focuses on new data concerning the deformation and metamorphic history of continental margins of the Mesozoic Ligurian Tethys. In the Tenda massif (NE Corsica), a slice of the European-Iberian continental margin, contractional shear zones show
HP/LT
metamorphic assemblages and top-to-the-west kinematics. These shear zones are overprinted by greenschist facies exhumation-related structures showing top-to-the-SW sense of transport and then top-to-the-NE extensional shearing. The presence of
HP/LT
metamorphism, together with the kinematics of syncontractional shear zones, supports the classic view of Cretaceous-Eocene east-vergent ‘alpine-subduction’ during the early evolution of the Corsica belt. By taking into account structural and metamorphic data on Tuscan continental units belonging to the other side (Adria margin) of the former Mesozoic Ligurian ocean, we ascribe the Corsica/Northern Apennine system to a polycyclic orogen.
Robert Stephenson (1803–1859) — the first groundwater engineer
Authors: Preene M.
Published: April 2008

From a humble background in the mining communities of Tyne and Wear, with little academic education, Robert Stephenson followed in the footsteps of his father, George, and became one of the foremost civil and mechanical engineers of the early 19th Century. While he is primarily associated with railways, Robert Stephenson had considerable dealings with groundwater during his professional life, applying a rational, empirical approach that would be familiar to modern practitioners. Stephenson’s approach to groundwater issues was probably shaped largely by the years spent battling water-bearing quicksands during construction of the Kilsby Tunnel near Rugby on the London to Birmingham Railway. Careful observations allowed him to conclude that local drainage by use of arrays of wells was possible, without the need to drain the whole aquifer body. Later in his career he advised on public water supplies from the Chalk for London and the Sherwood Sandstone for Liverpool. His careful observations and reasoned interpretation, allowed him to advance the concept of a ‘cone of influence’ around a pumped well and to develop tests and monitoring programmes to assess the impact of new abstractions on existing water features. Today, his work may seem basic, even obvious, but, in the days before the work of Darcy and Dupuit, there were many who disputed his findings. Stephenson preferred to let the facts to speak for themselves, but where this was not possible he vigorously publicised the benefit of applying a scientific approach to the management and control of groundwater.
‘Making water’: the hydrogeological adventures of Britain’s early mining engineers
Authors: Younger Paul L.
Published: April 2008

The earliest detailed technical descriptions of British mining practices still in existence (which date from the late 17th and early 18th centuries) dedicate many paragraphs to the problems posed by the unwanted ingress of ground water into underground workings. Excessive water in working areas seriously hinders production. More importantly, sudden inrushes of ground water to underground workings are a significant mortal hazard. In view of the problems experienced with water ingress to workings, the main preoccupations of the early mining engineers were utterly practical, focusing on the efficient removal of water which could not be prevented from entering the workings (by simple bailing, by adit drainage or by pumping), and on efforts to minimize water ingress in the first place (by the use of tubbing in shafts and the use of rock barriers and dams in working areas). Occasionally, the mining engineers took time to reflect upon the origins of the water they encountered in their work. In their writings we find some of the earliest accurate conceptualizations of issues of ground water origin, driving heads, hydraulic gradients (including vertical upward gradients) and natural heterogeneities in water quality. So successful were these early mining engineers in their endeavours that they bequeathed most of the technological basis for the development of large-scale public-supply ground water abstractions, and much of the basis for the geotechnical control of ground water during construction projects, from about 1820 onwards. By the late 19th Century, mining engineers concerned with ground water management became gradually isolated once more within their own specialist domain, where they went on to develop a vernacular hydrogeology of their own, replete with its own key concepts and vocabulary. Nevertheless, occasional interchanges of experience between mining and the water industry have continued to enrich both sectors down to the present day.
Chalybeate springs at Tunbridge Wells: site of a 17th-century new town
Authors: Fuller J. G. C. M.
Published: April 2008

Among Wealden towns Tunbridge Wells is comparatively new. Before the Civil Wars of the 1640s there was no village here, nor any name on a map. Chance finding of chalybeate springs a few miles south of Tunbridge (now
Tonbridge
) attracted attention at Court, and even gynaecological interest. Curiously, this provides explanations both for the supposed virtues of the waters and the founding of a summer resort. By repute, the springs were discovered in 1606, though this story was already 160 years old before it first appeared in print. Verifiable facts indicate that Thomas Neale, FRS, (1641–1699) was the main agent in organizing the nascent resort’s amenities, beginning in 1676 with plans to construct a chapel or assembly room. The springs themselves issue from Lower Cretaceous Wealden beds, a few feet above the Wadhurst Clay, in a shallow valley formed by the headwaters of the River Grom. Siderite (iron carbonate or chalybite) abounds in these formations.
British hydrogeologists in North Africa and the Middle East: an historical perspective
Authors: Lloyd J. W.
Published: April 2008

The main British hydrogeological contributions to a very extensive area are referenced and it is concluded that notable contributions have been made to the understanding of regional sedimentary basin hydrodynamics. The British hydrogeological involvement in much of the area, however, has unfortunately been less than that of the French, principally because of past colonial influences.
British attempts to develop groundwater and water supply on Gibraltar 1800–1985
Authors: Rose Edward P.F. , Mather John D. , Perez Manuel
Published: April 2008

The 6 km
2
peninsula of Gibraltar is unusual hydrogeologically as, in effect, a small but high limestone island, subject to a Mediterranean climate of cool wet winters and warm dry summers. Provision of an adequate water supply for its town and garrison has been a continuing problem, particularly as the population has grown from about 3000 in the 18th century to over 30 000 by the end of the 20th. The narrow peninsula is dominated by the Rock, a mass of Lower Jurassic dolomite and limestone whose main ridge has peaks over 400 m high. Early supplies of potable water were from roof and slope rainwater runoff, and from shallow wells in the Quaternary sands that cover ‘shales’ flanking the Rock at low levels. Intermittent hydrogeological studies through the 19th and 20th centuries, notably in association with the British Geological Survey in 1876, 1943–1952, and 1974–1985 attempted to develop inferred groundwater resources within the sandy isthmus which links the Rock to southern Spain and in the Rock itself. Problems resulted from inadequate understanding of the geology, of recharge, of the behaviour of aquifers containing saline water at depth and of the need to protect aquifers from pollution. Failure to extract adequate groundwater led to development of a separate supply of saline sanitary water to reduce demand for potable water and innovative attempts to improve slope catchment of rainwater, before near-total commitment to desalination for potable supplies in 1993.
Jack Ineson (1917–1970) The instigator of quantitative hydrogeology in Britain
Authors: Downing R. A. , Gray D. A.
Published: April 2008

Jack Ineson will always be associated with introducing quantitative methods to British hydrogeology. A geologist with a sound knowledge of mathematics and statistics, unusual for the time, he seized the opportunity in 1948 to apply to British aquifers the burgeoning theory of well hydraulics initiated by Theis. Ineson’s career was mainly spent with the Geological Survey of Great Britain, now the British Geological Survey, but in the period 1965–1970 as Chief Geologist of the Water Resources Board. It was, however, a relatively short career with the start postponed by the Second World War and tragically truncated in June 1970 as a direct consequence of his experiences in the war.
Groundwater in a national water strategy, 1964–1979
Authors: Downing R. A.
Published: April 2008

The Water Resources Board was formed in 1964, an outcome of the Water Resources Act of 1963. Its remit was to advise the Government and the new river authorities on ‘the proper use of water resources in England and Wales’. It made three major regional studies of water resources and, in 1973, advocated a national water strategy. The Water Resources Board was disbanded in 1974 following the reorganization of the water industry under the Water Act of 1973 which created the regional water authorities. In the 1970s, a decline in the rate of population growth together with an economic recession reduced the demand for water and the Board’s proposals were not fully implemented. After 1974 the Central Water Planning Unit continued the Water Resources Board’s role until it too was disbanded in 1979.
Late Archaean to Palaeoproterozoic evolution of the Trans-North China Orogen: insights from synthesis of existing data from the Hengshan-Wutai-Fuping belt
Authors: Zhao Guochun , Sun Min , Wilde Simon A. , Guo Jinghui
Published: April 2008

The Hengshan-Wutai-Fuping mountain belt constitutes the middle segment of the Trans-North China Orogen, which separates the North China Craton into the Eastern and Western Blocks. The belt consists of the high-grade Hengshan and Fuping complexes, and the intervening low- to medium-grade Wutai Complex. Previous tectonic models assumed that the high-grade complexes were an older basement (Archaean to Palaeoproterozoic) to the low-grade Wutai Complex. However, new geochronological data show that the emplacement of granitoid rocks and eruption of volcanic rocks in the Wutai Complex occurred essentially coeval with or slightly earlier than intrusion of the tonalitic-trondhjemitic-granodioritic (TTG) suites in the Hengshan and Fuping complexes. New isotopic data also reveal the widespread presence of Palaeoproterozoic granitoid rocks in these complexes. Structural and metamorphic data demonstrate similar tectonothermal histories for the three complexes, which are characterized by peak medium- to high-pressure metamorphism accompanied by the development of thrusting, isoclinal folding (F
2
) and penetrative foliations, followed by near-isothermal decompression and cooling and retrogression associated with the formation of large-scale ductile shear zones and asymmetrical folds (F
3
) with nearly vertical axial planes. These geochronological, structural and metamorphic data suggest that the tectonic evolution of the Hengshan-Wutai-Fuping mountain belt may not be related to local interaction of the three complexes, as suggested in earlier models, either through closure of a Wutai rift or collision between a Wutai arc and the Hengshan and Fuping micro-continental blocks. Instead, they may represent elements of a single Late Archaean to Early Palaeoproterozoic magmatic arc that was subsequently incorporated into the Trans-North China Orogen along which the Eastern and Western blocks amalgamated to form the North China Craton at around 1.85 Ga.
Basement heterogeneity in the Cathaysia crustal block, southeast China
Authors: Fletcher Chris J. N. , Chan Lung. S. , Sewell Roderick J. , Campbell S. Diarmad G. , Davis Donald W. , Zhu Jieshou
Published: April 2008

Isotope signatures and
T
DM
model ages in Hong Kong and neighbouring Guangdong Province have indicated that the basement of the Cathaysia Block is probably an amalgamation of narrow crustal slices, ranging in age from latest Archaean to Mesoproterozoic. Inheritance ages from zircons contained within Mesozoic volcanic and plutonic rocks also show Proterozoic and Archaean components. Regional gravity survey studies display NNE- to NE-trending Bouguer anomalies that are indicative of sharp changes in rock densities at middle and lower crustal levels. The anomalies displayed on the gravity profile from Guangdong to Hong Kong have been modelled as narrow slices of Archaean and Proterozoic crust. A substantial E-W-trending Bouguer anomaly, which largely parallels the trend of the foliation in the Proterozoic schists of the region, is present to the east of Guangzhou. It is proposed that the basement of the Cathaysia Block consists of an amalgamation of NE- to NNE-trending Palaeo- to Mesoproterozoic and Archaean crustal terranes, which in places have retained the pre-amalgamation E-W-trending tectonic fabric. The discontinuities between the basement terranes, and the E-W structures have strongly influenced the geological evolution of the Phanerozoic sequences and igneous complexes in southeast China. These are most obviously manifest in the regional NE-trending fault and shear zones that displace the cover sequences.
Cretaceous palaeomagnetism of Indochina and surrounding regions: Cenozoic tectonic implications
Authors: Chi Cung Thuong , Dorobek Steven L.
Published: April 2008

Results of a detailed palaeomagnetic study of Cretaceous-age volcanic, intrusive and sedimentary rock formations from southern Vietnam (24 sites, 163 core samples) are presented. The palaeomagnetic and supplementary rock magnetic studies indicate that magnetite and titanomagnetite are the predominant magnetic carriers in the volcanic and intrusive rock samples, whereas hematite is the principal carrier in the red-beds. The mean palaeomagnetic direction of twenty-one sites from southern Vietnam yields
D
= 14.5°,
I
= 33.3°,
α
95
= 6.3°,
k
s
/
k
g
= 1.04, which corresponds with a VGP at
λ
= 74.2°N,
φ
= 171.1°E,
A
95
= 5.9°. Comparison of the pole with the Eurasia mean Cretaceous palaeopole shows that relative to Eurasia southern Vietnam has experienced a southward displacement of 6.5° ± 5.1°, but with insignificant rotation since the Cretaceous.

Previously reported Cretaceous palaeomagnetic data, combined with new palaeomagnetic data from this study and analysis of regional structural trends, indicate that Sundaland can be divided into several fault-bounded tectonic domains (Shan-Thai, Indochina, offshore Sundaland), each with a different rotation and/or translation history. Such differential motion might explain, for example, Oligocene transtension and basin formation in the Gulf of Thailand and central onshore Thailand (between the Shan-Thai and Indochina blocks). Our data combined with previously acquired palaeomagnetic data across Southeast Asia, also suggest that, during the Cenozoic, Indochina and parts of Sundaland underwent complex internal deformation and did not behave as a rigid block.