bluuebunny/crossref_metadata_2025 huggingface dataset:
Pterosaur (Pteranodontoidea, Pterodactyloidea) scapulocoracoid from the Early Cretaceous of Venezuela
Authors: Kellner Alexander W.A. , Moody John M.
Published: April 2008

The discovery of a left scapula and coracoid (MBLUZ P-911) representing the first evidence of a pterosaur from Venezuela is reported here. The material comes from the Lower Cretaceous (Aptian) Apón Formation, in the northwestern part of the country. In MBLUZ P-911 the scapula is significantly smaller than the coracoid, a synapomorphy of the Pteranodontoidea, according to Kellner. The coracoid of the Venezuelan specimen is more elongated and gracile than those of
Istiodactylus
and
Pteranodon
, and also lacks the ventromedial coracoidal flange present in the latter. Overall MBLUZ P-911 is very similar to the scapulocoracoid of the Anhangueridae, including the presence of a longitudinal ridge on the medial surface of the coracoid and a comparatively short scapula, and is therefore tentatively referred to this taxon. This occurrence extends the pterosaur record to the northern part of the South American portion of Gondwana.
Pterosaur phylogeny and comments on the evolutionary history of the group
Authors: Kellner Alexander W. A.
Published: April 2008

A cladistic analysis based on 39 terminal taxa and 74 characters (several multistate) using PAUP (Phylogenetic Analysis Using Parsimony) (3.1.1 for MacIntosh and 4.0b10 for Microsoft Windows) presents a new hypothesis of pterosaur inter-relationships. This study suggests that the most primitive taxon is the Anurognathidae, followed by
Sordes
and all remaining pterosaurs.
Dendrorhynchoides
is confirmed as a member of the Anurognathidae, being closely related to
Batrachognathus. Preondactylus
occupies a more derived position than
Sordes
, which questions its previous assignment as the most primitive pterosaur. The hypothesis of rhamphorhynchoid paraphyly is confirmed, with the Rhamphorhynchidae more closely related to the Pterodactyloidea than to more basal forms. The Pterodactyloidea shows a basal dichotomy: the Archaeopterodactyloidea and the Dsungaripteroidea. The Archaeopterodactyloidea is formed by
Pterodactylus
+
Germanodactylus
and a clade formed by Gallodactylidae + Ctenochasmatidae. The Nyctosauridae occupies the basal position within dsungaripteroids and is followed by the Pteranodontoidea and the Tapejaroidea. Pteranodontoids have
Pteranodon
at the base, followed stepwise by
Istiodactylus, Ornithocheirus
and the Anhangueridae. Tapejaroids are composed of the Dsungaripteridae at the base followed by the Tapejaridae and the Azhdarchidae.

Major trends within pterosaur evolutionary history are: general increase in size (wing span and body); increase of wing metacarpal and pteroid; decrease of proportional length of the second and third wing phalanx relative to the first; gradual increase of rostrum (anterior to external nares); and anterior shift of the skull-mandible articulation. Cranial crests are present in most pterodactyloids, but markedly in the Ornithocheiroidea, where all taxa show some sort of crest on the skull. The loss of teeth, previously assumed to have occurred independently in several lineages, seems to be a general trend among dsungaripteroids.

Several nodes recovered by this analysis are supported by very few characters, a result at least partially attributable to the limited available information from several taxa due to poor preservation and/or preparation.
Arc-trench rollback and forearc accretion: 1. A collision-induced mantle flow model for Tethyan ophiolites
Authors: Flower M. F. J. , Dilek Y.
Published: April 2008

Tectonically active remnants of Neo-Tethys represented by Mediterranean and western Pacific marginal seas are characterized by rapidly propagating backarc extension episodes. These appear to be triggered by random subduction nucleation events, commonly signalled by the appearance of refractory boninites in volcanic ‘proto-arcs’. As backarc basins evolve, active arcs separate from their ‘proto-arc’ remnants and may split again if more than one basin-opening episode occurs. Accreting arc-forearc terranes are therefore likely to incorporate proto-arc, backarc, and (in some cases) inherited continental fragments, as evidenced by their structural complexity and lithological diversity. Forearc complexes typically show positive Bouguer gravity anomalies and significant age discrepancies within and between their crustal and mantle components. Where exposed, their lower stratigraphic horizons may include boninite-bearing assemblages along with tectonized fragments of mid-ocean ridge basalt (MORB) basement and hydrated refractory peridotite. These are typically intruded by sodic plagiogranite (adakite) and high-temperature Mn-, Fe-rich hydrothermal veins (‘epidosites’), further indications of subduction nucleation at, or close to a pre-existing spreading axis. Where the arc-trench rollback process is terminated by collision with an approaching continent, or with another retreating forearc complex, MORB-like backarc lithosphere is rapidly reconsumed, in some cases following a change in subduction polarity. In contrast, given their preponderance of ultra-refractory serpentinized peridotite, forearc complexes are relatively buoyant, resist subduction, and are prone to entrapment during early stages of an orogeny. The associated interplay of extension and compression offers a compelling scenario for resolving the so-called ophiolite ‘conundrum’ and explaining the near-ubiquity of ophiolites in orogenic belts. We propose that rapid arc-trench rollback pulses are driven largely by collision-induced mantle flow in addition to commonly cited ‘slab pull’ effects. This is supported by the evidence of isotopic mantle flow tracers, seismic tomography, and the coupled kinematics of marginal basins and continental escape. Model applications to some well-known Tethyan ophiolites are developed in a companion paper.
Tethyan- and Cordilleran-type ophiolites of eastern Australia: implications for the evolution of the Tasmanides
Authors: Spaggiari Catherine V. , Gray David R. , Foster David A.
Published: April 2008

The preservation of diverse ophiolitic rocks in the Tasmanides of eastern Australia reflects a period of complex oceanic crust formation off the east Gondwana margin from
c.
560 to 495 Ma. This involved development of oceanic crust possibly at a spreading ridge (now preserved as the
c.
560 Ma Marlborough ophiolite, New England Orogen), development of forearc crust in a suprasubduction zone between
c.
530 and 515 Ma (Tyennan-Delamerian ophiolites), possible synchronous formation of suprasubduction zone crust further outboard (southern New England Orogen ophiolites), emplacement of Tyennan-Delamerian ophiolites onto the Gondwana margin at
c.
515 Ma, followed by development of new forearc and backarc crust between
c.
505 and 495 Ma (Lachlan Orogen). Tasmanide orogenesis has resulted in the production of both Tethyan-type and Cordilleran-type ophiolites. Tethyan types are represented by the Tyennan (Tasmanian) and possibly Delamerian Orogen ophiolites that were emplaced onto the passive continental margin. The Tasmanian ophiolite has been interpreted as having been emplaced as one or more thrust sheets, concurrent with the development of a metamorphic sole. In contrast, Lachlan Orogen ophiolites were emplaced within major fault zones by accretionary processes such as offscraping, underplating, and duplexing via underthrusting and basin closure during Late Ordovician to Silurian times. Cordilleran-type ophiolites, for example the Lachlan Orogen ophiolites, are dominated by disrupted upper oceanic crustal stratigraphies, whereas Tethyan-types tend to be dominated by mantle and gabbroic sequences, or preserve more complete stratigraphies.
Volcanic history of the back-arc region of the Izu-Bonin (Ogasawara) arc
Authors: Ishizuka Osamu , Uto Kozo , Yuasa Makoto
Published: April 2008

The laser-heating
40
Ar/
39
Ar dating method was applied to volcanic rocks systematically collected from the back-arc region of the central part of the Izu-Bonin arc. Dating results combined with whole-rock chemistry and other geological information reveal the volcanic history of the back-arc region of the Izu-Bonin arc. In the back-arc seamount chains area, andesitic-basaltic volcanism initiated at
c.
17 Ma, slightly before the Shikoku Basin ceased spreading, and continued until
c.
3 Ma. Relatively old volcanism (>8 Ma) has been found only from the western part of the seamount chains, and younger volcanism mainly occurs in the eastern part of the chains, indicating the western margin of the active volcanic zone of the Izu-Bonin arc has migrated eastward with time. At around 2.8 Ma, volcanism initiated in the western part of the back-arc knolls zone. This volcanism is characterized by eruption of clinopyroxene-olivine basalt. In the first stage of rifting, this type of basalt erupted from N-S-trending fissures and/or vents aligned in this direction and formed N-S-trending ridges. Between 2.5 and 1 Ma, many small knolls were formed by eruption of basalt and minor felsic rocks. Volcanism younger than 1 Ma occurred only in the currently active rift zone and its adjacent area.

The active volcanic zone in the back-arc seamount chains area converged to the volcanic front with time from 17 to 3 Ma. Active rifting and rifting-related volcanism also migrated or converged eastward after 1 Ma. The observed temporal variation of locus of volcanism may be explained by rapid retreat of the Philippine Sea Plate relative to the Pacific Plate and resulting steepening of the subducting slab.
Metamorphic monazite and the generation of P-T-t paths
Authors: Foster Gavin , Parrish Randall R.
Published: April 2008

Monazite is the mineral of choice in pelitic rocks for providing time constraints on metamorphic rocks and metamorphic processes. However, unlike rock-forming mineral chronometers such as garnet, the petrogenesis of monazite is relatively poorly understood. Consequently, although it is possible to generate precise monazite ages, the significance of the age in metamorphic rocks is often uncertain. In this contribution, we show how the petrogenesis of monazite can be linked to pressure and temperature information. Four complementary approaches, each illustrated by examples, are discussed: (i) the textural relationships of accessory minerals are used to relate the petrogenesis of monazite to that of the rock-forming mineral assemblage, and through this to P-T; (ii) monazite composition, in particular Y content, is used to relate monazite to the rock-forming mineral assemblage, and thus, to P-T; (iii) the bulk compositional control on monazite stability has been empirically determined and this relationship allows the temperature of initial monazite growth to be estimated in a given bulk composition; (iv) monazite-xenotime thermometry is utilized to provide estimates of the temperature of monazite growth. Either individually or combined, these approaches successfully enable monazite age data to be placed in a P-T framework.
Stacking fault-enhanced argon diffusion in naturally deformed muscovite
Authors: Kramar Nicolas , Cosca Michael A. , Buffat Philippe-André , Baumgartner Lukas P.
Published: April 2008

Recent advances in microscale
40
Ar/
39
Ar geochronology have revealed argon concentration gradients in naturally deformed muscovite that are incompatible with volume diffusion uniquely, and have been interpreted to result from intragranular defect-enhanced diffusion. Defects and heterogeneously spaced stacking faults observed by transmission electron microscopy in such muscovites are evaluated as potential fast pathways for argon diffusion.

Two-dimensional defects, such as stacking faults, are of particular interest for noble gas diffusion because of the net dilatation effect that a stacking fault is able to generate in minerals. In micas, partial dislocations (and the area between them known as stacking faults) within the interlayer displace the potassium atoms from a stable hexagonally centred position between opposing tetrahedral layers to an unstable position relative to one of the tetrahedral layers such that repulsive forces lead to a localized net dilatation effect within the interlayer. Such a dilatation effect may have direct consequences for argon retention in micas. Numerical modelling of the effects stacking faults have on argon diffusion was performed on the basis of the calculated interlayer spacing, measured isotope data, and observed linear stacking fault density. These calculations result in effective diffusivity ratios defined by volume diffusion to defect-enhanced diffusion of 10
6
to 10
7
, which are comparable with diffusivity ratios in other materials (ceramics or metals).

In the absence of defects causing physical grain size reduction (e.g. kink bands or subgrain boundaries), stacking faults are potentially the main defect in sheet silicates exerting a measurable influence on intragranular argon diffusion. Stacking-fault-enhanced argon diffusion differs from pipe diffusion, whose significance on bulk diffusion depends on high dislocation densities, by the small volume fraction of dislocations required to affect bulk diffusivities. In contrast to pipe diffusion, the linked occurrence of dislocations and stacking faults within mica interlayers represents a potentially significant volume fraction, even in samples that do not have high apparent dislocation densities.
Foreland basin evolution around the western Alpine Arc
Authors: Ford Mary , Lickorish W. Henry
Published: April 2008

The arcuate form of the external western Alps was generated during Tertiary NW-directed collision between the Apulian indentor and the southward-subducting European passive margin. The evolution of peripheral syn-collisional depocentres around this arcuate orogen (in France and Switzerland) is reconstructed using a compilation of stratigraphic and tectonic data. This reveals fundamental changes in the flexural behaviour of the European lithosphere during collision. During early collision (Eocene), an increasingly arcuate, peripheral flexural basin migrated rapidly NW across the European plate. During peak collision (early Oligocene), frontal flexure, recorded in the North Alpine Foreland Basin (NAFB), steepened markedly, while lateral flexure of the European plate, affecting SE France, effectively ceased. Here, Oligocene sedimentation was confined to small thrust-sheet-top basins. Two rift systems initiating in the late Eocene, the West European rift system and the West Mediterranean oceanic basin (that created the Gulf of Lion passive margin), are superimposed in space and time on the outer margins of the alpine flexural depocentres. During waning collision (Mio-Pliocene) the NAFB became overfilled, then uplifted and abandoned while, in SE France, a local depocentre (Digne-Valensole) developed between uplifting blocks and continued to accumulate sediments until the late Pliocene.
The turbidite fill of the Annot sub-basin (SE France): a sequence-stratigraphy approach
Authors: Callec Y.
Published: April 2008

New sedimentological and biostratigraphical data on the Annot sub-basin (southern Alps, France) provide a good overview of a fore-deep basin infill with well-known Annot turbiditic complex. This basin shows a total thickness of more than 1100 m, where the Grès d’Annot exceeds 500m with well-longitudinal and transversal outcrops. Our study is to define a chronostratigraphical framework, which allows comparisons of local signatures of sea-level fluctuations with eustatic curve, and also identification of tectonic effects. The Annot succession could be interpreted as a second-order cycle. We identify a deepening and transgressive Priabonian interval, represented by the transition from platform of the Calcaires Nummulitiques to hemipelagic marls of the Marnes Bleues where tectonic subsidence rate outpaces third-order eustatic fluctuations and sedimentary influx. Priabonian to early Rupelian Annot turbidites progressively appear with a thickening- and coarsening-upward stacking pattern of four different sand-rich turbiditic systems with lobes, megaslide, channelized lobes and erosional/depositional channel. Each prograding system is separated by an erosive surface corresponding to a third sequence boundary. A possible sequence stratigraphy interpretation may be modelled as a forced regression during foreland basin closure, where the upper turbiditic systems correspond to lowstand prograding complexes from basin floor fan to proximal slope fan.
The influence of syndepositional basin floor deformation on the geometry of turbiditic sandstones: a reinterpretation of the Côte de L’Âne area (Sanguinière-Restefonds sub-Basin, Grès d’Annot, Late Eocene, France)
Authors: Broucke Olivier , Guillocheau François , Robin Cécile , Joseph Philippe , Calassou Sylvain
Published: April 2008

The Côte de l’Âne section has been previously interpreted as shallow marine deposits (deltaic system with delta-front to bay head and back-barrier environments). The purpose of this article is (1) to suggest a reinterpretation of these facies of the Grès d’Annot in this area as deep marine deposits and (2) to discuss the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits. The facies analysis of the sedimentary succession is based on eight measured sedimentological logs and on the visual correlation of identified surfaces. Detailed sedimentological observations permitted the identification of a turbidite facies spectrum, schematized in nine facies associations. Outcrop-scale analysis highlights a downstream thickening of the sedimentary sequence resulting from a strong control by tectonic deformation. This deformation is mainly a flexure with a half-wavelength longer than 500m. Associated normal faults may be related to a gravity slide of unconsolidated sediments accommodated within the flexure. Finally, detailed correlations based on the genetic unit model in the Restefonds-Sanguinière system establish the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits.
The influence of a lateral basin-slope on the depositional patterns of natural and experimental turbidity currents
Authors: Amy L. A. , McCaffrey W. D. , Kneller B. C.
Published: April 2008

Understanding topographic effects upon the depositional processes of turbidity currents and the resulting deposit characteristics is key to producing reliable depositional models for turbidity currents. In this study, the effect on depositional patterns of a lateral slope whose strike is parallel to the principal direction of flow is explored using field and experimental results. This type of basin topography is commonly found in confined turbidite systems. Field data from the Peïra Cava turbidite system of the Tertiary Alpine Foreland Basin (SE France) and experimental data show that a characteristic depositional pattern is produced by surge-type waning flows that interact with a lateral slope. This pattern comprises beds that thin (and fine in the field study) not only downstream but also markedly away from the lateral slope (Type I beds). In the Peïra Cava system, this pattern is also observed in average values of sandstone bed thickness, sandstone percentage and grain-size, derived from measured sections, demonstrating that the processes responsible for this pattern also control gross properties within this sheet system. The characteristic thinning-away-from-slope deposit geometry is interpreted as an effect of the lateral slope via its influence on spatial variations in flow properties and on the suspended load fallout rate (SLFR) from currents. Flow velocity non-uniformity cannot explain thinning into the basin because flow has a higher deceleration along streamlines away from the slope that should cause higher SLFR and thicker deposits away from the slope instead of close to the slope. A concentration non-uniformity mechanism is invoked that has the effect of maintaining relatively high flow concentrations and hence SLFR in medial and distal locations close to the slope. Experiments suggest that this may arise due to different rates of flow expansion on the obstructed and unobstructed sides of the current in proximal regions. Velocity non-uniformity can, however, explain the geometry of deposits that thicken away from slope. Beds of this type do occur occasionally in the Peïra Cava system (Type II beds). Flow velocity non-uniformity patterns have been used previously to successfully explain the spatial distributions of depositional facies of turbidity currents that have interacted with topography. The analysis in this study demonstrates that velocity non-uniformity, by itself, cannot explain depositional patterns in all basin settings. Future depositional models need to incorporate the effects of spatial changes in other flow properties, such as flow concentration, upon deposition to be able to predict turbidite facies in many different types of basin setting.
Factors controlling foredeep turbidite deposition: the case of Northern Apennines (Oligocene-Miocene, Italy)
Authors: Cibin U. , Di Giulio A. , Martelli L. , Catanzariti R. , Poccianti S. , Rosselli C. , Sani F.
Published: April 2008

Three major controlling factors affect turbidite deposition in foredeep basins: tectonics in the source area, tectonics in the belt-basin system, and variations of sea-level (local or global). These factors are expected to have different effects on the volume, grain size, provenance and distribution of clastic sediments during the evolution of the basin. The interplay of these factors is investigated for the latest Oligocene-Middle Miocene Northern Appennines Foredeep turbidite wedges by means of turbidite-system-based lithostratigraphy and field mapping, integrated with nannoplankton biostratigraphy and sedimentary petrography. Almost all recognized turbidite systems, unless tectonically truncated, show an overall stacking pattern formed by a lower sand-rich, thickly bedded stage (
depocentre stage
) passing upward into mud-rich, thinly bedded stages, eventually grading up to mostly mudstone units (
abandonment stage
). This rhythmically repeated pattern is interpreted as the result of the abrupt switching on and off of coarse-grained input, coupled with an alternating increase/decrease of depositional rate recorded in all detected systems. Biostratigraphy makes it possible to distinguish the switching-off of turbidite systems due to depocentre migration (a new system is switched on basinward) from that due to a regional decrease of clastic input. Sandstone petrography records the compositional variation related to tectonically induced source reorganization. In the latest Oligocene-Middle Miocene NAF foredeep wedges, this integrated dataset allows us to recognize: two different phases of source tectonics in the latest Oligocene and the middle Burdigalian; two major episodes of basin tectonics and related depocentre shift in the latest Oligocene and the Langhian, plus a minor middle Aquitanian phase; and three intervals of reduced regional turbidite deposition during the Late Aquitanian, Middle Burdigalian and Early Serravallian, possibly linked to sea-level rises.
Comparing the depositional architecture of basin floor fans and slope fans in the Pab Sandstone, Maastrichtian, Pakistan
Authors: Eschard R. , Albouy E. , Gaumet F. , Ayub A.
Published: April 2008

Basin-floor fans and slope fans present major differences in their internal architecture related to changes in: (1) margin morphology, (2) relative sea-level change, and (3) sediment supply. These variations are illustrated in the outcrops of the Pab Sandstone in Pakistan. The Pab Sandstone third-order sequence was deposited on the Indo-Pakistani margin during the Upper Maastrichtian. Uplift of the margin induced erosion on the shelf, incision of submarine canyons on the slope and the development of a sand-rich, high-efficiency basin-floor fan extending over hundreds of kilometres on the basin floor. During transgression, sediment accumulated in backstepping shoreface deposits on the shelf, and a minor mud-rich slope fan was deposited in the basin. Finally, a sand-rich braided delta prograded across the shelf, feeding a sand-rich slope fan where it reached the shelf margin. This slope fan was of more limited lateral extent. The Lower Pab basin-floor fan shows the effects of flow funnelling and confinement due to a canyon incised into the slope. It consists mainly of channel complexes deposited by superconcentrated density flows to low-density turbidity currents. In contrast, the Upper Pab slope fan shows little confinement and low transport efficiency. It consists of tabular lobes, aggrading mid-fan channels and conglomeratic channels in the upper fan. The low transport efficiency of the gravity flows probably explains the low degree of organization of the slope fan.
Asymmetric lithosphere as the cause of rifting and magmatism in the Permo-Carboniferous Oslo Graben
Authors: Pascal Christophe , Cloetingh Sierd A. P. L. , Davies Gareth R.
Published: April 2008

Compared to other Permo-Carboniferous rift basins of NW Europe, the Oslo Graben has two distinct characteristics. First, it initiated inside cold and stable Precambrian lithosphere, whereas most Permo-Carboniferous basins developed in weaker Phanerozoic lithosphere, and second, it is characterized by large volumes of magmatic rocks despite relatively little extension. Seismic reflection surveys show that the crust thickens from southern Norway to southern Sweden, the most significant Moho deepening occurring from the Oslo Region eastwards. Deep seismic studies also suggest that the base of the lithosphere deepens markedly eastwards from the Oslo Region. Such a long-wavelength lithospheric geometry cannot be explained by the Permian or post-Permian evolution of the area, hence the Oslo Graben appears to have evolved at the transition between two lithospheric domains with contrasting thickness. Numerical thermo-mechanical modelling is applied to test if this transitional position can influence the dynamics of rifting. Different models with varying lithosphere thickness contrast are considered. Model results show that a crust and lithosphere thickness contrast comparable to the Oslo Region can explain rifting and focusing of magmatism in a narrow zone with minor thinning of the crust. Models also account for the major characteristics of the Oslo Graben in terms of location and strain distributions in the crust.
Magmatism of the late Variscan intermontane Saar-Nahe Basin (Germany): a review
Authors: von Seckendorff Volker , Arz Christoph , Lorenz Volker
Published: April 2008

The Saar-Nahe Basin is a late Variscan intermontane basin that developed on the site of an earlier island arc, the Mid-German Crystalline Rise. Within the
c.
6500m-thick continental sedimentary fill of the basin, a large variety of igneous rocks was emplaced over a period of
c.
4 Ma from 296 to 293 Ma as high-level intrusions and lava flows, extrusive domes, diatremes and pyroclastic deposits, ranging in composition from basalt and basaltic andesite to rhyodacite, rhyolite and trachyte. Composite intrusive-extrusive complexes consist of andesite, rhyodacite and alkali feldspar trachyte with up to 10 wt% K
2
O. The geochemical characteristics of the most primitive mafic magmas indicate a slightly enriched upper mantle source modified by subduction-related fluids. Nd-Sr-O isotope data indicate that crustal contamination was important in the petrogenesis of the more differentiated magmas.
Microstructural evolution in a mylonitic quartz simple shear zone: the significant roles of dauphine twinning and misorientation
Authors: Lloyd Geoffrey E.
Published: April 2008

SEM/EBSD-based orientation and misorientation analyses are described for a lower amphibolite facies simple shear zone (Torridon, NW Scotland). It is shown that as well as conventional crystal-slip processes (i.e. basal-

a

, prism-

a

, rhomb-

a

and negative second order rhomb-

a

slip), dauphine twinning also plays a role in both microstructural and petrofabric evolution. Twinning assists in the initial grain size comminution processes, including dynamic recrystallization, from originally coarse wall rock grains to a typical mylonitic microstructure in the centre of the shear zone. Subsequently, twinning helps to accommodate high shear strains in the mylonite whilst maintaining a stable microstructure and constant ‘single crystal’ petrofabric. The role of dauphine twinning appears to be to allow efficient switching between relatively ‘soft’ and relatively ‘hard’ slip directions that possibly exploit a distinction between negative and positive crystal forms. Misorientation analysis emphasizes the relationships between crystal-slip systems and grain boundary network, including dauphine twin planes, and suggests that the mylonitic microstructure contains preferred orientations of both tilt and twist boundaries that help to explain shear zone microstructural evolution and stability.
Strain removal within the Hercynian Shear Belt of Central Brittany (western France): methodology and tectonic implications
Authors: Gumiaux C. , Brun J. P. , Gapais D.
Published: April 2008

Central Brittany comprises a major shear belt formed during the Hercynian Orogeny. In this paper, we present a model for the restoration of the belt, based on an exhaustive compilation of available structural data. The model uses a geostatistical analysis of cleavage orientation data. The analysis shows that the eastern part of Central Brittany has been deformed by bulk dextral strike-slip, a feature that validates previous structural interpretations. It also provides explanations for: the strain patterns observed within and around the restored domain; the nature of domain boundaries and of associated kinematics; and the occurrence of local superimposed deformations.
Strain and deformation history in a syntectonic pluton. The case of the Roses granodiorite (Cap de Creus, Eastern Pyrenees)
Authors: Carreras J. , Druguet E. , Griera A. , Soldevila J.
Published: April 2008

The Roses granodiorite is a Variscan stock with well developed syn- and post-magmatic deformation structures that crops out in the Pyrenean Axial Zone. Analysis of structures reveals a continuous deformation history during and after magma cooling. The deformation history is divided on the basis of mechanical behaviour into two stages: an early one with the development of magmatic structures and a late stage with the development of mylonitic fabrics along shear zones. Both stages are separated in time by the emplacement of aplite-pegmatite dykes. Time of dyke emplacement is thought to coincide with a sudden change in rheology of the granodiorite. The abundance of quartz dioritic enclaves permits the use of shape analysis to characterize the magmatic fabric as a homogeneous deformation. Later solid-state deformation led to the development of an inhomogeneous deformation pattern with different sizes of anastomosing shear zones wrapping around lozenge-shaped domains. The displacement/width ratio measured in shear zones ranges between one and two orders of magnitude. The Roses granodiorite is thought to be a synkinematically emplaced stock which records a continuous deformatioinal history with two distinct deformation stages, both recording bulk finite strains of similar order of magnitude but with a marked difference in finite strain distribution.
The water-related work of William Smith (1769–1839)
Authors: Torrens H. S.
Published: April 2008

In 1797 Smith recorded his first known ‘Order of Strata’. This was based on his work as a land, colliery and canal surveyor around Bath, Somerset. It already shows a clear awareness of the occurrence of spring lines (especially in the Fuller’s Earth, soon to cause such problems in the construction of the Somerset Coal Canal). In his better known June 1799 version, Smith much extended this, with a new third column showing springs, now tabulated for five of his 23 strata. Smith thus had a keen awareness of both the importance of, and the problems raised by, how water was, or was not, retained in rocks and how it was released at stratigraphically controlled spring lines. This paper briefly reviews five of his involvements with ‘water-related’ geology. The first was as canal engineer. Here one of the two branches of his first canal later had to be abandoned because it could not be made to retain water where it passed over the Dolomitic Conglomerate. The second was as a land drainer. This he first attempted at Camerton in about 1796. This skill brought him most of his early employments after his dismissal from canal work in June 1799. Third, Smith was next a significant exponent of the art of creating water meadows, particularly in Bedfordshire and Norfolk. Smith was active next in a fourth field, erecting sea defences along the east coast of England. Finally he was often consulted on how to find or control new water supplies, as at Swindon or Scarborough. It was this last work which used his stratigraphic skills to their fullest extent.
Joseph Lucas (1846–1926) — Victorian polymath and a key figure in the development of British hydrogeology
Authors: Mather J. D. , Torrens H. S. , Lucas K. J.
Published: April 2008

Joseph Lucas joined the Geological Survey in 1867 and spent almost 9 years mapping in Yorkshire. Forced to resign in ignominious circumstances, for the rest of his life he earned his living advising on groundwater supplies. In 1874 he was the first to use the term hydrogeology in its modern context and defined this new subject in a series of papers in the 1870s. He drew the first British maps showing groundwater contours and described how to carry out a hydrogeological survey. For many years he lobbied for such a survey to be carried out over the whole country and for it to be used as a basis for water resource planning. He was an accomplished linguist, translating material from a variety of European languages, and wrote books on natural history and genealogy. He and his family lived at Tooting, in south London, where he is buried in the Churchyard of Saint Nicholas.
British hydrogeologists in West Africa — an historical evaluation of their role and contribution
Authors: Hazell Robin
Published: April 2008

The Colonial Office established and funded geological surveys in British West African colonies, from 1903 until self government in c. 1960. Provision of water supplies, at first a minor component of the services provided, later often dominated departmental activities. Understanding of the nature of groundwater mirrored the state of the art elsewhere: supply kept pace with demand. Exploration of sedimentary basins led to development of major aquifers. In the 1930s innovative refinements of geophysical siting and well sinking techniques were developed. From 1980 major water borehole programs were largely supervised by British consultants, who continued to pioneer siting and construction techniques.
Developments in UK hydrogeology since 1974
Authors: Brassington F. C.
Published: April 2008

The last quarter of the 20th century has seen the most rapid development of hydrogeology in terms of both the depth of understanding of hydrogeological processes and of the hydrogeology of Britain, with an associated rapid growth in the number of people employed as professional hydrogeologists in the UK. The four main influences that brought about these developments are changes in the structure of the UK water industry and environmental regulators, particularly in England and Wales; influences of EC directives on UK environmental regulation; a growing public awareness of environmental issues and the pressure they applied on successive governments; and developments in computing power, software development and electronic instrumentation. The paper examines the fields in which hydrogeologists have worked during the last three decades and concludes that it has been the richest period for hydrogeological achievement in the history of the science.
The Central Asian Orogenic Belt and growth of the continental crust in the Phanerozoic
Authors: Jahn Bor-Ming
Published: April 2008

Asia is the world’s largest composite continent, comprising numerous old cratonic blocks and young mobile belts. During the Phanerozoic it was enlarged by successive accretion of dispersed Gondwana-derived terranes. The opening and closing of palaeo-oceans would have inevitably produced a certain amount of fresh mantle-derived juvenile crust. The Central Asian Orogenic Belt (CAOB), otherwise known as the Altaid tectonic collage, is now celebrated for its accretionary tectonics and massive juvenile crustal production in the Phanerozoic. It is composed of a variety of tectonic units, including Precambrian microcontinental blocks, ancient island arcs, ocean island, accretionary complexes, ophiolites and passive continental margins. Yet, the most outstanding feature is the vast expanse of granitic intrusions and their volcanic equivalents. Since granitoids are generated in lower-to-middle crustal conditions, they are used to probe the nature of their crustal sources, and to evaluate the relative contribution of juvenile v. recycled crust in the orogenic belts. Using the Nd-Sr isotope tracer technique, the majority of granitoids from the CAOB can be shown to contain high proportions (60 to 100%) of the mantle component in their generation. This implies an important crustal growth in continental scale during the period of 500–100 Ma. The evolution of the CAOB undoubtedly involved both lateral and vertical accretion of juvenile material. The lateral accretion implies stacking of arc complexes, accompanied by amalgamation of old microcontinental blocks. Parts of the accreted arc assemblages were later converted into granitoids via underplating of basaltic magmas. The emplacement of large volumes of post-accretionary alkaline and peralkaline granites was most likely achieved by vertical accretion through a series of processes, including underplating of basaltic magma, mixing of basaltic liquid with lower-crustal rocks, partial melting of the mixed lithologies leading to generation of granitic liquids, and followed by fractional crystallization. The recognition of vast juvenile terranes in the Canadian Cordillera, the western US, the Appalachians and the Central Asian Orogenic Belt has considerably changed our view on the growth rate of the continental crust in the Phanerozoic.
Nb-depleted, continental rift-related Akaz metavolcanic rocks (West Kunlun): implication for the rifting of the Tarim Craton from Gondwana
Authors: Yuan Chao , Sun Min , Yang Jingsui , Zhou Hui , Zhou Mei-Fu
Published: April 2008

The Akaz metavolcanic rocks of the West Kunlun Mountains possess low to intermediate SiO
2
(42.3–64.7 wt%) and MgO (2.69–7.54 wt%) and high TiO
2
(0.94–3.05 wt%) and Fe
2

O
3
T

(7.64–18.47 wt%), indicating a basaltic to andesitic protolith. These rocks have high contents of Zr (89.6–470 ppm), Nb (10.0–40.3 ppm), Y (19.7–52.7 ppm), Th (0.86–15.96 ppm) and total REE (67.7–407 ppm), and are characterized by relatively high Ti/Y (183–649), Th/Yb (0.5–3.9), and low Hf/Ta (3.0–8.6) ratios. They are LREE-enriched (La/Yb = 5.4–20) and most have small negative Nb anomalies (Nb/Nb* = 0.20–1.16). These characteristics are transitional between within-plate and subduction-related basalts. The relatively high Gd/Yb ratios (1.4–2.9) distinguish these rocks from island-arc tholeiites and the high Zr/Y (3–12), Ta/Yb (0.3–0.7) and low Zr/Nb (<12) ratios strongly support a continental affinity. The protoliths for the Akaz metavolcanic rocks are interpreted to be continental rift basalts formed during rifting of the Tarim Craton from Gondwana. Stratigraphic and palaeontological data indicate that the rifting occurred in Sinian to Cambrian times, roughly contemporaneously with rifting in the East Kunlun and North Qilian orogenic belts farther to the east.
UHP rocks and the Dabieshan Orogenic Belt
Authors: Wang Qingchen , Cong Bolin
Published: April 2008

The Dabieshan Orogenic Belt, which contains ultra-high-pressure (UHP) metamorphic rocks, is the Mesozoic collision zone between the Sino-Korean and Yangtze cratons. With respect to the exhumation of the UHP rocks, the Dabieshan Orogenic Belt can be divided into four units, i.e. allochthonous, parautochthonous, autochthonous and reworked units. The allochthonous unit is composed of UHP rocks. The parautochthonous unit is represented by the non-UHP rocks of the Yangtze sedimentary cover and crystalline basement, as well as an accretionary wedge. The autochthonous unit includes Jurassic and Cretaceous sedimentary and igneous rocks. The reworked unit is characterized by migmatization. The deep structure of the Dabieshan Orogenic Belt is characterized by a Moho offset and dome structure in the middle and upper crust, as recording a compressional state. A northward subduction of the Yangtze craton is evidenced by geological, geophysical and geochemical data. In the formation of the Dabieshan orogenic belt, a precondition is the low density of the subducted continental materials. If the UHP unit is the
piston
to build up the orogenic belt, then the continuous compression between the Sino-Korean and Yangtze cratons is the
motor
to trigger the mountain-building processes.
About this title
Authors: Malpas J , Fletcher C.J.N. , Ali J.R. , Aitchison J.C.
Published: April 2008

The subject of this Special Publication is one of the most interesting in global geoscience, the tectonic evolution of China. The assemblage of terranes that underlie this part of the world provides outstanding opportunities to elucidate global processes, and many of the factors that shape the Earth's lithosphere are best exemplified by the geology of China and its immediately adjacent areas

In addition, there are geological features that are particular and unique to the region. Some have been the focus of recent attention and have attracted international interest because of their global importance. This volume provides accounts of up-to-date research by Chinese and international geological teams on key aspects of the tectonic evolution of China and its surrounding areas. The papers describe the formation of the geological terranes that make up this part of east Asia, place constraints on plate tectonic models for their assembly and provide accounts of unique geological feature of the subcontinent.
Termination of strike-slip faults at convergence zones within continental transform boundaries: examples from the California Continental Borderland
Authors: Legg M. R. , Kamerling M. J. , Francis R. D.
Published: April 2008

Continental transform plate boundaries are broad, composed of numerous active and subparallel strike-slip fault zones. Irregular geometry along the major transform structure creates convergence and divergence zones within the plate boundary where other strike-slip faults terminate. Some prominent irregularities result from microplate interactions. Relative fault displacement, diminishing to zero at fault terminations, must be accommodated or transferred to other structures, laterally or vertically, away from the fault end-point. Distinct styles of strike-slip fault termination may represent different degrees of vertical strain partitioning within the plate boundary.

The Western Transverse Ranges (WTR) of California mark a major structural discontinuity that cuts at high angle across the Pacific-North America transform boundary. Within the California Continental Borderland, two end-member classes of right-slip fault termination against the WTR are apparent. (1) Several major faults, including the San Clemente, San Pedro Basin, Ferrelo and Newport-Inglewood, intersect the southern boundary of the WTR at high angles, with negligible to minor local deflection and minor dissipation of right shear at the Earth’s surface. These faults are inferred to cut through the entire borderland crust and continue in the lower crust beneath the WTR, as evident in geophysical data. These ‘blind’ near vertical faults may control segmentation and earthquake activity on the overlying west-trending WTR structures. (2) In contrast, the Palos Verdes and possibly Whittier faults appear broadly deflected westward to merge at low angle with WTR structure. NW-trending faults rotate counterclockwise, away from the axis of principal shortening as observed in pure shear models, and slip is dissipated through folding, thrust transfer and rotation. Deflected faults are inferred to be predominately upper crustal features, detached from the lower crust and unable to underthrust the WTR. These two distinct right-slip fault termination styles, and associated convergent structures, suggest that basal shear drives vertical-axis rotation of the WTR block over the underthrust Inner Borderland plate. Furthermore, the lower plate, slivered by these right-slip faults, is incompletely coupled with the Pacific plate.
Distributed strike-slip faulting, block rotation and possible intracrustal vertical decoupling in the convergent zone of SW Japan
Authors: Fabbri Olivier , Iwamura Kazumasa , Matsunaga Satoshi , Coromina Guilhem , Kanaori Yuji
Published: April 2008

Between the Median Tectonic Line (MTL) and the Japan Sea, the western Chugoku region of SW Japan is cut by a series of N45°E first-order faults and oblique (N60°–N170°E) second-order faults. This fault network, probably formed during Late Cretaceous-Palaeocene times (70–60 Ma), defines a regional block structure. Pre-Plio-Quaternary kinematical indicators suggest left-lateral motion along the first-order faults and right-lateral motion along some of the second-order faults. Geomorphological evidence and earthquake focal mechanisms indicate that Plio-Quaternary slip senses are opposite to Pre-Plio-Quaternary ones.

The overall fault pattern is geometrically and kinematically similar to patterns obtained by experimental modelling of simple shear deformation distributed at the base of a brittle layer analogue over its entire width. This similarity suggests the possibility of a mid-crustal, flat-lying partial attachment zone which could have controlled the formation of the western Chugoku fault network in Cretaceous to Palaeocene times. The zone, presently inactive, could correspond to the ‘proto-MTL’, a low-angle fault recently imaged by seismic reflection studies and whose trace approximately coincides with the present-day MTL.

Reactivation of the system occurred twice after its formation: firstly in Miocene times, during the opening of the Japan Sea and concomitant clockwise rotation of the entire SW Japan arc; and secondly in Late Pliocene to Quaternary times, after a shift of the relative direction of convergence between the Philippine and Eurasia plates. Unlike the first reactivation, the second reactivation led to an inversion of the sense of slip along the faults.
A re-evaluation of the relationship between trace fossils and dysoxia
Authors: Martin Kate D.
Published: April 2008

Geochemical and palaeontological methods are used to determine the oxygenation histories of Jurassic sequences at Ravenscar, North Yorkshire, and Lyme Regis, Dorset. The ichnology of these sequences is compared with interpreted oxygen levels, allowing current models of oxygen-related trace fossil occurrence to be tested. These case studies support pre-existing models of trace fossil occurrence in demonstrating that burrow diversity, diameters and depth of infaunal tiering increase with increasing oxygen levels. The case studies suggest that trace fossil ethologies may not always be a reliable indicator of palaeo-oxygenation: in some cases, substrate consistency may have a greater influence over ethology than oxygen levels.
Chondrites
is confirmed as a common constituent of dysoxic settings; however, other trace types may also be indicative of such settings.