bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclicity of Devonian fluvial sedimentation, Cunningsburgh Peninsula, SE Shetland
Authors: Allen P. A. 
Published: December 2007

The Cunningsburgh area, SE Shetland, contains approximately 1000 m of fluvial sediments deposited in four sub-environments. Ripple cross-laminated siltstones and sandstones represent levee-type sediments, horizontally- and solitary cross-stratified sandstones were deposited by overbank sheet floods; red mudstones with sandstone lenses represent floodbasin sediments and grouped cross-stratified sandstones are substratum sediments deposited in the channellized zone as transverse bars. point bars and megaripple channel-fills.
Transition, entropy and substitutability analyses indicate that in the S of the Cunningsburgh area cyclicity was controlled by two processes: one was that of channel migration, cut-off or avulsion, producing scoured surfaces overlain by substratum cross-stratified sandstones. The other was that of overbank flooding, producing an interbedding of overbank sheet flood deposits, levee-type sediments and floodbasin fines. Further to the N, distant from the main channellized zone, overbank sheet flood deposits are more common and are interbedded with levee and floodbasin deposits. Cyclicity in this zone was, therefore, controlled essentially by overbank flooding alone but not by channel migration or shifting.
The fluvial system was characterized by a central zone containing channellized high-sinuosity flow which was bordered, within the same alluvial valley, by low-lying floodplains subject to flooding by both crevassing and overtopping of levees. The main stream only rarely migrated into this outer floodplain.
The Cenozoic subduction history of the Pacific margin of the Antarctic Peninsula: ridge crest–trench interactions
Authors: Barker P. F. 
Published: December 2007

New magnetic anomaly identifications W of the Shackleton Fracture Zone show 5 spreading sections, separated by fracture zones. In the 2 most southerly, the ridge crest collided with a trench at the margin of the Antarctic Peninsula only 6.5 and 4 Ma ago, the latest of a series of collisions starting at the base of the peninsula SO Ma ago. Following each collision, spreading and subduction both stopped. Opposite the South Shetland trench and actively extending Bransfield Strait, spreading also stopped 4 Ma ago, but before the spreading centre reached the trench. The tendency of the subducting plate to continue sinking probably initiated the opening of the Bransfield Strait.
The parallelism between fracture zone orientation on the descending plate and convergence direction, previously thought responsible for the tectonic segmentation of the peninsula, was effective for only 10–30 Ma before collision. Before that, either the fracture zones did not extend to the trench, or the subducting ocean floor formed at the Farallon–Phoenix (Nazca–Aluk) boundary, with fracture zones oblique to the subduction direction. The Aleutian Arc–Kula Ridge model, in which arc magmatism virtually ceases when ocean floor younger than 25–30 Ma occurs beneath the arc, fits the distribution of Antarctic Peninsula radiometric dates, explaining a 50–60 Ma gap between collisions and youngest ages in the S, and possibly the migration of the youngest activity towards the trench. Thus, gaps in the geologic record of arc magmatism need not imply cessation of subduction. The progressive steepening of the peninsular margin towards the 4 Ma collision site suggests tectonic erosion of the fore-arc as the ridge crest approached.
Tectonic evolution of SW Wales during the Upper Palaeozoic
Authors: Dunne William M. 
Published: December 2007

During the Upper Palaeozoic the development of several strike faults strongly influenced the deformation history of SW Wales. This aspect of the deformation is emphasized in this new description of the tectonic evolution of the region.
After the Caledonian orogeny, several strike faults caused crustal extension by normal dip-slip and partially controlled the subsidence of depositional basins. These faults ceased moving before the initiation of Variscan deformation in SW Wales. Two of the earlier faults were reactivated with reverse-slip translations during Variscan deformation, when three strike faults were initiated as a result of gravitational spreading. Two of the new faults formed sole thrusts for northward-translating nappes, and the other developed as a subsidiary lag fault. The sole thrusts transected some of the pre-existing faults, causing along-strike variation in their motion. The strike faults in SW Wales were therefore initiated at different times and display contrasting displacement histories.
Fluid-absent metamorphism
Authors: Thompson A. B. 
Published: December 2007

Many interpretations of metamorphic parageneses tacitly assume that a free fluid phase was always present during metamorphic equilibration (fluid-present metamorphism), as opposed to the circumstance that, while volatile species are certainly released from minerals during metamorphism, these species may not saturate the grain boundaries to produce free fluid (fluid-absent metamorphism). H
2
O-activity has meaning for both fluid-present and fluid-absent metamorphism and may be evaluated if an equilibrium may be written involving H
2
O and the temperature and rock-pressure of equilibration are known. P

H
2
O

has only a physical meaning for fluid-present metamorphism.

Although the effects of an aqueous fluid on displacing reactions in P–T space are well known, as are the enhanced kinetic and deformational effects of excess fluid, there is actually little compelling evidence to suggest that the presence of aqueous fluids is common during metamorphism of the middle and lower crust, and the mantle, for the duration of most dynamic processes, including partial melting. Possible exceptions are discontinuous dehydration reactions which affect large compositional ranges of metamorphic rock over narrow pressure–temperature intervals and which could locally produce a free liquid if production rate exceeds escape rate.
Evidence from stable isotopes and fluid inclusions obviously points to the accumulation of free aqueous fluid in definite locations for limited duration, but cannot, unfortunately, be used as evidence for generalized fluid transport during regional or contact metamorphism. Both mineralogical and textural criteria presently used to infer ubiquitous fluid, must be examined in terms of crustal volume and duration of dynamic processes to deduce the presence or absence of free fluid. If volatile components ever saturate grain boundaries, then the fluid-phase may only exist locally and perhaps only for short periods of time. Flow of metamorphic fluid may be focused into narrow regimes that could be quite widely spaced. Fluid-present metamorphism should not be considered as typical of whole crust evolution.
The petrology and geochemistry of dykes of the Lizard Ophiolite Complex, Cornwall
Authors: Kirby G. A. 
Published: December 2007

Dykes from the coastal section of the Lizard ophiolite, SW England, have been analysed for both major and trace elements. The dykes vary from fresh olivine dolerites to lower amphibolite grade metadolerites. All are basaltic and tholeiitic and possess broadly oceanic characteristics.
Three magma groupings can be defined geochemically on the basis of trace element contents, particularly rare earth elements and P/Y ratios. These magma groupings are thought to have been generated by differing degrees of partial melting and from differing source rocks. Each group is thought to have undergone fractional crystallization. The spatial and suggested temporal separation of these groups supports a pulsatory magma chamber model for the spreading centre at which the Lizard ophiolite developed.
Applications of electron microscopy in metamorphic and structural geology
Authors: Brodie K. H. 
Published: December 2007

Report on a joint meeting of the Metamorphic Studies Group and Tectonic Studies Group at Burlington House on 24 November 1982.

The meeting was opened by two introductory talks on the techniques of electron microscopy and microanalysis. Knipe outlined the basic principles involved in various formsof electron microscopy(scanning, transmission and high resolution) and the range of applicability of such methods for tackling geological problems. The combination of microstructural, crystal-lographic and geochemical information which can be obtained simultaneously from samples makes these techniques ideal for application to metamorphic rocks. Champness introduced the method of thin film analysis, contrasting this with conventional electron probe microanalysis and noting some of the problems involved and how they could be minimized. As an example of the applications of this technique she described work to examine the cause of brown staining in an olivine. TEM and microanalysis showed that particulate phases of diopside, chlorite and Fe oxide were all included in the olivine.
Lloyd described the method of backscattered SEM, both for atomic number contrast and electron channelling. He outlined the optimum sample preparation methods and illustrated someof the applications of both methods. Atomic number differences in the order of 0.1 can be imaged, enabling complex chemical zoning and inclusions to be studied, and indexing of electron channelling patterns allow variations in crystallographic orientations to be investigated between, for example, subgrains. between, for example, subgrains.
Two talks illustrated the usefulness of electron microscopy in studying experimental charges, where very small amounts of material are involved and
Contemporaneous faulting, and the eruption and preservation of the Lough Guitane Volcanic Complex, Co. Kerry
Authors: Avison Mark 
Published: December 2007

Interbedded with the clastic fluvial sediments of the Munster Basin, the Lough Guitane Volcanic Complex represents a rare volcanic episode in the Upper Devonian of SW Ireland. From three distinctly separate volcanic centres, an exclusively rhyolitic suite of thick lava flows and tuffs were erupted. The largest of the centres possessed a system of contemporaneous faults producing a subcircular depressed area, itself enclosed within a graben 1.5 km across. These faults lead to rapid thickness variations in many volcanic units, and a pooled lava flow reaches a thickness of 300 m. The site of a major elongate vent lies along one such fault, and rapid erosion of its poorly lithified walls generated coarse sandstone boulder agglomerates and is related to the absence throughout the complex of normal air-fall tuffs unmixed with terrigenous sand.
The containment of the bulk of the volcanics by contemporaneous faults, and subsequent rapid burial by terrigenous sediments has led to preservation of the volcanic succession virtually intact.
Geodynamic and magmatic stages on a traverse through the Andes between 20° and 24°S (N Chile,S Bolivia, NW Argentina)
Authors: Breitkreuz C. , Zeil W. 
Published: December 2007

Metamorphic Precambrian basement is exposed in the Chilean Pre-Cordillera in the form of a narrow horst, and also in the Argentinian Puna. Miogeosynclinal pelites and psammites of Devonian age dominate in the western part of the Andes, while early Palaeozoic clastics occur in the E. Insignificant Triassic sediments were followed by wide-spread shallow-marine Jurassic deposition. Cretaceous and Tertiary strata are predominantly terrestrial deposits. Whereas the Precambrian and Palaeozoic series were intensely deformed by folding, block-faulting dominates in the volcano-sedimentary cover.
Magmatic activity has been significant since the Precambrian. While S-type intrusives and extrusives occurred mainly in the Palaeozoic, I-type magmatic rocks predominated in the Mesozoic. The Cenozoic volcanism in the Cordillera Occidental originated in the lower and upper crust. Magnetotelluric and seismic investigations on the traverse show extremely low electric resistivity values coinciding with a strong absorption of seismic waves below the Chilean Pre-Cordillera and the Cordillera Occidental. This phenomenon can best be explained by the existence of partial melts at depths of more than 10 km. The Bouguer values decrease by about -430 mgal from the coast to the Cordillera Occidental.
In the Precambrian and Palaeozoic, the continent apparently extended farther to the W. The change from a passive to an active continental margin took place at the Palaeozoic/Mesozoic boundary with the break-up of Pangea. In order to grasp better the tectonic and magmatic evolution as well as the recent structure of the crust in the Central Andes, a combined geological-geophysical investigation has been made along a traverse through the Andes between 20° and 24°S (Fig. 1). The following pages present a review of the geological development together with the first results of work from the Chilean section of the traverse.
The Patagonian Batholith S of Tierra del Fuego, Chile: timing and tectonic implications
Authors: Hervé M. , Suárez M. , Puig A. 
Published: December 2007

Reconnaissance field studies on the Patagonian Batholith exposed S of Tierra del Fuego, together with 49 new K-Ar and Rb-Sr mineral dates, render new insights into two main aspects of the late Mesozoic geology: the geochronology and composition of the batholith, and time relations between the emplacement of the plutons and deformation. The envelope of the batholith in this area is mainly composed of late Jurassic-early Cretaceous sedimentary and volcanic rocks formed in an island arc-marginal basin system.
Three main plutonic groups have been recognized which have yielded mineral dates, interpreted as crystallization ages, ranging from 141 to 34 Ma. The earliest is a gabbroic assemblage, including gabbros, diorites and hornblendites exposed as relicts within later granitoids and with dates ranging from 141 to 103 Ma. The Canal Beagle Plutonic Group is composed of granitoids characterized by a penetrative syn-magmatic foliation and with dates of 113 to 81 Ma. The Seno Ano Nuevo Plutonic Group is formed of granitoids with dates of 60 to 34 Ma and is mainly exposed in the outer islands, indicating a local oceanwards shift of plutonism with time.
Lower Cretaceous island arc volcanism was contemporaneous with the intrusion of the gabbroic assemblage, and, in part at least, of the Canal Beagle Plutonic Group. Folding of the marginal basin infill, which has been related to the closure of the marginal basin, occurred from about 100 to 93 Ma ago. The gabbroic assemblage was apparently mainly pre-tectonic, whereas the Seno Ano Nuevo Plutonic Group was clearly intruded after this deformational event. A post-tectonic or possibly late-tectonic emplacement for the youngest plutons of the Canal Beagle Plutonic Group and a pre- or syn-tectonic intrusion for the oldest is inferred.
The geochemistry, metasomatism and petrogenesis of the granites of the English Lake District
Authors: O’Brien C. , Plant J. A. , Simpson P. R. , Tarney J. 
Published: December 2007

New geochemical data for the Carrock, Threlkeld, Ennerdale, Shap, Skiddaw and Eskdale granites of the Lake District are presented and discussed with particular reference to the metasomatism and petrogenesis of the intrusions.
The Caledonian granites of the Lake District have more associated hydrothermal activity and mineralization than their equivalents north of the Iapetus suture in Scotland. Pervasive high-temperature metasomatism which affects the Shap, Skiddaw and Eskdale intrusions is accompanied by remobilization of the large ionic lithophile elements (K, Rb, Sr, U) and Li and B, although high field strength elements, including the rare earth elements, remain unaffected except near greisen and mineral veins. The Threlkeld intrusion appears to have suffered loss of a Ba and Sr during a low-temperature event. However, there is no consistent relationship between granite composition, hydrothermal activity and mineralization which could be used to support the granite cupola model for mineralization in the province. Rather, the episodic mineralization which affects the Lake District may be related more to the broad geothermal field consequent upon the emplacement of the deeper Lake District batholith, identified from geophysical data.
Despite the variable metasomatic perturbations of their primary chemistry, three distinct groups of intrusions can be recognized on geochemical grounds. The Carrock granophyre is a product of tholeiitic fractionation and the Threlkeld and Ennerdale bodies are more typical calc-alkaline intrusions, whereas the Eskdale, Shap and Skiddaw plutons show a progressive evolution towards more complex geochemical patterns, suggesting decreasing hornblende but increasing plagioclase control of fractionating processes. The culmination of this trend may have been the emplacement of a large, high heat production granite beneath the Lake District at the end of the Caledonian orogeny. The suggestion made on geophysical grounds that the Eskdale intrusion is a cupola of the Lake District batholith cannot be simply reconciled with geochemical modelling. None of the Lake District granites has geochemical or isotopic characteristics which are convincingly S-type (i.e. formed by partial melting of a sedimentary protolith), and a model of subcrustal magmagenesis beneath an evolving arc or continental margin appears to be more appropriate.
Variscan facies and structure in central SW England
Authors: SELWOOD E. B. , THOMAS J. M. 
Published: December 2007

The character and distribution of middle Devonian to upper Carboniferous facies in central SW England is described. These may be interpreted in terms of the simple model of a shelf extending from a continent to the north, across most of SW England in earliest Devonian times. Within it a major E–W trending basin developed during the middle Devonian, possibly as a half graben structure with an active northern hinge. On this shelf in mid and late Devonian times, argillite successions accumulated to the north and a carbonate complex on the now starved platform to the south of the basin. In the early Carboniferous, basinal conditions extended northwards over the shelf, but to the south, at first flysch and then paralic sediments with a southern origin were ponded against the carbonate complex. Flysch penetrated through and across the platform into the intra-shelf basin. This flysch prograded northward to cover the whole area by early late Carboniferous times.
The western part of the main basin suffered structural inversion in late Visean times and semiconsolidated sediments spread northward across its margin. The eastern extension of the basin was not deformed until the late Namurian, at which time successions were folded and disrupted into nappe structures showing northward transport. The most far-travelled nappes are represented at the highest structural levels.
The stratigraphy of the coastal section of N Cornwall, which has been used to devise a structural model involving a major autochthonous south-facing overfold, is reassessed. The nappe structures and successions recognized inland are identified on the coast, and the overfold model is disproved. The whole of central SW England forms part of southerly derived thrust and nappe terrane.
The Sticklepath-Lustleigh fault zone: Tertiary sinistral reactivation of a Variscan dextral strike-slip fault
Authors: HOLLOWAY S. , CHADWICK R. A. 
Published: December 2007

Dextral strike-slip movement on the Sticklepath-Lustleigh fault zone (SLFZ) is indicated by displacements of ?Permian and older rocks. Previous authors have inferred that the main dextral movement which caused these displacements was post- Permian and, noting the presence of small Tertiary pull-apart basins along the fault zone, probably of Tertiary age. However, the geometry of these early Tertiary pull-apart basins indicates sinistral rather than dextral strike-slip movement. We present an alternative model for the history of the Sticklepath-Lustleigh fault zone, summarized below:
1 Late Variscan strike-slip movement, with a total displacement of up to 10 km, produced the SLFZ and offset dextrally an earlier Variscan thrust.
2. Extensional reactivation of this thrust led to rapid Permo-Triassic subsidence in the Crediton Trough and a dextrally offset neighbour, the Hatherleigh outlier.
3. Approximately 6 km of early Tertiary sinistral movement on the SLFZ produced small pull-apart sedimentary basins, and reduced the net dextral offset across the fault.
4. In mid-Tertiary times, minor dextral movements on the SLFZ may have produced reverse faulting on the margins of the Tertiary basins.
The occurrence and diversity of Coal Measure insects
Authors: JARZEMBOWSKI E. A. 
Published: December 2007

Insects are generally considered to be rare in the Upper Carboniferous Coal Measures. However, recent work in the Westphalian D of SW England suggests that many have been overlooked in the past. This is because wings, which are the most characteristic insect fossils, may be mistaken for detached ‘fern’ pinnules, which are much more common. The resemblance may be functional convergence rather than leaf-mimicry.
The earliest members of the class Insecta in the strict sense occur in the Upper Carboniferous. Eleven major divisions or orders are represented in the Coal Measures of which only four are still living. Primitively wingless insects (Archaeognatha) are present, relatives of familiar living insects such as the silverfish. There are numerous winged insects, some of which could fold their wings (Neoptera) and others which could not (Palaeoptera). Palaeopterous insects were more diverse than today. They include three extinct orders (Palaeodictyoptera, Megasecoptera, Diaphanopterodea) which were probably plant suckers like present clay bugs. Other extinct palaeopterous insects (order Protodonata) were probably aerial predators like modern dragonflies, and included some of the largest insects of all time (‘giant dragonflies’).
By far the most common neopterous insects were cockroaches (Blattodea) which outnumber all other insects in the Upper Carboniferous. This abundance is perhaps less surprising when one considers the general picture of the coal forests as warm, humid, and rich in organic matter. Another important neopterous group was the extinct order Protorthoptera, which is probably related only in part to extant Orthoptera (grasshoppers, crickets and locusts). There is no evidence at this time of higher insects such as flies, fleas, beetles, moths and butterflies, ants, bees and wasps.