bluuebunny/crossref_metadata_2025 huggingface dataset:
Sedimentation and tectonic geomorphology adjacent to major active and inactive normal faults, southern Greece
Authors: LEEDER M. R. , SEGER M. J. , STARK C. P.
Published: December 2007

The active Psatha–Skinos normal fault is uplifting a contrasting variety of lithologies in its footwall, including Mesozoic limestones, ophiolitic peridotites and poorly-consolidated Plio-Pleistocene sediments of the inactive Megara basin. In the latter basin, linear marginal uplands border the sedimentary fill and are interpreted as degraded and segmented scarp lines which exhibit features such as facetted spurs.
Drainage domains
are defined as groups of drainage basins sharing a common tectono-geological substrate. Contrasting domains in the footwall of the active fault have given rise to spectacular differences in drainage basin growth and form. In the uplifting footwall, raised coastal terrace levels are present at about 10 and 40 m. The latter have yielded corals dated at between 90–126 Ka, and have enabled us to calculate uplift and erosional rates. Extrapolation of these rates indicate that some 350 m of footwall relief has been produced over approximately 1 Ma. Most of the sediment eroded from the uplifting footwall is presumed to have been re-sedimented into the Alkyonides Gulf basin plain during this time. The prominent footwall unconformity so-produced forms a fine modern analogue to features seen in ancient syn-rift tilt blocks such as the Viking Graben. Footwall uplift has also backtilted the former depositional surface of the Megara Basin and caused reversal of flow in its axial drainage domain. A variety of depositional environments are documented in the subsiding hangingwall to the coastal fault, including syn-quake talus cones, alluvial fans, intra-fan marshes and swamps, truncated fans, transgressive barriers and spits.
Upper Cretaceous tectonic disruptions in a placid Chalk sequence in the Anglo-Paris Basin
Authors: MORTIMORE R. N. , POMEROL B.
Published: December 2007

Syn-Upper Cretaceous tectonic movements are recognized along tectonic axes including the Portsdown-South Downs axis, Sandown pericline, Kingston anticline, the Fécamp-St Valery fault blocks and at the Bresle Valley axis. A spatial relationship is described between surface structures, chalk sedimentation and deeper level fault systems identified on seismic sections. The Ouse valley between Lewes and Newhaven, Sussex, provides the strongest evidence for this relationship in the Chalk of the Anglo-Paris Basin.. The sedimentary features that can be related to tectonic lines are local thickness changes, anomalous sequences including scour surfaces such as Strahan's Hardground, Rowe's Flintless Belt (Isle of Wight), the Downend slump sequence (Portsdown). These discordant surfaces and slumps relate to particular tectonic 'hinge lines' whilst other sedimentary features such as the Tilleul Hardgrounds appear to have formed flat-ramps over blocks. These two types of tectono-sedimentary feature are used to delineate horst-like structures from tilted surfaces or half grabens which underlie the surface periclinal fold-belts. Rejuvenation movements along tectonic axes during the Cenomanian to Campanian are discussed in relation to the currently recognized sequence stratigraphy and sea-level curves for the period.
The influence of tectonics on early Cretaceous sedimentation in Bedfordshire, England
Authors: EYERS J.
Published: December 2007

The Lower Cretaceous sediments of the Bedfordshire area are Aptian and Albian in age. During this time the area was situated within an extensional tectonic regime, and the pattern of sedimentation, in terms of lateral variation both in sediment type and thickness, reflects the influence of normal faulting. Jurassic topography, created by block faulting and erosion, controlled the distribution of later facies largely by continued tectonic processes, especially the reactivation of the Jurassic fault block system, which produced syn-sedimentary faulting of the overlying sequence. Thus the ‘traditional’ view of the infill of an erosional basin by the Lower Greensand is challenged.
A revised model for the Pleistocene development of the River Avon, Warwickshire
Authors: MADDY D. , KEEN D. H. , BRIDGLAND D. R. , GREEN C. P.
Published: December 2007

A re-examination of the Pleistocene river deposits in the valley of the Midland Avon indicates that the conventional post-Hoxnian model for their development has to be revised. Reinvestigation of two key localities, Cropthorne in the Lower Avon valley and Ailstone on the Warwickshire Stour, a left bank tributary of the Avon, shows that the deposits of at least two separate temperate episodes are represented within the sequence. Amino-acid ratios on non-marine Mollusca from the temperate deposits allow these episodes to be correlated with oxygen isotope stages 5 and 7. Since the stage 7 temperate deposit lies within sediments which post-date the Wolston glacial sequence. an older age is indicated for that sequence than is proposed in the conventional stratigraphic succession of the British Pleistocene.
Salt-marsh accretion and sea-level movement in the inner Severn Estuary, southwest Britain: the archaeological and historical contribution
Authors: ALLEN J. R. L.
Published: December 2007

The sea defences of the inner Severn Estuary may be dated partly by reference to historical sources and partly by the detection through field-walking of early settlements on the reclaimed wetlands. Largely as the result of an intensive programme of levelling from reclaimed to active tidal marshes across dated defences, it is shown that relative sea-level (
c
. mean high-water spring tides) has risen in the area by at least 1.3 m since the later Roman Period. The rise since
c
. 1945 is given by a geochemical method which exploits the presence of metal pollutants in the deposits of the active marshes. A marked acceleration in the upward movement of the relative level is suggested by the assembled data. The minimum average rate of rise is apparently 0.40 mm a
−1
between the later Roman Period and the Medieval Period, 0.79 mm a
−1
from then to the start of the Modern Period, 1.49 mm a
−1
through the Modern Period to
c
. 1945, and 4.65 mm a
−1
since
c
. 1945. Depending on the extent to which the Severn Estuary has experienced marine transgression over the period covered by the measurements, the relative rise of mean high-water spring tide level to the present could amount to about 1.75 m.
Experimental evidence for water weakening of quartzite by microcracking plus solution–precipitation creep
Authors: DEN BROK S. W. J. , SPIERS C. J.
Published: December 2007

Natural quartzites have been experimentally deformed at a temperature of 1073 K, a confining pressure of 1.2 ± 0.1GPa, strain rates of 10
−5
, 10
−6
and 10
−7
s
−1
and in the presence of 0.4 wt% of added water. Microstructures after deformation indicate that at strain rates of 10
−5
–10
−6
s
−1
crystal plastic deformation is predominant. This is evident from abundant deformation lamellae in the original grains, and the fact that these grains show a (weak) crystallographic preferred orientation. New grains are absent or of relatively minor volumetric importance. In contrast, samples deformed at 10
−7
s
−1
show numerous arrays of fine, new polygonal to euhedral quartz grains developed in axially aligned transgranular and grain boundary microcracks. These new-grain aggregates are characterized by abundant microscale voids, fine intergranular channels and fluid inclusion trails. Syntaxial overgrowth structures on crack walls are also widespread. The aggregates of new grains are thus interpreted to have formed by precipitation from solution. In addition, old grain boundaries oriented perpendicular to the shortening direction show evidence for dissolution. The old grains show almost no deformation lamellae, subgrains or c-axis preferred orientation. It therefore appears that at strain rates of 10
−7
s
−1
microcracking and solution-precipitation creep are the dominant deformation mechanisms.
Experimental pressure solution in halite: the effect of grain/interphase boundary structure
Authors: HICKMAN STEPHEN H. , EVANS BRIAN
Published: December 2007

To investigate the mechanisms and kinetics of pressure solution, we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50.2 ± 0.2°C and fluid pressures of 0.1 MPa. Loads, applied using small springs, ranged from 0.1–4.2 N; mean effective normal stresses within the contact zone ranged from 1–14 MPa. The geometry and diametric growth rate of the contact spot (neck growth) and the rate at which the lenses approached one another (convergence) were monitored during deformation using transmitted and reflected light photomicrography. Time-dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine. Convergence rates in the halite/silica experiments were 0.01–0.05 μm/day. Although the initial deformation during loading involved elastic and plastic processes, control experiments without brine showed no time-dependent convergence, indicating that dislocation creep did not contribute to the observed rates. No undercutting or cataclasis was observed in any experiments. Residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine, indicating non-zero wetting angles.
Monitoring active volcanoes
Authors: McGUIRE W. J.
Published: December 2007

A meeting of the Volcanic Studies Group was held at Burlington House on 6 December 1989, to review establkhed and innovative techniques used in monitoring active volcanoes. Ten of the fourteen papers offered were presented orally.

The meeting was topical, being held on the eve of the United Nations International Decade for Natural Disaster Reduction, and at the end of a decade which saw the worst series of volcanic crises and disasters since 1902 (
Tilling 1989
). During the 1980s, three major volcanic events at Mount St Helens, USA (1980); El Chichon, Mexico (1982); and Nevado del Ruiz, Columbia (1985), accounted for over 25 000 deaths. These and volcano-related phenomena, both increased the level of volcanological research, and raised the public awareness of the problems associated with living on or near active volcanoes.

The great majority of the world's active volcanoes are situated in the third world or in developing countries that are experiencing high rates of population growth. Competition for living space and for the fertile volcanic soils that break down to produce prime agricultural land, is resulting in a dramatic increase in the numbers of people living within the ‘danger zones’ around active volcanoes. This trend is not confined simply to the less developed parts of the world where both the expertise and funding for useful volcano monitoring are deficient. Population densities have also increased significantly on the slopes of active volcanoes in the industrialized countries, in particular, around volcanoes such as Vesuvius, which have demonstrated no real activity
Ground deformation monitoring at Mt Etna; evidence for dyke emplacement and slope instability
Authors: McGUIRE W. J. , MURRAY J. B. , PULLEN A. D. , SAUNDERS S. J.
Published: December 2007

Ground deformation monitoring at Mount Etna has successfully enabled the sub-surface paths of two shallow feeder-dykes to be traced, and their dimensional parameters, depths and departures from the vertical, to be constrained. Determinations of horizontal movement have recorded the displacement, by 3.6 m (maximum), of a rim segment of the Valle del Bove flank caldera, due to dilation associated with dyke emplacement adjacent to the rim over the period 1981 to 1989. Small-scale collapse along this rim segment, associated with the opening of the 1989 fissure, points to increasing slope instability, and highlights the potential for major failure and debris avalanche generation.
Preservation of siliceous sponges in the Jurassic of southern England and northern France
Authors: MOCK S. E. , PALMER T. J.
Published: December 2007

Reef-forming lithistid sponges in the Middle Jurassic (Bathonian) of Normandy, France, were lithified on the sea floor by a peloidal cement, probably of an original low-Mg calcite composition precipitated under bacterial influence. This early lithification permitted early dissolution of the siliceous skeleton without the collapse or distortion of the resulting moulds. These moulds were encrusted and bored. This pathway for the fossilization of sponges is shown by other examples of Jurassic lithistids and is likely to be widely applicable throughout the fossil record, particularly at times during which calcite was the primary marine precipitate.
A possible basaltic deep source of the south-central England magnetic anomaly
Authors: KEAREY P.
Published: December 2007

The group of large, positive, magnetic anomalies in south-central England is shown to originate from two sources at different depths. The shallow source originates from Silesian basic igneous rocks. The anomaly of the deeper source has been isolated by upward continuation and inverted via pseudofield transformation. The magnetic model is interpreted as a large body of basaltic rocks intruding the middle crust. It is proposed that the body was emplaced by buoyant ascent and may be the cause of the stability of the London Platform during Mesozoic times. It is speculated that the basalt was intruded in a back-arc environment during the period preceding the Variscan orogeny.
Some observations on basin evolution and dynamics
Authors: BLUNDELL D. J.
Published: December 2007

Sedimentary basin evolution is intimately bound in with continental lithosphere dynamics. Deep seismic reflection profiling has revealed images of the crust and upper mantle that suggest linkages between the shape and structure of sedimentary basins as they evolve with the rheological responses to tectonic stress of upper and lower crust and upper mantle components of the lithosphere. This is well illustrated by the European Geotraverse lithosphere profile from North Cape, Norway to Tunisia. The Alpine mountain belt has a lithospheric root as well as a crustal root. By virtue of its asymmetric disposition, this may be the cause of compressive and tensile forces in close association in the upper crust, which have created mountain uplift and basin subsidence, extension and thrusting, all in juxtaposition. Evidence for an elastic upper layer of crust above a plastic substratum can be used as a basis for modelling basin geometry, structure and stratigraphy built upon the flexural nature of the upper crust. Such models go a long way towards simulating the evolution of basins such as the North Sea Viking Graben. In more detail, analogue structural models can reveal the geometry of basin fill in relationship to crustal movement, and the relationships between structure and sedimentation patterns. However, sedimentary basin modelling needs to begin with the quantitative simulation of depositional environments in relation to such factors as tectonics, sea level variations, sediment supply and erosion, in order to match sedimentary architecture. Only then can the range of deposits be placed in space and time within a basin environment, as building blocks within a dynamically evolving structural framework, to create predictive models for comparison with geological reality.
A ‘hot’ new shale facies from the Upper Carboniferous of Northern England
Authors: MAYNARD J. R. , WIGNALL P. B. , VARKER W. J.
Published: December 2007

A new radioactive shale lithology from the Upper Carboniferous of the Pennine Basin of northern England is described. It shows geochemical and lithological characteristics similar to the well studied Marine Bands, hut only contains an impoverished marine nektonic fauna. Thus shales of the new lithology have considerable potential for miscorrelation with the Marine Bands in wirelie logs. The presence of such shales in the basin increases its source rock potential. These shales occur as part of a transgressive systems tract.
Mineralogical and chemical variation of francolites with geological time
Authors: McCLELLAN G. H. , VAN KAUWENBERGH S. J.
Published: December 2007

Francolites, carbonate fluorapatites, occur in temporally and spa- tially related sedimentary phosphorite deposits that range in age from the Proterozoic to the Neogene. Previous mineralogical studies of francolites have established that systematic relationships exist between chemical composition and crystdlographic data. The unit-cell dimensions and indices of refraction of francolites decrease with increasing substitution of CO;’ for POT3 in the francolite structure. Accompanying cation substitutions of Na+’ and Mg+’ for Ca+’ also are significant. Fluorine contents of more than 2 moles/unit-cell also are typical of francolites, and the ‘excess’ fluorine is related to the basic CO;’ for PO;’ substitution.

Francolites are thermodynamically metastable with respect to fluorapatite. Studies of francolites from deposits of various geologi- cal ages demonstrate systematic trends in chemical composition and crystallographic properties with time. Francolites in rocks of Palae- ozoic or older ages usually have compositions close to fluorapatite. Mesozoic and younger francolites have wide range of compositions that vary with the type and intensity of post-depositional alteration. These alteration processes can result in mobilization of cations and anions, decarbonation of the francolite, and changes in crystal- lographic properties. The extent and intensity of alteration proc- esses often are restricted by variations in francolite composition and associated accessory minerals.
Ordovician magnetostratigraphy: a correlation of global data
Authors: TRENCH A. , McKERROW W. S. , TORSVIK T. H.
Published: December 2007

Palaeomagnetic studies where primary magnetizations are established from well-dated rocks have been compiled to construct a magnetostratigraphic time-scale for the Ordovician period. An excellent correlation of magnetozones is observed between independent studies of the Baltic and South Siberian platform sequences. Supplemental datasets from other continents concur with the Baltic and Siberian polarity data.

Early Ordovician times were mainly characterized by a reverse field. Rapid reversals then occurred during Llanvirn and Llandeilo times. Late Ordovician times were dominated by a normal polarity field.

Some gaps remain in the polarity record, notably for late Caradoc-early Ashgill and mid-Tremadoc times.
Subcontinental mantle plumes, hotspots and pre-existing thinspots
Authors: THOMPSON R. N. , GIBSON SALLY A.
Published: December 2007

The magmatism occurring when a hot convective mantle plume is sited beneath a lithospheric plate may be more complex if the latter is continental, rather than oceanic, because of the characteristic local physical inhomogeneity of continents. Thus, the surface volcanic expression of the plume (hotspot) may be displaced from immediately above its rising stem, if the continent has been previously locally thinned nearby. The magmatism of the British Tertiary Igneous Province and Parana basin, South America, appears to fit this model, and it may also explain why the Miocene Columbia River basalts of the NW United States overlie an Early Tertiary sedimentary basin.
Fluid disturbed hornblende K-Ar ages from the Dalradian rocks of Connemara, Western Ireland
Authors: MILLER W. M. , FALLICK A. E. , LEAKE B. E. , MACINTYRE R. M. , JENKIN G. R. T.
Published: December 2007

The results of K-Ar age determinations and hydrogen and oxygen stable isotope measurements on hornblendes from the poly-metamorphic Dalradian schists of Connemara, western Ireland indicate that the hornblende K-Ar systems have been significantly disturbed by low temperature fluid reaction. Correlations between K-Ar ages, δD values, structural water contents and the occupancy of the hornblende structural ‘A’ sites suggest that excess water as H
3
O
+
occupies vacant ‘A’ site positions during stable isotope exchange and displaces Ar
*
causing lowering of the K-Ar ages. This process occurs below the normally accepted closure temperature for Ar in hornblende and is not detectable by optical or X-ray investigation of the mineral. This process may not be unique to Connemara hornblendes and so is of potential importance to geochronology in other metamorphic terranes.
A sulphur isotopic investigation of the potential sulphur sources for Lower Palaeozoic-hosted vein mineralization in the English Lake District
Authors: LOWRY D. , BOYCE A. J. , PATTRICK R. A. D. , FALLICK A. E. , STANLEY C. J.
Published: December 2007

Current models for Cu–Fe–As (Devonian), Pb–Zn (Carboniferous) and barite (Upper Carhoniferous/Permian) vein mineralization in the Lake District invoke a variety of sources for fluids and metals including the Skiddaw Group sediments, the Borrowdale Volcanic Group, the Lake District batholith, meteoric water and Carboniferous seawater. This study isotopically characterizes the sulphur reservoirs within the Lower Palaeozoic sedimentary and igneous sequences and Late Caledonian intrusives, and assesses their importance as sources of sulphur for the vein mineralization.

The Ordovician Skiddaw Group is a reservoir of isotopically heavy sulphur with a range of δ
34
S from +11‰ to +29‰ [& x~ (1
σ
)
=
18.53 ±6.7‰ (
n
= 10)]. Four analyses of Borrowdale Volcanic Group rocks yielded values of +1‰ to +15‰. Such positive values are thought to be the result of closed system bacteriogenic reduction of Ordovician seawater sulphate in the case of the Skiddaw Group, and mixing of mantle-derived magmatic sulphur with Ordovician seawater sulphate for the Borrowdale Volcanic rocks. The sulphides in the vein systems hosted by the Skiddaw Group in the Vale of Newlands formed from fluids with δ
34
S

H
2
S

signatures ranging from +16.7‰, to +22.5‰: partially homogenized Skiddaw Group sulphur is considered to be the source. Mineralization at Coniston, hosted by the Borrowdale Volcanic Group, shows similar sulphur isotopic characteristics, and Skiddaw Group at depth is considered to be the predominant source of sulphur with a possible minor input from the wallrock volcanic rocks at the site of deposition. Although the Lake District batholith provided a heat source for the Cu–Fe–As vein mineralization, the granite did not supply any sulphur to those systems. However, magmatic sulphur was an important constituent in mineralization associated with the Shap and Skiddaw granites. The δ
34
S values for barite mineralization at Force Crag, Greenside, Skiddaw and Shap ranges from +13‰ to +18‰, and Carboniferous seawater provides the most reasonable source for sulphate.
Neogene to Quaternary rifting, sedimentation and uplift in the Corinth Basin,Greece
Authors: COLLIER R. E. LI. , DART C. J.
Published: December 2007

Normal faulting, regional uplift and glacio-eustacy have controlled patterns of sedimentation on a variety of scales during the active rift history of the Corinth Basin. Extensive sections through 800 m of early rift deposits are exposed in the north of the basin. These are overlain by andesites dated at 3.62 ± 0.18 and 4.00 ± 0.40 Ma.

Early in the rifting process, basin relief controlled by normal faulting determined broad environmental conditions. Slope gradients determined transport process within an east-west asymmetric graben. Palaeoflow and provenance data allow lateral and axial sediment dispersal systems to be distinguished, and indicate that the Corinth basin was separated by a drainage divide from the larger Gulf of Corinth basin, to the west, during the Lower Pliocene. Sedimentary facies and thickness changes across faults, and the distribution of unconformities and soft-sediment deformation features define active tectonism at this time. As such, the Corinth Basin provides a model for the recognition of syn-rift unconformities and associated depositional patterns in other extensional basins.

Since the mid-Pliocene, a combination of regional, crustal uplift and of more localized, fault-controlled, extensional subsidence have determined basin form. In the north of the basin, Lower Pliocene and Quaternary marine sediments have been uplifted up to 300 m above present-day sea-level. Normal faulting during the same episode separated successive intrabasinal depocentres from emergent highs that were subject to erosion.

The competition between uplift and extensional subsidence has important implications for the back-arc evolution of the central Aegean area. The uplift suggests that crustal underplating by the subducted Mediterranean plate may have advanced as far north as northern Peloponessus and Corinth by the Upper Pliocene-Lower Pleistocene.
Geological evidence for a Proterozoic to Mesozoic link between southeastern Africa and Dronning Maud Land, Antarctica
Authors: GROENEWALD P. B. , GRANTHAM G. H. , WATKEYS M. K.
Published: December 2007

Comparison of crustal provinces in Southeastern Africa and Dronning Maud Land, Antarctica, reveals considerable similarity in their evolution from the Archaean until the Mesozoic separation. Archaean granites and mid-Proterozoic supracrustal successions in these regions are so comparable that correlation is suggested. A major mid- to late Proterozoic orogenic terrain in Dronning Maud Land, comprising the H.U. Sverdrupfjella and Heimefrontfjella subprovinces and termed the Maudheim Province, is very similar in age, lithology, structural style and metamorphic history to the Mozambique and Natal orogenic provinces of Kibaran age (1000 Ma) in southeastern Africa. Deformed supracrustal sequences in all three provinces host syn-tectonic granites intruded during upper amphibolite- to granulite-facies metamorphism. Isoclinal folding was accompanied by thrusting towards adjacent cratonic areas. Development of orogenic provinces of Kibaran age in southeastern Africa and Antarctica reflects accretion of marginal basin–volcanic arc sequences onto older continents. The 500 Ma Pan African event was a widespread, predominantly thermal, overprinting of parts of the older orogenic provinces. Faulting and rifting of the supercontinent preceded break-up and influenced the stratigraphy of Phanerozoic sedimentary successions in SE Africa.
Oxygen-isotope geochemistry of the Scourian complex, northwest Scotland
Authors: CARTWRIGHT I. , VALLEY J. W.
Published: December 2007

The Scourian complex of northwest Scotland underwent granulite-facies metamorphism at 2.7 Ga. Granulite-facies orthogneisses have whole-rock δ
18
O values similar to those of igneous rocks of comparable compositions (ultrabasic gneisses 5.5–5.9‰, basic gneisses 6.4–6.8‰, tonalitic gneisses 9.5–9.7‰), and steep
18
O gradients of up to 3‰in 10cm are recorded at two lithological contacts. These data suggest that large volumes of pervasive metamorphic fluids have not infiltrated the rocks, but do not preclude localized fluid-rock interaction. Scourian paragneisses have lower δ
18
O values (8.5–9.9‰) than typical metasediments, and may have undergone fluid-hosted isotopic exchange with the surrounding orthogneisses. Felsic sheets within tonalitic and basic gneisses have similar δ
18
O values to their hosts: these data, combined with petrological and geochemical information, suggest that the sheets were formed by local anatexis during granulite-facies metamorphism. Fluid infiltration during the 2.5 Ga amphibolite-facies Inverian retrogression caused homogenization of δ
18
O values of the Scourian gneisses. Unaltered tholeiitic Scourie dykes have low δ
18
O values of 2.0‰. It is unlikely that heated, surface-derived fluids infiltrated the Scourian complex, and these dykes were probably emplaced as low-δ
18
O magmas.
Post-Laxfordian magnetic imprint in the Lewisian metamorphic complex and strike-slip motion in the Minches, NW Scotland
Authors: PIPER J. D. A.
Published: December 2007

The palaeomagnetic imprint in the Lewisian metamorphic basement was acquired during early post-Laxfordian times and resides in magnetite-filled microfractures. An early magnetizing event dated
c.
1820–1750 Ma was largely overprinted by a second event between 1700 and 1500 Ma which was probably linked to retrogressive amphibolite fades metamorphism. It reaches its greatest intensity in the south of the outcrop while the relict remanence survives most prominently in Scourian terranes. Populations of magnetic components are offset by
c.
95 km of (presumed Caledonian) sinistral strike slip in the Minches. Intensities and susceptibilities of magnetization are enhanced in zones of Laxfordian reworking relative to the relict Scourian zones. Their distributions in the Outer Hebrides are reproduced in the Mainland outcrop and can be matched following correction for the same sinistral strike slip. A third line of evidence suggesting this motion is the offset of the deep crustal contribution to the aeromagnetic anomalies. The fault zone accommodating this motion may now be represented by one or more of the low angle detachments bordering the western margin of the Minches Basin. Post-Laxfordian remanences in the Outer Hebrides are rotated by an average of 4° with respect to equivalent vectors on the Mainland and may record later block rotations. A mid-Proterozoic reconstruction of the Lewisian complex derived from the magnetic evidence is presented.
The Inishkea Division of northwest Mayo: Dalradian cover rather than pre-Caledonian basement
Authors: KENNEDY M. J. , MENUGE J. F.
Published: December 2007

Pre-Caledonian basement rocks have been recognized structurally beneath the Dalradian cover in NW County Mayo for over 20 years and have more recently been subdivided into an older Annagh Division, dominantly of orthogneisses which contain granitic components of Grenvillian age, and a younger Inishkea Division, dominantly of semi-pelitic and psammitic lithologies. Part of this division was originally interpreted as having been derived from probable Annagh Division rocks by structural and metamorphic reconstitution, but has more recently been considered as an entirely meta-sedimentary sequence older than the Dalradian cover. A structural and metamorphic history older than that of the Dalradian cover has been assumed, but is difficult to substantiate. Re-examination of critical localities confirm that the Annagh Division is older than the Inishkea Division, but also demonstrates that the exposed contact of the latter with the cover is stratigraphic. The Inishkea Division includes lithostratigraphic units that occupy different parts of the Dalradian cover successions.
Petrology and dynamics of the Waimihia mixed magma eruption, Taupo Volcano, New Zealand
Authors: BLAKE S. , WILSON C. J. N. , SMITH I. E. M. , WALKER G. P. L.
Published: December 2007

The Waimihia pumice deposit was erupted from Taupo volcano about 3.3 ka BP. It comprises a plinian tephra fall deposit divisible into two volumetrically subequal fall units and a late-stage, volumetrically minor, near-vent ignimbrite. About 7.5km
3
of magma were erupted at an average rate of
c.
8 × 10
8
kg s
−1
. Whole rock, glass and mineral compositions define three crystal-poor magma types: rhyolite, rhyodacite and andesite. The proportions of the three magmas varies with stratigraphic position in the two fall units. The lower Waimihia fall unit shows a steady upward increase in rhyodacite from <1% to 5.5% and a near absence of andesite (<0.05%). Rhyodacite in the upper Waimihia fall unit decreases upward from 28% to 2% while andesite increases (0.2% to 0.8%) before decreasing (0.3%). The composition of the ignimbrite coincides with that of the top part of the upper fall unit (consistent with its stratigraphic position), suggesting that partial column collapse occurred towards the close of activity. Rhyolite dominates the total Waimihia deposit (
c
. 92%) and is similar to other post-22 ka Taupo rhyolites in terms of major element, trace element and Sr isotope composition, mineralogy and Fe-Ti oxide temperature and oxygen fugacity. The rhyodacite (
c.
7.3%) formed by hybridization of rhyolite and andesite prior to the eruption, and occurs as grey pumices and with rhyolite in streaky pumices. Andesite (
c.
0.3%) occurs as black scoria, sometimes containing traces of rhyodacite; it is an unusual high TiO
2
tholeiitic andesite whose
87
Sr/
86
Sr ratio of 0.7062 is indistinguishable from that of the rhyolite. The heterogeneous pumice and scoria clasts were formed in a second magma mixing process that was active when the magmas were being transported to the surface during the eruption. The order in which the magmas were erupted, and the decoupling of the peaks in rhyodacite and andesite production, are explained by withdrawal from a three-layer sill that had formed following the injection of
c.
0.16 km
3
of andesite into a ≥ 7.5 km
3
sillshaped rhyolitic magma chamber.
Radiocarbon dating of late Quaternary fault segments and systems
Authors: VITA-FINZI C.
Published: December 2007

Recent developments in radiocarbon dating contribute to the analysis of fault evolution both at the level of individual fault segments and with regard to entire fault systems.
14
C assay by accelerator mass spectrometry and the use of high-precision radiometric counting systems have both improved the resolution of fault chronologies. In conjunction with other sources of numerical ages they make it possible to trace fault-related folding, warping and regional deformation and thus to analyse a fault assemblage in its geodynamic context. At Dungeness (SE England)
14
C dating of redeposited shells gives a minimum age for a planation surface and a fault that predates it; in the Gulf of Corinth (Greece) dating of
Lithophaga
shells in their borings reveals 2.3m of differential Holocene uplift of the south shore of Gulf relative to the north. Improved chronologies should make it possible to complement the search for seismic recurrence intervals with analysis of deformation processes.
Gold mineralization associated with low-temperature, off-axis, fluid activity in the Troodos ophiolite, Cyprus
Authors: PRICHARD H. M. , MALIOTIS G.
Published: December 2007

Silicification of umbers in the Troodos ophiolite complex in Cyprus provides evidence for low-temperature hydrothermal activity occurring late in the process of ocean-crust formation, after the crust had moved away from the oceanic spreading centre. Umbers, which are Mn–Fe-rich sediments, precipitate some distance away from oceanic spreading axes. The movement of the fluids partially silicifying the umbers must post-date umber formation and therefore also occurs off axis. These fluids may form part of low-temperature hydrothermal circulation similar to those identified by off-axis heat anomalies in the modern oceans. In Cyprus the silicified umbers often are located away from volcanogenic massive sulphide (VMS) deposits and are aligned along sea-floor faults. They are characterized by quartz veins as well as pervasive silicification. Recent analyses have revealed unexpectedly anomalous, 1–5 ppm, concentrations of Au in these silicified umbers.

Gold mineralization is known to occur in ophiolite complexes as part of the metal concentrations in VMS deposits. These deposits are thought to be formed by ancient hydrothermal circulation similar to that associated with black smokers observed at modern mid-ocean ridges. The research presented in this paper provides evidence for a second phase of Au mineralization in Cyprus caused by low temperature silicifying fluids resulting from oceanic hydrothermal activity which occurred away from the spreading centre. The mineralizing fluids which silicified the umbers may have been more widespread, impregnating other lithologies, and may have overprinted the first phase of Au mineralization in some VMS deposits after they had become inactive and had been moved away from the spreading centre. The mineralizing fluids passing through these VMS may have used the same structural pathways as the original base-metal-rich hydrothermal solutions which formed the VMS.
Sedimentary response to intra-arc extension: controls on Oligo-Miocene deposition, Sarcidano sub-basin, Sardinia
Authors: SOWERBUTTS ALISON A. , UNDERHILL JOHN R.
Published: December 2007

The Oligo-Miocene Sardinian rift is a rare example of a well exposed intra-arc basin comprising several independent depocentres. Synthesis of field observations from one such depocentre, the Sarcidano sub-basin in central Sardinia, not only allows a new and integrated sedimentological and tectonostratigraphic history for the area, but also provides insights into controls on syn- and post-rift sedimentation in intra-arc settings. Initial rifting during the late Rupelian–early Chattian (Oligocene) occurred on NW–SE-trending normal faults and produced a half-graben topography which controlled the dispersal of locally supplied coarse continental clastic sediments. Latest Chattian–Aquitanian (Miocene) NE–SW-trending normal faulting defined a more complex ‘block’ topography that remained underfilled in all areas except those which received voluminous ignimbritic volcanic material. Subsequent marginal- and shallow-marine sedimentation progressively infilled the fault topography as sea level rose. Deposition of coarse clastic sediments eroded from fault scarps was focused in the hanging-wall depocentres of the intersecting fault trends, whilst platform carbonates became established in topographically higher areas protected from clastic sedimentary supply. Finally, as the relative rise in sea level drowned sediment source areas in the Burdigalian, deeper-marine marlstones dominated sedimentation. The results demonstrate that the Sarcidano sub-basin was dominated by a mixed volcanic–siliciclastic–carbonate basin fill with abrupt facies changes developed in response to complex fault-defined topography, relative rise in sea level and an episodic volcanic supply. Whilst the rift structure largely controlled the provenance, supply and accumulation of sediments, relative sea level primarily controlled the types of facies that developed.
Garnet provenance studies, juxtaposition of Laurentian marginal terranes and timing of the Grampian Orogeny in Scotland
Authors: HUTCHISON A. R. , OLIVER G. J. H.
Published: December 2007

A study of the composition and zoning patterns of detrital garnets from Ordovician greywackes from the Northern Belt of the Southern Uplands terrane of Scotland reveals characteristics of the metamorphic sources very similar to the Dalradian Supergroup of the Scottish Grampian terrane. The radiometric cooling and uplift ages of the Dalradian metamorphic zones and the depositional ages of the Southern Uplands greywackes support the hypothesis for local provenance. Detrital metamorphic garnet, identical to Dalradian garnet, has also been identified in the Upper Ordovican sandstones of the Highland Border Complex. These observations do not support proposals that the Grampian, Midland Valley and Southern Uplands terranes were exotic to each other in the Late Ordovician time. These new results, together with a review of published age dates, clarify the Late Ordovician palaeogeography for this part of the Laurentian margin. The distances between the Grampian, Midland Valley and Southern Uplands terranes may have been similar to the present day. It is concluded that large rivers flowed out of the uplifting mountainous Grampian terrane and across the Midland Valley into a Southern Uplands trench during the Late Ordovician time. The main orogeny (i.e. mountain building) in the Grampian terrane was therefore post-Cambrian, producing the first high mountains and resultant flysch in the Caradoc.
A Neoproterozoic supra-subduction terrane in northern Eritrea, NE Africa
Authors: DE SOUZA FILHO C. R. , DRURY S. A.
Published: December 2007

The western part of a tectonic block in the complex Pan-African architecture of northern Eritrea contains partly re-equilibrated low-
T
, high-
P
assemblages (550°C, 14.5 kbar), basalts with oceanic geochemistry and a major olistostrome containing lenses of serpentinite. These features demonstrate subduction zone products. East of this accretionary wedge the block is dominated by island-arc volcanic and volcaniclastic rocks, and various calc-alkaline plutons. A bimodal volcanic suite of primitive andesitic basalts and evolved dacites and ignimbrites represents early submarine arc development and emergent volcanism, respectively. Intense, polyphase deformation culminated in sinistral transpression with crustal-scale imbrication between several east-verging thrusts. A tectonically bounded unit in the internal part of this arc association also contains relict high-
P
assemblages (650°C, 10–13 kbar) in oceanic basalts, which are possibly products of tectonic underplating as the arc developed. Oceanwards collapse of the tectonically inflating arc may explain formation of evolved, subaerial volcanic rocks within small extensional basins. Down-to-west extensional structures may have been inverted during terrane accretion to act as east-verging shear zones during late thickening. The area remains to be correlated with those areas in Arabia that were juxtaposed with it before Red Sea opening.
Eclogites from the Czech part of the Erzgebirge: multi-stage metamorphic and structural evolution
Authors: KLÁPOVÁ HELENA , KONOPÁSEK JIØÍ , SCHULMANN KAREL
Published: December 2007

A structural and petrological study of Saxothuringian eclogites in the central Erzgebirge, Czech Republic, revealed their polyphase thermal and tectonic evolution. The first stage of deformation is related to eclogite-facies metamorphism of mafic rocks at pressures of 26 kbar and temperatures of 650–700°C. The clinopyroxene crystallographic preferred orientation is consistent with high-temperature flow.

The second stage of deformation is characterized by transport of eclogitic rocks at the base of a crustal nappe and their large-scale folding. During this stage, HP–HT metamorphic assemblages developed in the surrounding metapelites (14.5 kbar/600°C) while eclogite assemblages were preserved in passively transported eclogitic boudins. Heat advection and similar
P–T
conditions in the surrounding crustal material are responsible for the stability of mineral assemblages and preclude closure of isotopic systems in the eclogites. Therefore the published isotopic ages of the eclogites do not reflect the subduction stage but the age of cooling under crustal conditions. Subsequent large-scale (D3) folding is responsible for reorientation of previously flat-lying earlier fabrics (D1–D2).

The final stage of deformation is marked by the development of a heterogeneous network of ductile retrograde shear zones. The thermometry and geochemical study of amphibolitized eclogites in the cores of shear zones indicates thermal conditions not exceeding those in surrounding metapelites and fluid influx. The fluid influx is interpreted to be the result of water-producing prograde reactions in the footwall metasediments and fluid chanelling into the base of the nappe during brittle deformation of the eclogites.
Siegenian generation of the Lizard ophiolite: U-Pb zircon age data for plagiogranite, Porthkerris, Cornwall
Authors: CLARK A. H. , SCOTT D. J. , SANDEMAN H. A. , BROMLEY A. V , FARRAR E.
Published: December 2007

The long-controversial age of the Lizard ophiolite is resolved by U-Pb dating of three single magmatic zircons from a plagiogranite dyke near Porthkerris Point. This demonstrates that the axial oceanic crust was undergoing extensional ductile shearing, mylonitization, amphibolite facies metamorphism and, probably, anatexis at 397 ± 2 (2σ) Ma. In conjunction with published K–Ar,
40
Ar–
39
Ar and Rb–Sr data for the complex, this Early Devonian age predicates a protracted interval between intra-oceanic magmatism and deformation, on the one hand, and obduction during Late Devonian, northwestward displacement of the Normannian High, on the other.
Emplacement of Hebridean Tertiary flood basalts: evidence from an inflated pahoehoe lava flow on Mull, Scotland
Authors: KENT RAY W. , THOMSON BONITA A. , SKELHORN RAYMOND R. , KERR ANDREW C. , NORRY MIKE J. , WALSH J. NICK
Published: December 2007

The lower 200 m of the Tertiary lava pile on Mull, western Scotland, consists mainly of small volume (0.01–1 km
3
), high-magnesian basaltic lava flows. Eruption of these flows probably occurred from fissures or point-source vents, producing pahoehoe-textured sheets averaging about 5 m in thickness. Certain lavas cropping out in northwest Mull greatly exceed this average thickness and may represent inflated pahoehoe flows akin to those described at Kilauea, Hawai’i. Structural features of a 16–30 m thick lava at Port Haunn, northwest Mull, that conform to this proposal include sub-horizontal sheets of amygdales up to 14 cm thick separated by amygdale-poor zones, pipe amygdales at the base of the flow and a low-relief flow top. Alternating olivine-rich and olivine-poor bands in the Port Haunn lava are suggestive of lava pulses during a continuous eruption, also consistent with inflation. Elsewhere in western Mull, there is evidence for filled lava tubes and pahoehoe toes, both of which are characteristic of inflated sheet flows formed on gentle ground slopes (<4° and perhaps <0.5°). Fluid dynamical considerations suggest that each sheet flow in the lower part of the Mull lava sequence probably was active for a short period, permitting the build up of small lava fields over several months or years. This is commensurate with the small volume and limited areal extent of the Tertiary Mull lavas when compared to basalts in igneous provinces such as the Columbia River and Deccan.
Oceanic plateau formation: a cause of mass extinction and black shale deposition around the Cenomanian–Turonian boundary?
Authors: KERR ANDREW C.
Published: December 2007

The Cenomanian–Turonian boundary (90.4 Ma) represents a major period of worldwide environmental disturbance. The physical manifestations of this are: elevated atmospheric and oceanic temperatures; a significant sea-level transgression; and a period of widespread anoxia, leading to the formation of oceanic black shales, and the extinction of 26% of all genera. Elevated δ
13
C values and enrichment of trace elements in Cenomanian–Turonian boundary sediments, combined with a reduction in
87
Sr/
86
Sr, also imply a severe environmental perturbation. At this time oceanic crustal production rates reached their highest level of the last 100 million years. This was principally caused by extensive melting of hot mantle plumes at the base of the oceanic lithosphere, and the development of vast areas (up to 1×10
6
km
2
) of thickened oceanic crust in the Pacific and Indian Oceans. The anomalous volcanism associated with the formation of these oceanic plateaux may have been responsible for the environmental disturbances c. 90 Ma. These eruptions would also have resulted in the emission of large quantities of CO
2
into the atmosphere, leading to global warming. Additionally, the emission of SO
2
, H
2
S, CO
2
and halogens into the oceans would have made seawater more acidic resulting in the dissolution of carbonate, and further release of CO
2
This run-away greenhouse effect was probably put into reverse, by the decline of the anomalous volcanic activity, and by increased (CO
2
-driven) productivity in oceanic surface waters,leading to increased organic carbon burial, black shale deposition, anoxia and mass extinction in the ocean basins