bluuebunny/crossref_metadata_2025 huggingface dataset:
Transcurrent faults and associated cataclasis in Shetland
Authors: FLINN DEREK
Published: December 2007

A series of transcurrent faults with northerly trend is well exposed in the cliffs of Shetland. The Walls Boundary Fault which cuts through the middle of Shetland has a continuously changing trend so that it forms a very flattened S. Dextral movement along the fault seems to have created further dextral transcurrent faults, including the Nesting Fault, across the eastern concavity in the trend. These main faults lie within broad zones of cataclasis, subsidiary faulting and local folding. The offsets on the subsidiary faults are very much less than on the main faults, and the crushed rocks have isotropic fabrics. The zones probably arose during faulting from varying local stresses caused by the interaction of the unevennesses on the two sides of the non-planar main faults. Gouge in the Walls Boundary Fault contains analcite. Gouge-like laumontite in subsidiary shears was probably formed by mechanochemical reactions. The occurrence of these minerals and of blastomylonitic scapolite veins near the Walls Boundary Fault may indicate up to three phases of movement taking place between Cretaceous and Devonian times under different depths of overburden. Slices of secondarily cataclastic mylonite occurring along the Walls Boundary Fault are probably relics of the Great Glen Fault now partially cut out by the nearly coincident Walls Boundary Fault.
Quantitative limits to palaeogravity
Authors: STEWART A. D.
Published: December 2007

Limits to the former magnitude of the gravity force at the Earth’s surface,
g,
with respect to the present magnitude
g

o

,
have been determined by five methods,
i
. The permanent existence of a terrestrial atmosphere over the last 37 x 10
9
years (0.33
g

o

<
g)
2. Dimensions of vertebrates: Jurassic
Apatosaurus (g
< 1.2
g

o

)
and Upper Cretaceous
Pteranodon (g
< 2
g

o

)
3. Miocene overconsolidation of the London Clay (0.5
g

o

< g < g

o

)
4. Phanerozoic upper mantle mineralogy (0.4
g

o

< g <
2.2
g

o

)
5. Crustal mineralogy during the Phanerozoic (0.5
g

0

<
g

<

1.4
go)
and Precambrian (0.5
g

o

< g
< 1.9
g

o

)
These limits can be used to put constraints on hypotheses involving Earth expansion and changes in the universal constant of gravitation.
Thermal convection
Authors: ELDER J. W.
Published: December 2007

The definition and specification of a convective system is outlined. For example for a global system we have: very small Reynolds number (slow ‘viscous’ flow); very large Prandtl number (heat transfer independent of inertial effects); large Peclet numbers (advection dominant in forced convection); very large Rayleigh number (free convection strong and turbulent).

The very wide range and type of convective systems is briefly described. These include systems ranging from the macro-geological scale to small-scale systems such as found in multilayered intrusions.
Anorogenic magmatism, plate motion and Atlantic evolution
Authors: MACINTYRE R. M.
Published: December 2007

Emplacement of carbonatites at 0–15, 25, 40, 60–70, 130 Ma (and possibly 80 and 100 Ma) may coincide with major changes in plate motion. This suggests a common triggering mechanism which previously may have operated at intervals of about 230 Ma.
Grenville events in Moine rocks of the Northern Highlands, Scotland
Authors: BROOK M. , BREWER M. S. , POWELL D.
Published: December 2007

A 14 point Rb/Sr whole rock isochron obtained from the Morar Pelite in the Morar area of the Northern Highlands suggests an age of 1024± 96 Ma for the main metamorphism of the Morar Moines. Within error this age overlaps that recently given for the Ardgour Gneiss and thus confirms the existence of Grenvillian elements within the Northern Highland Block. It suggests that the tectono-metamorphic history of the southwestern Moines is more complex than hitherto thought.
The distribution of palynomorphs in the Jurassic rocks of the Brora Outlier, NE Scotland
Authors: LAM K. , PORTER R.
Published: December 2007

The stratigraphical distribution of palynological taxa in the Liassic to Kimmeridgian succession of the Brora Outlier is presented mainly in charts. The palynological implications in terms of depositional environment and correlations with other Mesozoic sections are briefly discussed.
Deformation associated with the Ploumanac'h intrusive complex, Brittany
Authors: BARRIERE M.
Published: December 2007

The Ploumanac'h
massif
in Brittany is a funnelshaped, late-orogenic granitic diapir. Strain associated with the emplacement of this diapir is analysed with reference to the structure of the envelope, the form of the mafic
schlieren
and
enclaves
and fracture patterns in the coarsegrained granites. The behaviour of the country rocks was first brittle, then plastic. In the granites successive deformations seem to have been more or less continuous: viscous flow—identified in layered
schlieren
and suspected elsewhere—gave way to plastic flow and cataclasis as crystallization developed. The viscosity of the surrounding rocks decreased as the viscosity of the crystallizing magmas increased. The form of the intrusion and its changing mechanism of emplacement are related to this decrease in viscosity contrast between the granite and its envelope.
Diagenesis of Jurassic sandstones in the Viking Graben
Authors: Sommer F.
Published: December 2007

The development of reservoir qualities during the diagenetic evolution of sand bodies of the Brent Sand Formation in the Viking Graben is described. There are 3 main diagenetic phases: early silicification; strong leaching by circulating fresh waters resulting in kaolinization; and late illitization contemporaneous with the migration of hydrocarbons and associated water. The illitization processes are shown to be more complicated than previously indicated; a source rock outside the Brent Sand Formation is postulated. Analysis of the diagenetic minerals and the pore waters is used to elucidate migration behaviour in reservoirs. Migration is dated as probably occurring during Lower Eocene times.
Clay mineral diagenesis and oil migration in the Middle Jurassic Brent Sand Formation
Authors: Hancock N. J. , Taylor A. M.
Published: December 2007

Authigenic clay minerals, in an almost complete sequence of oil-saturated Brent Sand from an oilfield in the Viking Graben in the northern North Sea, show a transition from kaolinite in the upper part into illite in the basal part of the reservoir; replacement textures indicate that the illite has replaced kaolinite.

After early kaolinite formation, it is suggested that illite diagenesis took place synchronously with oil migration, and that the progressive extension of oil saturation down through the reservoir terminated diagenetic processes. Early diagenetic stages are thus 'frozen' and preserved in the upper part of the reservoir.
Late Nagssugtoqidian stress rientation derived from deformed granodiorite dykes north of Holsteinsborg, West Greenland
Authors: Davidson L. M. , Park R. G.
Published: December 2007

A suite of granodiorite dykes, of varied but non-random orientation, cuts basement gneisses in a 15 km x 8 km coastal strip around lat. 67°N in central West Greenland. The dykes which were metamorphosed in the granulite facies have been deformed by simple shear and vary from apparently unstrained to highly strained. The deformation occurred during a late stage of Nagssugtoqidian deformation (Lower Proterozoic). The orientation of the principal stress planes and of the σ
1
axis are determined on a best-fit basis from the change in sense of shear direction observed in the horizontal and in the vertical plane. The positions of the σ
2
and σ
3
axes are determined by a method involving a comparison of the observed shear directions with those predicted from a model stress system with known σ
1
and σ
2
= σ
3
. This stress model gives a σ
1
with a plunge of 28° on a bearing of 161°, a horizontal σ
3
and a steep σ
2
. This result is consistent with other more approximate estimates of the Nagssugtoqidian stress orientation near the Nagssugtoqidian front in W Greenland.
On the deformation of quartz containing bubbles
Authors: Knipe R. J. , White S. H.
Published: December 2007

Analysis of the interaction of dislocations with bubbles in quartz indicates that the distribution of bubbles during deformation is critically important to the deformation of quartz by dislocation processes. The estimated stress necessary to ensure large scale dislocation movement in inclusion rich quartz (bubbles and voids in the case considered here) is higher than the predicted stresses available during geological creep. Consequently dislocations are likely to remain attached to the bubbles for long periods of time and thus the strain rate of dislocation creep is likely to be strongly influenced by the rate at which the bubble-dislocation system can migrate. Bubbles can also affect the recrystallization of quartz by inhibiting the movement of sub-grain walls and may reduce the size of sub-grains. Finally, it is suggested that the stability and distribution of bubbles in quartz should be considered as an important factor in quartz deformation.
Infra-red techniques for volcano monitoring and prediction—a review
Authors: Francis P. W.
Published: December 2007

Infra-red radiation from volcanoes can be studied in the 3–5 and 8–14 μm wavebands by ground-based, aerial. and satellite surveys. The occurrence of a volcanic eruption is preceded by the introduction of hot magma beneath the volcano which may give rise to a detectable surface thermal anomaly, especially in the case of slow-moving andesitic magmas. Ground-based surveys employing simple infra-red telescopes are capable of rapidly producing thermal maps of volcanoes, but consistent monitoring is required to distinguish between apparent and real thermal anomalies. Aerial surveys employing scanning instruments to create thermal images provide better data, but present the same problems of interpretation. Satellite infra-red systems do not have resolutions below 120 m, but offer great potential for the future. Aerial surveys are too expensive to be used for routine volcano monitoring. Ground-based surveys are advocated until satellite infra-red resolution is improved.
Discussion on 'Chemistry, thermal gradients and evolution of the lower continental crust' by J. Tarney & B. F. Windley
Authors: Taylor S. R. , McLennan S. M.
Published: December 2007

Tarney & Windley (1977)
questioned the andesite model for crustal growth (
Taylor & White 1966
;
Taylor 1967
;
Jakes & Taylor 1974
;
Taylor 1977
). Much of their argument is based on rare earth element (REE) data from Archaean granulites, which they claim are representative of the lower continental crust.

The most damaging comment against the andesite model is their calculation (
Tarney & Windley 1977
, fig. 1) of the REE pattern in the lower continental crust. Using a value for andesite (representing the bulk crust) and average sedimentary rocks (representing the upper crust)they calculated a lower crustal composition which has a strong positive Eu-anomaly and extremely low LREE (in fact there is no La or Ce!). They stated that their andesite value was taken from
Nance & Taylor (1976)
; this is incorrect, since no andesite value is reported in that paper, nor is an andesite value reported in the only other paper by those authors (
Nance & Taylor 1977
).

Tarney & Windley do not tabulate their REE values, but estimates can be made from their chondrite-normalized plots. Their values are compared (Table 1) with the estimates of
Taylor (1977
,
1979
) for the bulk continental crust, based on the andesite model.The upper crustal estimate (
Nance & Taylor 1976
) and the correct calculation for the lower crust (assuming the upper crust is 1/3 of the whole crust) are also given in Table 1.

These values are plotted in Fig. 1. In marked contrast to Tarney & Windley's calculations, the REE pattern for the lower
Continental growth, island arc accretion and the nature of the lower crust—a reply to S. R. Taylor & S. M. McLennan
Authors: Tarney J. , Windley B. F.
Published: December 2007

It commonly happens that the less factual information we have on a problem, the more argument is generated. The lower crust is no exception. In fact the main thrust of our review paper on the lower crust was to demonstrate just how little factual data was available on which to construct reliable models for rustal growth, but that the data which was available (largely on Precambrian lower crustal granulites) did not fully support popular concepts that the lower continental crust is predominantly made up of cumulates or the refractory residues from partial melting. We did not set out to criticize Taylor's andesitic model for crustal growth directly, although in view of the important role the model has played over the last decade we could not avoid referring to it. Taylor & McLennan's defence of the andesite model, coupled with their critique of our own paper, nevertheless behoves us to comment on the andesite model both in relation to their specific points and in relation to our further observations since the paper was written.

With the andesite model there are basically three components to the equation: island arc = upper crust + lower crust. Knowledge of the geochemical characteristics of each is vital in order to test whether the equation will balance. Of the three, only the upper crust composition is known sufficiently well, and as far as the mean rare-earth distribution is concerned it can be approximated by the average sedimentary pattern given by Taylor (1977). There is much less
The Southern Uplands of Scotland: A Lower Palaeozoic accretionary prism
Authors: Leggett J. K. , McKerrow W. S. , Eales M. H.
Published: December 2007

The Southern Uplands contain 10 or more distinct deep-water stratigraphic sequences consisting of basalt and chert and/or graptolitic shale, below thick greywackes. These sequences are separated by major reverse strike faults. Adjacent sequences differ in sedimentary characteristics and age, indicating that they were originally deposited far apart. Within each fault-bounded tract the individual sequences are disrupted and repeated by further, less important, strike faults and by folding. In the N (away from the site of the Iapetus Ocean) the sequences are older than in the S, but the majority of the beds within each sequence young to the N. This structure is compared with modern accretionary prisms, which develop on active continental margins where the oceanic plate has a thick sedimentary cover.
Occurrence and significance of inverted metamorphic gradients in the western Scandinavian Caledonides
Authors: Andreasson P. G. , Lagerblad B.
Published: December 2007

In the Scandinavian Caledonides, the basement with a thin veneer of cover sediments can be traced from the frontal autochthon far westwards towards the centre of the orogen. The changing metamorphic grade can be recorded and compared with that of the overlying nappes. The metamorphic nature of these cover sediments is examined in the deepest structural levels of two windows, 200 km to the W of the Caledonian front. The emplacement of nappes above the cover caused a progressive recrystallization under greenschist facies conditions, with development of quartz + margarite + muscovite, quartz + chlorite + muscovite and quartz + white mica + graphite among parageneses defining the penetrative foliation related to the nappe displacement. The final overburden pressure is estimated to be 6–8 kb. Temperatures reached peak values around 550°C first after nappe emplacement. Despite the westerly situation and deep tectono-stratigraphic level of the metasediments, their metamorphic history is incompatible with a location close to an orogenic interior. The overlying cover sequence displays at least 2 inversions of metamorphic zonation. These developed as a result of the emplacement of high-grade nappes above low-grade or unmetamorphosed units, with incomplete subsequent restoration of the thermal profile, and in response to the catalytic effect of concentrated strain during thrusting. The imprinted saw-tooth pattern of the thermal profile in the western windows requires that tectonic discontinuities exist in this part of the western Scandes, considered by some geologists the axial zone of the orogen. It also suggests that the uplift and the formation of late regional syn- and antiforms followed soon after, or were simultaneous with, the late translation of the Caledonian front allochthon.
Diapirism and gravity collapse in the Scandinavian Caledonides
Authors: Ramberg H.
Published: December 2007

Two gravity-driven tectonic processes are common in orogenic belts, such as the Scandinavian Caledonides. (1) The rise of buoyant granitoid basement in the form of domes and diapirs into the column of geosynclinal metasediments and metalavas. In the Scandinavian Caledonides some of the nappes also acted as a buoyancy-inducing overburden. This is particularly true for the heavy Seve nappe. (2) The gravitational collapse of the pile of supracrustals and nappes. The collapse is associated with a horizontal spreading which contributes to the horizontal displacement of the thrust sheets. In the Scandinavian Caledonides there are numerous examples of basement diapirism, particularly among the ‘Nordland granites’, but also within the huge Möre-gneiss complex in SW Norway. Closer to the eastern edge of the chain the basement was less hot and plastic during the orogenesis, and cataclastic conditions prevailed during the rise of the row of peripheral uplifts extending parallel to the belt. Evidence of horizontal spreading and vertical shortening of some of the nappes is found in the form of boudinage, mineral lineation and prevailing horizontal schistosity over large regions within the nappes. The collapse-spreading process has been treated theoretically and experimentally, but experimental results are only briefly mentioned.
Mechanisms of autocorrelation
Authors: Funnel B M.
Published: December 2007

The phenomenon of autocorrelation of major physical,chemical and biological processes, which underlies the recognition of geological rhythms and cycles in the outer Earth, deserves further study.Study of the mechanisms which link driving changes with responding changes will be particularly important. 3 Main drives are identified: (1) sea-level change, (2) calcium sulphate deposition, and (3) carbon dioxide injection. All other changes are thought to be direct or indirect responses. Brief consideration is given to the significance of stable carbon isotopes,oceanic sedimentation and magnetic reversal/sea-level variations in elucidating the operation of autocorrelation mechanisms in the past.
The E Greenland rifted continental margin: an examination of the coastal flexure
Authors: Nielsen T. F. D. , Brooks C. K.
Published: December 2007

The structure of the E Greenland coastal flexure, a major structure developed during continental break-up, is interpreted on the basis of field observations. An earlier model, which involves normal inland-dipping, antithetic faulting and seaward rotation of fault blocks is confirmed and amplified. This model requires that regional dips are very much less than dips measured on bedding planes thus leading to considerably reduced thicknesses for the Tertiary volcanic succession in E Greenland. Detailed mapping confirms the validity of these thickness estimates and leads to the conclusion that the volcanic extrusion rate was similar to that of present-day Iceland, thus obviating the need for special mechanisms of magma generation. Comparable structures occur in other regions of continental break-up and voluminous basalt discharge and it is suggested that the flexure developed by collapse of the attenuated crust subsequent to the massive extrusion of plateau basalts.
Computer files and the formal database in support of hydrocarbon exploration and development offshore
Authors: Farmer D. G.
Published: December 2007

The rapid build-up of the British National Oil Corporation (BNOC) since its establishment in 1975/76 and the pressing need to handle and assimilate the massive volume of geological, geophysical and related data to which it has access, afforded the opportunity of identifying natural priorities in the introduction of computer systems and files of digital data in support of hydrocarbon exploration (and development) offshore. Following the installation of a computer in the Exploration Department of BNOC in 1978, data files were quickly established and used. A two-phase plan for the introduction of data handling systems included, first, the setting-up of fundamental software for report generation and limited selective retrieval from individual files, in order to feed application programs and to enable immediate use of data as it was progressively compiled. Secondly, and following review of data and systems during this initial phase, a generalized DBMS was selected to enable the efficient integration and use of the broad range of data components involved in the conceptual exploration database. The nature of these data types, their structure and inter-relations is summarized in relation to applications, based on both conventional files and the formal data base, and the role of these data systems in the exploration process is indicated.
Revisions in the pyroclastic stratigraphy of Mt Misery volcano, St. Kitts, Lesser Antilles:
14
C ages and recognition of pyroclastic flow deposits
Authors: Roobol M. J. , Smith A.L. , Wright J. V.
Published: December 2007

New radiocarbon dates reveal that unlithified pyroclastic deposits erupted from Mt Misery, St. Kitts (principally the Mansion ‘Series’) range from older than 42 000 years to younger than 1750 years B.P. Previously published accounts of Mt. Misery have only described air-fall deposits. However, a newly recognized sequence of pyroclastic flow deposits within the Mansion ‘Series’ is dated as 2000 to 3000 years B.P. The presence of these young deposits indicates that Mt Misery,. like other Lesser Antillean volcanoes, also has a potential pyroclastic flow volcanic hazard.
The role of Hercynian granites in the deformation and metamorphism of Brioverian and Palaeozoic rocks of Central Brittany
Authors: Hanmer S. K. , Le Corre C. , Berthé D.
Published: December 2007

The late Proterozoic rocks of Central Brittany, represented essentially by Upper Brioverian sediments, are considered to be a late to post-tectonic molasse to the Cadomian chain. The poly-orogenic character (Cadomian and Hercynian) of the deformation structures affecting these rocks is noted from the Baie de Douarnenez to the Rennes region. However, the main syn-metamorphic deformation event is clearly of Hercynian age. Furthermore, we show that this event and the associated metamorphism are directly related to the emplacement of the Hercynian leucogranites. The syntectonic nature of the leucogranites, with respect to the deformation of their envelope, is therefore affirmed and the concept of a ‘Brioverian basement’, in the mechanical sense of the term and contrasted with a ‘Palaeozoic cover’, must be abandoned.
The E Greenland continental margin: a transition between oceanic and continental magmatism
Authors: Brooks C. K. , Nielsen T. F. D.
Published: December 2007

The E Greenland continental margin differs from typical margins in having a superimposed regional uplift which has exposed the early rift products for direct examination. Most of the igneous rocks in this region find counterparts in the oceanic setting with the proviso that the area is part of an aseismic ridge. Thus, picrites, basalts, sheeted dyke swarms and layered gabbros are present and these can be used to shed light on oceanic magmatic events. Nephelinitic rocks are products of off-axis volcanism and find no counterparts in the present oceanic rift system, although they occur in marginal regions of the ocean basins and were generated in distal regions at the initiation of rifting in Icelandic anomaly. Voluminous salic rocks in the area owe their generation largely to continental crust which has undergone extensive melting. They find no direct counterparts in oceanic areas. The outstanding degree of exposure in this area combined with its transitional nature and wide spectrum of rock types make it a unique laboratory for the elucidation of a variety of problems regarding both oceanic and continental volcanism together with the nature of rifted continental margins in general.
Late Proterozoic rifting in NW Scotland: the genesis of the ‘Torridonian’
Authors: Stewart A. D.
Published: December 2007

The two major “Torridonian” successions,
viz
. the Stoer Group (~968 Ma) and the Sleat–Torridon Groups (~777 Ma) occupy NNE-trending rifts cutting Archaean and early Proterozoic crust. Palaeocurrents, pebble petrography and age, and the initial
87
Sr/
86
Sr ratios of clay-rich sediments indicate derivation from flanking areas of this old crust, rather than from late Proterozoic Grenville or Morarian metamorphic rocks. The earlier rift seems to be roughly contemporaneous with Grenville metamorphism but genetically unrelated to it. The rifts perhaps mark initiation of an Iapetus-related ocean in the same way as very similar fault-bounded Triassic and Lower Jurassic sediments mark the start of continental break-up and initiation of the present Atlantic. The western margin of both rifts probably coincides with the Outer Hebrides Thrust and the eastern margin with the Moine Thrust Zone. Reactivation of the old rift-margining faults by Caledonian compression may have generated the lower thrusts of the Moine Thrust Zone, while the Moine nappe itself, by analogy with Lower Devonian events in southern Appalachia, represents a slice of the Grenville microcontinent emplaced after closure of the intervening ocean.
The Highland Border rocks and their relation to marginal basin development in the Scottish Caledonides
Authors: Henderson W. G. , Robertson A. H. F.
Published: December 2007

It has long been known that the Highland Border includes an assemblage of altered serpentinites, gabbros, spilitic lavas, ferruginous and manganiferous cherts, black phyllites, quartzose clastics and amphibolites. New work confirms that many of these rocks represent a dismembered tectonically emplaced ophiolite of Caledonian age, which originated in a narrow oceanic basin within or bordering the Dalradian sedimentary pile. The ophiolitic rocks were expelled from the basin as thrust sheets transecting D1 structures. Studies in the SW Highlands suggest emplacement during D2 synchronous with SE translation of the Tay Nappe. This implies that the ophiolite originated in the N. The Highland Border rocks are seen as marginal to a long-lived northward-dipping subduction zone within the Southern Uplands. The evolution of the Ballantrae ophiolitic complex, the Midland Valley and the Dalradian sedimentary basin are considered within this framework.
Late Mesozoic bivalve biostratigraphy of the Antarctic Peninsula region
Authors: Crame J. A.
Published: December 2007

Two groups of bivalves, the inoceramids and buchiids, are particularly useful zone fossils in the Mesozoic sedimentary formations of the Antarctic Peninsula region. In the Upper Jurassic, species of the generaRetroceramus,Malayomaorica,Buchia and Anopaeacan be traced considerable distances around the margins of Gondwana, and as such are especially valuable for regional correlations. Some of them, such as theR. haasti-subhaastigroup, can also be employed in detailed local correlations. In the Lower Cretaceous, the presence of cosmopolitanInoceramusspecies, such as members of theneocomiensis,concentricus and anglicusgroups, permits correlation with Northern Hemisphere faunas for the first time. Other stratigraphically important inoceramids are theI. ovatusgroup in the Lower Neocomian, theI. heteropterusgroup andAnopaea trapezoidalisin the Upper Neocomian andAn. cf.mandibulain the Albian. The only buchiids present in the Lower Cretaceous of Antarctica belong to the extensiveAucellina andina-radiatostriatagroup. Two types of Antarctic Upper Cretaceous inoceramids that are particularly important for regional correlations are the Upper CenomanianI. pictusgroup and the Turonian-ConiacianI. madagascariensis-ernstigroup. Senonian inoceramids are still poorly known but would seem to offer considerable scope for further studies.
Review of the Upper Cretaceous–Lower Tertiary sequence on Seymour Island, Antarctica
Authors: Zinsmeister William J.
Published: December 2007

The thick sequence of fossiliferous marine and non-marine sandstones and siltstones on Seymour I. represents the most complete well-exposed section of Upper Cretaceous to Lower Tertiary rocks known in the Southern Hemisphere. The succession has been divided into the Upper Campanian to possibly lowermost Tertiary Marambio Group comprised of the Lopez de Bertodano and Sobral formations and the Lower Tertiary Cross Valley and La Meseta formations of the Seymour Island Group.

The Lopez de Bertodano Formation consists of
c
. 1067 m of medium-grained to silty concretionary sandstones of Middle Campanian to possibly Maestrichtian age, and the Sobral Formation of
c
. 210 m of medium- to coarse-grained glauconitic concretionary sandstones. The precise age of the Sobral Formation is uncertain, but may be Maestrichtian to possibly Danian. The lower 110 m of the Seymour Island Group consists of non-marine gravelly to pebbly sandstones and tuffaceous plant-bearing siltstones of the Cross Valley Formation, overlying which are 450 m of fine-grained marine sandstones and siltstones with interbedded fossiliferous pebbly conglomerates. Recent studies of the diverse and abundant faunas and floras of the Seymour Island Group have shown that they are older than previously thought, the Cross Valley Formation being Palaeocene and the La Meseta Formation late Eocene to possibly earliest Oligocene.
The Middle Devonian shoreline in North Devon, England
Authors: Tunbridge I. P.
Published: December 2007

The Hollowbrook Formation is an early Middle Devonian regressive succession of sandstones and heterolithic facies marking a passage from shallow marine shelf muds, through a sandy shoreface to continental, ephemeral stream sheet sands. Ten facies are recognized, arranged in two sequence types. The shelf sequence consists of alternations of bioturbated muddy sandstone (fair weather sediment) and shelly concentrates or parallel laminated fine sandstone (storm deposits). The nearshore and foreshore sequences coarsen upwards, and pass from bioturbated muddy sandstone (shelf) to lenticular beds (inner shelf), then either wavy and flaser beds (fair weather lower shoreface) or hummocky beds and multistorey parallel laminated sands with bioturbated tops (lower shoreface storm shoals). Upper shoreface wave ripple cross laminated sandstones follow, then parallel and planar cross laminated sandstones (foreshore) and parallel laminated lithic sandstone (continental sheet flood).

The lower parts of the shoreface sequence and inner shelf are burrowed by
Skolithos. Arenicolites
and
Chondrites
. The sequence differs from the high energy 'Oregon Coast' shore in the absence of a megarippled facies and presence of much bioturbation, but closely matches the sequence found in modern low energy, wave influenced sandy shores such as Sapelo Island, Georgia.
The age and nature of the basement of southern Britain: evidence from Sr and Pb isotopes in granites
Authors: Hampton C. M. , Taylor P. N.
Published: December 2007

The isotopic study of granitic intrusions in southern Britain provides an indication of the age and geochemical nature of the South British basement, which is otherwise generally obscured from observation by sedimentary cover. This paper reports Pb isotopic compositions of feldspars in granites from SW England, Lundy, Mountsorrel and Shap, in addition to age and initial
87
Sr/
86
Sr data on two of the granites.
A
review of published Rb–Sr age and isotope data for southern Britain and consideration of the new Pb data using the plumbotectonics model of Doe & Zartman (1979) indicate that the basement to southern Britain has an age of ∼800 Ma with an upper limit of 1200 Ma. The granites studied in this work have substantial components of crustally derived Sr and Pb.
Fluids and melting under upper amphibolite facies conditions
Authors: Powell R.
Published: December 2007

Internal buffering paths on temperature-water activity diagrams for the pelitic model system:

NaAIO
2
- KAIO
2
- CaAI
2
O
4
- Al
2
SiO
5
- SiO
2
- H
2
O

give rise to sequences of assemblages which correspond to those observed in upper amphibolite facies terranes. In particular, the persistence of the assemblage quartz-alkali feldspar-plagioclase-muscovite-sillimanite across a zone and the rapidly changing composition of plagioclase across this zone can be accounted for in a natural way.
Continental fault structure and the shallow earthquake source
Authors: Sibson Richard H.
Published: December 2007

Plate boundaries in continental crust are generally less sharply defined than in the oceans, with seismicity spread over broad areas. Interplate displacements appear to be largely accommodated by networks of major fault zones.
A
simple 2-level model for these important structures accounts for the depth distribution of most continental earthquakes, and for the observed range of faulting styles and associated rock deformation textures. The model consists of a seismogenic frictional slip regime overlying quasi-plastic mylonite belts wherein shearing is largely accommodated aseismically, due mainly to the changing response of quartz to deformation with increasing temperature. Shear resistance increases with depth to a peak value in the vicinity of the frictiona1/quasi-plastic transition and then decreases rapidly. The depth to which microseismic activity extends appears inversely related to regional heat flow and can be satisfactorily modelled as the frictional/quasi-plastic transition for different geotherms using laboratory determined flow laws for quartz-bearing rocks. Larger earthquake ruptures (
M
> 5.5) tend to nucleate near the base of the seismogenic regime in the region inferred to have the highest shear resistance and concentration of distortional strain energy. Consideration is also given to the depression of isotherms and seismic activity in regions of thrusting, and to the question of the downward continuation of major fault zones through the lithosphere. Decoupling of the upper crust on flat-lying shear zones may accompany higher-level dip-slip (and perhaps in some circumstances, strike-slip) faulting, being favoured by above average continental heat flow and a high quartz content in the middle or deep crust. The average level of deviatoric stress within the seismogenic regime remains an outstanding problem.
On a gold mineralization in the Precambrian Tartoq Group, SW Greenland
Authors: Appel Peter W. U. , Secher Karsten
Published: December 2007

In the Precambrian Tartoq Group, SW Greenland, gold occurs in three parageneses associated with arsenopyrite-pyrite, tennantite and chalcopyrite. The gold-bearing sulphide mineralizations appear as conformable quartz layers, lenses and veins in greenstones of basaltic composition. Gold particles in the arsenopyrite-pyrite layers have a true fineness ofc.990, in the tennantite-rich veins a fineness ofc.720 and a fineness ofc.500 in the chalcopyrite quartz veins. The arsenopyrite-pyrite layers are of submarine exhalative origin, whereas the tennantite and the chalcopyrite quartz veins and lenses are of diagenetic and/or metamorphic origin.
The seventh UK Geophysical Assembly
Authors: Khan M. A. , Maguire P. K. H. , Hill I. A.
Published: December 2007

Report of the seventh annual UK Geophysical Assembly held at the University of Leicester from the 11–14 April 1983.

The seventh annual UK Geophysical Assembly on 11–14 April 1983 was sponsored by the Geological Society, London and the Royal Astronomical Society, who also published the abstracts of the 108 papers in the April issue of the Geophysical Journal (vol. 73). It included the Bullerwell lecture on 'Seismic stratigraphy and the evaluation of depositional sequences and fades' by P. Vail of Exxon, in which he demonstrated how depositional environments and facies can be predicted from seismic data through an orderly approach to the interpretation of seismic reflections. A. H. Cook (Univ. Cambridge) gave a second invited lecture on 'The physics of matter at high pressures in planetary interiors'. At high pressures hydrogen will become metallic, melting behaviour will be affected and electrical properties altered. He discussed their implications for our understanding of the structure of the planets and of the physics of condensed matter. B. F. Windley (Univ. Leicester) gave the third invited lecture on 'The tectonic evolution of the Himalayas', which is the subject of multidisciplinary study by a number of international groups at present.

The meeting was attended by over 200 geophysicists and graduate students from universities in the UK and Ireland and from industry. Three parallel sessions were held each day and were supplemented by about 30 research and commercial exhibits. The sessions comprised talks on lunar studies and geochronology; continental and oceanic structure; earth magnetism; earthquake and
Internal structure of the Erlend Tertiary volcanic complex, north of Shetland, revealed by seismic reflection
Authors: Gatliff R. W. , Hitchen K. , Ritchie J. D. , Smythe D. K.
Published: December 2007

Detailed seismic reflection mapping 100 km N of Shetland has revealed a large subcrop of Palaeocene basalts proved by exploration drilling. The geometry of internal reflectors within the buried basalt suggests the existence of two partially eroded volcanoes. A vent of about 2 km in diameter, surrounded by radially outward-dipping basalts, is centred over the Erlend igneous complex, whose existence had been postulated previously on gravity and magnetic evidence alone. A new volcano, the more deeply eroded West Erlend centre, is postulated by interpretation of seismic data and by gravity modelling. An approximately cylindrical mafic or ultramafic pluton is inferred from the gravity modelling to underlie each of the two centres; the diameter of the Erlend pluton is about 14 km and that of West Erlend about 5–7 km. The seismic stratigraphy of volcanic rocks can now be recognized as a valid new field of study with particular relevance to hydrocarbon exploration.
Development of rift basins illustrated by the structural evolution of the Oseberg feature, Block 30/6, offshore Norway
Authors: Badley Michael E. , Egeberg Tom , Nipen Olav
Published: December 2007

The Mesozoic tilted fault block in Norwegian North Sea block 30/6 containing the giant Oseberg oil and gas field is used to illustrate basin development during the Jurassic and Cretaceous. There is seismic evidence for an early rifting phase in the northern Viking Graben, on which the Jurassic/ Cretaceous rifting phase (early Bathonian to Berriasian) is overprinted. The Oseberg structure is representative of other fault blocks bordering the northern Viking Graben axis. Planar normal faults, and listric faults which were restricted to the rifting phase, dominate. Both fault types exhibit syn-fault sedimentation. Listric faulting is recognized on seismic sections by the differential tilting, reverse drag, antithetic faulting, and a wedge-shaped syn-rift reflector package. The initiation of rifting is dated by baselap onto pre-rift reflectors, and cessation is dated by an unconformity beneath the generally onlapping post-rift sediments. Steeply-dipping planar normal faults, often active along previously established fault zones, played a significant part in the post-rift development of the basin. The last movement on planar normal faults in the Oseberg fault scarp becomes younger away from the rift axis, and this produced the complex fault scarp visible on many seismic lines. The topography, defined by the post-rift unconformity, is a composite surface which formed in response to subsidence processes; it is not the result of orogenic events such as the Kimmerian 'orogeny'. Footwall uplift associated with planar normal faults caused local unconformities in complex fault scarps and on fault block crests.
A petrogenetic grid for pelites in the Ballachulish and other Scottish thermal aureoles
Authors: Pattison D. , Harte B.
Published: December 2007

The Ballachulish ‘Granite’ is a composite Devonian intrusive complex surrounded by a distinctive thermal aureole developed in regionally deformed and metamorphosed Dalradian sediments on the W coast of Scotland. The most abundant rocks in the aureole are pelites, which show a progression of assemblages from quartz–muscovite–chlorite up to a variety of high-grade assemblages involving combinations of cordierite, corundum, spinel and, rarely, hypersthene and garnet.

Metamorphic zones have been mapped around the granite, which are defined by the following reactions going upgrade:

Mu
+
Chl
+
Q
=
Cd
+
Bi
+
V

{

Mu
+
Bi
+
Q
=
Cd
+
Kf
+
V

or

   
Mu
+
Cd
=
Q
+
Bi
+
As
+
V

Mu
+
Q
=
As
+
Kf
+
V

{

Q
+
Bi
+
As
=
Cd
+
Kf
+
V

or

   
Mu
+
Cd
=
Bi
+
As
+
Kf
+
V

Mu
=
Cor
+
Kf
+
V

Bi
+
As
=
Cor
+
Kf
+
Cd
+
V

The restricted occurrences of assemblages involving spinel, hypersthene and garnet do not allow higher grade zones to be mapped. Variations in the reaction sequence as a consequence of bulk compositional factors, in particular the development of quartz-bearing versus quartz-absent assemblages, are described.

Details of the mineral assemblages from Ballachulish are combined with high-grade assemblage data from the Belhelvie, Lochnagar and Comrie aureoles to construct a comprehensive schematic petrogenetic grid. The grid involves the minerals quartz, chlorite, muscovite, biotite, cordierite, alumino-silicate, K-feldspar, corundum, spinel, hypersthene and garnet, whose assemblage relationships are modelled in the system K
2
O-FeO-MgO-Al
2
O
3
-SiO
2
-H
2
O (KFMASH).
Isotopic dating in metamorphic belts
Authors: Cliff R. A.
Published: December 2007

Isotopic dating in metamorphic rocks is concerned with the timing of processes whose operation is controlled by continually changing physical conditions. Of these, temperature has a pervasive influence and the use of physical models to elucidate the ways in which temperature is likely to vary is briefly reviewed.

The central concept of closure temperature is critically discussed and quantitative estimates for biotite and hornblende are evaluated, in order to illustrate the factors which control closure temperatures and limit their application in practice. The possibility of dating crystallization using minerals which crystallize below their respective closure temperatures is examined, taking examples involving K-Ar, Rb-Sr, Sm-Nd and U-Pb analyses. The indirect dating of metamorphism via structurally dated plutons is briefly considered, and the problems of interpreting both discordant U-Pb zircon ages and Rb-Sr whole rock isochrons in metamorphosed granites are discussed. The value of near-concordant zircon ages is emphasized. The extent of isotopic equilibration during metamorphism, specifically of Sr-isotopes in metasediments, is shown not to be a simple function of metamorphic grade. The flow of fluids produced by metamorphic reactions appears to be crucial and there is a potential for dating metamorphism using whole rock samples where such flow can he demonstrated independently. The concluding discussion briefly examines existing data for the Dalradian and indicates the potential for further progress using both well-established and novel approaches.
Cretaceous tholeiites of the northern continental margin of South America: the Sans Souci Formation of Trinidad
Authors: Wadge G. , Macdonald R.
Published: December 2007

The Sans Souci Formation of northeastern Trinidad is a sequence of basaltic clastic rocks and lavas, gabbros and terrigenous sedimentary rocks at the eastern end of the Caribbean Mountain orogen. A distinctive clastic character to many of the igneous rocks suggests a process of thermal erosion after internal brecciation of thick submarine lava flows and shallow intrusions. The tholeiites of the Sans Souci Formation were erupted on to the passive continental margin of northern South America during the interval Aptian–Santonian. The associated sedimentary rocks are limestones, shales, sandstones and conglomerates with a continental provenance. Chemically, the Sans Souci lavas have MORB affinities which distinguish them from the island arc tholeiites found on neighbouring Tobago. The Los Naranjos member of the Tucutenemo Formation of central Venezuela is probably the metamorphic equivalent of the Sans Souci Formation. A speculative source for these volcanic rocks is a period of mid-Cretaceous intraplate flood basalt volcanism. This appears to have occurred both to the north and to the south of the island arc which collided with the continental margin in the late Cretaceous.
On the supposed Precambrian palaeosuture along the Dead Sea rift, Jordan
Authors: Abed Abdulkader M.
Published: December 2007

The evidence that the Dead Sea rift has existed as a zone of crustal weakness since Precambrian time is critically examined based on (i) the distribution and abundance of dykes in the Precambrian basement and (ii) the distribution of the Lower Cambrian basal conglomerates. It is shown that dyke and clastic sediment occurrence is not preferentially associated with the modern rift zone, and thus that some earlier tectonic interpretations must now be discounted.
Flow separation—a physical process for the concentration of heavy minerals within alluvial channels
Authors: Best James L. , Brayshaw Andrew C.
Published: December 2007

Flow separation is a common feature within alluvial channels that occurs at abrupt changes in the bed geometry. At a wide range of scales, it is a process that can exert considerable control over the segregation and deposition of heavy mineral grains. Fluid separation generates a region of high bed shear stress that can entrain heavy minerals, and a region of low velocity that is a preferred site for the deposition of denser particles. Significant concentrations of heavy minerals, sometimes up to eight times the background value, may be formed by flow separation processes. A review of the occurrence of flow separation illustrates that it may be responsible for the accumulation of heavy mineral grains at a range of geomorphological scales.
Diamond-bearing upper Karoo fluvial sediments in NE Swaziland
Authors: Turner B. R. , Minter W. E. L.
Published: December 2007

Upper Karoo sediments (Middle to Upper Triassic) in NE Swaziland consist of an upward-fining, fluvially dominated sequence (Molteno and Elliot Formations) followed by the mainly aeolian Clarens Formation. Diamonds and associated kimberlitic garnets are strata-bound in two thin upward-fining sequences (4–16 m) at the base of the Elliot Formation. These sequences comprise erosionally based, clast-supported conglomerate channel-fill, overlain by coarse, feldspathic, cross-stratified sandstone and rippled siltstone with gritty layers. Diamonds and garnets occur in the matrix of the conglomerate, but are five times more abundant in the coarse feldspathic sandstone. They also occur in the sandy mode in the overlying siltstone, but in greatly diluted concentrations. The diamonds were locally derived and released to the sedimentary system following a climatic change when conditions favoured more intense erosion of nearby kimberlite pipes. Diamonds and garnets released to the passing sediment were concentrated locally in thin (<2m), extensive channel sands deposited by overloaded ephemeral flood flows. Source area denudation and the increasing aridity of the climate during Upper Karoo times led to a gradual reduction in slope and sediment supply, with the result that river energy and bedload diminished, producing a gross upward-fining trend in the succession.