bluuebunny/crossref_metadata_2025_split huggingface dataset:
K/Rb ratios and metasomatism in metabasites from a Precambrian amphibolite–granulite transition zone
Authors: FIELD DENNIS , CLOUGH PETER W. L. 
Published: December 2007

Potassium and rubidium values are reported for a suite of 181 metabasites from the amphibolite–granulite transition zone in the Precambrian Bamble sector of south Norway. Both alkalis are more abundant, and the K/Rb ratios lower, in the rocks from the amphibolite facies. Rubidium has been strongly fractionated with respect to potassium.
The K/Rb ratios exhibit a regular and systematic variation and this defines a linear trend which is markedly different from established igneous fractionation trends. The chemical fractionation occurred as a result of the metamorphism, and the chemical changes are in keeping with the concept of a vertical chemical fractionation within the continental crust. Similar linear trends established in other high grade metamorphic terrains may have the same (metasomatic ?) origin.
A Caledonian plate tectonic model
Authors: ADRIAN PHILLIPS W. E. , STILLMAN CHRISTOPHER J. , MURPHY THOMAS 
Published: December 2007

A plate tectonic model for the Caledonides of the British Isles with three non-parallel lower Ordovician-lower Devonian subduction systems is presented. In the north-west, the Caledonian thrust front is interpreted as the site of multiple, slow ESE.-directed subduction (Sd1) of Lewisian-bearing continental foreland plate beneath continental crust containing an ensialic Dalradian basin. South of the continental crust of the Southern Uplands zone lay a ENE.–WSW.-trending plate boundary (Sd2) where Iapetus oceanic crust was subducted to the NNW. The convergence of subducted lithosphere beneath the Moine-Dalradian plate is linked to its prolonged history of diachronous deformation, metamorphism, intrusion and uplift. The oblique subduction on Sd1 and Sd2 caused collision below the Moine-Dalradian outcrop generating sinistral strike-slip faults with downthrown south-east sides, spreading north-east with time. Sinistral displacement on the Great Glen Fault system, and of the Connemara inlier is linked to this model. A third (Ordovician-Silurian) subduction system (Sd3) is defined to the north-west of a volcanic arc from the Lake District in England, through southern Ireland. Iapetus oceanic crust was subducted to the south-east here.
Evidence is presented for oblique collision between Sd2 and Sd3 from late Ordovician to early Devonian, followed by an unstable triple point migrating south-westwards across the British Isles region, and subsequent dextral strike-slip movement on the suture.

Triple-point migration to the south-west is measured using diachronous ending of volcanism and plutonism on Sd
2
and Sd
3
Opposed lower Devonian collision points now appear to be dextrally offset by about 900 km. Calculated closure rates on Sd
2
and Sd
3
give minimum Arenig widths for Iapetus of 600–800 km. About 1270 km of late Ordovician-Devonian dextral displacement on the Iapetus suture could have generated 570 km of foreland convergence in the East Green­land-Scandinavian Caledonides.
Intensity and direction of magnetization in oceanic basalts
Authors: LOWRIE WILLIAM 
Published: December 2007

The magnetic properties of oceanic basalt samples from 55 DSDP sites (301 samples) and 112 dredge haul sites (311 samples) show wide variations, indicative of heterogeneity in the basaltic layer. Remanent intensity and
Königsberger
ratio are log-normally distributed and range over three orders of magnitude for each collection. For DSDP samples between-site variation is greater than within-site variation, suggesting horizontal variation of magnetization within the source layer of magnetic anomalies. Crustal magnetization estimates from inversion of short-wavelength oceanic magnetic anomalies may therefore be in error. By using arithmetic means rather than the geometric means appropriate for log-normal distributions, estimates of the magnetization of Layer 2 of around 4 × 10
−3
Gauss are obtained for the Indian, Pacific and north Atlantic oceans and Caribbean Sea, while lower averages are found in the south Atlantic and Antarctic oceans. Using this as a representative value for abyssal areas, the thickness of the magnetic source layer is greater than commonly assumed, and probably more than a kilometre. This interpretation is supported by DSDP data from some individual sites, notably the deep holes of Leg 37.

The DSDP median destructive fields average only 123 Oe. Although many sites have much higher stabilities than this, there is evidence for unstable NRM at many sites where samples exhibit a strong tendency to acquire viscous remanence components. The low coercivity secondary magnetizations confuse identification of the stable direction during magnetic cleaning. Acquisition of high coercivity secondary remanence (CRM) as a result of maghemitization, which is extensive in the DSDP collection, may also have altered the original NRM direction.
Remanent inclination data from four Tertiary DSDP sites (ages 38–40 Ma) have been combined to give a tentative Eocene VGP for east Antarctica at 68°S 64°E. It has not been possible to compare DSDP data in this way at other sites. Palaeolatitudes deduced from DSDP basalt remanent inclinations show large discrepancies from values expected from plate reconstructions at many sites. Incompletely removed secondary magnetizations, tectonic effects and palaeo-reconstruction errors, alone or in combinations, may be responsible for these discrepancies. A major source of deviation from the expected direction may be the rapid cooling of the basalt which does not allow adequate averaging of secular variation.
Palaeomagnetic data and radiometric ages from the Cretaceous of West Kalimantan (Borneo), and their significance in interpreting regional structure
Authors: HAILE N. S. , McELHINNY M. W. , McDOUGALL I. 
Published: December 2007

Potassium-argon ages of biotite and hornblende from sixteen samples of mainly granitic plutonic rocks from West Kalimantan indicate a complex history of magmatism and cooling from the Middle Jurassic to late Cretaceous, with most ages in the range 75 to 112 Ma. Samples from the Schwaner Zone in the northern part of the area give measured ages ranging from 76 to 116 Ma. In the southern region most samples are in the range 79 to 86 Ma, but two are older (127 Ma, early Cretaceous, and 153 Ma, Middle Jurassic). In both areas, concordant ages from biotite and hornblende indicate a well-defined event at about 80 to 85 Ma, which has also been recognized to the north in Sarawak, on islands of the South China Sea, in the Malay Peninsula, south Sumatra, and in the Java Sea.
Palaeomagnetic measurements on thirty-nine samples of dyke rocks, lavas, tuffs, granites, hornfels and metatuff, all believed to be late Cretaceous, yield a mean palaeomagnetic pole at 21°E 41°N, and a palaeolatitude for West Kalimantan of 0°. The palaeomagnetic pole does not differ significantly from the Cretaceous pole estimated for the Malay Peninsula. It is concluded that since the Middle Cretaceous West Kalimantan and the Malay Peninsula have behaved as a unit, have remained in much their present latitude, but have rotated anticlockwise about 50 .
Structure and mineralization in the Cligga granite stock, Cornwall
Authors: MOORE J. McM. , JACKSON N. 
Published: December 2007

In the Cligga stock there are two groups of fractures, produced by separate episodes of brittle deformation which affected the granite and adjacent slates. Generalized models constructed by interpretation of fault and fracture traces on geological cross-sections provide a coherent explanation of the formation mechanisms for the two groups of structure: A—curved primary flat-lying joints, granite-veins and porphyrydyke fissures, early normal faults in slates, marginal thrusts and reverse faults, and B—conjugate normal faults and extensional fissures. The fractures were produced by stresses exerted from within the underlying St Agnes–Cligga cupola which forms part of the buried batholith ridge. The stress system was modified during the first deformation by local conditions within the stock.
Structures of one or both generations controlled the widespread greisen (phyllic) wallrock alteration, hydrothermal mineralization and kaolinization (argillic alteration). Time/space models illustrate relationships during the major episodes of ore mineral deposition which produced telescoped metal zonation in the belts of W/Sn/Cu/Fe veins which traverse the intrusion. The relationships between structure and mineralization at Cligga and in other small granites, indicate that undiscovered stocks in SW England may contain potentially economic W/Sn-sheeted vein or stockwork ore bodies.
The Mesozoic development of aseismic continental margins
Authors: KENT P. E. 
Published: December 2007

Mesozoic basin development with in the North-west European Continental Shelf took place in belts peripheral to old Palaeozoic massifs. The area was dominated by vertical tectonic movements from the end of the Hercynian orogeny, and basin development along characterized by intermittent marginal faulting and graben formation dated as Permian, Triassic, and Lower, Middle and Upper Jurassic.
On a world scale the Mesozoic basin development and the subsequent late-Mesozoic separation of the elements of the North Atlantic and Gondwanaland was the final episode of a long-continued subsidence, peripheral to ancient blocks defined during Palaeozoic times. Marine transgression on or close to the later sutures is recognized in the Lower Palaeozoic in eastern America, West Africa, South Africa and Western Australia. Faulted basin development along what were to become the world's Atlantic-type ('aseismic') margins became widespread by the Permian, and continued intermittently until the Middle Cretaceous.
Widely around the world the long-established Mesozoic regime of synsedimentary graben formation and intermittent major faulting ended with an Aptian transgression, and was replaced by a regime of simple miogeosynclinal subsidence with prograding sedimentation which has continued to the present day. In Greenland and the Grand Banks of Canada, in Gabon and Australia, the history is strikingly similar to that of Northwest Europe, on what are now open ocean coasts. Thick earlier sediments are related to fault-controlled subsidences and rifts, a regime which was replaced worldwide within a very short period, by prograding basinal sedimentation in which faulting played a minor or very local role, and in which beds of Middle Cretaceous or somewhat earlier date transgress the planed-off structures of the previous regime.
Although this relationship is not universal, there is a broad uniformity in the dating of the fundamental change in the style of aseismic marginal basins despite the different dates ascribed to opening of adjoining oceans. This requires a world-wide mechanism, not yet understood.
The petrography and reservoir properties of some triassic sandstones of the Northern Irish Sea Basin
Authors: Colter V. S. , Ebbern J. 
Published: December 2007

Triassic sandstones of the Northern Irish Sea have been correlated on wire-line logs with the succession at the outcrop in Cheshire (Colter & Barr 1975). Recent work on well sections confirms the lithological similarities of these units with the supposed onshore equivalents.
Porosity and permeability of the sandstones are related in the first place to original grain size, particularly argillaceous content. Superimposed on this primary variation are the effects of various diagenetic phenomena: (1) Tangential illite coatings; (2) Platy illite normal to grain surfaces; (3) Calcite cement; (4) Compaction and pressure solution; (5) Quartz overgrowths. Porosities and permeabilities measured in core plugs have been related to primary textures and to the occurrence of these diagenetic changes.
A gravity survey across the Gardar Igneous Province, SW Greenland
Authors: Blundell D. J. 
Published: December 2007

The Gardar Igneous Province is believed to involve the remains of Proterozoic rifting which evolved through repeated phases of activity around 1300 Ma, 1250 Ma and 1170 Ma ago. A gravity survey across part of the province has established the presence of a gravity 'high' of some 300 g u amplitude which is 30 km wide and elongated ENE–WSW, centred on Tunugdliarfik and axially along one of the main zones of Gardar intrusives. This gravity anomaly is similar to that of other ancient rift systems and appears to be a residual of the axial anomaly to be found in modern active rifts. It is interpreted in terms of a basic mass underlying a late Gardar rift, some 50 km long and 25 km wide, intruding the crust. Evidence suggests the Gardar rifting cannot be explained in terms of a major crustal separation as an extension of the mid-continental rift and Keweenawan systems of North America. It is more consistent with crustal stretching of no more than 10 km and possibly diapiric mechanisms.
The coastal gravity gradient appears to be due to a change in crustal thickness coincident with the coastline, some 25 km beyond the present ice cap limit. Although Greenland may be in overall isostatic balance, it seems that the coastal zone remains overcompensated.
Vertical and lateral building of river sandstone bodies, Ebro Basin, Spain
Authors: Friend P. F. , Slater M. J. , Williams R. C. 
Published: December 2007

Six examples of river sandstone bodies are described from well exposed sections of Oligocene and Miocene age in the Ebro Basin, northern Spain. Three of these are of ribbon form, varying in cross-section from 10 m wide × 2 m high to 20 m wide × 9 m high. In plan these ribbons vary from straight to highly sinuous. The sandstone bodies, in two cases, are multi-storey, clearly demonstrating a series of vertical building episodes. The fourth sandstone body may have a ribbon or sheet geometry, and is of special interest because it demonstrates lateral building by a laterally migrating channel, as well as some vertical building. The fifth and sixth sandstone bodies are of sheet geometry, and demonstrate lateral migration of channels and depositional surfaces.
Factors that appear to be most important in determining whether a river migrates laterally or remains stable laterally are: (1) river mean flow strength, (2) bank strength, (3) flood periodicity and duration, (4) vertical movement of the alluvial area.
Early Cambrian transgression
Authors: Matthews S. C. , Cowie J. W. 
Published: December 2007

There is widespread evidence of a major transgression near the base of the Cambrian. It is difficult to establish time-controls, and therefore difficult to produce worthwhile estimates of rate of transgression. Neither the palaeontological nor the radiometric information is sufficiently exact.
Alternative means of comparing the Cambrian transgression with later events of the same kind are sought; the possibility that it is due to post-glacial (i.e. post-Varangian) rise of sea level is examined and rejected; the separation in time seems too large. The preferred explanation is that the Cambrian transgression had tectonic causes and it is argued that among the major transgressions of later geological time, it is the Cretaceous case which most closely resembles the Cambrian.
Structure, metamorphism an geochronology of the Arequipa Massif of coastal Peru
Authors: Shackleton R. M. , Ries A. C. , Coward M. P. , Cobbold P. R. 
Published: December 2007

The Arequipa Massif, between the Andes and the Pacific, is an extensive pre-Devonian metamorphic complex. The sequence of deformations, metamorphisms and magmatism in this complex has been established. Mollendo, Atico and Marcona events are distinguished by structural and metamorphic methods and dated by Rb-Sr whole-rock isochrons, at about 1918, 440 and 392 Ma respectively. The Mollendo event led to partial melting, followed by granulite-facies metamorphism, in sediments buried to about 30 km. Further NW, sillimanite-bearing migmatites and staurolite-andalusite schists are thought to represent the same event. The tectonic trend is uncertain but the structures and metamorphism suggest a collision orogeny which probably pre-dated the Pacific Ocean.
The early Caledonian Atico and Marcona events are associated with coast-parallel batholiths, amphibolite- to greenschist-facies metamorphism and penetrative deformations. The Atico and Marcona events are separated by the deposition of the Marcona Formation, which is therefore thought to be Lower Palaeozoic (between about 440 and 392 Ma). The early Caledonian deformations are attributed to a subduction zone near the present Pacific margin. There is no penetrative Hercynian or Andean deformation in the Arequipa Massif.
Palaeomagnetic study of Jurassic andesites and dykes suggests that there has been no latitudinal motion of the Arequipa Massif relative to the Brazilian shield during the evolution of the Andes.
Stratigraphical relationships of the early Palaeogene ash-series of NW Europe
Authors: Knox R. W. O’B. , Harland R. 
Published: December 2007

Lithostratigraphical correlation and dinoflagellate cyst evidence point to the presence of a pronounced hiatus at the base of the London Clay and equivalent beds in NW Europe. Following a late Palaeocene regression, the sea became restricted to a small area in the central part of the North Sea Basin. In the subsequent 'London Clay' transgression the sea at first remained confined to the inner basin area, but during deposition of the ash-series it extended southwards over the southern North Sea area and into Germany, the Netherlands, and East Anglia. It was apparently not until after eruption of the ashes that the 'London Clay' sea became established over the S of England, Belgium, and northern France. Sedimentation was then more or less continuous in these southern areas during the lower Ypresian, but a phase of uplift and non-deposition in the central North Sea and Denmark resulted in a second hiatus above the ash-series.
The proposed presence of a stratigraphical break beneath the London Clay (and the equivalent Ypres Clay) is relevant to the problems of defining the Palaeocene/Eocene boundary and associated stage boundaries in their type areas.
New age determinations and the geology of the Kenya Rift-Kavirondo Rift junction, W Kenya
Authors: Jones W. B. , Lippard S. J. 
Published: December 2007

The area of the triple-rift junction in W Kenya, between the E-W Kavirondo Rift, the N-S Northern Kenya Rift and the NW-SE Central Kenya Rift, has been the site of continuous volcanic and tectonic activity since the Middle Miocene. From about 20 to 7 Ma the area was dominated by the accumulation of a thick pile of nephelinitic and phonolitic volcanics in the Timboroa area. From 7 Ma to the present day, apart from local eruptions of basanite in the W, the volcanic and tectonic activity has been progressively concentrated towards the axial zone of the Kenya Rift with alkali basalt-trachyte sequences predominating. During this period the Kavirondo Rift was inactive. The stratigraphic sequence in the area has been dated by 19 new K-Ar age determinations. These enable the absolute and relative ages of the Tinderet, Timboroa, Kapkut, Londiani and Kilombe volcanoes to be established for the first time.
Topographical and structural considerations show that the Kavirondo Rift largely fades out 50 km W of the Kenya Rift and is barely perceptible at its edge. The W wall of the Kenya Rift adjacent to the Kavirondo Rift is a monocline and is very similar to the South Turkana region. Although the area is adjacent to major rift-bounding faults there is little faulting within it, the tectonic pattern being dominated by monoclines and volcano-tectonic structures.
Caesium from former Dartmoor volcanism: its incorporation in New Red sediments of SW England
Authors: Merefield J. R. , Brice C. J. , Palmer A. J. 
Published: December 2007

High concentrations of caesium occur in the New Red Sandstone of Devon, England. Values are most abundant in breccias at the base of the Permian and decrease upwards through the sandstones and marls. Caesium resides in the clay fraction (<2 μm) where it reaches 468 ppm in Watcombe breccia, 146 ppm in Exmouth mudstone and 35 ppm in Triassic Otter sandstone. Credition Trough values attain 108 ppm in the Cadbury breccia.
Extensive volcanic activity on the south eastern edge of the Cornubian Massif provided a supply of Cs. Due to its low ionic potential, this alkali was concentrated at source under extreme weathering in the hydrolysate fraction of red bed sediments. The source area was largely exhausted by late Permian, reflected by a reduction in Cs content of New Red Sandstone detritus.
Online searching of bibliographic geological databases and their use at the Science Reference Library
Authors: Leigh B. 
Published: December 2007

Bibliographic databases consist of records of publications and many are now available for online computer searching as well as being used in the production of abstracting and indexing journals. The three major online databases of interest to geologists are GeoRef (produced by the American Geological Institute), GeoArchive (produced by Geosystems, London), and the earth sciences subfile of PASCAL (produced by the Centre de Documentation Scientifique et Technique, CNRS, Paris).
Online searching is very much quicker than manual searching of abstracting journals and allows more complex and complete searches to be carried out. The costs involved in online searching include database access fees, telecommunications charges, and the cost of equipment and staff time.
The Science Reference Library runs a publicly available online search service with access to over 50 scientific and technical databases. 1000 searches were carried out in the last financial year.
Marine geological databases: their nature, implementation and problems
Authors: Botbol J. M. 
Published: December 2007

An overview of the marine geological database activity at the U.S. Geological Survey, Woods Hole, Massachusetts, is presented. Spatially-dependent, time-dependent, and topical data are collected. Major categories of data include navigation, seismicity, grab-samples and cores, photo and scanner, gravity, magnetics, physical oceanography and cruise management. Research projects in all categories generate large volumes of data that must be stored and retrieved. Seismic projects, for example, generate 700 tapes of raw seismic data each year. In order to locate data for further analysis and reference, a database index is being devized. Because of the large size of the overall database, data sets have been assigned to either active or archival status. Retrieval programs have proved to be more useful than a Data Base Management System (DBMS) in marine geologic database activity.
A major concern is the design of interactive application programs that treat retrieved data. The user interfaces are intentionally as uncomplicated as possible in order to facilitate user-computer dialogue. Data is regularly exchanged without side groups, and commercial bibliographic services employed.

Major database problems relate to the role of databases
vis-a-vis
project support and computer involvement, the relevance of data to other than original projects, generation of data on hybrid devices, effect of delays in data reduction, database user education, file maintenance and financial support.

Database activity requires support because, given modern computing advances, databases are the basis for major advances in geology.