bluuebunny/crossref_metadata_2025_split huggingface dataset:
‘Older’ granites as time-markers in Dalradian evolution
Authors: BRADBURY H. J. , SMITH R. A. , HARRIS A. L. 
Published: December 2007

The ‘older’ granites of Perthshire were emplaced in the Dalradian between the second and third deformation episodes of a Caledonian D1–D4 sequence.
Pankhurst & Pidgeon (1976) have furnished a zircon U-Pb and Rb/Sr whole-rock age (514 +6/–7 Ma) for emplacement of the Ben Vuirich granite which provides a minimum age for the D2 event. A somewhat younger Rb/Sr whole-rock isochron age (491 ± 15 Ma) obtained from the Dunfallandy Hill granite may date D3.
Migmatisation which occurred in the D2–D3 interval is, by inference, also dated.
Dl and D2, which deform Arenig rocks of the Southern Highlands Group are pre-514 Ma events implying a pre-514 Ma time base for the Ordovician.
Palaeozoic volcanism in Great Britain and Ireland
Authors: STILLMAN C. J. 
Published: December 2007

IT IS APPARENT that the study of Palaeozoic volcanism attracts a multi-disciplinary approach involving sedimentologists as closely as volcanologists, and utilizes techniques ranging from field mapping to the statistical handling of geochemical data. This interdependence was revealed by the list of contributions and even more by the discussion stimulated by the papers read at the September 1976 meeting of the Volcanic Studies Group, held in the Geology Department, Trinity College, Dublin. It is also clear that for a fair proportion of workers in both Caledonian and Hercynian volcanism, plate-tectonic models are now being invoked both to explain the petrogenesis of volcanic suites and to account for regional variations in petrochemistry.
Speakers who eschewed this 'armchair' approach were concerned with regional field aspects and emphasized the need for detailed field mapping as a basis for any interpretation. Dr Max described work in progress on the correlation, distribution and deformation of the South Connemara Group volcanics, including the extension of land-based studies by surveys of islands in Galway Bay. Dr Howells demonstrated the relationship between the Bedded Pyroclastic Formation of central Snowdonia, and the Middle Crafnant Volcanic Formation of eastern Snowdonia, and showed that, whilst synchronous, two very different volcanic facies derived their material from different sources––the Bedded Pyroclastics from the Snowdon area and the Middle Crafnants from sources east of Betwsy Coed. In the region of Dolwyddelan a rising submarine ridge is invoked to provide separation between the shallow-water, bedded basaltic tuff sequence of the former and the acid
Pressure solution and Coble creep in rocks
Authors: McCLAY K. R. 
Published: December 2007

On 5 November 1976, the Tectonic Studies Group of the Geological Society held a lively discussion meeting at Imperial College on the subject of pressure solution and Coble creep.
Deformation mechanisms may be divided into three broad categories:
(1) Cataclastic processes
(2) Intracrystalline processes involving dislocations
(3) Diffusive mass transfer processes.
We are concerned here with group (3) processes, flow by diffusive mass transfer of matter from grain boundaries which are subjected to high normal stress to less highly stressed grain boundaries. If the diffusion is predominantly through the grain the process is termed Nabarro-Herring creep whereas if it is predominantly around grain boundaries, the flow is termed Coble creep. In general, grain boundary sliding must occur to accommodate the grain shape changes due to diffusion. For these processes to proceed at rates which are detectable, the temperature must be at a large fraction of the absolute melting temperature of the material.
Geologists have long recognized in low grade metamorphic rocks, textures in-dicative of deformation by diffusive mass transfer. Even over the relatively long time available for geological deformations, at the low temperatures concerned, solid state diffusivities would be too slow to account for the observed strains. It is therefore inferred that the rate of diffusive mass transfer is enhanced by the presence of an intergranular fluid film. Hence the use of the term ‘pressure solution’ to describe the process. Thus Coble creep and pressure solution are similar in that they both involve intergranular diffusion.
The meeting was intended to
Structural style of continental margins: a discussion
Authors: AUDLEY-CHARLES M. G. 
Published: December 2007

Publication of the results of continuous seismic reflection surveys around the continental margins (Beck & Lehner 1974, Seely
et al.
1974, Lehner & Ruiter, in press) and discoveries made by drilling in the deep-sea by JOIDES and IPOD (Initial Reports of the Deep Sea Drilling Project) have shown that seismically active continental margins display structures very different from the structures associated with aseismic margins.

Lehner showed that after the initial rifting phase of evolving aseismic margins the main structural features are vertical movements manifested by the development of sedimentary basins at the margin of the new ocean and complementary basins on the craton. Some of these cratonic basins may be associated with aulacogens (Dewey & Burke 1974), others appear to be separated from the continental margin basins by a geanticlinal structure.
The structural style of the present aseismic margins of West Africa, northwest Australia and elsewhere can be summarized as asymmetric in cross section showing a ‘steep, mostly faulted landward flank on continental basement and a gentle seaward flank on oceanic basement' (Lehner).

Evidence is available from parts of the Mediterranean region (Smith) and from northern Australia (Garter
et al.
1976) which shows how within few Ma an aseismic continental margin can become seismically active and be involved in orogenic processes such as major overthrusting.

Recent papers by Fischer (1975) and Bally (1975) have greatly influenced the way we think about the structural style of seismically active continental margins. Fischer’s suggestion that oceanic lithosphere has a maximum life of about
The Kannaviou Formation, Cyprus: volcaniclastic sedimentation of a probable late Cretaceous volcanic arc
Authors: ROBERTSON A. H. F. 
Published: December 2007

In SW Cyprus the upper pillow lavas of the Troodos Igneous Complex are directly overlain by up to 75° m of volcaniclastic sediments, ranging in age from Lower Campanian to Mid-Maastriehtian. The basal sediments are pre-dominantly non-calcareous bentonitic clays and radiolarian mudstones representative of relatively slow deposition, probably below the carbonate compensation depth. In contrast, stratigraphically higher calcareous bentonitic clays, volcaniclastic siltstones and volcaniclastic sandstones show evidence of much more rapid deposition by a combination of mass flow, traction and minor turbidity currents.
The basal volcaniclastic sandstones were partly derived by submarine erosion of the subjacent Troodos lavas. In contrast, the overlying sequences contain abundant fine-grained pumice, basic to acid volcanics, and also terrigenous material derived predominantly from outside the present area of southern Cyprus. The hetero-geneous provenance of the Kannaviou sediments can be explained by postulating late Cretaceous subduction of Troodos-type oceanic-crust with genesis of a related volcanic arc and eventual tectonic juxtaposition of the Troodos Massif with a Mesozoic continental margin.
Depositional environment and diagenesis of Permian Rotliegendes sandstones in Leman Bank and Sole Pit areas of the UK southern North Sea
Authors: Glennie K. W. , Mudd G. C. , Nagtegaal P. J. C. 
Published: December 2007

Early diagenetic features of the Rotliegendes are related to deposition in a desert environment. Wadi sands suffered early calcite cementation as the sediment dried. Aeolian sands were cemented with halite and gypsum where the water table was close to the surface and all grains became coated with ferric oxide and clay after passing below the water table.
Later diagenesis is recognised by the presence of pore-destroying cements (recrystallized clays, authigenic feldspar, quartz, dolomite and anhydrite). Their occurrence is related to deep burial followed by faulting and late Cretaceous uplift. In Leman Bank and Sole Pit, the top Rotliegendes reached depths of about 11000 and 14000 ft (3350 and 4250 m respectively) prior to maximum uplift of 6000 ft (1800 m).
Porosity gradients in North Sea oil-bearing sandstones
Authors: Selley R. C. 
Published: December 2007

The relationship between porosity and burial depth of sandstone reservoirs is complex. It depends on primary porosity, which is related to grain-size and depositional process and also on the porosity gradient (the change in porosity with depth) which, in most cases, is linear.

This relationship may be expressed as:

φ
d
=φ
p
−

G.D, where

φ
d

is the porosity at depth D below surface,

φ
p

is the primary depositional porosity, and G is the porosity gradient in % porosity per 1000 ft (305 m). Porosity gradients decrease with increasing quartz content, abnormal pressures, and in the presence of hydrocarbons. They increase with increasing geothermal gradient. There are at present insufficient data to quantify these relationships.

Empirically derived porosity gradients for North Sea Rotliegendes, Jurassic and Palaeocene reservoir sandstones are 2.2, 2.6 and 2.9 per cent per 1000 ft (305 m) respectively.
When calibrated with the porosity spectra of the various facies, graphs can be drawn showing the depth: porosity windows within which economic reservoirs may be found.
Dendrites
Authors: Van Straaten L. M. J. U. 
Published: December 2007

Two categories of dendrites exist: those in which the shape is mainly determined by crystal structure, and those where this is not the case, the material being amorphous or ultra-finely crystalline. Only dendrites of the second category are dealt with in this paper, and especially those found in the Solnhofen Limestone of southern Germany. These dendrites consist either of Mn- or Fe-(hydr)oxides.
Two classes occur: (1) fissure dendrites, limited to joints and bedding plane fissures, etc.; (2) internal dendrites, branching in three dimensions, and penetrating from dendrites or other Mn-or Fe-accumulations on joint surfaces or bedding planes into the non-fissured rock. Both types form by deposition in pores, not wider than a few μm, thus constituting ramified systems of host rock, cemented by Mn- or Fe-material.
The first generation of Mn-dendrites in the Solnhofen Limestone evolves in two steps: (1) manganiferous solutions, derived from residual loams and alluvial deposits overlying the limestone, penetrate into joints, and from there into bedding plane fissures and unfissured rock; (2) from these solutions solid dendrite material is deposited. The precipitation starts from older deposits of the same composition: specks, lumps, crusts etc., or from newly generated nuclei. In this way either 'tree'- or 'star'-shaped dendrites are produced. 'Tree'-shaped dendrites on bedding planes, starting from joints, grow in directions away from these joints, the material being supplied from the opposite directions. Once formed, renewed supply of Mn-material results in thickening and broadening of stems and branches, the ‘texture’ thereby becoming coarser, but the total size remaining unchanged.The first formation of Fe-dendrites takes place in the same manner, but their further growth is more complicated.
The branching of these dendrites is due to the circumstance that diffusion of the components of the solution is limited to a system of micropores. This inhibits the production of ‘massive’, round patches around the points of origin, because the average distances to be covered by the ions, molecules or sol particles before they are fixed on the growing deposits, are much smaller for branched shapes.
Most dendrites are the result of repeated deposition. The transportation of Mn and Fe to the fissures or other sites of precipitation probably occurs chiefly as dissolved chelates. In most cases the precipitation itself may be due to a rise in pH as a consequence of dissolution of CaCO3.
Computer programmes for the analysis and presentation of orientation data
Authors: Nuttall D. J. H. , Cooper M. A. 
Published: December 2007

This letter gives a brief preliminary description of computer programmes for use by structural geologists. Since the GODPP was described at the Tectonic Studies Group meeting at Dundee in December 1976 a number of workers have expressed interest and this letter is intended to make the existence and scope of the package more widely known. Copies of the programmes involved may be obtained from the authors at University of Bristol.
The Geological Orientation Data processing package (GODPP) is a package of computer programmes principally aimed at helping the field geologist to process large quantities of structural and sedimentological orientation data. The programmes have been so written as to be independent of the model of computer used (see Appendix).
The package offers the plotting of orientation data on stereograms, maps, and rose diagrams and also offers reorientation routines.

Stereograms.

This section of the package has facilities for producing Pi diagrams and contoured Beta diagrams with options for a vector mean or a best fit great circle, with the appropriate statistics (
Mardia 1972
). A large number of programmes to plot stereograms have been published (

Robinson
et al.
1963

, Spencer & Clabaugh 1967,
Warner 1969
and Bonyun & Stevens 1970). The majority produce line printer output, although a graph plotter has been utilised for the plotting of Pi diagrams (
LaFountain 1970
), but not apparently for contoured diagrams. GODPP has the advantage of producing Pi diagrams and contoured stereograms on a graph plotter. It also produces line printer output of contoured diagrams which allows
Strain study of the Caledonides in the Islay region, SW Scotland: implications for strain histories and deformation mechanisms in greenschists
Authors: Borradaile G. J. 
Published: December 2007

Metasediments of the NW foreland have a deformation phase older than the first phase in metasediments of the internal part of the Caledonides to the SE. They also suffered constrictive deformation with NE-SW extension of more than 100%. In contrast, rocks in the adjacent internal zone were extended 70 ± 10% upwards in a NW direction and also thrust in the same direction; they were extended less than 10% along strike. An important concealed boundary separates the foreland from the internal zone. Total strains determined for foreland metasediments (Colonsay Group) and for metasediments of the internal zone (Dalradian Supergroup) allow a partial pretectonic reconstruction. Total cross-strike shortening for both zones averages 55 ± 5%. It is not possible completely to unfold the profile through Islay by removing the measured strains. This is partly because those strain analyses based on grain shapes fail to detect the important component of intergranular slip and partly because mechanisms not involving penetrative rock deformation helped produce the folds.
Strain histories for the Dalradian rocks are generally coaxial within the limits of a test applied so that the primary cleavage of the Dalradian rocks and its extension lineation may be mapped as total strain trajectories. The fan of primary cleavage and examples of extreme non-coaxial strain near the hinge of the Islay Anticline may be associated with hinge migration during its growth.
Several lines of evidence favour grain boundary sliding as an important deformation mechanism in these low grade metasediments. It may have been enhanced by elevated pore fluid pressures and three classes of grain boundary sliding are proposed, dependent on the prevailing fluid pressure.
Melting in the crust and upper mantle beneath the Kenya Rift: evidence from Geomagnetic Deep Sounding experiments
Authors: Banks R. J. , Beamish D. 
Published: December 2007

A Geomagnetic Deep Sounding experiment in and around the Kenya Rift Valley has shown that telluric currents are concentrated by 3 regions with high electrical conductivity. Two of the anomalies are related to the rift structure, and the combination of different lines of geophysical evidence strongly suggests that the high conductivity is due to the presence of molten material in the rocks of the lower crust and upper mantle.
The shallower zone where melt is present, is located directly beneath the floor of the rift valley. Its upper surface is no deeper than 20 km; it may be as shallow as 5 km. The electrical conductivity is compatible with an average melt concentration of 5–10%, but could also be explained by discrete magma chambers where the concentration was much higher.
The deeper conductor is located to the E of the rift valley beneath the Aberdare Mountains, and possibly extends beneath Mount Kenya. The Geomagnetic Deep Sounding data suggest a depth of 100 km to the high conductivity body, which appears to correspond to the core (the region with the highest melt concentration) of a zone of more diffuse melting in the mantle, that is responsible for seismic and regional gravity anomalies, and which supports a part of the topographic elevation of the Kenya dome.
The structural evolution of a Mesozoic continental margin, Othris Mountains, Greece
Authors: Smith A. G. , Woodcock N. H. , Naylor M. A. 
Published: December 2007

The detailed structure of a telescoped Mesozoic continental margin sequence in the Othris (=Sub-Pelagonian) zone of eastern central Greece is described. Prior to thrusting in Upper Jurassic/Lower Cretaceous time, the Triassic and Jurassic facies showed an ordered lateral transition from a carbonate platform in the NE, through a submarine fan to a pelagic basin in the SW. The platform is autochthonous and has a continental basement; the pelagic basin probably lay in part on oceanic crust.
Carbonates on platform and fan were abruptly succeeded by siliceous deposits. Soft-sediment slumps in the siliceous sequence show a slope to the SW. Soon after this slumping, the slope reversed: olistostromes formed in front of a NE-sloping thrust pile advancing northeastward. Tectonic mélanges also accompanied thrust emplacement. The activation of the margin may be due to initiation of a NE-dipping subduction zone lying to the SW of the map area. Shortly after emplacement of the thrust stack, it was cross-folded, uplifted, eroded and by mid-Cretaceous time transgressed by shallow water deposits. Cenozoic thrusting in the area is absent, though minor rejuvenation of the NE-trending folds took place. High angle late(?) Cenozoic normal faulting is common.
Structural frame work of the fore-arc basin, NW Sumatra
Authors: Karig D. E. , Lawrence M. B. , Moore G. F. , Curray J. R. 
Published: December 2007

The fore-arc basin of the Sunda Arc off Sumatra is a strongly subsiding trough contained between the rising subduction complex and the elevated continental core. Up to 4 km of Miocene–Recent strata on the eastern flank of the basin have transgressed over an unconformity cut across a Palaeogene continental margin that was uplifted and structurally disrupted during the late Oligocene. The large step-like offsets of the palaeo-shelf edge, and probably some of the structural disruption, can be attributed to right-lateral strike-slip faults that splay across the fore-arc basin from the Sumatra Fault Zone. Offsets range up to 100 km+, producing marginal re-entrants that became sites of turbidite-filled basins trapped behind the growing Neogene accretionary prism. The larger re-entrants may be floored with oceanic crust, but the proximity of exposed subduction complex to the palaeo-margin precludes the existence of a continuous band of oceanic crust beneath the fore-arc basin.
The seaward flank of the fore-arc basin has migrated westwards during Neogene subduction, but not so much as the trench, and in a much more complicated fashion. During the early Miocene, the inner trench slope had a juvenile terrace-like morphology. By late mid-Miocene time, the trench slope break was near sea level and formed a shelf edge high. Thrusting and folding related to subduction probably decreased gradually upslope until late-Pliocene, when large flexures and E-directed reverse faults developed, marking an arcward shift in the rear or eastern boundary of the deformation associated with subduction. The episodic development of arcward-directed structures, involving previously stabilized fore-arc basin strata, suggests periods of increased stress levels along the base of the accretionary prism.
Dating mineralization
Authors: Ineson P.R. 
Published: December 2007

Report of the Mineral Deposits Studies Group Meeting held at Burlington House, 15 May 1979. The meeting was organized by Dr P. R. Ineson.

The varied applications, advantages and disadvantages of Rb-Sr, K-Ar, U-Pb and Pb-Pb analytical dating techniques were outlined by the speakers.
Beckinsale admitted that in the study of the tin granites of SE Asia, the Rb-Sr technique had not been directly applied to the elucidation of the mineralization. In describing the varied environmental, mineralogical and geochemical characteristics of the ‘I’ and ‘S’ types of granites, he noted that the mineralization was either of the finely disseminated type in greisenized hosts or pegmatite vein occurrences. The SE Asian granites had been involved in basinal structures which had undergone a number of re-heating phases. K-Ar isotopic geochronology on the granites had given excessively young ages. It was advanced, therefore, that Rb-Sr techniques were more applicable to dating the intrusion of the granites, while K-Ar techniques may elucidate re-setting events due to subsequent hydrothermal activity.
Wilson reported various techniques which had been applied in order to date the uranium mineralization in northern Sweden. After outlining the general geological history of the Arjeplog–Arvidsjaur–Sorsele uranium province, he indicated that it was characterized by strong sodium metasomatism, development of skarn deposits and the presence of uranium and urano-titanites in both epigenetic and stratabound occurrences. U-Pb analyses on pure uraninite concentrates and whole-rock Pb-Pb dates had been used. The latter produced the most meaningful results, which were equated with the peak of
Comparison of major sequences of organic-rich mud deposition in the British Jurassic
Authors: Morris K. A. 
Published: December 2007

The British Jurassic contains 3 major sequences of organic-rich shales: the Jet Rock Formation (Lower Toarcian), the Lower Oxford Clay (Callovian), and the Kimmeridge Clay (Kimmeridgian). In addition minor sequences are found in the Blue Lias Formation and the Shales-with-Beef Formation (Hettangian-Sinemurian).
The Lower Oxford Clay has the lowest average organic carbon content and was deposited in mildly oxygenated bottom waters. The sediment profile consisted of a thin upper oxidizing layer, with reducing conditions occurring a few cm below the sediment surface.
The Jet Rock Shales were laid down in very poorly oxygenated bottom waters. Here reducing conditions extended up to the sediment surface and this resulted in the preservation of a higher organic carbon content.
The Kimmeridge Clay shows a much wider variation in organic carbon content than the other examples, indicating accumulation in an environment which periodically fluctuated between mildly oxygenated and totally anoxic.