bluuebunny/crossref_metadata_2025 huggingface dataset:
The petrology of the Lower Palaeozoic Fishguard Volcanic Group and associated rocks E of Fishguard, N Pembrokeshire (Dyfed), South Wales
Authors: Lowman R. D. W. , Bloxam T. W.
Published: December 2007

The petrology of the Fishguard Volcanic Group and associated rocks is described from a remapped area of Cambrian and Ordovician rocks between Fishguard and Newport, N Pembrokeshire (Dyfed). The volcanic rocks are mainly rhyolitic in composition and consist of pyroclastic flows, falls, lavas, epiclastic deposits, and alloclastic intrusions; welded pyroclastic flows comprise the major component. A small area of basaltic pillow lavas and hyaloclastites is associated with the rhyolitic rocks. The volcanic rocks are accompanied by numerous sheets of dolerite and gabbro, together with diorites and microgranitic intrusions. The sequence at Lower Fishguard Harbour shows an intimate association of welded and non-welded pyroclastic flows with graptolitic shales and other marine sediments, which suggests that welding may have occurred subaqueously. The cooling rate of submarine pyroclastic flows and lavas is thought to be significantly reduced by the formation of a steam jacket and a quenched marginal crust, both providing low thermal conductivity. The hydrostatic pressure of seawater maintains cohesion and retains heat and volatiles within the flow. In addition, water saturation of the rhyolitic melt throughout its cooling maintains mobility and is conducive to subsequent welding.
Rb-Sr whole-rock isochron evidence for the age of the Malvern Hills complex
Authors: Beckinsale R. D. , Thorpe R. S. , Pankhurst R. J. , Evans J. A.
Published: December 2007

The Malvernian igneous complex of the Malvern Hills consists mainlyof plutonic rocks and their locally deformed equivalents. The igneous rocks are calc-alkaline and range from ultra mafic diorite to granite in composition, although diorite and tonalite are the most abundant rock types. A Rb-Sr whole-rock isochron plot for representative samples yields an age of 681 ± 53 Ma with an initial
87
Sr/
86
Sr ratio of 0.7049±0.0005(2σ errors).This is interpreted as the age of crystallization of the igneous complex, and the relatively low initial
87
Sr/
86
Sr ratio is considered to preclude a long crustal history for the source region. The Malvernian complex is thus regarded as a late Precambrian addition to the crust. It has been compared on geological grounds with the Johnston Complex and the Stanner-Hanter Complex, and isotopic ages between 640 and 700 Ma for all these complexes indicate that they may represent the earliest phase of igneous activity in the evolution of continental crust below England and Wales.
Implications for Caledonian plate tectonic models of chemical data from volcanic rocks of the British Old Red Sandstone
Authors: Thirlwall M. F.
Published: December 2007

Volcanic rocks associated with the continental sediments known as the Old Red Sandstone outcrop widely in northern Britain and form a dominantly calc-alkaline suite comparable to those developed on modern continental margins. Rocks rich in Ni and Cr are unusually abundant, and are thought to have incompatible element concentrations little different from those of primary magmas. Such rocks show pronounced spatial chemical variation, with concentrations of Sr, Ba, K, light rare earth elements and P
2
O
5
, and the ratio La/Y showing up to a six-fold increase in a northwestward traverse across Scotland. In more evolved rocks a similar increase is shown by Sr, Ba and La/Y, but regional comparisons are made difficult by the varying effects of fractional crystallization. The chemistry of all Old Red Sandstone volcanic rocks N of the Southern Uplands Fault is consistent with the former existence of a subduction zone that changed in strike from ENE in Ireland and southern Scotland to N in the North Sea. This orientation, in conjunction with almost E–W plate motion, may explain the great contrast in end-Silurian deformation styles between Britain and Scandinavia. Old Red Sandstone volcanic and plutonic rocks S of the Southern Uplands Fault are thought to be younger and are perhaps unrelated to subduction activity.
Tectonic controls of Phanerozoic sedimentary rock cycling
Authors: Mackenzie F. T. , Pigott J. D.
Published: December 2007

The cyclic nature of the Phanerozoic sedimentary rock distribution, carbon-sulphur coupling, and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors. The distribution of preserved sedimentary mass in terms of rock mass remaining
U.
geologic age shows a minimum
c
. 300-350 Ma ago, which separates two subcycles of erosion and deposition of sedimentary rocks. The older subcycle was interrupted because of the major continental collisions of the Devonian and late Carboniferous. These collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses, leading to a decline in the probability of destruction and an increase in half-life of these older sediments.

A strong correlation exists between the long-term cyclicity in the Phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs. This correlation is related to two principal tectonic modes of the Phanerozoic: oscillatory and submergent.

It is postulated that the submergent mode of active plate convergence, obduction and subduction of sediments, large ridge volume, and high sea level gave rise to low erosion and sedimentation rates, less restricted environments of carbonate deposition, and relatively high atmospheric CO
2
levels (high temperatures ?), resulting from an increased rate of production of CO
2
from diagenetic and metamorphic reactions at subduction zones. As sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones, whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir. As sea level fell, reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors. These reservoir transfers are consistent with secular changes observed in the distribution of δ
13
C and δ
34
S in Sedimentary materials during the Phanerozoic.

Petrographic examination of Phanerozoic oolite formations shows that öoids with preserved calcitic relict textures are characteristic of pre-Carboniferous carbonate rocks, whereas öoids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age. These changes in öoid mineralogy may be interpreted as reflecting changes in CO
2
levels of the ocean-atmosphere system consistent with the above tectonic considerations. Atmospheric CO
2
levels were higher prior to Carboniferous time, favouring formation of calcitic öoids and skeletal parts; after the Carboniferous, CO
2
levels fell and aragonite and Mg-calcites of greater than 8 mol % Mg increased in abundance as precipitates.
Chronology of Earth’s glacial and tectonic record
Authors: Harland W. B.
Published: December 2007

The glacial record yields a pattern of ice-ages that shows distinctive characters for different periods. However, ages of deposits generally provide constraints on the time sequence which because of uncertainties are still too wide to be used critically for or against any regular or cyclic history. It seems better to assume no periodicity until such can be argued. Models for cyclic mechanisms with a longer period than the Milankovitch cycle that have been proposed include major chancge in tilt of Earth’s spin axis, galactic year, and tectonic cycles. Evolutionary tectonic changes or changes in atmospheric CO
2
are more likely to have been contributing factors; but the late Proterozoic (Vendian-Varangian) ice-ages with at least equatorial glaciation remain enigmatic.
Low-temperature mineralization
Authors: Ineson P. R.
Published: December 2007

Report of the Mineral Deposits Studies Group Sixth Annual General Meeting held at St. Peter’s College, University of Aston in Birmingham,
17–19
September
1980.

The Conference, ably organized by Dr R. A. Ixer with the co-operation of the University and the Department of Geological Sciences, to whom the Mineral Deposits Studies Group extend their thanks, was subdivided into 3 sections. The first day was devoted to a number of papers which covered varied aspects. Isotopic studies on the mineralization of the Ophir Valley, Colorado (Jackson), and the Ba-Zn deposit at Aberfeldy (Willan) were presented together with 2 papers on U mineralization in Namibia (Marlow and Clemmy). Ineson and Walters indicated the problems of correlating horizons and interpreting the attendant alteration associated with the igneous rocks in the South Pennine Orefield, while Alabaster & Pearce described the geological setting of the sulphide deposits in the Oman ophiolite complex. For this type of meeting, an unusual but interesting contribution by Broadbent et al. reviewed European Pb-Zn production and indicated recent research into new recovery processes for Pb, Zn and Cu as well as improving hydrometallurgical techniques.

Well over 100 people attended the second day, and were no doubt attracted by a number of papers related to Permo-Triassic mineralization. A review of the Permo-Triassic rocks and related mineralization was given by Clarke who, in proposing new genetic models, caused some disquiet amongst the audience. On a more localized scale, isotopic evidence indicating possible inter-relationships was presented by Harwood & Coleman, while Turner &
Post-deposition structures in the Bushveld Complex mafic sequence
Authors: Lee C. A.
Published: December 2007

The stratigraphy of the Bushveld Complex is characterized by laterally continuous horizontal layering. At the interface of some of these layers there are phenomena analogous to flame, load-cast, ball-and-pillow and liquid escape structures of sedimentary rocks. Three plastic deformation styles recognized in the Complex are (
i
) vertical, (
ii
) vertical followed by horizontal, and (
iii
) vertical fluid movement with brittle failure. These post-deposition structures are used to estimate viscosity and density of adjacent layers during consolidation. The distribution of the structures through the mafic sequence provides some information on magma movement and rates of crystal accumulation.
Remanent magnetization in penecontemporaneous structures of the Pleistocene Scarborough Formation, Ontario, Canada
Authors: Yagishita K. , Westgate J. A. , Pearce G. W.
Published: December 2007

Detrital remanent magnetization (DRM) of sediments comprising two penecon-temporaneous structures in the deltaic facies of the upper Pleistocene Scarborough Formation, near Toronto, Ontario, displays a concentrated orientation that suggests remagnetization after deformation. The two sampled sedimentary structures consist of (1) a load deformation of silty sands in a coarser-grained silty sand matrix, and (2) slump folds of thinly layered silty sands in a fine sand bed. The sediments from both structures possess a bimodal grain size distribution. Remagnetization is ascribed to the free rotation of detrital magnetic grains under high porewater pressure conditions that developed as a consequence of rapid burial by younger sediments. Liquefaction of the sediments under the effect of this high fluid pressure was achieved by the reverse gradient of hulk density and accentuated by differential overloading, as is shown by the presence of the load deformation. Elsewhere, the high porewater pressure reduced the strength of the sediments enough to cause them to slump down the gentle delta slope. Associated sedimentary features, such as a clay-silt sealing bed and a sand dyke, suggest that the subsequent locking in of DRM by dewatering took place at a time significantly later than that of initial deposition. The tight clustering of DRM orientations in both sedimentary structures point to rapid acquisition of DRM once the sediments had been drained.
MinSys: An information system for the mining and mineral industries
Authors: Lea G.
Published: December 2007

MinSysis
a fourth-generation computerized information system developed by Geosystems for the mining and mineral industries. It consists of the
MinSys Datorium,
the database, together with derived products and associated services. Information sources include the mining industry itself, mining publications and general publications. Subject coverage includes exploration, development, environmental aspects, management, market aspects and government. Indexing is based on
Omnisaurus
, a multi-level system based on
Geosaurus
(Geosystems thesaurus),
Minsaurus
(Geosystems’ list of locations, consisting of organisations, resources and sources),
Datasaurus
(Geosystems’ data element definitions), and
Geosaurus
(Geosystems free text controlled terms).
MinSys
will be made available from computer terminals via telecommunication networks such as Tymnet, Telenet and Euronet.
A world coal resource database
Authors: Duncan S. V.
Published: December 2007

Resource data for coal occurrences throughout the world are being gathered into a database which aims to provide the energy and chemical resource analysis with the fundamental deposit characterizations to plan the future exploitation of coal. The data concerning the properties of all coal-in-place are obtained for both published and unpublished sources and entered into the database in their original language and conventions. The relational database management system employed is appropriate to such variegated data. The resource data will be run though lexicographic algorithms designed to provide the best available equivalences between source conventions: thus multinational aggregations of the results may become meaningful. The source and derived files will be available for alternative interpretations as required. It is concluded that the database, once developed, is expected to provide a unique and valuable source of information for decision making up to, and beyond, the time when coal replace soil as the principal remaining fossil resource of energy and petro-chemicals.
Lower Silurian distal shelf storm-induced turbidites in the Welsh Borders: sediments, tool marks and trace fossils
Authors: Benton M. J. , Gray D. I.
Published: December 2007

The Upper Llandovery Hughley Shales of Shropshire are interpreted as storm-induced distal shelf turbidites. They comprise a sequence of calcareous sandstones interbedded with purple mudstones. The trace fossils, body fossils, and palaeogeography indicate a deep shelf position for their deposition. The thin sandstone units are interpreted as having been deposited from density current bedload and suspension. Storm surge ebb traction currents, arising from intermittent major offshore storms, are considered to have initiated the density currents. A deepened storm wave base allowed transportation of fine sand in suspension out onto the distal shelf.

Internally, the resultant sands are differentiated from distal (fan) turbidites by multi-directional bedload currents, which are shown most clearly by spectacular tool marks on sandstone bases. The tools are clearly identifiable in many cases as indigenous benthonic organisms such as horn corals, coral colonies, crinoids, brachiopods and trilobites. The sandstone beds were later colonized by burrowers and other track-producing organisms. The trace fossils include
Diplocraterion
(or
Corophioides
),
Palaeophycus
,
Skolithos, Chondrites
,
Scolicia
,
Rusophycus
,
Cruziana
and
Diplichnires (Cruziana
facies assemblage). A new ichno-species,
Walcottia devilsdingli
is established for small burrows with regular lateral appendage marks at certain points.
A geochemical comparison of the Dalradian Leven Schists and the Grampian Division Monadhliath Schists of Scotland
Authors: Lambert R. St. J. , Holland J. G. , Winchester J. A.
Published: December 2007

Suites of samples from the type area of the Leven Schist and from localities within the Monadhliath Schists of the Central Highlands have been analysed for major and trace elements and for their Sr isotopes. Petrologically the two schist groups are consistently different: the Leven Schists are muscovite-rich, plagioclase-poor semipelites to pelites, whereas the Monadhliath Schists are a typical ‘Moinian’ semipelite, consisting almost entirely of biotite, sodic andesine and quartz. Equally, consistent geochemical differences between the two include more Nb, Zr, Y and Rb, and less Ca, Sr and Ni in the Leven than the Monadhliath Schists. Ratios of Rb: Sr and of Y to P
2
,O
5
, Sr and CaO discriminate the Leven from the Monadhliath schists. Factor analyses of the chemical data also serve to distinguish the two suites

Rb-Sr isochron studies give 655±f2.5Ma, initial
87
Sr/
86
Sr = 0.7232±f10, for the Leven Schists, and 486±9Ma, initial "Sr
87
/"Sr
86
= 0.7190±1, for the Monadhliath Schists and also separate the two formations from one another. The 655 Ma age for the Leven Schists is thought to record sedimentation and diagenesis, whereas the 486±9 age for the Monadhliath Schists is probably related to the cessation of Rb and Sr migration at or after the peak of the Grampian orogeny.

Their Sr isotopic compositions were also completely different hack to 1300 Ma ago and serve to confirm the lack of any continuity between the Leven and Monadhliath schists. Sets of schists located between the main outcrop areas were also analysed and can be assigned without ambiguity either to the Leven or the Monadhliath schists on the basis of their chemistry. The results of this study imply that the Lower Dalradian Appin Group rests on the Grampian Division unconformably and that the latter is closely related, through its geochemistry, to the Moinian NW of the Great Glen.
Marginal basin ophiolites at Oramar and Karadađ, SE Turkey
Authors: Özkaya Ismail
Published: December 2007

Two ophiolite outcrops at Oramar and Karadađ, SE Turkey, of possible Upper Cretaceous age, occupy the same tectonic position on the northern margin of the African-Arabian continental crust as the Troodos, Kizildađ, Baer Bassit, and Oman ophiolites. Field relationships suggest that they were generated in a marginal basin. Southward subduction under the northern extension of the Arabian plate probably resulted in island are volcanism and metamorphism, as well as development of a marginal basin to the S in the Late Cretaceous. Continental convergence caused displacement of the marginal basin ophiolites as well as the northern are-trench complex southward onto the Arabian shelf towards the end of the Cretaceous and Tertiary. Another possibility is that the ophiolites are products of a leaky trans-tensional faults activated by changes in relative plate motions during the Upper Cretaceous.
Jurassic volcanic rocks of the northern North Sea
Authors: Fall H. G. , Gibb F. G. F. , Kanaris-Sotiriou R.
Published: December 2007

The lavas and minor intrusive rocks from the Jurassic volcanic province of the Forties-Piper area of the North Sea can be subdivided into three distinct series on the basis of petrography, whole-rock chemistry and mineral chemistry. These series, which probably evolved from one or more alkali olivine basalt parent magmas are: (
i
) an ankaramite-basaltic hawaiite-hawaiite series, (
ii
) an alkali olivine basalt-hawaiite series, and (
iii
) an intrusive hawaiite-intrusive mugearite series. Variations within series are due mainly to differential distribution of mafic phenocryst phases but liquid immiscibility and magmatic fractionation are also believed to have contributed. The Middle Jurassic volcanism in the North Sea area is thought to be related to the tensional tectonic regime which existed in NW Europe during the Jurassic or to be due to a region of high heat flow extending northeastwards from the contemporary spreading axis between Iberia and Newfoundland and possibly to a combination of the two.
Geo-tectonic framework of the Himalaya of N Pakistan
Authors: Coward M. P. , Jan M. Q. , Rex D. , Tarney J. , Thirlwall M. , Windley B. F.
Published: December 2007

In the Karakorum Range there is a structurally complicated Cretaceous are comprising the Kohistan sequence. On its northern side the Northern Suture consists of a mega-mélange and is bounded to the S by tightly folded pillow-bearing volcanics and sediments. To the S the Kohistan Plutonic Belt consists of (southwards): (a) early foliated and late post-tectonic tonalites and diorites, (b) aplites and pegmatites (up to 30% of rock volume), (c) basic dykes up to 10 m thick, (d) the Chilas Complex, a stratiform cumulate body over 300 km long and 8 km thick (chromite-layered dunites, gabbros and norites) with a low pressure granulite-facies mineral fabric of tectonic origin, (e) an amphibolite belt with a complex mixture of other rocks, and (f) the Jijal Complex, a 200 km
2
tectonic wedge of high pressure granulites and chromite-layered dunites. Cumulate graded units in the Chilas Complex show that it is folded by an isoclinal anticline (F
1
). The mid-upper crust of the are is folded by a 50 km half-wavelength F
2
, syncline. The whole Kohistan sequence with its two phases of isoclinal folds was tilted during Himalayan collision so that the structures are now subvertical. The Southern Suture (Main Mantle Thrust) has a wedge of glaucophane schists. The Indian plate contains a basement of psammites and schists intruded by Cambrian granites and overlain by isoclinally folded and metamorphosed carbonates and shales.
Dalradian deposition and the late Precambrian–Cambrian history of the N Atlantic region: a review of the early evolution of the Iapetus Ocean
Authors: Anderton R.
Published: December 2007

During the late Precambrian the Dalradian environment evolved from a relatively stable subsiding shelf into a series of fault-bounded blocks and basins. This increase in tectonic instability can be interpreted as a precursor to the continental rifting which led to the inception of the Iapetus Ocean at the end of the Precambrian, or base of the Cambrian, and was marked in the Dalradian terrain by the eruption of the Tayvallich Volcanics. A comparison of the late Precambrian history of the areas now adjacent to the Iapetus suture suggests that prior to this rifting the Greenland–northern Britain–NW Newfoundland area and Scandinavia formed part of the same plate with northern Norway lying close to northern Britain. As the evolution of all these areas was dominated by the opening of Iapetus during the Cambrian followed by closing initiated by subduction in the early Ordovician, many aspects of their history are similar. Southern Britain and SE Newfoundland, however, had a quite different late Precambrian history. They probably formed a microcontinental plate which originated at a considerable distance from northern Britain and which, until the closure of the Iapetus Ocean, was never in contact with the rest of the Caledonian belt.
The significance of a reliable Ordovician age for some Highland Border rocks in Central Scotland
Authors: Curry G. B. , Ingham J. K. , Bluck B. J. , Williams Alwyn
Published: December 2007

A Lower Arenig fauna with North American affinities has been rediscovered at Dounans, Aberfoyle, Central Scotland. This discovery makes part of the Highland Border Complex younger than the adjacent Dalradian rocks, and suggests a provenance from the S.
Igneous activity in the southern Andes and northern Antarctic Peninsula: a review
Authors: Saunders A. D. , Tarney J.
Published: December 2007

The Antarctic Peninsula and the southern Andean continental margin have been the sites of extensive and varied magmatic activity since at least late Palaeozoic time. The dominant activity has been of calc-alkaline character and, although andesite and tonalite are the main rock types, there are well-marked transverse variations in the major and trace element chemistry of the magmas erupted in both areas. Thus, calc-alkaline magmas erupted farthest from the ancestral trench are generally more silicic, potassic and light-REE enriched than magmas erupted closer to the trench. In both regions, the locus of calc-alkaline activity has tended to move trenchwards since the Palaeozoic, although activity began to wane during the mid-Cenozoic when subduction of the Pacific Plate slowed down and ceased. A northward cessation of calc-alkaline magmatism along the Antarctic Peninsula can be linked in broad terms to the progressive northwards subduction of sections of the Aluk Ridge during the Cenozoic. Extensional tectonics within and behind the main igneous belts caused the development of narrow back-arc basins in southern Chile during the Mesozoic and in Bransfield Strait along the northern Antarctic Peninsula during Recent times. Tholeiitic magmas with transitional calc-alkaline characteristics were erupted in these basins. In addition, alkalic basalts and related undersaturated magma types were erupted onto the stable continental platform well behind the main calc-alkaline and marginal basin magmatic belts during Cenozoic and Recent times, probably in response to extensional tectonics as subduction slowed or ceased.
The composite floor of the Cretaceous back-arc basin of South Georgia
Authors: Storey B. C. , Mair B. F.
Published: December 2007

Part of an ophiolite sequence and pre-Jurassic continental basement rocks are remnants of the composite floor of the Cretaceous back-arc basin system on South Georgia. The partially preserved ophiolite consists of pillow lavas and breccias, inter-bedded tuffs, basic and silicic dykes and occasional sills. It is intruded by a composite gabbro-plagiogranite pluton and smaller gabbroic plutons. The basement gneisses are intruded by layered gabbros, diorites, granitic rocks and numerous basic dykes. A migmatitic aureole surrounds the plutonic rocks, which are fragmented and net-veined by remobilized crustal rocks.

The mafic rocks of the ophiolite sequence and basement complex are geochemically similar and both formed by differentiation of a mantle-derived, sub-alkali tholeiitic magma in a former back-arc basin tectonic setting. The plagiogranite and silicic dykes and lavas of the ophiolite and some of the silicic rocks within the basement formed by differentiation of the basic magma. The remainder of the granitic rocks within the basement are geochemically distinct, comprising remobilized basement rocks and a calc-alkaline pluton of a remnant magmatic arc.

The back-arc basin formed by emplacement of the tholeiitic magma within pre-existing basement rocks. Up to 80% extension of the continental crust occurred prior to rifting and development of the back-arc basin.
Invertebrate and vertebrate pathways of anaerobic metabolism: evolutionary considerations
Authors: Livingstone D. R.
Published: December 2007

A review of anaerobic metabolism (end-products, energy-substrates and enzymes) of the invertebrate and vertebrate phyla reveals three main pathway-types. The lactate and opine pathways yield, respectively, high and medium rates of energy production and are used for maintaining or increasing metabolic activity. The glucose-succinate pathway is a high (relatively) efficiency pathway used for anoxia survival.

The distribution of the pathways amongst the phyla is consistent with their phylogeny. A relationship between the Mollusca and Sipuncula is possibly indicated. A hypothetical scheme of the evolution of the pathways indicates early presences for amino acid based pathways, the opine pathways and a fourth pathway-type, the aspartate-succinate pathway.

A consideration of chemical, fossil and functional approaches to the reconstruction of the beginning of life suggests an early role for the opine pathways in providing energy for the burrowing of infaunal worms of the Precambrian era. Biological rather than chemical factors are concluded to have been the main pressures for the evolution of anaerobic metabolism.
Cretaceous high pressure metamorphism in NE Oman and its relationship to subduction and ophiolite nappe emplacement
Authors: Lippard Stephen J.
Published: December 2007

An occurrence of glaucophane-bearing schists is reported from near Muscat in NE Oman in rocks which underlie the Upper Cretaceous Semail ophiolite nappe. These blueschists formed by the metamorphism of quartz sandstones, shales and basic igneous rocks belong to a pre-Permian basement in the area. Metamorphic micas (phengites) from these rocks have been dated at between 101 and 80 Ma (K-Ar ages) indicating a mid- to late-Cretaceous age for the high pressure event. A syn- to late-F
1
assemblage of almandine + glaucophane + phengite in the pelites shows that the peak of metamorphism reached about 400–450°C and 4–8 kbars pressure. This was followed by a greenschist facies overprint with the formation of epidote and albite porphyroblasts in the meta-igneous rocks and a widespread retrogression to chlorite. The high pressure metamorphism is ascribed to the effects of partial subduction of the NE Oman continental margin during the initial stages of ophiolite obduction and the subsequent greenschist facies event to uplift of the area during the later stages of emplacement of the nappes.
The upper mantle and deep crust beneath the British Isles: evidence from inclusions in volcanic rocks
Authors: Upton B. J. G. , Aspen P. , Chapman N. A.
Published: December 2007

Coarse-grained inclusions in Upper Palaeozoic alkali basalts, occurring in over 60 localities in the British Isles, include samples of the underlying mantle and lower crust. The ultramafic assemblages imply an extremely heterogeneous upper mantle involving a tectonized spinel lherzolite and harzburgite matrix transected by younger bodies of wehrlite, websterite, clinopyroxenite, orthopyroxenite, garnet-pyroxenite and assorted kaersutite- and biotite-rich ultramafites. Associated megacrysts include anorthoclase, sanidine, clinopyroxene, kaersutite, Ti-biotite, garnet, Ti-magnetite, Mg-ilmenite, apatite, zircon and corundum. These originated in part from disaggregation of pegmatoidal bodies of alkaline felsic rocks, pyroxenites, lherzites and glimmerites. Plagioclase-pyroxene rocks (basic granulites) are probably samples of the lower crust, with quartzo-feldspathic gneisses possibly derived from shallower levels in a chemically-zoned crust. Other inclusions described include apatite-magnetite rocks, biotite- and hornblende-albite rocks and unfoliated tonalites, diorites, trondhjemites and granites.

A high-grade (granulite-facies) feldspathic basement is inferred to underlie all the major N British structural provinces, including the Midland Valley and Southern Uplands. Anorthosite xenoliths imply that anorthositic rocks compose some part of the 'basement' in S and central Scotland.
Late Proterozoic lavas of the Central Arabian Shield—evolution of an ancient volcanic arc system
Authors: Roobol M. J. , Ramsay C. R. , Jackson N. J. , Darbyshire D. P. F.
Published: December 2007

A petrological assessment of 11 volcano-sedimentary belts in the Central Arabian Shield (CAS) using 118 new analyses is presented. The same samples have been used in a Rb-Sr dating programme also reported in this volume. The oldest volcano-sedimentary belts (‘sequence’ C; >900 Ma) are chemically immature bimodal suites of low-K tholeiites and sodic dacite/rhyolite depleted in lithophile elements. These lavas have chemical characteristics similar to immature island arcs such as the Tonga–Kermadee and Lesser Antilles arcs. Younger lavas of ‘sequence’ B (900–700 Ma) are slightly more mature in composition, being predominantly calc-alkaline and low-K arc tholeiite series with higher lithophile element contents. They are comparable with Pacific island are averages. The youngest voluminous lavas (‘sequence’ A; 700–570 Ma) are generally calc-alkaline or high-K, calc-alkaline series lavas with moderately high lithophile element abundances. They are comparable to volcanic arcs such as Central America and Indonesia, which are transitional between island arcs and continental margin volcanic arcs.

The cratonization process in the CAS thus involved the superimposition of three volcano-sedimentary sequences, formed in progressively maturing volcanic arcs. Early-formed, immature island arcs were succeeded by chemically more mature island arc deposits and then by deposits formed in volcanic arc(s) transitional between island arcs and continental margins. The evolution ceased at this stage and probably did not advance to the equivalent of an Andean continental margin.
Calcrete and other soils in Quaternary limestones: structures, processes and applications
Authors: Braithwaite C. J. R.
Published: December 2007

Quaternary limestones commonly include descriptions of calcrete, caliche and soils which embrace both surficial deposits in which dissolution and cementing phenomena interact on a calcareous substrate, and soils or other sediments where carbonates are precipitated as cements. Three genetic groups are recognized, in which (1) a soil profile is developed by surface alteration of existing marine sediments; (2) deposits accumulate superficially on a lithified surface; and (3) soil-like materials have been added to unconsolidated marine sediments by surface processes including infiltration.

Sediments range from unaltered marine grainstones through poorly sorted wackestones to mudstones. Diagnostic structures include pisoliths and other glaebules. laminae, grain aggregates, birdseyes and other vugs, and rootlets as well as fractures and brecciation not found in other environments. The most common precipitated carbonates are micrites, but needle fibres, whiskers and prismatic crystals occur. Crystal morphology is controlled in part by the level of supersaturation. rapid evaporation leading to micrite precipitation and whiskers, but also by the pressure of organic contaminants. Distribution of cements and structures is irregular, relating to percolating groundwater streams. Cements may be isopachous but meniscus structures, cement bridges and microstalactites occur. These vadose textures may not be developed where evaporation rates are high. Irregular areas of replacive (neomorphic) spar and displacive calcite growths occur in some examples but criteria for recognition are not firmly established.

Dated recent examples lie between 400 and 18,300 years B.P. but deposits on Aldabra and in Kenya are intercalated with marine sediments which extend to 200,000+ years B.P. The recognition of these terrestrial intervals within otherwise marine sequences enables sea level changes to be identified and correlated with other climatic data to separate local patterns of uplift or subsidence.
Petroleum geochemistry of the Southern Santos Basin, offshore Brazil
Authors: Gibbons M. J. , Williams A. K. , Piggott N. , Williams G. M.
Published: December 2007

Significant thicknesses of hydrocarbon source rocks (up to 1000 m) were identified in 1–SPS–17, l–SCS–4A, –5 and –6, in the Southern Santos Basin. These marine shales of Cenomanian to Coniacian ages generally contain l–2.5% organic carbon. Pyrolysis maximum potential yields are moderate rather than good, averaging 3–4 kg hydrocarbons/tonne of rock over the hydrocarbon source intervals. Oil will be the principal product, although horizons of gas-prone kerogens are also present.

Palaeotemperature indicators (spore colour and vitrinite reflectance measurements) show that the basin is characterized by relatively low maturation gradients; calculated depths to the oil generation threshold (OGT) range from
c
. 3600–4500 m. The identified source rocks generally lie within ±500 m of the OGT and the presence of 1000–1500 m of Miocene and later sediments therefore restricts the time available for significant generation and migration to, at most, about 10 Ma, i.e. from late Miocene onwards. However, a variety of basin models predict substantially greater maturities and, in some instances, suggest oil generation commenced in Palaeogene times. Direct measurements of evolved hydrocarbons give support to some of the modelling predictions by apparently demonstrating hydrocarbon evolution at depths less than the palaeotemperature OGTs. The absence of significant hydrocarbon accumulations is probably a function of inadequate source richness and the short time available for generation. Migration from thick shale source beds bounded above and below by non-generative shales may also be a problem.
The role of fluids in the development of a granulite facies transition zone in S India
Authors: Holt R. W. , Wightman R. T.
Published: December 2007

The Bodinayakkanur area of Tamil Nadu lies in the transition zone (P = 5 kbar, T = 700°C) from amphibolite to granulite facies metamorphism, in the Archaean high grade terrain of S India. Within the zone 3 closely associated rock units occur: (1) Precursor grey gneiss. (2) Pink migmatitic and metasomatic gneiss, (3) Green charnockitic granulites. Field observation shows that the complex inter-relations between these 3 rock types can be related to influx of fabric- and layer-guided CO
2
- and H
2
O + K
2
O-rich fluid phases, derived from a deep-seated source.
The Black Stockarton Moor subvolcanic complex, Galloway
Authors: Leake R. C. , Cooper C.
Published: December 2007

The Black Stockarton Moor subvolcanic complex is a composite of intersecting porphyrite dyke swarms, granodioritic sheet intrusions, small granodiorite stocks and breccia pipes of late Caledonian age, emplaced within the Lower Palaeozoic turbidite sequence of the Southern Uplands of Scotland. Evolution from the subvolcanic to the plutonic igneous regimes can be traced in a first phase of activity with the successive intrusion of dykes, sheets, stocks and the adjacent Bengairn and Criffel plutonic complexes. The minor intrusions were partially preserved from obliteration by the subsequent plutonism, as the centre of igneous activity shifted progressively from W to E. A second phase of intrusion, post-dating most, if not all, of the plutonic activity, took place within an entirely different stress field producing
en echelon
sigmoidal porphyrite dykes with maximum dilation roughly at right angles to that of the earlier intrusions. Deep crustal shear is postulated as the source of the tension fractures, which were subsequently filled by the second phase dykes, and also of 2 of the 3 sets of wrench faults which cut the area.
Compaction-sensitive accretionary lapilli: a means for recognizing soft-sedimentary deformation
Authors: Boulter C. A.
Published: December 2007

In a region of negligible tectonic overprint, soft-sedimentary folding has affected beds of accretionary lapilli. The folds, which range from upright convolute to intraformational recumbent, are truncated by the overlying beds and their pre-lithification origin is further confirmed by their association with forcefully injected clastic dykes of accretionary lapilli, and fluidized channel-ways. Shape factor analysis using Elliott polar graphs shows that the accretionary lapilli define weak to moderate planar fabrics that are coincident with the regional bedding attitude and which have a compactional strain symmetry
(X = Y ≥ Z)
. The lapilli fabrics were superimposed on the folds and clastic dykes and hence are axial planar to the recumbent folds and transect the convolute lamination. The geometrical relations and strain pattern establish a pre-tectonic timing for the folds and for their formation in unconsolidated sediment. The fabrics were not generated during folding by processes akin to tectonic dewatering, but were later superimposed on the folds. Compaction-sensitive strain markers give an additional criterion for distinguishing between soft-sedimentary and tectonic structures; post-lithification deformation would be recognized by the dispersal of the planar compaction fabrics defined by the accretionary lapilli.
Buried granites within the Mid North Sea High
Authors: Donato J. A. , Martindale W. , Tully M. C.
Published: December 2007

A gravity survey of the UK sector of the North Sea reveals the presence of three gravity lows over the Mid North Sea High. Seismic data eliminate the possibility that these lows are due either to thicker sediments or to salt structures. Consequently, the anomalies may be related to buried granites within the Palaeozoic basement. Gravity modelling demonstrates that the amplitude and shape of the observed anomalies may be explained by buried batholith-shaped bodies with densities appropriate for granites. The tectonic influence of the buried granites may explain to some extent the continued stability of the Mid North Sea High throughout much of the development of the North Sea basins.
The Rb-Sr isochron age of the Kennack Gneiss and its bearing on the age of the Lizard Complex, Cornwall
Authors: Styles M. T. , Rundle C. C.
Published: December 2007

An acid vein from a borehole in the Kennack Gneiss has given a whole-rock Rb-Sr isochron age of 369 ± 12 Ma. This is interpreted as a metamorphic age recording the time of emplacement of the Lizard Complex. This emplacement in late Devonian times was part of an early phase of the Hercynian Orogeny which also affected the Gramscatho 'Series' of S Cornwall.
Palaeomagnetism of the Lizard Complex, SW England
Authors: Hailwood E. A. , Gash P. J. R. , Andresen P. C. , Badham J. P. N.
Published: December 2007

The Lizard Complex of SW England has recently been interpreted as representing a fragment of oceanic lithosphere that was thrust on to the continental crust of S Cornwall in the Devonian as a result of tectonic processes at a convergent plate margin. A palaeomagnetic study has been carried out on the ultramafics, gabbros and dykes of the E coast section to examine possible tectonic movements that might have been associated with this history of formation. A component of stable magnetization having a shallow to intermediate negative inclination and a SSW declination has been identified in each of these lithologies. This direction is similar to the Permian geomagnetic field direction for SW England, and one interpretation of the results is that the Lizard rocks were remagnetized in the early Permian, perhaps as a result of heating associated with emplacement of the Variscan batholiths. However, no mineralogical or other evidence for widespread heating of the Lizard Complex in the Permian has yet been identified. Available Rb-Sr and K-Ar geochronological data indicate a probable Devonian crystallization age, with no evidence for a Permian overprint. Therefore it is considered equally likely that this magnetization is primary, and dates from the time of original formation of the rocks. After application of a 90° tilt correction to restore the E Coast section of the complex to its postulated original orientation in the oceanic lithosphere the corresponding palaeomagnetic pole position is brought into close coincidence with the mean UK pole for the interval Silurian to Devonian. If the stable magnetization is primary, and was acquired during the original formation of the complex by sea floor spreading at a mid-ocean ridge, then it may be inferred that movement in a latitudinal sense prior to emplacement was small, and below the resolution of the present palaeomagnetic data (10° to 15°).
Borehole sections through the Traboe hornblende schists, a cumulate complex overlying the Lizard peridotite
Authors: Leake R. C. , Styles M. T.
Published: December 2007

Three borehole sections in the Traboe area provide a partial section through a layered basic-ultrabasic complex, previously referred to as the Traboe hornblende schists. This complex, though dismembered into thrust sheets, shows an overall NE-dipping stratigraphy with a generalized upward sequence from dunite and pyroxenite to gabbro and anorthosite. The bulk composition of the ultramafic rocks is quite different from the dominantly lherzolitic composition of the main Lizard peridotite. The composition of the basic rocks is also markedly different from that of the Landewednack hornblende schists with which they have previously been correlated. The deformation and recrystallization of the rocks has been complex and locally intense, producing a fine granular fabric in many rock types. Amphibolitization has affected many rock types to give assemblages dominated by hornblende. Mineral composition varies with position in the stratigraphic sequence and is consistent with crystallization of the complex from differentiating basic magma pulses.
Carboniferous volcanicity in England with special reference to the Westphalian of the E and W Midlands
Authors: Kirton S. R.
Published: December 2007

In the East Midlands, volcanic activity occurs at numerous stratigraphic levels in the Carboniferous but terminates in the Westphalian A. In the Vale of Belvoir (E Midlands) the Westphalian activity is represented by a continuous lava pile (volume approximately 45 km
3
) that interdigitates with conventional sediments to the W. This is cut by one or more periods of sill emplacement, at least one of which was later than the Westphalian A/B boundary. Conversely, in the W Midlands igneous activity was confined mostly to the emplacement of isolated sills in the Westphalian C.

The E Midlands pile is composed of intimately-associated alkaline and subalkaline (tholeiitic) basalts, whereas the sills of the W Midlands are alkaline. The alkaline basalts of both areas range from basanite/basalt to hawaiite. New ultrabasic nodule localities have been recorded in the most alkaline basalts of the E Midlands.
Pillow lavas and the Leidenfrost effect
Authors: Mills A. A.
Published: December 2007

Field observations of the formation of pillows by hot, de-gassed lava entering the sea have proved that their generation involves the underwater exposure and movement of
incandescent
material. This is made possible by the Leidenfrost effect, the phenomenon whereby film boiling replaces the usual nucleated boiling above a certain temperature, thereby forming an insulating sheath of vapour around any sufficiently hot body immersed in a liquid. Only on cooling below a certain temperature (defined here as the Nukiyama temperature) will rapid heat exchange occur between water and hot, gas-free lava. Near the surface, this could produce phreatic explosions and extensive clouds of steam.
Alternative model for the derivation of gold in the Witwatersrand Supergroup
Authors: Reimer Thomas O.
Published: December 2007

Present models of the derivation of the gold in the Witwatersrand conglomerates of South Africa as detrital grains directly from primary deposits in a source area consisting mainly of Archaean schist belts meets with a volume problem. Witwatersrand deposits have yielded about 923 kg/km
2
Au compared to about 65 kg/km
2
Au in the richest known schist belts. Differences in the extent of mining activities cannot account for these differences in yield. Gold fineness, grain size, and morphology of the gold particles are also difficult to reconcile with a purely detrital derivation. Data on the mobility of gold in the hydrosphere and in the weathering cycle are used to erect a model which predicts that most of the gold in the Witwatersrand conglomerates was derived from a source area in trace amounts in a 'dissolved' form and precipitated at or close to the edge of the depositional basin, possibly under organic influences. Subsequent sedimentary reworking and metamorphic/diagenetic remobilization led to the formation of the complex association of minerals observed now in the conglomerates.