bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemistry, thermal gradients and evolution of the lower continental crust
Authors: TARNEY J. , WINDLEY B. F.
Published: December 2007

Precambrian granulites are representative of the lower continental crust. They are, relative to upper crustal gneisses, refractory and low in heat-producing elements, being 'depleted' in K, Rb, Cs, U and Th; they have normal or even higher than normal abundances of Zr, Sr, and Ba, highly fractionated REE patterns and high Ba/Rb, Ba/Sr, Ce/Yb, K/Cs and K/Rb ratios. Having low Rb/Sr, U/Pb and Sm/Nd ratios they are likely to be unradiogenic with respect to Sr, Pb and Nd isotopes. They do not seem to have marked positive Eu anomalies which might compensate for the significant negative Eu anomalies observed in upper crustal granitic rocks and sediments. The granulites formed largely under an intermediate goethermal gradient with P of 7–12 kbar and T of 700–1000°C.

The continental crust completed a substantial part of its growth by 2500 Ma ago. We suggest that growth took place at Cordillerantype continental margins with underthrusting of oceanic crust, generation and underplating of extensive calc-alkaline tonalitic-granodioritic material containing early remnants of hornblende gabbro/calcic anorthosite complexes, and that it was associated with widespread nappe stacking and imbricate interthrusting. This crustal generation process culminated in the granulite metamorphism deep in the tectonically and magmatically thickened continents.
The influence of erosion upon the mineral fades of rocks from different metamorphic environments
Authors: ENGLAND P. C. , RICHARDSON S. W.
Published: December 2007

Metamorphism of tectonically thickened continental crust or subducted sediment wedges is likely to take place in a thermal regime where temperature increases by conductive relaxation whilst concurrently pressure decreases by erosion of the pile. The mineral facies of rocks reaching the surface do not reflect any one geotherm through the pile but lie on a locus of P–T conditions, the metamorphic geotherm, which will generally be concave towards the temperature axis. Maximum pressures on the metamorphic geotherm are significantly less than maximum pressures experienced by rocks during the early stages of recrystallization. The metamorphic geotherm is polychrome, points at lower temperatures reflecting conditions earlier in the development than those at higher temperature; crustal melts are developed after low-medium temperature metamorphism and the amount of such melts could be significant.

Blueschists develop on the low temperature end of the metamorphic geotherm and are succeeded in exposure at the surface by greenschist- or amphibolite-facies rocks; the time-scale for this process is consistent with the virtual absence of Precambrian blueschists. Crust thickened by addition of hot magma is likely to yield a metamorphic geotherm convex towards the temperature axis. Recognition of differently curving metamorphic geotherms can be used to assess the part played by magmatic activity in older metamorphic terrains.
Geochemical evolution of the suboceanic mantle
Authors: HANSON G. N.
Published: December 2007

The suboceanic mantle has on the basis of incompatible element and isotope ratios two chemically distinct units; the mantle source for ocean island basalts and the mantle source for ocean ridge basalts. Ocean island alkali basalts have an enriched light rare earth element (REE) source with K/Rb = 400, K/Ba = 28, Zr/Nb = 6.6. Ocean ridge tholeiites have a depleted light REE source, with K/Rb = 1060, K/Ba = no, and Zr/Nb = 37.
87
Sr/
86
Sr and
206
Pb/
204
Pb ratios are generally lower in the ocean ridge basalts than in the basalts from ocean islands. It is suggested that these differences are not a result of simple partial melting, fractional crystallization, zone refining, residual minerals or isotopic disequilibrium between minerals and melt during melting. Instead, the differences between the sources are real, and have existed for some 1500 Ma or more.

Nephelinite, alkali basalt, and tholeiites from ocean islands have similar isotopic and incompatible element ratios. The nephelinites and alkali basalts are, however, progressively much more enriched in the light REE than are the tholeiites, yet the light REE in nephelinites and alkali basalts appear to be incompatible. This may be explained by the occurrence of small (average 4 cm thick), closely spaced pyroxenite veins (within tens of cm) in the mantle source for ocean island basalts. The occurrence of a network of veins which melt preferentially may lead to melts which have apparent sources with a much greater enrichment in incompatible elements than the total mantle source and may also give the appearance of a source whose ratio for slightly compatible elements changes as a function of extent of melting.
How rigid are the lithospheric plates? Fault and shear rotations in southeast Asia
Authors: HOLCOMBE C. J.
Published: December 2007

Evidence is presented to show that significant fault movement occurred during the Tertiary in continental southeast Asia, within an area generally regarded as part of the Eurasia plate. Three separate but linked rotations can be recognized: an Indochina subplates wrench rotation, a Sunda shear rotation, and the rotation of the Malay Peninsula and the Sunda Platform in
toto
by movements along the Ranong and Semangko faults. Spherical geometry constraints on rotation allow a pre-Oligocene map reconstruction of southeast Asia to be made which offers explanations for the patterns of Quaternary faulting, of Tertiary sedimentation, and of pre-Tertiary geosynclinal and mineralization belts.
The Flinders Ranges breccias of South Australia—diapirs or
d’ecollement?
Authors: BURNS K. L. , STEPHANSSON O. , WHITE A. J. R.
Published: December 2007

Breccia-cored domes in the Northern Flinders Ranges, South Australia, have been regarded as diapirs analogous to diapiric salt structures in northwestern Germany and the Gulf Coast. It is shown that the core of the Blinman Dome is not intrusive and is not composed of less dense rocks; hence a diapiric process cannot apply. It is suggested that much of the breccia of the core is formed by deformation of a stratigraphic unit composed of interbedded competent and incompetent beds at a Flinders Ranges
décollement
and results from folding. If this model is correct, the Flinders Ranges structures should occur at
décollements
in other parts of the world.
Current research on fluid inclusions and on mineral deposits
Authors: EVANS A. M.
Published: December 2007

T
he principal theme
of this three-and-a-half-day conference (13–17 December 1976) at Durham University was the value of fluid inclusion studies in investigations into the origin of mineral deposits and rocks. Other sessions covered opaque mineralogy, studies on natural and synthetic sulphide systems and various other aspects of ore geology. For this conference the Mineral Deposits Studies Group joined forces with the Applied Mineralogy Group of the Mineralogical Society. There was also official participation by representatives from the Groupe Inclusions of the Société Française de Minéralogie et de Cristallographie and from C.N.R.S. centres at Paris and Nancy.

Fluid inclusion papers were mainly concerned with studies of economic mineral deposits. It was stressed (Deicha) that they can now yield valuable data on the genesis of minerals formed over the full range of temperatures from magmatic (Althaus) to sedimentary (Sabouraud
et al
.). Four papers were concerned with fluid inclusions in fluorite. In one, P. J. Rogers showed that fluids in Derbyshire fluorites have similar salinities to those from the northern Pennine orefields, but a lower K/Na ratio. In another, F. W. Smith demonstrated how homogenization temperatures could be used to reconstruct the distribution of isothermal surfaces in veins so as to outline flow paths and calculate cooling gradients. There have been far too few intensive investigations of this sort on single veins. Such studies combined with Conolly diagrams could become important exploration tools and it is to be hoped that other workers will follow this lead. In work on other vein deposits
Possible causes of Rotliegend sandstone diagenesis in northern West Germany
Authors: Hancock N. J.
Published: December 2007

The Rotliegend sandstones of northern West Germany are characterised by severe diagenesis with growth (in approximate time sequence) of: (1) iron oxide, (2) tourmaline, (3) authigenic feldspar (mainly albite), (4) illite, (5) quartz, (6) chlorite, (7) kaolinite, (8) anhydrite and carbonate. The illite forms
(a)
tangential rims,
(b)
radial rims,
(c)
mesh-work,
(d)
dense homogeneous masses. The chemical conditions responsible for this diagenesis involved alkaline pore fluids with high K
+
and Na
+
. These conditions were initiated very early, sometimes only a few centimetres below the surface. The diagenetic materials came from detrital volcanic grains, and the key to extent of diagenesis may be in the amoung of dissolution of these grains.
Control of diagenesis by depositional environment within a fluvial sandstone sequence in the northern North Sea Basin
Authors: Taylor J. C. M.
Published: December 2007

Mesozoic sandstones cored in a well in the northern North Sea Basin show at least 78 superimposed fining-upward units varying from about 1 to 5 m thick, interpreted as fluvial deposits. Repetitive fluctuations in cementation, porosity, and permeability were controlled directly or indirectly by conditions during and soon after deposition. At the base of each unit poorly sorted sandstones bearing shale clasts tend to be cemented by early diagenetic dolomite and have relatively low porosity and permeability. Above them, well-sorted fine- to medium-grained cross-bedded sands forming the major part of each unit contain little dolomite and are moderately porous and permeable. At the top of each unit, ripple-bedded micaceous sands have low porosity and permeability because of their silt and clay content. Authigenic clay may be present in all parts of the units, but is particularly prominent as a thin layer around detrital grains in the clean non-dolomitic sands forming the centre of each unit where it inhibited later quartz overgrowths; lacking the support of cements or matrix, these sands were the most susceptible to compaction on deeper burial.
Rb-Sr whole-rock age determination of the Jersey Andesite Formation, Jersey, C.I
Authors: Duff B. A.
Published: December 2007

A whole-rock Rb-Sr isochron age of 533±16Ma determined for the Jersey Andesite Formation is interpreted as the age of crystallization, and suggests that Upper Brioverian sedimentation continued into the Cambrian. It provides a maximum age limit of Middle Cambrian for the late Cadomian molasse-type Rozel Conglomerate, and supports the existence of a late orogenic (post 533±16Ma) phase of Cadomian deformation, which was followed by molasse sedimentation. There are, therefore, at least two separate phases of Cadomian deformation in the northern part of the Armoricain Massif, the previously recognized earlier event being late Precambrian in age.
Orthopyroxene development in crustally deformed peridotites
Authors: Brodie K. H. , White S. H.
Published: December 2007

The development of ortho-enstatite from olivine has been observed in sheared peridotites and in basalt xenoliths, presumably due to the introduction of a silica–rich fluid phase into the rocks under crustal conditions; deformation appears to enhance the reaction. Care must be taken when using defect structures in orthopyroxene to determine mantle deformation conditions and mechanisms as not all grains are of mantle origin.
Analysis of mesoscopic fractures in the Dhruma-Nisah segment of the central Arabian graben system
Authors: Hancock P. L. , Kadhi A.
Published: December 2007

The central Arabian graben and trough system is a 560 km arcuate intraplate fault zone cutting gently tilted Mesozoic-Cenozoic sedimentary rocks in eastern Saudi Arabia. The mesoscopic fracture pattern in the 150 km Dhruma-Nisah segment provides an excellent example of extensile brittle deformation, and is also of interest because palaeostress trajectories inferred from it suggest that the segment evolved as a result of early Cenozoic stretching of the Mesozoic cover above a major fault zone in the crystalline basement.

The ten sets of vertical or high-angle joints, veins, and small faults are arranged symmetrically about the
en echelon
graben. During the development of the five sets comprising System 1 there was elongation perpendicular to graben and the formation of a single set of extension fractures, and two subsystems of small dihedral angle sets in the shear-extension fracture transition. System 2 resulted in elongation parallel to graben, and consists of a single set of extension fractures plus a pair of small dihedral angle sets. Conjugate shear sets enclosing a large dihedral angle form System 3. All sets developed during several episodes of fracturing. The range of conjugate angles is attributed to variations in rock strength, differential stress and fluid pressure.
Mesozoic–Cenozoic metallogenesis in Iran
Authors: Förster H.
Published: December 2007

A short description of the regional geology of Iran is followed by new data concerning grade of metamorphism, palaeomagnetism, continental drift and radiometric age determinations.

Mineralization in Iran is considered in terms of four metallogenic epochs: Lower and mid-Cretaceous lead-zinc deposits in limestones, late Cretaceous chromium, copper and manganese associated with ophiolites, early Tertiary copper veins, skarns and porphyries and late Tertiary and Pleistocene porphyry copper deposits and lead-zinc veins.

Eight areas are examined as regional exploration targets. In the Yazd-Golpaigan area Lower and mid-Cretaceous stratabound lead-zinc ores of Mississippi Valley type are associated with magmatism related to the initial rifting of Gondwanaland. In western Azerbaijan Upper Cretaceous chromite ores in serpentinised dunite are regarded as part of a plate boundary environment. In northern Azerbaijan Oligocene granodiorite intrusions, related to porphyry copper deposits in Russia, have given rise to copper-molybdenum skarns. The Sabzevar zone is thought to be a 200 km wide area of oceanic crust. Cretaceous ophiolites with chromite deposits occur in its northern part, while the southern part contains chalcopyrite and pyrolusite ores in submarine lavas and sediments and low grade copper ores associated with Eocene island arc volcanism. Eastern Lut contains Cretaceous chromite deposits and lead-zinc-copper-gold veins possibly related to Plio-Pleistocene intrusions. The Neogene-Pleistocene portion of the central Iranian volcanic belt is a chain of large stratovolcanoes and granodiorite intrusions, apparently fault-controlled, which includes important porphyry copper deposits. The Oligocene volcanics of western Alborz contain veins with galena, sphalerite and chalcopyrite and a large hydrothermal alunite deposit. The flows and tuffs are intruded by granodiorite, granite and monzonite, with potential for porphyry-type copper ores.
Emplacement and crystallisation of minor intrusives
Authors: Upton B. G. J.
Published: December 2007

A joint Tectonic Studies Group and Volcanic Studies Group meeting was held at the Department of Geology, University of Edinburgh on 20 May 1977, for the purpose of exploring the common ground between structural and petrological/volcanological interests in the subject of minor intrusives.

In the course of the eleven papers presented a wide range of ground was covered although, not surprisingly, the problems associated with the intrusion and congelation of basic magmatic sheets occupied the greater part of the meeting. By way of contrast, however, two of the papers presented were directed towards the deformation phenomena within and around granitic intrusions.

Basic sheet swarms were considered from a diversity of viewpoints ranging from petrochemical to structural. G. P. Durant highlighted the wide compositional range from transitional basalt to trachyte within the Islay and Jura dyke swarms and concentrated on their penological relationships. T. J. Halsall demonstrated that, from a detailed study of the south Arran dyke swarm, it is possible to recognise a sequence of emplacement episodes within which the change of magma type is a reflection of changing stress patterns. M. K. Wells, speaking of the Centre 2 intrusions of Ardnamurchan, indicated how the processes of cone-sheet intrusion, gabbro emplacement and updoming were intimately inter-related processes associated with the lateral spread of magma from a central feeder system. In a detailed treatment of the emplacement and crystallisation of a single sheet intrusion (the Dippin sill, Arran), F. G. F. Gibb and C. M. B. Henderson discussed the role of crystal fractionation
Late Precambrian sedimentary rocks in East Finnmark, north Norway and their relationship to the Trollf jord-Komagelv fault
Authors: Johnson H. D. , Levell B. K. , Siedlecki S.
Published: December 2007

The late Precambrian sedimentary rocks of the Varanger Peninsula, north Norway, occur in the Tanafjord–Varangerfjord (autochthonous) and Barents Sea (allochthonous) regions. The autochthonous region includes 4-5 km of shallow water clastic sediments with subordinate carbonates and also tillites, of late Precambrian (Upper Riphean) to Tremadocian age. The allochthonous region includes about 14 km of deep and shallow water clastic sediments with subordinate carbonates, all of Precambrian age. On Varanger Peninsula these two regions are always separated by a major strike-slip tectonic disturbance, the Trollfjord–Komagelv fault. This is a single, high-angle fault in Inner Varanger Peninsula, but in the Trollfjordalen–Lille Molvik area a braided fault pattern occurs in which an early trace of the Trollfjord-Komagelv fault has been later folded and faulted. Some structural observations support strike-slip movement along the Trollfjord-Komagelv fault, while comparison with recent strike-slip fault zones suggests that the folded fault in the Trollf jordalen-Lille Molvik area represents an inactive, curved fault trace which was abandoned and subsequently tightened by (? Caledonian) folding.

Stratigraphic and structural data support recent geochronological and palaeomagnetic results which suggest the geological separation of the two regions during their deposition and perhaps during their principal deformations.
Ultramafic and mafic nodule suites in shield-forming lavas from Mauritius
Authors: Baxter A. N.
Published: December 2007

An ultramafic-mafic suite of nodules characterises the basic-intermediate shield-forming lavas on Mauritius. A close mineralogical coherence is seen between highly porphyritic host lavas and nodule type, with peridotite occurring only in picrite basalt, olivine gabbro in olivine basalt, bytownite anorthosite and feldspathic gabbro in feldspar-phyric basalt, and kaersutite gabbro, labradorite-andesine anorthosite and titanomagnetite-pyrrhotite assemblages in hawaiite.

Prominent layering fabrics, crystallisation sequences, variations in chemical mineralogy and in mineral assemblages, together with phase equilibria constraints suggest that the nodules are derived from a compositionally and cryptically layered cumulate sequence which crystallised in a subjacent magma chamber at depths of 5–10 km (1.5–3.0 kb). The extensive development of kaersutite-rich assemblages and of marked compositional reversals in plagioclase is interpreted as evidence for the development of significantly hydrous conditions in the magma chamber by the hawaiitic stage of evolution. Combined olivine-clinopyroxene and plagioclase geother-mometry calculations suggest temperatures of c. 1000°C with P

H
2
O

/P
Tot
ratios possibly fluctuating between 0.5–1.0 at this stage.

Fractionation of kaersutite-rich assemblages is thought to have maintained the transitional character of the magma until the final stages of evolution. The mineralogical coherence of the nodule/lava association indicates a simple model of magma chamber evolution. A process relating eruption of phenocryst-enriched magma from close to the magma/cumulate interface, with possible incorporation of unconsolidated crystal mushes, and elutriation of only the highest, most recently consolidated cumulates is proposed.
Ore forming processes
Authors: Evans A. M.
Published: December 2007

THE MINERAL DEPOSITS STUDIES GROUP held its third residential conference at Sheffield University from 10 to 14 December 1977. Following two days' field excursions examining mineralization in northern Derbyshire twenty papers were presented by Group members. All but two were dominantly concerned with ore genesis and the majority of these dealt with deposits in the British Isles, four of them with Irish mineralization. A. M. Boast presented textural and isotopic evidence showing that much of the material, particularly the sulphur, of the Tynagh deposit was of synsedimentary origin. The weight of evidence for this and similar Irish ores undoubtedly suggests a very early time of deposition and M. J. Russell favoured a synsedimentary origin for all the larger Irish base metal deposits in the Lower Carboniferous. He discussed a mechanism whereby circulating sea water could have leached the metals from buried Lower Palaeozoic rocks. J. P. N. Badham put forward a fresh interpretation of the stratigraphy of the mineralized zones at Avoca and suggested that the stockwork feeder zone, a further possible orebody, has yet to be found. P. McArdle's work on Donegal base metal mineralization also suggests a revision of exploration philosophy in that he demonstrated that deposits in the Dalradian were originally of stratiform type.

Rock alteration processes in two very different environments and their relationship to mineralization were discussed by five workers. D. H. M. Alderton presented an excellent documentation of wall rock alteration assemblages developed in the Cornish granites. He made considerable use of isotopic and
Trace element studies of the origin of igneous rocks
Authors: Rea W. J.
Published: December 2007

TRACE ELEMENT STUDIES are increasingly important in igneous petrogenetic investigations in as much as they place constraints on possible modes of origin of igneous rocks and also give evidence of the nature and composition of the mantle/crust systems within which magmas are generated and modified.

The conference saw trace element studies applied to a wide range of igneous rock compositions, occurring within a wide range of environments. Four papers were concerned with areas in which basalt lavas predominate, i.e. Mull (Beckinsale
et al.),
the islands associated with the axial trough of the Red Sea (Henderson & Parry), the East Scotia Sea (Saunders & Tarney) where basalts are generated within an intra-oceanic marginal basin and the South Shetland Islands and Antarctic Peninsula (Weaver
et al.)
where different periods of magma genesis have been related to subduction and extension. Other papers dealt with metabasalts from ophiolite complexes (Pearce), K-rich volcanics (Parker), diorites and granodiorites (Brown
et al),
granites and charnockites (Petersen) and the ultramafic to granitic rocks of the Fongen-Hyllingen Gabbro Complex (Esbensen).

An important recent development in geochemistry has been to extend the range of material which can be usefully analysed. For example, important petrogenetic information is now being obtained from altered and metamorphosed igneous rocks using ratios based on trace elements such as Ti, Zr, Y, Nb, P, Ce, Sm, Yb, abundances of which appear to be unchanged by secondary processes (Pearce). Volcanic rock geochemistry, which until recently was virtually synonymous with lava geochemistry, has now expanded its scope to
The Finnmarkian phase of the Caledonian Orogeny
Authors: Sturt B. A. , Pringle I. R. , Ramsay D. M.
Published: December 2007

The Kalak nappe complex of N Norway involves late Precambrian to Middle Cambrian sediments and a Precambrian gneiss basement on which the sediments were deposited. While the uppermost nappe in Finnmark was emplaced during the Silurian the members of the Kalak nappe complex were emplaced in late Cambrian/early Ordovician times during the Finnmarkian orogenic stage—probably the analogue of the Grampian stage of the British Caledonian. The tectonic-metamorphic events of the Finnmarkian stage were broadly coeval with the emplacement of basic and alkaline igneous bodies of the Seiland Igneous Province which were introduced from 552 ± 17 Ma (syn-D1) until 501 ± 27 Ma (late D2) and which themselves reflect magmatic evolution from tholeiitic to alkaline types.
Discussion on pressure solution
Authors: Beach A. , King M.
Published: December 2007

The papers contained in Vol. 135, Part 1, represent a considerable advance in knowledge of the diagenesis of sandstones. The importance and nature of mineral reactions (e.g. replacement of feldspars, modification of clay minerals) and the role of pressure solution during diagenesis, are repeatedly discussed. However, on reading the terminal written discussions to these papers, one finds some misunderstanding about the exact meaning and nature of pressure solution. Our aim is to clarify this misunderstanding by examining the mechanism of pressure solution during the diagenesis and deformation of terrigenous sediments.

In theoretical studies (
Rutter 1976
,
de Boer 1977
), pressure solution is defined as the transfer of material by diffusion through an intergranular pore fluid phase in response to stress gradients around grains. A stress gradient gives rise to a gradient in chemical potential, and diffusive transfer of material from the point of high stress to that of low stress occurs to dissipate this gradient. The distance of diffusion will be determined by
(a)
the scale on which the stress gradient is developed, and
(b)
the kinetics of intergranular diffusion (
Rutter 1976
). Stress gradients may arise in sediments through
(i)
the generation of heterogeneous stresses at point contacts of detrital grains, leading to a variation in normal stress around a grain surface, and
(ii)
the formation of gradients in mean stress through a rock in relation to the regular development of sedimentary or tectonic structures (cusps, nodules, spaced cleavages, folds, etc.).

A relation between the extent of pressure solution (as recorded
Palaeontological evidence for the age of some supposedly Precambrian rocks in Anglesey, North Wales
Authors: Muir M. D. , Bliss G. M. , Grant P. R. , Fisher M. J.
Published: December 2007

The supposed worm burrows from the South Stack Group have been interpreted as dewatering structures. The stromatolites from the melange are identified as the Vendian–Cambrian form
Georginia
, and microfossils from the Lianddwyn Spilitic Group give a Lower Cambrian age for the Gwna Group.
Mesozoic cherts on crystalline schists in Sulawesi and Timor
Authors: Haile N. S. , Barber A. J. , Carter D. J.
Published: December 2007

In both Sulawesi and Timor Mesozoic cherts rest unconformably on metamorphic schists and gneisses. These occurrences are unusual in that radiolarian cherts are commonly associated with ophiolites, pelagic sediments or turbidites. No other occurrences are known where such cherts rest directly on rocks of continental derivation. These two occurrences are now separated by a distance of 900 km. According to some plate-tectonic hypotheses for the region, Sulawesi and Timor were juxtaposed during the Mesozoic and were subsequently separated by the development of the marginal Banda Sea during the Tertiary. These now widely separated occurrences lend support to this interpretation.
Catastrophic lake drainage in Glen Spean and the Great Glen, Scotland
Authors: Sissons J. B.
Published: December 2007

The 260 m ice–dammed lake in glens Spean and Roy finally attained a volume of 5 km
3
. It is suggested that it was initially drained subglacially and catastrophically through the Spean gorge and Loch Ness. Maximal flow of water may have been about 22,500 m
3
s
−1
. In Glen Spean the ice dam, 7 km long and up to 200 m high, collapsed. Near Fort Augustus a vast deposit of sand and gravel was laid down in relation to a Loch Ness suddenly raised in level. Subsequently, the level of the Spean–Roy lake varied constantly as it was intermittently emptied by other sudden floods of lesser volume, some of which followed the Lundy gorge and one of which produced a now abandoned waterfall site near Loch Lochy. Some of these events are related to the formation of end moraines and fluvial terraces in the area around Spean Bridge and Gairlochy.
Assessing volcanic risk
Authors: Booth B.
Published: December 2007

The assessment of volcanic risk is vital in areas of social and/or economic importance. Volcanic risk is denoted by the probability that an event of a certain type and magnitude will occur within a specified time period and will affect a designated area, and is a factor which must be evaluated with regard to the different types of volcanic hazards and their various degrees of severity. New methods for the presentation of data in volcanic hazard and risk maps are introduced, and proposals are made for high-risk areas, especially those where volcanoes have particularly long repose periods.
A Grenville age for pre-Caledonian rocks in NW Co. Mayo, Ireland
Authors: Max M. D. , Sonet J.
Published: December 2007

Pink Gneisses at Erris Head in NW Co. Mayo, Ireland have yielded a Rb-Sr whole rock age of 1070±70Ma (λ
87
Rb = 1.42×10
–
11
year
–
1
). Interbanded Grey Gneisses show a somewhat younger but probably related age with a slightly higher
87
Sr/
86
Sr initial ratio. Isotopic homogenization appears to have been locally controlled by lithology, with the mineralogically more stable suite of tectosilicate-rich gneisses giving the older age. The ages of these 2 main components of the Annagh Gneiss unit at Erris Head may reflect a reworking event rather than the formation of the gneisses as there is evidence locally for a lengthy, tectono-thermal history.

At both Erris Head and nearby Cross Point, K-Ar whole rock analyses of the same specimens confirm a metamorphic overprint which is consistent with an early Caledonian metamorphic history seen in the adjacent Moine and Dalradian rocks.
Teaching mineral deposit geology
Authors: Evans A. M.
Published: December 2007

T
here has been
a gradual trend during the last two decades towards the inclusion of more applied geology teaching in geology courses at British universities and polytechnics. This period has also seen the establishment of a number of applied geology degrees at both undergraduate and graduate levels. Clearly there is a new awareness in academic circles that all degree courses should contain a significant element of vocational training and the response of industry to the new applied courses indicates that they are filling a real need. It was therefore apposite that the Mineral Deposits Studies Group, in conjunction with the Earth Science Education Group, should organize a conference at which both industrial and academic geologists could take stock of the current situation in the teaching of mineral deposit geology.

As an aid in this assessment, Taylor had circulated 50 departments with a questionnaire. This was kept simple to encourage replies, which had been received from 28 departments. It is impossible to tell whether or not these were mainly from those who had something positive to report, and therefore there may be a degree of bias in the returns. The substance of the replies is summarized in the abstract and indicates that there is still very little or no teaching of mineral deposit geology in some departments. One of the interesting and valuable trends which emerges from this inquiry is the increasing inclusion of time spent on industrial mineral deposits in undergraduate courses. This was reflected by Dixon and by Steed
Comparison between Sumatra and the Andes
Authors: Cobbing E. J.
Published: December 2007

The geology of Sumatra presents many similarities to the Mesozoic belt of the northern Andes and some to the central Andes, in features such as paired geosynclines, composition of volcanic material, of intrusives, presence of ultramafic bodies, major faults and structures. This suggests that the fundamental tectonic control of a subducting oceanic plate beneath a sialic continental margin produced broadly comparable results in 2 widely separated areas. Substantial differences also exist, e.g. the widespread presence of marginal basins in SE Asia, their absence in the Andes, and the superabundant granitoid plutonism of the central Andes compared to that of Sumatra.
A model for the interpretation of wave ripple-marks using their wavelength, textural composition, and shape
Authors: Allen J.R.L.
Published: December 2007

Two graphs based on field and experimental data assembled from a variety of sources are given showing how the wavelength, flatness (vertical form-index or ripple index), and grain size of wave ripple marks in the stratigraphic record can be interpreted in terms of the near-bed water particle orbital diameter and maximum orbital velocity induced by progressive surface waves. The graphs lead to estimates of wave period, from which the environmental setting and possible water depths and wave heights can be judged. Wave ripple-marks are the response of a mobile bed to multi component currents that are more complex than is generally recognized. The asymmetry and slow translation of the structures is shown empirically to depend on the relative importance of 2 of the 3 minimum recognizable components.
The Ophiolite Mélange of Masirah, Oman
Authors: Moseley F. , Abbotts I. L.
Published: December 2007

The Masirah Ophiolite consists of serpentinites, gabbroic intrusions, an extensive sheeted dyke complex, pillow lavas, and sediments. It is truncated to the W by a NNE-trending, 5 km wide vertical mélange zone: a megabreccia with blocks up to 2 km long of all the above lithologies. The mélange trend is perpendicular to that of the sheeted dyke complex, a common relationship between a transform fault and spreading centre. Many of the features of the mélange can be explained by serpentinite diapirism along a major ocean crust fracture. However, the distribution of other reported ophiolites along the SE coast of Arabia and the intrusion of the Masirah Ophiolite by granite, whose geochemistry indicates melting of continental crust, both suggest upthrust of ocean crust onto the Arabian continent.

The Masirah Mélange and the dyke trends within the ophiolite are parallel, respectively, to the Owen Fracture (and other transforms) and to magnetic anomalies in the Indian Ocean. It is suggested that both mélange and ophiolite are related to a late Cretaceous stage in the evolution of the Indian Ocean, and may not correlate with the Semail Ophiolite of the Oman Mountains, as has been previously supposed.
The Loch Doon granite: an example of granite petrogenesis in the British Caledonides
Authors: Brown G. C. , Cassidy J. , Tindle A. G. , Hughes D. J.
Published: December 2007

The Loch Doon igneous complex lies to the N of the Solway–Shannon Iapetus Ocean suture line through the British Isles, but in a region lacking the Proterozoic continental basement which is known to exist further N. It comprises a genetically related magma suite ranging from hypersthene diorite margins through quartz monzonite to granite at the centre. Petrochemical data, studies of xenolith and autolith densities and field radiometric mapping indicate that the suite lacks sharp internal boundaries but is gradational and based on a monzodiorite parental magma which evolved through a two-stage crystal fractionation process. The early crystallization of dioritic margins was dominated by pyroxene-plagioclase precipitation and these minerals were joined later by biotite as acidic residual liquids developed. Biotite formation and fractionation at the expense of pyroxenes is related to contamination of the magma by water from the roof zone. Partial assimilation of roof material, particularly in the form of xenoliths, and mixing between cumulates and residual liquids are also recognized but are of relatively minor importance.

These petrochemical, geophysical and isotopic studies of the Southern Uplands granites indicate the generation of parental magmas by the partial fusion of metabasaltic lower crust or crustal underplate as a late event in the evolution of the Iapetus Ocean.
Environmental events recorded in Quaternary sediments of the Black Sea
Authors: Degens E. T. , Stoffers P.
Published: December 2007

Stratigraphic correlation of Quaternary Black Sea basin sediments reveals an upper terrigenous and a lower chemical facies. The last 3 glacial periods (Weichselian, Saalian, Elsterian) produced the top terrigenous section. Older glacial incidents yielded varved clays and seekreide. Interglacial events are registered in the form of sapropels, bituminous megavarves and oil shales. Sapropel intercalations are restricted to the terrigenous upper section and oil shales to the lower chemical one. The bituminous megavarves deposited in Cromerian time can be considered an intermediate between sapropel and oil shale. The above facies pattern is caused by 3 principal factors: (
i
) tectonic forces, (
ii
) water depth (= distance from shoreline), and (
iii
) mid-water stratification. Rapid tectonic subsidence, starting during the Cromerian and still active today, transformed the old Quaternary shallow water Black Sea into its present +2000m deep water basin. Mid-water stratification produced by salinity or temperature gradients triggered a periodic decoupling of the upper from the lower water layer and created in due course a meromictic environment. The shallow meromictic sea produced oil or black shales, whereas sapropels formed in anoxic deep water; megavarves represent a transtional facies.
Rb-Sr dating of the Plouézec volcanics, N Brittany: implications for the age of red beds(‘Series rouges’) in the northern Armorican Massif
Authors: Auvray B. , Mace J. , Vidal Ph. , Vander Voo R.
Published: December 2007

The whole-rock Rb-Sr isochron date of 472 ±5 Ma obtained on the Plouézec volcanics, N Brittany, is interpreted as an emplacement age and thus indicates that the 'Séries rouges' in the Bay of St Brieuc (including probably the Erquy-Fréhel Group as well), generally considered to be the equivalent of the Old Red Sandstone, is in fact of Lower Palaeozoic age.
The stratigraphy and structure of the Moine rocks N of the Schiehallion Complex, Scotland
Authors: Thomas P. R.
Published: December 2007

Sedimentary structures are used to establish a 'Younger' Moine stratigraphical succession in Strathtummel. Polyphase re-folding of the Moine sequence between Schiehallion and Drumochter can be clearly subdivided into primary and secondary deformations. Primary NE-SW trending deformational events D
1
and D
2
include the formation of the south-eastward facing D
1
Atholl nappe re-folded by strongly overturned D
2
folds which become upright on the crest of the Drumochter dome. Secondary deformation resulted in D
3
(oblique) and D
4
(transverse) major folds, both of which plunge into the SE quadrant.
Tertiary volcanism in northern E Greenland: Gauss Halvø and Hold with Hope
Authors: Upton B. G. J. , Emeleus C. H. , Hald N.
Published: December 2007

Subaerial plateau basalts, initially
c
. 1 km thick, overlie Cretaceous or older formations and are locally separated from pre-Tertiary rocks by (
a
) a quartzitic conglomerate and (
b
) a (younger) sequence of tuffaceous sediments and hyaloclastites. The plateau lavas are divisible into a Lower (typically microphyric, quartz tholeiitic) Series and an Upper (typically porphyritic, olivine tholeiitic) Series. N–S and NE–SW trending antithetic faults give rise to ocean-facing fault-line scarps and landward-facing dip slopes. Dolerite sills, abundant beneath the lava pile, occasionally cut the Lower Series lavas. While dykes trend in various directions, a very prominent NE–SW swarm (mainly quartz tholeiitic) traverses Hold with Hope, deflecting to more nearly N–S across Gauss Halvø.

A large volcanic centre (Myggbukta Complex) lies across the main dyke swarm in the vicinity of the deflection and may be genetically related to the swarm. The complex involves propylitized basaltic, rhyolitic and intermediate lavas and pyroclastic rocks, together with volcanogenic sediments, cut by a profusion of basic to acid intrusive sheets. Formation of this complex at a late stage in the volcanic history of the region was attended by subsidence and crustal down-sagging. The main dyke swarm, whose trend roughly parallels that of the spreading axes N and S of the Jan Mayen Fracture Zone, may reflect subordinate rifting to the W of the principal rift zones along which spreading was taking place.

30 km E of Myggbukta, the Kap Broer Ruys granophyre/felsite is a partially unroofed intrusion around which a broad metamorphic aureole has been superimposed on the Mesozoic and Tertiary sediments and lavas. The southern coastal region of Hold with Hope, connecting the Myggbukta and Kap Broer Ruys centres, may indicate a zone of crustal weakness which determined the initiation of the Jan Mayen Fracture Zone.
Environmental and health consequences of shale oil production in the U.S.A.
Authors: Chappell Willard R.
Published: December 2007

Oil shale is one of the world's most important energy resources. The world resource of oil shale is estimated to be 1500 trillion (15 × l0
14
) short tons with an energy content of approximately 10
16
barrels. A rich oil shale will yield 30–40 barrels of oil/ton of oil shale. A million barrel per day industry would require the processing of approximately 5 × 10
8
tons/yr of shale (a single plant would process 25 × 10
6
tons/yr). Interdisciplinary research being conducted to determine the potential impact of such a large industry on human health is described, in such areas as release of suspected carcinogens and toxic trace metals, worker safety, and exposure to oil, gas, and water. Research by other groups in the U.S. working on this important issue is also summarized.
Microstructural contrasts between some sedimentary francolites
Authors: Hewitt R. A.
Published: December 2007

Phosphatic nodules contain early diagenetic francolite cements and carbonate replacements. Lower Cambrian phosphatized carbonates are composed of granular and mammillated fabrics. They show large (112) X-ray diffraction peaks, and probably consist of fluorapatite. Granular and prismatic francolites are found in concentrically banded nodules from the Lower Lias (Lower Jurassic) of Blockley, England. They are interpreted as originally phosphatic burrows. The francolite microstructures of
Lingula, Linnarssonia, Micromitra, Hyolithellus, Torellella, Serpuloides, Trachyteuthis
and Mesozoic teuthids, contain variably recrystallized granules and needles.
Intraclast and pellet phosphorite sedimentation in the Miocene of Florida
Authors: Riggs Stanley R.
Published: December 2007

The structural framework of the Florida peninsula produced an extensive system of coastal, shallow nearshore shelf and platform marine environments which controlled Miocene phosphorite formation, deposition, and accumulation. Microsphorite-intraclast sedimentation was dominant within the inner perimeter belt around the Ocala Upland, and pelletal phosphorite sedimentation in the outer belt, down the depositional slope and offshore from the Ocala Upland. Optimum phosphorite formation took place in the coastal and shallow platform environments. The resulting intraclastic and pelletal phosphate grains were then transported as clastic particles alone and off the shoals, diluted by the associated terrigenous and dolomitic sediment, and deposited in basins on the structural highs, on the flanks of the structures, and in adjacent deeper basinal environments.
Phosphate peloids from the Negev phosphorites
Authors: Soudry D. , Nathan Y.
Published: December 2007

The most common components of the Negev phosphorites are phosphate peloids (undifferentiated brown ovoid grains lacking internal structure). A systematic study of these peloids indicates that they are the result of convergent diagenetic processes, the more important being: 1, growth around a foreign grain (usually a foraminifer); 2, phospho-micritization of bone fragments; 3, fragmentation and abrasion of intraclasts (laminated and unlaminated); 4, pelletization of aggregates; and 5, phosphatization and fragmentation of faecal pellets. The Negev 'pelletal phosphorites' (as well as others), and what the French call 'phosphate sableux' are therefore the products of diagenesis.
Concretionary phosphorite from SW Africa
Authors: Bremner J. M.
Published: December 2007

Phosphorite concretions, fish debris, quartz, rock fragments and minor amounts of molluscs occur along the eastern edge of a diatomaceous mud belt off the coast of SW Africa (Namibia). The concretions consist of light- and dark-coloured coprolites and dreikanters, predominantly of pebble and granule size; and irregular, tabular, and oval to spherical particles that predominante in the granule to very coarse sand fractions. Only the dark-coloured concretions were analysed geochemically, and these consist of francolite with minor amounts of Si, Al, Fe and K. The most abundant trace elements present are Sr, Zn, Ba and Th.

The interstitial fluids of the diatomaceous mud are supersaturated in phosphate along the landward flank of the mud belt, and this causes slow precipitation of apatite on diatom frustules. Concurrently, the fluids enhance the elimination or replacement of allogenic impurities from the concretions through diagenesis. Adsorption of phosphate by slow-settling mica–illite is a possible mechanism by which the phosphate concentration of the interstitial fluids is raised.
Devonian lake margin environments and processes, SE Shetland, Scotland
Authors: Allen P. A.
Published: December 2007

The Devonian lake or lakes of SE Shetland were characterized by 4 environments: (1)a marginal environment dominated by the high energies of the surf zone and just lakeward of the breaker zone; (2) an additional marginal environment consisting of small, shallow, oxidizing lakes on a low-gradient coastal flood plain over which waters from the main body of the lake fluctuated; (3) an intermediate environment characterized by continuous to intermittent wave agitation, in water depths of probably <5 m; and (4) an offshore environment characterized by a lack of evidence for current or wave action, at depths of >5–10m.

The marginal environment was influenced by both wave and current processes. A friction dominated outflow produced sedimentary structures that indicate a south-easterly flow and depositional slope. Outflow competed with shoaling waves which advanced from E to W onto the lake shoreline. Where outflow was weakest, wave processes dominated. Longshore drift was an additional component in the movement of the nearshore waters. The Devonian lake or lakes of SE Shetland possessed rather shallow shoaling margins.