bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geothermometry and geobarometry of inverted metamorphic zones in the W central Scottish Dalradian
Authors: Watkins Keith P. 
Published: December 2007

The attitude of the garnet isograd surface in the Balquhidder region of the Scottish Dalradian is such that the metamophic zones must be inverted, higher-grade rocks overlying lower-grade rocks. Textural and structural information indicates that peak Barrovian metamorphism post-dates emplacement of the Tay Nappe. As post-metamorphic folds are open and upright, no tectonic means of overturning the isograd surface can be invoked. Metamorphism must have occurred in a negative thermal gradient.
The metamorphic temperature at the garnet isograd is about 500°C and increases along a negative metamorphic gradient, perpendicular to the isograd surface, of about 27°C/km. Metamorphic pressure is about 9 kbar.
The initial temperature inversion was probably caused by emplacement of the Tay Nappe. It is unlikely that subsequent conductive thermal relaxation alone would have caused inverted metamorphic zonation. However, the relaxative process may have been sufficiently modified, by convective transfer of heat by fluid evolved from metamorphic reactions, for this to occur.
Northern Scotland as an Atlantic–North Sea divide
Authors: Watson Janet 
Published: December 2007

President's anniversary address 1984

From the end of the Caledonian orogeny until the present, northern Scotland has acted as a structural high separating the North Sea and Atlantic basins or their forerunners. The geological history of this positive massif is discussed in relation to that of the adjacent cratonic basins, with the objective of determining the extent to which it adapted to regional tectonic developments and the manner in which its responses were modified by the pre-existing basement structure.
From Devonian to early Palaeocene times, the massif was generally low-lying and its behaviour with respect to vertical movements was essentially neutral. The land surface carved in the crystalline basement during the Devonian period was preserved with relatively small modifications and little metamorphic detritus was supplied to the adjacent basins. Tectonic events of major importance in the basins, such as the formation of the North Sea and Hebridean rift systems, produced little change of conditions in the intervening massif. It is inferred that the underlying keel of lithospheric mantle was protected from the effects of lithospheric stretching.
The uneventful history of the massif was interrupted by two phases of mafic igneous activity—in late Carboniferous and Palaeocene times—which record responses to regional plate motions. The formation of the Palaeocene igneous province was followed by a unique phase of uplift as a result of which the ancient sub-Devonian land surface was elevated and dissected and abundant crystalline detritus was supplied to the North Sea. The style of these events and the anomalous character of the continental margin off NW Britain may have been determined by the refractory nature of the Precambrian basement which inhibited stretching prior to sea floor spreading.
Alkaline igneous rocks: a review symposium
Authors: Fitton J. G. , Upton B. G. J. 
Published: December 2007

Report of a meeting of the Volcanic Studies Group of the Geological Society held at Heriot-Watt University, Edinburgh, on 13–16 September 1984. The organizers were Dr J. G. Fitton and Professor B. G. J. Upton. The papers presented at the symposium will be published as a Special Publication of the Geological Society.

The symposium was held to mark the passage of 10 years since the publication of the review volume The Alkaline Rocks, edited by Henning Sørensen, who opened the meeting and presented a summary of the proceedings at the end. Two and a half days were devoted to the presentation of papers and one and a half days to local field excursions. The meeting was well attended with about 150 delegates, 60 of whom were from overseas. In addition to the 30 papers presented there were several poster displays.
Presentations included specific case histories of individual alkaline volcanoes and regional reviews of alkaline rock occurrences in both continental and oceanic settings. Reviews were presented of the occurrence of various alkaline associations, including kimberlite, lamproite, lamprophyre, nephelinite, and carbonatite, and the impact of isotopic and experimental petrological studies on the subject was emphasized.
Alkaline magmas are characterized by high concentrations of large-ion lithophile elements (LILE). The causes of this have been the subject of debate over the past decade, with metasomatic enrichment of the mantle source before melting being a currently favoured hypothesis. Studies of mantle enrichment and melting processes are clearly essential to an understanding of alkaline magma
U-Pb Isotopic evidence for the accretion of a continental microplate in the Zalm region of the Saudi Arabian Shield
Authors: Stacey J. S. , Agar R. A. 
Published: December 2007

The area covered by this work includes three of the main tectonic units of the Arabian Shield: the Afif continental terrain, the Nabitah suture with its associated mobile belt, and the Asir ensimatic arc terrain. The geology of the Zalm area is well understood, and this geochronologic and isotopic study confirms that the southern Afif terrain was a continental microplate in the late Proterozoic. The study also provides a time frame for the crustal evolution of this part of the Shield.
The Kabid formation is the oldest in the region and comprises pelitic, arkosic and felsic high-grade paragneisses. U-Pb zircon data from a pelitic garnet-sillimanite gneiss show that this part of the continental basement in the southern Afif terrain may be as old as 1770 Ma. Isotopic nalyses indicate that lead from the Kabid gneiss resided in the upper continental crust for a long period before 1770 Ma, and consequently Archaean source rocks may be present within the southern Afif terrain.
Pb and Rb-Sr isotopic data in the Zalm region reveal a change in the nature of the underlying crust, from continental basement in the northeast, to less radiogenic marginal arc rocks in the southwest. This change is coincident with both aeromagnetic data, and a facies change within a pre-collision marginal basin. Miogeosynclinal continental shelf facies of the Siham group lie unconformably over the Kabid formation, and are in the area of continental lead signatures. Eugeosynclinal deep water sediments and volcanics, in association with ultramafic rocks, occur in the area of marginal arc signatures.
U-Pb zircon age determinations show that this 'Andean' continental margin developed before about 720 Ma, and emplacement of calc-alkaline plutonic rocks continued until about 690 Ma. During the period 685-640 Ma, the continental Afif microplate collided with the Asir terrain as part of the Nabitah orogeny. At approximately 640 Ma ago, the Najd strike-slip faulting commenced with a dextral phase that controlled the emplacement of granitic plutons as well as the development of a series of large pull-apart grabens. Some of these grabens were floored by new oceanic crust and were filled with volcanosedimentary rocks of the Bani Ghayy group. Subsequently, the Najd fault system changed to sinistral strike-slip motion at about 620 Ma ago.
Metamorphic studies: research in progress
Authors: Brodie Kate 
Published: December 2007

Report of a meeting of the Metamorphic Studies Group held at Burlington House, 6 March 1985. The meeting was organized by Dr K. H. Brodie.
A Metamorphic Studies Group Meeting on ‘Metamorphic studies: research in progress’ and the fourth Annual General Meeting of the Group were held on 6 March 1985. Fifteen papers were presented, on a wide range of metamorphic subjects, ranging from very low-grade metamorphism to high-grade granulites and migmatites. Half the papers were presented by research students, and each contribution was followed by lively discussion.
The morning session was chaired by Ben Harte, the retiring Chairman of the Group, and concentrated on high-grade metamorphic rocks, and regional deformation and metamorphism. I. Cartwright presented a joint paper with A. C. Barnicoat which considered reactions within partially melted corundum-bearing metapelites from the Lewisian Complex. They demonstrated that silica-undersaturated restites can co-exist with silica-saturated partial melts under appropriate conditions. This was followed by a contribution from T. F. Emmett on the magmatic and metamorphic evolution of high-grade rocks from the Jotun Nappe in Norway. The Group was then pleased to welcome J. C. Schumacher from the Mineralogisches Institut in Kiel, F. R. Germany, who presented a paper describing microstructural evidence for reactions producing a range of Al-rich assemblages and discussing the relative roles of diffusion versus reaction in controlling the reactions. P. J. Treloar then gave a paper describing some unusual and colourful mineral assemblages from a Cu-Zn massive sulphide body in Finland, where high concentrations of Cr in the
Sedimentation and evolution of the Cretaceous Gyeongsang Basin, southeastern Korea
Authors: CHOI H. I. 
Published: December 2007

The sedimentation and evolutionary history of the Gyeongsang Basin, and their implications for plate tectonics are reviewed based mainly on sedimentological work on the Gyeongsang strata, and the regional geology of the Japanese Islands. During the Cretaceous, E Asia was characterized by an Andean-type continental margin formed by subduction of the Kula plate and Kula–Pacific ridge. The marginal zone was subjected to precursory extensional tectonism of the magmatic arc so that fault-bounded continental depressions developed, including the proto-Gyeongsang Basin.
The Gyeongsang strata (about 9,000 m thick) consist in ascending order of the Sindong, the Hayang with volcanic' stics, and volcanic Yuchon Groups. During the Sindong period extensional tectonism prevailed a the proto-Gyeongsang Basin was a graben occupied by alluvial fan, fluvial plain and lake environments from the margins to the centre of the basin. Streams flowed from the upthrown lip areas to the centre. Alluvial fans expanded periodically with rejuvenation of fault activity, while the fluvial plaid/lake boundary shifted in response to climatic changes.
During the Hayang period the faults were no longer active and consequently the basin extended beyond them (probably by back faulting). The water level of the lake(s) at the basin centre fluctuated with changes of the evaporation/precipitation ratio. During parts of the period, the marginal fluvial plain was drained by ephemeral streams which disappeared before reaching the lake(s), depositing fluvial sequences lacking channel sandstones. Localized volcanism formed volcanic terrains and supplied pyroclastics: this volcanism was climactic during the Yuchon period and terminated the sedimentation. Granitic plutons intruded all the Gyeongsang strata at about the end of the cretaceous.
Glacial sediments and erosional pavements near the Cambrian—Precambrian boundary in western Henan Province, China
Authors: BAODE GUAN , RUITANG W. U. , HAMBREY M. J. , WUCHEN GENG 
Published: December 2007

Exceptionally well-preserved glaciated pavements and a variety of glacigenic sediments comprising the Luoquan Formation in Henan Province, central China, are believed to have formed close to the Cambrian–Precambrian boundary. They may therefore be younger than the better known Sinian tillites representing the Changan and Nantuo ice ages. They perhaps belong to a distinct glacial epoch that is recorded elsewhere in China and in other continents, but for which there is less evidence than for earlier Late Proterozoic glacial periods.
Lithofacies represented in the Luoquan Formation are massive diamictite (signifying deposition as lodgement or melt-out till), bedded diamictite (waterlain till or glaciomarine/glaciolacustrine sediments with dropstones), rhythmites with dropstones (glaciolacustrine or fjord deposits, possibly varves), tabular conglomerates and sandstones (outwash, deltaic or sub-aqueous mass-flow deposits), lens-shaped breccia deposits (sub-aqueous mass-flow deposits) and gravel-sand wedges (frost contraction crack infillings).
The glaciated pavements reveal well-preserved striations, grooves (often intersecting), 'plastically moulded' forms, crescentic gouges and steps. On a regional scale the linear features are of variable orientation, but they indicate a dominant ice flow direction towards the southeast. All this evidence points to upland glaciation with erosion followed by deposition in a terrestrial glacial and glaciolacustrine environment.
Neotectonics
Authors: HANCOCK P. L. , WILLIAMS G. D. 
Published: December 2007

The study of neotectonics is carried out by workers from a wide variety of disciplines, including structural geology seismology, regional geophysics, geomorphology and engineering geology. Landsat MSS imagery is a particularly effective tool for the investigation of neotectonic structures. The aim of the meeting was to bring together workers from the various contributory disciplines in order to discuss the development of modern techniques in each subject area. These modern approaches were exemplified by descriptions of neotectonically active regions ranging from NW Europe to China.
In order to stimulate a debate on the temporal scope of neotectonics, the meeting commenced with a short discussion paper by Hancock. He argued that the selection of an arbitrary Neogene or Quaternary date to be applied globally for the beginning of the period during which neotectonic structures form is unhelpful. He proposed as an alternative the notion that for a given region the neotectonic phase might be regarded as having begun when the present-day configuration of relevant plate boundaries and motions was established.
Blenkinsop suggested modifying Hancock’s proposal by defining the neotectonic phase as having commenced when the contemporary stress field of a region was established. Blenkinsop’s proposal possesses the great practical merit of permitting the geologist to compare regionally significant directions of horizontal compression and extension inferred from structures, known from field evidence to have been active during an appropriate time frame, with those determined from in situ measurements or fault plane solutions.
Recent earth movements give rise to geomorphological features indicative of the
Interpretation of the gravity and magnetic anomalies over the Mull Tertiary intrusive complex, NW Scotland
Authors: BOTT M. H. P. , TANTRIGODA D. A. 
Published: December 2007

A 50 mGal local positive gravity anomaly over the Mull intrusive complex is interpreted as caused by an underlying dense body of mafic (basic and/or ultrabasic) rocks extending to a depth of between 6.5 and 13 km and occupying a volume of between 2000 and 3600 km
3
, depending on density contrast. The granites produce smaller superimposed negative gravity anomalies, which indicate that the granites of the late Loch Bà centre extend to a depth of about 2 km and those of the early Glen More centre occupy a significantly smaller volume. The granites occupy between 5 and 9% of the total volume, consistent with a derivative origin.

The complicated aeromagnetic anomalies have been simplified by applying the pseudogravimetric transformation. The most conspicuous positive pseudogravimetric anomaly occurs over the rocks of centres 1 and 2. This is of much smaller areal extent than the positive gravity anomaly, and it is attributed to highly magnetic rocks extending to a depth of about 2 km beneath centres 1 and 2, including cone sheets. The magnetization of the deeper parts of the complex is much weaker and has not been resolved. A partial ring of linear or arcuate negative magnetic anomalies occurs along the SE, S and W margins of the deep-seated intrusive complex and may mark an unexposed early ring dyke with strong reverse magnetization.
It is estimated that up to a quarter of the volume occupied by the intrusive complex may have been provided by various types of forceful intrusion but that most of the upper crustal space has been made available by ring subsidence and other types of stoping. This is feasible because the magma was demonstrably lower in density than the Moine and Lewisian. The mantle-derived magma probably rose through the more ductile lower crust by diapirism, thereby causing a slight thickening of the underlying crust which may provide isostatic support for the excess mass of the intrusive complex and its associated topography.
Two-phase flow in crust and mantle
Authors: ROBINSON D. 
Published: December 2007

The fortieth William Smith meeting of the Geological Society was a one-day lecture meeting held at Burlington House on 30 April 1986, with the William Smith Lecture presented by Professor R. K. O'Nions. The meeting was convened by Dr K. Coe (University of Exeter) and Professor D. McKenzie (University of Cambridge).
The meeting’s theme ‘Two-phase flow in crust and mantle’ relates to the interaction between, and relative movements of, the ‘solid’ and ‘fluid’ phases within the crust and mantle. The terms solid and fluid, while being convenient terms to distinguish two such phases in upper levels of the crust, become increasingly imprecise at greater depths. It then becomes better to refer to differences between two phases of sharply contrasting viscosities; a matrix of high viscosity and an ‘intergranular’ component of much lower viscosity. The behaviour of the two phases can be described in terms of fluid dynamics, and application of this technique has much potential for producing major advances across the spectrum of the geological sciences. There is also potential for the field and laboratory based geologist to integrate with the theoretical fluid dynamicist for the advancement of the science. This set of papers aims to demonstrate this link and there is much to be gained from this thematic set for both types of specialist. This theme is particularly topical in the geological sciences at the present time with active interest in the field of fluid processes and fluid-rock interaction.
The seven papers presented at the meeting form this thematic
Ordovician volcano-tectonics in the English Lake District
Authors: BRANNEY M. J. , SOPER N. J. 
Published: December 2007

Although the major late Caledonian (Acadian) deformation of the British slate belts south of the Iapetus suture took place in early Devonian time, two intra-Ordovician unconformities are present in the Lower Palaeozoic succession of NW England which have been interpreted as due to regional compressional events. These unconformities are at the base and top of the Caradocian Borrowdale Volcanic Group (BVG) and have been associated respectively with a pre-BVG orogenic cycle affecting the early Ordovician Skiddaw Group (SG) and with ‘pre-Bala’ folding of the BVG. A problem has been that no consistent sets of minor structures attributable to these deformations have been demonstrated in the Skiddaw Group.
Recent advances in understanding of the volcanic history of the Lake District lead to a radical reinterpretation of the significance of these two unconformities. In the ‘pre-Bala’ (intra-Caradocian) deformation of the BVG, flexuring is now seen to be much less important than volcano-tectonic faulting and block tilting associated with caldera collapse and the eruption of voluminous ash flows in the upper part of the pile. Foundering of the volcanic edifice accounts for the preservation of this thick subaerial sequence beneath the overstepping late Ordovician marine deposits.
More tentatively, we suggest that the unconformity beneath the Borrowdale Volcanic Group reflects regional uplift due to buoyancy effects associated with the generation of andesitic melt by Iapetus subduction and its rise through the over-riding wedge of continental lithosphere; several such mechanisms have been proposed to account for the topographic elevation of present day continental margin magmatic arcs.
The new model removes the evidence for Ordovician N–S regional compression from the geological record of NW England and this has geotectonic implications: the evidence for late Ordovician collision is weakened and the direction of Iapetus subduction beneath southern Britain may not have been southward.
The Leka Opholite Complex, central Norwegian Caledonides: field characteristics and geotectonic significance
Authors: FURNES H. , PEDERSEN R. B. , STILLMAN C. J. 
Published: December 2007

The Leka Ophiolite Complex (LOC) of Lower Ordovician age (U-Pb zircon age of 497 ± 2 Ma) contains the following components: (1) A lower, strongly deformed harzburgite unit, representing the depleted upper mantle. This unit becomes progressively richer in dunite towards (2) a sequence of ultramafic cumulates, ‘unconformably’ overlying the harzburgite tectonite. The crystallization sequence in the ultramafic cumulates is: olivine→chromite→clinopyroxene→orthopyroxene. In the south-western part of the ultramafic cumulate sequence, layers of metagabbro appear interlayered with banded dunite/wehrlite. The above-mentioned rock sequences may be in tectonic contact with (3) layered metagabbros which give way upwards to laminated and vari-textured metagabbro. Within the laminated/vari-textured metagabbro is the first appearance of (4) metabasalt dykes, which increase upwards in abundance from scattered single dykes to a 100% sheeted dyke swarm. Associated with the vari-textured metagabbro and metabasalt dykes are minor acid intrusions. Within the upper part of the dyke swarm is the first appearance of (5) pillow lavas, which are associated with thick volcaniclastic metasediments at apparently higher stratigraphic levels.
Geochemically the metabasalt dykes and associated pillow lavas range from predominant island arc tholeiite (IAT) to MORB character, and typical metaboninites are also present. This range of geochemical composition, as well as the crystallization sequence of the cumulates, strongly suggests that the first stages in the formation of the LOC was by spreading above a subduction zone. The pillow lavas associated with volcaniclastic rocks, are of MORB or WPB type, and these probably represent the later spreading stages of the LOC in a back-arc basin, but at sufficient distance to be unaffected by the geochemical ‘fingerprints’ of the subduction process.