bluuebunny/crossref_metadata_2025 huggingface dataset:
East Greenland Caledonides—an extension of the British Caledonides
Authors: Higgins Anthony K. , Phillips W. E. Adrian
Published: May 2008

The major part of the Caledonian fold belt in East Greenland comprises gneiss complexes, which in the south have yielded Archaean and early Proterozoic isotopic ages; their features may be compared to those of the Scourian and Laxfordian divisions of the Lewisian. They are overlain by middle Proterozoic supracrustal sequences, which in some areas are involved in migmatitic activity and granite emplacement of Grenville age; parallels may be drawn with events recorded in the Morar Division of the Moine in Scotland, and in Ireland with those in the Annagh gneiss complex in N Mayo and perhaps in the Ox Mountains sequence. The late Precambrian lower Eleonore Bay Group is similar in development to the Grampian Group (Dalradian) of the British Isles, and the upper Eleonore Bay Group bears comparison with the Appin Group of the Dalradian. The Vendian glacial event is well represented in both regions. The early Palaeozoic succession in Greenland shows marked similarities with the Durness Limestone succession. The pattern of Caledonian deformation, metamorphism and plutonic activity show many similarities but also differences. The marked marginal thrust zone in the west of the E Greenland fold belt is the logical continuation of the Moine thrust belt. Late Palaeozoic continental deposits overlie Caledonian folded units in both regions.
The continuation of the Canadian Appalachians into the Caledonides of Britain and Ireland
Authors: Kennedy M. J.
Published: May 2008

Three zones can be recognised in the Canadian Appalachian-British Caledonian belt. The NW Marginal Zone extends from NW Scotland and Ireland through N Newfoundland to Quebec. It consists of late Precambrian to early Palaeozoic clastic sequences and an extensive Cambro-Ordovician carbonate platform. Orthotectonic deformation and metamorphism occurred in the early Ordovician, and middle Ordovician allochthons and obducted ophiolite characterise this zone in N America. The SE Marginal Zone extends from Wales and the English Midlands through SE Ireland to E Newfoundland, Nova Scotia and S New Brunswick. It is characterised by extensive late Precambrian volcanicity, late Precambrian orthotectonic deformation and metamorphism and the development of lower Palaeozoic basins in Wales and Nova Scotia. Late Precambrian orogenic activity locally involved ophiolite. The Axial Zone can be subdivided into a number of subzones, some of which do not extend for great distances along strike. It contains local ophiolites, trench complexes and calc-alkaline volcanics ranging in age from Cambrian to Silurian. Volcanicity was most pronounced in the Ordovician on both sides of this zone and extended into the marginal zones. Middle Ordovician deformation and metamorphism is locally intense but elsewhere Ordovician and Silurian sequences are apparently conformable. The Axial Zone and adjacent parts of the marginal zones have all suffered Siluro-Devonian, generally paratectonic, deformation and metamorphism. The history of the whole belt indicates that subduction was active on the SE in the late Precambrian, on the NW and in the Axial Zone in the lower and middle Ordovician and extended into the Silurian. Final closure of the Iapetus ocean was delayed until the upper Silurian-Devonian. Plate-tectonic models must involve multiple subduction zones.
Observations on eclogite- and granulite-facies rocks in the basement of the Caledonides
Authors: Sanders Ian S.
Published: May 2008

Eclogite-facies metamorphism in the Glenelg inlier, NW Scotland, occurred after a phase of basic dyke intrusion (?Scourie dykes), and before a period of ?Caledonian mylonitisation. It possibly occurred during the Precambrian Morarian event since banded eclogitic rocks share the same ESE-dipping foliation as the overlying Moines. P-T conditions of metamorphism estimated as 750–600°C and 10–15 kb, suggest that the inlier is an upthrust segment of stable continental lower crust. Granulite-facies rocks of the NE Ox Mountains inlier, W Ireland, show evidence of Caledonian retrogression. Inferred P-T conditions (900–750°C, >10 kb) are those of a heated, lower crustal environment. The rocks are very similar to xenolithic material from the Scottish Midland Valley.
Basement-cover relationships at Lewisian inliers in the Moine rocks
Authors: Rathbone Paul A. , Harris Anthony L.
Published: May 2008

Lewisian basement of the N Highlands occurs (a) as an autochthonous massif, the Strathy Complex, (b) in parautochthonous fold cores, e.g. Morar, and (c) as slices along zones of high strain, e.g. the Sgurr Beag Slide. Structural features, within the Morar Division psammites adjacent to the Glenfinnan Division and to Lewisian inliers, have been used to define zones of increasing strain within some of which Lewisian strips now occur. The psammites show evidence of high strain where slides occur and massive, cross-bedded psammites give way to thinly banded platey psammites with a total absence of sedimentary structures. Folds progressively tighten. Quartz veins are re-orientated into parallelism with the foliation in the psammite and discordant fabrics are lost. In contrast to psammites at slides, those adjacent to Lewisian rocks in parautochthonous fold cores show only some of these features and those adjacent to the autochthonous massif show none of these features.
Dating of the tectono-metamorphic history of the southwestern Moine, Scotland
Authors: Brewer Martin , Brook Maureen , Powell Derek
Published: May 2008

New Rb-Sr whole-rock data are presented which confirm a Grenvillian age for widespread, early, regional metamorphism of the Moine in the SW Highlands of Scotland. It further suggests that Caledonian metamorphic activity occurred between
c.
470 and 410 Ma ago. Previous isotopic analyses of mineral separates from schists, gneissose pelites and pegmatites are reviewed in the light of the new data, and the work of Purdy & Jaeger (1976). This suggests a cooling history, following the Caledonian metamorphism, which involved sequential uplift of crustal segments.
The ‘Central Highland Granulites’: cover-basement tectonics in the Moine
Authors: Piasecki M. A. J. , van Breemen O.
Published: May 2008

The Central Highland Granulites have been split into a cover assemblage of medium grade, little disturbed metasediments named the Grampian group, separated by a zone of sliding referred to as the Grampian Slide, from an underlying basement assemblage of high grade gneissose and migmatitic metasediments called the Central Highland Division. The Central Highland Division rocks are correlated on lithological, tectonic, metamorphic and radiometric grounds with the high grade Grenvillian rocks of the western Highland Moine, and are believed to represent their extension southeast of the Great Glen fault.

The discovery of Precambrian (
c
.720 Ma) pegmatites sheared by Caledonian (<570 Ma) sliding in the Central Highlands, enables the separation of Caledonian from Precambrian orogenic events in the rocks of both assemblages; their Precambrian orogenic history is so different, that the Central Highland Division rocks are considered to form a Grenvillian basement to the younger (Morarian) cover succession of the Grampian group. The western Highland Moine region is examined in the light of the tectonic cover-basement relationship postulated for the Central Highlands. The Loch Eil Division contains rock assemblages indistinguishable from the Central Highland Division, and others similar to the Grampian group. Evidence is put forward for a post Grenvillian, Morarian age for the Morar Division.

The distribution of metamorphic zones in the Moine would seem to reflect the distribution of high grade basement and lower grade cover rocks, and may be in part determined by movements on a series of Caledonian slides, though this has not been demonstrated.
The status of the Banff nappe
Authors: Ramsay Donald M. , Sturt Brian A.
Published: May 2008

The status of the major horizon of gneisses (Cowhythe, Donside, Ellon and Inzie Head gneisses) in NE Scotland has been reinterpreted, on the basis of geochronological and fabric evidence, as the basal element of a major nappe, the Banff nappe. It is suggested that these gneisses represent a pre-Caledonian basement gneiss-complex, thrust into its present structural position during the Grampian phase of the Caledonian orogeny, after the formation of the Tay nappe. The basal zone of this unit is characterised by the development of distinctive mylonitic assemblages. In this interpretation, the rocks of the overlying Banff division form part of the allochthonous assemblage, as a Caledonian cover sequence, uncoupled from the basement along the Boyne line during emplacement.
The distribution of pre-Caledonian basement in the Ox Mountains inlier, Ireland
Authors: Long Charles Barry , Yardley Bruce William
Published: May 2008

Studies in the Ox Mountains inlier of NW Ireland in recent years have led to conflicting views by two groups of workers as to whether the inlier comprises (1) mainly pre-Caledonian basement with small areas of Dalradian (Caledonian) rocks, or (2) mainly Dalradian rocks excepting a pre-Caledonian area in the northeast. Both views are outlined here with the main arguments of the protagonists.
Pre-Caledonian basement to the paratectonic Caledonides in Ireland
Authors: Kennan P. S. , Phillips W. E. A. , Strogen P.
Published: May 2008

In NW Ireland the exposed pre-Caledonian basement adjacent to the paratectonic Caledonides contains Grenville gneisses in N Mayo. A pre-Caledonian age is preferred for the amphibolite- and granulite-facies metasediments of the Ox Mountains, Lough Derg and Central Tyrone inliers. Gneissic xenoliths in lower Carboniferous agglomerates indicate that a comparable basement extends southwards beneath a considerable part of the Longford-Down zone in central Ireland. Pre-Caledonian basement is also exposed in SE Ireland. An important change of basement composition is inferred across central Ireland from regional magnetic data and from lead isotope data. This change occurs in the vicinity of the Iapetus suture both in Ireland and Britain.
Deformation in the Caledonides of England, Ireland and Scotland
Authors: Johnson M. R. W. , Sanderson D. J. , Soper N. J.
Published: May 2008

The past few years have witnessed a remarkable change in our view of the British Caledonides resulting from radiometric work, application of plate tectonic models as well as basic field work. Overshadowing all else has been the acceptance of a later Proterozoic (probably Grenville) orogeny in the Moine rocks occurring between the Moine thrust and the Great Glen fault. The northern Moines are clearly polymetamorphic in character, but several matters are still controversial, for example the separation of Proterozoic and Caledonian fabrics and the areal extent of the older orogeny. This northern block was subjected to intense and repeated tectonism and, above all, large thrust translation during the Caledonian orogeny and the rocks are now juxtaposed with the older Proterozoic and Archaean gneisses of the Caledonian foreland. In Ireland small areas of Grenville basement are in slide contact with the younger Moine and Dalradian rocks.

South of the Great Glen fault above a postulated Grenville basement, are late Proterozoic sediments (Central Highland Granulites and Dalradian) which were orogenically deformed in lower Ordovician times. In this area the essence of the structural pattern established some years ago stands unquestioned for the most part, but significant modifications have been made, notably the recognition of a slice of ‘Cadomian’ basement in the Dalradian pile of NE Scotland, and possible pre-Caledonian basement in W Ireland. In Ireland the structural pattern in the Scottish Highlands may be recognised in the north, but becomes considerably modified in the west where the strike becomes E-W.

The picture of the Scottish Highlands as a metamorphic Alpine-type orogen, dating from the early Ordovician, and undergoing uplift during Ordovician and later times, is complemented by the recent recognition of the Southern Uplands zone (later, non-metamorphic Caledonides) as being an accretionary prism, on the Aleutian model, in which imbricate thrusts developed in series towards the south above the subducting oceanic crust of Iapetus. The Iapetus suture lies between the Southern Uplands and northern England and passes through central Ireland. The pattern of Ordovician vulcanicity in northern England, Wales and SE Ireland has been attributed to southerly directed subduction of the Iapetus crust beneath the opposing continental margin.

Final closure of Iapetus in Silurian and Devonian times, seems to have been marked by relatively mild tectonic activity in the ‘metamorphic Caledonides’, but by considerable compression across the slate belts of the Lake District, Wales and SE Ireland with polyphase structural evolution.
The tectonic evolution of the Welsh Caledonides
Authors: Coward M. P. , Siddans A. W. B.
Published: May 2008

The succession, metamorphism, geochronology and major structure of the Mona Complex, Arvonian and Lower Palaeozoic rocks of N Wales are outlined. This results in a model which relates early (pre-Ordovician) NW-verging structures to the closing of an early Caledonian ocean and obduction of deep water sediments, slide breccia and basic volcanic rocks on to the sediments previously metamorphosed, locally at high temperatures, and intruded by granites in central and N Anglesey.

The pattern of folds, cleavages, thrusts and finite strain states in N Wales are described. A maximum of 43 km shortening between the Menai Straits and the Welsh Borderlands is estimated across the more highly deformed part of central Snowdonia, during end-Silurian deformation. The amount of shortening decreases to the northeast (Denbighshire Basin) and south (Harlech Dome) ends of the arc. This is attributed to compression of Snowdonia against a rigid block situated in the Berwyn Hills. The SE-verging structures are thought to pass downwards, with listric geometry, into a decollement zone at some unknown depth in the basement, which accommodated Caledonian crustal shortening across Wales, and must itself either descend into the mantle or root in any Caledonian suture beneath the Irish Sea.
Stratigraphical and structural correlation between the Dalradian rocks of the SW and Central Highlands of Scotland
Authors: Roberts J. L. , Treagus J. E.
Published: May 2008

The stratigraphical continuity between the SW and Central Highlands of Scotland is clarified with particular reference to the lower Dalradian rocks. The structural disposition of the rocks reveals the presence of the same two structural elements as found in the SW Highlands, namely, the Ardrishaig anticline and the Ben Lui fold. The mushroom structure of the Central Highlands is rejected, while the Boundary Slide is shown to be a diffuse D
2
structure, which is probably of no great mechanical importance.
Geometry and emplacement of nappes in the Central Scottish Highlands
Authors: Bradbury H. J. , Harris A. L. , Smith R. A.
Published: May 2008

A deformation history related to polyphase nappe formation is presented for the Central Scottish Highlands as a model for the Dalradian tract. The genesis of a four-fold pattern of tectonic belts recognisable throughout this tract is discussed. The fan structure of the Tummel steep belt is argued to be a deep-seated rotation zone. Movements within this zone spanned the climax of Barrovian metamorphism and were responsible for creating the major belt of inverted rocks—the Loch Tay inversion—which forms the lower limb of the Tay (fold) nappe. The early-formed Tay nappe, nucleated at a relatively high tectonic level, was translated as a result of movements within the deeper rotation zone progressively towards the SE principally by simple shear. The core of the Tay nappe is recognised within the Highland Border steep belt at Aberfoyle, but does not root within the deeper levels of the Central Highlands Dalradian. The Highland Border steep belt at Dunkeld was formed by late orogenic downbending of the previously flat-lying inverted limb of the Tay nappe probably resulting from sub-vertical movements within the basement along the ancestral line of the Highland Boundary fault. A kinematic model explains the nappe geometry by density inversion of the Dalradian succession consequent on the pre-orogenic evolution of the Dalradian (marginal) basin.
The Tarfside succession and the structure and stratigraphy of the eastern Scottish Dalradian rocks
Authors: Harte Ben
Published: May 2008

Limestones and quartzites within the Tarfside culmination of Glen Esk (Angus) are correlated with the upper part of the Dalradian Argyll Group, and form part of a right way up succession extending upwards into the Southern Highland Group. This correlation makes the Tarfside limestones stratigraphically equivalent to the Loch Tay and Deeside limestones in the inverted flat belt of the Tay nappe. The zone of inversion between the Tarfside succession and that of Deeside and Loch Tay lies in the headwaters of Glen Esk and further south; the Tarfside succession occupies the structural position of the right way up limb of the Pitlochry-Kirkmichael recumbent syncline beneath the Tay nappe. The actual inversion is thought to take place across a slide which also causes the sudden disappearance of the Green Beds. Evidence for sedimentary facies variation in the Tarfside rocks and their stratigraphical equivalents supports the interpretation of some of Read’s Boyne Line phenomena (in Aberdeenshire and Banffshire) as being sedimentary facies variations.
Pre-tectonic reconstruction of the Islay anticline: implications for the depositional history of Dalradian rocks in the SW Highlands
Authors: Borradaile Graham J.
Published: May 2008

The shape and orientation of the finite strain ellipsoid has been determined at more than 50 locations around the Islay anticline. Restoration of the ellipsoids to their original spherical form with the appropriate adjustments in orientations and positions of parts of the Anticline allow it to be ‘unfolded’. Original stratigraphical thicknesses were generally twice present day values and constant across the area with the exception of those of the Jura Quartzite which had much more marked thickness variations than are now observed. These probably resulted from syndepositional normal faulting with NE-SW crustal tension (a similar stress system controlled the intrusion of the Jura epidiorite dykes subsequently). This unstable phase in the depositional environment interrupted the otherwise uniform subsidence during Argyll Group deposition. A NE-SW striking (Caledonide) palaeostope did not develop until the close of the Argyll Group with the very energetic deposition of the Crinan Grit turbidites.

Palaeocurrent data, especially for the less competent lithologies, are unreliable unless the suggested corrections are made for the effects of penetrative tectonic strain.
Dalradian structure in the Creeslough area, NW Donegal, Ireland
Authors: Hutton D. H. W.
Published: May 2008

The principal structure of the Appin Group metasediments in the Creeslough area is a series of D
2
NW-facing recumbent folds and two important slides that are thrusts (to the northwest). D
3
produces large open folds that face to the southeast. D
4
is associated with a major synform and shear zone in the aureole of the Main Donegal granite. No major F
1
fold hinges are present, although D
1
faces northwest. It is concluded that of the early deformations in Donegal, D
2
can be regarded as the Caledonian thrust front.
Structure and stratigraphy of the Dalradian rocks of the Bennabeola area, Connemara, Eire
Authors: Tanner Peter William Geoffrey , Shackleton Robert Milner
Published: May 2008

The geology of an area of 400 sq km of Lower and Middle Dalradian rocks is described. It consists mainly of rocks belonging to the Appin and Argyll Groups which have been strongly deformed during four stages (F
1
–F
4
) with the major development of tectonic slides occurring before F
3
. Eighteen major F
3
folds, whose geometry is described, are correlated across the Connemara antiform (F
4
); they refold an earlier nappe-like (? F
2
) antiform, the Derryclare fold. All of the Appin Group rocks and the Cleggan Boulder Bed Formation are contained within the core of the Derryclare fold, which locally has attenuated limbs. A zone of vertical foliation, the ‘steep belt’, is present in the south of the area. It is superimposed upon the originally steeply inclined, south-facing Derryclare fold and appears to have developed during F
4
.
Strain adjacent to the Iapetus suture in Ireland
Authors: Phillips W. E. A. , Flegg A. M. , Anderson T. B.
Published: May 2008

The Iapetus suture, extending northeastwards through Silvermines and Navan, separates distinct structural provinces of the paratectonic Caledonides. On the north side, F
2
and F
3
folds and a shallow pitching stretching lineation become increasingly important southwards over a zone up to 50 km wide. S
1
cleavage here shows an anomalous relationship to F
1
folds, with a consistent clockwise offset of cleavage strike away from F
1
axial planes. Dextral simple shear along strike appears to have been important during ductile deformation in this zone. South of the suture, upright F
1
folds of varied plunge are the dominant ductile structures. Strain varies from pure flattening to often a component of down dip extension. Within 50 km on either side of the suture, analysis of faulting suggests control by dextral simple shear parallel to the suture. Outside this zone a different ‘intra-plate’ conjugate system is developed.
A structural profile of Caledonian deformation in Down
Authors: Anderson T. B. , Cameron T. D. J.
Published: May 2008

Coastal exposure in County Down provides an almost complete cross section of the continuation of the Southern Uplands fold belt in Ireland. Intensely folded Ordovician and Silurian turbidite successions are segmented by at least ten major strike parallel faults. In each segment the fold envelope descends northward but the strike faults throw up progressively younger sediments to the south. A system of upright folds, with slaty cleavage axial plane, but locally transecting, becomes progressively complicated southward by the clear development of two further phases of folding and cleavage with constant geometry and opposing vergence. The chronology of cleavage, folding, later kink-band and brittle deformation is punctuated by successive late Caledonian lamprophyre dyke swarms. The total structure is consistent with a model of diachronous deformation and northward translation and rotation at a destructive plate margin.
Structure of the Southern Uplands of Scotland
Authors: Eales Martin H.
Published: May 2008

In the Moffat Shale lithology of the Southern Uplands, the primary Caledonian structure consists of thrusting at a low angle to the bedding. Thrusting was associated with minor and large scale folding and northwesterly rotation of beds and thrust planes. Wrench faulting is considered as the final major Caledonian event. All these structural phases were caused by similar principal stress orientations. The primary thrusting is best studied in the Moffat Shale inliers where stratigraphical control is excellent. It is possible that these beds overlie a major plane of décollement.

Thrusting is less conspicuous in the overlying greywacke sequence where the beds are more competent, and the stratigraphy is less well defined. Otherwise, the Caledonide structural evolution of the greywacke is essentially the same as that in the underlying pelagic sequence. Consequently it is suggested that nearly all the Caledonian structures of the Southern Uplands can be broadly explained by a common but evolving stress system.
A strain section across part of the Caledonian orogen in W Ireland
Authors: Kelly Thomas J. , Max Michael D.
Published: May 2008

Quantitative strain analysis supports the concept of tectonic compartmentation within the western Irish Caledonides. Older rocks do not always show higher strains and this may be due to each compartment’s particular response to stress. Strain variation also occurs within individual tectonic compartments.
The state of strain adjacent to the Great Glen fault
Authors: Parson Lindsay M.
Published: May 2008

Fabric and pebble studies near Fort Augustus indicate that strong NW-SE compression has acted but structures indicative of lateral NE-SW displacement are absent.
Caledonian thrusting in NW Scotland
Authors: Mendum J. R.
Published: May 2008

Several major thrusting events, ranging in age from Precambrian to Middle Devonian, have affected the Moine assemblage and adjacent foreland. An early thrusting event is primarily responsible for the emplacement of lenticular Lewisian Gneiss inliers within the Moines. The main Caledonian (
sensu stricto
) event (F
2
) at about 480 Ma was complex in nature with widespread marginal and internal ductile thrusting, related recumbent folding, metamorphism and locally migmatisation. Later open to tight folding (F
3
, F
4
) and minor ductile thrusting (F
3
) modified this pattern. Subsequently in Silurian to Lower Devonian times marginal major brittle thrusting, and internal faulting, minor thrusting and uplift, occurred.
Pelite facies series and the temperatures and pressures of Dalradian metamorphism in E Scotland
Authors: Harte Ben , Hudson Neil F. C.
Published: May 2008

An attempt is made to synthesise data on the regional metamorphism of pelites in the eastern Scottish Dalradian. Zonal sequences (facies series) of mineral assemblages are presented and variants of the traditionally recognised Barrovian and Buchan metamorphism are separated. A Schreinemakers net and petrogenetic grid for the system KFMASH is presented and fixed in P-T space using experimental data. The P-T data for the various facies series are used in conjunction with other constraints to develop a model of isotherm and isobar distribution in the region, and the effects of post metamorphic folding of the isopleths are noted. P-T gradients normal to isobars suggest overall ‘geothermal’ gradients for most of the area to be convex to the T-axis, and it is suggested that they result from magma intrusion at depth. The region adjacent to the Highland Boundary fault shows strong horizontal and vertical temperature gradients which are tentatively interpreted to indicate the presence of a synmetamorphic tectonic boundary to the Dalradian metamorphic belt.
Thermal evolution of metamorphic rocks in the Central Highlands of Scotland
Authors: Wells P. R. A. , Richardson S. W.
Published: May 2008

Conditions of the metamorphic maxima in lower Dalradian kyanite zone pelites from Kinloch Rannoch, Schichallion, Glen Tilt, Glen Ey and Glen Avon are calculated from analyses of coexisting kyanite, garnet, biotite, plagioclase and quartz (staurolite or chlorite also coexist in some samples). Temperatures of 550–620°C were reached at pressures of 9–12 kb corresponding to depths of burial of 35–40 km. Compositional gradients in zoned garnets indicate that pressures were falling at the time maximum temperatures were reached. The high values of pressure are confirmed by observations of the sub-assemblages kyanite-zoisite (not anorthite-margarite) and kyanite-garnet-chlorite-quartz (not staurolite or chloritoid). The pressure of intrusion of a Newer Igneous complex in upper Glen Tilt is 5–6 kb. The present results are contrasted with conditions at a similar structural/stratigraphical level 50 km WNW where comparable temperatures were reached at depths around 20 km. It is concluded that either erosion rates early during metamorphism were lower or the tectonic cover was greater in the Central Highlands than to the west.
Migmatisation, deformation and porphyroblast growth in the Dalradian of Tayside, Scotland
Authors: Bradbury Harry J.
Published: May 2008

In Tayside, migmatisation of kyanite zone Argyll and Southern Highland Dalradian metasediments occurred between the regional D2 and D3 episodes in the Grampian orogeny. The U-Pb zircon age for the emplacement of the ‘Older’ Ben Vuirich Granite (514 + 6/ − 7 Ma), which intervenes between D2 and D3, provides an approximate age for migmatisation. This is significantly younger than recent isotopic ages of migmatites from the W Scottish Highlands with which the Tayside migmatites were previously correlated. In Tayside, migmatisation largely post dated the development of the Tay nappe but pre-dated the late-stage modification of the Tummel steep belt and the Loch Tay inversion. Textural evidence indicates that migmatisation was broadly coeval with the climactic Barrovian metamorphism, the age of which is discussed.
Textural and mineralogical evolution of migmatites
Authors: Ashworth J. R.
Published: May 2008

Textures and muscovite compositions in regional migmatites from the Central Highlands of Scotland are compared with those of the Huntly-Porsoy area, where early retrograde muscovite retains compositions appropriate to the sillimanite-potash feldspar zone. In samples from the upper Findhorn area, textural relics from this zone are found, even though textures are strongly modified by recrystallisation, and sillimanite no longer coexists with potash feldspar. Muscovite composition varies within a leucosome, between compositions appropriate to the sillimanite zone and others adjusted to much lower grade. In samples from mid-Strathspey, mineralogy is low-grade and textural modification profound, despite relatively little deformation. The grade at which these latter samples were migmatised is difficult to deduce from internal evidence.
Time, space and intensity relationships of the Precambrian and lower Palaeozoic metamorphisms of the Scottish Highlands
Authors: Lambert R. St J. , Winchester J. A. , Holland J. G.
Published: May 2008

Isotopic evidence suggests that a complex sequence of events, collectively known to us as the Morarian event, affected the Morar and Glenfinnan divisions of the Moine from 1000 to 750 Ma. A regional thermal anticline, with a minimum age of 750 Ma, extends north from Ardgour to northern Ross-shire: it probably extends southwards under the eastern Dalradian. This thermal anticline is cut across and shifted westwards south of Monar by the Sgurr Beag slide, on which up to 25 km thrust movement is estimated. The Loch Eil Division lacks old isotopic ages; it appears to be structurally and metamorphically simpler than the Morar and Glenfinnan divisions and it also differs from them geochemically. The simplest explanation of these facts is that Loch Eil Division rests unconformably on the metamorphosed Glenfinnan Division. The Central Highland Group (including the Monadhliath Schists) is presumed to occupy the same tectono-stratigraphical niche as the Loch Eil Division. Grampian events (510-480 Ma) produced three thermal highs of sillimanite grade: one in the Monadhliaths, the second in the NE Grampians, and the third affecting E Sutherland. Throughout most of the area under consideration, Grampian age isograd surfaces appear to dip at low angles.
Patterns of metamorphism in the Ox Mountains and adjacent parts of Western Ireland
Authors: Yardley Bruce W. D. , Long C. Barry , Max Michael D.
Published: May 2008

Three types of regional metamorphism are present in the Ox Mountains inlier. High pressure granulites occur in the northeast, but elsewhere most Ox Mountains rocks show a single progressive Barrovian metamorphism from garnet zone to kyanite zone. Conditions of metamorphism for the kyanite zone were near 600°C and 6–7 kbar total pressure. Regional retrogression occurs principally in the north central Ox and affects both granulites and the lower grade metasediments. The tectonic contact between granulites and Barrovian kyanite zone rocks in the Ox is analogous to that in southern Donegal and the conditions of metamorphism of the (Dalradian) staurolite-kyanite schists are the same in both areas.
Oxide-sulphide-silicate mineral phase relations in some thermally metamorphosed graphitic pelites from Co. Donegal, Eire
Authors: Atkin B. P.
Published: May 2008

A chemical control over the oxide-sulphide-silicate phase relations of the graphitic pelites from the aureoles of Donegal granites is demonstrated. Kyanite-bearing rocks (M/FM ratio >0.54) have the ore assemblage of rutile + pyrite or pyrrhotite and kyanite-free rocks have the assemblage ilmenite + pyrrhotite. The stabilisation, during prograde metamorphism of pyrrhotite over pyrite and ilmenite over rutile accompanied by an increase in the Mg content of ferromagnesium phases is also demonstrated. Phase relations between oxide and silicate phases are illustrated by AFMT(i); tetrahedral diagrams and sulphide-silicate phases by AFMS tetrahedral diagrams. Retrograde reactions especially the replacement of ilmenite by rutile and pyrrhotite by marcasite are also described.
Evolving life of the developing Caledonides
Authors: Holland C. H. , Hughes C. P.
Published: May 2008

This review is largely confined to the evolution of life during the late Precambrian to early Devonian period of earth history represented by the developing Caledonides of the British Isles. It begins with reference to Precambrian floras and faunas tantalisingly glimpsed in the Dalradian of Scotland and Ireland and in isolated occurrences in Charnwood Forest and in South Wales. Cambrian life is variously represented in the Durness Limestone, in the younger Dalradian rocks, in the Bray Group and its equivalents, and in the classical sequences of Wales and England. Summary treatment only is possible of the vastly detailed palaeobiological record in the Ordovician and Silurian rocks of the British Isles. There is cross-reference to other contributions in this section of the present volume. The vascular plants and vertebrates are treated separately by other authors.
The early history of vascular plants based on late Silurian and early Devonian floras of the British Isles
Authors: Edwards D.
Published: May 2008

Vascular plant assemblages are described from late Silurian (Ludlow and Downtonian), Gedinnian, Siegenian, and Emsian localities in Britain. Various kinds of evidence are used in an attempt to reconstruct the habitats and life histories of early land plants.

The later stages of the Caledonides in the British Isles coincided with one of the most important events in plant evolution—the appearance of vascular plants. As today the majority of such plants are terrestrial, it may be assumed that the macrofloras occurring in late Silurian and Early Devonian sediments of southern Britain and Scotland record episodes early in the colonisation of land surfaces. Plants of quite different affinities but which also possess anatomical modifications indicating tolerance of hostile drying sub-aerial conditions are sometimes present in the floras. These together with microfossils will be omitted from this account.
Early vertebrates and the Caledonian earth movements
Authors: Dineley D. L. , Loeffler E. J.
Published: May 2008

Vertebrate remains from Ordovician formations indicate a conservative mode of life in marine environments but which seems to have become more diverse by the invasion of varied
non-marine
aquatic habitats in Siluro-Devonian time. The spread of Old Red Sandstone facies results from Caledonian tectonism and provides the earliest Phanerozoic example of an adaptive radiation of both agnathan and gnathostome vertebrates. Prior to the late stages in the closure of Iapetus the ‘European’ and ‘American’ vertebrate faunal assemblages were distinct. Closure brought an immediate influx of ‘American’ agnatha into the European area, and a rapid increase in numbers of species. Subsequent earth movements and changes in palaeogeography favoured the development of internal basins with accompanying differentiation of vertebrate stocks. Some primitive forms, perhaps relatively isolated geographically, persisted until the Late Devonian by which time non-marine gnathostomes had spread to most of the continents.
New evidence for the age of the Manx Group, Isle of Man
Authors: Molyneux S. G.
Published: May 2008

Acritarch assemblages which are sufficiently well preserved to date the rocks in which they occur have been obtained from five formations in the Manx Group of the Isle of Man. The acritarch evidence indicates that the Niarbyl Flags, Glen Dhoo Flags, and Lonan Flags are most probably Tremadoc in age, the last two very late Tremadoc. The Maughold Banded Group is probably Arenig and the Lady Port Banded Group is probably either late Arenig or early Llanvirn. The minimum time interval represented by the Manx Group is late Tremadoc to late Arenig and a correlation of the Manx Group with the Skiddaw Group in NW England and the upper part of the Ribband Group in SE Ireland is proposed. The contemporaneous volcanic rocks in the Manx Group at Peel, here named the Peel Volcanic Formation, are probably upper Arenig in age.
The distribution of trilete spores in Irish Silurian rocks
Authors: Smith David G.
Published: May 2008

Trilete spores of land-plant type have been recovered from probable late Llandovery to early Ludlow sediments in several widespread parts of Ireland, and they have proved to be stratigraphically useful in otherwise unfossiliferous outcrops. In many cases, spores have been found in offshore marine sediments of turbidite facies in which they are accompanied by only minor quantities of marine palynomorphs (acritarchs, chitinozoa). Possible explanations for this unexpected association are considered in the light of what is known of Irish Silurian palaeogeography; they include reworking of nearshore shelf assemblages by turbidity currents and contour currents, and transport of land-derived spores by wind and surface-water currents. The possibility that the spore-bearing plants were pelagic is also considered.
Microfossil distribution in the Silurian of Britain and Ireland
Authors: Aldridge R. J. , Dorning K. J. , Hill P. J. , Richardson J. B. , Siveter D. J.
Published: May 2008

Microfossils are diverse, abundant, and well-preserved in the Silurian shelf sediments of the British Isles, but are scarcer in graptolitic shale and greywacke sequences. Most work has concentrated on the Welsh Borderland where acritarchs, miospores, conodonts, and ostracodes have all proved stratigraphically valuable. Acritarchs, chitinozoa, and scolecodonts are all abundant from middle Llandovery to upper Ludlow strata and ostracodes are common from the upper Llandovery to the Downtonian. Conodont abundance is highest in the Whitcliffian, but diversity and biostratigraphical value are greatest in the upper Llandovery. Ostracodes are of particular correlative use from the middle Ludlow to Downtonian and acritarchs are important from the middle Llandovery to the upper Ludlow. Miospores are very scarce in Llandovery sediments but in Ludlow and Downtonian strata they are abundant and diverse. All groups display some facies dependence, but miospores occur in a range of nearshore shelf, estuarine, and alluvial deposits and, of the marine groups, acritarchs show least environmental control. Arenaceous foraminifera, hydrozoa, and melanosclerites are sporadically abundant.
The environmental significance of some faunal changes in the Upper Ardmillan succession (upper Ordovician), Girvan, Scotland
Authors: Harper D. A. T.
Published: May 2008

A series of discrete, distinctive faunules has been established for the Upper Ardmillan succession in the Girvan district. The faunules, collected from a diverse suite of clastic sedimentary rocks in a well defined stratigraphical framework, belong to the Whitehouse Group, the Shalloch Formation, the Drummuck Group, and the High Mains Formation; these rock units range in age from late Caradoc (Onnian) to late Ashgill (Hirnantian). The brachiopod associations identified within each faunule are outlined; few are considered indigenous. The series of faunal changes is fundamental to the assessment of the depositional environment of the sequence.

The changing composition and structure of the brachiopod associations appear to reflect deposition in a predominantly unstable and often turbulent offshore continental slope environment. The faunal and sedimentary evidence supports the existence of a submarine fan throughout at least much of Upper Ardmillan times at Girvan.
Trilobite associations in the British Wenlock
Authors: Thomas A. T.
Published: May 2008

Five common trilobite associations occur in the British Wenlock. The associations are characterised by increased abundance of particular genera and their distribution is related to changes in lithofacies and position on the palaeoslope. Comparable associations are widespread in the Silurian of other parts of the world. Similar lithofacies of different ages often contain generically identical trilobite assemblages thus highlighting the dangers of basing correlations upon comparisons made above the specific level.
Caledonian echinoderms of the British Isles
Authors: Paul C. R. C.
Published: May 2008

The Lower Palaeozoic echinoderm fauna of the British Isles is meagre in the Cambrian, but much more diverse in the Ordovician and Silurian. A change from blastozoanto crinozoan-dominated faunas is probably a real evolutionary change, but is largely due to the exceedingly rich Ashgill cystoid fauna and the equally varied Wenlock Limestone crinoids. Changes in the echinoderm fauna from the early Ordovician to the Silurian imply that provincialism gave way to cosmopolitanism; a cooler climate became subtropical, despite the Upper Ordovician glaciation; and that crinoids replaced blastozoans because they were more efficient filter-feeders.
Extinction of the graptolites
Authors: Koren’ T. N. , Rickards R. B.
Published: May 2008

Graptoloids became extinct in latest Early Devonian (Pragian) times, and dendroids in the late Carboniferous. There is insufficient information for the other six graptolite orders to suggest when they might have become extinct, so that in these cases it is impossible as yet to speculate how extinction occurred. The dendroids survived apparently unchanged from their first appearance in the Mid-Cambrian until the late Carboniferous, whereas the graptoloids enjoyed four major and spectacular evolutionary bursts in a planktonic, largely tropical environment: those of the Arenig/Llanvirn; the
gracilis
Zone; the Llandovery; and the Ludlow. The post-Ludlow strata record three further smaller diversifications, of successively decreasing speciation, one in the Silurian (Přídolí) and two in the Devonian (Lochkov & Pragian), the last marking the extinction of the graptoloids. Between the evolutionary bursts are evolutionary lows in terms of species diversity. After examining these major revolutionary events (for which speculative reasons are given) as preludes to the extinction of the graptoloids, it is concluded that this final act was result of a gradual restriction of the particular ecological niche occupied by the morphologically less varied Devonian monograptids. The nature of this and other planktonic niches is as yet unknown. A general reduction, following the Ordovician, of the planktonic biomass, and the phytoplankton component on which the graptolites probably fed, was probably largely responsible for the extinction of this order of graptolites. Further, the changes in the nature of the sea margins during the Caledonian orogeny, and the rise of the land plants, are speculatively related to both the extinction of the graptoloids and, later, the dendroids. Competition with other active nekton feeders, except possibly the dacrionarids, is considered unlikely.
O. T. Jones and after: A multitude of models
Authors: Holland C. H. , Kelling G. , Walton E. K.
Published: May 2008

The geosynclinal synthesis by O. T. Jones can be taken as the first major model for the British and Irish Caledonides. It was followed by a period of consolidation and exploration in which ground was covered (though by no means all of it); biostratigraphy was treated with increasing rigour; there were developments relating to faunal provincialism; new techniques and understanding of sedimentology transformed the palaeogeographical picture; and structural studies increased in sophistication with the recognition of polyphase deformation and strain patterns. Since the advent of the plate-tectonic hypothesis, an evolution of models can be traced as workers have explored the many and increasingly complicated possibilities. No model is entirely satisfactory; some earlier models can now be discarded with some confidence; others deserve further development, but many critical facts remain to be collected.
Slopes, submarine fans, and syn-depositional faults: sedimentology of parts of the Middle and Upper Dalradian in the SW Highlands of Scotland
Authors: Anderton R.
Published: May 2008

The depositional palaeogeography of the metasediments between the Jura Quartzite and Craignish Phyllites was dominated by a series of fault-bounded blocks and basins. The position of the basin margins, and hence the faults, is inferred from the location of submarine fan and slope facies and lateral thickness variations. These syn-depositional faults had trends either approximately parallel with, or normal to, the subsequent Caledonoid grain and had throws of up to several kilometres. Such faults may have exerted a major control over sedimentation throughout the Middle and Upper Dalradian. Many of the Dalradian sedimentary bodies therefore have a complex geometry, and persistent stratigraphical horizons may reflect regional climatic and tectonic events, rather than persistent sedimentary facies.
Stratigraphy of the aureole of the Cairnsmore of Fleet pluton, southwest Scotland
Authors: Cook D.R. , Weir J.A.
Published: May 2008

This Lower Palaeozoic succession is cut by four major strike faults of which the southeasternmost, the Pibble fault, is correlated with the Ettrick Valley fault. NW of the Pibble fault, Moffat Shales are overlain by greywackes of the Craignell Formation. Upper Birkhill Shales in the northwestern fault segment give way southeastwards to greywackes, extending downwards to the
M. gregarius
Zone. SE of the Pibble fault, greywackes comprise the Knockeans Formation, correlated with the Hawick Rocks and overlying the Craignell Formation. Maturity increases upwards. Within the Craignell Formation a basic source gives way to a dominant, granitic source, and this in turn to a metamorphic source. The Knockeans Formation is strongly silicic and probably recycled. Southward passage from pelagic to flysch facies may indicate a southward source for higher levels of the succession.
Oceanic sediments from the Ordovician of the Southern Uplands
Authors: Leggett J. K.
Published: May 2008

Fe-rich mudstones are intimately associated with Ordovician basalts in the Northern Belt of the Southern Uplands of Scotland. Field relations and geochemistry suggest that a significant proportion of the mudstone may be of hydrothermal-exhalative origin, having formed in a manner analogous to metalliferous sediments from modern active ridges. Cherts of Arenig to Llandeilo age overlie the basalts and contain abundant radiolarian remains. Carbonaceous mudstones replace the cherts near the base of the Caradoc. These are devoid of benthos, and herald the first of two euxinic phases (Caradoc and lower Llandovery) during the pelagic mudstone (Moffat Shale) regime. Coincidence with periods of transgression suggests that euxinification may have been induced by oceanographic factors relating to changes in sea level.
The north-western margin of the Iapetus Ocean
Authors: Leggett J. K. , McKerrow W. S. , Morris J. H. , Oliver G. J. H. , Phillips W. E. A.
Published: May 2008

A review of the stratigraphy, sedimentology, petrography, and structure of the Ordovician and Silurian rocks of the Southern Uplands (Scotland) and the Longford-Down zone (Ireland) identifies many features which are typical of accretionary wedges developed at Mesozoic-Recent subduction zones. The bedding becomes gradually more inverted in the west and northwest parts of the Longford-Down zone. Slumping becomes increasingly important along strike southwestwards from Scotland to Ireland. The roles of transform movement along the continental margin and of back arc spreading are also considered.