Northwest Highlands Research Articles

The minor intrusions of Assynt, NW Scotland: early development of magmatism along the Caledonian Front

AbstractThe Assynt Culmination of the Moine Thrust Belt, in the northwest Scottish Highlands, contains a variety of Caledonian alkaline and calc-alkaline intrusions that are mostly of Silurian age. These include a significant but little-studied suite of dykes and sills, the Northwest Highlands Minor Intrusion Suite. We describe the structural relationships of these minor intrusions and suggest a classification into seven swarms. The majority of the minor intrusions can be shown to pre-date movement in the Moine Thrust Belt, but some appear to have been intruded during the period of thrusting. A complex history of magmatism is thus recorded within this part of the Moine Thrust Belt. New geochemical data provide evidence of a subduction-related component in the mantle source of the minor intrusions.

Reconfiguring the Countryside: Power, Control, and the (Re)Organization of Farmers in West Mexico

This article examines the effects of the North American Free Trade Agreement (NAFTA) on Mexico's agricultural economy, with particular emphasis on the role of the government in economic restructuring aimed at privatization and global competitiveness. Government policy and practice have sought to revitalize select agricultural sectors that have faltered with the opening of the Mexican economy. This process will be explored through the analysis of the shifting relationship between the state and local elites in the northwest highlands of Michoacan, an area dominated by small-scale dairy farming. Much of rural Mexico has a long history of powerful caciques (local political strongmen) and their patronage networks, that have arisen in the service of state interests only to be replaced when political-economic conditions change. In this instance, neoliberal reforms have resulted in the reconfiguration of power and authority, and the emergence of new-style techno-caciques--well-educated political and economic entr...

Holocene reworking of drift-mantled hillslopes in Glen Docherty, Northwest Highlands, Scotland

Sections exposed within a colluvial debris cone in Glen Docherty, Scotland, reveal in-situ palaeosols intercalated with debrisflow diamictons and horizons of slopewash deposits. Radiocarbon dating of the palaeo sols suggests that drift reworking at this site involved brief, intermittent episodes of debrisflow and slopewash activity since c. 6.5 cal. ka BP. At least four such phases can be recognized: c. 6.5–6.2, 5.6–5.3, 4.9–4.6 cal. ka BP and after c. 450 cal. BP. The palaeosols examined show no evidence of local burning of vegetation. A calibrated radiocarbon age for the onset of the most recent phase of reworking may be interpreted as reflecting woodland clearance and/or the influence of extreme rainfall events during the ‘Little Ice Age’ period of regional climatic deterioration. The combined chronostratigraphic and palaeoecological evidence points to discrete, local rainstorms that are seemingly unrelated to long-term climatic change as the most likely cause of enhanced slope reworking, at least prior to c. 450 cal. BP. If this interpretation is valid, it implies that the formation of Holocene debris cones elsewhere in upland Britain may have been due primarily to a small number of localized, extreme rainstorm events. Consequently, caution is necessary in using debrisflow chronostratigraphy alone as a means of reconstructing long-term climate patterns.

The Migration Intentions of Young People in Ullapool

This article reports the results of a small research project, which investigated the migration intentions of a group of people aged 14-16 from the area in and around Ullapool, in the North-West Highlands, and compared the results with (hose of a similar study carried out in rural Ireland some 25 years ago with a comparable age group. Hannan (1969) examined voluntary migration from rural areas, the basic assumption of his study being Einsenstadl's assertion that 'migration results primarily from the belief that certain basic aspirations can not be satisfactorily fulfilled in the home community' (quoted by Hannan (1969, p. 196)).

Sir Archibald Geikie (1835-1924) and the "Highlands Controversy": New Archival Sources for the History of British Geology in the Nineteenth Century

With the help of new archival material relating to Archibald Geikie, discovered fairly recently at the Haslemere Educational Museum, some revisions are offered to my account of the "Highlands Controversy" (relating to the structure of the Northwest Highlands of Scotland), published in 1990.1 Also further light is thrown on the so-called "Archaean Controversy," especially with regard to the debates about the rocks at St. David's, Pembrokeshire. It is shown that Geikie did visit the north coast of Scotland before 1884, but made no observations there that had a bearing on the Highlands Controversy. He was, however, well prepared for a change of mind before he actually examined the rocks at Loch Eriboll in 1884. It appears that Geikie's chief "bête noire" was the petrologist Thomas Bonney, and to a lesser extent Charles Callaway. Some new information about Edward Greenly is revealed, and also the procedures of the Wharton Committee which looked into the affairs of the Survey in 1900, and led to Geikie's retirement.

Fertility characterization of soils at six research sites in NW Cameroon

Fertility capability of surface (0–20 cm) soils was evaluated at six sites in the North-West Cameroon highlands. Two main soil groups, designated as Classes A and B, were identified based on elevation. The Class A soils from low elevations (600–1178 m) had higher Ca, Mg, K, pH, sorbed less P and were lower in organic carbon and sesquioxides than the highland (> 1200 m) soils. Soil acidity (Al saturation > 30%) and high P sorption appeared to be the most limiting factors to crop production especially on the Class B soils where the Standard P Requirement exceeded 500 mg kg−1. Phosphorus sorption data were best described by the Freundlich equation. Amorphous aluminium was the most important determinant of solution P concentration (r = 0.85,p < 0.001) followed by soil organic carbon, (r = 0.80,p < 0.001) at high P rates. Nitrogen deficiency symptoms of maize were pronounced on the Class B soils. Consequently, crop growth and yield were lower on Class B than on Class A soils despite the high organic carbon in B. We hypothesize that the supply of high quality organic material (high in N and low in lignin and polyphenols) at site B through agroforestry and related cropping systems, would improve the fertility of the soil and crop yield.

The morphology of glacially fluted terrain: examples from the Northwest Highlands of Scotland

The aim of this paper is to describe the morphological variation present within the fluted terrain of the Highland ice-field which existed in the Scottish Highlands during the Loch Lomond Stadial (Younger Dryas). Three types of fluted landform are identified in the Torridon area: (1) ‘hummocky-flutes’; (2) regular megaflutes; (3) streamlined hills. The morphological characteristics and mode of formation of each of these three types of fluted terrain is discussed and their distribution within other parts of the Highland ice-field is examined.

Strandflat development and Quaternary shorelines on Tiree and Coll, Scottish Hebrides

AbstractThe islands of Tiree and Coll in the Scottish Inner Hebrides are dominated by staircases of glaciated rock‐platform surfaces in Lewisian gneiss that are interpreted here as areas of strandflat. The rock platform surfaces exhibit differential glacio‐isostatic uplift from east to west and are considered to indicate at least four separate periods of strandflat formation during prolonged intervals of Quaternary cold climate. It is suggested that many of the well‐known areas of high rock platform located farther east in the Scottish Inner Hebrides represent eroded remnants of the strandflat surfaces described here. The existence of the Tiree and Coll strandflat surfaces in conjunction with their formation during periods of Quaternary glaciation implies that they were produced during periods when mainland Scotland was ice‐covered yet when the western margin of the ice sheet was normally located east of these islands. A prominent Late‐glacial raised shoreline also occurs on both islands and declines in altitude to the west, from 22 m in northeastern Coll to 9 m in western Tiree. It is believed that this shoreline, whose regional gradient is 0.39 m km−1, may represent part of the Main Wester Ross Shoreline that was formed in the Northwest Highlands of Scotland during a period of glacial advance that interrupted the decay of the last (Late Devensian) ice sheet. The general similarity in altitude between the Late‐glacial shoreline features and rock platform surfaces implies that during each period of Quaternary strandflat formation, relative sea‐level returned to the same approximate position. This would appear to indicate that the glacio‐isostatic and glacio‐eustatic components affecting the positions of relative sea level in Scotland have remained in approximate equilibrium throughout the duration of the Quaternary.

Investigating the crustal structure of a strike‐slip “step‐over” zone along the Great Glen fault

Strike‐slip step‐overs and bends are regions of anomalous deformation that may yield clues to the mechanical behavior of the Earth's crust. Experimental reprocessing of a marine deep seismic reflection profile cutting across an ∼35‐km‐wide right‐stepping step‐over developed on the Great Glen fault system north of the Inner Moray Firth basin (east of Northwest Highlands, Scotland) reveals a restricted zone of prominent reflections and diffractions beginning at 7–8 km depth, continuing as deep as the interpreted Moho discontinuity at 26–27 km. Geological interpretation of this zone suggests a concentration of possible diffractors marking sharp structural disruption underlain by a ∼12‐km thick layer of subhorizontal and moderately dipping reflectors that dominates the lower crust in the step‐over region. The known kinematic history of the Great Glen fault system, together with the observed direction of the step‐over, implies that a zone of contraction would have formed within the step‐over during early Caledonian sinistral strike slip. The seismic reflection structure can be interpreted as developing by deformation associated with contraction and possible block rotation between the two fault segments such that the diffractive zone represents steep structure in a near‐vertical zone of strike slip which passes deeper into a layer of low‐angle dipping thrusts or shear zones. The results of this study are consistent with a concept of mechanical detachment in the middle crust as documented for areas of contraction along active strike‐slip faults.

Deep seismic reflection structure of the Caledonian orogenic front west of Shetland

Although the Moine Thrust has been well studied on land in northwestern Scotland, the subject of its deep crustal structure and regional continuation offshore remains controversial. Here, we use post-stack migration and filtering of deep seismic reflection profiles crossing the projection of the Moine Thrust and coincident Caledonian orogenic front around the western margin of the Shetland Platform in order to characterize the crustal structure of the thrust in an area not substantially affected by basin formation and extension, and where onshore geological constraints can be more readily applied. This study provides for the first time seismic reflection constraints on middle and lower crustal structure down to the level of the Moho discontinuity underlying the thrust. The seismic data reveal a thick wedge of east-dipping reflections in the lower crust capped by a highly coherent reflection which can be correlated to the postulated Moine Thrust as previously mapped on Shetland. The continuation of this wedge from the middle crust down to the Moho, against which individual reflections are abruptly truncated, suggests a ‘thick-skinned’ interpretation for the Caledonian orogen beneath the, western flank of the Shetland Platform. The available seismic data from around Shetland imply that the Moine Thrust/Caledonian front forms a boundary between an upper plate which is relatively featureless structurally and a lower plate composed of interpreted northwest-verging thrusts, possibly a crustal duplex, structurally below the level of the Moine nappe. Our observations are thus in contrast with previous interpretations made from seismic data in the West Orkney Basin north of the Northwest Highlands that describe a highly reflective Moinian upper plate.

Age and Regional Relationships of Granitoid Rocks of the Adirondack Highlands

Approximately 55% of the Adirondack highlands is underlain by granitic to tonalitic rocks that can be subdivided into five groups based on age, composition, and field occurrence: (1) early calcalkaline tonalites (ca. 1300 Ma) and associated granitic rocks (ca. 1250 Ma) of the southern and eastern highlands, (2) older anorogenic plutonic rocks (1145-1160 Ma) that occur throughout the highlands, (3) younger anorogenic plutonic rocks (ca. 1130 Ma) that envelop anorthosite massifs in the central highlands, (4) younger granitic rocks (1095-1105 Ma) of the northwest highlands, and (5) late leucogranitic rocks (1060-1080 Ma) that occur throughout the northern highlands. The data presented here are in good agreement with zircon ages from the Green Mountains of Vermont as well as from southern Ontario and Quebec and suggest similar geologic histories for these regions. These results document a protracted and complicated evolution for this portion of the Grenville Province.

A note on the regional context of the Loch Monar synform

AbstractThe Loch Monar Synform folds the Sgurr Beag slide in the central northwest Highlands of Scotland. The east–west trend of the synform is oblique to the regional trend of the slide. However, when late-stage strain effects associated with superimposed folds on the synform are removed using computer techniques, the trace of the synform axial surface becomes perpendicular to the regional trace of the slide. The synform also becomes tighter and recumbent in attitude. The synform axis is parallel to strongly developed lineations. Folds of this generation appear to be localized in the vicinity of the slide. These observations suggest a model of folding associated with movement of the slide, followed by locking up of the slide and internal strain resulting in the superimposed folds and rotation of the synform.

Early proterozoic continental accretion in the canadian shield: Evidence from U-Pb geochronology of reactivated Archean crust in the labrador trough and Thompson Belt

The Glenelg-Attadale Inlier of the northwest Highlands of Scotland comprises a Western Unit (WU) containing Trondhjemite-Tonalite-Granodiorite (TTG) gneisses and subordinate mafic bodies and an Eastern Unit (EU) containing abundant mafic rocks (eclogite), minor ultrabasic bodies and manganiferous metasedimentary rocks and marbles intercalated with intermediate to acid gneiss. The boundary between these two units is an amphibolite facies ductile shear zone, which contains kinematic criteria indicating a top-to-the-west (contractional) sense of shear. The EU was exhumed from eclogite facies to amphibolite facies conditions of the mid-crust at ca. 1000 Ma via amphibolite facies ductile shearing. A series of shear zones with identical metamorphic grade and kinematics occur at the contacts of the EU with the WU and the surrounding Moine Supergroup.In this study, an attempt is made to directly date the shear zone between the EU and WU, which also contains Moine Supergroup metasediments. A U–Pb titanite age of 669 ± 31 Ma, from syn-kinematic titanite within a mylonite, indicates a minimum age for movement on this shear zone, demonstrating that it must be Late-Proterozoic in age, and not Caledonian as previously supposed. If the shear zone is Grenvillian (ca. 1000 Ma) in age, this would then require that the Moine be deposited before ca. 1000 Ma in order to undergo burial to the mid-crust at this time. However, the youngest detrital zircons in the Moine indicate a maximum deposition age of 1000 Ma and, therefore, preclude this possibility. An alternative possibility is that movement along this shear zone was punctuated, with an initial phase involving uplift of eclogites to the mid-crust at ca. 1000 Ma, followed by a further period of top-to-the-west shearing, coupling of the Moine Supergroup and EU in the mid-crust during a putative Neoproterozoic “Knoydartian” orogenic event. However, since there are now three contractional “orogenic” events affecting the Moine, ca. 820, 740 and 670 Ma, it is suggested here that the term “Knoydartian” is no longer well-defined and requires re-appraisal.A later phase of extensional ductile shearing and large-scale folding, during a period of lower amphibolite facies metamorphism, is shown to be broadly Caledonian, based on a 437 ± 6 Ma U–Pb titanite age from a pegmatite, that is deformed during this event, and prior to movement along the Moine Thrust Zone. This further suggests an Ordovician “Grampian” orogenic event within the Northwest Highlands of Scotland.

A samarium-neodymium isotopic survey of modern river sediments from Northern Britain

A Sm&.zsbnd;Nd isotopic survey of 32 river and estuarine sediments from northern Britain has been carried out with the aims of comparing model ages for the sediments with rocks which make up the source areas and providing a data base for the mean age of the Scottish basement. Model ages for river sediments from the Northwest Highlands, Grampian Highlands and Southern Uplands of Scotland are directly comparable with the mean model ages for the various lithologies which comprise these areas. This confirms the validity of using sedimentary Sm-Nd model ages for studying variations in the mean age of the continental crust. The data illustrate southwards younging of the Scottish basement from mean ages > 2.2 Ga in the NW Highlands to ∼ 1.63 Ga in the Grampian Highlands to < 1.44 Ga in the Southern Uplands. This variation may be explained by increasing remoteness from the Archaean Lewisian shield, southwards increase in Palaeozoic magmatism and the effect of sedimentary recycling.

Owner motivation and land use on landed estates in the north-west Highlands of Scotland

Although rarely defined, the terms misuse and underuse have been widely used in relation to the land uses of large Highland estates. This paper considers the results of a study of estates in north-west Sutherland which examined the links between owner motivation and land use. The estates are classified according to land use and use intensity, and differences in these are considered as the product of owner motivations and management objectives, and of the financial backgrounds of owners. The dominant owner motivation is private enjoyment, particularly on sporting estates. Management structures are typically simple, reflecting the restricted range of uses. Most decision-makers are non-resident and their management input is more important on commercially-orientated estates than on those associated with private sport. Government agencies, except those associated with grants and subsidies, have little influence on management: owner motivation is more important. Most estates in the survey identified development potential, but few had invested in developments. Amenity rather than economic potential, particularly on sporting estates, is the most important constraint. More commercially-orientated estates generated investment capital internally from their enterprises. There seems to be a growing difference between estates associated with private sport and all other types of estates. Even on land of similar quality, the latter are expanding their enterprises, while the former are contracting. In the absence of a coherent public policy framework, landholders are the rural decision-makers. If land development and employment creation are to be pursued in the rural Highlands, a more positive and interventionist approach is required.

Long-Term Declines of Red Grouse in Scotland

(1) Shooting bag records of red grouse were obtained by a questionnaire survey. Data from 160 Scottish moors were analysed to show temporal and spatial variations in grouse abundance. (2) Red grouse bags declined in two stages. The first occurred during the 1939-45 War and affected the whole country. The second stage occurred between the mid-1970s and 1983. During it, most moors in the Central Highlands and the South-West experienced a steep decline in grouse bags. The South-East showed only a slight decrease, while in the North-West Highlands bags increased.

Pentameral fossils from the Lower Cambrian Pipe Rock of the North-West Highlands

Synopsis Star-shaped pentameral fossils occur commonly on a single bedding surface of the Lower Cambrian Pipe Rock at Allt nan Uamh, south of Inchnadamph. They occur as pure white quartzite fills in a yellow quartzite matrix, but preserve no trace of a body wall. The original shape is believed to have been like a five-lobed ctenophore. Each lobe has a median partition, but no trace of any orifice has been seen. The fossils are interpreted as body fossils. They are not echinoderms despite their consistent pentamery, but we can suggest no other phylum.

Palaeomagnetism of late Precambrian-Cambrian volcanics and intrusives from the Armorican Massif, France

Summary. Results are presented for a magnetotelluric and magnetovariational study in northern Scotland. For nine of the 20 sites at which observations were made the results of the analysis are presented fully together with one-dimensional (1-D) Monte-Carlo inversions for representative sites from the Lewisian Foreland, the North-west Highlands, the Great Glen region and the Grampian Highlands. For the remaining sites, the results are summarized. The 1-D models of all sites situated in a traverse extending from the Lewisian Foreland to the neighbourhood of the Highland Boundary Fault have been used as the basis for preliminary 2-D modelling. Maps of magnetic field induction vectors and transfer functions for an inducing field perpendicular to the average geological strike are presented for periods of 23-819s. The 2-D conductivity models were constrained by both the magnetotelluric and magnetovariational responses. The period range of observation in this study was too limited to resolve structural differences in the upper crust but adequate to reveal a moderately good conductor at upper mantle/lower crustal depths in the Caledonian metamorphic zone. In contrast the whole of the crust in the Lewisian Foreland is highly resistive and there is no evidence of an intermediate conducting layer between the crust and mantle in this region.

Studies in the vegetational history of Scotland IV. Pine stumps in Scottish blanket peats

The palaeoecology of six Scottish blanket peat profiles containing pine stumps was investigated by means of peat stratigraphy, pollen analysis, and radiocarbon dating. In addition, several other pine and birch remains from peat in other areas of Scotland were radiocarbon dated. Three peat profiles were selected in each of two contrasting regions. The Cairngorm area is within the distributional area of native pine today and pollen analysis has shown that pine has been a major component of the upland forest since about 7000 b.p. The Galloway region in southwest Scotland is south of the native pine area, and pollen analysis has shown that pine has never been a major component of the upland forest. Despite the limitations of the methods used, it has been established that there were several different circumstances for the growth and death of the pines studied, and that their ages are asynchronous within and between the two areas. Thus little regional climatic significance can be assumed from their occurrence, and they cannot be taken as evidence in support of dry Boreal and sub-Boreal periods in the Blytt and Sernander climatic scheme. In the northwest Highlands dates from pine stumps and major declines of pollen in pollen diagrams are consistently around 4000 b.p. This overall demise of pine may have a regional climatic cause in this area.

Summer Field Meeting in the North-West of Scotland: 11–18 September 1971

The report provides an itinerary for a week's Field Meeting in the north-west Highlands of Scotland. The main purpose of the Meeting was to visit areas along the Moine Thrust Belt which have been the subject of recent work. The structure of the Eriboll, Assynt and Lochalsh areas is described in some detail and a running commentary is provided to the geology encountered en route .