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

The 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.     

Loch Lomond Stadial and Flandrian shorelines in the inner Moray Firth area,Scotland

Morphological mapping and stratigraphical investigations have identified surface and buried relict marine features in the inner Moray Firth area. The features consist of a buried gravel layer formed during the Loch Lomond Stadial, a buried beach of early Flandrian age, and surface beaches and estuarine flats of mid-late Flandrian age. Analysis of the altitudes of morphological features has identified two buried and five (possibly six) surface glacio-isostatically tilted raised shorelines. The steepest shoreline is associated with the buried gravel layer and slopes down towards N20°E at a gradient of 0.20m/km. Younger shorelines have lower gradients between 0.16–0.03m/km. The shoreline sequence combined with published data defines relative sea-level movements in the area during the last 11000 years. The inner Moray Firth shorelines are correlated with similar features in other areas of Scotland which include the Main Lateglacial, Main Buried and Main Postglacial Shorelines.     

Examining the geometry,age and genesis of buried Quaternary valley systems in the Midland Valley of Scotland,UK

Buried palaeo‐valley systems have been identified widely beneath lowland parts of the UK including eastern England, central England, south Wales and the North Sea. In the Midland Valley of Scotland palaeo‐valleys have been identified yet the age and genesis of these enigmatic features remain poorly understood. This study utilizes a digital data set of over 100 000 boreholes that penetrate the full thickness of deposits in the Midland Valley of Scotland. It identified 18 buried palaeo‐valleys, which range from 4 to 36 km in length and 24 to 162 m in depth. Geometric analysis has revealed four distinct valley morphologies, which were formed by different subglacial and subaerial processes. Some palaeo‐valleys cross‐cut each other with the deepest features aligning east–west. These east–west features align with the reconstructed ice‐flow direction under maximum conditions of the Main Late Devensian glaciation. The shallower features appear more aligned to ice‐flow direction during ice‐sheet retreat, and were therefore probably incised under more restricted ice‐sheet configurations. The bedrock lithology influences and enhances the position and depth of palaeo‐valleys in this lowland glacial terrain. Faults have juxtaposed Palaeozoic sedimentary and igneous rocks and the deepest palaeo‐valleys occur immediately down‐ice of knick‐points in the more resistant igneous bedrock. The features are regularly reused and the fills are dominated by glacial fluvial and glacial marine deposits. This suggests that the majority of infilling of the features happened during deglaciation and may be unrelated to the processes that cut them.     

Multicomponent magnetization in the helmsdale granite, north Scotland; geotectonic implication

A palaeomagnetic study of the Helmsdale granite (U/Pb-420 m.y., K/Ar-400 m.y.), northeast Scotland, has revealed a multicomponent remanence dominated by two characteristic axes of magnetization. The suggested oldest of these magnetizations, the direction of which is nearly horizontal and directed N-S, is thought to have been acquired in Upper Silurian-Lower Devonian times. The existence of this shallow direction of magnetization discounts a recent hypothesis of a ca. 2000 km sinistral offset along the Great Glen Fault. The second component of magnetization appears to be partly carried by haematite that apparently formed through disintegration of biotite and/or plagioclase. This secondary magnetization has a direction that can be associated with a Permian-early Mesozoic age. Similar overprinted magnetizations are characteristic features also in the Devonian sedimentary sequences north of Helmsdale.     

关于巴罗式变质带的最新研究及其对研究秦岭杂岩的意义

本文对苏格兰高地Grampian造山运动中产生的经典巴罗变质带进行了讨论,重点介绍了近年来关于其变质作用的特征及发生机制认识方面的重大变化。强调巴罗变质作用仅发生在整个造山运动过程中的部分时段,纪录了短暂的加热过程,时空上与区域内大规模的双峰式岩浆活动有关。经典的巴罗变质系列并非形成于地壳增厚及其热弛豫,而是代表了中地壳内大规模的接触变质作用。参考经典地区的变质特征,对发育巴罗式变质作用的秦岭杂岩进行了初步对比分析,指出其中与夕线石有关的变质P-T-t轨迹可能是等压冷却过程,而不是等温降压的顺时针演化模式。秦岭杂岩的变质作用时间仍需要进一步准确厘定。结合其它相关地质特征的分析和对比,得出如下推论:巴罗式变质带发育地区的变质作用、混合岩与花岗岩均属于同一动力系统作用的结果,花岗质岩体不是变质作用的原因;基性岩浆可能提供了巴罗式变质作用发生所需要的热能,但不是必要条件;巴罗式变质作用可以发生在正常地壳厚度情况下,不是碰撞构造的标志;伴随热异常的变形过程中产生了变质带的梯度分布(巴罗式变质带)和一些花岗岩,形成类似于底辟的冲起构造。     

Amphibolitization of metagabbros in the Scottish Highlands

Abstract Compositions of actinolite, hornblende and cummingtonite, together with pyroxene and plagioclase, are studied in basic intrusions in the Dalradian of north-east Scotland, and the Glen Scaddle complex in the West Moine. Amphibolitization is due to influx of water from the country rocks. Pyroxene compositions are found to have adjusted to the regional metamorphic environment. Owing to the difficulty of diffusion of Al and Si, calcic amphiboles are zoned and commonly contain quartz blebs. Discontinuities in zoning give rise to actinolite-hornblende pairs. Compared with north-east Scotland, disequilibrium is less strong in the Glen Scaddle area: in the latter, plagioclase compositions have been greatly changed, Na partition between hornblende and plagioclase is close to equilibrium, the maximum Al content of hornblende is lower and zoning patterns are more consistent. The Fe/Mg ratio in calcic amphiboles varies with Al content, while approaching equilibrium partition with other minerals. Both zoning patterns and Fe/Mg partition with cummingtonite suggest that Fe/Mg of the calcic amphiboles increases more strongly with increasing (Al^vi+Fe³⁺) than can be explained simply by substitution of Al,Fe³⁺ for Mg on M2. Model reactions for amphibole formation are constructed. Cummingtonite formed at lower chemical potential of CaO than actinolite: Ca was exchanged for Mg,Fe between orthopyroxene-derived and clinopyroxene-derived local systems. Both cummingtonite and actinolite were formed because of kinetic constraints, as intermediate reaction products: actinolite-hornblende pairs represent disequilibrium. This work suggests that many occurrences of actinolite with hornblende, where the minerals are zoned, may also be due to diffusion kinetics.     

A method for modelling coastal erosion risk: the example of Scotland

It is thought that 70% of beaches worldwide are experiencing erosion (Bird in Coastline changes: a global review, Wiley, Hoboken, 1985), and as global sea levels are rising and expected to accelerate, the management of coastal erosion is now a shared global issue. This paper aims to demonstrate a method to robustly model both the incidence of the coastal erosion hazard, the vulnerability of the population, and the exposure of coastal assets to determine coastal erosion risk, using Scotland as a case study. In Scotland, the 2017 Climate Change Risk Assessment for Scotland highlights the threat posed by coastal erosion to coastal assets and the Climate Change (Scotland) Act 2009 requires an Adaptation Programme to address the risks posed by climate change. Internationally, an understanding and adaption to coastal hazards is imperative to people, infrastructure and economies, with Scotland being no exception. This paper uses a Coastal Erosion Susceptibility Model (CESM) (Fitton et al. in Ocean Coast Manag 132:80–89. https://doi.org/10.1016/j.ocecoaman.2016.08.018 , 2016) to establish the exposure to coastal erosion of residential dwellings, roads, and rail track in Scotland. In parallel, the vulnerability of the population to coastal erosion, using a suite of indicators and Experian Mosaic Scotland geodemographic classification, is also presented. The combined exposure and vulnerability data are then used to determine coastal erosion risk in Scotland. This paper identifies that 3310 dwellings (a value of £524 m) are exposed to erosion, and the Coastal Erosion Vulnerability Index (CEVI) identifies 1273 of these are also considered to be highly vulnerable to coastal erosion, i.e. at high risk. Additionally, the CESM classified 179 km (£1.2 bn worth) of road and 13 km of rail track (£93 m to £2 bn worth) to be exposed. Identifying locations and assets that are exposed and at risk from coastal erosion is crucial for effective management and enables proactive, rather that reactive, decisions to be made at the coast. Natural hazards and climate change are set to impact most on the vulnerable in society. It is therefore imperative that we begin to plan, manage, and support both people and the environment in a manner which is socially just and sustainable. We encourage a detailed vulnerability analysis, such as the CEVI demonstrated here for Scotland, to be included within future coastal erosion risk research. This approach would support a more sustainable and long-term approach to coastal management decisions.     

Staurolite at anomalously high grade

In the Huntly — Portsoy area, north-east Scotland, staurolite occurs in muscovite-free migmatized semipelites. This occurrence in the Sillimanite-potash feldspar Zone is petrographically distinct from lower-grade staurolite found nearby. Petrographic and chemical data indicate that the staurolite formed stably during the migmatization episode. It was stabilized by high zinc-content. Its formation was probably an early retrograde effect.     

Sidescan sonar applications in limnoarchaeology

Sidescan sonar, a well known marine geophysical exploration technique, widely utilized in maritime archaeology, has great potential as a reconnaissance tool in limnoarchaeological surveys. Its application in the identification of manmade structures on the floor of a flooded valley (Glenfarg Reservoir, Scotland) and the location of nearshore settlements (crannogs) in a natural water body (Loch Tay, Scotland) are described and discussed. It is suggested that sidescan sonar is a more efficient method of underwater archaeological reconnaissance than diver surveys.     

Lateglacial and postglacial shorelines in western Scotland

Some recent studies of raised shorelines in western Scotland, which are gaining international acceptance, are assessed in the light of subsequent criticisms. Fieldwork has revealed that there are differences in altitude measurements, interpretations, and conclusions between these studies and the present one in Lorn and eastern Mull. Two short lateglacial shorelines are tentatively suggested, but there is a general abesence of clear, widespread shorelines of this age. The Main Postglacial Shoreline has a gradient of 0.05 m/km, considerably less than found in previous studies in both western and south-cast Scotland. Subsequently, as relative sea level fell to its present level, two fairly clear shorelines with low gradients were formed together with traces of intermediate ones. The influences of the. Falls of Lora rock bar and of exposure on showline altitude are also examined.     

Subduction-related shoshonitic and ultrapotassic magmatism: a study of Siluro-Ordovician syenites from the Scottish Caledonides

Syenites are important or predominant components of several plutonic complexes, emplaced between 456 and 415 Ma along the NW margin of the Caledonian orogenic belt, adjacent to the Lewisian foreland, in W and NW Scotland. Although there are, in detail, chemical differences between the syenites from each centre, they form a well-defined compositional group overall. Ratios amongst their trace elements (especially very high values of La/Nb) are quite different from those trachytes and syenites formed by fractional crystallisation of ocean-island basalts and their continental equivalents, emplaced in regions of anorogenic crustal tension. Instead, the Scottish Caledonian syenites closely resemble chemically the fractional-crystallisation residua of potassic subduction-related magmas, such as the shoshonitic series. A comendite minor intrusion from a swarm associated with the Loch Borralan and Loch Ailsh syenitic complexes is remarkably similar in composition to Recent obsidian from the shoshonitic volcano of Lipari, in the Aeolian Arc. Published Sr- and Pb-isotopic ratios preclude a significant component of either upper (Proterozoic Moine schists) or lower crust (granulite-facies Archaean Lewisian or Proterozoic Grenvillian gneisses) in all these syenites, except in local syenitic facies of the Glenelg-Ratagain complex. Fractional crystallisation appears to be the mechanism by which the liquids which formed these syenites evolved from basic parental magmas. The phases involved in this process may have included plagioclase, alkali feldspar, pyroxene, amphibole, biotite, garnet, Fe-Ti oxide, sphene, allanite, apatite, zircon and zirconolite, and therefore all the ratios amongst even the so-called incompatible elements may have changed during the evolution of the leucocratic magmas. Nevertheless, a detailed study of the Glen Dessarry complex shows that the changes are insufficient to disguise the geochemical nature of the parental magmas. These appear to be picritic shoshonite (MgO> 15%, Ni>400ppm, La/Yb20, La/Nb>5) for the Glen Dessarry, Loch Borralan and Loch Ailsh syenites, and picritic ultrapotassic magmas (MgO>15%, Ni>400 ppm, La/ Yb60, La/Nb>7) — such as would crystallise to minettes — for the Loch Loyal and Glenelg-Ratagain syenites. Mafic shoshonites were erupted amongst the 410 Ma Lome lavas of this region and also occur as widespread approximately-contemporaneous volcanic feeder plugs. Minettes of similar age are also common as dykes in NW Scotland. Numerous large tonalite-granite complexes, with minor diorites and gabbros, were emplaced in W and NW Scotland between 435 and 400 Ma. These are generally acknowledged to be mixtures of magmas from crustal and mantle sources. Their more mafic members show compositional features, such as very high Ba and Sr, which group them with the rare syenites and the Lorne lavas of the same region into a distinctive geochemical province, within which shoshonitic and allied magmas were the mantle-derived component. Two models are presented to account for the generation of strongly-potassic, subduction-related magmas several hundred km behind a NW-directed subduction zone, or during the period immediately following continental collision.     

Crystallization of melts, pegmatite intrusion and the Inverian retrogression of the Scourian complex, north-west Scotland

Abstract Partial melting of tonalitic gneisses in the 2.7 Ga Badcallian granulite facies metamorphic episode in the Scourian complex of north-west Scotland produced a suite of granitic to trondhjemitic liquids. On cooling and excavation of the complex, these melts underwent fractional crystallization and the residual liquids eventually became water saturated. Comparison with experimental data suggests that water saturation would have occurred in these melts at around 620–700°C. From the retrograde P–T -time path followed by the complex it is estimated that H₂O-dominated fluids were exsolved from these melts at c. 2.5 Ga. It is proposed that these fluids were the cause of the 2.5 Ga Inverian retrogression of the Scourian complex and that water-saturated melts formed during the crystallization of the leucogneisses were intruded as a suite of pegmatites. The timing of pegmatite intrusion is consistent with this proposition as are the temperature estimates, timing, distribution and nature of the Inverian phase of metamorphism. It is likely that the crystallization of melts is an important process in bringing about hydrous retrogressive metamorphic episodes in a number of other basement terrains, such as West Greenland and Australia.     

Geochemistry of mafic and ultramafic xenoliths from Fidra (Southern Uplands, Scotland): implications for lithospheric processes in Permo-Carboniferous times

Several types of xenoliths occur in a Permian basanite sill in Fidra, eastern central Scotland. One group consists of spinel lherzolites, which have geochemical and isotopic characteristics similar to those of lithospheric upper mantle from elsewhere in western Europe, with both LREE-depleted and LREE-enriched compositions. A separate group comprises pyroxenites and wehrlites, some of which contain plagioclase; these have compositions and textures that indicate that they are cumulates from mafic magmas. In terms of Sr and Nd isotope compositions, the pyroxenites closely resemble the host basanite and most likely formed by high-pressure fractionation of Permo-Carboniferous alkaline magmas at lower crustal depths. They also have mantle-like δ¹⁸O values. A third group is composed of granulite xenoliths that vary between plagioclase-rich and clinopyroxene-rich compositions, some of which probably form a continuum with the pyroxenites and wehrlites. They are all LREE-enriched and most have positive Eu anomalies; thus, they are also mostly cumulates from mafic magmas. Many of the granulites also have Sr and Nd radiogenic isotope ratios similar to those of the host basanite, indicating that they have formed from a similar magma. However, several of the granulites show more enriched isotopic compositions, including higher δ¹⁸O values, trending towards an older crustal component. Thus, the pyroxenites and granulites are largely cogenetic and are mainly the product of a mafic underplating event that occurred during the widespread magmatism in central Scotland during Permo-Carboniferous times.     

Seafloor glacial features reveal the extent and decay of the last British Ice Sheet,east of Scotland

Three‐dimensional (3D) seismic datasets, 2D seismic reflection profiles and shallow cores provide insights into the geometry and composition of glacial features on the continental shelf, offshore eastern Scotland (58° N, 1–2° W). The relic features are related to the activity of the last British Ice Sheet (BIS) in the Outer Moray Firth. A landsystem assemblage consisting of four types of subglacial and ice marginal morphology is mapped at the seafloor. The assemblage comprises: (i) large seabed banks (interpreted as end moraines), coeval with the Bosies Bank moraine; (ii) morainic ridges (hummocky, push and end moraine) formed beneath, and at the margins of the ice sheet; (iii) an incised valley (a subglacial meltwater channel), recording meltwater drainage beneath former ice sheets; and (iv) elongate ridges and grooves (subglacial bedforms) overprinted by transverse ridges (grounding line moraines). The bedforms suggest that fast‐flowing grounded ice advanced eastward of the previously proposed terminus of the offshore Late Weichselian BIS, increasing the size and extent of the ice sheet beyond traditional limits. Complex moraine formation at the margins of less active ice characterised subsequent retreat, with periodic stillstands and readvances. Observations are consistent with interpretations of a dynamic and oscillating ice margin during BIS deglaciation, and with an extensive ice sheet in the North Sea basin at the Last Glacial Maximum. Final ice margin retreat was rapid, manifested in stagnant ice topography, which aided preservation of the landsystem record. Copyright © 2008 John Wiley & Sons, Ltd.     

Staurolite-forming reactions in the eastern Dalradian rocks of Scotland

Data on mineral and rock compositions along with textural relations are used to deduce the staurolite-forming reactions in eastern Dalradian rocks in Scotland. Initially staurolite is formed as a product of the breakdown of the assemblage chloritoid +quartz in iron-rich metapelites. With increase in grade the iron-rich rocks are succeeded by more magnesium-rich ones and staurolite is formed as a product of the breakdown of the assemblage chloritoid +chlorite+muscovite.     

The importance of air escape processes in the formation of dish-and-pillar and teepee structures within modern and Precambrian fluvial deposits

Attributed to escape of water from unconsolidated deposits, teepee and dish-and-pillar structures are common features in the Late Proterozoic Torridonian red bed succession of NW Scotland. Study of the first annual flood on a modern depositional analogue, in Wadi Baysh, Saudi Arabia, revealed that a layer of mud, initially deposited across the alluvium, restricted the escape of air being displaced through the normally unconfined aquifer by waters entering the aquifer from the river channels. As air bubbled through high level pool-floor muds, it generated dish-and-pillar structures. The formation of teepee structures by similarly combined air and water escapes nearer to the channel later in the annual cycle of flooding is foreseen. It is suggested that the two sediment structures are generated in response to different parts of the aquifer recharge spectrum. The role of air displacement by influent waters is important in the initial phases of structure formation, and combined air and water escape creates greater disturbance to the sediments. The sedimentary structures formed are not, therefore, solely due to water escape, as has been previously suggested. Ephemeral seasonal flooding appears to have characterized the deposition of at least the Stoer Group and Diabaig Formation sediments in the Torridonian.     

Geomorphological signature and flow dynamics of The Minch palaeo‐ice stream,northwest Scotland

Large‐scale streamlined glacial landforms are identified in 11 areas of northwest Scotland, from the Isle of Skye in the south to the Butt of Lewis in the north. These ice‐directional features occur in bedrock and superficial deposits, generally below 350 m above sea level, and where best developed have elongation ratios of >20:1. Sidescan sonar and multibeam echo‐sounding data from The Minch show elongate streamlined ridges and grooves on the seabed, with elongation ratios of up to 70:1. These bedforms are interpreted as mega‐scale glacial lineations. All the features identified formed beneath The Minch palaeo‐ice stream which was ca. 200 km long, up to 50 km wide and drained ca. 15 000 km² of the northwest sector of the last British‐Irish Ice Sheet (Late Devensian Glaciation). Nine ice‐stream tributaries and palaeo‐onset zones are also identified, on the basis of geomorphological evidence. The spatial distribution and pattern of streamlined bedforms around The Minch has enabled the catchment, flow paths and basal shear stresses of the palaeo‐ice stream and its tributaries to be tentatively reconstructed. © British Geological Survey/Natural Environment Research Council copyright 2007. Reproduced with the permission of BGS/NERC. Published by John Wiley & Sons, Ltd.     

A qualitative risk assessment for the impacts of climate change on nationally and internationally important geoheritage sites in Scotland

Climate change is a significant concern for nature conservation in the 21?st century. One of the goals of the 2014 Scottish Climate Change Adaptation Programme is to identify the consequences of climate change for protected areas and to put in place adaptation or mitigation measures. As a contribution to the process, this paper develops a methodology to identify the relative level of risk to nationally and internationally important geological and geomorphological sites in Scotland from the impacts of climate change. The methodology is based on existing understanding of the likely responses of different types of geosite to specific aspects of climate change, such as changes in rainfall, rising sea levels or increased storminess, and is applied to assess the likelihood of damaging impacts on groups of similar geoheritage features in sites with similar characteristics. The results indicate that 80 (8.8%) of the ～900 nationally and internationally important geoheritage sites in Scotland are at ‘high’ risk from climate change. These include active soft-sediment coastal and fluvial features, finite Quaternary sediment exposures and landforms in coastal and river locations, active periglacial features, sites with palaeoenvironmental records, finite or restricted rock exposures and fossils. Using this risk-based assessment, development of indicative geoheritage climate-change actions have been prioritised for these sites. Depending on the characteristics of the sites, management options may range from ‘do nothing’ to rescue excavations and posterity recording. Monitoring is an essential part of the management process to trigger evidence-based interventions.     

新疆西准噶尔红山岩体地质地球化学特征及对下地壳性质的启示

准噶尔盆地基底性质历年来一直存在争议, 而花岗岩地球化学特征对下地壳性质具有指示意义.研究发现, 红山岩体的岩石类型主要为碱长花岗岩, 具有高SiO₂、低Al₂O₃、偏碱性、准铝质、轻重稀土分馏相对明显且富集轻稀土、明显的Eu异常、富集Rb、Th、K等大离子亲石元素及Zr、Hf等高场强元素而强烈亏损Sr、Ba、P、Ti等元素的A型花岗岩特征, 形成于后碰撞的张性环境中.SIMS和LA-ICP-MS测试获得的岩体侵位年龄分别为315.7±2.4Ma(MSWD=0.82)和317.8±3.8Ma(MSWD=2.8), 指示该岩体为晚石炭世早期的产物, 与西准噶尔后碰撞岩浆活动的时限一致.红山碱长花岗岩的结晶温度为680~860℃, Lu-Hf、Sr-Nd同位素特征共同表明西准噶尔的基底是由亏损地幔演化而来的年轻地壳物质组成.