Central Perthshire Research Articles

Briza media L.

A loosely tufted perennial with short rhizomes from which arise vegetative shoots. Culms 15-60 (-100) cm high, slender, erect, 2-3-noded, solitary, smooth. Leaves with dull glaucous to mid-green adaxial and abaxial surfaces, hairless; blades usually 4-20 (-28) cm long, 2-4 (-7) mm wide, with minute acroscopic teeth on the margins, with a slender boat-shaped tip; ribs numerous, closely packed, less obvious on the abaxial surface; sheaths smooth, entire, soon splitting, dark reddish-brown at base; ligules up to 1.5 mm long, membranous, blunt with irregular margins. Culm leaves 3 or 4, uppermost with long sheaths. Panicles 410 (-18) cm long, lax, roughly pyramidal, with up to 20 branches, and up to 60 spikelets, sparsely divided, spreading, with scabrous hair-like pedicels 5-20 (-50) mm long and slightly thickened below the spikelets. Spikelets 4-7 mm long and wide, loosely scattered and drooping, broadly elliptic to broadly ovate, laterally compressed, generally purplish-brown, usually breaking up at maturity beneath the lemmas but many spikelets remaining undispersed on the branches and shed from the panicle intact, 4-9 (-12)-flowered. Glumes slightly unequal, deeply concave, hooded at the apex, boat-shaped, 2.5-3.5 mm long, with 3-5 veins, firmly membranous, dull-purple with white and shiny margins. Lemmas 3.7-4.1 mm, strongly cordate at the base, bluntly keeled in the lower half, closely overlapping, rounded on the back, with 7-9 veins, variegated purple and green, with hyaline margin. Paleas flat, thin, almost as long as the lemma, with two keels, narrowly winged. Lodicules 2, linear-lanceolate, acute. Grain enclosed within the papery lemma and palea, c. 2 mm long, rounded on the back, flattened on the front; mean oven-dry weight 0.53 mg. The root system is a dense mat of whitish fibrous roots. The primary roots are up to 1 mm in diameter and are largely unbranched, but there is a dense network of branching secondary roots. The root mass is fairly vertical with an average root length of c. 40 cm. The species produces pale brown rhizomes up to 13 cm long and 1.5 mm in diameter. Native. Subspecies media occurs throughout the range; subspecies elatior (Sibth. & Sm.) Rohlena occurs in south-east Europe.

Koeleria macrantha (Ledeb.) Schultes (K. alpigena Domin, K. cristata (L.) Pers. pro parte, K. gracilis Pers., K. albescens auct. non DC.)

<i>Koeleria macrantha</i> (Ledeb.) Schultes (<i>K. alpigena</i> Domin, <i>K. cristata</i> (L.) Pers. pro parte, <i>K. gracilis</i> Pers., <i>K. albescens</i> auct. non DC.)

Polymetamorphism in the Dalradian of the central Scottish Highlands

AbstractSystematic variations in both timing and conditions of metamorphism are observed in the Dalradian rocks of Central Perthshire, Scotland. Early (D2–D3 and syn-D3) relatively low-pressure metamorphism (550 °C, 7 kb) occurs in the Flat belt rocks of the Tay Nappe to the south, and later (post-D3) higher-pressure conditions (550 °C, 9 kb) dominate the Steep belt to the north. The latter appear to be superimposed on earlier low pressure assemblages (chloritoid–biotite) with the pressure increase probably relating to formation of the Tummel Steep Belt, possibly near 460 Ma. This polymetamorphism, in addition to the generally high pressures of Barrovian metamorphism throughout Perthshire, may account for the poor development of the metamorphic zonal pattern in this region compared to the eastern Dalradian.

Soils and Their Related Plant Communities on the Dalradian Limestone of Some Sites in Central Perthshire, Scotland

(1) The characteristic soils and plant communities developed on Dalradian limestone at particular locations in central Perthshire were studied. Representative sites were selected from field data collected in the course of a soil and vegetation survey. (2) For the free-draining soils there is a succession of development corresponding to a progressive increase in leaching. Soil formation is determined by the degree to which the local influence of parent material has countered the regional influence of climate. (3) Soils developed on limestone rock in situ are assigned to the brown rendzina sub-group. Their characteristic properties include an A/C or AR profile sequence, coarse texture and a well-developed crumb structure. Although surface horizons are slightly leached, the soils have high base saturation. Shallow brown calcareous soils, which have an incipient B horizon, comprise another subgroup. Both rendzinas and brown calcareous soils are very rare in central Perthshire. (4) Deeper soils developed on the mixed schist-limestone glacial drift are brown forest soils with free drainage. They display a wide range of base status; high (>50%) and low (<50%) categories are recognized. (5) The rendzinas and shallow brown calcareous soils support mainly the PolygonoHelictotrichetum pratensis association whereas the leached brown forest soils are colonized by either the Galium verum-Koeleria cristata community or the AchilleoFestucetum tennifoliae association. (6) Gley soils close to limestone outcrops are flushed by lime-rich water and have high surface pH and base saturation. They support different mire communities.

Metamorphic conditions and uplift history in central Perthshire: evidence from mineral equilibria in the Foss celsian–barite–sulphide deposit, Aberfeldy

Interlayered lithologies of diverse mineralogy enclosing the Middle Dalradian syngenetic Ba–Zn–Pb deposit at Foss, S of Loch Tummel in Perthshire, allow estimates of the P–T conditions of metamorphism using several new geothermometers and geobarometers. Temperatures of 500–560°C are derived from calcite–dolomite geothermometry and from data on Mg–Fe partitioning within garnet–hornblende and garnet–biotite pairs. Plagioclase–biotite–garnet–muscovite and biotite–muscovite–chlorite equilibria indicate peak metamorphic pressures of 8–10 kbar which are in agreement with the results of sphalerite geobarometry. Textural evidence indicates that the rare platy mineral cymrite (BaA1 2 Si 2 O 8 H 2 O) was widespread in mineralized lithologies during penetrative deformation, and has since largely been replaced by celsian. The P–T location of the experimentally determined reaction line, cymrite ss = celsian ss + H 2 O, places further constraints on the peak metamorphic conditions and suggests that the final episode of penetrative deformation (D 3 ) was followed by a period of near-isothermal uplift during which celsian became stable. The cymrite field appears to have been re-entered during late brittle deformation. Peak metamorphic conditions recorded by mineral equilibria at Foss differ from those of areas 10 km to the N and S.

Geothermometry and geobarometry of Dalradian metapelites and metabasites from the Central Scottish Highlands

Synopsis Temperatures and pressures of metamorphism have been estimated for a suite of Dalradian garnetiferous mica schists, calcareous pelites, and hornblende schists (‘Green Beds’) from Central Perthshire. Garnet-biotite, calcite-dolomite, and muscovite-paragonite geothermometers indicate temperatures ranging from about 500°C, corresponding to the lowest grade, to a maximum of about 580°C, corresponding to the highest grade. Garnet-kyanite-plagioclase-quartz, and epidote-plagioclase-garnet-quartz equilibria indicate pressures of 8–11 kb. These temperature, pressure estimates agree well with the experimentally determined phase stabilities. A thermal gradient of 60–65°C/kb (20–22°C/km geothermal gradient) characterizes this area.

Zoned garnets in some Scottish Dalradian pelites

AbstractZoning in garnets in Barrovian garnet zone rocks of central Perthshire is shown to be dependent on the continuous prograde reaction histories in which the garnet was involved. In highly aluminous rocks, garnet grows at the expense of chloritoid and staurolite whereas in less aluminous rocks garnet grows at the expense of chlorite. Minerals included in garnet such as ilmenite, plagioclase, chlorite, and chloritoid show compositional changes which with the garnet zoning elucidate the garnet-forming reactions. Where garnet is resorbed to produce staurolite the former loses Fe at its rim to staurolite so that ‘reverse’ zoning of decreasing Fe and increasing Mn and Ca towards garnet rim develops.

Chemographic analysis of metabasite assemblages from c central Scottish Highlands

From the observed textures and mineral associations, chemographic relations have been derived in isobaric T-X CO 2 space for the minerals actinolite, ankerite, calcite, chlorine, epidote, and hornblende in Scottish Dalradian metabasites from Central Perthshire. Mineralogical variations in the carbonate-bearing metabasites within the distances of 0.5-1 km or so, are attributed to varying partial pressures of CO 2 operating during metamorphism.

Chloritoid-staurolite assemblages from Barrow's Zones in Central Perthshire, Scotland

SummaryChloritoid-biotite- and chloritoid-staurolite-bearing rocks occur around Blair Atholl, Perthshire. Textures suggest staurolite to be produced from chloritoid by a prograde ionic reaction involving muscovite. Chloritoid rocks are aluminous, lying above the muscovite-chlorite join, and staurolite formation involves the breakdown of chloritoid and muscovite. Their presence indicates that the chloritoid-biotite zone of Stonehaven continues as far SW as Central Perthshire, although its occurrence is severely limited by a lack of aluminium-rich rocks. The use of the chloritoid outcrop in the NE as an indication of pressure decrease to the SW is therefore queried.

A complete Lower Dalradian succession in the Schiehallion district, Central Perthshire

Synopsis Remapping of the Schiehallion district of Central Perthshire has led to the recognition of a new succession, stratigraphically interposed between the Moine and the Blair Atholl “Series”. A description of the lithologies and comparison with type areas in the SW Highlands clearly shows that this succession comprises the Ballachulish and Lochaber Subgroups of the Lower Dalradian. The succession, although greatly compressed, is considered to be the most complete sequence of the Lower Dalradian yet described.

The genus Abies in Scotland

Summary The genus Abies extends across much of the Northern Temperate Region in the form of about fifty species and ten well-marked geographical varieties. Thirty-two species and eight varieties have been found recently in Scottish gardens, policies and collections. Sixteen of these are potentially trees of great stature, and in no less than twelve of these sixteen, the largest and finest specimens in the British Isles are found in Scotland. The concentration of very big trees, still growing, is remarkable in three broad regions, Western Argyll, Central Perthshire with Angus, and NE Inverness-shire with adjacent parts of Ross-shire.

The variation in garnet, biotite and chlorite composition in medium grade pelitic rocks from the Dalradian, Scotland, with particular reference to the zonation in garnet

Garnet, biotite and host rock have been analysed along a traverse from the garnet isograd to the kyanite zone in the Dalradian of Central Perthshire, Scotland. FeO and MgO increase and MnO and CaO decrease in the garnet with increasing grade. Microprobe analyses of the garnets reveal zoning, which indicates that a garnet crystal as a whole does not equilibrate with the matrix during growth. Coexisting biotite varies in composition as a result of the abstraction of MnO, FeO etc. from the rook by the growing garnet, i.e. the mg/mg + fe ratio increases with grade. The microprobe analyses also reveal the size of the system from which garnet abstracted material varied from 0.100 to 2.000 g and the nucleation was frequently “instantaneous”. It also reveals the equilibrium or non-equilibrium nature of the assemblage, and explains the variation in garnet composition with grade in terms of a segregation model with a changing distribution coefficient. Primary chlorite was analysed from rocks near to the garnet isograd containing garnet and biotite. It has a similar mg/mg + fe value to the coexisting biotite. The results show that the three phase field defining the garnet isograd moves towards the mg corner with increasing grade. The higher grade fields lie to the mg rich side of the three phase field so that the sequence of mineral assemblages across the Barrovian zones in Perthshire, from the garnet isograd to the kyanite zone, can be summarized and displayed on a phase diagram.

The metamorphic history of the Loch Tummel area, central Perthshire, Scotland

AbstractIn the Dalradian rocks of the Loch Tummel area it is possible to establish a series of metamorphic events which are both syntectonic and post‐tectonic in relation to the polyphasal sequence of structures established in the area. Mineral assemblages which have developed during successive phases of metamorphism have been distinguished by their textural relationships, and are assigned to the appropriate metamorphic facies. Comparisons have been made with the metamorphic sequence established by Rast in the Schichallion area.

The evolution of quartz fabrics in the metamorphic rocks of central Perthshire

Structural and metamorphic studies in the Moinian and Dalradian rocks between Pitlochry and Kinloch Rannoch (Perthshire) have led to an investigation of the behaviour of quartz in response to regional metamorphism. The tectonic structures of the area indicate that the rocks have been subjected to three episodes of folding. Textural analysis by means of thin sections has led to the establishment of a sequence of mineral transformations which can be related to the tectonism which affected the rocks of the area. Investigations with the Universal Stage—in part involving the A.V.A. method—of specimens of diverse lithological types have indicated the relationships between the orientated quartz fabrics and megascopic structures encountered in the field. Various types of quartz girdles and maxima have been identified. Changes resulting from the working of metals described by metallurgists are suggested to have a parallelism in the changes observed in rock fabrics during regional metamorphism, and this has led the authors to propose a new theory for the orientation of quartz in tectonites.

Crystallographic and Geological Factors in the Growth of Garnets from Central Perthshire

IN the process of mineralogical and petrological studies of the metamorphic rocks in the Central Highlands of Scotland, it has been found that in certain minerals, particularly garnets, there is evidence of interplay of crystallographic and geological factors. Such is seen in the sample which has been collected from central Perthshire (National Grid No. NN 913602). It consists of compact impure graphitic limestone studded with numerous dodecohedral garnets, up to 5 mm. in diameter, but normally of the order of 2 mm. In addition to calcite and garnet, the rock contains an appreciable amount of quartz, muscovite, chlorite and ores. Graphitic dust is concentrated in calcite, muscovite and chlorite.