bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial, compositional and rheological constraints on the origin of zoning in the Criffell pluton, Scotland
Authors: Stephens W. E.
Published: November 2011

The Criffell pluton in southwestern Scotland (397 Ma, a Newer Granite of late Caledonian age) is concentrically zoned with outer granodiorites of typically I-type aspect passing into inner granite with more evolved characteristics. The zonation is examined in terms of the compositional surfaces of bulk parameters such as SiO2 and Rb/Sr and compositional variation is best modelled as multi-pulse, there being greater variation in bulk composition between pulses than within pulse. Published variations in Sr, Nd and O isotopes reflect the derivation of the pulses from separate and isotopically distinct sources. Other evidence for open-system behaviour includes mingling with mafic magmas to form enclaves, whereas closed-system behaviour is indicated by restite separation in the early granodiorites, and fractional crystallisation in the late granites. A dominant infracrustal I-type magma formed the first pulse followed by magma derived from more evolved crustal rocks (mainly metasediments of varying ages and maturities). Experimental fluid-absent melting of amphibolite and metapelite at about 900°C has shown that significant quantities of melt can be generated, respectively with I-type and S-type characteristics. Despite having similar bulk compositions, these melts have very different viscosities and densities for the same H2O contents (ηS-type>ηI-type and ρS-type≤ρI-type). It is argued that the rheological controls on magma escape from the source region along complex and tortuous pathways favour the more fluid I-type melts over the more viscous (and only slightly less dense) S-type melts. This constraint could have the effect of reversing the expected buoyancy-driven emplacement sequence, and may represent an alternative rheological differentiation mechanism for the formation of some zoned plutons.
The relationship between crustal magmatic underplating and granite genesis: an example from the Velay granite complex, Massif Central, France
Authors: Williamson B. J. , Downes H. , Thirlwall M. F.
Published: November 2011

The Velay granite pluton (Massif Central, France) is the youngest (304 ± 5 Ma) and largest (∼6,900 km2) of the major Massif Central monzogranites/granodiorites and was formed nearly 50 Ma after the cessation of Hercynian continental collision (Pin & Duthou 1990). It is a highly heterogeneous pluton consisting of I-type, high-Sr granites (Sr = 500-900 ppm) with low (+35 to +41) and high (-3 to -5), at its centre, grading into S-type and mixed I-S-type heterogeneous granites of more normal Sr content (100–420 ppm) and higher (+40 to +210) and lower (-3·8 to -7.3) at its margins.

The metasedimentary lower crust of the Massif Central was underplated/intruded by mafic mantle-derived magmas between 360 Ma and 300 Ma. From 300-280 Ma (Downes et al. 1991) underplating led to partial melting and granulite facies metamorphism of the underplated material (represented by felsic and mafic meta-igneous lower crustal xenoliths, = –11 to +112, = +2·2 to 8·2, Downes et al 1990). The partial melts assimilated mainly schist but also felsic gneiss and older granite country rock material ( = +100 to +300, = - 5 to -9) to produce the heterogeneous granites. Plagioclase and biotite were accumulated at the base of the intrusion which was intruded to high levels to form the high-Sr granites.
A stable isotopic (δ18O, δD) study of the late-Hercynian granites and their host-rocks in the Central Iberian Massif (Spain)
Authors: Recio C. , Fallick A. E. , Ugidos J. M.
Published: November 2011

Stable isotopic ratios (mainly 18O/16O, but also D/H) have been measured for the three most important types of late-Hercynian granites, and their hosts, in the western area of the Central Iberian Massif (CIM), Spain. These granites are amphibole-bearing biotite granites, biotite granites and cordierite-bearing biotite granites. No intrusive relationships have been observed among them; the contact of each granite with the others is always gradational. Host-rocks are Precambrian/Cambrian metasediments, ranging from low-grade schists to migmatites (nebulites).

Whole-rock δ18OSMOW values are as follows: amphibole-bearing biotite granites 8·9 ± 0·58% (1σ, n = 17); biotite granites 9·0 ± 0·35% (1σ, n = 11); cordierite-bearing biotite granites 9·6 ± 0·24% (1σ, n = 21). δ18O values for nebulites, into which some of these granites were emplaced, are significantly higher, at 11·1 ± 0·58‰ (1σ, n = 13). The Precambrian to Cambrian shales gave an average value of δ18O = 11·9 ± l·23‰ (lδ, n = 5). Whole-rock oxygen isotope ratios indicate that the origin of the granites was in neither purely sedimentary/metasedimentary rocks nor pristine mantle melts. δ18O values close to 9·0‰ require a crustal protolith, having an important recycled component.

Oxygen isotope results are compatible with the cordierite-bearing granites being generated by assimilation of nebulite-like material by a biotite granite magma. However, 18O/16O of mineral separates obtained from the three different granites and the nebulite indicate that isotopic equilibrium, if ever reached, has not been preserved. The modified isotopic equilibrium is attributed to fluid activity, but mineral-pair δ-δ plots suggest that the granite system behaved as a closed system, and that the fluid was deuteric (magmatic) in origin. This implies that if assimilation did happen, it occurred at a temperature higher than the closure temperature of the different minerals to isotopic exchange. In a δ18O vs δD plot, hornblende and biotite separates from the granites plot within the igneous field. A simple mesocrustal anatectic origin for the peraluminous late Hercynian granites of the western area of the CIM is difficult to sustain on the basis of the stable isotope data, consistent with other field, petrographic and geochemical evidence. Cordierite in the cordierite-bearing granites is not “restitic” from a deep source area, but rather is xenocrystic from the high-grade metamorphic country rock (nebulites).
Rhyolites as probes of the crust: examples from Tertiary volcanism in Arizona, southwestern U.S.A.
Authors: Esperança Sonia , Moyer Thomas C.
Published: November 2011

Geochemical and isotopic data obtained from three bimodal basalt-rhyolite fields in west-central Arizona point to significant variation in the sources of the siliceous products despite petrological similarities between them. The studied fields, which straddle the boundary between the Basin and Range and Colorado Plateau physiographic provinces, include Castaneda Hills (CH) in the Basin and Range, Kaiser Spring (KS) in the Transition Zone, and Mount Floyd (MF) in the Colorado Plateau. Two types of rhyolite (high-silica [HSR] and low-silica [LSR]) occur as lavas in the KS and MF fields, whereas all analysed CH samples are HSR. These lavas generally post-date low-angle extension of the Basin and Range crust and become generally younger towards the Colorado Plateau. Our isotopic data illustrate that the CH rhyolites require a source with comparatively radiogenic Sr, that most rhyolites require a source with comparatively unradiogenic 206Pb/204Pb, and that the MF-HSR require a source with comparatively radiogenic Nd and 206Pb/204Pb. The isotopic data clearly indicate that the western Arizona rhyolites contain a large crustal component. Importantly, the Pb isotopic compositions of the rhyolites illustrate the transition between two crustal provinces identified by other workers on the basis of Nd and Pb isotopic studies of Proterozoic granites. The Sr, Nd, and Pb isotopic compositions of our rhyolites can be modelled by mixing a basaltic component with three hypothetical crustal end-members which themselves may be formed by mixing two crustal components. One crustal component, which is characterised by unradiogenic Pb and Sr, may be similar to the mafic gneiss xenoliths of Tule Tank on the Colorado Plateau. The second crustal component, which has more radiogenic Sr and Pb, may be similar to the Proterozoic Fenner Gneiss of southeastern California. This conceptual model indicates an apparent increase in the contribution of the depleted Tule Tank source from the Basin and Range onto the Colorado Plateau and accommodates the notion that there is an underlying consistency to the petrogeneses of the western Arizona rhyolites as suggested by their chemistry and mineralogy. Although the CH and KS lavas require only one crustal end-member, the MF-HSR and LSR require two isotopically distinct sources. This difference may be attributed to the homogenisation of diverse crustal lithologies by ductile stretching during crustal extension.
Calculated melt and restite compositions of some Australian granites
Authors: Burnham C. Wayne
Published: November 2011

The thermodynamic relations embodied in the Quasicrystalline Model of Burnham and Nekvasil (1986), as recently extended by the author, have been used to quantitatively assess the feldspar-quartz liquidus relations in two I-type (Jindabyne and Moruya) and two S-type (Bullenbalong and Dalgety) suites of Australian granites, using analytical data provided by B. W. Chappell and co-workers. Among the more notable results obtained from these calculations at a constant pressure of 5·0kbar and = 0·30 (≍2·8 wt% H2O), for purposes of comparison, are that: (1) felsic melts of remarkably uniform, but distinctive composition can be extracted from each suite, leaving solid residues in amounts up to 65 mol%; (2) all melts from both S-type suites have two feldspars plus quartz on their liquidii, whereas both I-type suites have only plagioclase plus quartz on their liquidii; (3) the total solid residue ranges from 27-63% in the Jindabyne suite, from 15–62% in the Moruya suite, from 30–65% in the Bullenbalong suite, and from 27–65% in the Dalgety suite; (4) liquidus temperatures of the S-type Bullenbalong and Dalgety melts are similar (856° and 860°C), reflecting similar feldspar compositions of An53, Or75 and An60, Or77, respectively; (5) liquidus temperatures of the I-type Jindabyne and Moruya melts, however, are distinctly different (950° and 894°C), reflecting correspondingly different plagioclase compositions of An80 and An52; (6) the calculated liquidus plagioclase composition throughout a given suite is very uniform (±1%) and amounts to as much as 46% of the total rock; and (7) these calculated liquidus and residual plagioclase compositions are also the same, within the uncertainty of measurement, as those of the plagioclase crystal-cores determined optically by A. J. R. White. The only plausible explanation for this remarkable consanguinity in plagioclase liquidus, residue, and crystal-core compositions, hence liquidus temperatures, is that the bulk of the residue is restite, in accordance with the model of White and Chappell (1977). This explanation is corroborated by the very systematic variations in the amounts of individual restite minerals with respect to total restite contents. Accordingly, those members of each suite that contain more than 60% total restite probably closely represent the bulk composition of the source rock, which is dioritic or andesitic for the Jindabyne suite, tonalitic or dacitic for the Moruya suite, pelitic metagreywacke for the Bullenbalong suite, and feldspathic metagreywacke for the Dalgety suite. As a corollary, those members with less than 60% restite must have undergone melt-restite segregation (unmixing), probably during ascent and emplacement.
The nature of zircon inheritance in two granite plutons
Authors: Paterson B. A. , Stephens W. E. , Rogers G. , Williams I. S. , Hinton R. W. , Herd D. A.
Published: November 2011

Using zircons taken from two granite plutons, Strontian (Caledonian, northwestern Scotland) and Kameruka (Bega Batholith, southeastern Australia), this study presents observations that have a bearing on refractory zircons as provenance indicators. Two broad textural types of refractory zircon were identified: (1) those which show simple two-stage growth histories; and (2) those which have apparently undergone repeated periods of growth, resorption, mechanical abrasion, fracturing and fracture-healing. SHRIMP U-Pb ages obtained from the Kameruka zircons indicate that the cores are the textural manifestation of inheritance. The shapes of refractory cores are not unambiguously indicative of their ultimate origin, since they may also be modified by processes that occur before and after incorporation into the magma. The cores within the two populations show a great diversity in types and styles of zoning, and in composition, implying that they have not chemically equilibrated internally, or externally with their host melt.
A SHRIMP ion microprobe study of inherited and magmatic zircons from four Scottish Caledonian granites
Authors: Pidgeon R. T. , Compston W.
Published: November 2011

Using the ion microprobe SHRIMP we have analysed zircons from the Ben Vuirich, Glen Kyllachy, Inchbae and Vagastie Bridge granites from the Scottish Caledonides, in an attempt to resolve the ages of inherited zircons shown to be present in these granites by previous conventional multigrain analyses. Middle Proterozoic age components were found in inherited zircons from all four granites. Late Proterozoic (900–1,100 Ma) components have been identified in zircons from the Glen Kyllachy and Ben Vuirich granites in the Grampian Highlands. A Late Archaean age has only been detected in one zircon from the Glen Kyllachy granite. The distribution of inherited components in the granite zircon populations could reflect fundamental divisions in the age composition of granite source rocks; however, detailed assessment of this possibility must await further ion microprobe analyses on zircons from many more granites.

SHRIMP isotopic and U, Th and Pb analyses were made on successive shells of zoned zircon surrounding inherited cores from the Glen Kyllachy granite to monitor chemical changes during magmatic zircon growth. Results show that zircon shells have characteristic but significantly different Th, U and Pb concentrations. Magmatic zircon from the Vagastie Bridge granite also forms as clearly defined oscillatory zoned shells around unzoned nuclei of inherited zircon. However, the distinction between magmatic and inherited zircon in zircons from the Inchbae granite is less clear. Zircons from the Ben Vuirich granite occur as euhedral, magmatic zircons, or as rounded, subhedral, inherited zircon grains. A SHRIMP age of 597 ± 11 (2σ) Ma for euhedral magmatic zircon from this granite is identical, within the uncertainty, to the conventional multigrain zircon age of 590 ± 2 (2σ) Ma reported by Rogers et al. (1989) and confirms the conclusions of those authors that sedimentation of the Dalradian sequence took place in the Precambrian.
The use of graptolites in the stratigraphy of the Southern Uplands: Peach's legacy
Authors: Rushton A. W. A.
Published: November 2011

Lapworth, at the time of his 1878 paper on the Moffat Series, was the world's foremost expert on graptolites, and in that paper he gave the first great demonstration of the biostratigraphical value of graptolites. Peach & Home's resurvey of the Southern Uplands of Scotland extended Lapworth's ideas and his use of graptolites across the entire region. Peach's graptolitic work for the Survey is discussed: even though he identified a smaller repertoire of graptolites than Lapworth had, and often identified their general horizons rather than exact zone, his results are considered broadly correct. His faunal lists often emphasise the oldest faunas from the Moffat Shale inliers, presumably in order to stress their supposedly anticlinal structure. Subsequent work has seen a great extension of graptolite taxonomy and provided more detailed biostratigraphical subdivision, especially in the Silurian. The model of the Southern Uplands as an imbricate thrust stack is constrained by identifying the youngest (rather than oldest) fauna from the Moffat Shale inliers or, where possible, graptolites from the overlying greywacke formations. Such work has enabled the identification of about 25 thrust tracts in SW Scotland and of out-of-sequence thrusting in the Moniaive and Peebles areas to the NE.
A global perspective on the Scottish Caledonides
Authors: Dalziel Ian W. D.
Published: November 2011

The Scottish Caledonides constitute less than 10% of the length of the Caledonian-Appalachian orogen, the rocks of which define one major margin of the Laurentian craton in Neoproterozoic-Palaeozoic times. Scotland was located, however, in a critical position at the tip of a major cratonic promontory bounded by the Caledonian and Appalachian segments of that margin. Isotopic dates from minerals and rocks collected in the Scottish Highlands have been regarded for 40 years as indicating a Neoproterozoic history of compressive orogenesis that is absent in N America and Greenland. They have therefore been taken by some authors to indicate an origin exotic to Laurentia for rocks of the Northern and Grampian Highlands S and E of the Moine thrust belt. An alternative explanation is that the Neoproterozoic rocks in the Scottish Highlands are all related to the two-stage ‘breakout’ of a discrete rift-bounded Laurentian continent from the core of the Rodinian supercontinent, believed to have assembled at the end of the Mesoproterozoic.

Traditional reconstructions of the late Neoproterozoic–Early Palaeozoic Earth oppose the proto-Caledonian/Appalachian margin of Laurentia and the W African craton of the newly assembled Gondwanaland. However, consideration of the global inventory of late Precambrian rifted margins, their relation to Grenvillian orogenic belts and of scale, leads to the hypothesis that the conjugate was the proto-Andean margin of S America. Recent recognition that the Cambrian and Lower Ordovician strata of the northwestern Argentine Precordillera and their underlying Grenvillian basement are unquestionably of Laurentian derivation, while not definitive, does point in this direction. If correct, this means that even the presence of Neoproterozoic orogenesis need not imply an exotic origin, as Neoproterozoic orogens are widespread in S America.

Traditional models show an Early Ordovician lapetus ocean basin approximately 4500 km wide, but the remarkably synchronous Ordovician collision of arcs and other terranes with the Laurentian and Gondwanan cratons from Argentina to the British Isles, suggests that this premise may be incorrect. The Appalachian–Caledonian orogen may rather have resulted from close and complex tectonic interaction between Laurentia and Gondwana, involving intervening volcanic arcs and other terranes. The interaction may have taken place during a clockwise transit of Laurentia around the proto-Andean margin to its late Caledonian–Scandian collision with Baltica, and the final suturing of Pangaea at the close of the Palaeozoic era. A modern analogue may be the interaction between Australia and Asia, involving intervening volcanic arcs and other terranes of the western Pacific Ocean basin, from ~ 50 Ma through the Present, and into the future.
Duplex structures and their tectonic implication for the Southern Uplands accretionary complex
Authors: Ogawa Yujiro
Published: November 2011

Various order duplex structures are described from oceanic sequences of basaltic and associated pelagic–hemipelagic sedimentary rocks in the Ordovician (northern) part of the Southern Uplands accretionary complex. The general structure of the terrane as a whole strikes ENE, but each component lithological tract strikes NE or more northerly, oblique to the regional trend, making an en echelon outcrop pattern. Further oblique relationships between structures and lithologies can be mapped at larger scales, up to 1 km scale or more. These duplex structures are thought to be originally SE-verging, now partly overturned to the NW. Differences in the en echelon geometry, either sinistral or dextral, are explained by variable plunge of the original structures.

Peach & Home's first regional map of the Southern Uplands suggests an en echelon pattern of lithologies, implying large-scale duplex structures across the whole terrane. Here, the duplex structures are regarded as ubiquitous at both regional and smaller scales, suggesting considerable horizontal shortening. This was accommodated by such structures during underplating and out-of-sequence thrusting, in all parts of the accretionary prism, but particularly in the deeper tectonostratigraphic levels. The duplex structures are characteristic of ancient décollement zones.
Palaeozoic granitoid plutonism of southern Newfoundland: contrasts in timing, tectonic setting and level of emplacement
Authors: Elias Peter , Strong D. F.
Published: November 2011

Fourteen granitoid plutons studied in the Baie d'Espoir area of southern Newfoundland are divisible into a northern group of eight and a southern group of six. The former tend to be undeformed, have thermal aureoles, and intrude greenschist facies Ordovician and Silurian rocks of the Dunnage zone following a period of folding and thrusting towards the SE. Four Rb-Sr whole-rock isochrons yield similar ages around 430 Ma for these plutons, fixing the deformation within early Silurian times. The latter plutons syntectonically intruded without aureole effects, and are all foliated and elongate parallel to the regional fabric of amphibolite facies gneisses and migmatites of the Gander zone. Whole-rock Rb-Sr isochrons around 350 Ma for both syntectonic and post-tectonic plutons indicate a rapid metamorphism, deformation, intrusion and uplift of the Gander zone in this area. There appear to be no systematic relationships between petrological and geochemical characteristics of the plutons and their tectono-stratigraphic setting. This study conclusively invalidates earlier hypotheses that deformed granitoid rocks of the Gander zone are older than the undeformed granitoids of the Dunnage zone; indeed, just the reverse is true.
Geochemistry and chemostratigraphical correlation of slates, marbles and quartzites of the Appin Group, Argyll, Scotland
Authors: Hickman Arthur H. , Wright Alan E.
Published: November 2011

Approximately 700 samples from five slate, three marble and five quartzite units have been analysed for 26 elements to determine the use of geochemistry in stratigraphic correlation. Statistical treatment of the data has established that for all the slates and marbles, and certain of the quartzites, geochemistry is a viable method of distinguishing units of similar lithology. The most useful elements for distinguishing the four main slate units are P, Cr. Zn, Cu and, to a lesser extent, Rb, Sr, Y, Nb, Ba, La and Ce. Sr may indicate climatic changes or variable organic activity. The three marble units were considered as three limestone and three dolostone types. Dolostones are distinguished by high insoluble residue contents and the elements that distinguish between the dolostones are heavily influenced by these. Limestones, however, have very large differences in Sr. SiO2, Al2O3, K2O, Cr, Mn, Cu, Rb, Sr, Y and Zr have been used in discrimint function analysis. These parameters are strongly controlled by the insoluble residue with Al2O3, K2O, Cr and Rb being correlated with shaley impurities and SiO2, TiO2 and Zr with sandy impurities. Sr, Pb, Y and Zn, and to a lesser extent S and Mn, appear to be associated with the carbonate fraction.

The quartzites were found to be of three major types: (1) a very variable deltaic deposit (Appin Quartzite Formation), (2) marine bodies of immature quartz sands (Glen Coe and Eilde Quartzite formations) and (3) highly mature quartz sands (Binnein Quartzite Formation and northerly outcrops of the Glen Coe Quartzite Formation). It is possible to distinguish these three types on the basis of some trace elements (Zn, Rb, Sr, Y, Ba, La, Ce) but it is not feasible to distinguish between the Glen Coe and Eilde quartzites purely on geochemistry. The Eilde Flags, an immature estuarine sandstone, has a geochemistry intermediate between that of the quartzites and the pelites, although with higher CaO, Zr and Ba than either.
Role of the Midland Valley of Scotland in the Caledonian orogeny
Authors: Bluck B. J.
Published: November 2011

The Midland Valley of Scotland was an arc–interarc region during most of Ordovician—Devonian time. This arc terrane extends beneath the allochthonous Southern Uplands and probably beneath the southern Highlands. Models of Caledonian plate tectonism which regard the Midland Valley as a fore-arc basin are rejected principally on the grounds that (i) the Ordovician sequence at Girvan, in the very SW of the Midland Valley, was generated in a proximal fore-arc basin to the immediate S of a contemporaneous plutonic–volcanic arc, and (ii) the source for Silurian sediments in the southern part of the Midland Valley could not have been a rising trench-slope-break, but igneous basement and conglomerates with clasts of metamorphic basement, i.e. the southward extension of the Midland Valley.

The Midland Valley arc first comprised mainly plutonic rocks, some of which may have been basic but most of which were certainly granitic. Little is known of the ages of volcanic clasts in Silurian conglomerates (this time may have been a period of relative volcanic quiescence), but the Silurian–Devonian sequence is considered to have formed in an interarc basin which, like many other basins of this kind, began as marine (Early Silurian) and ended as fluvial (Devonian). At this final Silurian–Devonian stage, the Midland Valley arc was dominated by effusive rocks which made a substantial contribution to the sediments.

In this interpretation, the present Old Red Sandstone volcanic rocks are seen as the final stage of a volcanic arc which occupied the position of the present Midland Valley from at least Llanvirn to Early Devonian time.
Microdiorite sheet intrusions as incompetent time- and strain-markers in the Moine assemblage NW of the Great Glen fault, Scotland
Authors: Talbot C. J.
Published: November 2011

Radiometrie evidence suggests a complex evolution for some parts of the Moine assemblage NW of the Great Glen fault in Scotland. Four generations of microdiorite sheet intrusions are distinguished and used as time- and strain-markers in this region. Two are found to record different tectonic episodes in the Morar and Glenfinnan divisions and their Loch Eil division cover during the c 750 Ma Knoydartian orogeny. These demonstrate that F1 and F2 (of the Grenvillian orogeny) and F3 folds (of the Knoydartian orogeny) in the Morar and Glenfinnan divisions are absent from the Loch Eil division. Two later generations of microdiorites record successive episodes (F4 and F5) of the c. 455 Ma Caledonian orogeny.

The tectonic history of the region is considered after a discussion of the use of microdiorite sheet intrusions as strain-markers. This is because, rather than fold or boudinage, they deformed as incompetent single layers and foliated, mullioned or thinned uniformly instead. The attitudes of different elements of the microdiorites and their internal foliation are used to construct strain ellipsoids for four tectonic episodes on scales of 4–400 m and >4000 m. Three of these episodes are found empirically to have involved irrotational plane strain and all are close to coaxial even though the principal axes of strain appear to have swapped one for another in space as well as time.
Petrochemical evidence for the genesis of a Lower Carboniferous transitional basaltic suite in the Midland Valley of Scotland
Authors: MacDonald J. G. , Whyte F.
Published: November 2011

Studies of the chemistry of Lower Carboniferous igneous rocks in the Midland Valley of Scotland throw light on the nature and magmatic evolution of transitional basaltic suites. Major oxide and trace element chemistry of least altered lavas of the Campsie Fells reveals a lower group of basalts, basaltic hawaiites and hawaiites, and an upper, more variable group, ranging from basalt to trachyte. Chemical composition of associated vent intrusions confirms their association with the lower group of flows. The magmatically evolved condition of the erupted material indicates high-pressure fractionation of clinopyroxene at depth followed by fractional crystallisation of olivine, plagioclase and Ti-Fe ores at lower pressures. In the case of the upper lavas, further differentiation appears to have taken place in a shallow magma chamber under a central volcano.

The observed chemical variations in the Campsie Fells and other areas of Lower Carboniferousvolcanic activity can be attributed to a number of different factors during the evolution of the magmas. Detailed studies of the cumulative phases of the lavas may throw further light on the various stages involved.
Diplodoselache woodigen. et sp. nov., an early Carboniferous shark from the Midland Valley of Scotland
Authors: Dick John R. F.
Published: November 2011

A new fossil elasmobranch from the Lower Carboniferous Oil Shale groups (Viséan) of the Edinburgh area shows a mosaic of characters typical of at least two groups of early sharks. Its most distinctive feature is the small bicuspid teeth of “Diplodus” type. This, together with the long dorsal fin and the structure of the single, shallowly inserted dorsal spine, form a suite of characters previously considered unique to late Palaeozoic xenacanth sharks. Other features, such as the large equilobate tail and the structure of the pectoral fins, may have been retained from an ancestor of a more typical Palaeozoic elasmobranch appearance found in anacanthous and ctenacanth sharks. It is suggested that the xenacanths evolved from an ancestor within the anacanth-ctenacanth assemblage early in Carboniferous times and became adapted to a freshwater environment. This ancestor probably possessed a complex dermal skeleton including growing scales with both thickened and thin concave bases.

The fauna of the fish-bearing nodules amongst which this shark has been found is interpretedas being lagoonal in origin. The shark was probably a medium sized (c.0·75–2·0 m lng)predator inhabiting the surface waters of the lagoon.
Isotope, trace element and major element geochemistry of Tertiary igneous rocks, Isle of Arran, Scotland
Authors: Dickin A. P. , Moorbath S. , Welke H. J.
Published: November 2011

Pb- and Sr-isotope, major element and trace element analyses are presented for 38 Tertiary igneous rocks and older country rocks from Arran. Tertiary igneous rocks define silica-undersaturated and -oversaturated differentiation trends, but acidic and basic examples of the latter trend, exemplified in composite dykes, are separated by a wide Daly gap. In contrast, Pb-, and to some extent Sr-isotope compositions of these rocks display continuous variation, almost independent of major element composition.

Isotopic variations are interpreted as resulting principally from crustal contamination of the differentiation products of mantle-derived basic magma. A dominant rôle by mantle heterogeneity or crustal anatexis in producing the isotopic variation is ruled out. Contamination is believed to have occurred primarily after differentiation, but some rocks, such as the fine unit of the Northern Granite, display evidence of post-contamination differentiation.

Tertiary igneous rocks define an array on a Pb/Pb isochron diagram whose slope corresponds to an apparent age of 770±180 Ma (2σ). This points to the existence of a late Proterozoic basement complex under Arran.

Acidic and basic members of composite dykes are interpreted as basaltic differentiates which have been variably affected by contamination, yielding wide ranges of isotopic composition. Composite intrusion is ascribed to the simultaneous presence of acidic and basic magma in the crust.
The Ordovician trilobite Calyptaulax brongniartii (Portlock)
Authors: Clarkson E. N. K. , Tripp R. P.
Published: November 2011

Calyptaulax brongniartii (Portlock) from the Caradocian Bardahessiagh Formation, Pomeroy, Northern Ireland is redescribed. Equivalent material from Scottish horizons (Balclatchie and Ardwell groups) is regarded as belonging to separate populations. Campbell's system of notation is used to describe variation in the arrangement and number of lenses in the eye. The most closely related species is C. strasburgensis (Ulrich & Delo) from the Edinburg Limestone of Virginia, U.S.A.
Field and isotopic evidence for a c. 750 Ma tectonothermal event in Moine rocks in the Central Highland region of the Scottish Caledonides
Authors: Piasecki M. A. J. , van Breemen O.
Published: November 2011

Evidence is presented for a late Proterozoic, tectonothermal event which affected the rocks of the Moine assemblage in the Central Highland region of the Scottish Caledonides c. 750 Ma ago. This is about 200 Ma before the early Palaeozoic Grampian orogeny, whose effects are superimposed on the Moine rocks as well as dominating the tectonism in the Dalradian Supergroup.

Field and isotopic studies are integrated in zones of ductile thrusting (sliding) which are typified by belts of tectonic schists with related swarms of quartz and muscovite-bearing pegmatite veins. Of particular significance is a ductile thrust (the Grampian slide) which separates deeper crustal rocks (the Central Highland division), interpreted as showing the imprint of the Grenville orogeny, from shallower rocks (the Grampian division) representing a supracrustal assemblage formed between the Grenville and the c. 750 Ma events.

The Grampian slide is the structurally highest member of a system of related, previously unrecorded slides affecting the Central Highland division. New structural, petrographic and Rb-Sr isotopic data, obtained largely from a recently recognised inlier of the Central Highland division at Laggan, bear out that the quartz and pegmatite veins are segregations formed during ductile shearing under amphibolite facies conditions. Muscovites from these veins yield ages between 780 and 730 Ma, and a regression analysis of tectonic schists and the muscovites gives an age of 740 ± 40 Ma. These data substantiate our previous hypothesis that the deeper-seated Moine rocks were affected by a distinct orogenic event at 750 ± 30 Ma.

In the Northern Highlands, similar vein swarms are related to the Sgurr Beag slide and to belts of previously unrecorded tectonic schists in the Glenfinnan division of the Moine assemblage. A new, 755 ± 8 Ma age obtained from such a tectonic schist at Kinloch Hourn, combined with previous, similar age data from lensoid pegmatites, imply that the c. 750 Ma event may have also affected the Morar and Glenfinnan divisions.
A chemical–mineralogical classification of common plutonic rocks and associations
Authors: Debon F. , Le Fort P.
Published: November 2011

A classification is proposed, based mainly on major element analytical data plotted in a coherent set of three simple chemical-mineralogical diagrams. The procedure follows two complementary steps at two different levels. The first is concerned with the individual sample: the sample is given a name (e.g. granite, adamellite, granodiorite) and its chemical and mineralogical characteristics are determined. The second one is more important: it aims at defining the type of magmatic association (or series) to which the studied sample or group of samples belongs. Three main types of association are distinguished: cafemic (from source-material mainly or completely mantle-derived), aluminous (mainly or completely derived by anatexis of continental crust), and alumino-cafemic (intermediate between the other two types). Subtypes are then distinguished among the cafemic and alumino-cafemic associations: calc-alkaline (or granodioritic), subalkaline (or monzonitic), alkaline (and peralkaline), tholeiitic (or gabbroic-trondhjemitic), etc. In the same way, numerous subtypes and variants are also distinguished among the aluminous associations using a set of complementary criteria such as quartz content, colour index, alkali ratio, quartz–alkalies relationships and alumina index.

Although involving a new approach using partly new criteria, this classification is consistent with most of the divisions used in previous typologies. The method may also be used in the classification of the volcanic equivalents of common plutonic rocks.
Stratigraphical palaeontology of the Westphalian of the Ayrshire Coalfield, Scotland
Authors: Brand P. J.
Published: November 2011

A brief account of the stratigraphy of the Westphalian (Upper Carboniferous) of the Ayrshire Coalfield is given. Older rocks are found to be overlain by Westphalian strata of differing age in various parts of the coalfield. A correlation of the coal seams known by numerous local names in various areas of the coalfield is shown. The vertical distribution of species of non-marine bivalves is illustrated and the faunas associated with various horizons discussed. The presence of variants of Anthraconaia pulchella Broadhurst at more than one horizon is noted. The lateral distribution of species at given horizons is examined and it is shown that elements of the overall fauna of an horizon may be absent in parts of the coalfield. The occurrence of marine bands in the succession is noted and their distribution discussed. It is suggested that during the Aegiranum Marine Band incursion the northern and north-western parts of the coalfield were nearer a land mass. A new stratigraphical name, the Bogton Marine Band is proposed. The band occurs within the Upper Similis-Pulchra Chronozone.
The earliest known (Namurian A, E1) haplolepids (Osteichthyes: Actinopterygii)
Authors: Lowney Karen A.
Published: November 2011

Two new genera and species of haplolepids (Chondrostei), Protohaplolepis scotica and Blairolepis loanheadensis, are described from the ironstones of Loanhead, Midlothian (Namurian A, E1); this represents the earliest known record of the family. Protohaplolepis scotica (= Traquair's nomen nudum “Eurylepis scoticus”) shows many features in common with Westoll's hypothetical haplolepid “common ancestor X”, and is possibly ancestral to the Haplolepis–Microhaplolepis line within the family. Blairolepis loanheadensis, known only from a skull roof, shows greater similarities to Parahaplolepis and Pyritocephalus, but differs from these genera in having separate dermopterotics and parietals. Two subfamilies, the Haplolepinae and the Parahaplolepinae, are suggested to reflect the distinct evolutionary lines within the family.

A new species, Parahaplolepis westolli, is also described from Newsham, Northumberland (Westphalian B). This species shows a close resemblance to the American species Parahaplolepis tuberculata from Linton, Ohio.

A brief discussion of the evolutionary history of the family is presented, along with a summary of its stratigraphical and geographical distribution.
Introduction to the palaeontology of the Dinantian of Foulden, Berwickshire, Scotland
Authors: Wood S. P. , Rolfe W. D. Ian
Published: November 2011

The Foulden Site of Special Scientific Interest is one of the few Cementstone Group localities that yields significant fauna and flora. Excavations in 1980 and 1981 removed a 1·3 m2 slab of the Fish Bed for laboratory study of the vertical and spatial distribution of the biota. Layer by layer analysis revealed an almost mutually exclusive relationship between the vertical distribution of the palaeoniscoid fishes and malacostracan crustaceans, as well as a horizon crowded with juvenile acanthodians. Elongate elements of this biota showed slight preferred orientations at that prolific horizon. Some 27 m of strata including the Fish Bed, Plant Bed and Shell Bed are recorded in detail, and their biota noted. Interim results of work on the main groups collected are summarised in associated papers in this part of Transactions. Brief reports are given here on the euryhaline marine bivalve mollusc Modiolus latus (Portlock), a rare durophagous bradyodont shark tooth and an Eogyrinus-like amphibian scute.
Malacostracan Crustacea from the Dinantian of Foulden, Berwickshire, Scotland
Authors: Briggs D. E. G. , Clarkson E. N. K.
Published: November 2011

TheTealliocarisandCrangopsispreviously recorded from Foulden are shown to beBairdops elegansandBelotelson traquairi, respectively. This locality thus yields the oldest KnownBairdops. The two species are confined to the lower Carboniferous sedimentary basin S of the Southern Uplands massif. Elsewhere, these genera are thought to characterise the nearshore marine fauna. The reciprocal relationship noted between malacostracans and actinopterygians may therefore be a function of fluctuating salinity.
A vermiform problematicum from the Dinantian of Foulden, Berwickshire, Scotland
Authors: Almond John E.
Published: November 2011

A unique specimen of an unusual elongate segmented compression fossil, Polylurida aenigmatica n. gen., n. sp., is described and illustrated. The bilaterally-symmetrical, dorsoventral structure (c. 6·5 cm long × 0·8 cm maximum width) narrows towards both ends and is subdivided into approximately 19 similar tapering segments, showing no evidence of tagmosis, appendages or an internal gut. The segments are covered with a substantial papillose organic cuticle, each segment bearing towards one end a pair of transverse calcareous bars. These bars are perforated by simple canals filled with strands of dark organic material which traverse their whole thickness and flare out superficially to form pores on both their lower and upper surfaces. Internal horizontal lamination of the bar material suggests an episodic accretionary pattern of skeletal growth. The bars appear to represent internal skeletal structures and are restricted to one side (dorsal or ventral) of the body, where the adjacent cuticle is locally thickened to form a corresponding series of discrete paired densely papillose transverse bands. Although Polyurida may be an unusual segmented worm, its singular suite of characters and lack of data prevent assignment to any higher taxon.
Acanthodian and coelacanth fish from the Dinantian of Foulden, Berwickshire, Scotland
Authors: Forey P. L. , Young V. T.
Published: November 2011

Acanthodians are represented by numerous young and poorly cranially ossifiedAcanthodes ovensiWhite, the earliest known acanthodid. Study of the smallA. ovensitogether with the type series shows that squamation begins posteriorly, and spreads anteriorly along an initially triangular front, as inA. bridgeiZidek.Gyracanthussp. occurs at several horizons in the sequence. The coelacanth remains include the first articulated specimen known from Foulden, but preservation only allows an assignment to cf.Rhabdoderma. Although these taxa are distinctive, resemblances to other taxa occur only in generalised features. Hence, unlike the Foulden actinopterygian fish, the acanthodians and coelacanths cannot be used to suggest closer affinities with any other fish of this age, on which information is sparse.
Rhizodont crossopterygian fish from the Dinantian of Foulden, Berwickshire, Scotland, with a re-evaluation of this group
Authors: Andrews S. M.
Published: November 2011

Material of crossopterygian fishes from Foulden, Berwickshire, is important in including the first known entire specimen giving a clear picture of the body form of the Family Rhizodontidae (sensuAndrews 1973). This group is specialised in having numerous subsidiary lateral lines on the body, a ventrally expanded shoulder girdle, fins with peculiar stiffened structure, the pectorals forming greatly enlarged paddles and other fins being reduced in size. The Foulden remains fall into large and small size-ranges occurring largely at different levels in the sequence, but although these may represent growth in one taxon the available parts of the body are mostly complementary. Separate preliminary descriptions of the two size-ranges are therefore given, the small complete form being named?Strepsodus anculonamensissp. nov., and the large form remaining unnamed pending further study. An abridged historical account of previously named rhizodont genera (Rhizodus, Strepsodus, SauripterusandPycnoctenion) is given in order to explain why the new Foulden form(s) cannot at present be generically assigned more closely. A revised diagnosis of the Family Rhizodontidae leads to a discussion of the functional morphology and mode of life of fish of this type. Analogies with modern forms indicate that, like some sharks and crocodiles, they may have fed by tearing flesh off large prey, rotating or shaking against its inertia. Ways in which variously shaped rhizodont teeth (recurved, sigmoid etc.) may have functioned are suggested. Addenda deal with (1) the possible occurrence at Foulden of a large lungfish and (2) (after considering primitive and advanced rhizodont features) the renaming ofRhizodus ornatusTraquair 1878 from higher in the Scottish lower Carboniferous, as the type of a new genus,Screbinodus.
Structure and habits of living branchiopod crustaceans and their bearing on the interpretation of fossil forms
Authors: Fryer Geoffrey
Published: November 2011

Branchiopods are primitive crustaceans whose history extends back at least to the Devonian, yet some are highly successful today. Most fossil branchiopods do not show many features that lead to an understanding of function, but the Devonian lipostracan Lepidocaris is an exception. Recent work on living branchiopods, especially anostracans and anomopod cladocerans, enables Lepidocaris to be considered as a living animal. Work on extant anostracan nauplii also makes it possible to deduce how its larval stages swam and collected food.

Other early crustaceans are briefly considered and comments are made on the concept of “living fossils”. While rates of morphological and genomic evolution are often discordant, the concept is still useful. Some branchiopods, such as the Notostraca, display remarkable morphological stasis: on the basis of morphology, a Triassic and a present-day form appear to be conspecific. The latter may be referred to as a “living fossil”.

The outstanding morphological stasis of the crustacean nauplius is noted. Its existence in Cambrian times, deducible from its distribution among modern taxa, has been confirmed by Müller's finds. Such stasis, involving part of the genome of organisms whose adults display enormous adaptive radiation, has persisted with relatively small modifications since before the commencement of the entire radiation of vertebrates.
Swimming in Crustacea
Authors: Hessler Robert R.
Published: November 2011

An analysis of swimming in living crustaceans is presented in order to elucidate the range of ways this function has been achieved, and to reveal the principles which constrain it. The study focuses onGnathophausia ingens, a primitive, bathypelagic malacostracan that swims with thoracic exopods and pleopods. These structures consist of a muscular peduncle and one or two flagella that are fringed with setulate setae. The basic motion is rowing with the limb and setal fan extended on the power stroke and flexed on recovery.

A survey of other crustaceans shows that rowing with this type of swimming structure dominates throughout, although paddles often replace the flagella. Particularly pervasive is the large relative area of setae, whose effectiveness must stem from the ability to extend and flex passively and from the high drag generated on the power stroke by the setules at low Reynolds numbers.

A review of reconstructions of Palaeozoic trilobites and marrellomorphs reveals the likelihood that if swimming was the function of the exites, they operated inefficiently or were employed in other methods as well. Sculling and drag reduction on the recovery stroke through feathering rather than flexion are possible alternatives. The more common occurrence of paddle-like limb shafts and blade-like marginal structures in other Palaeozoic arthropods is also noted.