petrology and tectonic setting of some ordovician volcanic rocks from the southern uplands of scotland abstract summary within the ordovician sequence of the southern uplands of scotland numerous basaltic units occur forming local basement to sequences of chert graptolitic mudstone and greywacke the basalts are fault bounded at their base although they have suffered secondary alteration to varying degrees the least mobile elements ti zr y and nb show a correlation between relative chemical abundances and supposed tectonic level the most northern tectonic slice contains alkali basalts the central slice contains 11 examples of what are apparently ocean floor tholeiites and 4 mildly alkaline basalts a third slice found at one locality only also contains tholeiites whose chemistry is comparable with the most primitive basalts samples of ordovician extrusives from bail hill have calc alkaline to alkaline affinities while extrusives from wrae hill are quartz keratophyres the geochemical pattern is consistent with a model of an opening iapetus ocean in which rifting pre dated spreading such that the basement to the lower palaeozoic sequence of the southern uplands was oceanic

implications for caledonian plate tectonic models of chemical data from volcanic rocks of the british old red sandstone volcanic rocks associated with the continental sediments known as the old red sandstone outcrop widely in northern britain and form a dominantly calc alkaline suite comparable to those developed on modern continental margins rocks rich in ni and cr are unusually abundant and are thought to have incompatible element concentrations little different from those of primary magmas such rocks show pronounced spatial chemical variation with concentrations of sr ba k light rare earth elements and p 2 o 5 and the ratio la y showing up to a six fold increase in a northwestward traverse across scotland in more evolved rocks a similar increase is shown by sr ba and la y but regional comparisons are made difficult by the varying effects of fractional crystallization the chemistry of all old red sandstone volcanic rocks n of the southern uplands fault is consistent with the former existence of a subduction zone that changed in strike from ene in ireland and southern scotland to n in the north sea this orientation in conjunction with almost e w plate motion may explain the great contrast in end silurian deformation styles between britain and scandinavia old red sandstone volcanic and plutonic rocks s of the southern uplands fault are thought to be younger and are perhaps unrelated to subduction activity

a soil chronosequence in northwestern italy morphological physical and chemical characteristics abstract a chronosequence of soils developed on fluvial terraces dating from lower middle pleistocene to upper upper pleistocene was studied to identify the morphological physical and chemical soil properties most sensitive to soil development and to further test the usefulness of iron oxides as indicators of relative age a relative horizon distinctness rhd index and the buntley westin and hurst colour indices clearly reflected differences in soil development with age among physical characteristics clay content and aggregation obtained by comparison of clay dispersion before and after removal of cementing agents were most efficient in indicating differences in duration of pedogenesis cation exchange capacity as related to clay content was the chemical property most useful to distinguish soils of different terraces iron oxide ratios were again useful as indices of soil development

deep water facies processes and models a review and classification scheme for modern and ancient sediments abstract a review of previous work on modern and ancient deep water facies processes and models is presented with a new classification scheme involving 40 distinct facies related to 15 conceptually distinct facies groups these facies are fixed points in a spectrum of facies generated in a process continuum from resedimentation processes through semi permanent bottom currents to pelagic settling in essence the scheme is descriptive of the sedimentary attributes of sediments although it is designed to aid interpretation of possible sediment transport deposition processes the classification scheme is three tier with facies classes groups and constituent facies and is hierarchical to allow flexibility in its use there are seven facies classes with classes a e defined largely on the basis of grain size differences class f on the basis of internal organization and class g on composition the facies classes are class a gravels muddy gravels gravelly muds and pebbly sands with 5 gravel grade class b sands with 80 sand grade and 80 mud 40 silt and 0 20 sand class e muds and clays with 95 mud grade for the purpose of large scale mapping or reconnaissance fieldwork either the level of facies classes or groups may be appropriate whereas for more detailed sedimentology the more detailed facies level will be necessary

parent material uniformity and degree of weathering in a soil chronosequence northwestern italy abstract the uniformity of the parent material and degree of weathering of the soils of a chronosequence developed during the pleistocene were investigated using optical microscopy x ray fluorescence and scanning electron microscopy sem techniques uniformity of the parent material was assessed by two criteria the ratios of resistant minerals and their specific elements in the heavy fraction s g 2 96 g cm 3 there was some variation between heavy mineral ratios but there was less variation between ratios from the chemical data and on this basis it was concluded that the parent material of each of the three soils in the sequence was uniform sem examination confirmed that the resistant minerals had remained unaltered although some ti bearing minerals showed some alteration the degree of chemical weathering as expressed by the ratio of mobile to non mobile elements and by parker s index increased from the youngest to the oldest soil

assessing parent material uniformity of a red and black soil complex in the landscapes abstract the distribution of red and black soil xeralfs xerolls associations in the monarto area south australia is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known the objectives of this study were i to assess zr and ti bearing grains as minerals resistant to chemical weathering prior to employing zr and ti in determining parent material uniformity and ii to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles scanning electron microscopy sem and energy dispersive x ray analysis edax were used to study chemical weathering and elemental composition of surfaces of zr and ti bearing grains x ray fluorescence xrf analysis was used to determine elemental concentrations in various soil fractions results showed that zr bearing grains consisted of only zircon having smooth clean surfaces which are characteristic of a mineral resistant to chemical weathering edax spectra confirmed that zr was a specific element to represent zircon suggesting its reliability to be used in assessing parent material uniformity on the other hand ti derived not only from minerals rutile anatase resistant but also from minerals ilmenite pseudorutile biotite susceptible to chemical weathering this limited the usefulness of ti as an index mineral for soil development studies except for zr ti ratio all other indicators of parent material uniformity i e depth distribution curves of zr and y in various fractions and y zr ratio showed no considerable inflection and variation with depth in a xeralf red soil this indicated the xeralf derived from a uniform parent material mica schists thereby texture contrast within a profile is due to pedological processes on the other hand depth distribution curves showed clear inflection and variation in xerolls black soils indicating soils developed from lithologic discontinuities so different trends in particle size fractions between 0 48 cm for ma5 and 0 59 cm for ma3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis the presence of complex red and black soil association in the landscape is attributed to the difference in parent materials where the red soil developed from mica schist and the black soils from calcareous deposits

the mineralogy and chemistry of the anorogenic tertiary silicic volcanics of s e queensland and n e new south wales australia the late oligocene early miocene volcanism of this region is chemically strongly bimodal the mafic lavas volumetrically dominant comprise basalts hawaiites and tholeiitic andesites while the silicic eruptives are mainly comendites potassic trachytes and potassic high silica rhyolites the comendites and rhyolites have distinctive trace element abundance patterns notably the extreme depletions of sr ba mg mn p cr v and eu and the variable enrichment of such elements as rb zr pb nb zn u and th the trachytes exhibit these characteristics to lesser degrees the comendites are distinguished from the rhyolites by their overall relative enrichment of the more highly charged cations e g lree nb y and especially zr and zn the phenocryst mineralogy of the trachytes and rhyolites comprises various combinations of the following phases sodic plagioclase albite andesine calcic anorthoclase sanidine quartz ferroaugite ferrohedenbergite ferrohypersthene fayalitic olivine ilmenite titanomagnetite and rarely biotite near annite and fe hastingsitic amphibole accessories include apatite zircon chevkinite ferrohedenbergite bearing rhyolites only and allanite amphibole and botite rhyolites only the comendites generally contain ca poor anorthoclase sanidine quartz fluorarfvedsonite aegirine and aegirine augite zr bearing aenigmatite and ilmenite coexisting fe ti oxides are absent in the comendites and relatively uncommon in the rhyolites and trachytes where present they indicate equilibration temperatures of 885 980 c and fo2 between qfm and wm buffers the magmas are thus interpreted to have been strongly water undersaturated during phenocryst equilibration which is also consistent with the general paucity of pyroclastics the rarity of hydrous mineral phases and the extreme fe enriched ferromagnesian phenocryst compositions the chemical and mineralogical data are interpreted to indicate the operation of extreme fractionation processes controlling the development of the silicic magmas and the comendites trachytes and certain trachyte rhyolite series are considered to have evolved from a mafic parentage the available oxygen sr and pb isotopic data however point to some modification of the magnas through crustal equilibration processes the remaining high silica rhyolites are considered to most likely represent crustal partial melts but are again modified by extensive fractionation

the northern belt of the longford down inlier ireland and southern uplands scotland an ordovician back arc basin the northern belt of the southern uplands longford down zone contains two compositionally distinct clastic petrofacies suites each ranging from mid to late ordovician age they extend throughout the length of the belt and are generally separated by a strike fault the northwestern metaclast petrofacies suite is characterized by felsic igneous and metamorphic detritus derived from a continental source to the nw whereas the southeastern basic clast petrofacies suite contains abundant calc alkaline detritus derived from an island arc and plutonic metamorphic root zone complex to the s or se a similar source but located to the north is indicated for younger clastic sequences of similar composition in the northern part of the central belt immediately south of a major sinistral shear zone which defines the boundary between the northern and central belts it is concluded in light of other facets of regional geology and possible palaeogeographic configurations that this pattern reflects a back arc basin in the northern belt margined by a volcanic arc massif which once occupied the space now represented by the shear zone and a fore arc basin to the se central and southern belts the northern belt back arc basin is postulated to have been closed and deformed at the end ordovician and subsequently overthrust northwestward by the allochthonous thrust stack imbricated central and southern belts fore arc sequence at the end silurian this in the northern belt resulted in the development of a major recumbent structure downward facing on regional end silurian cleavage

the southern uplands controversy report of a discussion meeting held at burlington house on 12 february 1986 the idea for a discussion meeting followed from remarks made by professor c h holland 1986 in his presidential address to this society in 1985 when he expressed concern about the uncritical application of the accretionary prism model to the southern uplands of scotland it has since become apparent that divergent views are held both among those against the model and those in favour of it this meeting served to air some of these different opinions even if it has not immediately resolved many of the arguments most of the contributors to the meeting see the society newsletter for january 1985 have produced written papers for this volume and so far only one or two have modified their views between writing their abstract and submitting their paper the concept of an accretionary prism model developed gradually a comparison of scotland with burma suggested that the southern uplands were like western burma where trench and oceanic sediments are being underthrust by subduction processes mitchell mckerrow 1975 with the development of modern analogues from the pacific seeley et al 1974 karig sharman 1975 the model was applied to the southern uplands with more emphasis mckerrow et al 1977 leggett et al 1979 a b 1982 moseley 1977 1978 was one of the first to express doubts about this model he believed that the iapetus ocean had closed by the end of the ordovician and thus like many others

weathering of the new albany shale kentucky usa i weathering zones defined by mineralogy and major element composition abstract comprehensive understanding of chemical and mineralogical changes induced by weathering is valuable information when considering the supply of nutrients and toxic elements from rocks here minerals that release and fix major elements during progressive weathering of a bed of devonian new albany shale in eastern kentucky are documented samples were collected from unweathered core parent shale and across an outcrop excavated into a hillside 40 year prior to sampling quantitative x ray diffraction mineralogical data record progressive shale alteration across the outcrop mineral compositional changes reflect subtle alteration processes such as incongruent dissolution and cation exchange altered primary minerals include k feldspars plagioclase calcite pyrite and chlorite secondary minerals include jarosite gypsum goethite amorphous fe iii oxides and fe ii al sulfate salt efflorescence the mineralogy in weathered shale defines four weathered intervals on the outcrop zones a c and soil alteration of the weakly weathered shale zone a is attributed to the 40 a exposure of the shale in this zone pyrite oxidization produces acid that dissolves calcite and attacks chlorite forming gypsum jarosite and minor efflorescent salt the pre excavation active weathering front zone b is where complete pyrite oxidation and alteration of feldspar and organic matter result in increased permeability acidic weathering solutions seep through the permeable shale and evaporate on the surface forming abundant efflorescent salt jarosite and minor goethite intensely weathered shale zone c is depleted in feldspars chlorite gypsum jarosite and efflorescent salts but has retained much of its primary quartz illite and illite smectite goethite and amorphous fe iii oxides increase due to hydrolysis of jarosite enhanced permeability in this zone is due to a 14 loss of the original mass in parent shale denudation rates suggest that characteristics of zone c were acquired over 1 ma compositional differences between soil and zone c are largely attributed to illuvial processes formation of additional fe iii oxides and incorporation of modern organic matter

a model for the crustal evolution of southern scotland in the late silurian southern scotland was a mature accretionary active margin of sumatra type on the southeastern edge of north america while england was on a passive margin on the opposite side of the iapetus ocean southward subduction below england during the middle ordovician produced a magmatic arc which now lies close to the iapetus suture and thus argues for a missing forearc terrane tectonic erosion or strike slip removal may be responsible for some of this missing terrane to the north of the lake district but we now suggest that underthrusting below southern scotland may also be an important cause if the ordovician forearc terrane of northern england is now below the southern uplands we would have an explanation for the evidence for similar lower crustal foundations on either side of the surface trace of the iapetus suture velocity structure from the lispb study sr u pb isotopic signatures and geophysical attributes of the c 400 ma granites the under thrusting model still leaves room for considerable modification of both margins by large strike slip faults seismic refraction profiles of modern accretionary active margins sumatra sw japan allow us to propose a likely velocity profile for late silurian southern scotland we choose a mesozoic forearc truncated by strike slip faulting the queen charlotte islands margin of the ne pacific as an analogue for the late silurian southern iapetus margin following previous suggestions of highly oblique and slow convergence during the final stages of closure of iapetus we combine the two profiles by under thrusting the southern margin to produce a model which involves minimal shortening in the collision zone the crustal profile resulting from such a collision would be very similar to the modern southern scotland profile both in terms of the scale of the tectono stratigraphic terranes involved and of the resulting crustal velocity structure the cessation of accretion after the mid wenlock may be related to impingement of the english continental crust against the scottish trench subsequent uplift of the southern uplands may be connected with the appearance of coarse detritus in the lake district during the silurian

scanning electron microscope study of zircons and rutiles from a podzol chronosequence at cooloola queensland australia summary a chronosequence of four soils derived from aeolian deposited sand at cooloola along the eastern coast of southern queensland has been studied to document predepositional and pedogenic changes in zircon and rutile grains in the fine sand fraction 53 125 m with increasing soil age the soils range in age from holocene typic quartzipsamment presently drifting sand to mid pleistocene spodic quartzipsamment 90 ka bp parent materials are moderately stratified sands with irregular depositional layers in places having high concentration of heavy mineral grains scanning electron microscopy was used to characterize grain surface microtexture by a semi quantitative method based on frequency of occurrence of ten classes of surface microtextures pedogenic changes were quantified and differences between horizons in the same profile between different profiles within the same horizon and between minerals were tested for significance using the 2 distribution zircon grains are less chemically weathered during pedogenesis than rutile possibly due to the higher iron content of the latter however zircons tend to show more features which can be associated with physical alteration rutile grains in the illuviated b2hs horizons of the troporthod and spodic quartzipsamments are more thickly coated with poorly crystalline iron and alumino silicate compounds compared with zircon grains and the presence of grain coatings does not seem to have prevented the surfaces of grains from developing solution pits with increasing age there is a preponderance of weathering features on grains of both minerals the presence of various shapes and surface microtextures on grains from the different soils suggests a multiple grain source for zircon and rutile and a complex predepositional history for these minerals nevertheless microtextural features of zircons and rutiles are valuable for the interpretation of the extent and nature of post depositional weathering

is the southern uplands of scotland really an accretionary prism we argue that there is little which demands the accretionary prism model for the widespread silurian rocks of the southern uplands of scotland and ireland with new data from ireland we reinterpret these rocks as the turbidite fill of a successor basin that formed after the subduction of iapetus oceanic crust finally stopped at the end of the ordovician the structure of the basin is a sinistral transcurrent imbricate stack the result of oblique terminal collision of cadomia with laurasia at the end of the silurian

style scale and significance of sand bodies in the northern and central belts southwest southern uplands sedimentological and biostratigraphical data from the rhinns of galloway and adjacent areas in sw scotland confirm that deep water depositional systems consistently operated along and were sourced from the northwestern margin of an asymmetrical basin during the late ordovician and early silurian while pelagic facies accumulated simultaneously to the se providing a scenario analogous to many modern trench systems most of the observed sedimentological anomalies with regard to this general model can be explained within the context of the varied styles of trench filling depositional systems briefly reviewed here and the major stratigraphic and sedimentologic features can be best explained in terms of a geotectonically evolving fore arc region two main phases of development are recognized a llandeilo late ashgill during this time interval the fore arc trench region was tectonically juxtaposed against an active continental margin arc small to medium scale se prograding sand rich fans were formed within a relatively narrow trench leading to axial diversion of the fans initially to ne but later mainly to sw simultaneously a coarse volcanilithic sediment apron flanking the arc migrated gradually northeastwards probably in response to relative fault displacement of the arc and trench b llandovery during this time interval the fore arc trench region was dominated by a variety of mainly fan type depositional systems which were exclusively sourced at least until the uppermost llandovery from the northwestern margin the juxtaposition of coeval depositional systems differing significantly in sedimentological style and composition strongly suggests that the llandovery sedimentation in this region occurred in several structurally separated sub basins within the main trench system

geochemistry of soils of king george island south shetland islands west antarctica implications for pedogenesis in cold polar regions fine fractions of soils on the barton peninsula king george island west antarctica have been forming during the last 6000 yr since the last deglaciation texturally they are mostly composed of mineral and rock fragments with some volcanic ashes which are also indicated by geochemical compositions representing for the nonclay silicate minerals and low values of chemical index of alteration no significant changes are observed in major and trace element abundances such geochemical characteristics suggest that chemical weathering of bedrocks on the barton peninsula seems insignificant and that the soils are composed of physically weathered mineral and rock fragments which are mixed with eolian additions of volcanic ashes and patagonian dusts chondrite normalized rare earth element ree distribution patterns of the barton peninsula soils are slightly different from those of bedrocks indicating that the ree abundances and characteristics were influenced by eolian additions mixing calculations which mass balance the rees suggest that volcanic ashes blown from deception island were the major eolian contributor followed by atmospheric dusts sourced from patagonia south america even in the warmer and humid climatic conditions in the maritime antarctic region the chemical weathering of bedrocks appears to be insignificant probably due to the relatively short duration of weathering since the last deglaciation

geochemistry of acidic volcanic clasts in silurian conglomerates of the midland valley of scotland implications on the caledonian orogeny 20 clasts of acidic volcanic rocks from silurian conglomerates of the midland valley of scotland are similar in their geochemical composition to rhyolithes rhyodacites and dacites of recent island arcs and active continental margins they differ from the geochemical composition of upper ordovician peralkaline rhyolites of the tweed valley in the southern uplands scotland because of their lower zr nb ce and y contents it is argued that these volcanic clasts represent erosional remnants of an island arc or active continental margin which was situated in the midland valley during upper ordovician or lower silurian time this has implications on palaeogeographic models which have been suggested for the scottish caledonides

a sequential back arc and foreland basin thrust duplex model for the southern uplands of scotland thrust imbrication of ordovician and silurian submarine fan sequences overlapping pelagic deposits in the southern uplands has been interpreted in terms of an accretionary prism formed above a nw directed subduction zone structural features invoked to support accretion are not definitive and could be explained in terms of a thin skinned thrusting model new palaeocurrent and compositional evidence from llandeilo to mid llandovery age turbidites in the northern part of the southern uplands proves interdigitation of sediments with strongly contrasting petrography turbidites derived from the south contain significant quantities of fresh andesitic detritus whereas those from the north form more mature quartz rich formations this implies a back arc situation the turbidites being deposited in a basin with a relatively mature continental landmass to the north and a rifted continental fragment containing an active volcanic arc to the south oblique collision of the opposing continental margins of the iapetus ocean during the llandovery caused the cessation of subduction underthrusting of the southern margin initiated a se propagating thrust stack which deformed the back arc basin sequence and may eventually have ramped over the eroded and faulted remains of the volcanic arc a southward migrating foreland basin formed ahead of the rising thrust stack and is now represented by the late llandovery hawick group and wenlock sequences mid to end silurian sinistral strike slip resulted from oblique collision and produced a transpressional regime during which reactivation of deep seated structures allowed the intrusion of lamprophyre dykes and granites

volcanic clasts in silurian conglomerates of the midland valley hagshaw hills inlier scotland and their meaning for caledonian plate tectonics 34 igneous clasts of predominantly rhyolitic composition of the parishholm and hareshaw conglomerate silurian hagshaw hills inlier midland valley scotland have been analysed for major and trace element contents the geochemical composition of the clasts indicates different source areas firstly some clasts are derived from rhyolites of a within plate setting peralkaline rhyolites of oceanic islands or continental rifts and secondly other clasts are derived from calc alkaline to high k rhyolites such rhyolites erupt mainly above convergent plate boundaries but occur also in continental areas of crustal extension both conglomerates were shed from the direction of the southern uplands into the midland valley since no calc alkaline rhyolites are known in the southern uplands a volcanic terrane should have been situated during the silurian in the area where the southern uplands lie now the geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts therefore several models are discussed

strike slip terranes and a model for the evolution of the british and irish caledonides evidence is presented that many of the major strike faults in the british and irish caledonides were active as sinistral strike slip zones in the end silurian to pre mid devonian period some such as the highland boundary fault moved in this way at an earlier stage in the ordovician these data allow the caledonian rocks lying between the laurentian miogeocline whose basement is represented by the lewisian moine and possibly the dalradian and the gondwanaland miogeocline midland platform and welsh basin to be re analysed as a group of disorganized terranes which originated to the southwest in north america and southwest europe africa prior to the silurian the highland border terrane and northern belt terrane are interpreted as duplicated pieces of a mid ordovician sequence which was a back are to northwest subduction the midland valley terrane is interpreted as a slice of laurentian foreland onto which ophiolites were obducted in the lower ordovician but which became the basement of a continental margin arc to northwest subduction in the mid ordovician the cockburnland terrane is inferred to be part of the same arc repeated and then broken up and dispersed by continuing strike slip the connemara terrane is regarded as an allochthonous piece of the dalradian miogeocline and the south mayo terrane as a remnant of an early ordovician arc and fore arc which in mid ordovician times became a back arc marginal basin to northwest subduction the lake district wexford terrane is part of an arc to southeast subduction under gondwanaland whose activity climaxed in the mid ordovician the central terrane is interpreted as a silurian overstep assemblage which blankets the junction between laurentian and gondwanaland derived oceanic terranes and therefore iapetus is regarded as an ordovician ocean which closed prior to the silurian the model suggests that at the end of the silurian a clockwise rotating gondwanaland having carried laurentia into collision with baltica broke free and created a major sinistral strike slip zone which disrupted the ordovician palaeogeography in the british isles north american sector of iapetus

determination of kerogen maturity by the pyrolysis carbon isotope method abstract the premise of the proposed maturation procedure is that immediately after post depositional microbial alteration of organic matter there is a degradable but not renewable pool of non extractable methane precursor carbon that becomes smaller as methane is produced with increasing time and temperature in addition the methane progressively becomes isotopically heavier because of mass balance and bonding considerations a maturity index based on the isotopic difference between the total accumulated methane produced by pyrolysis and the kerogen carbon and or the mole ratio of methane to kerogen carbon is presented published data by chung and sackett geochim cosmochim acta43 1979 1988 1979 for a suite of 19 coals and 12 shales of various ranks and maturities support this procedure