late precambrian u pb ages for the brookville gneiss southern new brunswick tonalitic orthogneiss from the brookville gneiss in southern new brunswick has an igneous protolith age of 605 pm 3 ma based on u pb dating of zircon metamorphic titanite from the same sample gives a minimum age of 564 pm 6 ma for upper amphibolite facies metamorphism of the unit based on u pb analyses of single detrital zircons a maximum sedimentary protolith age of about 641 ma is suggested for associated paragneiss these ages indicate that the igneous protolith of the orthogneiss was at most 35 ma younger than the sedimentary rocks it intruded and that the brookville gneiss is younger than the green head group to which it was previously considered basement both orthogneiss and paragneiss in the brookville gneiss contain proterozoic and archean detrital zircon grains suggesting an old heterogeneous continental source we conclude that the brookville gneiss does not represent the basement to the avalon terrane

structural setting and age of the partridge island block southern new brunswick canada a link to the cobequid highlands of northern mainland nova scotia the partridge island block is a newly identified tectonic element in the saint john area of southern new brunswick located south of and in faulted contact with proterozoic and cambrian rocks of the ganderian brookville and avalonian caledonia terranes it includes the lorneville group and tiner point complex the lorneville group consists of interbedded volcanic and sedimentary rocks subdivided into the taylors island formation west of saint john harbour and west beach formation east of saint john harbour a sample from thin rhyolite layers interbedded with basaltic flows of the taylors island formation at sheldon point yielded a late devonian early carboniferous u pb zircon age of 358 9 6 5 ma petrological similarities indicate that all of the basaltic rocks of the taylors island and west beach formations are of similar age and formed in a continental within plate tectonic setting west of saint john harbour basaltic and sedimentary rocks of the taylors island formation are increasingly deformed and mylonitic to the south and in part tectonically interlayered with mylonitic granitoid rocks and minor metasedimentary rocks of the tiner point complex based on magnetic signatures the deformed rocks of the tiner point complex can be traced through partridge island to the eastern side of saint john harbour where together with the west beach formation they occupy a thrust sheet above a redbed sequence of the mid carboniferous balls lake formation the tiner point complex includes leucotonalite and aegirine bearing alkali feldspar granite with a type chemical affinity and early carboniferous u pb zircon ages of 353 6 5 7 and 346 4 0 7 ma respectively based on similarities in age petrological characteristics alteration iron oxide copper gold iocg type mineralization and deformation style the partridge island block is correlated with late devonian early carboniferous volcanic sedimentary plutonic rocks of the cobequid highlands in northern mainland nova scotia deformation was likely a result of dextral transpression along the cobequid chedabucto fault zone during juxtaposition of the meguma terrane

40ar 39ar whole rock phyllite ages from late precambrian rocks of the avalon composite terrane new brunswick evidence of silurian devonian thermal rejuvenation several variably deformed and metamorphosed late precambrian volcanic sedimentary successions have been recognized within the avalon composite terrane exposed in the caledonian highlands of southern new brunswick whole rock samples of metasedimentary phyllite and phyllitic metatuff from the oldest ca 600 635 ma avalonian succession display similar internally discordant 40ar 39ar age and apparent k ca spectra intermediate temperature gas fractions were experimentally evolved solely from very fine grained cleavage aligned white micas these yield apparent ages between ca 430 and 410 ma and are interpreted to closely date a static late silurian early devonian thermal rejuvenation evidence for a silurian devonian thermal event has not been previously documented in avalonian rocks of the caledonian highlands caledonia assemblage however a thermal overprint of similar age ca 400 ma is recorded by metamorphic muscovite in high grade gneisses and platformal metasedimentary rocks brookville a

age of the brookville gneiss and associated rocks southeastern new brunswick the brookville gneiss is a medium to high grade quartz feldspar biotite and hornblende quartz feldspar biotite gneiss found north and northeast of saint john new brunswick the green head group

effects of acidic and basic parent materials on formation of some soils in quebec canada abstract five profiles developed on basic or acidic parent materials were sampled in southern quebec canada physical chemical and mineralogical properties were determined among the three profiles developed on basic parent materials one formed in disaggregated metabasalt whereas the two others developed in preglacial saprolites derived from the metabasalt as indicated by till cover in a nearby area in the lower part of the latter profiles the saprolites had a loamy texture and the mineralogical plus chemical data indicated very slight changes with respect to the metabasalt in these profiles cbd extractable fe content was 1 in most horizons and the pyrophosphate extractable fe was generally higher in the ah than in the b horizons in the profiles developed on acidic till cbd extractable fe was 1 only in the b horizons which also contained the maximum of pyrophosphate extractable fe in the latter profiles free fe and al sesquioxides were associated with the clay fractions whereas in the former profiles one third of the fe came from the sand and silt fractions chlorite was the dominant phyllosilicate in the basic material and it was transformed into interstratified minerals and smectite several hypotheses about smectite formation and distribution were discussed in the profiles developed on acidic till illite and chlorite were the major phyllosilicates and through weathering transformed into interstratified minerals vermiculite and smectite major differences in the properties of the profiles developed on the two parent materials were not reflected by current soil classification

minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

dynamics of giant volcanic ash clouds from supervolcanic eruptions 1 the largest explosive volcanic eruptions that have occurred on earth generated giant ash clouds from rising plumes that spread in the stratosphere around a height of neutral buoyancy with estimated supply rates that are in the range 1011 to 1013 m3 s these giant ash clouds are controlled by a balance between gravity and coriolis forces forming spinning bodies of nearly fixed proportions after a few hours and are initially insensitive to stratospheric winds in contrast volcanic plumes from eruptions with small to intermediate magnitude spread as inertial intrusions under the influence of stratospheric winds with the earth s rotation being unimportant in the largest eruptions the giant spinning ash clouds typically develop diameters greater than 600 km and up to 6000 km in the most powerful super eruptions thus explaining why areas of continental size can be covered with volcanic ash the radial expansion and spinning velocities are calculated at tens of metres per second and increase with eruption intensity higher spreading velocities carry larger ash grain sizes to a given radius so that grain size at a given distance from the source increases with eruption intensity consistent with geological observations

derivation of isotope ratios errors and error correlations for u pb geochronology using 205pb 235u 233u spiked isotope dilution thermal ionization mass spectrometric data a comprehensive treatment of the derivation of u pb isotope ratios and their corresponding uncertainties from isotope dilution thermal ionization mass spectrometric measurements is presented standard parametric statistical methods of error propagation are utilized to convolve uncertainties associated with instrumental mass fractionation tracer subtraction blank pb and u subtraction and initial common pb correction derivations include errors and error correlations for total sample u pb and pb isotope ratios including radiogenic and initial common pb for two and three dimensional isochron calculations radiogenic u pb and pb isotope ratios for concordia and radiogenic model age calculations and the propagation of model age errors from radiogenic isotope ratios

u pb geochronology of devonian granites in the meguma terrane of nova scotia canada evidence for hotspot melting of a neoproterozoic source abstract u pb isotopic analyses of monazite and zircon from six granitic plutons in the meguma terrane yield nearly concordant ages of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 373 pm 3 end document ma interpreted as the time of intrusion u pb analyses of euhedral zircons with thick rims overgrowing cores which were abraded to remove all or most of the rim plot on chords between documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage p

petrology and age of the mechanic settlement pluton avalon terrane southern new brunswick the mechanic settlement pluton located at the northern margin of the caledonian highlands in southern new brunswick is composed of rocks ranging from ultramafic lherzolite plagioclase bearing lherzolite through mafic mainly olivine gabbronorite and gabbro to intermediate quartz diorite and monzodiorite spatial distribution of these lithologies textural features and geochemistry are consistent with evolution of a tholeiitic mafic parent magma by crystal fractionation processes with some evidence for magma mingling between evolved gabbroic and quartz dioritic magmas the dioritic rocks form most of the southwestern upper part of the pluton whereas the varied gabbroic rocks with ultramafic layers form the northeastern part u pb zircon dating of a quartz diorite sample from the southwestern part of the pluton indicates crystallization at 557 3 ma amphibole and phlogopite in two lherzolite samples from the northeastern part of the pluton gave 40ar 39ar dates of 550 5 and 539 5 ma re

multi proxy dating the millennium eruption of changbaishan to late 946 ce ranking among the largest volcanic eruptions of the common era ce the millennium eruption of changbaishan produced a widely dispersed tephra layer known as the b tm ash which represents an important tie point for palaeoenvironmental studies in east asia hitherto there has been no consensus on its age with estimates spanning at least the tenth century ce here we identify the cosmogenic radiocarbon signal of 775 ce in a subfossil larch engulfed and killed by pyroclastic currents emplaced during the initial rhyolitic phase of the explosive eruption combined with glaciochemical evidence from greenland this enables us to date the eruption to late 946 ce this secure date rules out the possibility that the millennium eruption contributed to the collapse of the bohai kingdom manchuria korea in 926 ce as has previously been hypothesised further despite the magnitude of the eruption we do not see a consequent cooling signal in tree ring based reconstructions of northern hemisphere summer temperatures a tightly constrained date for the millennium eruption improves the prospect for further investigations of historical sources that may shed light on the eruption s impacts and enhances the value of the b tm ash as a chronostratigraphic marker

injection of gases into the stratosphere by explosive volcanic eruptions 1 explosive eruptions can inject large amounts of volcanic gases into the stratosphere these gases may be scavenged by hydrometeors within the eruption column and high uncertainties remain regarding the proportion of volcanic gases which eventually reach the stratosphere these are caused by the difficulties of directly sampling explosive volcanic eruption columns and by the lack of laboratory studies in the extreme parameter regime characterizing them using the nonhydrostatic nonsteady state plume model active tracer high resolution atmospheric model atham we simulated an explosive volcanic eruption we examined the scavenging efficiency for the climatically relevant gases within the eruption column the low concentration of water in the plume results in the formation of relatively dry aggregates more than 99 of these are frozen because of their fast ascent to low temperature regions consideration of the salinity effect increases the amount of liquid water by one order of magnitude but the ice phase is still highly dominant consequently the scavenging efficiency for hcl is very low and only 1 is dissolved in liquid water however scavenging by ice particles via direct gas incorporation during diffusional growth is a significant process the salinity effect increases the total scavenging efficiency for hcl from about 50 to about 90 the sulfur containing gases so2 and h2s are only slightly soluble in liquid water however these gases are incorporated into ice particles with an efficiency of 10 to 30 despite scavenging more than 25 of the hcl and 80 of the sulfur gases reach the stratosphere because most of the particles containing these species are lifted there sedimentation of the particles would remove the volcanic gases from the stratosphere hence the final quantity of volcanic gases injected in a particular eruption depends on the fate of the particles containing them which is in turn dependent on the volcanic and environmental conditions

volcanic sulfate deposition to greenland and antarctica a modeling sensitivity study reconstructions of the atmospheric sulfate aerosol burdens resulting from past volcanic eruptions are based on ice core derived estimates of volcanic sulfate deposition and the assumption that the two quantities are directly proportional we test this assumption within simulations of tropical volcanic stratospheric sulfur injections with the maecham5 ham aerosol climate model an ensemble of 70 simulations is analyzed with so2 injections ranging from 8 5 to 700 tg with eruptions in january and july modeled sulfate deposition flux to antarctica shows excellent spatial correlation with ice core derived estimates for pinatubo and tambora although the comparison suggests the modeled flux to the ice sheets is 4 5 times too large we find that greenland and antarctic deposition efficiencies the ratio of sulfate flux to each ice sheet to the maximum hemispheric stratospheric sulfate aerosol burden vary as a function of the magnitude and season of stratospheric sulfur injection changes in simulated sulfate deposition for large so2 injections are connected to increases in aerosol particle size which impact aerosol sedimentation velocity and radiative properties the latter leading to strong dynamical changes including strengthening of the winter polar vortices which inhibits the transport of stratospheric aerosols to high latitudes the resulting relationship between antarctic and greenland volcanic sulfate deposition is nonlinear for very large eruptions with significantly less sulfate deposition to antarctica than to greenland these model results suggest that variability of deposition efficiency may be an important consideration in the interpretation of ice core sulfate signals for eruptions of tambora magnitude and larger

differential so2 column measurements of the mt pinatubo volcanic plume differential so2 column measurements of the mt pinatubo volcanic plume were made from a nasa electra aircraft flying in the caribbean in july 1991 the mean column content of the volcanic plume in the caribbean was 25 atm m 2 5 dobson units with periods of over 100 atm m observed the data indicate that an aerosol absorption or scattering effect occurs for long slant paths low sun elevation angles and 41 atm m an average obtained for 1 2 airmasses may be more representative of a true column average dispersion of the initial cloud from mt pinatubo and a one month so2 to sulfate conversion time constant are in good agreement with the column contents found here

applying the three dimensional model atham to volcanic plumes dynamic of large co ignimbrite eruptions and associated injection heights for volcanic gases 1 many of the past large volcanic eruptions like tambora in 1815 krakatau in 1835 and pinatubo in 1991 were secondary so called co ignimbrite eruptions that were forced over a large area instead of a point source as in the plinian case previous modeling studies were based on one dimensional plume models we used the fully three dimensional plume model atham active tracer high resolution atmospheric model to investigate the dynamics and the resulting plume heights of co ignimbrite eruptions in an idealized setup ash particles as well as a sulfur dioxide so2 tracer are included in the model in the analysis we focus on the behavior of so2 since the neutral buoyancy height is an ill defined parameter for gravitationally settling particles in contrast to plinian plumes the co ignimbrite plumes develop from multiple updrafts resulting in significantly reduced neutral buoyancy heights at least a two dimensional modeling framework is necessary to capture the relevant dynamical features

a review of tephra transport and dispersal models evolution current status and future perspectives abstract tephra transport models try to predict atmospheric dispersion and sedimentation of tephra depending on meteorology particle properties and eruption characteristics defined by eruption column height mass eruption rate and vertical distribution of mass models are used for different purposes from operational forecast of volcanic ash clouds to hazard assessment of tephra dispersion and fallout the size of the erupted particles a key parameter controlling the dynamics of particle sedimentation in the atmosphere varies within a wide range largest centimetric to millimetric particles fallout at proximal to medial distances from the volcano and sediment by gravitational settling on the other extreme smallest micrometric to sub micrometric particles can be transported at continental or even at global scales and are affected by other deposition and aggregation mechanisms different scientific communities had traditionally modeled the dispersion of these two end members volcanologists developed families of models suitable for lapilli and coarse ash and aimed at computing fallout deposits and for hazard assessment in contrast meteorologists and atmospheric scientists have traditionally used other atmospheric transport models dealing with finer particles for tracking motion of volcanic ash clouds and eventually for computing airborne ash concentrations during the last decade the increasing demand for model accuracy and forecast reliability has pushed on two fronts first the original gap between these different families of models has been filled with the emergence of multi scale and multi purpose models second new modeling strategies including for example ensemble and probabilistic forecast or model data assimilation are being investigated for future implementation in models and or modeling strategies this paper reviews the evolution of tephra transport and dispersal models during the last two decades presents the status and limitations of the current modeling strategies and discusses some emergent perspectives expected to be implemented at operational level during the next few years improvements in both real time forecasting and long term hazard assessment are necessary to loss prevention programs on a local regional national and international level

worldwide continental denudation and climatic deterioration during the late tertiary evidence from deep sea sediments a six fold increase in the rate of accumulation of al 2 o 3 in north and central atlantic and pacific ocean sediments indicates vastly increased denudation of the continents during the past 15 m y the increase is more apparent in hemipelagic than pelagic sites demonstrating widely distributed local controls similarities in the rate of increase in the atlantic and pacific show that tectonic elevation is not responsible for the difference in sedimentation rate also similarities in the difference at sites of low and high latitude suggest that glaciation is not the most significant source a lack of correspondence between sedimentation rates and vail9s sea level curve similarly rule out that effect the conclusion drawn here is that worldwide climatic deterioration during the late tertiary is the explanation for the striking increase in detrital sedimentation in the world ocean

alteration profonde preglaciaire d un gneiss a charlesbourg quebec canada abstract a saprolite derived from a gneiss has been sampled in a fault zone at charlesbourg near quebec city the weathering largely exceeding 6 m in depth and a till overburden suggest preglacial alteration under warmer climatic conditions this is further supported by the presence of high up to 15 percentages of crystalline iron oxides goethite and lepidocrocite four different facies were defined in the saprolite mineralogical analyses were performed on the clay fractions and the following associations were found swelling minerals kaolinite kaolinite kaolinite gibbsite swelling minerals kaolinite the degree of weathering of 2 1 minerals into kaolinite seemed to be related to internal drainage conditions cation exchange capacity of the saprolite was adequately explained by the clay and silt fraction contributions

evolution geochimique superficielle naissante des anorthosites cas du profil de château richer quebec canada the initial stages of the superficial geochemical weathering of anorthosites have been investigated in a deposit at ch teau richer quebec the parent rock consists almost exclusively of andesine and is weathered to a thickness of about 120 cm a till overburden indicates that the profile was truncated by the wisconsinian ice the rock is not extensively disintegrated but the chemical weathering is rather intense the parker diagram shows a strong decrease of the weathering index from the parent rock to the weathering zone while this is not the case for other crystalline rocks in the area it may be accounted for by the fragility of the plagioclase the 2 m fraction which amounts to 2 of the soil presents an evolution that is influenced by the site especially the drainage conditions at the base of the profile drainage is poor and 2 1 minerals smectite and vermiculite are present in addition to 40 kaolinite the 1 1 mineral increases to 60 near the contact with the till while the amount of 2

three decades of geochronologic studies in the new england appalachians over the past 30 years both isotope geochronology and plate tectonics grew from infancy into authoritative disciplines in the geological sciences previously mountain systems like the appalachians had been viewed almost entirely in the context of the classical geosyncline implying a gradualism in stratigraphic and structural change throughout the orogen age control determined largely from distant fossiliferous strata was unabashedly carried to high grade metamorphic rocks based only on lithological correlations with the new concepts in tectonics came the realization that abrupt breaks in stratigraphy and structure occur in many cases at the boundaries of lithotectonic zones fortunately the new techniques of isotope geochronology could be brought to bear directly on the rocks of the immediate study area this paper chronicles some of the major contributions to the geology of the new england appalachians that resulted from these efforts during the past three decades in tracing the history of geochronologic research one encounters an increasingly sophisticated approach to the analytical and interpretive aspects of the discipline today the geochronologist can under optimum conditions constrain the age of stratigraphic units igneous activity deformation and metamorphism with accuracy that is capable of resolving fine structure within individual orogenic pulses he participates in full partnership with other colleagues of the science in unravelling the mysteries of mountain building several of the topical problems of new england geology in which geochronology played a key role include 1 the recognition and delineation of avalonia as a late proterozoic eastern basement distinct from more western terranes 2 the dating of the white mountain plutonic volcanic suite a mesozoic igneous event spanning 100 m y and 3 the temporal and spatial separation of structural and metamorphic features imprinted by the taconic and acadian orogenies the existing geochronology is summarized into a map and table emphasizing the temporal construction of the new england appalachians by using lithotectonic zones as the building blocks of the orogen seven such zones are defined in terms of pre syn and post assembly geologic history from west to east these lithotectonic zones are 1 berkshire green mountain 2 rowe hawley 3 connecticut valley 4 bronson hill 5 kearsarge central maine 6 tatnic hill nashoba and 7 avalonia avalonia is further divided into three subzones hope valley esmond dedham and penobscot bay which themselves may have had distinct origins and assembly histories the boundaries between these zones are faults in most cases some of which may have had recurring movement to further complicate any plate tectonic scenario a delineation of underlying grenvillian chain lakes and avalonian basement is also attempted which now can make use of isotopes in igneous rocks as petrogenetic indicators to supplement the rare occurrences of basement outcrop within mobile zones of the orogen the belt of permian thermal disturbance within the kearsarge central maine zone is hypothesized to reflect rapid rebound following compressional thickening of underlying avalonian basement during the alleghanian orogeny

characteristics of residual and colluvial soils developed on granite and of the associated pre wisconsin landforms in north central new brunswick an area in north central new brunswick of approximately 20 km2 where tors are common was found to be undisrupted by glaciation the soils in this area are developed on grus and appear to be of pr

u pb geochronological constraints on the tectonothermal evolution of the paleoproterozoic basement of cadomia la hague nw france abstract the la hague region of nw france provides some of the best exposures of paleoproterozoic basement in the northernmost segment of the cadomian orogen one of several neoproterozoic arc fragments in the circum atlantic region the basement rocks which include orthogneiss metasediments and metabsites contain a comparable series of structures with a common metamorphic history thus the basement units are regarded to have undergone the same broad tectonothermal evolution the metasedimentary succession includes migmatites that preserve relict kyanite overprinted by sillimanite associated with the development of garnet bearing leucosome biotite dehydration at a metamorphic peak of 700 800 c and 8 9 kbar is considered responsible for the anatexis evident in both the metasediments and orthogneiss units a u pb zircon crystallization age of 2061 2 7 ma for the culeron orthogneiss a member of the metamorphic suite confirms the paleoproterozoic protolith age idioblastic rims to 2 06 ga zircons from the culeron orthogneiss yield shrimp u pb dates of c 618 ma providing the first geochronological constraints on the likely age of high grade metamorphism and anatexis of the paleoproterozoic basement in cadomia foliated c 615 610 ma intrusions that intrude the metamorphic units record magmatic to solid state fabrics that parallel metamorphic fabrics within the basement consistent with deformation and metamorphism being late neoproterozoic in age

the kingston terrane southern new brunswick canada evidence for an early silurian volcanic arc the fault bounded kingston terrane of southern new brunswick consists of felsic and less abundant mafic volcaniclastic rocks and flows and minor interbedded sedimentary rocks of the kingston group intruded by mainly granitic plutons and abundant younger mafic sheets the granitic plutons form about half of the terrane and are characterized by fine grain size and typically granophyric and porphyritic textures indicative of high level emplacement mafic sheets were emplaced in the granitic plutons and parallel to primary layering in the kingston group which is typically steeply dipping and trends northeast to north northeast hence in contrast to some earlier interpretations the kingston terrane does not consist of a bimodal dike complex the kingston group granitic rocks and mafic sheets contain mineral assemblages consistent with metamorphism to upper greenschist lower amphibolite facies new u pb zircon ages of 442 6 ma from a dacitic tuff unit and 437 10 ma from a granitic pluton corroborate previous u pb dates that had suggested that the volcanic and granitic rocks in the kingston terrane are early silurian rather than precambrian as had been earlier assumed the felsic volcanic and granitic rocks are interpreted to be comagmatic on the basis of their field relationships and similar u pb ages and chemical character compositions of both the felsic rocks and less abundant mafic and intermediate and mafic rocks are consistent with calc alkalic affinity and emplacement in a continental margin volcanic arc herein termed the kingston arc a u pb date of 435 5 ma was also obtained from compositionally similar granite that forms a dike in an adjacent fault bounded amphibolite facies metasedimentary unit the similarity in age and composition of the granite dike suggests a link between these metasedimentary rocks and the kingston terrane possibly as part of an accretionary complex if so its location southeast of the kingston terrane indicates that subduction was to the present northwest mafic sheets in the kingston terrane are tholeiitic but have some arc like characteristics consistent with their origin in a former arc setting but the sheets were likely emplaced in a subsequent extensional setting the compositional similarity of the mafic sheets to late silurian mafic volcanic rocks and plutons of the coastal maine magmatic province suggests that they may be related a possible model for evolution of the kingston terrane is proposed wherein the kingston group and related granite formed in an early silurian arc on the margin of ganderia as represented by the new river terrane of late precambrian and early paleozoic age northwestward subduction culminated in collision between the kingston arc and a continental block now represented by the brookville terrane to the southeast subsequent transpressive mo tions in the late silurian may have been responsible for the crustal scale extensional environment in which the coastal maine magmatic province was formed including emplacement of mafic dikes into the deformed former kingston arc transpressive motions related to juxtaposition of the avalon and meguma terranes with the previously accreted more inboard terranes continued through the devonian and into the carboniferous

chronology of devonian to early carboniferous rifting and igneous activity in southern magdalen basin based on u pb zircon dating fifteen u pb zircon radiometric age determinations have been made on igneous rocks of middle devonian to early carboniferous age from the southern margin of the magdalen basin in cape breton island and northern mainland nova scotia volcanic rocks interbed with early rift basin sedimentary rocks with some palynological biostratigraphy dated intrusive rocks cut these sedimentary units our biostratigraphically constrained ages are in close agreement with the current devonian time scale combined with previously published data the age determinations show that igneous activity occurred in four pulses middle devonian 390 385 ma early late devonian 375 370 ma latest devonian to early tournaisian 365 354 ma and late tournaisian to early visean ca 339 ma middle devonian 385 389 ma volcanic rocks are confined to the guysborough group the fisset brook formation basalt and minor rhyolite in the type area and elsewhere in cape breton island and northern mainland nova scotia is late devonian c

pluton emplacement by wall rock thrusting hanging wall translation and extensional collapse latest devonian plutons of the cobequid fault zone nova scotia canada

geochemistry and tectonic setting of late precambrian volcanic and plutonic rocks in southeastern cape breton island nova scotia late precambrian volcanic sedimentary belts in the mira avalon terrane of southeastern cape breton island display differences in rock types petrochemistry and age showing that they did not form contemporaneously above a single northwest dipping subduction zone as proposed in earlier models the oldest rocks are 680 ma mafic and felsic flows and tuffs and abundant mainly tuffaceous sedimentary rocks in the stirling belt they are interpreted to have formed in a trough within or peripheral to a volcanic arc complex northwest of the stirling belt the east bay hills coxheath hills and sporting mountain belts consist of ca 620 ma mafic to felsic subaerial pyroclastic rocks and flows and contemporaneous dioritic to granitic plutons both volcanic and plutonic rocks are calc alkalic to high k calc alkalic suites formed in a continental margin volcanic arc a correlative 620 ma plutonic suite intruded the western margin of the stirling belt suggesting that subduction may have been toward the prese

late precambrian volcaniclastic deposits of the avalonian eastport basin newfoundland appalachians petrofacies detrital clinopyroxene geochemistry and palaeotectonic implications abstract the eastport basin contains over 5 km of well preserved marine volcaniclastic deposits that comprise parts of the late precambrian avalonian connecting point and love cove groups of the eastern newfoundland appalachians basin infilling was dominated by deep sea resedimentation of pyroclastic and epiclastic sediments four petrographically and texturally distinct petrofacies have been designated viz tuffs tuffaceous sandstones and conglomerates feldspathic sandstones and conglomerates polymict sandstones and conglomerates a broad compositional spectrum of volcanogenic detritus a copious supply of pyroclastic basaltic andesitic dacitic and rhyolitic ejecta and the ubiquity of trace plutonic and metamorphic rock fragments are diagnostic provenance attributes of the basin fill and these indicate derivation from an evolved magmatic arc developed on a transitional or possibly continental crust detrital calcic clinopyroxenes and calcic amphiboles from the upper part of the connecting point group are low in ti and al display calc alkaline and calc alkaline to tholeftic affinity of the parental magma and plot in the field of orogenic basalts discriminant function analysis demonstrates that basalts and andesites were the main source of the detrital clinopyroxene the clinopyroxene major element chemistry is consistent with the evolved volcanic arc provenance suggested by petrographic data both datasets independently support other sedimentological and stratigraphic evidence that the eastport basin records sedimentation adjacent to an active avalonian cadomian volcanic arc the remnants of which are preserved in part within the presently adjacent predominantly volcanic love cove group

40ar 39ar ages of detrital muscovite within early paleozoic overstep sequences avalon composite terrane southern new brunswick implications for extent of late paleozoic tectonothermal overprint concentrates of coarse grained detrital muscovite from the ratcliffe brook formation lowermost cambrian display internally discordant 40ar 39ar age spectra gas fractions evolved at intermediate and high experimental temperatures record apparent ages of ca 610 620 ma these are interpreted as dating initial cooling through temperatures appropriate for intracrystalline retention of 40ar and may indicate derivation from mylonite zones developed within proximal late precambrian granitic rocks gas fractions evolved at lower experimental temperatures record patterns of spectra discordance that suggest the constituent grains experienced partial intracrystalline diffusive loss of 40ar during a late paleozoic low grade thermal overprint a muscovite concentrate from pelitic schist beneath the allochthonous latest precambrian cranberry head granite records a 40ar 39ar plateau age of 318 1 ma this is interpreted as closely dating late carboniferous thrust emplacement of the allochthon

insights into the formation and dynamics of coignimbrite plumes from one dimensional models coignimbrite plumes provide a common and effective mechanism by which large volumes of fine grained ash are injected into the atmosphere nevertheless controls on formation of these plumes as a function of eruptive conditions are still poorly constrained herein two 1 d axysymmetric steady state models were coupled the first describing the parent pyroclastic density current and the second describing plume rise global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained for a range of initial mass flow rates between 108 and 1010 kg s modeled liftoff distance the distance at which neutral buoyancy is attained assuming radial supercritical flow is controlled by the initial flow radius gas mass fraction flow thickness and temperature the predicted decrease in median grain size between flow initiation and plume liftoff is negligible calculated initial plume vertical velocities assuming uniform liftoff velocity over the pyroclastic density current invasion area are much greater several tens of m s than those previously used in modeling coignimbrite plumes 1 m s such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes highlighting an unavailability of large clasts possibly due to particle segregation within the flow prior to plume formation source radius and initial vertical velocity have the largest effect on maximum plume height closely followed by initial temperature modeled plume heights are between 25 and 47 km comparable with plinian eruption columns highlighting the potential of such events for distributing fine grained ash over significant areas

u pb geochronological constraints on precambrian stratified units in the avalon composite terrane of nova scotia canada tectonic implications concordant u pb ages of detrital zircons in several proterozoic units in the avalon composite terrane of nova scotia along with previously published data indicate that deposition of low and high grade stratified units in the cobequid highlands gamble brook formation and central cape breton island variously assigned to the george river group or george river metamorphic suite and the bras d or gneiss started after 977 ma extended through a period of volcanic activity between 694 and 637 ma and ended before the 629 612 600 ma volcanic activity associated with deposition of the georgeville and jeffers groups in the antigonish and cobequid highlands and the east bay hills and coxheath groups in southern cape breton island these age data along with u pb analyses of metamorphic and igneous zircon and monazite also constrain three late proterozoic tectonothermal events i oblique sinistral ductile shear deformation and greenschist amphibolite facies metamorphism probably occurred between 694 an

use of motion estimation algorithms for improved flux measurements using so 2 cameras abstract article history received 3 april 2014accepted 18 august 2014available online xxxxkeywords so 2 uxso 2 cameraplume speedplume modellingoptical owmotion estimation so 2 cameras are rapidly gaining popularity as a tool for monitoring so 2 emissions from volcanoes severaldifferent so 2 camera systems have been developed with varying patterns of image acquisition in space timeand wavelength despite this diversity there are two steps common to the work owsofmostofthesesystems aligning images of different wavelengths to calculate apparent absorbance and estimating plume transportspeeds both of which can be achieved using motion estimation algorithms here we present two suchalgorithms adualtreecomplexwavelettransform basedalgorithmandthefarnebackopticalflowalgorithm weassesstheiraccuracyusingasyntheticdatasetcreatedusingthenumericcloud resolvingmodelatham andthen apply them to real world data from villarrica volcano both algorithms are found to perform well and theatham simulations offer useful datasets for benchmarking and validating future algorithms 2014 the authors published by elsevier b v this is an open access article under the cc by license http creativecommons org licenses by 3 0

improving on mass flow rate estimates of volcanic eruptions 1 we introduce a novel analytical expression that allows for fast assessment of mass flow rate of both vertically rising and bent over volcanic plumes as a function of their height while first order physical insight is maintained this relationship is compared with a one dimensional plume model to demonstrate its flexibility and then validated with observations of the 1980 mount st helens and of the 2010 eyjafjallajokull eruptions the influence of wind on the dynamics of volcanic plumes is quantified by a new dimensionless parameter and it is shown how even vertically rising plumes such as the one associated with the mount st helens 1980 eruption can be significantly affected by strong wind comparison between a one dimensional model and the analytical equation gives anr2 value of 0 88 while existing expressions give negativer2 values due to their inability to adapt to different source and atmospheric conditions therefore this new expression has important implications both for current strategies of real time forecasting of ash transport in the atmosphere and for the characterization of explosive eruptions based on the study of tephra deposits in addition this work provides a framework for the application of more complete three dimensional numerical models as it greatly reduces the parameter space that needs to be explored

tectonic setting of avalonian volcanic and plutonic rocks in the caledonian highlands southern new brunswick canada the caledonian highlands of southern new brunswick consist of late proterozoic to cambrian rocks generally considered typical of the avalon terrane of the northern appalachian orogen mainly tuffaceous volcanic and sedimentary rocks of the broad river group and cogenetic dioritic to granitic plutons with ages ca 620 ma form most of the eastern caledonian highlands they have petrological features indicative of origin in a continental margin subduction zone significantly younger ca 560 550 ma dacitic to rhyolitic lapilli tuffs and flows laminated tuffaceous siltstone basaltic and rhyolitic flows and clastic sedimentary rocks of the coldbrook group form most of the western highlands and occur locally throughout the highlands the mainly tuffaceous lower part of the group has been intruded by gabbroic and syenogranitic plutons that are interpreted to be cogenetic with basaltic and rhyolitic flows in the upper part of the group this voluminous subaerial magmatism may have formed during postorogenic ex

late proterozoic tectonic model for the avalon terrane in maritime canada the avalon terrane in maritime canada extends from cape breton island through northern nova scotia antigonish and cobequid highlands to southern new brunswick the terrane contains abundant late proterozoic volcanic rocks 570 680 m y old the geochemistry of the volcanic rocks of southern cape breton island and southern new brunswick indicates that they were erupted in a volcanic arc environment in both regions the mafic rocks display a remarkably similar compositional zonation which resembles the across arc variations observed in modern volcanic arcs the progressive compositional changes that include a transition from island arc tholeiites along the southeastern coasts to calc alkaline rocks inland to the northwest are probably due to a northwest dipping subduction zone with a trench located to the southeast in the antigonish and cobequid highlands continental tholeiites and calc alkaline volcanic rocks are interbedded and overlain by turbidites that have probably been deposited in a back arc or intra arc environment the superimposed positive gravity and magnetic anomalies that may be traced discontinuously from the grand banks through nova scotia collector anomaly and along the northern side of the gulf of maine to near boston probably represent late proterozoic ophiolitic remnants preserved by incomplete suturing along a late proterozoic plate boundary northeast trending segments are inferred to mark subduction zones and the e w portions could correspond to transform faults thus the present geographical distribution of the late proterozoic volcanic rocks is explained by a tectonic model involving a single subduction zone offset by two late proterozoic transform faults located approximately along the minas fault and the scatarie ridge

ascent dynamics of large phreatomagmatic eruption clouds the role of microphysics 1 we examine the impact of abundant surface water interaction on the development of volcanic clouds from large scale 108 kg s 1 magma phreatomagmatic eruptions presenting the first 2 d large eddy simulations of wet volcanic plumes that incorporate the effects of microphysics the active tracer high resolution atmospheric model was forced with field derived inputs from an exceptionally large phreatomagmatic eruption the 27 ka oruanui supereruption taupo volcano new zealand surface water contents were varied from 0 to 40 wt for eruptions with equivalent magma eruption rates of 1 3 108 and 1 1 109 kg s 1 our findings confirm that increased surface water has a pronounced impact on column stability leading to transitional column behavior and hybrid clouds resulting from simultaneous ascent of material from stable columns and pyroclastic density currents pdcs contrary to the suggestion of previous workers however abundant surface water does not systematically lower the spreading level or maximum height of volcanic clouds owing to vigorous microphysics assisted lofting of pdcs the simulated behavior and ash cloud dimensions provide a close match to field evidence from the oruanui case study cloud heights from the collapsing eruption columns also show a notable sensitivity to changes in the altitude of the tropopause while ambient humidity primarily impacts the abundance of airborne hydrometeors particularly ice associated with the volcanic clouds general relationships between eruption style meteorological conditions and the resulting vertical profiles of volcanic emissions outlined here could also be adapted for use in operational volcanic ash forecasting and deposit reconstruction techniques already in existence

magnetic and gravity models across terrane boundaries in southern new brunswick canada regional magnetic and gravity map patterns combined with modeling of magnetic and gravity data constrained by measured magnetic susceptibility and density information are used to develop a better understanding of the three dimensional character of major lithostratigraphic subdivisions terranes in southern new brunswick models and long wavelength map patterns indicate that the boundaries between the caledonia brookville kingston and new river terranes are sub vertical or dip slightly to the southeast and that some map units in each terrane extend to depths ranging from 5000 8000 m the mascarene and st croix terranes are less well constrained than the more outboard terranes on the models in part because of limited physical property data but also because of the presence of the saint george batholith which obscures relationships among stratigraphic units the models are consistent with the mascarene terrane being a cover sequence over the boundary between the st croix and new river terranes the specific location and nature of which is now revealed by the geophysical models the terranes appear to be associated at depth with geophysically distinct bodies that are interpreted to correspond to the basements from southeast to northwest of avalon terrane sensu stricto brookville bras d or terrane and exploits gander composite terrane the latter gander basement underlies the kingston new river mascarene and st croix terranes

geology and geochemistry of the late precambrian coldbrook group near saint john new brunswick the late precambrian coldbrook group comprises basal basaltic flows and pyroclastic rocks fragmental andesitic to rhyolitic rocks and minor capping sedimentary strata all deformed and metamorpho

large eddy simulation of gas particle kinematic decoupling and turbulent entrainment in volcanic plumes abstract in the framework of the iavcei international association of volcanology and chemistry of the earth interior intercomparison study on volcanic plume models we present three dimensional 3d numerical simulations carried out with the ashee ash equilibrium eulerian model the ashee model solves the compressible balance equations of mass momentum and enthalpy of a gas particle mixture and is able to describe the kinematic decoupling for particles characterized by stokes number i e the ratio between the particle equilibrium time and the flow characteristic time lower than 0 2 or particles smaller than about 1 mm the computational fluid dynamic model is designed to accurately simulate a turbulent flow field using a large eddy simulation approach and is thus suited to analyze the role of particle non equilibrium in the dynamics of turbulent volcanic plumes the two reference scenarios analyzed correspond to a weak mass eruption rate 1 5 10 6 kg s and a strong volcanic plume mass eruption rate 1 5 10 9 kg s in absence of wind for each scenario we compare the 3d results averaged in space and time with theoretical results obtained from integral plume models such an approach enables quantitative evaluation of the effects of grid resolution and the subgrid scale turbulence model and the influence of gas particle non equilibrium processes on the large scale plume dynamics we thus demonstrate that the uncertainty on the numerical solution associated with such effects can be significant of the order of 20 but still lower than that typically associated with input data and integral model approximations in the weak plume case 3d results are consistent with the predictions of integral models in the jet and plume regions with an entrainment coefficient around 0 10 in the plume region in the strong plume case the self similarity assumption is less appropriate and the entrainment coefficient in the plume region is more unstable with an average value of 0 24 for both cases integral model predictions diverge from the 3d plume behavior in the umbrella region the presented analysis of 3d numerical simulations thus enables identification of the critical hypotheses that underlie integral models used in operational studies in addition high resolution 3d runs allow reproduction of observable quantities such as infrasound signals which can be useful for constraining eruption dynamics during real events

determination of the mass eruption rate for the 2014 mount kelud eruption using three dimensional numerical simulations of volcanic plumes abstract using a three dimensional fluid dynamic model for eruption cloud dynamics we present numerical simulations of the development of a volcanic eruption column and umbrella cloud formed during the 13 february 2014 eruptions of mount kelud indonesia the model used in this study quantitatively reproduces the observed data and in particular the plume height and the horizontal expansion level and rate of the umbrella cloud the simulation results suggest that on the basis of the plume height and structures and the horizontal expansion level of the umbrella cloud the mass eruption rate mer for the 2014 kelud eruptions was 3 107 to 4 107 kg s 1 on the basis of the horizontal expansion rate of the umbrella cloud on the other hand the estimated mer was 1 108 kg s 1 the difference between these two estimates implies the strong diffusion in the umbrella cloud or the efficient entrainment of ambient air by eruption column

characteristics and significance of two pre late wisconsinan weathering profiles adirondacks usa and miramichi highlands canada abstract the properties of two weathering profiles developed from granitic rocks and covered by deposits of wisconsinan age were studied in order to characterize saprolites and non saprolite residuum of the glaciated area of northeastern north america the warrensburg profile adirondacks new york is more than 9 m thick and formed on a hornblende granitic gneiss total chemical analysis of the sandy saprolite shows slight losses compared to bedrock kaolinite is the main weathering product in the

climate response to the toba super eruption regional changes climatic consequences of the young toba tuff ytt eruption about 73 ka are a crucial argument in the current discussion about the fate of modern humans especially in africa and asia earth system model esm simulations of the ytt eruption are used to investigate its regional climate impacts in particular focusing on areas relevant to human evolutionary issues during that time uncertainties concerning the stratospheric sulphur emission for the ytt eruption are addressed by comparing esm simulations of a 100 times pinatubo like eruption as an upper and a 3 times pinatubo like tambora eruption as a lower estimate information about transient changes in vegetation types after the ytt eruption are obtained by forcing an offline dynamical global vegetation model with the climate anomalies simulated by the esm under both glacial and interglacial background climate conditions the simulated temperature changes in those areas that were inhabited by humans suggest thermal discomfort but not a real challenge for survival precipitation is reduced in all regions during the first two years but recovers quickly thereafter some catchments in these regions ganges brahmaputra nile experience an over compensation in precipitation during the third to fifth post eruption years which is also reflected in anomalously strong river runoffs change in vegetation composition may have created the biggest pressure on humans who had to adapt to more open space with fewer trees and more grasses for some decades especially in the african regions the strongest environmental impacts of the ytt eruption are simulated under interglacial background conditions suggesting that the climate effects of the ytt eruption did not impact humans on a major scale and for a period long enough to have dramatic consequences for their survival

u pb age constraints on the stratigraphy and tectonic history of the avalon terrane new brunswick canada six new u pb ages for avalonian plutonic and volcanic rocks from the eastern caledonia highlands southern new brunswick indicate that magmatic activity occurred between 625 600 ma ago with another probably separate major episode at ca 550 ma this gap in igneous activity is consistent with differences in the metamorphic and deformational character of rocks from the two episodes the 625 600 ma activity was calc alkalic and probably occurred in an andean type magmatic arc it correlates with most volcanism and plutonism in the type avalon terrane of newfoundland the ca 550 ma activity formed bimodal volcanic rocks and high level plutons probably in an extensional setting u pb ages of xenocrystic zircons from avalonian igneous rocks indicate both archean and proterozoic components at depth in avalonian basement an observation consistent with pb isotopic signatures which suggest an old radiogenic crustal source the african craton for the magmatic products

satellite observations and interpretation of the 1991 mount pinatubo eruption plumes we demonstrate the use of hourly geostationary meteorological satellite gms and noaa polar orbiting advanced very high resolution radiometer avhrr satellite images of the june 1991 mount pinatubo volcanic eruption plumes in providing details of the timing changing eruptive style and umbrella plume movement and dynamics a chronology of explosive events which culminated in a 9 hour long climactic phase on june 15 has been determined from satellite data and favorably compared to ground based and other ancillary information maximum eruption column altitudes of 40 km and column top undercooling in excess of 55 c below the ambient atmosphere occurred during the climactic phase phases dominated by plinian versus coignimbrite eruptive plumes can be distinguished on the images analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4 5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds we compare the rate of plume growth to a model of a radially symmetric continuously fed intrusion to describe the motion the rate of plume growth shows good agreement with this simple model for the first 4 5 hours from column top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from june 12 16 of 5 5 km3 dense rock equivalent dre in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5 3 km3 dre we also show that secondary explosions in the pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in september 1991 this study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data

contrasting u pb ages from plutons in the bras d or and mira terranes of cape breton island nova scotia u pb dates from zircon titanite and monazite in plutons of the bras d or and mira terranes of southern cape breton island combined with 40ar 39ar and other radiometric age data indicate that th

u pb zircon geochronology of roxbury conglomerate boston basin massachusetts tectono stratigraphic implications for avalonia in and beyond se new england high precision ca tims 206pb 238u zircon dates from sandstone and brighton igneous rocks associated with roxbury conglomerate in the boston basin eastern massachusetts provide constraints on the age and tectonic significance of these deposits detrital zircon suites from roxbury related sandstones representing in ascending order the franklin park member proposed name the brookline member and the squantum member establish closely comparable maximum depositional ages of 595 14 0 90 598 87 0 71 and 596 39 0 79 ma respectively the youngest of these is the best maximum age estimate of the conglomerate brighton dacite near the base of the brookline member and amygdaloidal andesite near the top yield respective crystallization ages of 584 19 0 70 ma and 585 37 0 72 ma these virtually identical dates support previous interpretations of these particular units as shallow intrusions and thus represent minimum ages of associated conglomerate the roxbury brighton sequence is traditionally shown as inter fingering northward with 570 ma mudstone of the cambridge argillite but the age range of the conglomerate makes this impossible conglomerate lacking quartzite clasts typical of the roxbury proper and associated with 593 19 0 73 ma rhyolite on the south side of the basin is re assigned to the lynn mattapan volcanic complex which rests unconformably on dedham granite in basement exposed west and north of the basin as well calc alkaline geochemistry and ages of the 609 to 584 ma dedham lynn mattapan brighton assemblage link it with 630 to 580 ma arc sequences in other northern appalachian avalonian terranes roxbury conglomerate accumulated in fault bounded intra arc basins near the end of this magmatic cycle

suspect terranes and accretionary history of the appalachian orogen the north american connection or the grenvillian continental crust that separated from eastern north america during the initiation of the appalachian orogenic cycle is poorly defined within the present orogen a variety of terranes occur outboard of the north american miogeocline all structurally uncoupled and therefore suspect stratigraphic analysis indicates that appalachian accretion progressed from the miogeocline outward the boundaries of the earliest accreted western terranes are marked by melange and ophiolite complexes later boundaries between eastern terranes are steep mylonitic zones and brittle faults accretionary events defined by stratigraphic analysis correspond to times of major deformation plutonism and metamorphism in the history of the orogen

geochronological constraints on late precambrian intrusion metamorphism and tectonism in the anti atlas mountains the bou azzer inlier anti atlas morocco is a critical element for understanding gondwanan geology because it exposes rocks formed during the paleosuturing of the gondwanan margin with peri gondwanan arc terranes numerous intrusions within the inlier allow specific tectonic events associated with the tectonic evolution of the gondwanan margin to be bracketed detailed examination of plutons within the inlier reveal down temperature magmatic to solid state fabrics and contact relationships indicative of emplacement during oblique collision between the margin and one or more arc terranes u pb geochronological data for the ao t abdulla diorite ma and 653 8 1 6 bou offroh granodiorite ma provide a limit to the onset of collision and regional metamorphism a 653 0 1 3 precise age of ma for the ousdrat quartz diorite provides an indication of the lower limit of the collision 640 8 1 4 in the region tectonothermal activity in the anti atlas at ca 650 ma correlates with similar periods of tectonism in the peri gondwanan terranes of avalonia and cadomia and points to the emergence of continent wide tectonism in western gondwana as early as 650 ma

tectonic deformation and magmatism along the southern flank of the maritimes basin the northeastern cobequid highlands nova scotia distributed crustal scale faulting in the cobequid highlands in the middle devonian to carboniferous resulted from the oblique convergence of the meguma and avalon terranes in the northeastern cobequid highlands seismic reflection profiles show neoproterozoic and lower paleozoic rocks together with enigmatic foliated rocks overlying the early carboniferous fountain lake group the foliated rocks form the hanging wall of a north vergent thrust fault their protolith is inferred from petrography and geochemistry to be principally neoproterozoic rhyodacitic tuff and late paleozoic hypabyssal intrusions the age of thrusting is stratigraphically constrained to the late tournaisian mid visean and sericite from mylonite yielded a tournaisian k ar age of 352 8 ma the thrusting occurs at the base of a tectonic escape sheet and resulted from a restraining bend in the rockland brook master fault farther west where the rockland brook fault trends almost east west tournaisian extensional features include

inter comparison of three dimensional models of volcanic plumes abstract we performed an inter comparison study of three dimensional models of volcanic plumes a set of common volcanological input parameters and meteorological conditions were provided for two kinds of eruptions representing a weak and a strong eruption column from the different models we compared the maximum plume height neutral buoyancy level where plume density equals that of the atmosphere and level of maximum radial spreading of the umbrella cloud we also compared the vertical profiles of eruption column properties integrated across cross sections of the plume integral variables although the models use different numerical procedures and treatments of subgrid turbulence and particle dynamics the inter comparison shows qualitatively consistent results in the weak plume case mass eruption rate 1 5 106 kg s 1 the vertical profiles of plume properties e g vertical velocity temperature are similar among models especially in the buoyant plume region variability among the simulated maximum heights is 20 whereas neutral buoyancy level and level of maximum radial spreading vary by 10 time averaging of the three dimensional 3d flow fields indicates an effective entrainment coefficient around 0 1 in the buoyant plume region with much lower values in the jet region which is consistent with findings of small scale laboratory experiments on the other hand the strong plume case mass eruption rate 1 5 109 kg s 1 shows greater variability in the vertical plume profiles predicted by the different models our analysis suggests that the unstable flow dynamics in the strong plume enhances differences in the formulation and numerical solution of the models this is especially evident in the overshooting top of the plume which extends a significant portion 1 8 of the maximum plume height nonetheless overall variability in the spreading level and neutral buoyancy level is 20 whereas that of maximum height is 10 this inter comparison study has highlighted the different capabilities of 3d volcanic plume models and identified key features of weak and strong plumes including the roles of jet stability entrainment efficiency and particle non equilibrium which deserve future investigation in field laboratory and numerical studies

volcanic particle aggregation in explosive eruption columns part i parameterization of the microphysics of hydrometeors and ash abstract the aggregation of volcanic ash particles within the eruption column of explosive eruptions has been observed at many volcanoes it influences the residence time of ash in the atmosphere and the radiative properties of the umbrella cloud however the information on the processes leading to aggregate formation are still either lacking or very incomplete we examine the fate of ash particles through numerical experiments with the plume model atham active tracer high resolution atmospheric model in order to determine the conditions that promote ash particle aggregation in this paper we describe the microphysics and parameterization of ash and hydrometeors in a companion paper this issue we use this information in a series of numerical experiments the parameterization includes the condensation of water vapor in the rising eruption column the formation of liquid and solid hydrometeors and the effect of latent heat release on the eruption column dynamics are considered the interactions of hydrometeors and volcanic ash within the eruption column that lead to aggregate formation are simulated for the first time within a rising eruption column the microphysical parameterization follows a modal approach the hydrometeors are described by two size classes each of which is divided into a liquid and a frozen category by analogy with the hydrometeor classification we specify four categories of volcanic ash particles we imply that volcanic particles are active as condensation nuclei for water and ice formation ash can be contained in all categories of hydrometeors thus forming mixed particles of any composition reaching from mud rain to accretionary lapilli collisions are caused by gravitational capture of particles with different fall velocity coalescence of hydrometeor ash aggregates is assumed to be a function of the hydrometeor mass fraction within the mixed particles the parameterization also includes simplified descriptions of electrostatics and salinity effects

geochemical evolution of earliest carboniferous continental tholeiitic basalts along a crustal scale shear zone southwestern maritimes basin eastern canada abstract continental tholeiites were extruded locally within the extensional wrench maritimes basin from about 375 to 330 ma late devonian early carboniferous basalts of the early carboniferous diamond brook formation are up to 1 5 km thick and overlie a succession of predominantly felsic volcanic rocks reaching several kilometres in thickness the volcanic rocks and co genetic plutons occur along a crustal scale strike slip fault that facilitated the transport of relatively primitive magma resulting in basalts with high mg number ni and cr end 4 and relatively low tio2 v y and zr fractional crystallization of plagioclase and lesser clinopyroxene in the absence of iron oxide fractionation resulted in repetitive extrusion cycles hundreds of metres in thickness that show an upward increase in plagioclase phenocrysts or megacrysts and in tio2 and other high field strength elements hfses rare andesites are interpreted as products of partial melting of underplated gabbro the relatively primitive basalts resemble low ti basalts found in other continental flood basalt provinces and have trace element and isotopic characteristics that have been ascribed in the literature either to partial melting of or contamination of asthenospheric melts by subcontinental lithospheric mantle in the maritimes basin similar continental tholeiites were extruded intermittently over a 45 ma period high feot 12 normalised to 8 mgo suggests high potential temperature in the source mantle presumably within a mantle plume the youngest eruption products geochemically and isotopically resemble himu oib plume activity may have gradually migrated eastward from late devonian to permian from the maritimes basin through scotland to norway and north germany

late paleozoic strike slip faults in maritime canada and their role in the reconfiguration of the northern appalachian orogen major late paleozoic faults many with documented strike slip motion have dissected the ordovician devonian appalachian orogen in the maritime provinces of atlantic canada activity alternated between east west faults minas trend and ne sw faults appalachian trend nw se faults canso trend were probably conjugate to minas trend faults major dextral movement on faults with appalachian trend in total between 200 and 300 km began in the late devonian this movement initiated the maritimes basin in a transtensional environment at a releasing bend formed around a promontory in the laurentian margin and thinned the crust accounting for the major subsidence of the basin appalachian trend strike slip continued in the mississippian but was accompanied by major movement on e w minas trend faults culminating around the mississippian pennsylvanian boundary juxtaposing the meguma and avalon terranes of the appalachians close to their present day configuration however strike slip continued during the pennsylvanian permian interval resulting in transpressional deformation that reactivated and inverted earlier extensional faults a final major episode of transtension mainly sinistral occurred during the mesozoic opening of the atlantic ocean restoration of movements on these faults amounting to several hundred kilometers of slip explains anomalies in the present day distribution of terranes amalgamated during early paleozoic appalachian tectonism in the restored geometry the nashoba and ellsworth terranes of ganderia are adjacent to one another and the meguma terrane lies clearly outboard of avalonia a restored post acadian paleogeography not the present day geometry of the orogen should be used as a basis for reconstructions of its earlier paleozoic history

u pb geochronology and sm nd isotopic composition of proterozoic gneisses channel islands uk gneissic units of the channel islands united kingdom have traditionally been considered to be palaeoproterozoic basement to the late neoproterozoic cadomia terrane based on lithological correlations and imprecise or ambiguous isotopic data a new precise u pb date of 2061 2 ma based on analyses of single zircons for the icart granitic orthogneiss of guernsey confirms a palaeoproterozoic age of its igneous protolith the nd depleted mantle model age t dm of this gneiss is 2220 ma only slightly older than its crystallization age indicating that it represents juvenile crust other gneisses from guernsey have similar t dm ages ranging from 2210 to 2370 ma suggesting that they are also exposures of juvenile palaeoproterozoic crust a component from a penetratively deformed orthogneiss from sark previously correlated with icartian gneisses on guernsey yields a u pb zircon date of 616 4 2 ma this crystallization age demonstrates that the protolith was a cadomian intrusion and that penetrative deformation and amphibolite facies metamorphism in the northern channel islands were cadomian in age the use of gneissic features as a means of invoking the antiquity of many other undated gneissic units in the region is thus considered unreliable the presence of 2170 7 ma zircon xenocrysts within the sark orthogneiss combined with its initial e nd 615 9 5 are strong evidence that pre cadomian basement was a significant source component and that documenting the extent and age of pre cadomian basement may be possible by indirect geochemical methods

chemical weathering studies in relation to geomorphological research in southeastern canada abstract although chemical weathering provides fundamental information relevant to geomorphology the subject has been overlooked during the 20th century in canada this paper provides an overview of the current state of canadian research on chemical weathering in southeastern canada and takes into account three spatial and temporal contexts 1 the formation of bedrock morphology by chemical weathering 2 occurrences characteristics and age of saprolites and 3 contemporary chemical denudation rates long term geomorphological evolution of southeastern canadian landscapes shows that chemical weathering has played an important role an example is taken from the laurentide region of the canadian shield north of montreal quebec the present topography resulted from the stripping of the former weathering mantle and from the probable subsequent modification of the weathering front first by the action of hillslope processes and rivers and then by glaciers before and during plio pleistocene times the present landscape reflects the timing of the formation of erosion surfaces and of the stripping of the paleozoic cover rocks and exposure of the shield since the late seventies several isolated occurrences of saprolite soil profiles have been discovered in eastern canada and prompted a renewal of the study of these materials about the cenozoic evolution of these regions one of the problems in this field of research is the dating of saprolites and their inclusion in a chronostratigraphic framework along with the other cenozoic surficial deposits and landforms because of the multiple factors involved in the development of secondary minerals in saprolites during the course of weathering it is preferable to distinguish the dating of saprolites from the study of their mineralogical and geochemical evolution fortunately several new techniques are becoming available for the absolute dating of surficial deposits and saprolites including the use of cosmogenic radionuclides saprolites provide a strong potential field of research for our understanding of the geological evolution of eastern canada during the cenozoic contemporary weathering and erosion rates are fields of research that have gained increasing interest recently since modeling landscape geochemical response can be applied to various environmental stress situations such as acidification by rain and forest harvesting rock type may be the main factor explaining the large differences between watersheds in fact variability of cation removal in the temperate zone is probably most closely related to flow paths of water investigations at different scales from entire watersheds to slopes to individual pedons highlight the problem in the catamaran brook watershed new brunswick water chemistry is explained by a mix of groundwater and soil solution from the horizons at the base of the floodplain soils geochemical mass balances based on net outputs give little information on the weathering reactions of primary minerals the weathering products or on the nature of the weathering processes that provide the dissolved load of streams mineralogic and petrographic analysis of selected soil pedons are necessary to determine weathering reactions and their role as sources or sinks for bases silica aluminum and iron in the various compartments through which water percolates before it reaches the stream

nd isotopic characteristics of terranes within the avalon zone southern new brunswick nd isotopic data are presented for rock units in four terranes within the traditional avalon zone of southern new brunswick initial end values for igneous rocks within the caledonia terrane range from 1 6 to 4 6 whereas values for sedimentary rocks range from 8 4 to 3 6 a granite within the kingston terrane has end 438 ma 4 0 nd isotopic compositions for the kingston and caledonia terranes are similar to those of the mira terrane in cape breton island the antigonish highlands of nova scotia and plutonic rocks of eastern newfoundland each of these regions may be a dismembered part of a single terrane the avalon terrane sensu stricto initial end values for rocks from the brookville terrane range from 1 3 to 2 8 the coverdale anorthosite within the brookville terrane has a present day end value of 12 1 and a depleted mantle model age of 1 3 ga similar to mesoproterozoic anorthosites in laurentia clastic sedimentary rocks in the green head group have end 750 ma values of 2 0 and 10 9

a prognostic turbulence scheme for the nonhydrostatic plume model atham the presented turbulence scheme was developed for the active tracer high resolution atmospheric model atham to parameterize the effect of subgrid scale turbulence in contrast to the commonly used assumption of local isotropy in high resolution atmospheric modeling this scheme differentiates between horizontal and vertical turbulent exchange to represent the strong influence of buoyancy forces and vertical transports its computational efficiency is similar to classical turbulent kinetic energy approaches while preserving one of the main feature of higher order schemes the present extensions to include anisotropic effects in a turbulent kinetic energy approach do not need any ad hoc assumptions and are equivalent to the classical formulation in the isotropic limit the presence of high tracer concentrations in a particle laden plume is taken into account as well as supersonic effects at low mach numbers the turbulent exchange coefficients used in the equations of motion are derived from a set of three coupled differential equations for the horizontal and vertical turbulent energy and the turbulent length scale no turbulent equilibrium is assumed all turbulent quantities are treated prognostically numerical simulations of convective plumes of a typical plinian volcanic eruption with the nonhydrostatic plume model atham reveal that a complex treatment of turbulent quantities is necessary in order to capture the bulk characteristics of the plume such as the plume height the horizontal extent and plume development in time anisotropic effects of turbulence have a significant impact on the stability and internal structure of the plume for the first time results from a fully three dimensional simulation of a volcanic plume are presented because of its general formulation the presented turbulence scheme is suitable for a wide range of atmospheric applications

an algorithm for u pb isotope dilution data reduction and uncertainty propagation this is the publisher s version also available electronically from http onlinelibrary wiley com