the application of geochemical methods in earthquake prediction in china several geochemical anomalies were observed before the haichen longling tangshan and songpan earthquakes and their strong aftershocks they included changes in groundwater radon levels chemical composition of the groundwater concentration of ca mg cl so4 and hco3 ions conductivity and dissolved gases such as h2 co2 etc in addition anomalous changes in water color and quality were observed before these large earthquakes before some events gases escaped from the surface and there were reports of ground odors being smelled by local residents the large amount of radon data can be grouped into long term and short term anomalies the long term anomalies have a radon emission build up time of from a few months to more than a year the short term anomalies have durations from a few hours or less to a few months

a new stratigraphic framework for the gaspe belt in southern quebec implications for the pre acadian appalachians of eastern canada the post taconian units in the quebec and northern new brunswick appalachians constitute the gaspe belt and geological studies have mostly focussed on its eastern quebec segment biostratigraphic data indicate that the succession in southern quebec is no older than late silurian and extends into the early devonian two distinct stratigraphic assemblages are present the first assemblage saint luc cranbourne and lac aylmer formations and glenbrooke group unconformably overlies the humber and dunnage zones the units show a basal alluvial conglomerate that passes progressively to deeper marine facies upsection which have recorded a post late silurian transgressive event the second assemblage saint francis group and frontenac formation is faulted against either dunnage units or autochthonous post taconian units it locally unconformably overlies units of the dunnage zone the succession shows progressively deeper marine conditions upsection and also has recorded a post late silurian transgressive ev

preseismic hydrogen gas anomalies caused by stress corrosion process preceding earthquakes simultaneous monitoring of he h2 ar n2 ch4 and rn in gas bubbles of groundwater from the 1 500 m deep nagashima well in the active yoro fault zone central japan reveals that three microearthquakes with m 1 6 2 6 in the fault zone are accompanied and preceded by increases of h2 as is a moderately large event with m 5 4 in the same fault zone all the focal distances of the earthquakes are within 25 km no comparable anomalies were seen in the gas species other than h2 we suggest that the selective and preseimic increases of h2 in groundwater gas bubbles are geochemical signals of the earthquake nucleation process of stress corrosion mechanism aseismic slips preceding earthquakes in the active fault zone are likely to have enhanced h2 production by mechanochemical reaction of fractured rock surface with water in pre existing fault planes as groundwater conduits

the red island road formation early devonian terrestrial fill in the anticosti foreland basin western newfoundland more than 100 m of nearly flat lying fluvially derived thick bedded and lensoid clast supported conglomerate and sandstone are found on red island off the coast of the port au port peninsula western newfoundland formally described herein and named red island road formation the strata represent a unique lithologic formation not exposed or known anywhere else in the region characteristic features include abundant rounded highly weathered and varnished cobbles and boulders derived from an unknown mixed volcanic and very low to low grade metamorphic terrane although the unit is largely unfossiliferous a thin sandstone bed near the top of the type section contains primitive dichotomously branched plant remains and biostratigraphically significant palynomorphs among more than 25 species of spores it is the diversity of emphanisporites dictyotriletes and dibolisporites and in particular dibolisporites echinaceus dictyotriletes canadensis emphanisporites annulatus e erraticus and e schultzi

anomalous changes of ch4 ar ratio in subsurface gas bubbles as seismogeochemical precursors at matsuyama japan the results of seismogeochemical monitoring of subsurface gases associated with ground waters from deep artesian wells in matsuyama japan are presented the weekly collections of bubble gas samples from the two borehole wells and gas chromatographic determinations of their he ar h2 ar n2 ar and ch4 ar ratios for the recent nineteen months have revealed that the bubble gas ch4 ar ratios at the two stations are correlated with the seismic activity in this area positive anomalies of the ch4 ar ratio were accompanied by five earthquakes with relatively large magnitudes and or relatively small epicentral distances among thirty earthquakes that occurred during the monitoring period the anomalous increases in the ch4 ar ratio had evidently begun prior to the respective earthquakes

palaeozoic amalgamation of central europe new results from recent geological and geophysical investigations abstract multidisciplinary studies of geotransects across the north european plain and southern north sea and geological reexamination of the variscides of the north bohemian massif permit a new 3 d reassessment of the relationships between the principal crustal blocks abutting baltica along the trans european suture zone tesz accretion was in three stages cambrian accretion of the bruno silesian lysogory and malopolska terranes end ordovician early silurian accretion of avalonia and early carboniferous accretion of the armorican terrane assemblage ata palaeozoic plume influenced metabasite geochemistry in the bohemian massif explains the progressive rifting away of peri gondwanan crustal blocks before their accretion to baltica geophysical data faunal and provenance information from boreholes and dated small inliers and cores confirm that avalonian crust extends beyond the anglo brabant deformation belt eastwards to northwest poland the location and dip of reflectors along the tesz and beneath the north european plain suggest that avalonian crust overrode the baltica passive margin marked by a high velocity lower crustal layer on shallowly southwest dipping thrust planes forming the heligoland pomerania deformation belt the variscan orocline of southwest poland masks two junctions between the armorican terrane assemblage ata and previously accreted crustal blocks to the east is a dextrally transpressive contact with the bruno silesian and malopolska blocks accreted in the cambrian while to the north is a thrust contact with easternmost avalonia deeply buried beneath younger sedimentary cover in the northeast bohemian and rhenohercynian massifs devonian early variscide deformation dominated by wnw and nw directed thrusting records closure of ordovician devonian seaways between detached islands of the ata and avalonia

the detection and interpretation of hydrogen in fault gases hydrogen gas can be released by chemical and mechanical changes in crustal rocks once released it is highly mobile buoyant and almost insoluble in groundwater a fault system may act as a conduit allowing hydrogen to accumulate in soil gases near a surface expression since hydrogen is scarce in ambient air its presence at elevated levels in soil gases may be a tool for fault mapping in order to evaluate this tool we surveyed eleven different faults by measuring the concentration of hydrogen and methane in 2 to 21 soil gas samples that were collected near each of them the sense of motion at four of those faults is normal western united states greece at five it is strike slip or dip slip california colorado japan and at two it is thrusting california at four of these faults hebgen lake yellowstone yamasaki burro mountain maximum concentrations of hydrogen ranged from 80 ppm to 70 and methane from 300 ppm to 5 all other sites showed ambient levels of both gases except for one sample taken at mt borah idaho that was 2 methane from this preliminary study it is not clear whether the presence of hydrogen is correlated uniquely to the location of faults or whether it occurs randomly the conditions required to produced and accumulate hydrogen are also not clear excess hydrogen may well be produced by different mechanisms in different geological regimes for example if ferrous hydroxide is present in local rocks it may react to produce hydrogen detailed and extensive studies are needed to clarify the connection between hydrogen and tectonic faulting

integration and spatial analysis of high resolution geophysical and geological data eastern gaspe peninsula in the vicinity of the town of gaspe the relationships between the silurian devonian sedimentary succes sion of the gaspe belt and the humber and the dunnage zones are complex to unravel these relationships we used high resolution aeromagnetic data and regional gravimetric data coupled with field tectonostratigraphic information the magnetic vertical derivative located several magnetic anomalies associated with near surface features in the silurian devonian cover sequence in particular a conglomerate with magnetic fragments that overlies the late silurian salinic unconformity is clearly recognizable large ovoid anomalies of significant intensity located in the silurian devonian sedimentary cover area cannot be associated with any known geological feature the interpretation of the high pass and low pass filtered aeromagnetic survey indicates that the ovoid anomalies originate below the silurian devonian cover sequence the most significant of the ovoid anomalies is associated with a gravimetric anomaly it is proposed that these geophysical anomalies are probably associated with ultramafic and or volcanic rocks correlative in the subsurface with outcrops of the cambrian ordovician lithologies of the lady step complex and or the shickshock group resume dans la region de gaspe les relations entre la couverture sedimentaire siluro devonienne de la ceinture de gaspe et les zones de humber et de dunnage sont complexes pour mieux comprendre ces relations nous avons utilise des donnees aeromagnetiques de haute resolution et des donnees gravimetriques regionales appariees aux donnees tecto nostratigraphiques de terrain le gradient magnetique vertical a mis en evidence plusieurs signatures magnetiques peu profondes dans la couverture sedimentaire siluro devonienne en particulier un conglomerat a fragments magnetiques surmontant la discordance salinique du silurien tardif est aisement identifiable de grandes anomalies ovoides d intensite importante localisees dans la couverture siluro devonienne n ont pu etre associees a aucun element geologique connu le passage du leve magnetique dans des filtres passe haut et passe bas a permis de mieux cerner cer taines signatures magnetiques et de determiner que les anomalies ovoides prennent source sous la couverture siluro devonienne la plus grande des anomalies ovoides est associee a une anomalie gravimetrique il est propose que ces anomalies geophysiques soient vraisemblablement associees a des roches ultramafiques et ou volcaniques correlatives en profondeur a des lithologies affleurantes des unites cambro ordoviciennes du complexe de lady step et ou du groupe de shickshock

deciphering the neoproterozoic history of the hollow fault avalon terrane mainland nova scotia abstract recognition and deciphering of the early history of fault zones is difficult because younger fabrics commonly overprint and obscure older ones the hollow greendale fault system in the avalon terrane of the northern antigonish highlands in mainland nova scotia has suffered many episodes of motion in the paleozoic during development of the appalachian orogen field relationship and petrographic observations indicate that its neoproterozoic history is preserved as ca 610 ma ne and nw trending ductile shear zones within the georgeville group contact aureole of the intrusive syn to late tectonic greendale complex kinematic indicators within the ne trending shear zone along the southwestern contact indicate dextral shear and are compatible with dextral shear indicators within the greendale complex and with the orientation of coeval regional f1 fold structures within the antigonish highlands the nw trending shear zone along the northeastern contact represents either a step over fault within a dextral shear zone or a zone of localized transpression associated with the emplacement of the greendale complex local preservation of neoproterozoic shear zone fabrics within the georgeville group host rocks is attributed to the shielding effects of the proximal greendale complex which acted as a rigid unit during paleozoic deformation so that subsequent motion along the hollow fault was partitioned along the northeastern and southwestern contact of the complex the neoproterozoic history combined with paleocontinental reconstructions indicates that the hollow greendale fault system was part of an important regional strike slip fault zone within a volcanic arc regime along the periphery of gondwana murphy et al 1999a murphy et al 1999b

tectonometamorphic evolution of the southern quebec appalachians 40ar 39ar evidence for middle ordovician crustal thickening and silurian early devonian exhumation of the internal humber zone published age data from the humber zone of the southern quebec appalachians indicate that deformation and metamorphism occurred during middle to late ordovician time this paper presents the results of a regional scale geochronological study of 70 amphibole and mica single grains by the 40 ar 39 ar laser step heating method which brings forward a more complete middle ordovician early devonian tectonometamorphic evolution of the quebec appalachian humber zone biotites have plateau ages varying between 420 and 411 ma amphiboles are often compositionally rimmed and or contain biotite inclusions their age spectra are generally disturbed but may suggest the occurrence of two distinct events silurian 429 424 ma and middle ordovician 462 460 ma two main groups of muscovite ages have been obtained middle ordovician 469 461 ma and silurian early devonian 431 411 ma but middle to late devonian 387 376 ma ages are also locally present middle ordovician ages are interpreted to record crustal thickening by nappe emplacement during regional taconian metamorphism silurian early devonian ages are attributed to consequences of backthrusting and normal faulting a statistical analysis of silurian early devonian muscovite age spectra reveals an irregular decrease in weighted apparent age maxima across the internal humber zone this age decreasing trend is interpreted to result from the temporal ca 431 411 ma and possibly spatial northwest to southeast progression of deformation recrystallization and fluid circulation during tectonic exhumation of the internal humber zone in southern quebec tectonic models for the northern appalachian internal humber zone should take into account the strong body of evidence for silurian early devonian hinterland directed and extensional deformation as documented in southern quebec

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

silurian tectonics of western avalonia strain corrected subsidence history of the arisaig group nova scotia the arisaig group is a silurian succession of predominantly shallow marine clastic sediments overlying volcanics exposed in northern mainland nova scotia sediment accumulation provides a record of the subsidence of western avalonia during the interval when terranes were being accreted within the canadian appalachians to calculate the amount of subsidence one must correct the measured thicknesses for the effects of tectonic strain deformed fossils on bedding surfaces indicate strain ratios mainly between 1 2 and 1 6 an empirical porosity depth relationship is used to correct for compaction the subsidence curves are then adjusted to allow for variations in water depth and eustatic sea level the resulting curves show significant variations in subsidence rate regardless of which version of the silurian time scale is used an initial episode of rapid subsidence followed eruption of llandoverian volcanics slower subsidence took place in wenlockian and ludlovian time with deeper water sedimentation dur

tectonic evolution and significance of silurian early devonian hinterland directed deformation in the internal humber zone of the southern quebec appalachians in the southern quebec appalachians the early tectonic history of the laurentian margin humber zone comprises foreland propagating northwest directed thrust faulting nappe emplacement and regional prograde metamorphism in response to the obduction of large ophiolitic nappes during the taconian orogeny in the internal humber zone this event is dated at 462 3 ma late middle ordovician which is interpreted to represent the timing of near peak taconian metamorphism superimposed hinterland directed structures are accompanied by retrograde metamorphism and consist of back thrusts and normal faults which respectively delimit the northwestern and southeastern limbs of the sutton and notre dame mountains anticlinoria both salient structures of the internal humber zone of southern quebec geochronologic data on the timing of hinterland directed deformation vary from 431 to 411 ma two tectonic models are presented and discussed which may account for the silurian early devonian evolution of the la

silurian extension in the upper connecticut valley united states and the origin of middle paleozoic basins in the quebec embayment pre silurian strata of the bronson hill arch bha in the upper connecticut valley nh vt are host to the latest ludlow comerford intrusive suite consisting east to west of a mafic dike swarm with sheeted dikes and an intrusive complex the rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite the suite is truncated on the west by the monroe fault a late acadian thrust that carries rocks of the bha westward over silurian devonian strata of the connecticut valley gaspetrough cvgt dikes intrude folded strata with a pre intrusion metamorphic fabric taconian but they experienced acadian deforma tion twenty fractions of zircon and baddeleyite from three sample sites of gabbro diorite spanning nearly 40 km yield a weighted 207 pb 206 pb age of 419 1m a greenschist facies dikes sampled over a strike distance of 35 km were tholeiitic basalts formed by partial melting of asthenospheric mantle with little or no influence from mantle or crustal lithosphere the dike chemistry is similar to mid ocean ridge within plate and back arc basin basalts parent magmas originated in the astheno sphere and were erupted through severely thinned lithosphere adjacent to the cvgt extensive middle paleozoic basins in the internides of the appalachian orogen are restricted to the quebec embayment of the laurentian rifted margin and include the cvgt and the central maine trough cmt separated from the bha by a silurian tectonic hinge the ne trending comerford intrusions parallel the cvgt cmt and the tectonic hinge and indicate nw se extension during post taconian convergence the irregular margins of composite laurentia and avalon permitted continued colli sion in newfoundland st lawrence promontory and coeval extension in the quebec embayment extension may be related to hinge retreat of the northwest directed brunswick subduction complex and rise of the asthenosphere following slab break off an alternative hypothesis is that the basins originated as pull apart basins between northwest trending left stepping sinistral strike slip faults along the southern flanks of the new york and st lawrence promontories

sm nd isotopic systematics as tectonic tracers an example from west avalonia in the canadian appalachians abstract the tectonothermal evolution of west avalonia in mainland nova scotia appalachian orogen provides an excellent example of the application of sm nd isotopic analyses to tectonic studies regional syntheses indicate that west avalonia originated in the neoproterozoic as one of a number of terranes collectively known as peri gondwanan terranes along the gondwanan margin these terranes are characterized by late neoproterozoic voluminous arc related magmatism west avalonia became detached from gondwana in the early ordovician was accreted to laurentia by the silurian and was deformed by post accretionary strike slip tectonics in the late devonian and carboniferous associated with the amalgamation of pangea all stages of this evolution can be recognized in the sm nd isotopic signature in various neoproterozoic and paleozoic volcanic and sedimentary successions in mainland nova scotia crustally derived felsic volcanic rocks of late neoproterozoic ca 615 ma early cambrian and early silurian ages define an envelope that provides gross constraints on the sm nd isotopic composition of the underlying basement source e nd values range from 0 78 to 2 92 in the neoproterozoic rocks from 2 0 to 5 0 in the cambrian rocks and from 0 1 to 2 5 in the silurian rocks t dm model ages for each of these suites are remarkably similar they typically range from 0 9 to 1 2 ga suggesting that the sm nd isotopic composition of these suites was profoundly influenced by repeated melting of the same basement source this sm nd envelope provides a reference by which other suites may be compared and interpreted for example turbidites in a late neoproterozoic volcanic arc basin have sm nd compositions that lie within this envelope suggesting that they are derived from the coeval volcanic rocks that flank the basin the genetic significance of the model ages can be investigated by the analysis of felsic and metasedimentary rocks that pre date the main arc phase two felsic complexes have compositions that lie within the envelope and have similar model ages the presence of this signature in early avalonian rocks suggests that the model ages represent a genuine tectonothermal event at ca 1 0 to 1 2 ga that formed juvenile proto avalonian crust by implication the main arc phase in avalonia recycled this crust sm nd isotopic analyses of the metasedimentary sequences are incompatible with previous interpretations of deposition in a passive margin setting that pre dated avalonian arc activity instead the data indicate derivation from two distinct sources ancient gondwanan basement and juvenile avalonian arc suggesting deposition in a western pacific type back arc environment this re interpretation has important implications for neoproterozoic reconstructions the sm nd isotopic composition of west avalonian basement contrasts with that of other peri gondwanan terranes for example similarly aged felsic rocks in the cadomian terrane of nw france are characterized by more negative e nd values and older t dm model ages 1 0 1 9 ga these data together with detrital u pb data suggest that west avalonia was developed along the amazonian margin whereas cadomia was developed along the west african margin of gondwana sm nd isotopic analyses of early silurian clastic rocks in mainland nova scotia show fundamental differences with unconformably underlying neoproterozoic and early paleozoic avalonian successions these data have e nd values ranging from 5 7 to 6 1 with t dm model ages of about 1 4 to 1 7 ga indicating that the clastic rocks cannot have been derived from underlying successions a variety of geologic data and regional constraints suggests that they may have been derived from the caledonide orogen of western europe thereby providing a minimum age for the accretion of west avalonia to laurentia baltica sm nd isotopic analyses from late devonian early carboniferous continental clastic rocks deposited along the southern flank of avalonia in mainland nova scotia also show little influence from avalonian rocks and are compatible with derivation from the meguma terrane immediately to the south these data are consistent with regional synthesis which indicate uplift of the meguma terrane relative to west avalonia during dextral transpression

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

40ar 39ar dating of silurian and late devonian cleavages in lower greenschist facies rocks in the westminster terrane maryland usa 40 ar 39 ar dating of muscovite biotite and k feldspar combined with microstructural analysis of lower greenschist facies polymetamorphic phyllitic rocks and marbles were successfully used to decipher the thermal and tectonic histories of the westminster and adjacent terranes in western maryland the presence of unreset detrital muscovite in some samples demonstrates that temperatures in these rocks never exceeded the closure temperature for argon diffusion in muscovite 350 50 c minor biotite in some arkoses constrains the minimum metamorphic temperatures to 320 c these data show an early silurian ca 430 ma cleavage in the western part of the westminster terrane and a late devonian event ca 370 ma in the eastern westminster and adjacent potomac terranes these two cleavage domains are separated by the ne trending newly identified parrs ridge fault zone we propose that the sinistral transpressive collision of the carolina terrane with laurentia emplaced the western portion of the westminster terrane in the pennsylvania embayment along the martic fault where it was folded and cleaved at ca 430 ma but otherwise largely sheltered from later deformation the later late devonian dextral transpressive accretion of the outboard potomac terrane thrust rocks of the eastern westminster and potomac terranes to the west causing late devonian 360 370 ma s 2 cleavage in these rocks but only minimal discrete overprinting s 3 cleavages in rocks farther west final juxtaposition and thermal convergence of these terranes occurred along reactivated dextral strike slip faults in the alleghanian at ca 300 ma

post taconian shortening inversion and strike slip in the stephenville area western newfoundland appalachians deformed terrigenous and carbonate sedimentary rocks representing the early paleozoic laurentian continental margin form a series of elongate fault bounded blocks that plunge north beneath the humber arm allochthon in the stephenville area west newfoundland appalachians the continental shelf succession was folded and thrust faulted after emplacement of the humber arm allochthon in the west of the area table mountain is cut by a pop up structure bounded by downward converging reverse faults structures at the east margin of table mountain indicate both dextral and reverse slip the phillips brook structure farther east contains multiple fault bounded carbonate slices one slice carried by the west blanche brook fault is thrust over the humber arm allochthon the western edge of the indian head massif consisting of grenville basement is also a thrust contact these reverse faults and thrusts which cut the carbonate succession and postdate emplacement of the humber arm allochthon are in turn

basin evolution in western newfoundland new insights from hydrocarbon exploration the humber zone is the most external zone of the appalachian orogen in western newfoundland it records multiphase deformation of the cambrian ordovician passive margin and of the ordovician to devonian foreland basins by the taconian salinian and acadian orogenic events the recent phase of exploration drilling has provided new evidence for structural stratigraphic reservoir and source rock maturation models of western newfoundland the first well port au port 1 supported the hypothesis that the round head thrust had an earlier extensional history prior to the acadian compressional inversion that created the present day structural high of the port au port peninsula the well tested a small anticline formed in a footwall shortcut fault of the round head thrust the second well long point m 16 was drilled at the northern tip of long point to test a triangle zone identified by previous workers this well demonstrates that the frontal monocline at the western edge of the triangle zone is elevated by a stack of imbricate thrusts composed of rocks of the taconian allochthon and compressional basement involved faults that have uplifted the cambrian ordovician carbonate platform the structural model developed in the port au port area with the aid of these wells has been extended throughout the humber zone in western newfoundland changes in structural style illustrated by regional cross sections suggest that prospective trap geometries are only developed in the southern and central parts of the region the reservoir model proposed invokes exposure and karsting of the footwalls of extensional faults formed as the carbonate platform collapsed during a middle ordovician hiatus the st george unconformity structural relief became more pronounced as extensional collapse continued through the middle ordovician begin page 394 these structurally high fault footwalls became the foci for dolomitizing and mineralizing fluids that used major faults as fluid conduits during the devonian fluids deposited sulphide ores and created zebra and sparry dolomite and some sucrosic hydrothermal dolomites in the st george group and the table point formation the reservoir model maturity and source rock data and the structural models have been combined with seismic and onshore surface geology this enables the prospectivity of the western newfoundland cambrian ordovician play trend to be evaluated for further exploration

structural history of the metamorphic sole of the bay of islands complex western newfoundland displacement of the early ordovician ophiolitic bay of islands complex was accompanied by the development of a metamorphic sole in underlying accreted gabbro mafic pillow lava pelite and psammite the metamorphic sole contains up to 130 m of amphibolite underlain by up to 80 m of mafic and pelitic psammitic schist which in turn overlies chlorite bearing rocks that overlie mudstone matrix melange a major foliation locally mylonitic and or isoclinally folded is pervasively developed in the greenschists and amphibolites an extension lineation is widely developed and plunges north in amphibolite and trends east west in greenschist consistent with a changing direction of thrust transport from northerly to westerly as the mantle wedge cooled over time shear sense criteria in greenschist facies pelitic psammitic schist indicate thrusting towards the west in the southwestern blow me down massif two sets of folds postdate development of accretion related s l fabrics and resulted in a substantial w

earthquake prediction by means of change of chemical composition in mineral spring water since march 1977 we have measured cl concentration in the groundwater almost every day at shiota mineral spring near the yamasaki fault which is situated in the northern kinki and chugoku districts southwest japan to see if the cl concentration shows any variations which may be related to seismic activity near shiota mineral spring from march 1977 through december 1984 there occurred 6 earthquakes of m3 5 or greater near shiota mineral spring and two of m6 0 or greater in the northern kinki and chugoku districts the cl concentration anomalously changed four times before these earthquakes though the pattern of preseismic changes of the cl concentration was not uniform we conclude that measurement of cl concentration at a carefully chosen mineral spring near an active fault should give information useful for earthquake prediction

geological correlations between cape breton island and newfoundland northern appalachian orogen geological correlations between cape breton island and newfoundland are apparent both in surface geology and at deeper crustal levels based on similarities in sm nd isotopic signatures the mira terrane of southeastern cape breton island is part of the avalon terrane sensu stricto and is composed of neoproterozoic volcanic sedimentary plutonic belts and overlying cambrian rocks directly comparable to those in the western part of the newfoundland avalon terrane the bras d or terrane is also mainly of neoproterozoic age but shows lithological and isotopic contrasts with the mira terrane small areas of similar neoproterozoic rocks occur in southern newfoundland and to the north as inliers in the exploits terrane the bras d or terrane and similar rocks in newfoundland are interpreted to represent a peri gondwanan terrane where rocks of the gander terrane were later formed hence this area is part of the central mobile belt and distinct from avalon terrane sensu stricto the aspy terrane is a complex area

timing of peak metamorphism and deformation along the appalachian margin of laurentia in newfoundland silurian not ordovician u pb and ar ar isotopic age data from the corner brook lake region of the eastern appalachian humber zone in western newfoundland indicate that regional deformation and peak amphibolite facies metamorphism are early silurian a lower limit on deformation is provided by a u pb zircon age of 434 2 3 ma for a pegmatite that is affected by the regional foliation and is interpreted to be syntectonic monazite and rutile from a garnet kyanite staurolite schist which records peak metamorphic conditions and in which porphyroblasts have overgrown the regional foliation gave u pb ages of 430 2 ma and 437 6 ma respectively ar ar cooling ages for hornblende from amphibolites and muscovite from psammitic and pelitic schists range from 430 to 420 ma a silurian age for deformation and metamorphism of the laurentian margin is coincident with the timing of similar events along the newfound land gondwana margin and suggests that the silurian was a period of major continent continent collision

u pb dating of major and accessory minerals formed during metamorphism and deformation of metapelites abstract u pb isotope analyses on major and accessory minerals from pelitic schists in of southwestern connecticut are used to date metamorphism and deformation most of the major minerals have 206 pb 204 pb ratios less than 100 however u pb mineral isochron and mineral whole rock isochrons constructed using aliquots of the same mineral yield concordant ages with uncertainties as low as 5 ma staurolite kyanite and garnet are older than metamorphic monazites and zircons these data are summarized below 5 mineral 206 pb 204 pb system the straits schist trap falls fm monazite zircon 207 pb 206 pb 379 384 ma 380 2 ma staurolite 48 623 238 u 206 pb 394 400 ma 398 5 ma garnet 22 46 238 u 206 pb 383 ma 414 10 ma 235 u 207 pb 418 ma 207 pb 206 pb 623 ma kyanite 21 27 238 u 206 pb 399 ma chlorite anatase ilmenite 20 27 238 u 206 pb 350 370 ma apatite quartz kspar 18 19 transposed pegmatitic intrusions in the straits schist yield monazites with u pb ages analytically indistinguishable from those of metamorphic monazites and zircons in the schists growth of monazite and zircon in the schists may be related to high t fluid influx associated with pegmatite intrusion age discordance in the garnets from the straits schist is most consistent with continuous loss of intermediate daughter products of the 238 u decay chain from about 420 ma to 380 ma garnets from the adjacent trap falls formation do not display this behavior

the middle ordovician to early silurian voyage of the dashwoods microcontinent west newfoundland based on new u pb and 40ar 39ar geochronological and kinematic constraints the dashwoods microcontinent is an important tectonic segment in the peri laurentian setting of the newfoundland appalachians in order to better understand the tectonic history of dashwoods during the ordovician taconic orogeny we have undertaken field mapping microscopic studies and u pb and 40 ar 39 ar geochronological studies along the northern little grand lake fault lglf and western baie verte brompton line cabot fault zone bcz boundaries oblique dextral ductile deformation in the bcz occurred from late middle ordovician into the early silurian based on the presence of a late syn tectonic pegmatite dike 455 12 ma and a foliated granodiorite sheet 445 8 0 6 ma deformation is coeval with oblique sinistral accretion along the eastern margin of dashwoods which means that dashwoods and its notre dame arc had a southward translation with respect to the laurentian margin and the then present iapetus ocean during the late ordovician dextral movement along the bcz continued after the collision of dashwoods with the laurentian margin deformation along the little grand lake fault is bracketed between 463 5 ma and 440 ma these ages combined with other geological arguments indicate that motion probably took place during the late ordovician to earliest silurian contemporaneous with the southward translation of dashwoods a possible explanation is that the snooks arm arc moved independently from and faster southwards than the notre dame arc with its dashwoods infrastructure thereby underthrusting the dashwoods along the little grand lake fault our new u pb geochronological data including a muscovite granite 463 5 ma a schistose muscovite granite 459 17 21 ma and a tectonized tonalite 458 20 ma add to the geochronological database of the voluminous second phase of the notre dame arc additionally in all but one of our u pb samples inherited grains of mesoproterozoic circa 1 0 ga age have been obtained their regional presence fortifies the possible relationship of the dashwoods microcontinent with the long range inlier in western newfoundland furthermore it introduces a potential link with the blair river inlier in cape breton island

reconstructing the oxygen isotope composition of late cambrian and cretaceous hydrothermal vent fluid oxygen isotope analyses 18o of 16 quartz epidote pairs from late cambrian betts cove and mings bight newfoundland ordovician thetford mines quebec canada and cretaceous troodos cyprus ophiolites are used to calculate the 18o of the hydrothermal fluids from which they crystallized we combine these with 3 quartz fluid inclusion measurements and 3 quartz magnetite measurements from the cambrian ophiolites to explore how the range in the 18o of submarine hydrothermal vent fluid has varied between the late cambrian cretaceous and today the range of calculated 18o values of vent fluid 4 to 7 4 is larger than that of modern seafloor hydrothermal vent fluid 0 to 4 we employ two numerical models to ascertain whether this range is most consistent with changes in paleo seawater 18o or with changes in the reactive flow path in ancient hydrothermal systems a static calculation of the vent fluid oxygen isotope composition as a function of the water rock ratio suggests that in an ocean with a lower 18o than today the range of vent fluid 18o should be larger our data however show little evidence that the 18o of the ocean was much lower than the global ice free value of 1 2 a dual porosity model for reactive flow through fractured and porous media is used to model the relative evolution of the 87sr 86sr and 18o of vent fluid in contact with rock our 87sr 86sr and 18o for cretaceous epidotes suggest the strontium concentration of the cretaceous oceans may have been much higher than at present the 87sr 86sr and 18o data from cambrian epidotes are strikingly different from the younger samples and are difficult to model unless fluid rock interaction in the cambrian hydrothermal systems was substantially different it is also possible that some of the quartz epidote veins have been reset by obduction related metamorphism our data suggest that the high calcium to sulfate ratio in early and cretaceous seawater may have affected the degree of strontium isotope exchange causing hydrothermal fluids to have 87sr 86sr closer to that of seawater than in modern systems

experimental studies of the mechanisms of seismo geochemical precursors the following aspects of modeling experiments on seismo geochemical precursors are described 1 gas emission during laboratory stress loading and rupture of rocks 2 field measurements with explosion sources 3 aquifer mixing tests in the field 4 experimental studies of physico chemical processes caused by stress events from these studies three conclusions have been drawn 1 long term seismo geochemical anomalies appear to be related to the stage of elastic deformation of rocks under stress loading prior to a seismic event short term anomalies appear to be related to the plastic deformation of rock and spike like anomalies appear to be related to shear displacement before an earthquake 2 anomalous changes in chemical composition of groundwater and the escape of gases from the ground appear to result from rock fracturing which opens up pathways for the upward migration of water from deep confined aquifers and for the upward migration of gases from the deeper crust 3 chemical reactions induced by increasing stress in the epicentral region may result in the anomalous changes in chemical composition of groundwater observed before some large earthquakes

preliminary results of seismogeochemical research in china several kinds of geochemical anomaly before strong earthquakes have been observed in china since 1966 they include changes in groundwater radon levels ion content of water ca 2 mg 2 cl so4 2 f dissolved gases h2 co2 and gases escaping from the aeration zone through abandoned dry wells ar n2 co2 the radon anomalies may be grouped as long term and short term anomalies most of the geochemical anomalies observed are characterized by a pattern of increase the largest amplitude recorded was 37 times the base level preliminary study indicates that the types of seismogeochemical anomaly observed prior to strong earthquakes depend on tectonic geologic lithologic and hydrogeological conditions at the monitoring station results obtained from modelling experiments on the mechanisms of some anomalies are given

early ordovician orogenic event in galicia nw spain evidence from u pb ages in the uppermost unit of the ordenes complex new u pb data zircon monazite and rutile obtained from rocks of the uppermost allochthon in the variscan belt of nw spain indicate that the hangingwall to the suture includes an allochthonous unit with a pre variscan tectonothermal evolution this evolution is characterised by an early ordovician 498 500 ma bimodal magmatism followed almost immediately 493 498 ma by a barrovian style metamorphism up to the granulite facies the metamorphism subsequent to the igneous intrusions requires convergence and crustal thickening in order to generate the barrovian facies pattern shown by the lithologies of the uppermost allochthon the almost coeval magmatism and metamorphism and the chemistry of the metabasites suggest an accretionary complex probably related to a volcanic arc as the most probable setting for the origin of the uppermost unit the implications of the existence of early ordovician convergent plate boundaries are discussed in the context of gondwana laurentia avalon interactions

paleozoic age of the walden creek group ocoee supergroup in the western blue ridge southern appalachians implications for evolution of the appalachian margin of laurentia in the foothills of the great smoky mountains in tennessee low grade metamorphic rocks of the walden creek group ocoee supergroup contain a fossil assemblage composed of trilobites bryozoans ostracodes pelmatozoans algae and agglutinated foraminifers indicating a silurian or younger age the new paleontological data contradict older ideas on the neoproterozoic age of the walden creek group the walden creek group was not deposited in a continental rift basin preceding the opening of the iapetus ocean but possibly in a pull apart basin formed in a transtensional event during the acadian orogeny there is no field evidence indicating that the walden creek group is separated from the lower units of the ocoee supergroup by a basin wide unconformity and hiatus a tentative geodynamic model is presented for the ocoee supergroup basin the model is dependent on paleontological data indicating a paleozoic age for the walden creek group and concentrates on lithologic petrographic and basin characteristics the model allows for the possibility that the entire ocoee supergroup was deposited in a paleozoic transtensional basin

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

late devonian palinspastic reconstruction of the avalon meguma terrane boundary implications for terrane accretion and basin development in the appalachian orogen abstract a late devonian early carboniferous palinspastic reconstruction of atlantic canada restoring subsequent motion along the avalon meguma terrane boundary and other major faults facilitates re examination of the spatial distribution of important accretionary and post accretionary events in the northern appalachian orogen the reconstruction suggests a genetic relationship between 415 and 360 ma tectonothermal activity in both these terranes and the collision between laurentia and gondwana in a zone of anomalously intense shortening opposite the st lawrence promontory in the appalachian orogen erosional products of this collision are an order of magnitude greater than the thin ca 1 km veneer of latest devonian early carboniferous clastic rocks that were deposited in intermontane basins across the orogen this missing detritus may be found in the thick deposits of the catskill clastic wedge in the central appalachians

regional metamorphism of the appalachian humber zone of gaspe peninsula 40ar 39ar evidence for crustal thickening during the taconian orogeny geochronological studies on the timing of deformation and metamorphism along the laurentian margin have shown that the ages of metamorphic events change along strike within the newfoundland southern quebec segment of the canadian appalachians the gaspe peninsula is located at mid point of the two extremities of this segment new single grain laser 40ar 39ar plateau ages solely reflect latest middle late ordovician metamorphism samples taken within the internal humber zone in the shickshock group rocks yield 40ar 39ar muscovite and hornblende ages ranging from 457 to 454 ma samples from the amphibolite du diable the metamorphic sole of the mont albert ophiolite yield 40ar 39ar muscovite and hornblende ages ranging from 459 to 457 ma ordovician ages of the internal humber zone are consistent with 40ar 39ar ages from southern quebec and are interpreted as the result of the emplacement onto the margin of both the ophiolite and its metamorphic sole

evidence for forearc seafloor spreading from the betts cove ophiolite newfoundland oceanic crust of boninitic affinity abstract the ordovician betts cove ophiolite of newfoundland has a well developed cumulate sequence in which is rooted a sheeted dyke complex that grades up into pillow lavas dominant chromite olivine orthopyroxene cumulate peridotites and orthopyroxenites have phase assemblages and mineral chemistries consistent with crystallization from boninitic magmas dykes and lavas have phenocrysts of olivine high cr al chromite orthopyroxene low tio2 clinopyroxene they have high sio2 and mgo contents and depleted u shaped trace element profiles indistinguishable from those of bonin islands boninites field data imply that cumulates dykes and lavas all are comagmatic while geochemical and mineralogical data indicate that all are of boninitic affinity since boninites are only found in forearcs this implies that the betts cove ophiolitic crust formed in a forearc since the entire oceanic crustal section at betts cove is of boninitic affinity then this implies that true seafloor spreading can initiate in forearc

distinct taconic salinic and acadian deformation along the iapetus suture zone newfoundland appalachians structural mapping in central newfoundland has identified seven distinct phases of deformation d 1 to d 7 the most significant of which are d 1 d 2 and d 4 d 1 involved the formation of a middle and late ordovician southsoutheast directed thrust belt and concomitant development of mylonite and phyllonite a late ordovician to early silurian d 2 thrust and fold belt overprints d 1 mylonitic deformation and is the most distinctive deformation event in the study area late silurian to devonian d 4 is responsible for folds and north northwest directed dextral thrust and reverse faults that overprint d 1 to d 3 structures d 4 structures in central newfoundland include the exploits gander boundary subsequent deformation is generally of local significance only the arc back arc complexes making up the various terranes in central newfoundland are predominantly juxtaposed along d 1 shear zones which include the red indian line our data indicate that terrane boundaries initiated during d 1 may have protracted deformation histories spanning several deformation events this has important implications for the interpretation of terrane boundaries in newfoundland as d 1 terrane boundaries may be interpreted as d 2 or d 4 shear zones depending on the intensity of overprinting or reactivation the deformation history proposed in this paper corresponds closely to that of established appalachian orogenic cycles d 1 is correlated with the ordovician taconic orogeny and involved accretion of arc back arc complexes to the laurentian margin d 2 and d 4 are correlated with the ordovician silurian salinic and silurian devonian acadian orogenies which involved the subsequent accretion of the ganderia and avalonia microcontinents to the laurentian margin respectively

development of a folded thrust stack humber arm allochthon bay of islands newfoundland appalachians in the humber arm area of the western newfoundland appalachians four distinct stratigraphic successions derived from the laurentian continental margin are exposed each succession is believed to be characteristic of a separate thrust sheet the platform sheet represents the ancient laurentian shelf and its foreland basin cover the watsons brook sheet is characterized by a succession including shelf margin carbonates overlying foreland basin clastics the corner brook sheet comprises continental slope and rise clastic and carbonate sedimentary rocks of the humber arm supergroup and the woods island sheet includes clastics of the blow me down brook formation that overlie mafic volcanics sheets are subdivided by thrusts into tectonic slices disrupted units and melange with scaly s1 foliation are found along the boundaries of some slices thrust sheets and related structures have been deformed by f2 folds with axial planar s2 cleavage s1 scaly foliations are transposed into parallelism with s2 there

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

a systematic compilation of earthquake precursors article a survey of published scientific literature was undertaken to identify and catalog observed earthquake pre cursors the earthquake precursors selected for analysis included electric and magnetic fields gas emissions groundwater level changes temperature changes surface deformations and seismicity for each of these precursors the published scientific literature was searched to document the statistics of each reported earth quake precursor spatial extent time duration amplitude signal noise ratio to analyze dependence of the observable for each precursor on earthquake magnitude and to explore proposed physical models to explain eachearthquakeprecursor somegeneralcharacteristics wereobservedfortheseprecursoryphenomena first the largest amplitude precursory anomalies tend to occur before the largest magnitude earthquakes also the number of precursory anomalies tends to increase the closer in time to the occurrence of the earthquake finally theprecursoryanomaliestendtooccurclosetotheeventualepicenterof theearthquake ingeneral the physical models indicate that all of the precursory phenomena are related to deformation that occurs near the fault prior to the main earthquake while the models provide plausible physical explanations for the pre cursors there are many free parameters in the models that are poorly resolved

flexural modeling of paleozoic foreland basin subsidence offshore western newfoundland evidence for substantial post taconian thrust transport multichannel seismic reflection data gathered by the petroleum industry offshore of western newfoundland constrain the absolute thicknesses of the middle ordovician and post middle ordovician portions of the anticosti foreland basin immediately adjacent to the appalachian structural front these seismic lines which include 1970s vintage data in the public domain and recently acquired proprietary data indicate that the middle ordovician taconian portion of the foreland basin is more than an order of magnitude thinner than the preserved post middle ordovician salinian acadian portion the mechanical lithospheric coupling of foreland basins and their adjacent overthrust belts is a well understood phenomenon a thin taconian foreland succession and a thick salinian acadian succession imply that the overthrust loads responsible for flexural depression of the anticosti basin were much more distant and or much smaller during the middle ordovician taconian orogeny than they are today we quantify thi

origin of the odd twins anomaly magnetic effect of a unique stratigraphic marker in the appalachian foreland basin gulf of st lawrence the odd twins magnetic anomaly is a pair of linear asymmetric positive anomalies located in the gulf of st lawrence over the post taconian pre acadian foreland basin fill related to the development of the appalachians a marine magnetic survey allowed the anomaly to be traced close to the coast of newfoundland and an on land survey identified both peaks within the area of outcrop of the late ordovician long point group sandstones of high susceptibility sampled from sparse outcrops close to the locations of the anomaly peaks contain up to 0 58 magnetite models involving dipping sheets of sandstone having similar and slightly higher susceptibility can explain both the onshore and offshore anomaly the magnetite is of detrital origin and represents a paleoplacer heavy mineral concentration formed in a marginal marine environment the anomaly provides a unique tie point between the known onshore stratigraphy and the succession in the foreland basin known only from industry seismic profiles this tie

petrology and isotopic composition of a grenvillian basement fragment in the northern appalachian orogen blair river inlier nova scotia canada mesoproterozoic metaplutonic rocks in northern cape breton island introduction nova scotia occur in a tectonic inlier within the appalachian in eastern north america mesoproterozoic laurentian orogen although they have been multiply metamorphosed and basement rocks and their neoproterozoic to mid paleovariably deformed the petrology and geochemistry of these rocks zoic volcanic and sedimentary cover preserve a record provide insight into the tectonomagmatic evolution of easternmost of the proterozoic to mid paleozoic geologic history of laurentia anorthosite syenite and granitoid plutons eastern laurentia the record includes mesoproterozoic 1100 980 ma intruded the sailor brook and polletts cove river orogeny on the ancient north american craton breakgneisses new nd isotopic data are presented from a biotite rich up of a neoproterozoic supercontinent development of part of the sailor brook gneiss ndi 0 7 two anorthosite a passive continental margin and mid paleozoic orogeny samples ndi 2 1 and 2 8 and a charnockite unit exposures of mesoproterozoic laurentian basement in ndi 0 4 new u pb zircon data from the anorthosite yield easternmost canada and the usa occur in a dispb pb ages between 975 and 1095 ma disrupted u pb continuous band of inliers in the appalachian orogen systematics preclude a unique age interpretation but the 1095 ma from newfoundland to alabama fig 1 they consist single grain date is a minimum age for the anorthosite field relations mostly of rocks formed or deformed during major and trace element geochemistry and isotopic characteristics 1190 980 ma grenvillian tectonic and magmatic indicate that the anorthosite and charnockite were probably coexisting events and are distinct from neoproterozoic and melts but not differentiates of a single parent magma the lithological paleozoic units of accreted appalachian terranes in that and chemical characteristics of the lowland brook syenite are they include granulite facies metamorphic rocks and similar to those of a contemporaneous belt of ultrapotassic plutons in many cases anorthosite charnockite mangerite suites in the southern grenville province and both have the chemical bartholomew 1984 and papers therein pettingill et al characteristics of certain modern continental margin arc magmas 1984 rankin et al 1989 1993 owen erdmer 1990 these data indicate that the mesoproterozoic units in the blair hughes et al 1997 river inlier were juvenile crustal additions to eastern laurentia the sinuous trend of the band of basement inliers during grenville related orogenic events broadly reflects promontories and re entrants that formed

precambrian ammonium biogeochemistry a study of the moine metasediments scotland abstract the content and isotopic composition of ammoniacal nitrogen have been determined in a suite of amphibolite facies metasediments of precambrian age whole rock samples and mica separates from the moine succession proterozoic of scotland were analysed by a combination of capacitance manometry and static vacuum mass spectrometry prior to the analyses the presence of the ammonium ion was confirmed by obtaining infrared ir absorption spectra from the micas principally biotites whole rock ammonium contents are high for amphibolite facies metasediments 140 422 ppm the ammonium ion was not detected in the ir absorption spectra of biotites from one schist however this sample contains neither garnet nor white mica for most of the samples the 15n values are very positive between 12 4 and 16 6 with one sample having a lower value of 8 4 the major variations between samples can be interpreted in terms of original sedimentary features for the ammonium bearing samples muscovites have concentrations between 365 and 633 ppm biotites between 845 and 1739 ppm for individual samples nh4 mu nh4 bi varies between 0 31 and 0 43 a much narrower range than has been reported previously there are no significant or consistent differences in 15n between co existing biotite and white mica nor between the 15n values of the mineral separates and their respective whole rock values the latter suggests minimal selective partitioning of isotopes between micas and plagioclase feldspar the only other potential host for ammonium in the rocks assuming that the ammonium has been derived from organic matter originally present at the time of deposition and by comparison with previous studies it can be inferred that the original 15n value of the moine sediments was somewhere between 5 and 10 similar to recent sediments this suggests that the nitrogen cycle in the proterozoic shelf sea from which the moine sediments were deposited was broadly similar to the present day overall the study underlines how under developed the n system is compared to other stable isotope systems notably c and s and we use the opportunity to highlight some areas that could be developed in the future however one aspect is clear future ammonium studies of metamorphic rocks will need to be performed at high resolution visible scale of heterogeneity with strong mineralogical petrological and field controls

gas geochemistry applied to earthquake prediction an overview terrestrial gases in groundwater and soil air have been extensively studied in recent years in seismically active areas especially in ussr china japan and united states in search of premonitory changes that might be useful for earthquake prediction concentrations of radon helium hydrogen mercury carbon dioxide and several other volatiles have been found generally to be anomalously high along active faults suggesting that the faults may be paths of least resistance for the terrestrial gases generated or stored in the earth to escape to the atmosphere temporal gas concentration changes with durations of a few hours to many months have been observed before many large earthquakes at a relatively small number of favorably situated stations at epicentral distances of up to several hundreds of kilometers these sensitive stations are generally located along active faults especially at intersections or bends of faults or some other structurally weak zones possibly because of tectonic strain concentration at such places however gas concentrations especially those measured at or near the ground surface may also be significantly affected by meteorological hydrological and other nontectonic changes in the environment the nontectonically induced variations must be carefully eliminated or recognized in the search of true earthquake related anomalies

the late ordovician middle devonian gaspe belt in eastern canada recent advances the appalachian forelands and platform natmap national geoscience mapping program project in eastern canada is a multi discipline and multi organization research endeavour aimed at the understanding of the evolution and architecture of the ancient continental margin of laurentia this canadian journal of earth sciences special issue presents some recent research progress for our knowledge of the silurian devonian gaspe belt of that ancient margin

recent research on the physical aspects of earthquakes abstract recent developments in the field of physical aspects of earthquakes which encompasses in present day terminology the analysis of focal dynamics and of catastrophic effects of earthquakes are reviewed in particular individual sections of this review deal with the earthquake source effects of earthquakes on the ground the geographic and temporal distribution of earthquakes the characterization of seismic risk earthquake prediction and with the artificial release of earthquakes in this instance the review supplements earlier information by the author 1975 by new data published mainly between 1975 and 1984

geochemical and isotopic characteristics of early silurian clastic sequences in antigonish highlands nova scotia canada constraints on the accretion of avalonia in the appalachian caledonlde orogen avalonia is a terrane that accreted to laurentia baltica during the development of the appalachian caledonide orogen interpretations of the timing of accretion have been constrained by comparing faunal affinities overstep sequences age and kinematics of inferred accretionary deformational events and controversial paleomagnetic data we show that the time of accretion of avalonia may also be constrained by contrasts in the geochemical and isotopic signatures of its igneous rocks which reflect the characteristics of the underlying continental basement and mantle and sedimentary rocks which reflect provenance early silurian clastic sedimentary rocks of the beechill cove formation antigonish highlands nova scotia were deposited on avalonian crust the formation predominantly consists of approximately 80 m of siltstones and shales deposited in a nearshore environment and derived from the northeast their age is constrained by paleontological data and by directly underlying late ordovician early s

a comparison of microstructural and chemical patterns in garnet from the fleur de lys supergroup newfoundland this study uses compositional analyses of garnet porphyroblasts to test a previously published microstructure based model of garnet growth in the fleur de lys supergroup x ray maps reveal significant compositional anomalies within garnet including zoning reversals and steepened compositional gradients these anomalies occur at the margin of the proposed first stage of garnet growth g1 and coincide with truncations of inclusion trails and changes in the inclusion assemblage intervals of reversed composition zoning and steepened compositional gradients across this boundary are interpreted to represent a hiatus in garnet growth possibly accompanied by garnet consumption during which changes in the garnet forming reaction p t conditions and deformation kinematics occurred the junction of the proposed second and third stages of garnet growth g2 and g3 coincides with the transition between successive crenulation cleavages without substantial microstructural truncations or changes in the inclusion assemblage the g2 g3 boundary is generally marked by uninterrupted normal zoning with subtle compositional anomalies in some samples this boundary may in fact record continuous garnet growth or alternatively mark a relatively short intra orogenic pause in garnet growth with minimal affect on zoning patterns individual porphyroblasts with contrasting inclusion trail microstructures also have different zoning patterns and this supports the previous recognition of contrasting growth histories between individual porphyroblasts a combined structural metamorphic model is presented that integrates the timing of garnet growth and foliation development reaction history and the p t t path in the fleur de lys supergroup

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen