characteristic reflection patterns in the southeast canadian cordillera northern appalachians and swiss alps abstract there are some striking similarities and some differences between the seismic reflection sections recorded across the fold and thrust belts of the southeast canadian cordillera quebec maine appalachians and swiss alps in the fold and thrust belts of all three mountain ranges seismic reflection surveys have yielded high quality images of 1 nappes thin thrust sheets stacked on top of ancient continental margins 2 ramp anticlines in the hanging walls of faults that have ramp flat or listric geometries 3 back thrusts and back folds that developed during the terminal phases of orogeny and 4 tectonic wedges and regional decollements a principal result of the cordilleran and appalachian deep crustal studies has been the recognition of master decollements along which continental margin strata have been transported long distances whereas a principal result of the swiss alpine deep crustal program has been the identification of the adriatic indenter a crustal scale wedge that caused delamination of the european lithosphere significant crustal roots are observed beneath the fold and thrust belts of the alps southeast canadian cordillera and parts of the southern appalachians but such structures beneath the northern appalachians have probably been removed by post orogenic collapse and or crustal attenuation associated with the mesozoic opening of the atlantic ocean

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

harmonic distortion on a seismic reflection profile across the quebec appalachians relation to bouguer gravity and implications for crustal structure seismic reflection data obtained across the quebec appalachians using the vibroseis trademark conoco technique were recorded with parameters that allowed harmonic distortion arrivals to interfere with layered reflections the data exhibit reflections from layered miogeoclinal rocks dipping eastward beneath the allochthonous rocks of the orogen the layering appears to terminate beneath the notre dame anticlinorium however as the apparent termination of the layers also occurs at the arrival times of high amplitude noise harmonics it may have no geological significance precambrian grenville crust which probably underlies the layered sediments extends at least as far east as the apparent termination and may extend much farther examination of the bouguer gravity field in relation to the seismic reflection data shows that a major gravity change is due to density differences that occur considerably west of the eastern limit of precambrian grenville crust the gravity thus shows no correlation with sur

collision along an irregular margin a regional plate tectonic interpretation of the canadian appalachians discussion stockmal et al recently presented a simple three dimensional plate tectonic model by which they attempted to explain the pre carboniferous evolution of the northern appalachians this model which in part follows the basic principles of the two stage collision model of colman sadd 1982 is mainiy based on the results of a marine seismic profile across northem newfoundland and on large scale geometrical considerations such models are useful because they provide geologists with a framework that can be tested against field data however in this case the existing geological data base in our opinion is incompatible with the model we will discuss the inconsistencies and present an altemative model the main thesis of the stockmal et al model is that the taconian and acadian orogenies are explained in terms of continuous southeastward subduction of iapetus oceanic lithosphere during the collision between the taconic magmatic arc and the irregular margin of north america the benioff zone clogged first in newfoundland and then in mainland canada the continuing convergence between the taconic arc and north america in newfoundland was then achieved by delamination of lithospheric mantle while b subduction continued between the taconic arc and north america in mainland canada evidence in support of this model includes the 300 400 km right hand offset of equivalent tectono stratigraphic zones between newfoundland and mainland canada and a difference in style and vergence of the acadian structures in newfoundland and new brunswick the idea of a diachronous collision is not a new one but the sense of diachronism remains unresolved see e g dallmey er 1977 clague et al 1981 lux 1986 considered the allochthonous ophiolites in the humber zone and argued in favour of a north to south diachronism his conclusion is consistent with the fact that the oldest fossil dated autochthonous flysch is younger in quebec than in newfoundland since there is no overstepping autochthonous cover in quebec stockmal et al argue that the timing of the final emplacement of the allochthons and the closure of iapetus is not well constrained there and they explain the acadian orogeny in mainiand canada as

seismic refraction profiles in the gulf of saint lawrence and implications for extent of continuous grenville lower crust near the exposed grenville craton a two layer crust with velocities of 6 2 km s 1 and 6 65 km s 1 and low gradient is measured the 6 65 km s 1 velocity is observed at the shallow depth of 15 km and the moho at greater than 40 km depth towards the appalachian orogen a southwards dipping ramp is developed in the mid crust on the top of the 6 65 km s 1 layer a collinear reflection profile confirms the southwards dipping ramp the shallowing moho and the lateral changes in the lower crust a published refraction profile that crosses this reflection profile near the southern end confirms the termination of the 6 65 km s 1 layer and its replacement by a slower velocity with the publishing of wide angle reflection refraction war profile 88 2 two pairs of lines are now available in the gulf that cross the craton into the orogen with both war and deep seismic reflection coverage the combined data sets are used to distinguish the grenville lower crustal block based on patterns of reflectivity and associat

garnet geochemistry of tungsten mineralized xihuashan granites in south china abstract the xihuashan complex intrusion in south china which is emplaced at ca 154 ma mainly comprises medium grained porphyritic biotite granite medium grained biotite granite and fine grained two mica granite medium grained biotite and fine grained two mica granites are important tungsten bearing granites and contain an unusual amount of garnet garnets from this intrusion are dominated by almandine and spessartine which constitute 94 to 99 of the total molecular composition of the garnet these garnets display unusual compositional zoning the cores of these garnets are rich in heavy rare earth element hree y ca and contain abundant hree and y rich mineral inclusions their rims are free of mineral inclusions and have low of these elements two types of fluorite inclusions exist in garnet y fluorite and y poor fluorite garnet exhibits specific mn zoning with a relatively mn poor core but a relatively mn rich rim thus constituting a specific spessartine inverse bell shaped profile that belongs to typical magmatic garnets all analyzed garnets have high ree content and exhibit hree enriched and lree depleted patterns with strong negative eu anomalies the incorporation of ree into garnet is in part controlled by its crystal chemistry with ree3 following a coupled substitution of the type fe2 mn2 1viii ree3 1viii si4 1iv z3 1iv the texture and compositional zoning of garnet suggest that garnet growth is largely controlled by the pressure temperature composition condition of magmatic evolution internal crystal chemical parameters and kinetics during mineral growth the garnet core grows in near equilibrium with magmatic melt under a relatively high pressure temperature p t condition by contrast the garnet rim grows rapidly by the coexisting melt fluid phase and co2 rich volatile environment under a relatively low p t condition which is virtually unfavorable for the incorporation of ree into the magmatic garnet structure garnet fingerprints the magmatic hydrothermal transition during crystallization of these granites

structural analysis of bic fault a thrust related strike slip fault of the external domain of the taconic orogen appalachians quebec and metallogenic implications the bic fault is exposed along the shoreline of the st lawrence river 21 km southwest of rimouski for 210 m at cap a l orignal and for 100 m at cap enrage the fault brings in contact two major thrust sheets the des seigneuries and the des iles cambrian lithologies of the former overlying ordovician rocks of the latter in the taconic orogen such contacts are normally thrust faults but the bic fault is a dextral strike slip fault striking east west and dipping southward a study of a narrow zone straddling the fault and an adjacent part of the des seigneuries thrust sheet has led to the recognition of four successive stages of deformation all compatible with a northeast southwest trending strain ellipsoid the two first stages are most important stage 1 brought about regional folding and faulting whereas stage 2 was characterized by the development of various structural elements c s fabrics stretching lineation riedel shears and kink bands exclusive to the fault zone we infer that i in

in situ major and trace elements of garnet and scheelite in the nuri cu w mo deposit south gangdese tibet implications for mineral genesis and ore forming fluid records abstract garnet and scheelite are common hydrothermal silicate mineral and metal mineral in skarn or porphyry skarn deposits and can aid in constraining the composition of ore forming fluid based on in situ major and trace element analyses of garnet and scheelite from the nuri cu w mo deposit we discuss the factors and mechanisms controlling the incorporation of rare earth elements rees into the garnet and scheelite and investigate the associated hydrothermal fluid characteristics the garnets from the nuri deposit belong to the grossular andradite grandite solid solution series and range in composition from adr64grs34 to adr91grs8 the ree patterns of garnet are enriched in light rare earth elements lrees and depleted in heavy rare earth elements hrees the rees characteristics indicates that the incorporation of rees into the nuri garnet was controlled by the surface adsorption and element substitution in the mineral structure based on the cathodoluminescence cl images of scheelite two growth stages early and late stages are identified these two stages of scheelite belong to the scheelite powellite series and are enriched in lrees and depleted in hrees however the early scheelite exhibits negative or no eu anomalies 0 34 0 95 whereas the late scheelite presents positive eu anomalies 1 25 2 89 the mo content in the early scheelite is positively correlated with the eu value while the mo content in the late scheelite is negatively correlated with eu these characteristics indicate that the redox state of the ore forming fluid gradually changed from the oxidized state to the reduced state the preferred ree3 substitution for ca2 in the nuri scheelite is 3ca2 2ree3 ca where ca is a ca site vacancy the ree features of the scheelite are mainly controlled by the ree nature of the ore forming fluid according to the characteristics of trace elements in garnet and scheelite we suggest that the ore forming fluid of the nuri deposit is a magmatic fluid mixed with a slightly acidic external fluid chloride complexes may be the main transport ligand of the rees and the oxygen fugacity of the ore forming fluid gradually decreased

the extension of grenville basement beneath the northern appalachians results from the quebec maine seismic reflection and refraction surveys from 1983 to 1984 the united states geological survey and the geological survey of canada undertook a series of seismic experiments to determine the crustal structure of the appalachian mountain belt in maine and southeast quebec these experiments included four deep crustal seismic reflection profiles perpendicular to the strike of regional geological trends and several high resolution refraction wide angle reflection profiles both parallel and perpendicular to strike here the data recorded in quebec and the northwest part of maine are interpreted in conjunction with existing reflection profiles from quebec synthetic seismogram calculations in laterally varying media are used to model the refraction wide angle reflection data while reprocessing migration and attribute plotting are used in the interpretation of the reflection data a major zone of reflections extending over a distance exceeding 200 km can be traced from shallow depths beneath the st lawrence lowlands southeast to about 25 km depth beneath the southeast edge of the chain lakes massif this zone of reflections is interpreted as a master decollement separating autochthonous grenville basement from overlying allochthonous rocks of the appalachian orogen including foreshortened miogeoclinal rocks the remnants of one or more magmatic arcs the connecticut valley gaspe synclinorium and the chain lakes massif in the vicinity of the chain lakes massif extension has caused grenville basement to be thinned by as much as 40 reflections from the decollement show strong layering and evidence for basement faulting associated with the guadeloupe and other faults normal incidence and wide angle reflections are observed to be almost continuous beneath the baie verte brompton line and connecticut valley gaspe synclinorium indicating that the baie verte brompton line is confined to the upper crust the connecticut valley gaspe synclinorium is characterized by p wave velocities of about 5 3 km s 1 and is shown to be a shallow structure with a maximum depth of about 3 km rock velocities immediately below the connecticut valley gaspe synclinorium are typical of chain lakes material 6 1 km s 1 a new model for the tectonic development of the region is proposed in which all pre silurian units between the baie verte brompton line and the southeastern edge of the chain lakes massif are allochthonous and confined to the upper crust we infer that the chain lakes massif volcanics of the ascot weedon formation and associated deeper crustal rocks were thrust over grenvillian basement as a composite unit and may now underlie parts of the connecticut valley gaspe synclinorium

an appraisal of endmember energy and mixing properties of rare earth garnets abstract the thermodynamic properties of rare earth aluminum ree 3 al 5 o 12 iron ree 3 fe 5 o 12 and gallium ree 3 ga 5 o 12 garnets are assessed by means of critical evaluation of the existing experimental data and thermodynamic treatment of their vibrational static and volumetric properties the mixing properties of the various ree garnet components are calculated from these endmember thermodynamic data and the interionic static potential model developed earlier for major silicate garnet components these results permit evaluation of the solubility behavior for ree in natural phases the results suggest that the mixing of ree garnet components at trace level i e below about 10 2 ppm with major silicate garnet components is virtually ideal but strong positive deviations associated with generalized polyhedral distortion of the host phase at higher concentration level of the solute prevent bulk ree solubility from exceeding a few hundreds ppm the computed rare earth element fractionations between garnet and supercritical fluid at various p t conditions put in evidence the main control operated by the intrinsic energy properties of ree garnet end members in determining the light ree heavy ree lree hree fractionation observed in natural garnet specimens

fine scale study of a thick stratospheric ozone lamina at the edge of the southern subtropical barrier a large scale transport event resulting in a thick ozone lamina originating from midlatitudes is observed in the tropical stratosphere over reunion island 55 e 21 s this isentropic transport was detected from stratospheric balloon borne ozone measurements that showed the occurrence of the lamina and was investigated using different tools based on ertel s potential vorticity epv analyses an original software dybal using surface coordinate and the equivalent length of epv contours as diagnostic tools in conjunction with high resolution outputs from an epv advection model mimosa allows us to specify the origin of the lamina the results indicate that a broad layer of stratospheric air was isentropically advected from midlatitudes across the southern edge of tropical reservoir and reached reunion island on 12 july 2000 in addition eliassen palm s flux vectors calculated from ecmwf analysis show that planetary wave activity was quite large during that time period with wave breaking occurring around 30 km and could have driven that exchange in contrast with analyses of filamentation events based on model and satellite data the present study focuses on a fine scale vertical survey from in situ measurements the filament reported in this paper is characterized by a large vertical extension and is located around the maximum of ozone concentration in the tropical stratosphere 600 k the analysis of such events poorly documented in the tropics could complement satellite studies and contribute to a better determination of the transport between the tropics and the midlatitudes

scheelite elemental and isotopic signatures implications for the genesis of skarn type w mo deposits in the chizhou area anhui province eastern china scheelite is well developed in hydrothermal deposits providing a window into genetic processes and facilitating comparative studies however few studies have focused on characterizing scheelite in skarn type w mo deposits the primary ore mineral in the jitoushan and baizhangyan skarn type w mo deposits anhui province eastern china scheelite was analyzed for major trace and rare earth element ree abundance and for sr nd isotopes the analysis revealed two unique geochemical characteristics that distinguish the scheelite from skarn type w mo deposits to that from vein type au w and porphyry type w mo deposits higher mo content with a negative correlation between moo 3 and wo 3 and a strong hree depletion skarn type scheelite mainly inherited ree signatures from ore forming fluids and the early precipitation of skarn minerals e g garnet diopside and amphibole has most likely resulted in the observed strong hree depletion in scheelite and the decoupling of lrees and hrees of the numerous substitution mechanisms suggested by previous workers 3ca 2 2ree 3 ca where ca is a ca site vacancy is preferred for the substitution of ree 3 for ca 2 and in this study particularly given the low salinity of ore fluids as the scheelite eu anomalies were inherited from ore forming fluids with variable redox conditions and ph the complex deu mo correlation indicates that mo increasingly entered the scheelite under oxidizing conditions and reached a maxim at deu values of 0 8 to 1 in contrast under reducing conditions mo contents in scheelite decrease gradually and mo is precipitated as molybdenite as a result of the change in dominant valence state unlike the sr nd isotope compositions of scheelite from vein type au w and w sb au deposits the scheelite from skarn type w mo deposits has low 143 nd 144 nd t most 87 sr 86 sr t values most between 0 708 and 0 715 the end t values of the scheelite varied from 16 to 12 3 in the baizhangyan deposit and from 9 5 to 9 1 in the jitoushan deposit indicating that the ore forming materials in the two w mo deposits were mainly derived from crustal sources

geophysical evidence for thick skinned crustal deformation in central australia until now there has been no clear evidence from deep seismic reflection profiles of crustal faults that displace the moho new data from central australia show such a structure in a region characterized by large thrust structures large gravity anomalies and abrupt changes in teleseismic travel times here the principal thrust the redbank deformed zone cuts through the crust and the moho is significantly displaced across it the geological and geophysical evidence leads to a model of thick skinned crustal deformation which occurred in an intra cratonic environment in late devonian time

the logtung large tonnage low grade w scheelite mo porphyry deposit south central yukon territory mineralization is related to multiple felsic intrusions since mineralization is contained in fractures 95 rather than being disseminated logtung is not a skarn deposit the principal reason is that the reaction skarn host rocks which were derived from calcareous shales interbedded with graphitic quartzites are carbonate poor and competent hence permeable mineralization formed in permeability created by hydraulic fracturing and not by replacement logtung shows a scheme of several phases 4 of mineralization related to multiple intrusions which is similar to that which is so important in for example the evolution of the climax and urad henderson mo systems the logtung deposit shows many similarities to porphyry mo deposits in the western cordillera and may be classed as a porphyry w scheelite mo deposit with a w mo ratio of 3 3 1 0 the principal reasons are that mineralization is spatially associated with porphyritic intrusive phases and that much of the mineralization occurs as typical porphyry style crackle breccias modified journal abstract

a deep seismic reflection profile across the northern north sea the viking graben is a major mesozoic rift basin in the northern north sea1 seismic refraction data2 gravity surveys3 and theoretical modelling4 have led to the general acceptance of an extensional tectonic origin for the viking graben involving an early mesozoic phase of extension and fault controlled subsidence followed by a more regional thermal contraction subsidence the early success of the birps deep seismic reflection profiling5 and the results from cocorp6 led to the planning and acquisition during 1983 of a deep seismic line recorded to 15 s twt two way time across the north viking graben the aims of the present study were to provide constraints on the geometry of the viking graben and its extensional faults to provide data on the geometry of crustal thinning beneath the graben and to provide an insight into the relation between the shallow extensional features of the sedimentary basin and the deep crustal thinning here we present a specific interpretation of this seismic profile further details will be given elsewhere7

trace element zoning in a metamorphic garnet trace element zoning has been measured in an amphibolite garnet from the tauern window austria by using an ion microprobe humps in the zoning profiles of na sc v y and the heavy rare earth elements mark a period of open system behavior these humps correspond to a part of the major element zoning profile that is interpreted as a p t reversal the source of the mass excesses of these elements remains ambiguous they were derived either on a thin section scale by the breakdown of trace element enriched refractory minerals or externally from unusual trace element enriched fluids p t paths determined from garnet zoning may require modification if open system behavior is important during garnet growth

rare earth element systematics in hydrothermal fluids abstract rare earth element concentrations have been measured in hydrothermal solutions from geothermal fields in italy dominica valles caldera salton sea and the mid atlantic ridge the measured abundances show that hydrothermal activity is not expected to affect the ree balance of either continental or oceanic rocks the ree enrichment of the solutions increases when the ph decreases high temperature solutions 230 c percolating through different rock types may show similar ree patterns

laminae in the tropical middle stratosphere origin and age estimation in situ measurements of n 2 o and o 3 aboard the observations from the middle stratosphere oms balloon payload in the tropics are presented in november 1997 at 7 s very distinct laminated structures in the n 2 o profile were observed in contrast to earlier studies based solely on o 3 profiles the laminae probably are an observation of rossby wave breaking events that lead to transport of mid latitude air into the tropics using a photochemical model of the ozone response within those air parcels their residence time in the tropics is estimated to be 4 to 6 weeks in february 1997 at 7 s a similar vertical profile of n 2 o revealed no mid latitude laminae we present dynamical arguments to support the existence of such laminae in november but not in february

some comparisons of the structure and evolution of the southern appalachian ouachita orogen and portions of the trans european suture zone region abstract many aspects of the tectonic history of the appalachian ouachita orogen and the trans european suture region are similar in a tectonic sense they are geographically linked because at the end of the paleozoic one could travel from texas to poland following a continuous orogenic belt much of each of these orogenic belts is however buried by younger strata and thus geophysical studies are a key element of efforts to better understand them many more geophysical data are needed to provide a comprehensive picture of the deep structure but in several areas new models of the lithospheric structure are emerging in this paper we review some of these models and introduce two new ones for the southern appalachians in addition we explore the implications of these models for the evolution of these orogenic belts drawing attention to similarities and differences in their structure and evolution the appalachian and caledonian orogens represent temporally parallel development along irregular late proterozoic continental margins but the crustal structure is different because of different accretionary elements and complications in the geometry of the original margins lateral transport via thrusting can confuse efforts to tie geologic structures identified on the surface with deep structures for example in the appalachian ouachita orogen the thrust related transport distance for major features such as the blue ridge piedmont sheet and the benton uplift is at least 200 km on a crustal scale deformation in the appalachian ouachita orogen varies greatly in style and intensity in the ouachita orogen the late proterozoic continental margin seems to be preserved while in the northern appalachians crustal scale deformation is intense along the us appalachians the major crustal structure variation is the thin dense crust of avalonia abutting the relatively thick crust of laurentia along the ouachita orogen several large crustal blocks can be identified that are unlike anything seen along the appalachians

seasonal formation of nitrous oxide laminae in the mid and low latitude stratosphere the seasonal and global distributions of laminae in nitrous oxide n2o a long lived tropospheric source gas are examined in a multi year three dimensional model simulation the frequency of laminae occurrences is described as a function of geographical location and season enhanced laminae occurrence is found in the midlatitude surf zones of both hemispheres but there are zonal asymmetries especially in the northern hemisphere in boreal winter and spring laminae intruding from mid latitudes into the deep tropics are found across the pacific ocean on the southern flank of the aleutian high a quiet zone free of laminae lies on the summer side of the equator and separates the winter from the summer stratosphere it coincides in latitude with the location of the n2o low latitude maximum high laminae occurrences are again found in the extratropics of the summer hemisphere

ree controls in ultramafic hosted mor hydrothermal systems an experimental study at elevated temperature and pressure a hydrothermal experiment involving peridotite and a coexisting aqueous fluid was conducted to assess the role of dissolved cl and redox on ree mobility at 400 c 500 bars data show that the onset of reducing conditions enhances the stability of soluble eu 2 species moreover eu 2 forms strong aqueous complexes with dissolved cl at virtually all redox conditions thus high cl concentrations and reducing conditions can combine to reinforce eu mobility except for la trivalent ree are not greatly affected by fluid speciation under the chemical and physical condition considered suggesting control by secondary mineral fluid partitioning lree enrichment and positive eu anomalies observed in fluids from the experiment are remarkably similar to patterns of ree mobility in vent fluids issuing from basalt and peridotite hosted hydrothermal systems this suggests that the chondrite normalized ree patterns are influenced greatly by fluid speciation effects and secondary mineral formation processes accordingly caution must be exercised when using ree in hydrothermal vent fluids to infer ree sources in subseafloor reaction zones from which the fluids are derived although vent fluid patterns having lree enrichment and positive eu anomalies are typically interpreted to suggest plagioclase recrystallization reactions this need not always be the case

radiation pattern of crustal phases of new england earthquakes summary the amplitudes of pn waves from new england earthquakes recorded by a regional short period seismic network have been studied to determine the effects of the double couple source radiation pattern both observed and synthetic seismograms show that pn amplitudes change dramatically with source to receiver azimuth these changes are primarily due to the take off angles of the seismic rays relative to the nodal planes of the focal mechanism solution the recordings of a seismic refraction blast show no appreciable change of amplitude with azimuth the focal mechanism solutions found from inverting the pn amplitudes of several well recorded earthquakes are consistent with those obtained from the first motion readings this study has demonstrated that it is possible to calculate focal mechanisms of earthquakes using the polarities and amplitudes of pn waves recorded at a small number of azimuthally distributed local stations

the crustal structure in central maine from coherency processed refraction data in 1984 the u s geological surcvey and the canadian department of energy mines and resources conducted an extensive seismic refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surface velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from refraction experiment the quebec maine transect project as part of this project a 180 km long seismic refraction profile was recorded along the axis of the central maine synclinorium high near surf ace velocities of 6 0 6 2 km s made a conventional refraction analysis including first arrivals uninformative below about 10 km peak signal frequencies around 30 hz recorded at all offsets and a trace spacing of 800 m led to severe spatial aliasing effects for secondary arrivals on the record sections to allow a reliable deep structural interpretation a coherency processing technique was applied to the data to enhance phase coherent secondary arrivals in addition interpretation of a coincident wide angle reflection study provided constraints on the deep crustal velocities and structure the crust beneath the central maine synclinorium can be described by three major structural units the upper crust is interpreted as the metasedimentary rocks of the central maine synclinorium with velocities that range from 6 2 to 6 3 km s regions of relative lower velocity 6 0 6 1 km s within the upper crust are interpreted as granitic intrusions low velocity regions modeled at 2 7 km depth with velocities around 5 4 km s are interpreted as seismic evidence for folding and doubling within the upper crustal metasedimentary sequence at 12 15 km depth the base of the synclinorium appears alternately as a strong reflector indicating the presence of layering and also as a weak reflector especially ne of the sebago pluton a 4 km thick boundary layer at 24 km depth is interpreted as a major intracrustal shear zone in which the velocity increases from 6 4 to 6 8 km s the crust thickens from 36 to 40 km going from the ne to the sw end of the profile surface rocks at the sw end of the profile have a metamorphic depth of burial of at least 15 km indicating that the crust below the central maine synclinorium may have been thickened to at least 55 km during paleozoic collisions

subtropical stratospheric mixing linked to disturbances in the polar vortices randel et al 1 have observed tongues of stratospheric air stretching from the tropics into middle latitudes and conclude that such events may be responsible for transporting significant amounts of stratospheric air across the tropical mid latitude barrier2 here i examine the movements of air parcels during these events using high resolution contour trajectory calculations my calculations suggest that the tongues of tropical air are associated with disturbances of the stratospheric polar vortices the edge of the disturbed polar vortex reaches low latitudes and draws a long tongue of tropical air around the vortex into middle latitudes this process occurs in the winter of both hemispheres although the edge of the larger antarctic polar vortex reaches farther toward the equator and draws up material from lower latitudes than its arctic counterpart

thermal regime of the lithosphere in the canadian shieldthis article is one of a series of papers published in this special issue on the theme lithoprobe parameters processes and the evolution of a continent geothermal studies were conducted within the framework of lithoprobe to systematically document variations of heat flow and surface heat production in the major geological provinces of the canadian shield one of the main conclusions is that in the shield the variations in surface heat flow are dominated by the crustal heat generation horizontal variations in mantle heat flow are too small to be resolved by heat flow measurements different methods constrain the mantle heat flow to be in the range of 12 18 mw m 2 most of the heat flow anomalies high and low are due to variations in crustal composition and structure the vertical distribution of radioelements is characterized by a differentiation index di that measures the ratio of the surface to the average crustal heat generation in a province determination of mantle temperatures requires the knowledge of both the surface heat flow and di mantle temperatures increase with an increase in surface heat flow but decrease with an increase in di stabi

deep seismic reflection profile across the northern appalachians a marine seismic reflection line across the northeast extremity of the canadian appalachians in newfoundland indicates a collisional suture in the lower crust beneath the central ophiolitic dunnage terrane the thrust and fold belt miogeocline above the grenville basement and the dunnage and gander tectonostratigraphic terranes all appear to be allochthonous with respect to lower crustal basement the gander avalon terrane boundary to the east is a near vertical feature that penetrates the crust the data also suggest that the ancient passive margin of north america extends eastward under the dunnage terrane for about 70 km the newfoundland deep seismic experiment indicates major tectonic differences compared to results for the southern appalachians

vertical short scale structures in the upper tropospheric and lower stratospheric temperature and ozone at la reunion island 20 8 s 55 3 e the distribution and the nature of vertical short scale structures observed in ozone and temperature are investigated in the upper troposphere and the lower stratosphere at la reunion island located in the vicinity of the southern subtropical barrier by using wavelet based methods a climatology of dominant wavelike patterns with short vertical wavelengths reveals the presence of localized structures on both the ozone and the temperature perturbations extracted from ozonesonde and temperature data up to the middle stratosphere some case studies are presented to identify the nature of short scale structures with 1 to 5 km vertical wavelengths in the troposphere and the stratosphere a climatology of short scale structures induced by gravity waves and the horizontal advection shows that short scale structures are mainly detected in the middle and upper troposphere and in the lower stratosphere the weak value of the coefficient r z that links the ozone and temperature perturbations induced by gravity waves is a major limit to detecting such short scale structures above 21 km altitude some structures with vertical wavelengths ranging from 1 to 5 km are attributed to gravity waves produced by convection in summer and the subtropical jet in winter or quasi horizontal large scale motions from both sides of the subtropical barrier

noise and oscillatory zoning of minerals oscillatory mineral zonation is usually associated with crystal growth in an open system either a hydrothermal system or a melt after a period of magma mixing or degassing such systems may be driven sufficiently far from thermodynamic equilibrium to produce autonomous patterns by geochemical self organization the resulting zonation patterns will be the result of coupling between the generally nonlinear crystal growth dynamics and the boundary conditions imposed by externally controlled fluctuations we examine the effects of noisy boundary conditions on four different crystal growth models these are models for plagioclase growth in magmatic systems l heureux and fowler 1996 for carbonates in sedimentary systems wang and merino 1992 for garnets in hydrothermal systems jamtveit 1991 and for silicate growth from a melt wang and wu 1995 the plagioclase model is sensitive to noise even to low amplitude noise implying that an observed zonation pattern will be significantly affected by processes other than local growth and transport processes for the garnet model fluctuations in the external environment may cause synchronization so that different crystals develop similar zonation patterns even if the formation of zonation patterns is a consequence of nonlinear local dynamics this implies that similarity in intracrystalline zonation does not necessarily imply that the zonation pattern was produced by changes in the external environmental conditions the formation of a zonation pattern may be a consequence of local nonlinearities in the growth process but the pattern details may be strongly affected by subtle changes in the external environment copyright 2000 elsevier science ltd

more seismic evidence on the location of grenville basement beneath the appalachians of quebec maine summary high quality multichannel seismic 133 fold and refraction wide angle reflection 1 to 3 km receiver spacing and 30 to 60 km shot spacing data have been collected across the northern appalachians in quebec and maine an integrated interpretation of the seismic data from the southeastern quebec western maine region provides strong evidence that the rocks of the predominantly oceanic dunnage zone are allochthonous having been thrust westwards over precambrian grenville basement during and subsequent to the closing of the iapetus ocean

a synthesis of the geophysical characteristics of terranes in eastern canada abstract geological identification of terranes in the canadian appalachians has led in general to the proposing of terranes which have recognizably distinct geophysical signatures indicative of fundamental differences in crustal structure between the terranes the rapidly expanding geophysical data base has enabled an integrated approach to geophysical terrane analysis the geophysical data enable the humber with its diagnostic gravity low and variable magnetic anomalies to be recognized throughout the canadian appalachians deep seismic data suggest that it is found beneath the western part of the dunnage terrane the latter is typified by dominantly positive gravity anomalies in newfoundland these together with the magnetic data enable the zone to be subdivided into the notre dame and exploits subzones the seismic character clearly identifies the presence of the dunnage northeast of newfoundland and suggests that it may terminate south of newfoundland the gander terrane has typically negative gravity and magnetic anomalies which may be confidently traced from northeast of newfoundland south through cape breton a belt of similar anomalies occurs in new brunswick the deep seismic evidence suggests that the gander may represent the outcrop of a deep crustal block underlying the eastern part of the dunnage terrane the avalon terrane is identified throughout the canadian appalachians by a diagnostic set of arcuate alternating gravity and magnetic anomalies the boundary between the avalon and gander is clearly recognized on deep seismic sections as a near vertical feature cutting through the crust northeast of newfoundland the meguma avalon boundary is clearly delineated by a gravity and magnetic gradient throughout the system there is limited and ambiguous deep seismic data regarding the nature of it and the meguma terrane in general a subtle set of nw trending lineations perpendicular to the dominant regional trend has recently been identified geological evidence that suggests these are post carboniferous in age and may be related to the development of a tensional regime associated with the mesozoic rifting of the atlantic

tomographic inversion for the seismic velocity structure beneath northern new england using seismic refraction data the seismic velocity structure of the crust and the upper mantle beneath northern new england was investigated from the travel time data of the 1984 maine seismic refraction profile and the 1988 ontario new york new england seismic refraction profile seismic refraction experiments by using tomographic inversion techniques strong lateral seismic velocity variations were found in the upper 15 km of the crust and these variations are correlated with regional geologic and tectonic structures the grenville basement in the adirondack mountains of eastern new york is characterized by an unusually high p wave velocity of 6 7 km s in the upper 15 km of the crust this high velocity basement extends eastward below western vermont to a depth between 15 and 20 km from the surface more typical upper crustal p wave velocities of 5 6 to 6 4 km s were generally found in central and southern maine and in new hampshire and the anisotropic upper crustal zone west of penobscot bay in maine was imaged by locally slower velocities the correlation of the inversion velocity structure with the tectonic features of northern new england shows that the appalachian mountains in northern new england may extend tectonically to at least 20 km deep in the crust the velocity distribution at 20 km depth shows three northeast elongate juxtaposed belts which correspond to the connecticut valley gaspe synclinorium the bronson hill anticlinorium and the kearsarge central maine synclinorium respectively the connecticut valley gaspe and kearsarge central maine synclinoria have relatively high velocities from 6 94 to 7 12 km s while the bronson hill anticlinorium has relatively low velocities from 6 52 to 6 75 km s in the lower crust another low velocity area of 6 52 km s at 20 km depth is imaged beneath the white mountain batholith in central new hampshire and may be a lower crustal expression of this batholith upper mantle velocity structures were obtained for the grenville basement the appalachians in northern new england and the avalon terrane in southeastern maine from the long range seismic refraction data generally the older grenville lithosphere about 1100 ma in quebec has higher velocity in the upper mantle than does the younger avalon terrane no older than 650 ma in the southeastern part of northern new england the data suggest that the velocity of the upper mantle beneath the old north american craton increases stepwise with observable velocity discontinuities in depth while that beneath the avalon terrane does not increase through the first 40 km of the upper mantle the data analysis also shows that the upper mantle suture between the grenville basement and the avalon terrane occurs in a narrow belt beneath the appalachian mountains of central maine and new hampshire the did of the moho discontinuity beneath northern new england is modeled as nearly flat as 0 7 in the n57 w direction and as steep as 1 2 beneath the grenville basement

seasonal variation of isentropic transport out of the tropical stratosphere the seasonal variation of the isentropic transport out of the tropical stratosphere is examined using contour advection calculations with winds from meteorological analyses for the period july 1991 to june 1994 calculations using winds from three different meteorological analyses are compared there is good qualitative agreement between the different calculations for extratropical structures but not for structures in the tropics there is also reasonable agreement between area diagnostics for transport out of the tropics derived from these calculations transport out of the tropics occurs in rossby wave breaking events in which filaments of tropical air are drawn into middle latitudes in all years these wave breaking events occur during the fall to spring period when there are westerlies throughout middle latitudes late september to early may in the northern hemisphere this includes periods before the formation of and after the breakup of the polar vortex in the northern hemisphere the rate of transport out of the tropics during fall to spring fluctuates around a constant value whereas in the southern hemisphere there is a relatively quiet midwinter period with maxima in the transport in early and late winter