ground roll a potential tool for constraining shallow shear wave structure the objective of this study is to demonstrate that a laterally varying shallow s wave structure derived from the dispersion of the ground roll can explain observed lateral variations in the direct s wave arrival the data set consists of multichannel seismic refraction data from a usgs gsc survey in the state of maine and the province of quebec these data exhibit significant lateral changes in the moveout of the ground roll as well as the s wave first arrivals a sequence of surface wave processing steps are used to obtain a final laterally varying s wave velocity model these steps include visual examination of the data stacking waveform inversion of selected traces phase velocity adjustment by crosscorrelation and phase velocity inversion these models are used to predict the s wave first arrivals by using two dimensional 2d ray tracing techniques observed and calculated s wave arrivals match well over 30 km long data paths where lateral variations in the s wave velocity in the upper 1 2 km a

thermotectonic evolution of the ukrainian donbas foldbelt evidence from zircon and apatite fission track data abstract the donbas foldbelt forms part of a large devonian rift cross cutting the southern part of the eastern european craton it comprises a 20 km thick devonian and carboniferous sedimentary succession maximum burial occurred during early permian time and was followed by a major exhumation phase in this study we use zircon and apatite fission track dating to reconstruct the post depositional thermal evolution of the inverted basin modelling of the fission track data combined with modelling of vitrinite reflectance data reveals that large parts of the basin were affected by a permo triassic 250 ma heat flow event which was presumably related to permo triassic andesitic magmatism this permo triassic thermal event was predicted by previous modelling of vitrinite reflectance data but only the fission track data indicates its wide areal distribution probably large parts of the southern margin of the eastern european craton were affected by this event whereas rocks west of the city of donetsk krasnoarmeisk monocline experienced permo triassic temperatures in the range of 90 105 c rocks northwest of donetsk were heated to up to more than 240 c jurassic temperatures northeast of donetsk were in the order of 90 100 c these relatively high temperatures imply that a significant part of the carboniferous sequence became eroded only during early cretaceous times and or that the jurassic heat flow was significantly increased 90 mw m2 elevated heat flows may be related to jurassic magmatic activity sediments in the southern donbas foldbelt yuzhno donbassky region and the westernmost krasnoarmeisk monocline record cooling below 60 c during jurassic times whereas samples northeast of donetsk cooled below 60 c during cretaceous times a correlation between this last cooling and the present day depths of the samples suggests that the main episode of folding along the south syncline and the south anticline pre dates cretaceous cooling

reflection and refraction seismics in areas of complex geology an example in the northern apennines an experimental survey employing refraction wide angle reflection seismic techniques dss deep seismic soundings was carried out in the northern apennines north italy the main objective of the experiment was the application of dss to better define the structure of the upper crust down to about 15 km depth in the crucial alps apennines boundary zone a second objective was to understand the potential of dss as a complementary tool in areas of complex geology where the results of near vertical reflection nvr are generally poor the results of the experiment show that dss if properly planned can continuously follow deep markers and therefore impart a greater significance to faint and discontinuous nvr as well as data on the p wave velocity of the seismic units

crustal velocity structure of the omineca belt southeastern canadian cordillera travel time inversion and amplitude modeling of a 350 km lithoprobe seismic refraction wide angle reflection profile determined the velocity structure of the crust and upper mantle along strike in the omineca belt of the canadian cordillera the upper crust to 12 18 km depth has velocities from 5 6 to 6 2 km s 1 and two shear zones the monashee decollement and gwillim creek shear zone are imaged by the wide angle reflections and velocity trends minor velocity differences on either side of the monashee decollement may be related to separate rock origins prominent reflections define the boundaries of a low velocity midcrustal layer from 10 15 km to 20 25 km depth with velocities less than 6 1 km s 1 the low velocities of the midcrust associated with high electrical conductivities and high heat flow may be considered as support for the hypothesis of fluids in the cordilleran crust though other possibilities such as the effect of high temperatures on rock velocities are possible in the lower crust velocities range from 6 4 6 5 km s 1 at the top of the lower crust to 6 6 6 8 km s 1 at its base the moho is very clearly defined by the refraction wide angle reflection data and has a gentle southerly dip crustal thicknesses are 35 37 km a thin crust mantle transition zone of 1 2 km thickness in which velocities vary between 7 6 and 7 7 km s 1 is consistent with coincident reflection data upper mantle velocities range from 7 9 to 8 1 km s 1 with indications from the data of upper mantle layering in comparison with neighboring regions the omineca belt has an anomalously thin crust low crustal velocities and a low velocity upper mantle similar only to the basin and range province the velocity structure may partly mirror the temperature profile which has overprinted the geological signature of the region as measured by the seismic refraction method the characteristics of a thin crust and lithosphere along with low velocities from midcrust to mantle suggests that both the basin and range and the southern canadian cordillera are currently being heated from a source within the mantle

comparison of hydrocarbon gases c1 c5 production from carboniferous donets ukraine and cretaceous sabinas mexico coals abstract the main purpose of this contribution is to compare the ability of carboniferous coals from the donets basin of the ukraine and cretaceous coal from the sabinas basin of the mexico to generate hydrocarbon gases c1 c5 two bituminous coals from the donets basin 2c10yd and 1l1dim 0 55 and 0 65 rr respectively and one bituminous coal from the sabinas basin olmos 0 92 rr were studied using heating experiments in a confined pyrolysis system the highest rank reached during the heating experiments corresponds to the anthracite stage 2 78 and 2 57 rr for the 2c10yd and 1l1dim coals and 2 65 rr for the olmos coal the composition of the generated c1 c5 gases was evaluated using a thermodesorption multidimensional gas chromatography the results show that the carboniferous donets coals produced more wet gas and methane during pyrolysis than the cretaceous olmos coal this is probably due to their higher liptinite 6 20 and collodetrinite content and to the loss of a major part of the petroleum potential of the olmos coal during natural coalification c2 c5 compounds are mainly derived from the cracking of liquid hydrocarbons ethane is the most stable compound and formed from the cracking of higher hydrocarbon component large amounts of methane up to 81 mg g coal for the donets coals and 50 mg g coal for the sabinas coal were formed at high temperatures by cracking of previously formed heavier hydrocarbons and by dealkylation of the coal matrix a linear relationship was observed between methane generation and the maturity level of both coal types

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

biological mats in siliciclastic sediments of the paleoproterozoic gunflint formation northwestern ontario canada the gunflint formation of northwestern ontario canada contains an extensive array of stromatolite morphologies and associated fossilized bacteria it and correlative units in the united states

p wave velocity anisotropy in crystalline rocks summary compressional wave velocities and anisotropy coefficients determined at high hydrostatic pressures are compiled from the data published for the main types of crystalline rocks the crack free elastic anisotropy of igneous crustal rocks is generally very low between 1 and 3 per cent on average the anisotropy of metamorphic rocks is higher up to 22 per cent but very variable the average anisotropy coefficients in schists and amphibolites are about 10 per cent in gneisses between 3 and 7 per cent and in granulites less than 3 per cent the average anisotropy of olivine ultramafites is between 7 and 12 per cent whereas in pyroxenites and eclogites it is usually less than 4 per cent a comparison of ranges of average velocities and average anisotropies for the individual rock groups suggests that whereas in the crust the lateral velocity variations are mainly due to compositional changes in the olivine of the uppermost mantle the velocity variations due to anisotropic structures could be of the same magnitude as the variations due to inhomogeneities

the donets basin ukraine russia coalification and thermal history the donets basin donbas is one of the major late paleozoic coal basins in the world the donbas foldbelt is an inverted part of the donets basin characterized by wnw ese trending folds and faults the age of basin inversion is under discussion large parts of the donets basin host anthracite and meta anthracite low rank coals are restricted to the western and northern basin margins vitrinite reflectance patterns along the gorlovka anticline indicate syn deformational coalification vitrinite reflectance isolines are displaced along thrusts clear evidence that main coalification predates late faulting 1 d and 2 d numerical models were applied to elucidate the factors that control coalification in the western donets basin krasnoarmeisk monocline kalmius torets depression south syncline the models indicate that the depth of the seams and the heat flow during maximum permian burial are the most important parameters the thickness of late carboniferous and permian rocks increased from the southwestern basin margin towards the basin center permian erosion along the krasnoarmeisk monocline and in the kalmius torets depression was on the order of 2 3 km more rocks were eroded southeast of the donetsk kadievka fault zone 4 5 km heat flow during maximum burial was in the range of 40 75 mw m2 heat flow in the krasnoarmeisk monocline and the kalmius torets depression increased in a northeastward direction from 40 to 55 mw m2 heat flow at the eastern edge of the kalmius torets depression and in the south syncline was in the range of 60 75 mw m2 and increased towards the southeast the resulting coalification pattern in this area was overprinted by thermal events in the northern krasnoarmeisk monocline and the south syncline these are probably related to permian magmatic intrusions coked coal occurs at the contact to presumed permian sills and dikes southwest of donetsk

structure of the crust and upper mantle beneath the great valley and allegheny plateau of eastern pennsylvania 2 gravity modeling and migration of wide angle reflection data linear inversion of p composites for three different profiles suggests that the lower crust beneath eastern pennsylvania consists of material with high averaged p wave velocities 6 8 7 5 km s compared with 6 4 7 1 km s for most crustal models derived for surrounding areas within the appalachians and the grenville province of the canadian shield interpretations of these velocities in terms of rock type are limited by the low resolving power of the data and by the nonuniqueness in inferring rock type from p wave velocity alone the high averaged p wave velocities could be associated with substantial volumes of mafic rock perhaps emplaced by underplating or with high grade metamorphic assemblages of intermediate composition and sedimentary origin similar to those found in the ivrea zone in northern italy because of the sparseness of the s wave data averaged shear wave velocities are not well enough resolved over most depth ranges to distinguish among the different compositional models computations of gravity anomalies for two dimensional models using various linear velocity density relations however suggest that at least part of the crust beneath the scranton gravity high is mafic moreover if the entire basement section beneath this anomaly consists of mafic material then the gravity studies indicate that the lower crust beneath the great valley must be mafic as well migrated shot gathers show a concentration of reflectors at depths between 35 and 45 km a result that is controlled in part by the limited range of offsets used but that is also consistent with recent observations of a highly reflective lower crust reflections that are migrated to depths within the uppermost mantle could be multiples or primary reflections from upper mantle layering although the data are rather sparse the interpretation of these later arrivals as primary reflections is supported by their small ray parameters which suggests that they are not converted phases and by their large relative amplitudes which suggests that they are not multiples layering within the upper mantle could be in the form of alternating high and low velocity zones perhaps related to emplacement of eclogites or garnet granulites in the uppermost mantle during the process of underplating

stratigraphy and sequence stratigraphy of the moscovian in the donets basin new results are presented on the stratigraphy based on fusulinids and palynomorphs and the sequence stratigraphy of the moscovian in the donets basin they have been developed by comparison of our observations on cross sections near artemovsk and the published coal mine logs of artemovsk geological survey the moscovian of the donets basin is equivalent to the uppermost westphalian b and the westphalian c and d of western europe in the donets basin the moscovian forms a second order sequence as in the moscow basin that can be subdivided into four third order sequences subdivided into fourth order sequences the upper bashkirian shows two fourth order sequences the vereian exhibits two fourth order sequences the kashirian shows four fourth order sequences the podolskian offers eight fourth order sequences the myatchkovian presents four fourth order sequences these sequences begin with an erosive base and show a succession of elementary sequences with fluvial sandstone coal seam limestone and deltaic facies the fluvial sandstone corresponds with an aggradation period the coal and the limestone with a transgressive period and the deltaic facies with a progradation period a decrease of the sandstone thickness and an increase of the marine deposits that are transgressive and regressive upwards are observed from the base to the top of sequences these fourth order sequences present a higher spatial amplitude than the third order sequence and obscure these sequences the second order sequence equivalent to the moscovian shows a lowstand system tract with more fluvial sandstone in the lower part of the vereian a transgressive system tract in the upper part of the vereian tsinskaya and kashirian a maximum flooding period during the podolskian and lower part of the myatchkovian with more marine facies and a highstand system tract in the upper part of the myatchkovian with more lagoonal and swampy palaeoenvironments the sequences are controlled by the regional tectonic subsidence in the graben and the uplift of the horsts and or by eustasy with either a plate tectonic or a glacial origin other investigations particularly radiometric dating will be useful for solving this problem

tectonic variation in the dniepr donets basin from automated modelling of backstripped subsidence curves abstract the multiphase rift evolution of the dniepr donets dd basin is analysed by 1d backstripping and tectonic modelling of 66 stratigraphic sections mostly from well data distributed throughout the basin the backstripping results illustrate strong temporal and lateral variations in tectonic subsidence it is minor during an inceptive pre rift phase givetian early frasnian 380 8 370 ma and does not show clear spatial correlations within the dd basin framework the main rift phase frasnian famennian 370 362 5 ma corresponds to an acceleration in subsidence rates with tectonic subsidence up to 1500 m along the basin axis displaying a slight increase from the northwest to the southeast strong lateral variations perpendicular to the basin axis reflect the effects of major basin border faults a rift phase in the visean 345 340 ma is characterised by relatively minor subsidence up to about 500 m except for some wells in the southeast following a stage of extremely low rates of deposition in the earliest carboniferous the end of this rift phase can be taken to mark the onset of convex subsidence patterns in the later carboniferous and permian typical in shape of post rift thermal subsidence but significantly increasing in magnitude from northwest to southeast in the basin this trend shows no one to one relationship with late devonian syn rift subsidence the tectonic subsidence curves have been modelled using lithospheric stretching assumptions allowing different stretching factors for the crustal and sub crustal lithosphere and the incorporation of finite and multiple stretching phases a numerical technique was developed that automatically finds best fit stretching parameters for part or all of the tectonic subsidence data given the specification of onset and duration of the various rifting events maps of the 1d modelling results display intrabasinal variations in terms of timing and magnitude of rifting the results indicate that the observed spatial and temporal variations of tectonic subsidence in the dd basin specifically the increasing ratio of carboniferous to late devonian subsidence from northwest to southeast cannot be explained by either a uniform or depth dependent stretching model adopting only a single frasnian famennian rift phase a two phase model in which a significant part of carboniferous tectonic subsidence is related to visean rift activity strongly dominated by sub crustal lithospheric attenuation provides a satisfactory fit to the data although the tectonic implications of such a model are not easily reconcilable by independent constraints a semi quantitative investigation of the possible role of withdrawal of underlying devonian salt during the carboniferous to produce additional post devonian rift phase sediment accommodation space suggests that the effects of such a mechanism could be significant but that they are unlikely to preclude the necessity of the visean rifting event to explain the carboniferous basin evolution

1891 1883 ma southern bastar cuddapah mafic igneous events india a newly recognized large igneous province abstract a newly recognized remnant of a paleoproterozoic large igneous province has been identified in the southern bastar craton and nearby cuddapah basin from the adjacent dharwar craton india high precision u pb dates of 1891 1 0 9 ma baddeleyite and 1883 0 1 4 ma baddeleyite and zircon for two se trending mafic dykes from the bd2 dyke swarm southern bastar craton and 1885 4 3 1 ma baddeleyite for a mafic sill from the cuddapah basin indicate the existence of 1891 1883 ma mafic magmatism that spans an area of at least 90 000 km2 in the south indian shield this record of 1 9 ga mafic ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south eastern margin of the south indian shield is a widespread geologic phenomenon on earth similar periods of intraplate mafic ultramafic magmatism occur along the margin of the superior craton in north america 1 88 ga molson large igneous province and in southern africa along the northern margin of the kaapvaal craton 1 88 1 87 ga dolerite sills intruding the waterberg group existing paleomagnetic data for the molson and waterberg 1 88 ga large igneous provinces indicate that the superior and kalahari cratons were at similar paleolatitudes at 1 88 ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a limpopo like 2 0 ga deformation zone in the superior province the widespread occurrence of 1 88 ga intraplate and plate margin mafic magmatism and basin development in numerous archean cratons worldwide likely reflects a period of global scale mantle upwelling or enhanced mantle plume activity at this time

coalification pattern and thermal modelling of the permo carboniferous saar basin sw germany abstract palaeo heat flow values and thicknesses of eroded permo carboniferous sediments in the saar basin were evaluated using one dimensional thermal modelling techniques thermal burial and erosion histories for 16 wells were calibrated by comparing measured and calculated vitrinite reflectance using the kinetic easy r o algorithm and by comparing measured and calculated temperature data on the basis of 37 wells coalification maps were constructed revealing a syn kinematic coalification pattern thermal maturity of the sediments can only be explained by deep burial and moderate heat flows during time of maximum burial i e in the permo carboniferous calculated heat flow data range between 50 and 75 mw m 2 which implies a crustal thickness between 30 and 40 km during the time of maximum burial these values are in accordance with the geodynamic setting of the basin the influence of the permo carboniferous volcanism on the palaeo temperature distribution was overwhelmed by the subsequent deep burial during permian times between 1800 and 3000 m of permo carboniferous sediments were eroded different sedimentation and erosion histories are characteristic for anticlines and synclines respectively

paleoproterozoic basin development and sedimentation in the lake superior region north america abstract the peneplaned archean craton in the lake superior region was the platform upon which a continental margin assemblage was deposited extension resulted in localized rifts that received thicker accumulations of sediments and volcanic rocks than did adjacent parts of the platform seas transgressed onto the continent several times and an ocean basin opened south of the present day lake superior island arcs that formed during subduction collided with the craton margin as the ocean basin closed oceanic crust is poorly preserved as a dismembered ophiolite sequence the arc volcanics are preserved as the wisconsin magmatic terranes the collision resulted in a fold and thrust belt known as the penokean orogen to the north of the fold and thrust belt a northward migrating foreland basin the animikie basin developed thick turbidite successions were deposited along the basin axis and terrigenous clastics and lake superior type iron formation were deposited on the shelf along the northern margin of the basin the primary paleoclimatic indicators are 1 glaciogenic rocks at the base of the paleoproterozoic succession in michigan indicating ice house conditions 2 remnants of a paleosol on the glaciogenic rocks indicative of deep weathering probably under subtropical conditions and therefore of greenhouse conditions and 3 carbonate minerals after gypsum halite and anhydrite in stromatolitic dolomite indicative of aridity three second order depositional sequences are bounded by major unconformities and can be correlated throughout the lake superior region

the 40ar 39ar dating of magmatic activity in the donbas fold belt and the scythian platform eastern european craton 1 the donbas fold belt is the compressionally deformed southeasternmost part of the intracratonic late paleozoic dniepr donets rift basin it is situated in an intracratonic setting but close to the southern margin of the east european craton south of which lies the scythian platform a range of igneous rocks from the donbas fold belt and the scythian platform were dated by the 40ar 39ar method in order to constrain the ages of magmatic activity in these areas and compare them the plateau ages from the south margin of the donbas fold belt vary from 151 4 4 7 ma to 278 1 5 3 ma and define three main age groups middle late jurassic middle late triassic and early permian the age spectra obtained from the scythian platform samples are often disturbed as a result of limited alteration the proposed ages plateau and pseudoplateau vary from 174 4 2 1 ma to 243 7 1 4 ma and two major age groups are defined in early carboniferous and triassic jurassic times the early permian 285 270 ma and early triassic 245 250 ma ages of magmatic activity are the same in both areas in the late triassic the ages of magmatic activity are slightly different 220 and 205 ma and they are entirely different thereafter these data can be interpreted as indicating a mantle plume as common deep magmatic source

a new geodynamical thermal model of rift evolution with application to the dnieper donets basin ukraine abstract a model of the lithosphere incorporating both dynamic and thermal processes has been developed by solving a coupled system of differential equations governing stress and temperature in a 2 d block structured geophysical medium designed to study the roles of tectonic and geothermal factors in continental rift formation and evolution the model incorporates syn sedimentary and or erosional faulting of an upper crustal layer and allows the thermal regime of the lithosphere to be calculated through time the method has been applied to the formation and evolution of the northwest dnieper donets basin ddb along one regional profile controlled by seismic and other geophysical and subsurface data the results are compared with those published earlier for the same profile using different methods of modelling the rift and early post rift development of the region the final basement geometry at the end of the rifting stage predicted by the new model satisfactorily corresponds with geological data and is qualitatively similar to that predicted by the previously published models however the new results imply an important role for an active mechanism during rifting that generates greater mantle thinning than crustal thinning and elevated temperatures in the upper mantle beneath the rift

the donbas foldbelt its relationships with the uninverted donets segment of the dniepr donets basin ukraine abstract the donbas foldbelt df is a thrust faulted and folded inverted segment of the dniepr donets basin ddb it lies between the scythian and east european platforms north of the black sea and is conventionally thought to have formed in the early permian as part of the late palaeozoic hercynian uralian orogenic frame of cratonic europe the ddb itself formed as a result of late devonian intracratonic rifting and contains a thick up to 22 km late palaeozoic and mesozoic sedimentary succession the deformed strata preserved at the erosional surface of the df are mainly carboniferous the donets segment of the ddb displays mild inversion structures that are transitional to those in the df recently acquired regional seismic reflection data in the donets part of the ddb allow these structures to be imaged in the subsurface for the first time a widespread early permian unconformity occurring throughout the ddb is much more pronounced on its southern margin than on its northern one and appears to be related to profound uplift of the southern flank of the basin and the neighbouring ukrainian shield rather than to crustal shortening faults associated with the early permian unconformity are extensional in style gentle folds and other local structures in the southern flank and axis of the donets segment are mainly located in areas associated with early permian salt movements no significant development of compressional structures of early permian age can be seen in the seismic data where it is available in contrast there is ample evidence of latest cretaceous earliest tertiary compressional deformation in the ddb including the subsurface expression of structures along strike of the main folds of the df a review of geological evidence in the df also indicates that the main period of shortening that can be definitely constrained in time is latest cretaceous earliest tertiary the eastern part of the df records intense late triassic aged cimmerian deformation but none of clearly permian age it is tentatively concluded that the main phases of trans compressional tectonics forming the df were cimmerian and especially alpine rather than hercynian uralian

major geological features and lateral variation of crustal structure in southern new england abstract rg dispersion studies in southern new england sne provide a basis for comparing lateral variation in crustal structure with geological features rg waves reveal lateral variations at depths ranging from near the surface down to a few kilometers the similarity between rg results and those of other geophysical studies suggests that variations revealed by rg studies penetrate into the middle of the crust if not deeper the waterbury dispersion region wdr named after a local geological structure is characterized by the highest rg group velocities in sne 2 9 3 1 km s at a period of 1 s these higher velocities may be due to rocks enriched in oceanic type crust and or granulite facies metamorphic rocks the hartford and new haven dispersion regions hdr and nhdr comprise the northern and southern parts of the mesozoic hartford rift basin respectively the hdr is characterized by the lowest group velocities in sne 2 1 2 4 km s at a period of 1 s these lower velocities appear to be related to relatively thick pleistocene glacial sediments overlying a thick sequence of mesozoic sedimentary rocks higher velocities in the nhdr are attributed to a thinner cover of glacial sediments and a thinner package of sedimentary rocks these younger rocks overlie metamorphic basement which is on average closer to the surface in the nhdr than in the hdr the bronson avalon dispersion region badr east of the hartford rift basin represents several terranes that are geologically diverse but at the scale of this study not differentiated by rg dispersion the seismic structure beneath the badr appears to be quite homogeneous group velocities in this region range from about 2 6 to 2 8 km s at a period of 1 s the badr is interpreted to consist of stacked layers of gently dipping to nearly flat lying thrust sheets the torrington dispersion region tdr lies north of the wdr and west of the hdr and has group velocities similar to those of the badr

distribution of thermogenic methane in carboniferous coal seams of the donets basin ukraine applications to exploitation of methane and forecast of mining hazards abstract the main purpose of this contribution is to estimate methane production and to define its migration paths and storage in the donets basin formations for exploitation of methane and forecast of mining hazards in order to study methane migration and storage maps of production calculated by 2d modelling adsorption capacity of methane in coal and present day methane contents were constructed for an altitude of 300 m close to 500 m depth in this basin the results show that three principal factors influenced the methane migration and accumulation in donets basin 1 faults that acted as migration pathways 2 a replacement of thermogenic methane by endogenic co 2 in the central and se parts and 3 the occurrence of magmatic events in some areas in this basin finally in donbas the areas with the highest methane potential and the maximum risk of outburst are not the areas with anthracite that produce the highest volume of methane but areas with volatile bituminous coals where an impermeable cover preserved the accumulated gas until the cenozoic and where dextral shear belts facilitated its migration

crustal profile of mountain belt cocorp deep seismic reflection profiling in new england appalachians and implications for architecture of convergent mountain chains relatively shallow reflections from beneath the taconic allochthon and green mountain anticlinorium are suggested to mark a zone of detachment that carries precambrian grenville basement of the green mountains in its upper plate the data suggest that tectonic thickening of the shelf sedimentary and synorogenic flysch sequence beneath the taconic allochthon has occurred and that major thrust fault systems champlain thrust of western vermont which imbricate shelf lithologies project downplunge into the seismic profile eastward dipping reflections beneath the east flank of the green mountains appear to project across the connecticut river valley into new hampshire because some of these reflections can be projected into an exposed zone of probable thrust imbricated precambrian grenville basement and younger metasediments there is a strong implication that similar rock types exist in the deeper crust beneath new hampshire the gross geometry of the eastward dipping zone is a large thrust ramp that facilitated faulting of continental basement in the green mountains to higher structural levels thus suggesting the anticlinorium is a large hanging wall structure or ramp anticlinorium highly deformed satellitic massifs of grenville basement such as the chester dome and sub silurian and silurian devonian rocks of the bronson hill anticlinorium and merrimack synclinorium are probably transported along intracrustal detachments as well data suggest the possiblity of a tectonically buried continental margin transition zone much like that interpreted for the southern appalachians this zone would have been preserved from prior rifting of the proto atlantic ocean and its inherited geometry could have controlled subsequent convergent deformation during appalachian orogenesis although regional deep seismic reflection profiling has not been carried out across the alps existing data imply lateral changes in crustal reflection character similar to those observed in the appalachians deep seismic reflection data from convergent mountain belts raises the possibility of such preserved transition zones beneath transported rocks and provides an alternative interpretation to lithosphere penetrating sutures in explaining lateral geologic and geophysical contrasts in the crust modified journal abstract

a new constraint on the composition of the topmost continental mantle anomalously different depth increases of p and s velocity summary compared to clear crustal p and s waves as well as a strong refracted pn wave propagating in the topmost mantle i e 10 to 15 km below the moho an anomalously weak appearance of the corresponding refracted shear wave sn is observed on refraction seismic profiles in sw germany france coastal maine ne united states and fennoscandia it is possible that the observation of pn pmp ratios close to unity combined with small sn sms ratios i e small sn amplitudes is typical for the continental uppermost mantle since this was observed for quite different types of continental crust it is shown that the observed phenomenon is not a source effect several possible causes to explain the observations are studied also with the aid of synthetic seismograms the effects of temperature attentuation and anisotropy have been investigated their influence cannot explain the observations the most likely candidate is a depth increasing vp vs ratio an increase in the order of 0 027 over a depth range of 10 km forcing p and s waves to propagate on different paths in the topmost mantle the observed phenomenon provides new constraints on the change of composition with depth for the crust mantle transition zone with basalt depletion as the most likely explanation

mercury and trace element contents of donbas coals and associated mine water in the vicinity of donetsk ukraine abstract mercury rich coals in the donets basin donbas region of ukraine were sampled in active underground mines to assess the levels of potentially harmful elements and the potential for dispersion of metals through use of this coal for 29 samples representing c 11 to m 3 carboniferous coals mercury contents range from 0 02 to 3 5 ppm whole coal dry basis mercury is well correlated with pyritic sulfur 0 01 to 3 2 wt with an r 2 of 0 614 one outlier excluded sulfides in these samples show enrichment of minor constituents in late stage pyrite formed as a result of interaction of coal with hydrothermal fluids mine water sampled at depth and at surface collection points does not show enrichment of trace metals at harmful levels indicating pyrite stability at subsurface conditions four samples of coal exposed in the defunct open cast nikitovka mercury mines in gorlovka have extreme mercury contents of 12 8 to 25 5 ppm this coal was formerly produced as a byproduct of extracting sandstone hosted cinnabar ore access to these workings is unrestricted and small amounts of extreme mercury rich coal are collected for domestic use posing a limited human health hazard more widespread hazards are posed by the abandoned nikitovka mercury processing plant the extensive mercury mine tailings and mercury enrichment of soils extending into residential areas of gorlovka

high temperature programmed pyrolysis of paleozoic source rocks from northern germany and adjacent areas and its thermodynamic constraints abstract in order to determine the hydrocarbon generating potential of high maturity source rocks 2 rmax vr it is necessary to conduct pyrolysis experiments at high temperatures however kinetic and thermodynamic considerations suggest that with increasing temperatures the gas forming reactions become more and more unrealistic since there are no reliable alternative physical and chemical methods for the evaluation of late hydrocarbon potential pyrolysis conditions have to be optimized so as to minimize the secondary degradation of methane this necessitates the use of high temperature programmed micropyrolysis which permits the quick removal of pyrolysis products from the hot reaction zone this paper discusses how a pyrolysis procedure that is similar to rock eval pyrolysis was used to investigate the hydrocarbon potential of highly mature paleozoic rocks from northern germany and adjacent areas the objective of the experiments was to determine whether small amounts of dry gas formed at maturities beyond 2 rmax can fill commercially interesting gas reservoirs the finding was that coals coaly shales and also cambro ordovician alum shales retain a sufficiently large methane generating potential at high maturities in many of the rocks pyrolyzed the kerogen clearly contained organic material of different structures and different thermal stability these kerogen fractions decomposed one after another at different maturity stages an isotopic inversion of the carbon in the methane released could be observed as soon as a new and more stable structure was degraded

new late paleozoic paleopoles from the donbas foldbelt ukraine implications for the pangea a vs b controversy article i nfo the carboniferous to early permian apparent polar wander apw path for eurasia is not well constrained because of the paucity of reliable paleomagnetic poles this is at least partly responsible for the pangea a vs b controversy in the early permian is the overlap between the northern and southern continents during the early permian caused by a lack of reliable paleomagnetic data pangea a or must a large displacement along a mega shear zone be invoked pangea b here we present results from six paleomagnetic sampling sites ranging in age from the early carboniferous to the early permian from sedimentary rocks in the donbas foldbelt ukraine to improve the carboniferous early permian apw path for eurasia and to contribute to solving the pangea a vs b controversy six time intervals were sampled in the donbas foldbelt eastern ukraine which was filled with sediments and volcanic units during the late devonian to permian syn and post rift subsidence phases we present results from sediments that were corrected for inclination shallowing with the elongation inclination e i method we conclude that there is a general northward movement of the donbas foldbelt the resulting paleolatitudes are slightly but generally significantly higher than expected from existing apw paths the late carboniferous to early permian data provide three new reliable paleopoles for eurasia the early permian pole does not necessarily require a pangea b reconstruction it results in higher paleolatitudes for laurussia in the early permian and removes the overlap between gondwana and pangea we also reconstructed the position of laurussia based on carboniferous laurentian poles recently corrected for inclination shallowing which clearly favours a pangea b configuration it seems that the pangea a vs b debate is as lively as before the three early carboniferous paleopoles give reliable paleolatitudes but declinations significantly deviate from the expected directions we argue that the southernmost part of the donbas foldbelt underwent a counterclockwise rotation related to mesozoic compressional events that are recognised in paleostress analyses

predicting methane accumulations generated from humic carboniferous coals in the donbas fold belt ukraine the numerical modeling of the ukrainian part of the donbas fold belt indicates that the coalification pattern was controlled mainly by the maximum burial depth of coal seams and the heat flow hf 40 75 mw m2 during the permian the coalification pattern was overprinted by magmatic events during the late permian in the south syncline 150 mw m2 and during the permian triassic in the north of the krasnoarmeisk region 120 mw m2 the coalification pattern shows a strong increase in vitrinite reflectance values toward the east and southeastern parts of the study area likely caused by 1 an eastward increase in burial depth 2 a probable eastward increase in hf and 3 probable magmatic activity an increase in total erosion toward the eastern and southeastern parts was also observed with a maximum erosional amount of approximately 8 km 5 mi in the southeastern part of the study area the basin modeling of this area predicts that the main phase of hydrocarbon generation occurred during the carboniferous early permian subsidence the magmatic events that occurred during the permian triassic caused renewed pulses of hydrocarbon generation a large amount of the generated hydrocarbons was lost to the surface because of a lack of seals however the numerical simulation predicts accumulations of about 2 tcf 57 billion m3 of methane generated from carboniferous coals in the south and main synclines where lower permian seal rocks are preserved finally this study provides data on methane resources along the northern flank of the basin which remains a significant frontier for natural gas exploration

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

the penokean orogeny in the lake superior region abstract the penokean orogeny began at about 1880 ma when an oceanic arc now the pembine wausau terrane collided with the southern margin of the archean superior craton marking the end of a period of south directed subduction the docking of the buoyant craton to the arc resulted in a subduction jump to the south and development of back arc extension both in the initial arc and adjacent craton margin to the north a belt of volcanogenic massive sulfide deposits formed in the extending back arc rift within the arc synchronous extension and subsidence of the superior craton resulted in a broad shallow sea characterized by volcanic grabens menominee group in northern michigan the classic lake superior banded iron formations including those in the marquette gogebic mesabi and gunflint iron ranges formed in that sea the newly established subduction zone caused continued arc volcanism until about 1850 ma when a fragment of archean crust now the basement of the marshfield terrane arrived at the subduction zone the convergence of archean blocks of the superior and marshfield cratons resulted in the major contractional phase of the penokean orogeny rocks of the pembine wausau arc were thrust northward onto the superior craton causing subsidence of a foreland basin in which sedimentation began at about 1850 ma in the south baraga group rocks and 1835 ma in the north rove and virginia formations a thick succession of arc derived turbidites constitutes most of the foreland basin fill along with lesser volcanic rocks in the southern fold and thrust belt tectonic thickening resulted in high grade metamorphism of the sediments by 1830 ma at this same time a suite of post tectonic plutons intruded the deformed sedimentary sequence and accreted arc terranes marking the end of the penokean orogeny the penokean orogen was strongly overprinted by younger tectonic and thermal events some of which were previously ascribed to the penokean principal among these was a period of vertical faulting in the archean basement and overlying paleoproterozoic strata this deformation is now known to have post dated the terminal penokean plutons by at least several tens of millions of years evidence of the penokean orogen is now largely confined to the lake superior region comparisons with more recent orogens formed by similar plate tectonic processes implies that significant parts of a once more extensive penokean orogen have been removed or overprinted by younger tectonic events

petrography and geochemistry of carboniferous coal seams in the donets basin ukraine implications for paleoecology abstract the carboniferous succession in the donets basin hosts about 130 seams each with a thickness over 0 45 m nine economically important seams from the south western donets basin are studied using organic petrographical inorganic geochemical and organic geochemical techniques the main aim of the study is the reconstruction of peat facies of serpukhovian mississippian and moscovian middle pennsylvanian coals formation of major coal seams commenced during serpukhovian times early serpukhovian coal accumulated in a relatively narrow shore zone and is rich in inertinite and liptinite very low ash yields low to moderate sulphur contents and upward increasing inertinite contents suggest coal deposition in raised mires moscovian coal has a significantly wider lateral extension and is generally rich in vitrinite coal properties vary widely in response to different peat facies low sulphur low ash k 7 coal was formed in a raised mire or in a low lying mire without detrital input l 1 and l 3 seams containing several fluvial partings were formed in low lying mires both seams are more than 2 m thick seams m 2 and m 3 contain high sulphur coal a consequence of deposition in a peat with marine influence in contrast syngenetic sulphur content is low in the m 5 1 upper seam which was formed in a lacustrine setting the late moscovian n 1 seam up to 2 4 m thick accumulated in a swamp with a vegetation rich in bryophytes and pteridophytes the properties of the n 1 seam are transitional between those of serpukhovian and other moscovian seams differences in maceral composition between serpukhovian and moscovian coals probably reflect changes in climate and vegetation type tuff layers are observed in the l 1 l 3 and m 3 seams the l 3 and m 3 seams contain abundant authigenic quartz trace element contents are high in many seams as contents are especially high in seams c 10 2 k 7 l 3 and m 3 ash in the l 3 seam contains up to 8000 ppm as co is enriched near the base of several seams maxima up to 2400 ppm occur in the ash of the k 7 and l 3 seams cd contents in ash are frequently as high as 30 or 40 ppm

basin evolution and coal geology of the donets basin ukraine russia an overview abstract the donets basin is a major coal mining district in eastern ukraine and adjacent portions of russia it comprises the donbas foldbelt which is the uplifted and compressionally deformed part of the pripyat dniepr donets pdd basin and the significantly less deformed western donbas region the pdd basin is a late devonian rift structure located within the east european craton thick coal measures formed during the post rift stage of the basin in serpukhovian to moscovian times when about 130 seams each with a thickness over 0 45 m have been deposited early serpukhovian coal accumulated in a relatively narrow shore zone it is rich in inertinite and liptinite and very low in ash bashkirian and moscovian coal have a significantly wider lateral extension and are generally rich in vitrinite bashkirian and moscovian coal seams usually have high ash yields 12 18 and high sulfur contents 2 5 3 5 but these data vary significantly depending on peat facies coal rank ranges from subbituminous to anthracite and is mainly controlled by the depth of the seams and the heat flow during maximum permian burial permo triassic thermal events locally overprinted the resulting coalification pattern coked coal occurs at the contact to presumed permian sills and dikes southwest of donetsk deep permian burial was followed by major permian and mesozoic uplift events the donets basin hosts proven reserves in the order of 60 gt at the exploitable depth the thickness of coal seams currently mined is in the range of 0 6 to 2 5 m production during 2009 was 68 7 mt in the ukrainian and 4 9 mt in the russian part of the basin coal mines in the donets basin are among the gassiest in the world the average methane content of coal is 14 7 m t but numerous seams have significantly higher gas content the high methane content presents a severe mine safety problem on the other hand it represents also a high potential for coal mine bed methane projects emissions of coal gas released by mining and related structurally induced underground hazards coal and gas outbursts are a major problem for safe and efficient coal exploitation in the basin

reflection seismic measurements across the granulite belt of the polar profile in the northern baltic shield northern finland abstract reflection seismic measurements were carried out in 1985 on the central part of the polar refraction seismic profile in northern finland the survey was planned and executed jointly by the universities of helsinki uppsala and hamburg using digital equipment with a total of 144 channels by repeating the shots and moving the geophone spreads every day we were able to observe a 42 50 km recording spread referred to reflection elements a line of 84 km total length through the source receiver midpoints was recorded we processed the results up to normal moveout corrected time sections a number of reflectors dipping 8 15 to the northeast were recorded in the lapland granulite belt range these represent a system of sheared granulites which were observed on the surface in the southern part of the profile from gravity modelling the bottom of the dipping layers coincides with the lower boundary of the granulites between the depths of 22 and 35 km the crust in this area seems to be transparent to seismic signals this leads to the assumption that the middle part of the crust is characterized by gentle velocity and density gradients the crust mantle boundary seems to be a layered moho with good reflectors lying at depths between 40 and 44 km

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

dobrefraction 99 velocity model of the crust and upper mantle beneath the donbas foldbelt east ukraine abstract the donbas foldbelt df is the uplifted and deformed part of the up to 20 km thick dniepr donets basin ddb that formed as the result of rifting of the east european craton eec in the late devonian uplift especially of the southern margin of the basin occurred in early permian times in a trans tensional tectonic stress regime while folding and reverse faulting mainly occurred later mainly during the late cretaceous a seismic refraction wide angle reflection survey was carried out in 1999 dobrefraction 99 to complement existing deep seismic sounding dss data from the area that did not record significant pn phase arrivals because of insufficient maximum offset dobrefraction 99 comprised some 245 recording stations along a line of 360 km length with 11 in line shot points as well as a 100 km away parallel 190 km long subsidiary fan profile the main profile runs between the shores of the azov sea in the south to the ukraine russia border in the north across the azov massif ukrainian shield the foldbelt and the voronezh massif particular scientific targets include the nature of the crust mantle transition and the geometry of crustal upper mantle structures related to rifting and subsequent basin inversion tomographic inversion as well as ray trace based velocity modelling has been carried out the velocity signature of the sedimentary basin itself is well resolved indicating an asymmetric form with a steeper basement surface in the south than in the north and a total thickness of about 20 km a thick 10 km high velocity 6 9 km s lower crustal body lies beneath the rift basin itself offset slightly to the north compared to the main basin depocentre likely related to the rifting processes velocities in the crust below the ukrainian shield south of the foldbelt are in general higher than beneath the voronezh massif to the north the moho displays only slight topography around a depth of 40 km along the profile

constraints on the upper crustal structure of the long valley mono craters volcanic complex eastern california from seismic refraction measurements during the summers of 1982 and 1983 field work was completed on 10 new seismic refraction profiles in the long valley mono craters region located within the technically active zone between the eastern sierra nevada and the basin and range province the four profiles presented here sample the upper 7 10 km of the crust within the western half of long valley cladera the mono craters ring fracture system and the normal crust north and northeast of long valley the entire area shares a common crystalline basement consisting primarily of mesozoic granitic rocks at a depth of 2 km beneath the topographic surface the p wave velocity is uniformly 5 6 km s beneath which the velocity increases with a gradient of about 0 1 s 1 clear secondary arrivals observed on a profile crossing the west part of the caldera support evidence from 1972 seismic refraction profiles for a reflecting boundary at a depth of 7 8 km beneath the west margin of the resurgent dome which may represent the top of a magma chamber structural details resolved in the upper 2 km of the crust lead to the following conclusions 1 p wave velocities in the crystalline basement at depths shallower than 2 km vary from 3 6 to 5 0 km s this variation reflects differences in the degree of fracturing of the upper portion of the basement 2 an apparently homogeneous basement in the upper 7 10 km beneath the mono craters ring fracture system indicates that any extensive magma chamber must be at least 10 km deep there 3 the downdropped crystalline basement beneath the western half of long valley caldera dips genty 5 10 to the northeast apparent offsets along steeply dipping caldera bounding faults are 1 0 1 7 km along the northern western and southern sides of the caldera with largest offsets in the north 4 rocks forming the caldera fill fall into essentially three p wave velocity groups from the surface downward these velocity groups are 100 400 of 1 2 1 8 km s material corresponding to unconsolidated fluvial or lacustrine deposits or highly fractured rhyolite flows 200 400 m of 2 8 3 1 km s material corresponding to sparsely jointed postcaldera rhyolite rhyodacite and basalt flows and approximately 1000 m of 3 9 4 4 km s material corresponding to deposits of bishop tuff

stratigraphic distribution of macerals and biomarkers in the donets basin implications for paleoecology paleoclimatology and eustacy abstract more than one hundred and thirty coal seams and coaly layers occur in the donets basin donbas twenty eight 52 samples of them ranging in age from serpukhovian late mississipian to gzhelian late pennsylvanian 33 clastics and three limestones were studied in terms of maceral composition sulphur contents and biomarker distribution diterpanes are used to estimate the contribution of different groups of plants and the height of the water table in the swamp hopanes are a measure of bacterial activity in the peat and steranes indicate the relative input of wood and algae stratigraphic trends in these parameters are discussed in relation to paleoenvironment climatic changes and eustacy a tropical climate prevailed in the donbas from serpukhovian to kasimovian times nevertheless periods with drier and wetter conditions can be distinguished based on maceral and biomarker data relatively dry conditions are observed during serpukhovian and vereian times whereas wetter climates with a maximum of coal deposition occurred during the late bashkirian most of the moscovian and the earliest kasimovian no economic coal seams are hosted in upper kasimovian and gzhelian deposits a result of a change to an arid climate our data also suggest climatic changes during sequences of different order for the second order third order and fourth order sequences relatively dry or wet conditions occurred during coal deposition in the lowstand systems tract an intermediate climate during the transgressive systems tract and the maximum flooding and a wet climate during the highstand systems tract the results for high frequency sequences support the cecil s paleoclimatic model an intermediate paleoclimate during lst sandstone and levee siltstone a wet climate during early tst coal and a dry climate during late tst limestone mfs claystone and hst deltaic siltstone coals deposited during maximum flooding periods are more enriched in c27 steranes derived from algae and contain lower proportions of c29 steranes derived from the wood of higher plants

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

a comparison of reflection and refraction processing and interpretation methods applied to conventional refraction data from coastal maine abstract in 1984 the u s geological society collected 850 km of refraction data in lines parallel and perpendicular to regional strike of the appalachian orogen in maine and southeastern quebec a 100 km long strike line in coastal maine west of penobscot bay is here interpreted on the basis of both refracted and reflected phases techniques used in seismic reflection processing including normal movement velocity corrections and common mid point stacking were applied to the refraction data in order to enhance the visibility of reflected phases the geometries of the most laterally continuous reflections as defined by these techniques can be correlated with reflections seen on a crossing near vertical reflection profile conventional ray tracing analysis of refracted and wide angle reflected phases in the refraction data constrains the velocity structure to about 14 km depth and provides evidence for high veiocity material 6 5 km sec between 4 and 7 km depth and for lower velocities

the early proterozoic pre iron formation menominee group siliciclastic sediments of the southern lake superior region evidence for sedimentation in platform and basinal settings abstract the early proterozoic menominee group and equivalents of the southern lake superior region everywhere except in the marquette area michigan consist of quartzite gradationally overlain by iron formation with total thicknesses on the order of 0 5 1 km in the marquette area the siamo slate of the menominee group is present conformably between the basal quartzite and overlying iron formation and the total stratigraphic thickness is on the order of 2 km based on variations in regional stratigraphic thicknesses and sedimentary facies analysis it is suggested that the menominee group strata in the marquette area were deposited in a dominantly deeper water basinal environment whereas elsewhere in the lake superior region sedimentation took place in platformal and broad shallower wat r basinal environments the marquette basin filled with material deposited by turbidity currents and pelitic sediments whereas the platformal and broad basinal strata accumulated in a wave agitated offshore shelf environment banded iron formation occurs in both basinal and platformal environments indicating that deposition of these chemical sediments was perhaps independent of local variations in sedimentary tectonic setting the preferred regional tectonic setting evokes shelf and basin sedimentation on a rifted passive continental margin

sedimentary phosphate and associated fossil bacteria in a paleoproterozoic tidal flat in the 1 85 ga michigamme formation michigan usa abstract phosphorus is a nutrient fundamental to life and when it precipitates in modern environments bacteria are intimately involved in its release concentration and mineralization preserved fossil bacteria in phosphate crusts and grains from the ca 1850 million year old bijiki iron formation member of the michigamme formation michigan provide insight into the longevity and nature of this relationship the michigamme formation accumulated near the end of the earth s initial phosphogenic episode ca 2 2 and 1 8 ga to produce one of the first granular phosphorites phosphatic lithofacies consist of fine to medium sand sized francolite peloids concentrated on bedding surfaces in peritidal facies granular beds are up to 2 cm thick and peloids are often partially to completely replaced by dolomite and chert the grains contain organic matter and pyrite framboids that suggest bacterial breakdown of organic matter and bacterial sulfate reduction the peritidal nature of phosphorite in the michigamme formation is in sharp contrast to phanerozoic phosphogenic environments in deeper coastal upwelling settings peritidal settings were well suited for phosphogenesis under the very low oxygen and low dissolved sulfate levels of the paleoproterozoic as cyanobacteria produced oxygen in shallow water and evaporation led to increased sulfate concentrations such concomitant processes helped establish focused redox interfaces in the sediment that chemosynthetic bacterial communities sulfur oxidizers reducers forms that concentrate p and possibly iron oxidizers could exploit phosphate released from organic matter by heterotrophic bacteria and fe redox pumping was further concentrated by these chemotrophs a process that forms late neoproterozoic to phanerozoic phosphorites but on a much larger scale this early example of a granular phosphorite demonstrates that like their phanerozoic counterparts paleoproterozoic phosphorites are the concentrated indirectly biomineralized products of bacterial communities but unlike younger analogs which accumulated across subtidal shelves and shelf margins these ancient deposits formed only in tidal flat settings where phosphogenic redox processes could be established in the sediment from this early beginning the zone of phosphogenesis likely migrated into deeper water settings as oxygen and sulfate levels rose expanding the zone of chemosynthetic bacterial and associated phosphogenesis across the shelf

crustal architecture of the donets basin tectonic implications for diamond and mercury antimony mineralization abstract kimberlite like rocks and minor diamond finds are reported in the precambrian ukrainian shield south of the donets basin prolific mercury antimony mineralization occurs in carboniferous quartz arenites within the basin the tectonic setting is examined on the basis of recent data compilations and ongoing research in the ukraine and voronezh shield areas and the pripyat dnieper donets palaeorift in the donets region a straightforward analogy of any diamond district with the archangelsk province is not likely in the absence of a proterozoic shear comparable with the white sea belomorian mobile belt a deep reaching nnw striking lithosphere lineament is identified here as the kharkov donetsk lineament it transects the rift between the donets and dnieper basins the structures involved in this lineament have controlled palaeozoic sedimentation and the extent of late permian inversion of the donets basin during the inversion the lineament and associated deep reaching longitudinal structures provided pathways for the migration of mineralizing fluids from deep levels in the lower crust and upper mantle the intersection in the kharkov area of this lineament with a northeasterly striking lithosphere root should focus diamond exploration towards the northern shoulders of the rift the extreme attenuation of the crust beneath the donets basin relative to the western basins of the rift is associated with crustal detachment and subsidence during and possibly after inversion concomitant with emplacement of asthenospheric materials at higher levels together with the continued subsidence in the western donets basin during the late permian inversion this invokes a tectonic setting for the hg sb mineralization not unlike the orogenic collapse associated settings of hg sb deposits in western europe further investigation of the geodynamics of the donets basin would benefit from deep reflection seismics petrogenetic studies of magmatic products and their xenoliths and satellite remote sensing analysis

the moho in the northern basin and range province nevada along the cocorp 40 n seismic reflection transect cocorp seismic reflection profiles across nevada at about 40 n image a prominent essentially continuous band of reflectors at a two way traveltime of 9 to 11 s the approximate correspondence of this reflection time with estimates of the two way traveltime to the moho in this area provided by seismic refraction data suggests that the prominent reflections are from the moho the relief on these reflectors the reflection moho beneath nevada across a latitudinal transect of

on pollution of the biosphere in industrial areas the example of the donets coal basin abstract the distribution of heavy metals nitrates and other elements and compounds was studied in the donets basin biosphere the neomineralization processes in burning coal waste heaps were investigated more than 10 minerals were found for the first time in the donets basin the most frequently occurring are native sulphur and ammonium chloride in the process of geochemical mapping 30 000 soil samples were collected and analyzed the soil content of hg as pb zn cd and other elements was determined these concentrations often exceed the permissible level of concentration plc the soil mercury content is high in 90 of the donetsk city territory in some places it is 7 5 9 0 mg kg several times higher than the plc a high mercury concentration up to 19 mg kg was found in the soils of the central donbas area where the large coke chemical mercury and metallurgical plants are situated the air mercury content is about 25 30 pg l 1 pg 10 12 g in donetsk city and it is 300 1000 pg l or more near the nikitovsky mercury plant the background level is 1 6 1 8 pg l geochemical anomalies of arsenic mercury nitrates and other toxic elements and compounds were detected in 6000 donbas subsurface water samples near donetsk the arsenic content is up to 24 times and the mercury content is up to 3 10 times higher than the plc nitrate pollution of the donbas subsurface water covers 80 of the territory the nitrate content is as high as 500 1000 mg l and more plc is 45 mg l the sources of biosphere pollution by heavy metals and nitrates are coal waste heaps coal mines coke chemical plants metallurgical plants and other enterprises toxic pollution of the donbas biosphere negatively influences human health further systematic investigations of the donbas biosphere need to be conducted involving cooperation between scientists of different countries under joint programs

coal petrography mineralogy elemental compositions and palaeoenvironmental interpretation of late carboniferous coal seams in three wells from the kozlu coalfield zonguldak basin nw turkey abstract a number of coal seams of late carboniferous age in the coal bearing karadon kozlu and alacaagzi formations have been mined in several deep underground mines in the zonguldak basin nw turkey for this study a total of 154 coal core samples were collected from three research wells that were drilled in the tectonically complex settings of the kozlu coalfield all the coal samples were studied by means of coal petrography mineralogy and geochemistry special attention was given to the compositions and origins of fracture cleat filling minerals that were identified by sem edx on polished blocks the coal seams investigated are of bituminous rank they are characterized by low total sulphur contents 1 0 on dry basis and high gross calorific values 22 5 40 2 mj kg on dry ash free basis whereas ash yields and volatile matter contents are variable x ray powder diffraction data indicate that the mineralogical compositions of the studied coal seams are rather similar and clay minerals along with quartz and carbonate minerals were identified in almost all seams the statistical evaluations and sem data show that some elements such as mg ti zr nb and th are generally affiliated with silicate minerals whereas elements like cu zn mo and pb are mainly associated with sulphide minerals the silicate minerals are generally detrital and the majority of carbonate minerals are of epigenetic origin the epigenetic carbonate and sulphide minerals suggest that circulated solutions within coal seams were mainly derived from ca2 rich solutions leached from overlying formations such as cretaceous aged zonguldak formations and from hydrothermal solutions that likely were derived from andesitic dykes within the basin the regional tectonic activities during coalification seem to have deformed coal bearing formations and therefore intra basinal solutions could have penetrated into the studied coal seams the epigenetic mineralisation also resulted in elemental enrichments and elevated ash yields total sulphur and volatile matter contents in some coal seams thus deformation during coalification controlled some coal quality parameters in the studied wells the coal facies diagrams suggest that palaeomires mostly accumulated under limno telmatic conditions whereas a telmatic environment was more common in palaeomires of the kozlu formation coal petrography suggests that peat forming vegetation and water tables in palaeomires were changeable during the late carboniferous

migration of common shot gathers three depth migration methods which operate on common shot data are presented the first migration method maps digitized horizons from the x t domain to the x z domain because this method is based on ray tracing its computation time is short it is suggested for iterative velocity analysis the other two migration methods map the entire common shot gather into a depth section the common shot migration requires calculation of the arrival time of the direct wave from the source to all the depth points and is done through a direct solution of the eikonal equation all three methods are suitable for areas with both lateral and vertical velocity variation

the evolution of the avalonian plate abstract the avalon platform of newfoundland is the type locality of the avalonian plate that is characterized by late precambrian volcanic and clastic rocks marine at the bottom and terrestrial at the top all are intruded by 650 550 ma granites late precambrian rocks in the southern british isles are similar in both areas northeastern parts of the belt are affected by deformation and metamorphism that have orogenic aspects the orogeny is referred to as the avalonian in newfoundland and monian in britain to the southeast of the avalonian rocks in europe lies another late precambrian cadomian orogenic belt of rocks as a part of the pan african orogenic belt the cadomian and avalonian belts extend into north africa morocco since these belts are ophiolite bearing it is suggested that the plate was bordered by oceanic domains it is therefore proposed that a microcontinental volcanic arc that was generated in the late precambrian was orogenically deformed by collision with north america europe and africa and survived as a coherent terrain until the late carboniferous

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

numerical modelling of the thermal evolution of the northwestern dniepr donets basin ukraine abstract the dniepr donets basin ddb is a late devonian rift structure located within the east european craton numerical heat flow models for 13 wells calibrated with new maturity data were used to evaluate temporal and lateral heat flow variations in the northwestern part of the basin the numerical models suggest that heat flow was relatively high during late carboniferous and or permian times the relatively high heat flow is probably related to an early permian re activation of tectonic activity reconstructed early permian heat flow values along the axial zone of the rift are about 60 mw m2 and increase to 90 mw m2 along the northern basin margin these values are higher than those expected from tectonic models considering a single late devonian rifting phase the calibration data are not sensitive to variations in the devonian carboniferous heat flow therefore the models do not allow deciding whether heat flows remained high after the devonian rifting or whether the reconstructed permian heat flows represent a separate heating event analysis of the vitrinite reflectance data suggest that the northeastern dniepr donets basin is characterised by a low mesozoic heat flow 30 35 mw m2 whereas the present day heat flow is about 45 mw m2

precambrian atmospheric oxygen and banded iron formations a delayed ocean model abstract evidence and arguments increasingly in favor of free oxygen in the earth s early atmosphere renew the constraints on the environmental significance of precambrian banded iron formations an early moist greenhouse atmosphere with a delay in and gradual growth of the world oceans offers a mechanism to provide a geochemically and mechanically segregated source of iron and silica for banded iron formation while simultaneously cannibalizing evidence for early archean red beds the model supports the high rates of weathering necessary to remove initially outgassed co2 quickly favors continuity in early biogenic evolution provides a mechanism for hydrogen and strontium isotope partitioning and is consistent with iron oxide facies that are devoid of organic carbon or stromatolites that are not encrusted by iron oxide

wide angle deep crustal reflections in the northern appalachians summary seismic refraction data collected in the northern appalachians provide an unusual opportunity to use wide angle reflections to examine the lower crust and upper mantle the pmp phase clearly identified on several hundred records has been used to construct an isopach map of the crust which shows a stepwise regional thickening of the crust beneath the axis of the appalachians the data have been examined to times of up to 40 s two way travel time to investigate the possibility of coherent upper mantle reflections such as those recently observed by birps on near vertical data northwest of britain although substantial coherent energy appears after the pmp phase synthetic seismogram modelling shows that all of these arrivals are explicable by s phases converted phases and multiples from within the crust we conclude that in this region of the northern appalachians we have not detected any significant regionally extensive reflecting horizons within the upper mantle

discovery of distal ejecta from the 1850 ma sudbury impact event a 25 70 cm thick laterally correlative layer near the contact between the paleoproterozoic sedimentary gunflint iron formation and overlying rove formation and between the biwabik iron formation and overlying virginia formation western lake superior region contains shocked quartz and feldspar grains found within accretionary lapilli accreted grain clusters and spherule masses demonstrating that the layer contains hypervelocity impact ejecta zircon geochronologic data from tuffaceous horizons bracketing the layer reveal that it formed between ca 1878 ma and 1836 ma the sudbury impact event which occurred 650 875 km to the east at 1850 1 ma is therefore the likely ejecta source making these the oldest ejecta linked to a specific impact shock features particularly planar deformation features are remarkably well preserved in localized zones within the ejecta whereas in other zones mineral replacement primarily carbonate has significantly altered or destroyed ejecta features

structures associated with inversion of the donbas foldbelt ukraine and russia abstract the donbas foldbelt is part of the prypiat dnieper donets intracratonic rift basin belarus ukraine southern russia that developed in late devonian times and was reactivated in early carboniferous to the southeast the donbas foldbelt joins the contiguous deformed karpinsky swell basin inversions led first to the uplift of the palaeozoic series mainly carboniferous but also syn rift devonian strata in the southwesternmost part of the donbas foldbelt which are deeply buried in the other parts of the rift system and later to the formation of the fold and thrust belt the general structural trend of the donbas foldbelt formed mainly during rifting is wnw ese this is the strike of the main rift related fault zones and also of the close to tight main anticline of the donbas foldbelt that developed along the previous rift axis the main anticline is structurally unique in the donbas foldbelt and its formation was initiated in permian times during a period of trans tensional reactivation during which active salt movements occurred a relief inversion of the basin also took place at this time with a pronounced uplift of the southern margin of the basin and the adjacent ukrainian shield subsequently cimmerian and alpine phases of tectonic inversion of the donbas foldbelt led to the development of flat and shallow thrusts commonly associated with folds into the basin a fan shaped deformation pattern is recognised in the field with south to southeast vergent compressive structures south of the main anticline and north to northwest vergent ones north of it these compressive structures are clearly superimposed onto the wnw ese structural grain of the initial rift basin shortening structures that characterise the tectonic inversion of the basin are regionally orientated nw se and n s because of the obliquity of the compressive trends relative to the wnw ese strike of inherited structures major preexisting normal faults and the main anticline in addition to reverse displacements right lateral movements occurred along the main boundary fault zones and along the faulted hinge of the main anticline the existence of preexisting structures is also thought to be responsible for local deviations in contractional trends that are e w in the southwesternmost part of the basin

spatial variability in oceanic redox structure 1 8 billion years ago the deposition of iron formations ceased about 1 84 billion years ago reconstructions of ocean chemistry suggest that the advent of euxinic conditions along ocean margins preferentially removed dissolved iron from the water column in the form of the mineral pyrite inhibiting widespread iron oxide mineral deposition

microbial signatures in peritidal siliciclastic sediments a catalogue a catalogue of microbial structural signatures is presented based upon the coupling of fundamental biogeochemical microbial processes and local morphogenetic determinants it summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones temperate humid mellum island southern north sea subtropical arid coast of southern tunisia textural geometries reveal a high structural diversity but their determinants are primarily based upon six major parameters 1 intrinsic biofactors structural diversification of sedimentary microbial films and mats inherent in the organisms i e their construction morphology growth taxis and behaviour and local abundance of specific morphotypes most prominent are the ensheathed filamentous cyanobacteria microcoleus chthonoplastes and lyngbya aestuarii and the sheathless filamentous cyanobacterium oscillatoria limosa 2 biological response to physical disturbances sediment supply erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats 3 trapping binding effects physicobiological processes give rise to grain orientations and wavy to lenticular lamina lamina specific grain arrangements and sucrose calcium carbonate accumulations 4 secondary physical deformation of biogenic build ups mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures 5 post burial processes textural fabrics that evolve from mechanical effects of gas formation from decaying mats and features related to the formation of authigenic minerals calcium carbonates calcium sulphates pyrite 6 bioturbation and grazing post depositional structures such as skolithos type dwellings traces of burrowing insects gastropod grazing traces and faecal pellets in synopsis the catalogue firstly comprises a sound set of ubiquitous signatures this uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings the catalogue secondly documents signatures that are extremely sensitive to tidal position hydrodynamic regime and overall climatic conditions these kinds of signature indicate narrow facies zones which often coincide with the activity or dominance zones of certain organisms an overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings

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

low temperature thermal evolution of the azov massif ukrainian shield ukraine implications for interpreting u th he and fission track ages from cratons abstract the low temperature thermal evolution of the azov massif eastern part of the ukrainian shield ukraine is investigated by combined zircon fission track zft apatite fission track aft and apatite u th he ahe thermochronology the data help to better understand the geodynamic evolution of the azov massif and the adjacent intra cratonic rift basin dniepr donets basin as follows zft data reveal that the precambrian crystalline basement of the azov massif was heated to temperatures close to 240 c during the late palaeozoic the heating event is interpreted in terms of burial of the basement beneath a several kilometres thick pile of devonian and carboniferous sedimentary deposits of the adjacent dniepr donets basin during permo triassic times large parts of the basement were affected by a thermal event related to mantle upwelling associated magmatic activity and increased heat flow in the adjacent rift the major part of the basement cooled to near surface conditions in the early to middle triassic and since then was thermally stable as suggested by aft and ahe data further aft data confirm late triassic magmatic activity in the azov massif which however did not influence regional thermal pattern the northern part of the basement and its sedimentary cover record a cooling event in the jurassic which was probably related to erosion however although ar ar data of jurassic magmatic activity in the donbas foldbelt are about 20 my younger than the aft data thermal relaxation after elevated heat flow associated with this magmatic event cannot be completely ruled out our results reveal apparent inconsistencies between aft and ahe data the ahe ages corrected for alpha ejection according to the standard procedure farley k a wolf r a silver l t 1996 the effect of long alpha stopping distances on u th he ages geochim cosmochim acta 60 21 4223 4229 farley k a 2002 u th he dating techniques calibrations and applications mineral soc am rev mineral geochem 47 819 844 are older than corresponding aft ages in order to test the relevance of alpha ejection correction mechanical abrasion of several apatite grains was applied we found that in case of relatively slow cooling alpha ejection correction of raw u th he ages leads to erroneously high ages this shows that alpha ejection correction should be used with caution we propose that this correction should only be applied to samples with a fast cooling history whereas it should not be applied to slowly cooled samples and to samples whose thermal history is not constrained by other means

some results of cocorp seismic reflection profiling in the grenville age adirondack mountains new york state cocorp deep seismic reflection profiling in the adirondack mountains of northern new york state has revealed a prominent zone of layered reflectors in the lower crust of the east central adirondacks the strong layered reflectors here termed the tahawus complex occur between 18 and 26 km depth beneath the sparsely reflective granulite grade surface terrane which has been uplifted from depths greater than 20 km the tahawus complex apparently represents layered rocks of some type in the lower crust of the adirondacks possibilities include gneissic layering cumulate igneous layering a layered sill complex and underthrust sedimentary strata the tahawus complex may be spatially coincident with a previously detected high conductivity zone in the lower crust suggesting that either unusual mineralogies or interstitial electrolytes are present in the tahawus complex in contrast to layered reflections discovered in the lower crust of the east central adirondacks and southeast of the adirondacks cro