indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

tectonic stress within the new madrid seismic zone refraction data indicate a significant high density rift pillow beneath the new madrid seismic zone we present results of linear and nonlinear viscoelastic finite element modeling to determine whether support of the rift pillow may contribute significantly to the total present day stress field and we consider the implications for intraplate seismicity these models were run for a loading time of 100 m y to account for relaxation and transfer of stress since the last reactivation of the rift in the mid mesozoic results indicate that the nonlinear viscoelastic model with rheological stratification based on composition and temperature agrees well with the observed deformation within the seismic zone and with estimates of regional stress magnitudes the model predicts a maximum compression of 30 40 mpa above the rift pillow in the center of the rift axis if the magnitude of local compression predicted by the nonlinear model produces the inferred clockwise rotation of the order of 10 30 in the direction of shmax maximum horizontal compression near the rift axis the magnitude of regional compression is a factor of 1 to 2 times the magnitude of local compression and consistent with an origin due to ridge push forces the addition of the local stress associated with the rift pillow however results in an approximately 30 reduction in the resolved maximum horizontal shear stress thus while the stress associated with the rift pillow can rotate the stress field into an orientation favorable for failure reduction in the resolved shear stress requires a separate mechanism for strength reduction results of the modeling indicate that stresses from the load of the rift pillow may still be present in the upper crust even after 100 m y and may still play a role in present day deformation and seismicity of the new madrid seismic zone local stress fields of significant tectonic magnitudes may also occur around other ancient rift pillows and help explain the observed correlation between intraplate seismicity and failed rift zones

origin of zoned metal grains in the que94411 chondrite laser ablation inductively coupled plasma mass spectrometry la icp ms was used to measure distributions of the siderophile elements p v cr fe co ni mo ru rh pd w re os ir and pt in metal grains in the metal rich chondrite que94411 with a spatial resolution of similar to 30 mum the platinum group elements pges except pd exhibit radial zoning in these grains that mimics that previously observed in ni and co the concentrations of these elements decreases from the cores to the rims of the grains the pge distributions support a condensation origin for the enhanced refractory element abundances in the zoned grains the lack of zoning in pd refutes an origin by a redox controlled process and none of the pge ni relationships support an origin by fractional crystallization from a metallic melt several models of grain formation were explored including equilibrium fractional condensation which failed to yield the correct radial zoning the zoning may be the product of a nonequilibrium fractional condensation process in which the refractory siderophiles remained supersaturated in the cooling solar nebula or of diffusion between refractory enhanced fe ni cores and other fe ni metal that may have been deposited later from the solar nebula copyright c 2001 elsevier science ltd

formation of metal in the ch chondrites alh 85085 and pca 91467 abstract siderophile element distributions within individual metal grains in two ch chondrites allan hills 85085 and pecora escarpment 91467 were measured by laser ablation inductively coupled plasma mass spectrometry those metal grains that are zoned in ni were also found to be zoned in other refractory siderophile elements such as ru but not in pd which is not refractory but is highly siderophile this pattern is consistent with an origin by condensation from a gas of approximately solar composition but not with an origin by redox processes or fractional crystallization the unzoned metal grains in ch chondrites were found to be frequently depleted in ru but not in pd consistent with later stage condensation from a solar gas after removal of the zoned metal gold is inversely correlated with ni in the unzoned metal grains and mean au abundances in zoned metal are always low both zoned and unzoned metal in ch chondrites could plausibly be produced from a thermostatically regulated nebula followed by rapid removal of the zoned metal and slower removal of the unzoned metal both at temperatures near or above the condensation temperature of au 1250 k this is also consistent with the isolation temperatures inferred from silicate grains in ch chondrites by previous workers based on their volatile element inventories the volatile siderophile cu is enriched in the rims relative to the interiors of both zoned and unzoned grains and is interpreted as the product of diffusion during low grade thermal processing the similarity of cu distributions and degree of kamacite taenite exsolution between zoned and unzoned metal in ch chondrites suggests that the two populations of metal experienced modest thermal metamorphism after they were brought together in the same environment probably on the ch parent body fragmentation and size sorting of the metal must have post dated the cu zoning and may have occurred in a regolith on the ch parent body the compositions of ch metal like that of metal from que 94411 and hh 237 are consistent with a nebular origin and may be the most primitive nebular materials as distinct from presolar grains sampled by chondrites

control of tectonic inheritance on continental intraplate strain rate and seismicity abstract present day deformation and seismicity of continental lithosphere are characterized by a first order dichotomy between plate boundary zones pbz and stable continental regions scr whereas the former are associated with high strain and seismicity rates the latter tend to remain un deformed except in localized regions of higher strain and seismicity commonly related to fossilized paleo pbz acting as locally weaker domains because of their low amplitudes these intraplate strain and seismicity rates are particularly difficult to measure and characterize in this study we propose a simple model to explain and quantify first order continental strain rate variations focusing on intraplate regions assuming near failure equilibrium on 1d lithosphere profiles we derive steady state strain rates driven by tectonic forces as a function of rheological models that include new strain weakening rheologies in order to simulate tectonic inheritance within this framework inherited strain weakening plays a fundamental role in allowing for and explaining strain and seismicity concentration in intraplate weak zones our model predicts strain rates in intraplate weak zones up to two to three orders of magnitude higher compared to stable cratons due to the effect of tectonic inheritance on rheology weakening these model predictions are in agreement with empirical estimations in intraplate regions and can provide a conceptual framework for characterization of scr strain and seismicity rates

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

neotectonics of the southeastern reelfoot rift zone margin central united states and implications for regional strain accommodation the northeast striking new madrid fault system of central north america has been described as a right lateral strike slip system with a left stepping restraining bend thrust the fault system has one of the highest rates of seismic energy release in an intraplate setting and it has been regarded as a zone of significant earthquake hazard the new madrid fault system is the central part of the wider reelfoot rift fault system a northeast striking basement fault zone although component faults of the new madrid system are well defined by microseismicity recent geodetic surveys suggest that little if any strain is accumulating on the principal southern strike slip arm of the fault system seismicity and geologic data show that the restraining bend thrust continues past the southern strike slip arm to the southeastern reelfoot rift margin thus we suggest that earthquakes defining the southern arm of the new madrid fault system are primarily aftershocks of an earthquake on that arm during the last sequence of great earthquakes a d 1811 1812 and it is the southeastern rift margin fault system that is currently accommodating right lateral strain along the boundary of the thrust block this interpretation is consistent with recent geodetic results the southeastern rift margin coincides with a 150 km long linear topographic scarp from near memphis to the tennessee kentucky line and s wave reflection profiles auger data and a trench excavation reveal late wisconsin early holocene surface faulting and late holocene liquefaction associated with this fault line scarp variation in sense of throw along strike and flower structure geometry suggest that this is a strike slip fault recognition of this rift margin as an important element of active tectonism in the mississippi embayment has broad implications for assessment of the seismic hazard of this and similar intraplate settings temporal shifts in strain accommodation may give rise to short term seismicity patterns and or geodetic velocities that do not reveal long term tectonic patterns

condensates from vapor made by impacts between metal silicate rich bodies comparison with metal and chondrules in cb chondrites abstract the impact hypothesis for the origin of cb chondrites was tested by performing equilibrium condensation calculations in systems composed of vaporized mixtures of projectile and target materials when one of the impacting bodies is composed of the metal from cr chondrites and the other is an h chondrite good agreement can be found between calculated and observed compositions of unzoned metal grains in cb chondrites but the path of composition variation of the silicate condensate computed for the same conditions that reproduce the metal grain compositions does not pass through the measured compositions of barred olivine bo or cryptocrystalline cc chondrules in the cbs the discrepancy between measured chondrule compositions and those of calculated silicates is not reduced when diogenite eucrite or howardite compositions are substituted for h chondrite as the silicate rich impacting body if however a cr chondrite body is differentiated into core a relatively cao al 2 o 3 poor mantle and a cao al 2 o 3 rich crust and later accretes significant amounts of water a collision between it and an identical body can produce the necessary chemical conditions for condensation of cb chondrules if the resulting impact plume is spatially heterogeneous in its proportions of crust and mantle components the composition paths calculated for silicate condensates at the same p tot ni h and si h ratios and water abundance that produce good matches to the unzoned metal grain compositions pass through the fields of bo and cc chondrules especially if high temperature condensates are fractionated in the case of the ccs while equilibrium evaporation of an alloy containing solar proportions of siderophiles into a dense impact plume is an equally plausible hypothesis for explaining the compositions of the unzoned metal grains equilibrium evaporation can explain cb chondrule compositions only if an implausibly large number of starting compositions is postulated kinetic models applied to co condensing metal grains and silicate droplets in a region of the plume with very similar composition but with high cooling rate and sharply declining p tot during condensation produce very good matches to the zoning profiles of ir ni co and cr concentrations and fe and ni isotopic compositions observed in the zoned metal grains in cb chondrites but produce very large positive 56 fe in the cogenetic silicate which are not found in the chondrules

seismic activity and structural features in the charlevoix region quebec the charlevoix region is historically the most active earthquake zone in eastern canada understanding the links between its seismicity and the faults of the region is important for the assessment

petrology and raman spectroscopy of high pressure phases in the gujba cb chondrite and the shock history of the cb parent body abstract high pressure phases majorite possibly majorite pyropess wadsleyite and coesite are present in the matrix and in barred olivine fragments in the gujba cb chondrite grossular pyrope was also observed in some small inclusions the cb chondrites are metal rich meteorites with characteristics that sharply distinguish them from other chondrite groups all of the cb chondrites contain impact melt regions interstitial to their chondrules fragments and metal and a major impact event or events on the cb chondrite parent body is clearly a significant stage in its history we studied three areas interstitial to chondrules and metal in the gujba cba chondrite from raman spectra the barred olivine fragments and matrix in these regions have various combinations of olivine and low ca pyroxene as well as majorite garnet mg4si4o12 a phase that forms by high pressure transformation of low ca pyroxene and wadsleyite a high pressure product of olivine compositions of the majorite suggest both majorite and majorite pyrope solid solution may be present the mineral assemblage of majorite and wadsleyite suggest minimum shock pressures and temperatures of 19 gpa and 2000 c respectively the occurrences of high pressure phases are variable from one area to another on the scale of millimeters or less suggesting heterogeneous distribution of shock and or back transformation to low pressure polymorphs throughout the meteorite the high pressure phases record a high temperature pressure impact event that is superimposed onto and thus postdates formation of the chondrules and other components in the cb chondrites the barred chondrules and metal in the cb chondrites are primary materials formed prior to the impact event either generated in an earlier planetesimal scale impact event or in the nebula

modes of active intraplate deformation flinders ranges australia 1 the flinders ranges form one of the most seismically active zones within the australian continent with seismogenic strain rates over the last 30 years of 10 16 s 1 active deformation in the region reflects late neogene increases in stress levels in the indo australian plate as a response to increased plate boundary forcing from collision zones with the neighboring asian and pacific plates geological and geophysical observations suggest two modes of active deformation in operation in the flinders ranges over the last several million years 1 low amplitude 200 500 m long wavelength 200 km lithospheric flexure and 2 active reverse faulting along the range front with fault slip rates of up to 50 m myr 1 numerical models are developed to explore the contribution of each of these deformation modes to the observed geophysical signals an elastic mode of deformation is suggested by a distinctive long wavelength positive correlation between gravity and topography in which the flinders ranges are bordered by anomalous topographic and gravity lows now occupied by playa lake systems centered some 50 km outboard of range bounding faults numerical models show that flexural instabilities localized by vertical loads arising from older tectonic structuring produce a first order match with observed topography and gravity numerical models are also used to illustrate how the localized failure evident in the contemporary seismicity and quaternary faulting record within the flinders ranges reflects thermal weakening associated with extraordinary concentrations of heat producing elements in the crust as reflected in modern day heat flows of 90 mw m 2

structural analysis of supracrustal faults in the charlevoix area quebec relation to impact cratering and the st laurent fault system the charlevoix area which is host to an impact structure of devonian age straddles the boundaries among crystalline rocks of the grenville province the cambrian ordovician sedimentary succession of the st lawrence platform and accreted units of the appalachian orogen the area features well developed supracrustal fault systems attributed to impact cratering a major fault system oriented from northeast to northwest consists of normal faults marked by cataclastic and gouge breccias and less frequently by pseudotachylyte detailed mapping of faults both within and outside the charlevoix impact crater suggests that brittle faulting occurred both before and after impact cratering polymictic fault breccias occurring along some supracrustal faults are the clearest evidence of impact related fault rocks in the charlevoix area the st laurent fault trending to the northeast represents a major structure interpreted as being related to late proterozoic early paleozoic rifting of the iapetus ocean howev

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

sedimentary laminations in the isheyevo ch cbb carbonaceous chondrite formed by gentle impact plume sweep up abstract prominent macroscopic sedimentary laminations consisting of mm to cm thick alternating well sorted but poorly mixed silicate and metal rich layers cut by faults and downward penetrating load structures are prevalent in the isheyevo ch cbb carbonaceous chondrite the load structures give the up direction of this sedimentary rock that accumulated from in falling metal and silicate rich grains under near vacuum conditions onto the surface of an accreting planetesimal the isheyevo meteorite is the end result of a combination of events and processes that we suggest was initiated by the glancing blow impact of two planetesimals the smaller impactor was disrupted forming an impact plume downrange of the impact the components within the plume were aerodynamically size sorted by the nebular gas and swept up by the impacted planetesimal before turbulent mixing within the plume could blur the effects of the sorting this plume would have contained a range of materials including elementally zoned fe ni metal grains that condensed in the plume to disrupted unaltered material from the crust of the impactor such as the hydrated matrix lumps the juxtaposition of hydrated matrix lumps some of which have not been heated above 150 c together with components that formed above 1000 c is compelling evidence that they were swept up together sweep up would have occurred as the rotating impactor moved through the plume producing layers of material the isheyevo sample thus represents material accumulated while that part of the rotating planetesimal moved into the plume vibrations from subsequent impacts helped to form the load structures and induced weak grading within the layers via kinetic sieving following sweep up the particles were compacted under low static temperatures as evidenced by the preservation of elementally zoned fe ni metal grains with preserved martensite 2 cores distinct metal metal grain boundaries and metal deformation microstructures this meteorite provides evidence of gentle layer by layer accretion in the early solar system and also extends the terrestrial sedimentary source to sink paradigm to a near vacuum environment where neither fluvial nor aeolian processes operate

microfractures and their role in deformation of a quartz arenite from the central appalachian foreland abstract microfractures are pervasive in the massanutten sandstone a quartz arenite exposed in a doubly plunging synclinorium in the central appalachian foreland they are present as fluid inclusion planes fips and microveins parallel the fips fips occur in three orthogonal sets horizontal vertical and normal to the fold axis and vertical and parallel to the fold axis the geometry distribution and age of fips relative to other microstructures shows that microfractures developed during folding microfracturing followed layer parallel shortening by dislocation flow and was coeval with the peak of pressure solution that marked the final stages of folding microfracture densities are extremely high 160 mm 1 in many samples rapid closure of microfractures suppressed brecciation and prevented microfractures from propagating unstably to form joints microfracture opening accounts for significant finite strain with extensional strains of up to 11 1 and associated volume increases of over 16 0 the general lack of shortening microstructures indicates that a net volume increase is likely and that the massanutten sandstone may have served as a sink for dissolved phases from adjacent units undergoing volume loss deformation

shock melts in que 94411 hammadah al hamra 237 and bencubbin remains of the missing matrix we have studied the cb carbonaceous chondrites queen alexandra range que 94411 hammadah al hamra hh 237 and bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone iron nickel metal and chondrule silicates are the main components in these meteorites these high temperature components are held together by shock melts consisting of droplets of dendritically intergrown fe ni metal sulfide embedded in silicate glass which is substantially more feo rich 3040 wt than the chondrule silicates feo 5 wt fine grained matrix material which is a major component in most other chondrite classes is extremely scarce in que 94411 and hh 237 and has not been observed in bencubbin this material occurs as rare hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts and cl we infer that hydrated fine grained material compositionally similar to these matrix lumps was originally present between the fe ni metal grains and chondrules but was preferentially shock melted other shock related features in que 94411 hh 237 and bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments

is there a genetic relationship between selected regional joints and contemporary stress within the lithosphere of north america on the appalachian plateau of new york ene striking joints parallel the mid continent contemporary stress field and do not correlate with other structures joints within ohio indiana michigan and west virginia also parallel the mid continent maximum horizontal compression as indicated by hydraulic fracture measurements in northern indiana where the contemporary stress field deviates significantly from the orientation of the mid continent stress the attitude of the joints deviates accordingly in addition to joints structures on several scales from subcontinent size fracture systems to microfabrics in shales apparently parallel the mid continent stress field from this i conclude that these joints are mode i cracks whose orientation corresponds to the contemporary tectonic stress field in itself the formation of these structures constitutes a tectonic event that has often been overlooked in favor of tectonic events that produce the more spectacular but less pervasive faults and folds

a sem cathodoluminescence study of quartz in mildly deformed granite from the region of the atotsugawa fault central japan abstract cathodoluminescence cl images of quartz in granite distributed around the atotsugawa fault in central japan were observed by scanning electron microscopy and compared to optical microscope observations of the same crystals narrow or wide dark bands or dots were commonly recognized in the cl images almost all dots or narrow bands correlate with isolated bubbles or semi planar bubble arrays along healed cracks respectively some wide bands correspond to cracks filled with other minerals chlorite calcite mica etc or can be distinguished as zones with an extinction differing from that of surrounding areas in quartz crushed zones composed of healed crack arrays other wide bands are healed cracks where quartz is precipitated in optical continuity the quartz cl images displayed overall textures composed of mineral filled cracks bubble arrays along healed cracks and crushed zones more clearly than normal optical images healed cracks containing quartz precipitated in optical continuity with the enclosing grains were distinctly revealed as dark bands in cl images the abundance of these minor deformation structures as revealed in cl images increases with proximity to the fault therefore cl textures of quartz are an important aid in examining brittle deformation textures and understanding the tectonic processes that produce them

present day stress analysis of the st lawrence lowlands sedimentary basin canada and implications for caprock integrity during co2 injection operations abstract a geomechanical analysis of the st lawrence lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for co 2 injection that will not reactivate pre existing faults in the caprock thereby inducing a breeched co 2 reservoir this requires the determination of prevailing stresses orientations and magnitudes fault and fractures geometries and rock strengths the average maximum horizontal stress orientation s hmax is estimated n59 e 20 in the st lawrence lowlands the stress orientations were obtained from stress induced wellbore breakouts inferred from four arm dipmeter caliper data in 17 wells these wellbore failure features are confined to paleozoic lithological units of the st lawrence platform succession and frontal thrusts of the quebec appalachians at depths from 250 m to 4 km our results are consistent with the regional ne sw s hmax stress orientation trend that is generally observed in eastern canada and the u s the stresses pressure gradients estimated for the st lawrence lowlands depths hmin 20 5 3 kpa m s v 25 6 kpa m s hmax 40 7 5 kpa m pore pressure p p 9 8 kpa m indicating a strike slip stress regime s hmin v hmax the high angle ne sw regional faults and fractures in the paleozoic sedimentary succession and the grenvillian basement are oblique to the s hmax stress orientations 10 to 36 and could be reactivated slip tendency 0 34 to 0 58 under the present day stress field if fluid pressures exceeded the critical threshold further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults the regional pore pressure stress coupling ratio under assumed parameters is about 0 5 0 65 and may contribute to reduce the risk of shear reactivation of faults and fractures the maximum sustainable p p that would not cause opening of vertical tensile fractures during co 2 operations is about 18 5 20 mpa for the depth of 1 km

seismicity and faulting in the charlevoix zone of the st lawrence valley abstract continuous monitoring of the seismically active charlevoix zone since late 1977 has delineated the boundaries of the earthquake zone under the north shore and has enabled an association to be made with surface mapped faults that strike along the st lawrence valley and dip to the southeast within the active zone aseismic volumes are found under parts of the st lawrence river and another elongated zone of activity is found to the southeast on unmapped faults dipping under the river the previous suggestions that the activity is related to old rift faults which have been later weakened by a meteor impact would seem to be upheld

a three dimensional p wave velocity model for the charlevoix seismic zone quebec canada 1 a three dimensional p wave velocity model has been developed for the charlevoix seismic zone csz the csz is located along the st lawrence river 100 km northeast of quebec city canada and is one of the most active seismic zones in eastern north america five earthquakes with magnitudes equal to or exceeding 6 0 have occurred in the csz in historic time and around 200 earthquakes occur annually hypocenters are located in precambrian basement rocks basement rocks have been affected by numerous tectonic events including grenvillian collision iapetan rifting and meteor impact we performed a sequential tomographic inversion for p wave velocity structure based upon 3093 p wave arrivals from 489 earthquakes recorded by 12 stations high velocity is associated with the center of the impact crater the region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks an elongated high velocity region is present at midcrustal depths that trends parallel to the st lawrence river earthquakes avoid the high velocity body and separate into two bands one on either side of the feature larger earthquakes magnitude 4 have occurred along the northern edges of the high velocity region

dynamic analysis of deformed quartz grains from the folded middle miocene momonoki subgroup of central japan origin of healed microcracks abstract dynamic analyses have been performed on quartz detrital grains from the sandstones of folded middle miocene strata momonoki subgroup found along the itoigawa shizuoka tectonic line istl central japan these quartz grains contain numerous deformation lamellae kink bands and healed microcracks in this study in addition to the dynamic analysis using deformation lamellae the arrow method of carter and friedman the c axis preferred orientations of kinked and unkinked grains and the preferred orientations of healed microcracks in individual grains are analyzed in order to test if these fabrics can be used to determine the palaeostress field in the case of basal a slip being dominant which probably holds for the analyzed quartz the principal stress axes can be inferred from the c axis preferred orientations of kinked and unkinked grains referred to as the kink method here because the preferred orientations indicate the favourable and unfavourable orientations respectively under stress for basal a slip results of the dynamic analyses of deformed quartz by the arrow method and by the kink method are consistent with each other and presumably indicate the palaeostress field associated with the macroscopic folding of the momonoki subgroup although the origin and timing of healed microcracking in the deformed quartz are not completely resolved the preferred orientation of poles to healed microcracks seems to consist of two or three sets of orthogonally disposed maxima whose directions coincide with the principal stress axes responsible for the crystal plasticity i e the lamellae and kinks in the quartz it is suggested that the successive release of residual tectonic stresses in the principal stress directions led to this orthogonal orientation pattern of healed microcracks in the present study then combined dynamic analyses of deformed quartz using deformation lamellae kink bands and healed microcracks provide a more complete quantitative picture of the bulk stress field during deformation particularly the combination of the arrow method with the kink method the latter applied to naturally deformed quartz for the first time in this study provides an indication of the relative magnitude of principal stresses finally in the context of the influence of fluids on the deformation processes in rocks i would like to stress that microcracking in crystalline or consolidated rocks is essential for the incorporation of enough fluid into the constituent crystals to activate fluid assisted deformation processes such as solution precipitation creep and that the regional development of microcracks may be controlled by the stress field associated with the fold development in layered consolidated rocks

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

isotopically uniform 16o depleted calcium aluminum rich inclusions in ch and cb carbonaceous chondrites abstract in situ oxygen isotope measurements of calcium aluminum rich inclusions cais from the metal rich carbonaceous chondrites isheyevo ch cb like acfer 214 paired with acfer 182 ch que 94411 paired with que 94627 cbb and hammadah al hamra 237 cbb revealed the presence of a common population of igneous isotopically uniform 16o depleted inclusions 17o average 2 standard deviations 7 4 6 5 and 8 3 respectively all cais from cbs and a significant fraction of those from chs and isheyevo are 16o depleted most of the 16o depleted cais consist of ti poor al diopside spinel melilite and forsterite and surrounded by a single and double layered rim of forsterite diopside the 16o depleted cais composed of hibonite grossite melilite and spinel and surrounded by the multilayered melilite diopside forsterite rims are less common some of the 16o depleted refractory igneous inclusions composed of al diopside forsterite and spinel have chondrule like textures skeletal or barred they are mineralogically most similar to al diopside rich chondrules found in metal rich carbonaceous chondrites and composed of al diopside forsterite al rich low ca pyroxene glassy mesostasis and spinel suggesting there is a continuum between these objects we suggest that i most of the isotopically uniform and 16o depleted cais resulted from remelting of pre existing possibly 16o rich refractory inclusions the remelting may have occurred during formation of the magnesian non porphyritic cryptocrystalline and skeletal chondrules in chs cbs and isheyevo either by an unspecified late single stage highly energetic event or in an impact generated plume previously hypothesized for their origin both mechanisms probably occurred in the solar nebula i e in the presence of the nebula gas the forsterite pyroxene rims around 16o depleted cais may have resulted from evaporation recondensation of silicon and magnesium during this event some of the al diopside rich cais may have formed by evaporation of the al rich chondrule melts ii in addition to these components the chs and isheyevo contain a high abundance of chondrules and refractory inclusions formed by the commonly inferred nebular processes evaporation condensation and incomplete melting of dust aggregates during multiple transient heating events these include 16o rich cais amoeboid olivine aggregates and ferromagnesian and aluminum rich chondrules with porphyritic textures such components are also present in cb chondrites but they are exceptionally rare these observations indicate that there are multiple generations of cais in metal rich carbonaceous chondrites iii because the isotopically uniform 16o depleted igneous cais and the magnesian cryptocrystalline and skeletal olivine pyroxene chondrules are found almost exclusively in metal rich carbonaceous chondrites the hypothesized impact plume mechanism of chondrule formation and recycling of cais are not common processes

chondritic lithic clasts in the cb ch like meteorite isheyevo fragments of previously unsampled parent bodies the cb ch like chondrite isheyevo is characterized by the absence of fine grained interchondrule matrix material the only present fine grained material is found as chondritic lithic clasts in contrast to the pristine high temperature components of isheyevo these clasts experienced extensive aqueous alteration in an asteroidal setting hence the clasts are foreign objects that either accreted together with the high temperature components or were added later to the final isheyevo parent body during regolith gardening in order to constrain the origin and secondary alteration of the clasts in isheyevo we studied their mineralogy petrography structural order of the polyaromatic carbonaceous matter and oxygen isotopic compositions of carbonates three main groups of clasts were defined based on mineralogy and petrology group i clasts consist of phyllosilicates carbonates magnetite and lath shaped fe ni sulfides group ii clasts contain different abundances of anhydrous silicates embedded in a hydrated matrix sulfides magnetite and carbonates are rare with only a few exceptions groups i and ii clasts did not experienced significant thermal metamorphism group iii clasts are characterized by the absence of magnetite and the presence of fe ni metal in addition to aqueous alteration they experienced thermal metamorphism as reflected by the structure of their polyaromatic carbonaceous matter while there are some similarities between the isheyevo clasts ci chondrites and the matrices of cm and cr chondrites on the whole the characteristics of the clasts do not match those of any of these aqueously altered meteorite classes nor do they match those of similar material in various types of chondritic clasts present in other meteorite groups we conclude that the isheyevo clasts represent fragments of previously unsampled parent bodies

regional fractures ii fracturing of mesaverde reservoirs in the piceance basin colorado 1 cretaceous strata in the east central piceance basin of northwestern colorado were subjected to several phases of stress due to horizontal tectonic compression burial and uplift these rocks contain a regional set of west northwest extension fractures observed in abundant vertical and deviated core from the u s department of energy s multiwell experiment and slant hole completion test wells time depth relationships fracture orientation and fluid inclusion analyses indicate that the fractures formed at about 36 40 ma during a phase of increased laramide west northwest compression and in a pressure temperature regime compatible with the geologically reconstructed maximum burial depths this regional fracturing is an example of load parallel extension fracturing and basinwide dilatancy at depth under conditions of high pore pressure and anisotropic tectonically created horizontal stress

gps crustal strain postglacial rebound and seismic hazard in eastern north america the saint lawrence valley example 1 we present global positioning system gps measurements that constrain the amplitude pattern and origin of crustal deformation in the saint lawrence valley quebec one of the most seismically active regions of eastern north america the gps network shows coherent southeastward motion of 0 6 0 2 mm yr 1 relative to north america and uplift of 2 6 0 4 mm yr 1 network average horizontal strain rates are mostly ese wnw shortening at 1 7 1 0 10 9 yr 1 the shortening rate across the charlevoix seismic zone is about twice as big as the regional average these measurements are consistent with both postglacial rebound pgr models and the deformation style indicated by earthquake focal mechanisms although the gps data do not discriminate between various models of crustal deformation they provide important constraints on large earthquake recurrence assuming that the gps strain estimates are representative of seismic moment release they constrain the maximum magnitude of truncated gutenberg richter recurrence statistics in the charlevoix seismic zone to mx 7 8 0 6 one m 7 earthquake per 400 1300 years the remarkable agreement between the gps strain rates seismic catalogue statistics and pgr predictions suggests that in charlevoix most of the pgr driven crustal strain may be released by large m 7 earthquakes in the rest of the saint lawrence valley pgr strain rates are significantly larger than seismic strain rates suggesting either that pgr deformation remains mostly elastic or that large events are more frequent than indicated by small earthquake statistics i e characteristic earthquakes

stress induced by topography and crustal density heterogeneities implication for the seismicity of southeastern canada abstract the stress induced by the topography and density heterogeneities in the lithosphere has been calculated for a large region covering most of southeastern canada the calculations assume that the lithosphere consists of a three dimensional layered elastic slab overlaying an inviscid fluid the calculations show that the deviatoric stress difference induced by density heterogeneities and the topographic load is of the same order as the regional tectonic stress tens of mpa stresses appear largest along the saint lawrence valley where most of the seismicity is located e g the charlevoix and the lower saint lawrence areas the charlevoix seismic zone was analyzed in greater detail and theoretical focal mechanisms were computed this analysis shows that the stress induced by surface and internal loading is compressional in this area and the principal stress orientation is consistent with earthquake focal mechanisms and in situ measurements

a new metal rich chondrite grouplet abstract a new grouplet of primitive metal rich chondrites here called the cb c carbonaceous b bencubbinite chondrites has been recognized it includes bencubbin weatherford hammadah a1 hamra hh 237 and queen alexandra range que 94411 paired with que 94627 their mineral compositions as well as their oxygen and nitrogen isotopic compositions indicate that they are closely related to the cr and ch chondrites all of which are members of the more inclusive cr clan cb chondrites have much greater metal silicate ratios than any other chondrite group widely increasing the range of metal silicate fractionation recorded in solar nebular processes they also have the greatest moderately volatile lithophile element depletions of any chondritic materials metal has compositional trends and zoning patterns that suggest a primitive condensation origin in contrast with metal from other chondrite groups cb chondrites as well as other cr clan chondrites have much heavier nitrogen higher 15n 14n than that in other chondrite groups the primitive characteristics of the cb chondrites suggest that they contain one of the best records of early nebular processes another chondrite grosvenor mountains 9555 1 is petrographically similar to the cb chondrites but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir

very low strengths of interplanetary meteoroids and small asteroids we have assembled data on thirteen cases of meteorite falls with accurate tracking data on atmospheric passage in all cases we estimate the bulk strength of the object corresponding to its earliest observed or inferred fragmentation in the high atmosphere and can compare these values with measured strengths of meteorites in the taxonomic class for that fall in all thirteen cases the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites we find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law we estimate bulk strengths on entry being characteristically of the order of 10 1 to 10 2 times the tensile strengths of recovered samples

stress channelling and partitioning of seismicity in the charlevoix seismic zone quebec canada summary the charlevoix seismic zone csz in the st lawrence valley of quebec is historically the most active in eastern canada the structurally complex region comprises rift faults formed during the opening of the iapetus ocean superimposed by a 350 ma meteorite impact structure resulting in a circular highly fractured zone although seismicity is localized along two steeply dipping planar rift parallel zones previous work indicates that most of the large scale rift faults bound the low magnitude background seismicity rather than generate earthquakes themselves in order to gain insight into the mechanics of the partitioning of this seismicity a 2 d model of the csz was built using the stress analysis code flac the rift faults are represented by frictional discontinuities the heavily fractured impact structure is represented by an elastic continuum of reduced modulus boundary displacements are used to generate a regional stress field with the major horizontal component in the direction of tectonic loading given a high strength the rift faults have little effect on the stress patterns stress trajectories naturally flow around the crater of reduced elastic modulus leaving the fractured area with lower stresses than the background level however when the rift faults have low strength they are unable to support stress trajectories inclined to them due to the resolved shear stress exceeding their strength this prevents trajectories from flowing out of the rift effectively channelling higher magnitude stresses into the region of the impact structure between the faults low strength bounding faults can thus explain the localization of seismicity into linear bands rather than distributed seismicity throughout the impact structure it also explains how the rift faults act as boundaries to regions of low magnitude seismicity these results indicate that the interplay between faults of varying strength and zones of differing elastic modulus can give rise to complicated stress patterns and can explain many of the seismicity patterns observed in the csz this has implications for other intraplate seismic zones as it shows an example of how regional weak faults can modify stress conditions around local structures and drive seismicity the results are particularly relevant for other regions located within rifted crust such as the new madrid seismic zone which possibly display evidence of stress channelling

structural inheritance control on intraplate present day deformation gps strain rate variations in the saint lawrence valley eastern canada structural inheritance is one of the key factors commonly proposed to control the localization of strain and seismicity in continental intraplate regions primarily on the basis of a first order spatial correlation between seismicity and inherited tectonic structures in this paper we present new gps global positioning system velocity and strain rate analyses that provide strong constraints on the magnitude and style of present day strain localization associated with the inherited tectonic structures of the saint lawrence valley eastern canada we analyze 143 continuous and campaign gps stations to calculate velocity and strain rate patterns with specific emphases on the combination of continuous and campaign velocity uncertainties and on the definition of robustness categories for the strain rate estimations within the structural inheritance area strain rates are on average 2 11 times higher than surrounding regions and display strong lateral variations of the style of deformation these gps velocity and strain rate fields primarily reflect ongoing glacial isostatic adjustment gia their comparison with gia model predictions allows us to quantify the impact of the structural inheritance and the associated lithosphere rheology weakening outside of the major tectonic inheritance area gps and gia model strain rates agree to first order both in style and magnitude in contrast the saint lawrence valley displays strong strain amplification with gps strain rates 6 28 times higher than model predicted gia strain rates our results provide the first quantitative constraints on the impact of lithospheric scale structural inheritance on strain localization in intraplate domains

primitive feni metal grains in ch carbonaceous chondrites formed by condensation from a gas of solar composition some feni metal grains similar to 150 mu m in apparent diameter in ch carbonaceous chondrites are concentrically zoned in ni similar to 5 10 wt co 0 2 0 4 wt and cr 0 3 0 8 wt silicon is present at the similar to 0 1 wt level these observations are consistent with predicted gas solid condensation from a gas of solar composition at temperatures of similar to 1370 1270 k and total pressure of similar to 10 4 bar estimates of feni metal grain growth and cooling rates in this temperature range are consistent with brief and localized thermal episodes in the solar nebula compositionally similar feni metal grains have also been reported in cr and bencubbin like chondrites because feni metal is highly susceptible to secondary alteration i e metamorphism melting oxidation the observed feni metal condensates in ch bencubbin like and cr chondrites indicate that these meteorites experienced no thermal processing after their lithification and thus are among the most primitive meteorites in our collections

allan hills 85085 a subchondritic meteorite of mixed nebular and regolithic heritage abstract allan hills 85085 is a tiny 12 g meteorite whose closest relatives are the renazzo and al rais chondrites and the subchondritic host material in the bencubbin meteorite its bulk composition is generally chondritic but siderophile abundances are tens of per cent higher and abundances of moderately volatile elements factors of 2 4 lower than in known authentic chondrites in addition to this unusual composition alh85085 has an extremely small particle size metal that shows no evidence of metamorphic equilibration and a very high abundance of pyroxenitic lithic particles chondrules are rare and small most are pyroxenitic and chemically similar to the lithic particles previous workers have inferred that most or all of these strange features of alh85085 resulted from nebular processes but we suggest that melting vaporization outgassing condensation and size sorting in a cloud of impact ejecta offer a more viable alternative until additional similar materials have been discovered and characterized it seems safest to infer nebular properties and processes on the basis of the record in chondrites regarding which there is little doubt that nebular processes were dominant

correlation between deformation lamellae microfractures macrofractures and in situ stress measurements white river uplift colorado dynamic analyses of quartz deformation lamellae and microfractures in lower paleozoic quartzites from the white river uplift record a northwest direction of compression which can be related to joint and fault orientations and in situ stress determinations crystallographic orientations of deformation lamellae resemble those formed in the subbasal i relatively nonselective domain microfractures in quartz grains form orthogonal sets of generally north northeast and west northwest trending fracutres which are approximately normal to bedding the strongest set of microfractures in most samples lies in the 2 plane deduced from deformation lamellae analyses suggesting that the microfractures are extensional features maxima of microfractures correspond to maxima of joints measured at adjacent locations the strikes of prominent west northwest sets of microfractures and joints are subparellel to the dominant northwest strike of faults on the uplift in situ stress measurements conducted in the piceance basin and rangely colorado areas indicate principal stress orientations similar to those determined from quartz deformation lamellae microfractures and joints which are pre uplift to early uplift late laramide fabric elements

an updated global earthquake catalogue for stable continental regions reassessing the correlation with ancient rifts summary we present an updated global earthquake catalogue for stable continental regions scrs i e intraplate earthquakes that is available on the internet our database contains information on location magnitude seismic moment and focal mechanisms for over 1300 m moment magnitude 4 5 historic and instrumentally recorded crustal events using this updated earthquake database in combination with a recently published global catalogue of rifts we assess the correlation of intraplate seismicity with ancient rifts on a global scale each tectonic event is put into one of five categories based on location i interior rifts taphrogens ii rifted continental margins iii non rifted crust iv possible interior rifts and v possible rifted margins we find that approximately 27 per cent of all events are classified as interior rifts i 25 per cent are rifted continental margins ii 36 per cent are within non rifted crust iii and 12 per cent iv and v remain uncertain thus over half 52 per cent of all events are associated with rifted crust although within the continental interiors i e away from continental margins non rifted crust has experienced more earthquakes than interior rifts no major change in distribution is found if only large m 6 0 earthquakes are considered the largest events m 7 0 however have occurred predominantly within rifts 50 per cent and continental margins 43 per cent intraplate seismicity is not distributed evenly instead several zones of concentrated seismicity seem to exist this is especially true for interior rifts taphrogens where a total of only 12 regions are responsible for 74 per cent of all events and as much as 98 per cent of all seismic moment released in that category of the four rifts taphrogens that have experienced the largest earthquakes seismicity within the kutch rift india and the east china rift system may be controlled by diffuse plate boundary deformation more than by the presence of the ancient rifts themselves the st lawrence depression canada besides being an ancient rift is also the site of a major collisional suture thus only at the reelfoot rift new madrid seismic zone nmsz usa is the presence of features associated with rifting itself the sole candidate for causing seismicity our results suggest that on a global scale the correlation of seismicity within scrs and ancient rifts has been overestimated in the past because the majority of models used to explain intraplate seismicity have focused on seismicity within rifts we conclude that a shift in attention more towards non rifted as well as rifted crust is in order

the condensation origin of zoned metal grains in queen alexandra range 94411 implications for the formation of the bencubbin like chondrites thermodynamic analysis of the compositional profiles across large chemically zoned fe ni metal grains in the bencubbin like chondrite queen alexandra range que 94411 suggests that these grains formed by non equilibrium gas solid condensation under variable oxidizing conditions isolation degree and cr depletion factors the oxidizing conditions must have resulted from the complete vaporization of nebular regions with enhanced dust gas ratios similar to 10 40 x solar because the origin of each of the metal grains studied requires different condensation parameters dust gas ratio isolation degree and cr depletion factor a high degree of heterogeneity in the formation region of the bencubbin like chondrite metal is required to preserve compositional zoning of the metal grains and prevent their melting and sulfidization the grains must have been removed from the hot condensation region into cold regions where the accretion of the bencubbin like asteroidal body took place

a re examination of the 1925 charlevoix quebec earthquake the 1 march 1925 charlevoix earthquake is one of the largest earthquakes known to have occurred in southeastern canada because it occurred in one of the most active seismic zones of southeastern canada and near now heavily populated regions understanding this earthquake may have implications for seismic hazard assessments of the region previous attempts have been made to study this earthquake using modern waveform analysis techniques but the source parameters could be only partially constrained due to a lack of good data recently a number of seismograms that had not been previously studied were rediscovered warranting a second look at the earthquake the best overall solution is strike 42 7 dip 53 7 rake 105 10 depth 10 km seismic moment 3 1 2 5 1025 dyne cm mw 6 2 ms 6 2 0 3 mb 6 5 0 4 source duration 5 sec and stress drop 35 bars the focal mechanism is consistent with many recent earthquakes in the charlevoix seismic zone but inconsistent with the regional stress field

petrology of alh85085 a chondrite with unique characteristics abstract alh85085 has several characteristics which set it apart from any known chondritic group its chondrules are smaller 25 75 m the majority are cryptocrystalline and all are volatile na k s depleted feni metal is more abundant 40 9 wt than in any other chondrite and sulfide abundance is low 1 1 matrix material does not surround the chondrules and fragments but occurs as lithic clasts lumps up to 300 m across the bulk composition of alh85085 is lower in na si and s si and higher in ni si fe si and mg si than in other chondritic groups the ca si al si and mg si ratios are closest to those of the renazzo chondrite grouplet cr matrix lumps are most similar to cr and murchison group cm chondrite matrices survival of this fragile matrix material as lithic clasts indicates that they were added just prior to the agglomeration of the chondrite all components chondrules fragments matrix lumps fall within a narrow size range which may be the result of aerodynamic sorting if so the sorting must have occurred after chondrule solidification and following a period of chondrule breakage since fragments from larger chondrules are present the ni vs co trend in the feni metal overlaps that of metal in cr chondrites and bencubbin these trends are similar to those of calculated nebular condensation paths indicating a nebular origin the cryptocrystalline texture and volatile depletion of the chondrules indicate that most chondrules were heated to temperatures above the liquidus although alh85085 cannot now be assigned to any known chondrite group it shares many similarities with cr chondrites and the bencubbin metal silicate chondritic assemblage and may be part of a chondritic group closely related to these meteorites

recognition of eroded astroblemes abstract the morphology of lunar craters degrades only slowly by the formation of new impacts and their ejecta it is not the same on earth because of weathering and tectonism generally the typical crater topography has disappeared and the term impact structure or astrobleme is applied on planetary surfaces as on the moon two classes of craters are recognized based on their depth to diameter ratio simple bowl shaped and complex readjusted flat bottomed craters with a sharp transition from simple to complex pike 1977 1980 on earth small simple craters retain some of their typical rimmed pit morphology because they are generally recent many are associated with meteorite fragments large impact structures or astroblemes in addition to their specific circular features are recognized as such only by the presence of shock metamorphism criteria such as dense minerals coesite stishovite diaplectic minerals and glass maskelynite planar deformation features in minerals principaly in quartz and feldspars and shattercones which are commonly used these criteria are abundant in allochthonous breccia particularly in fall back breccia among which there are glass fragments such as tectite or microtectite glass spherules shards droplets rods etc but on the floor of the astroblemes the criteria of shock metamorphism are restricted to the central part which is often covered or eroded using the measurements of nine astroblemes visited a scaling model is presented for two types of craters readjusted along listric slip surfaces a well readjusted model based on data from charlevoix and manicouagan canada and a partly readjusted model based on data from the ries germany both possess a central uplift and a ring graben there is also on the floor of the astrobleme a specific type of breccia mylolisthenite and pseudotachylite associated with the displacement along the autochthonous masses of rocks in very large impact structures the shock metamorphism is able to melt a part of the floor grieve and cintala 1992 the heat resulting from the superheated impact melt destroys a part of the shock metamorphism criteria

paleoseismology of the southeastern reelfoot rift in western tennessee and implications for intraplate fault zone evolution 1 the southeastern reelfoot rift margin is expressed as a series of collinear scarps across western tennessee and shallow s wave reflection profiles coring and trenches show late quaternary faulting along this lineament at the north end our seismic profile and coring suggest 1 5 m of wisconsin down to the nw faulting coring and trenches across the central lineament show 3 m of up to the nw and 8 15 m of right lateral late wisconsin holocene faulting averaged late quaternary right lateral slip has been 0 85 0 37 mm yr on one fault plane at this locality suggesting that total slip across all southeast rift margin fault planes may accommodate much of the regional strain our seismic profile at this site shows up to the west faulting of eocene strata folded down to the west indicating structural inversion seismic profiles electrical surveys coring and a trench across the southern lineament segment show holocene faulting trenching exposed a vertical fault with 0 5 m of late holocene down to the nw displacement nearby coring and electrical surveys show 0 5 m of late holocene up to the nw faulting we conclude the southeastern reelfoot rift margin is a right lateral system with high angle faults showing both up to the nw and down to the nw separations age constraints permit an earthquake circa 2500 to 2000 years b p on the southwestern central segment of this fault system that ruptured 80 km we suggest the northeastern segment of the southeastern rift margin turned off in holocene when the reelfoot step over thrust turned on

the 6 june 2003 bardwell kentucky earthquake sequence evidence for a locally perturbed stress field in the mississippi embayment this article describes an unusually well behaved unusually well documented central and eastern united states ceus earthquake sequence detailed analysis of regional and local waveform data from the 6 june 2003 bardwell kentucky earthquake indicates that the mainshock has the seismic moment of m 0 1 3 0 5 10 15 n m m w 4 0 and occurred at a depth of about 2 1 km on a near vertical fault plane a temporary seismic network recorded 85 aftershocks that delineate an east trending fault approximately 1 km in length the hypocenters illuminate a vertical plane between 2 0 and 2 7 km depth the centroid of the aftershock distribution is at 36 875 n 89 010 w and a depth of 2 4 km the aftershock cluster is interpreted as a circular fault area with a radius of 0 44 0 03 km this source radius yields a static stress drop 67 14 bars for the mainshock the focal mechanism for the mainshock has strike 90 dip 89 and rake 165 with a subhorizontal p axis trending 135 a formal stress inversion based on the focal mechanisms of the mainshock and ten aftershocks indicates the maximum compressive stress trends 104 with a plunge of 5 the local stress field near bardwell is therefore rotated about 40 clockwise relative to 65 for eastern north america as a whole the bardwell earthquakes have the opposite sense of slip to earthquakes with east trending nodal planes that occur near new madrid missouri this requires a significant local rotation of the stress field over a distance of 60 km

shock induced volatile loss from a carbonaceous chondrite implications for planetary accretion solid recovery impact induced volatile loss experiments on the murchison c2m meteorite indicate that for an impact of a given velocity h 2o and total volatiles are driven from the sample in the same proportion as present initially we infer that the volatiles other than h 2o driven from the meteorite also have the same bulk composition as those of the starting material thus the early bulk composition of an impact induced atmosphere of a planet growing by accretion from material like murchison would be the same as the volatile composition of the incident planetesimals incipient devolatilization of murchison occurs at an initial shock pressure of about 11 gpa and complete devolatilization occurs at a pressure of about 30 gpa if an earth sized planet were formed from the infall of planetesimals of murchison composition incipient and complete devolatilization of accreting planetesimals would occur when the planet reached approximately 12 and 27 respectively of its final radius thus impact induced devolatilization of accreting planetesimals and of the hydrated surface would profoundly affect the distribution of volatiles within the accreting planet for example for a cold homogeneous accretion of a planet prior to metallic core formation and internal differentiation the growing planet would have a very small core with the same volatile content as the incident material a volatile depleted mantle and an extremely volatile rich surface

relationship between structures stress and seismicity in the charlevoix seismic zone revealed by 3 d geomechanical models implications for the seismotectonics of continental interiors 1 the charlevoix seismic zone in the st lawrence valley of quebec is the most active in eastern canada the structurally complex region comprises a series of subparallel steeply dipping iapetan rift faults superimposed by a 350 ma meteorite impact structure resulting in a heavily faulted volume the elongate seismic zone runs through the crater parallel to the rift most large events localize outside the crater and are consistent with slip along the rift faults whereas background seismicity primarily occurs within the volume of rock bounded by the rift faults within and beneath the crater the interaction between rift and crater faults is explored using the three dimensional stress analysis code flac3d the rift faults are represented by frictional discontinuities and the crater is represented by a bowl shaped elastic volume of reduced modulus differential stresses are slowly built up from boundary displacements similar to tectonic loading results indicate that weakening the rift faults produces a stress increase in the region of the crater bounded by the faults this causes a decrease in stability of optimally oriented faults and may explain the localization of low level seismicity additionally slip distribution along the rift faults shows that large events localize at the perimeter of the crater and produce focal mechanisms with p axes oblique to the applied stress field consistent with historic large earthquakes it is speculated that similar systematic rotation of focal mechanism p axes may be expected along other intraplate rift zones raising a potential caveat for the use of focal mechanisms for stress estimation in continental interiors

formation of metal and silicate globules in gujba a new bencubbin like meteorite fall gujba is a coarse grained meteorite fall composed of 41 vol large kamacite globules 20 vol large light colored silicate globules with cryptocrystalline barred pyroxene and barred olivine textures 39 vol dark colored silicate rich matrix and rare refractory inclusions gujba resembles bencubbin and weatherford in texture oxygen isotopic composition and in having high bulk 15n values 685 the 3he cosmic ray exposure age of gujba 26 7 ma is essentially identical to that of bencubbin suggesting that they were both reduced to meter size fragments in the same parent body collision the gujba metal globules exhibit metal troilite quench textures and vary in their abundances of troilite and volatile siderophile elements we suggest that the metal globules formed as liquid droplets either via condensation in an impact generated vapor plume or by evaporation of preexisting metal particles in a plume the lower the abundance of volatile elements in the metal globules the higher the globule quench temperature we infer that the large silicate globules also formed from completely molten droplets their low volatile element abundances indicate that they also formed at high temperatures probably by processes analogous to those that formed the metal globules the coarse grained bencubbin weatherford gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles a second class of bencubbin like meteorites represented by hammadah al hamra 237 and que 94411 may be a finer fraction derived from the same vapor cloud

a test of the longevity of impact induced faults as preferred sites for later tectonic activity the hypothesis that impact induced faults have been preferred sites for later deformation in response to lithospheric stresses has been suggested for several planets and satellites this hypothesis is investigated on earth by examining whether terrestrial impact structures show higher rates of nearby earthquake activity than do surrounding intraplate regions for 28 of 30 probable impact structures having an original crater 20 km or more in diameter the rates of nearby seismicity have been no higher than the regional background rates for two large probable impact structures vredefort and charlevoix with higher than normal rates of nearby seismicity factors other than slip on impact induced faults appear to control the occurrence of earthquakes it is concluded that impact induced faults at least on earth do not persist as lithospheric weak zones for periods in excess of several million years after the impact event

highly 15n enriched chondritic clasts in the cb ch like meteorite isheyevo the metal rich carbonaceous chondrites cb and ch have the highest whole rock 15n enrichments 15n up to 1500 among planetary materials they are also characterized by the absence of interchondrule fine grained matrix the only fine grained material is present as lithic clasts which experienced extensive aqueous alteration in contrast to the surrounding high temperature components chondrules refractory inclusions metal grains hence the clasts are foreign objects that were incorporated at a late stage into the final parent body of isheyevo their origin is poorly constrained based on mineralogy petrography and thermal processing of the aromatic carbonaceous component different types of clasts have been previously identified in the cb ch like chondrite isheyevo here we focus on the rare lithic clasts characterized by the presence of anhydrous silicates chondrules chondrule fragments and cais their mineralogy and oxygen isotopic compositions reveal them to be micro chondrules fragments of chondrules and refractory inclusions related to those in the isheyevo host suggesting accretion in the same region in contrast to previously studied idps or primitive chondritic matrices the fine grained material in the clasts we studied is highly and rather uniformly enriched in heavy nitrogen with bulk 15n values ranging between 1000 and 1300 it is also characterized by the presence of numerous 15n hotspots 15n ranging from 1400 to 4000 no bulk d 240 or localized deuterium enrichments were observed these clasts have the highest bulk enrichment in heavy nitrogen measured to date in a fine grained material they represent a unique material of asteroidal or cometary origin in our collection of cosmomaterials we show that they were 15n enriched before their incorporation in the final parent body of isheyevo they experienced an extensive aqueous alteration that most likely played a role in redistributing 15n over the whole fine grained material and may have significantly modified its initial hydrogen isotopic composition based on a review of isotopic fractionation models we conclude that the nitrogen isotopic fractionation process its timing and its location are still poorly constrained the 15n rich clasts may represent the surviving original carrier of the 15n anomaly in isheyevo whole rock

paleostress directions from the preferred orientation of closed microfractures fluid inclusion planes in sandstone east texas basin u s a abstract closed extensional microfractures are useful indicators of paleostress directions in shallowly buried quartz cemented quartz arenites of the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 670 m thick that was deposited in the gradually subsiding northern gulf of mexico basin the closed microfractures are syndiagenetic fluid inclusion rich planes that have an ene strike that is subparallel to contemporary quartz filled extension veins and regional normal faults indicating that closed microfractures contain the maximum paleostress direction these microstructures are potentially useful for mapping paleostress trajectories in passive margin and platform settings particularly where samples are obtained from core previous experimental studies of microfracture closure suggest that microfractures evolved into fluid inclusion planes by dendritic quartz precipitation in east texas microfracture closure may have occurred at temperatures as low as 85 c and depths as shallow as 1500 m

lake sediments and holocene seismic hazard assessment within the st lawrence valley quebec seismoacoustic profiling of 34 lacustrine basins within the st lawrence valley in southern quebec shows the presence of faulting convolution diapirs and gravitational slumping beneath within and at the surface of the holocene deep water sediment zone in small deep lakes in the highlands of the charlevoix tadoussac region a thin 2 6 m holocene organic sedimentary unit which directly overlies over a seismo opaque substratum exhibits considerable deformation these subaquatic sediment disruptions are exclusively restricted to lakes located within a radius of about 100 km of the well known charlevoix seismic zone according to the present seismicity of the region and the spatial distribution of the slump frequency the minimal triggering threshold for earthquakes was found to be as low as 0 17 g these results indicate that the charlevoix seismic zone has occupied the same area throughout at least the holocene and it appears that no major seismic shock has occurred over the past several thousand years outside of the zone

the role of geologic structure and stress in triggering remote seismicity in creighton mine sudbury canada a study was undertaken at the creighton mine near sudbury canada to investigate the relationships between geologic structure stress and seismicity creighton mine hosts numerous families of shear zones and experiences frequent microseismic and often macroseismic events underground structural mapping as well as microstructural and kinematic analysis are used to characterize faults fault geometries are then compared to those derived from seismic event focal mechanisms focal mechanism information is next used for stress inversion to obtain estimates of in situ principal stresses for three spatial clusters of events on the 7400 foot 2256 m level fault characteristics are then integrated into a numerical discontinuum model of the 7400 foot level of the mine to examine the distribution of stresses in the study volume the synthesis of these elements is used to determine the sources of seismicity within the deepest levels of the mine the major shear zones within the mine have not been found to contribute to seismicity via fault slip but do influence the flow of stress around the main excavation an anomalous cluster of microseismic events is postulated to be a result of induced stresses from mine development on deeper levels