iron magnesium order disorder in an orthopyroxene crystal from the johnstown meteorite abstract equilibrium reversals of fe 2 mg distribution between the m1 and m2 sites of an orthopyroxene from the johnstown meteorite were achieved at several temperatures between 700 and 1000 c one single crystal was used for the whole thermal treatment and for collecting all the x ray data after quenching the intracrystalline ion exchange for the bulk chemical composition mg 1 453 fe 0 441 cr 0 024 ca 0 054 mn 0 015 fe 0 005 ti 0 003 al 0 005 si 1 960 al 0 040 o 6 is given by ln k d 3027 39 t k 0 872 0 013 where k d is the distribution coefficient for the reaction fe m2 2 mg m1 mg m2 fe m1 2 a transmission electron microscopy tem study of part of the crystal showed the presence of very thin augite lamellae and guinier preston zones indicating a relatively rapid cooling of the host rock at temperatures close to 1000 c the new temperature scale yields a relatively high quenching temperature of 379 8 c for the pyroxene which appears consistent with a rapid cooling estimated few degrees per hundred years of a magmatic cumulate excavated by an impact on its parental body

observations of anomalous acoustic penetration into sediment at shallow grazing angles buried mines pose a difficult problem for mine countermeasures operations mines may naturally bury in coastal waters where wave induced effects are significant near the bottom current techniques for acoustic detection and classification of a buried mine require a high resolution imaging sonar with bottom penetrating capability recently anomalous acoustic penetration into sediment at shallow grazing angles was observed during a series of experiments which acoustically characterized the shallow water environment these experiments employed a stationary sonar tower complete with pan and tilt motors in the initial experiments backscattered returns from objects of opportunity were recorded these objects were either partially or completely buried near the water sediment interface in a later experiment buried calibrated retroreflectors and a buried hydrophone were also utilized the hydrophone was used to measure in sediment sound pressure levels results of the backscattered returns from the objects of opportunity and calibrated retroreflectors will be presented also the measured in sediment sound pressure levels will be compared to the safari seismic and acoustic fast field algorithm for range independent environments code and will be further compared to results reported in the literature work supported by the office of naval research

cooling history of lunar mg suite gabbronorite 76255 troctolite 76535 and stillwater pyroxenite sc 936 the record in exsolution and ordering in pyroxenes we have determined cooling rates of orthopyroxene crystals from two mg suite lunar samples gabbronorite 76255 and troctolite 76535 and one terrestrial sample orthopyroxenite sc 936 from the stillwater complex on the basis of their fe mg ordering states in addition a cooling rate of 76255 was determined by modeling the formation of exsolution lamellae in pyroxenes the m1 m2 site occupancies of the orthopyroxene crystals were determined by single crystal x ray diffraction and the rate constant for the ordering reaction was used along with calibrations of the equilibrium intracrystalline fractionation of fe and mg as a function of temperature to calculate cooling rates the closure temperatures tc of cation ordering are 525 c for 76255 500 c for 76535 and 350 c for sc 936 corresponding to cooling rates of 4 10 2 c year at the closure temperature for the lunar samples and 10 6 c year for the stillwater sample a cooling rate for 76255 determined by simulating the exsolution process is 1 7 10 2 c year at a closure temperature for exsolution of 700 c the fe mg ordering cooling rate determined for 76535 reflects a complex thermal history superimposed on the initial plutonic provenance established for this sample mccallum i s schwartz j m 2001 lunar mg suite thermobarometry and petrogenesis of parental magmas j geophys res 106 27969 27983 the preservation of a crystallization age of 4 51 ga and a metamorphic age of 4 25 ga for 76535 is consistent with a model in which excavation of this sample from the lower lunar crust took place while the sample was at a temperature above the closure temperatures for the sm nd u pb and ar ar isotopic systems temperatures in excess of the isotopic closure temperatures i e 600 c in the lower lunar crust were maintained by heat diffusing from concentrations of u and th rich kreep material at the base of the crust on the other hand 76255 formed at a much shallower depth in the lunar crust 2 km and was well below its isotopic closure temperatures at the time of excavation most likely during the serenitatis basin forming impact event both lunar samples were reheated during transport to the surface and deposition in hot ejecta blankets the reheating was short lived but apparently sufficient to redistribute fe and mg in m sites in orthopyroxenes for the lunar samples the cooling rates based on fe mg ordering represent final stage cooling within an ejecta blanket

cation ordering of orthopyroxenes from the skaergaard intrusion implications for the subsolidus cooling rates and permeabilities we have determined the quenched cation ordering states of five orthopyroxene crystals collected from the marginal border group and the lower zone a and b of the skaergaard intrusion and modeled these data to retrieve their closure temperatures tc of fe mg ordering and cooling rates according to existing thermal models for the skaergaard pluton conductive cooling dominated the high and low temperature regimes which were separated by an intermediate temperature regime in which the cooling was controlled primarily by convective fluid circulation the cooling rates retrieved from the quenched cation ordering states of the orthopyroxene crystals strictly apply to temperatures around the closure temperatures of the ordering states 340 400 c which fall at the transition from convective to the lower temperature conductive cooling the cooling rates obtained from the cation ordering states of orthopyroxene vary from 1 to 270 k ka these results agree well with a thermal model calculated using an assumed average permeability of 10 12 cm2 for the pluton but not completely with a model calculated on the basis of an average permeability of 10 13 cm2 although both values produced shifts of 18o that are comparable to those observed in the pluton

a new calibration to determine the closure temperatures of fe mg ordering in augite from nakhlites recently it has been shown that the relatively low closure temperature tc of 500 100 c calculated for augite from miller range nakhlite mil 03346 13 using the available geothermometers would correspond to a slow cooling rate inconsistent with the petrologic evidence for an origin from a fast cooled lava flow moreover previous annealing experiments combined with hr sc xrd on an augite crystal from mil 03346 clearly showed that at 600 c the fe2 mg degree of order remained unchanged thus suggesting that the actual tc is close to this temperature in order to clarify this discrepancy we undertook an ex situ annealing experimental study at 700 800 and 900 c until the equilibrium in the intracrystalline fe2 mg exchange is reached using an augite crystal from miller range nakhlite mil 03346 13 with a composition of about en36fs24wo40 these data allowed us to calculate the following new geothermometer calibration for martian nakhlites where the application of this new equation to other martian nakhlites nwa 988 and nakhla suggests that for augite with composition close to that of mil 03346 the tc is up to 170 c higher with respect to the one calculated using the previous available geothermometer equation thus suggesting a significantly faster cooling in agreement with petrologic evidence

activity along the osning thrust in central europe during the lateglacial ice sheet and lithosphere interactions abstract the osning thrust is one of the major fault systems in central europe with a length of approximately 115 km it underwent a polyphase tectonic evolution in the mesozoic that ranged from extensional movements in the jurassic to reverse faulting and thrusting during inversion in the late cretaceous a series of complex metre scale faults and related fold structures are developed within the upper pleistocene alluvial aeolian complex of the upper senne 1 km away from the thrust the faults dip towards the north and show offsets in a range of several decimetres growth strata indicate a two fold evolution of the structures the faults began as normal faults and were later transformed into reverse faults which resulted in the formation of small scale inversion structures with a typical harpoon shape glaciotectonics can be ruled out as the driving mechanism for these structures because new optically stimulated luminescence osl ages imply that the sedimentary succession was deposited during the late pleistocene between 29 3 2 9 ka and 13 1 1 5 ka at which time the ice margin was much further to the northeast we believe the inversion structures were caused by movement on the osning thrust due to generation of a forebulge of the late pleistocene weichselian ice sheet this led to normal faulting as a consequence of extension in the forebulge area during glaciation the osl ages for the normal fault related growth strata are in a range of 16 13 ka later reverse movements occurred during deglaciation due to the n s directed compressional stress field in northern germany numerical simulations of the deglaciation seismicity point to seismic events with a thrust mechanism in the study area between 15 5 and 12 3 ka bp although normal faulting is also possible in this time period numerous soft sediment deformation structures imply that movement on the osning thrust caused earthquakes with a significant magnitude in the autumn of 1612 an earthquake took place in this area it is very likely that this event is related to background seismicity on this fault although movement due to the influence of the ongoing glacial rebound in fennoscandia is also possible

active faults and paleoseismicity in fennoscandia especially sweden primary structures and secondary effects abstract fennoscandia today a region of low to moderately low seismicity was at the time of deglaciation with rates of uplift on the order of tens of centimetres per year a region of very high seismicity and active tectonics this is evident both from primary fault structures and from secondary sedimentary and hard rock effects in the region around the epicentral areas the map of active faults in fennoscandia includes numerous structures previously not recognised despite this the recording of active faults and paleoseismic events is still in its initial phase much more data will surely accumulate in the near future

deglacial and postglacial sedimentary architecture in a deeply incised paleovalley paleofjord the pennsylvanian late carboniferous jejenes formation san juan argentina quebrada de las lajas near san juan argentina preserves an early pennsylvanian deglacial postglacial succession in a highly confined paleofjord setting the sedimentary succession records four distinct stages in the evolution of the valley fill stage 1 is represented by the deposits of subglacial diamictites ice contact deltas and related deep water lacustrine environments including several subaqueous channels stage 2 records a glacio eustatic marine transgression and a slow down of the clastic supply into the paleofjord stage 3 records a sandy confined turbidite environment stage 4 consists of a coarse grained delta which represents a significant rejuvenation of the sedimentary system in the paleofjord the transition from stage 1 to stage 2 was abrupt and basinwide and has proven to be a good regional correlation marker in this paleovalley the glacio eustatic rise probably caused floating and consequent rapid melting of the valley glacier this resulted in a paleovalley wide turbidite event that is up to 5 m thick and indicates an overall waning character the rapid sediment emplacement in this event and resulting loading of the paleovalley sediments may have helped cause widespread mass transport events at the stage 1 2 boundary all stages show evidence of mass transport related deposits but stage 1 records the most widespread mass transport with a large spectrum of processes represented including coherently slumped material rafted blocks and completely mixed debris flow deposits these mass transport deposits range from a few meters to over 50 m thick and up to hundreds of meters wide and long most of the large mass transport deposits in the lower part of the fjord fill occurred at the transition to stage 2 implicating a rise in relative sea level as a possible trigger for the slope failures additionally stage 3 deposits were affected by several thrust sense dislocations that have large offsets relative to the scale of the sedimentary succession tens to over 50 m vertically and hundreds of meters laterally strata associated with the dislocations exhibit growth indicating very early movement and they are interpreted as the frontal ramp zones of mass transport deposits the abundance and size of mass transport deposits in stages 1 and 3 helped control sediment pathways throughout the paleofjord

trace element constraints on the differentiation and crystal mush solidification in the skaergaard intrusion greenland new major and trace element analyses of plagioclase and clinopyroxene in gabbros from the skaergaard intrusion are used to understand the mechanisms of crystallization in the main magma body and in the crystal mush crystal cores show a continuous chemostratigraphic evolution in the layered series with compatible elements e g cr and ni in clinopyroxene being progressively depleted from the bottom up whereas incompatible elements e g sr ba ree in plagioclase and clinopyroxene become progressively enriched we performed numerical models and showed that these trends can be explained by a simple process of fractional crystallization except for the upper 20 of the intrusion where plagioclase and clinopyroxene trace element compositions depart from fractional crystallization trends at this stage of magma chamber solidification fractional crystallization becomes less efficient and is replaced by a major proportion of in situ equilibrium crystallization trace elements also show significant variations in interstitial overgrowths on plagioclase and clinopyroxene cumulus crystals they result from crystallization of the interstitial liquid in the liquid crystal mush however incompatible elements and especially ree show a degree of enrichment in plagioclase rims 20 ppm ce that strongly exceeds the highest concentrations observed in plagioclase cores up to 4 ppm ce at the top of the layered series such a strong enrichment is difficult to reconcile with a simple process of fractional crystallization of the interstitial liquid in the crystal mush but may be related to the development of silicate liquid immiscibility in the crystal mush or to delayed nucleation of apatite after the crystallization of plagioclase and clinopyroxene overgrowths diffusive re equilibration during a period of 0 1 0 25 myr significantly changed the original zoning profiles ce flux from clinopyroxene into the plagioclase lattice of adjacent crystals could also have contributed to the strong ce enrichment observed in plagioclase rims

poly phase metamorphism of garnet bearing mafic granulite from the larsemann hills east antarctica p t path u pb ages and tectonic implications abstract a rare garnet bearing mafic granulite boulder has recently been identified from the larsemann hills east antarctica with the development of two stage decompression textures detailed petrographic study and p t estimates suggest three distinct metamorphic stages 1 peak ultrahigh temperature uht stage m1 represented by coarse grained garnet orthopyroxene bearing porphyroblastic assemblage with p t conditions of 9 3 kbar and 900 950 c 2 post peak decompression stage i m2 represented by relatively coarse grained orthopyroxene plagioclase ilmenite bearing corona assemblage with p t conditions of 7 2 7 6 kbar and 810 830 c and 3 post peak decompression stage ii m3 represented by fine grained orthopyroxene plagioclase ilmenite bearing symplectite assemblage on garnets and along garnet cracks with p t conditions of 6 2 6 9 kbar and 730 770 c combined with p t pseudosection calculation in the nckfmashto system these p t data define a clockwise p t path with post peak two stage decompression accompanied by important cooling la icp ms zircon u pb age dating results show two weighted mean ages of 927 13 ma and 547 30 ma suggesting that m1 uht stage occurred in the early neoproterozoic rayner orogeny 990 900 ma whereas m2 m3 stages occurred during the early palaeozoic pan african tectonic event 550 500 ma the peak p t conditions post peak two stage decompression p t path and age data resemble those of the early neoproterozoic garnet bearing mafic granulite on sostrene island it is inferred that the mafic granulite boulder may have been derived from the bedrock under inland ice sheet of the larsemann hills thus the early neoproterozoic metamorphism m1 may reflect crustal thickening followed by post orogenic extension likely associated with the assembly of rodinia continent while the overprinting of early palaeozoic metamorphism m2 m3 may reflect an extensive intra continental reworking

in absurdum long term predictions and nuclear waste handling abstract careful use of scientific knowledge allows predictions into the future when the time units for our predictions increases to hundreds of thousands of years we have extended our abilities in absurdum this is true for long term safety statements regarding the handling of our high level nuclear waste the fennoscandian shield has been claimed to offer exceptionally stable bedrock conditions over immense time periods we only need to go back to the last deglacial phase some 10 000 years ago to have a totally different situation from that of today at that time sweden was characterized by exceptionally high seismic activity both in amplitude and frequency these conditions like a number of related phenomena will be repeated at future ice ages in such an environment there can be no safe repository in the bedrock in the absence of true long term safety we can only recommend the utilization of the dry rock deposit drd method where the waste is stored in the bedrock under dry conditions under constant control and monitoring accessible for maintenance and possible future methods of rendering the waste harmless and even removal

reclassification and thermal history of trenzano chondrite we present a new single crystal x ray diffraction xrd study performed on a suite of six orthopyroxene grains from the low shocked h6 trenzano meteorite the quenched intracrystalline fe 2 mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature tc thus yielding useful constraints on the last thermal event undergone by the host rock the orthopyroxene tc of 522 13 c calculated using a new calibration equation obtained by stimpfl 2005b is higher than in previously published h chondrite data the orthopyroxene cooling rate at this tc is about 100 c kyr this fast rate is inconsistent with the much slower cooling rate expected for h6 in the onion shell structural and thermal model of chondrite parent bodies a petrographic study carried out at the same time indicated that the trenzano meteorite is an h5 chondrite and not an h6 chondrite as it is officially classified furthermore the two pyroxene equilibrium temperature of trenzano 824 24 c calculated with quilf95 is similar to the two pyroxene temperature of 750 840 c obtained for the carcote h5 chondrite kleinschrot and okrusch 1999

debris flow and glacioisostatic induced soft sediment deformation structures in a pleistocene glaciolacustrine fan the southern baltic sea coast poland abstract middle pleistocene glaciolacustrine fan sediments are exposed along a cliff at the baltic sea coast where plastic and brittle soft sediment deformation structures ssds commonly occur 1 fold structures various types of folds and flexures 2 load structures load casts pseudonodules and flame structures 3 water escape structures wes and 4 brittle deformation structures such as faults medium and small scale reverse and normal and fragments of broken up laminae the origins of the ssds can be linked to gravitational processes promoted by shear stresses in subaqueous debris flows on the glaciolacustrine fan and by the weight of overlying sediments and or to the glacial rebound of earth s crust during deglaciation because in the pleistocene the baltic sea and surrounding areas were covered by ice sheets many times the question investigated here concerns recognition of the trigger mechanisms responsible for the development of ssds and the criteria needed to recognize those mechanisms based on the lithological and deformational features of the sediments involved some types of ssds can look similar regardless of trigger mechanisms but some occur more often as a result of a specific mechanism is it possible to distinguish ssds of seismic origin in a glaciolacustrine fan succession affected by multiple debris flows and of ssds that evolved as a consequence of slope processes we suggest criteria to recognize ssds triggered by the glacioisostatic rebound as well as those which can develop as a result of the rebound and slope processes

the hofðaholar rock avalanche sturzstrom chronological constraint of paraglacial landsliding on an icelandic hillslope the hof aholar rock avalanche in the skagafjor ur area of northern iceland was investigated on the basis of a geomorphological analysis of its landforms and close surrounding environment thanks

penetration of acoustic waves into rippled sandy seafloors the helmholtz kirchhoff integral and the kirchhoff approximation are applied to model the penetration of sound waves into rough sandy seafloors at grazing angles above and below the critical angle as the seafloor of interest is anisotropic emphasis is placed on simulating the response from a two dimensional interface the analytical development of the method is first presented followed by numerical examples simulations and data acquired at sea are in very good agreement in the 2 15 khz band maguer et al j acoust soc am 107 1215 1225 2000 the model predicts in agreement with the 2 15 khz acoustic data the contributions due to roughness effects that dominate the evanescent wave component over most of this frequency band secondary effects such as coherent bragg influence patterns and the loss of signal coherence with grazing angle or depth are correctly predicted the model simulations strongly suggest that roughness of the sediment interface is most likely the cause of anomalous sound penetration into the seabed

thermal history of mesosiderites quantitative constraints from compositional zoning and fe mg ordering in orthopyroxenes abstract we have derived mathematical relations to calculate cooling rates from the extent of compositional zoning developed during cooling across the interface of a natural diffusion couple these relations were used to calculate the high temperature cooling rates of the mesosiderites lowicz and clover springs from the available data on compositional zoning across core overgrowth interface of orthopyroxene grains we have also determined the cation ordering in four selected orthopyroxene crystals from bondoc and estherville mesosiderites with very high precision and used these data to calculate their low temperature cooling rates the compositional zoning of orthopyroxene crystals reflects extremely rapid cooling rates at least 1 c 100 years in the temperature range 850 1150 c however simultaneous consideration of both metallographic and cation ordering data for estherville within the framework of either an asymptotic or an exponential cooling model requires a cooling rate of l c ma near 250 c the cation ordering data for bondoc for which no metallographic data are yet available are suggestive of even slower cooling rate which implies excavation from a somewhat greater depth in the parent body however within the limits of their uncertainties the measured site occupancies of the orthopyroxene crystals from bondoc can be reconciled with a cooling rate similar to that of estherville the calculated cooling rates at both high and low temperatures have been used to develop a thermal evolution model of mesosiderites the suggested model is not incompatible with an asteroidal parent body for these meteorites further it is shown that the closure temperature of ar ar age must be tied to the slow cooling rate below 500 c

paleoseismicity the swedish case abstract sweden is part of an old cratonic area it was repeatedly glaciated during the quaternary after the 20 ka glaciation maximum it has experienced a glacial isostatic uplift of over 800 m numerous paleoseismic indices have been recorded giving evidence of frequent high magnitude earthquakes from the time at around and just after the deglaciation late holocene archaeoseismic fracturing is also reported these observations violate all claims of a possible safe long term repository for high level nuclear waste some 500 m down in the bedrock

thermal history of acapulco and alha81261 acapulcoites constrained by fe2 mg ordering in orthopyroxene the quenched fe2 mg ordering states of four orthopyroxene crystals from the acapulco meteorite and two from the antarctic alha81261 acapulcoite were determined from x ray single crystal diffraction and electron microprobe analysis the closure temperatures of cation ordering were 49028 and 46543 c for acapulco and alha81261 respectively kinetic analysis of the fe2 mg intracrystalline reaction on the basis of mueller s theory 1 2 was carried out using the method developed by ganguly 3 to measure the cooling rates of the host rock assuming both asymptotic and exponential models the determined ordering states yield cooling rates near their closure temperatures of 0 17 and 0 05 c day for acapulco and alha81261 respectively slightly slower than that measured for the fro90011 lodranite 4 a break up of the a l parent body with subsequent radiative heat loss of small ejected fragments may explain such rapid cooling the closure temperatures obtained for the two acapulcoites were then compared with those calculated using the same method for other achondrites and their cooling rates with those measured for the fro90011 lodranite 4 and the estherville mesosiderite 5 the sequence of decreasing closure temperatures from the fro90011 lodranite to the landes iab iron meteorite reflects decreasing cooling rates silicates enclosed in iron meteorites and thus involved in core formation processes deeper in the interior of a parent asteroid seem to have cooled more slowly than meteorites that were affected by partial melting events

determination of the lower edges of magnetized bodies by using geothermal data summary the determination of the lower edges of magnetized bodies in the earth s crust is a complex geophysical problem although these values can be estimated by using geothermal data an analysis of the temperature regime and location of the lower edges of magnetized bodies has been carried out for the geosynclinal region of the southern caucasus and the area joining the ancient platform with the arabian shield in israel geothermal calculations for israel have been performed for three models of the thermal regime for the earth s crust and upper mantle the process of ultrabasic rock serpentinization is accompanied by the transformation of iron suboxide to iron oxide both these processes run under identical thermodynamic conditions within an average temperature interval of 200 400 c the curie surface controls the position of lower edges only in fault zones where oxidation conditions hold up to great depths

saline waters in basement rocks of the kaapvaal craton south africa abstract the chemical composition and geochemical evolution of saline waters found in deep 1 9 3 5 km gold mines in the kaapvaal craton south africa are reported and discussed twenty eight samples representing the most saline waters available were studied the salinity of the samples ranges between 2 5 and 99 g tds l 1 with chloride being the dominating anion magnesium is practically absent from most samples the kaapvaal waters were sampled in the carletonville region driefontein kloof mponeng and tau tona mines and at evander the samples defined as fracture waters were retrieved from the witwatersrand basin proterozoic quartzite rocks and from metamorphosed basalts and basaltic andesites based on water salinity na cl br cl ratios and ca mg so 4 relationship we conclude that the chemical composition of the waters stems from ancient seawater that experienced three major processes by the following order 1 concentration of seawater by freezing 2 density driven infiltration into the underlying crystalline basement accompanied by water rock interaction wri and 3 dilution of the brine by freshwater because the last glaciation in south africa occurred in carboniferous permian gastaldo et al 1996 we attribute this age to the kaapvaal brines rather than to a much earlier period proposed previously after their cryogenic concentration in a marginal trough around the gondwanan ice sheet the brines infiltrated and migrated into the underlying crystalline rocks through fissures and shear zones displacing less dense resident freshwater therein the brines were further modified via water rock interaction which included chloritization and albitization of ca plagioclase chloritization was responsible for the almost total removal of mg and so 4 from solution and for the significant ca enrichment observed albitization which affected only a part of the samples caused a loss of na and an additional equivalent gain in ca in view of similar findings limited so far to crystalline shields in the northern hemisphere our interpretation of the south african data may have a much farther reaching meaning we argue that similar saline waters should be expected at depth in all rocks crystalline and sedimentary alike in regions that were covered by major glaciers such as eastern south america large parts of australia india and antarctica during the carboniferous permian

impacts of post glacial rebound on landslide spatial distribution at a regional scale in northern iceland skagafjorður in de glaciated areas para glaciation i e the conditioning of landscapes by prior glaciation has often been considered a major predisposing factor in landslide occurrence its consequences have been particularly well identified at a fine scale especially on bedrock jointing hitherto the relative impacts of para glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically we examine skagafjor ur area northern iceland where landslides are widespread at least 108 were mapped in an area of c 3000km2 we compare the role of para glaciation debuttressing influence of post glacial rebound with that of classic factors topography lithology etc in landslide occurrence and location using a spatial analysis based on a chi square test on the one hand the results highlight that landslides are over represented in areas where post glacial rebound was at its maximum with a stronger concentration of landslides in the northern part of the fjord on the other hand the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing tschuprow coefficient highlights that the influence of post glacial rebound on landslide location is higher than the combined influence of slope gradient curvature or geological structure this result is supported by our initial evidence for the timing of landslides in the area most landslides occurred during the first half of the holocene and a period of hillslope instability was initiated when the post glacial uplift was at its maximum finally the mechanisms that link post glacial rebound and landsliding as well as the geomorphic impacts of landslides are discussed

thermal history of alh 84001 meteorite by fe2 mg ordering in orthopyroxene a single orthopyroxene crystal from the martian meteorite allan hills alh 84001 was studied by x ray diffraction xrd and electron microprobe analysis empa to retrieve information about its thermal history both sets of data were used to measure the fe 2 mg order degree between the m1 and m2 sites expressed by the distribution coefficient kd the 529 30 c closure temperature tc of the fe 2 mg ordering process of alh 84001 orthopyroxene fs28 was calculated using stimpfl 2005a 2005b lnkd versus 1 t equation obtained for intermediate iron sample at this tc the orthopyroxene cooling rate calculated by ganguly s 1982 numerical method was 0 1 c day this study puts new constraints on the last high temperature thermal episode recorded by orthopyroxene with reference to the geological history treiman 1998 we ascribe this episode to the i3 event and we interpret the tc of 529 c as a lower limit for this impact heating our data confirm that experimentally defined physical conditions for the formation of magnetite from decomposition of carbonates took place on the martian surface during event i3

recent fault movement and palaeoseismicity in western scotland abstract field study at two locations in western scotland is described and gives evidence for fault movement and seismic activity during the late and post glacial epochs the evidence comprises levelling survey of raised marine shorelines remote sensing study of lineaments radiocarbon dating of quaternary sediment and detailed field examination of faults and fault gouge material vertical fault displacements of up to 3 m are observed on a c 10 500 year old raised marine shoreline on the isle of mull and repeated predominantly lateral movement is observed on a prominent 14 km long fault lineament active since ice retreat and as recently as c 2000 yrs b p the fault movements are located close to the edge of the area formerly covered by the loch lomond readvance ice cap 11 000 10 000 yrs b p they are considered to have been caused by rapid rates of isostatic rebound soon after deglaciation

the post glacial landscape evolution of the north german basin morphology neotectonics and crustal deformation the recent evolution of the north german basin ngb which is presently a low seismic area was partly affected by glacial loading and unloading of the ice masses major stresses acting within the ngb are induced by the north atlantic ridge push the ongoing alpine collision and the post glacial rebound of fennoscandia present day horizontal stresses within the ngb are directed generally nw se but fan and bend north of 52 n towards nne major basement faults are directed nw se minor faults ne sw and nne ssw and are clearly detectable in geomorphological and satellite lineaments furthermore the drainage pattern and the distribution of lakes in northern germany follow exactly block boundaries and hence mark zones of present day subsidence the understanding of the post glacial morphology and reactivation of faults requires a view into the very heterogeneous crust and upper mantle below the ngb the re adjustment of the individual fault blocks during post glacial relaxation of the lithosphere leads to differential crust dependent uplift and probably to the formation of urstrom valleys the urstrom valleys and terminal moraines in northern germany appear to parallel the major tectonic lineaments and lithospheric block boundaries the lithospheric memory is expressed in the post glacial landscape evolution of the ngb

intense earthquakes and seismotectonics as a function of glacial isostasy abstract old shields and plate interiors have often been assumed to exhibit a high crustal stability during the last decade or two we have learnt more and more about the fragility not to say untenability of this concept however high magnitude earthquakes and large scale fault movements have been recorded where they were not supposed to be able to occur within formerly glaciated areas like northern europe scotland and northern north america a rapidly increasing number of field observations indicates that the glacial isostatic readjustment process was linked to intense seismotectonic activity we will here investigate the fennoscandian situation and propose a novel causation model for the high deglaciation seismicity in comparison with the present day situation

course and origin of the fennoscandian uplift the case for two separate mechanisms the classical glacial isostatic uplift paradigm of fennoscandia is in need of a thorough revision as to its course and origin the total uplift amounts to 830 m not 300 m the centre of uplift started to rise 13 000 bp not 9300 bp the uplift appears to be composed of two separate mechanisms one true glacial isostatic rebound and one linear uplift factor possibly representing a phase boundary adjustment calculations and modelling must treat these two factors independently which has not been the case

liquefaction and varve deformation as evidence of paleoseismic events and tsunamis the autumn 10 430 bp case in sweden coastal seismic events generate instantaneous changes in relative sea level i e land level vs sea level tsunamis may cause disastrous damage to coasts and coastal habitation liquefaction and deformations of annually varved sediments provide information on paleoseismic events the evidence for a major earthquake and associated tsunami waves in sweden are explored thanks to the varve chronology liquefaction structures and varve deformations caused by this event can be dated at the autumn 10 430 varve years bp the magnitude is estimated at 8 or more on the richter scale the tsunami washed the previously blocked outlet of the baltic free of icebergs and pack ice so that marine water could suddenly invade the entire baltic forming the yoldia sea

mechanisms for subcritical penetration into a sandy bottom experimental and modeling results this paper presents preliminary results of a recent study whose overall objectives are to determine the mechanisms contributing significantly to subcritical acoustic penetration into ocean sediments and to quantify the results for use in sonar performance prediction for the detection of buried objects in situ acoustic measurements were performed on a sandy bottom whose geoacoustical and geomorphological properties were also measured a parametric array mounted on a tower moving on a rail was used to insonify hydrophones located above and below the sediment interface data covering grazing angles both above and below the nominal critical angle and in the frequency range 2 15 khz were acquired and processed the results are compared to two models that account for scattering of sound at the rough water sediment interface into the sediment although all possible mechanisms for subcritical penetration are not modeled the levels predicted by both models are consistent with the levels observed in the experime

submarine holocene sedimentary disturbances in the olkiluoto area of the gulf of bothnia baltic sea a case of postglacial palaeoseismicity abstract high resolution echo soundings were used to study the fault activity in the olkiluoto area of the gulf of bothnia southwestern finland echo sounding profiles in holocene submarine sediments show normal faults structures related to gas or groundwater seepage submarine slides and slumps and debris flow type structures the faults and other disturbance structures occur along two bedrock lineaments all faults occur at the same stratigraphical level whose age is estimated at 10 700 calendar years bp 9500 radiocarbon years bp it is suggested that their movement has been triggered by palaeoseismic event s when the late weichselian ice sheet was retreating from the site and bedrock stresses were released through lineaments and fracture zones these are the first observations of postglacial fault movements in quaternary sediments from southern finland but the timing of these movements is contemporaneous with the incidence of postglacial bedrock faulting 9000 10 000 radiocarbon years bp in northern fennoscandia the origin of the gas groundwater seepages remains unclear their reflections in the echo sounding profiles imply that part of the gas is derived from the organic bearing litorina and recent gyttja clays however at least some part of the gas is derived from the bedrock deep gas

orthopyroxene as a geospeedometer thermal history of kapoeta old homestead 001 and hughes 004 howardites 1dipartimento di scienze della terra universitti di pavia via ferrata 1 27100 pavia italy 2dipartimento di mineralogia e petrologia universitti di padova c so garibaldi 37 35122 padova italy 3dipartimento di scienze della terra universitil di messina salita sperone 31 98166 messina s agata italy 4centro grandi strumenti universitti di pavia via bassi 21 27100 pavia italy correspondence author s e mail address domeneghetti crystal unipv it

linking continental slope failures and climate change testing the clathrate gun hypothesis it has been suggested that the release of clathrates rather than expansion of wetlands is the primary cause of the rapid increases observed in the ice core atmospheric methane record during the pleistocene because submarine sediment failures can involve as much as 5000 gt of sediment and have the capacity to release vast quantities of methane hydrates one of the major tests of the clathrate gun hypothesis is determining whether the periods of enhanced continental slope failure and atmospheric methane correlate to test the clathrate gun hypothesis we have collated published dates for submarine sediment failures in the north atlantic sector and correlated them with climatic change for the past 45 k y more than 70 by volume of continental slope failures during the past 45 k y was displaced in two periods between 15 and 13 ka and between 11 and 8 ka both these intervals correlate with rising sea level and peaks in the methane record during the bolling allerod and preboreal periods these data support the clathrate gun hypothesis for glacial interglacial transitions the data do not however support the clathrate gun hypothesis for glacial millennial scale climate cycles because the occurrence of sediment failures correlates with heinrich events i e lows in sea level and atmospheric methane a secondary use of this data set is the insight into the possible cause of continental slope failures glacial period slope failures occur mainly in the low latitudes and are associated with lowering sea level this finding suggests that reduced hydrostatic pressure and the associated destabilization of gas hydrates may be the primary cause the bolling allerod sediment failures were predominantly low latitude suggesting an early tropical response to deglaciation e g enhanced precipitation and sediment load to the continental shelf or warming of intermediate waters in contrast sediment failures during the preboreal period and the majority of the holocene occurred in the high latitudes suggesting either isostatic rebound related earthquake activity or reduced hydrostatic pressure caused by isostatic rebound causing destabilization of gas hydrates

the use of varved clay chronology for dating paleoseismic events the erstavik record in the stockholm area south sweden abstract geological structures suggest that the fennoscandian shield was subjected to a higher seismicity at the end of the last glaciation than today this article demonstrates the use of varved clay chronology for dating paleoseismic events it is argued that the deposited annually layered glacial varves were sensitive to past ground movements in the stockholm area the erstavik varved clay chronology suggests four paleoseismic events a first i dating from varve year 10 473 to 10 468 bp a second ii 10 451 to 10 445 bp a third iii 10 429 to 10 425 bp and a fourth iv 10 409 to 10 404 bp in de geer s old 1940 chronology the first i dating corresponds with 1117 to 1112 the second ii with 1095 to 1089 the third iii with 1073 to 1069 and the fourth iv with 1053 to 1048 the most pronounced event was the one at around varve year 10 429 bp varve 1073 in de geer s old chronology the recurrence time of about 20 years suggests a totally different seismic regime at the time of deglaciation than what exists today it coincided with the period of maximum isostatic uplift the complexity of the varved clay response to seismic events is also discussed

cooling rates of diogenites a study of fe2 mg ordering in orthopyroxene by single crystal x ray diffraction the iron magnesium exchange between m1 and m2 sites in orthopyroxene is a reversible reaction that records the latest event in the thermal evolution of the host rock a kinetic analysis of this process has been applied to 16 orthopyroxene single crystals from 7 different diogenites to constrain the cooling history of their parent body the fe2 mg ordering degrees have been determined by single crystal x ray diffraction the fe2 mg ordering closure temperatures were very homogeneous within each sample and ranged for all diogenites studied between 311 29 c and 408 10 c cooling rates at these closure temperatures were calculated using a numerical method developed by ganguly 1982 these ranged between 5 c 104 year in johnstown and 0 8 c year in roda a comparison with other achondrites studied with the same method showed that increasing closure temperatures correspond to increasing cooling rates and that meteorites from a same parent body exhibit similar closure temperature and cooling rate values the cooling rates obtained for these diogenites at their low closure temperatures should probably be ascribed to a complex thermal history of their parent body thus confirming miyamoto and takeda s theory 1994a of excavation of deep crustal material due to impact events the differences on cooling rate values for different diogenites could be due to different burial depths in the fragment ejected from the parent body

40ar39ar dating of the skaergaard intrusion we report the first 40ar 39ar data for the skaergaard intrusion based on analyses of hornblende and biotite from a transgressive granophyre from upper zone a uza of the layered series hornblende separates heated in a resistance furnace and laser heated single crystals of biotite from the granophyre give plateau ages that are consistent with isochron ages of 55 48 0 30 and 55 40 0 14 ma respectively 2 internal uncertainty with initial 40ar39ar ratios of 292 4 19 0 and 291 1 7 2 if uncertainties in the ages of 40ar 39ar standard fluence monitors are considered external uncertainties 2 errors are 0 76 and 0 72 ma respectively resistance heating analysis of biotite separated from a gabbro from lower zone a lza of the skaergaard layered series indicates that the sample has been extensively contaminated by ar inherited from old crust and does not constrain the intrusion age apart from indicating that it is less than approximately 57 ma old the ar cooling ages are consistent within uncertainty with both pluton cooling models presented by norton and taylor 1 but the data agree best with their model s2 which assumes a smaller permeability 10 13 cm2 combination of the new ages and the norton and taylor cooling models constrains the emplacement and final crystallization of the skaergaard magma chamber to be at 55 75 0 30 ma and 55 65 0 30 ma respectively evidence for late crystallizing quartz and tridymite near the sandwich horizon sh combined with phase equilibria constraints on the near solidus crystallization temperature of the sh 975 25 c require the pressure of sh solidification to be 60 15 mpa this means that the tertiary basalts and sediments overlying the kangerdlugssuaq region were 3 2 0 8 km thick at 55 65 0 30 ma assuming that the 6 7 km thick tertiary section exposed further east along the east greenland coast is representative of that which accumulated above the skaergaard we infer that the skaergaard emplacement occurred during the main stage of the east greenland flood basalt event after approximately half of the tertiary section had erupted the onset of coastal flexure in the kangerdlugssuaq region was after 55 48 0 76 ma

neotectonics and paleoseismicity within the stockholm intracratonal region in sweden abstract a number of sites with fresh faults and fractures have been mapped in detail their postglacial and sometimes late glacial age is confirmed they form simple and similar patterns consistent with stress release due to a combination of acting forces they are associated with the peak rate of glacial isostasy and increased strain rates by two orders of magnitude they often cut straight across bedrock hills between so called weak zones the fault throws correspond to approximately magnitude 7 on the richter scale sedimentary and morphological data confirm the seismo tectonic origin newly discovered large scale network of crossing faults is found to have changed the course of the stockholm esker in a way that reveals at least two major seismo tectonic events this is consistent with paleoseismic events of magnitude 7 or more

paleoseismicity and geodynamics in sweden abstract paleoseismicity denotes past pre instrumental earthquakes as recorded by bedrock structures morphological features and sedimentological criteria glacial varves eskers and deltas are excellent records of paleoseismic events data from sweden are presented faults fractures and various types of sedimentary disturbances of late pleistocene and holocene age frequently occur it is concluded that the seismic activity was very intensive in connection with the peak rates of glacial isostatic uplift and that this was a natural effect of the geodynamic processes operating

postglacial faulting in eastern canada nature origin and seismic hazard implications abstract at more than 70 locations in southeastern canada and the adjacent united states tiny bedrock faults displace glacial striations that are about 10 000 years old these reverse faults mostly of small displacement occur in a broad arc from western ontario to newfoundland the faults lie near the margin of the laurentian ice sheet strike generally tangential to it and imply compression nearly normal to the ene directed contemporary regional stress these observations and some age relationships suggest that the faults formed very soon after deglaciation perhaps in the first few thousand years after ice melting in each place and probably represent the release of stresses caused by flexural deformation of the upper crust although the individual offsets are small the faults are believed to be pervasive and individual outcrops reflect amounts of stress relief consistent with stresses implied by the postglacial tilt of nearby lake shorelines

sedimentological evidence of pleistocene earthquakes in nw poland induced by glacio isostatic rebound abstract soft sediment deformation structures are abundantly present in two levels within warthanian eemian lacustrine sediments at siekierki near the polish german border the two event horizons show intense folding collapse sag and load structures indicative of liquidization and fluidization the structures must have been caused by sudden shocks most probably resulting from earthquakes that were induced by glacio isostatic rebound probably after the warthanian deglaciation such seismites have not been previously recognized in polish quaternary sediments they provide supporting evidence for glacio isostatic movements that were interpreted up till now based on drilling lithostratigraphic geophysical and geodetic data the recognition of seismites in nw poland may help recognize other deformed event horizons in pleistocene sediments as glacio isostatic or neotectonic seismites

variable isostatic uplift patterns during the holocene in southeast sweden based on high resolution ams radiocarbon datings of lake isolations the construction of a new highway between uppsala and mehedeby in northern uppland southeastern sweden has motivated extensive archaeological excavations to describe changes in shoreline configuration over time the isolation of nine lake basins has been interpreted from diatom analysis their isolation ages were determined from 45 ams radiocarbon dates five per site of terrestrial macrofossils mainly betula and alnus seeds the isolation ages and the corresponding altitudes indicate a complicated pattern of isostatic uplift during the late holocene neither the present day isobases nor those for the neolithic sea seem to explain their isolation ages and corresponding altitudes in relation to their geographic distribution since at least some of the lakes are situated in a relatively pronounced topographic landscape we are inclined to explain the observations as the result of small scale irregular uplift earthquakes are rare in the area at present suggesting short term tectonic activities along e

geological evidence for neotectonic activity during deglaciation of the southern sperrin mountains northern ireland in the southern sperrin mountains northern ireland stacked glacigenic sequences that accumulated during deglaciation ca 17000 13000 yr bp overlie a basement of jointed and mascerated bedrock the glacigenic sequences comprise interbedded glaciotectonic shears diamictic breccias and rock rafts at one site a normal fault with a metre scale vertical displacement cuts through part of the sequence and is overlain by a glacial diamict sediments at an adjacent site show that faulting and associated hydrothermal activity was related to neotectonic reactivation of pre existing caledonian lineaments caused by ice unloading from stratigraphical and directional evidence fault reactivation occurred early in the deglaciation after north central ireland ice had retreated southwards into lowland areas but before sperrin mountain ice readvanced from the north this relationship provides evidence for the relative timing of neotectonic activity in northern ireland and demonstrates the effects of glacio isostatic unloading near ice sheet centres copyright 1999 john wiley sons ltd

soft sediment deformation of late pleistocene sediments along the southwestern coast of the baltic sea ne germany a 1 460 m long profile of a late glacial subglacial glacio fluvial glacio limnic and glacio deltaic sequence exposed at a cliff section on usedom island sw baltic sea coast is described the sequence is up to 31 m thick and shows sedimentary structures typical of a glacial setting soft sediment deformation is encountered and is associated with changes in lithology these deformations include liquefaction slumping and faulting as the most plausible cause earthquake induced shaking is discussed the associated neotectonic activity is seen as a consequence of the postglacial isostatic crustal rebound as the deglaciation earthquake ratio diminishes with time and as the rebound is phasing out no large earthquakes are anticipated for northern germany although in conclusion the lithosphere of the north german basin has to be regarded as weakened by repeated ice loading and deloading

late glacial and post glacial deposition in a large low relief epicontinental basin the northern baltic sea this paper presents a model of late glacial and post glacial deposition for the late neogene sedimentary succession of the archipelago sea in the northern baltic sea four genetically related facies associations are described i an ice proximal acoustically stratified draped unit of glaciolacustrine rhythmites ii an onlapping basin fill unit of rotated rhythmite clasts in an acoustically transparent to chaotic matrix interpreted as debris flow deposits iii an ice distal acoustically stratified to transparent draped unit of post glacial lacustrine weakly laminated to homogeneous deposits and iv an acoustically stratified to transparent unit of brackish water organic rich sediment drifts the debris flow deposits of the unit 2 pass laterally into slide scars that truncate the unit 1 they are interpreted to result from a time interval of intense seismic activity due to bedrock stress release shortly after deglaciation of the area ice berg scouring and gravitational failure of oversteepened depositional slopes may also have contributed to the debris flow deposition comparisons to other late neogene glaciated basins such as the hudson bay or glacial lakes formed along the laurentide ice sheet suggest that the archipelago sea succession may record development typical for the deglaciation phase of large low relief epicontinental basins the carboniferous permian glacigenic dwyka formation in south africa may provide an ancient analogue for the studied succession chronological control for the studied sediments is provided by the independent palaeomagnetic and ams 14c dating methods in order to facilitate dating of the organic poor early post glacial deposits of the northern baltic sea the 10 000 year long lake nautajarvi palaeomagnetic reference chronology ojala saarinen 2002 is extended by 1200 years

frost and soils implications for paleosols paleoclimates and stratigraphy abstract frost is a pedogenetic agent this paper describes the use of frost features in soil for paleoclimatic and stratigraphic interpretation it is possible to differentiate periods of frost activity from those of temperate pedogenesis by macroscopic and microscopic criteria and to distinguish between soils with pre syn and epigenetic frost effects an experimental approach is necessary to determine initial frost effects because they are usually difficult to observe at natural active sites work with ecologists also clarifies the evolution of frost affected soils under climatic and vegetational constraints vegetation has important effects on the thermal and hydraulic regimes of soils and on erosion susceptibility the recognition of fossil cryosoils often allows the reconstruction of sequences of paleoclimatic events in periods or environments with little or no micropaleontological evidence the interrelations between frost and other pedogenetic processes allow a better understanding of climatic evolution and deterioration throughout the neogene and especially during the quaternary and the holocene most of the inherited frost features in european soils are younger than 480 ka bp the differentiation between frost and tectonic perturbations is very important for calculation of soil erosional budgets