apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

detecting the thermal aureole of a magmatic intrusion in immature to mature sediments a case study in the east greenland basin 73 n the cretaceous and triassic argillaceous rocks from the passive margin of greenland have been investigated in order to detect the thermal aureole of magmatic intrusions ranging from metric dyke to kilometric syenite pluton rock eval data tmax generally 0 3 all indicate a maximum of 5km burial for the argillaceous rocks whatever the distance to an intrusion the k ar dating of the clays 2 m fraction suggests that illites are mostly detrital except near magmatic intrusions where younger ages are recorded to get more information about the extent of the thermal aureole rock magnetism data were determined at distance away from the thermal aureole of the syenite intrusion triassic argillaceous rocks reveal a standard magnetic assemblage compatible with their burial r 0 4 percent it is constituted essentially by neoformed stoichiometric magnetite fe o in contrast within the thermal aureole of the magmatic intrusions the cretaceous argillaceous rocks contain micron sized pyrrhotite fe s firmly identified through the recognition of besnus transition at 35k the thermal demagnetization of natural remanence carried by this pyrrhotite shows a diagnostic square shouldered pattern indicating a narrow grain size distribution of pyrrhotite the extension of this diagnostic pyrrhotite maps a 10 km thick aureole around the syenitic pluton away from this aureole the magnetic assemblage is diagnostic of those found in argillaceous rocks where organic matter is mature

eros rahe dorsum implications for internal structure an intriguing discovery of the near imaging and laser ranging experiments was the ridge system known as rahe dorsum and its possible relation with global scale internal structure the curved path of the ridge over the surface roughly defines a plane cutting through eros another lineament on the other side of eros calisto fossae seems to lie nearly on the same plane the near teams interpret rahe as the expression of a compressive fault a plane of weakness because portions are a scarp which on earth would be indicative of horizontal compression where shear displacement along a dipping fault has thrust the portion of the lithosphere on one side of the fault up relative to the other side however given the different geometry of eros a scarp may not have the same relationship to underlying structure as it does on earth the plane through eros runs nearly parallel to and just below the surface facet adjacent to rahe dorsum the plane then continues lengthwise through the elongated body a surprising geometry for a plane of weakness on a battered body moreover an assessment of the topography of rahe dorsum indicates that it is not consistent with displacement on the rahe plane rather the topography suggests that rahe dorsum results from resistance of the rahe plane to impact erosion such a plane of strength might have formed in eros parent body by a fluid intrusion e g a dike of partial melt through undifferentiated material creating a vein of stronger rock albedo color and near infrared spectra could be consistent with a distinct material composition and such a history although the instruments resolution was not adequate for a definitive detection of such a spatially limited component however the plane of strength formed such structural reinforcing might have enabled and controlled the elongated irregular shape of eros as well as rahe dorsum

early tertiary paleo thermal effects in northern england reconciling results from apatite fission track analysis with geological evidence abstract the paleozoic lake district block in northwest england has traditionally been thought of as tectonically stable since the late paleozoic receiving only small thicknesses of late paleozoic to mesozoic cover although some workers have put forward different views apatite fission track analysis afta data from outcrop samples across the region reveal early tertiary paleotemperatures around 100 c requiring kilometre scale late paleozoic and mesozoic cover removed during tertiary uplift and erosion with no evidence for elevated basal heat flow in nw england during the early tertiary and no a priori justification for invoking it earlier studies favoured an explanation involving burial by up to 3 km of overburden removed during tertiary uplift and erosion this conclusion was met with scepticism by many workers and provoked a range of comments and criticisms with a variety of alternative interpretations put forward although these are also open to criticism results from the west newton 1 hydrocarbon exploration well on the northern flank of the lake district gave the first indication of a possibly more realistic interpretation involving a combination of elevated heat flow and more restricted burial but some aspects of the interpretation of these data were equivocal more detailed sampling was therefore undertaken in order to shed more light on the origin of the elevated early tertiary paleotemperatures observed across nw england new afta data in outcrop samples from different elevations around sca fell characterised by the highest elevations in the lake district with the summit of scafell pike at 978 m asl define an early tertiary paleogeothermal gradient of 61 c km and require around 700 m of section removed from the summit during tertiary uplift and erosion these results together with those from the west newton 1 well provide strong support for an interpretation involving early tertiary paleogeothermal gradients between 50 and 100 higher than present day values providing clear evidence of elevated basal heat flow during the early tertiary contrary to earlier assumptions combined with amounts of section removed during tertiary exhumation varying between 0 7 km from mountain peaks and 1 5 2 km from coastal plains and glacial valleys near sea level over the region this interpretation finally provides a geologically plausible mechanism for the origin of the observed early tertiary paleo thermal effects in nw england

433 eros global basemap from near shoemaker msi images abstract during its year long orbital survey of asteroid 433 eros february 14 2000 to february 12 2001 the near shoemaker spacecraft returned over 160 000 images of the surface obtained under a wide variety of viewing conditions and resolutions to handle this large volume of images of eros we have utilized specialized techniques for projecting mosaicking and photometrically analyzing images of irregular objects local incidence and emission angles are calculated on a pixel by pixel basis from the global shape model to produce a normalized reflectance map of the entire asteroid this map provides not only a medium resolution 10 m pixel scientific product in its own right but also a regional context for high resolution

separation of palaeogene and neogene uplift on nuussuaq west greenland the geological record exposed on nuussuaq central west greenland shows that uplift in the palaeocene probably caused by impact of the iceland plume head was followed by kilometre scale subsidence analysis of apatite fission track and vitrinite reflectance data from borehole samples down to 3 km depth reveals that the samples cooled from maximum palaeotemperatures between 40 and 30 ma followed by two further cooling episodes beginning in the intervals 11 10 and 7 2 ma when the first cooling episode began the samples from the neighbouring gro 3 and gane 1 boreholes were buried 1500 2000 m deeper than at the present day and the palaeogeothermal gradient was 40 48 c km 1 it is not clear whether this cooling involved exhumation or if it was due solely to reduction in heat flow and a drop in surface temperature the two later episodes definitely involved exhumation because by then the palaeogeothermal gradient had declined to a value close to the assumed present value of 30 c km 1 which agrees with estimates from offshore wells the most recent cooling episode corresponds to the incision of the present day relief c 1100 m below the summits around the two boreholes we conclude that the present day high mountains of west greenland were not uplifted during the palaeogene but are erosional remnants of a landmass uplifted during the neogene

global survey of color variations on 433 eros implications for regolith processes and asteroid environments abstract high resolution imaging acquired with the near earth asteroid rendezvous shoemaker near shoemaker spacecraft is used to elucidate the spectral properties and spatial distribution of color units on asteroid 433 eros previous workers mapped four distinct types of color units on the surface bright streaks dark soils ponded materials average regolith these units exhibit albedo and color boundaries but there is no evidence to indicate they represent distinct rock types rather the units are thought to show evidence of complex regolith transport and sorting processes here we report the results of a comprehensive study of all viable color multispectral imager msi data to identify and characterize the distribution and nature of color units across the whole asteroid due to a spacecraft upset that resulted in contamination of the msi optics color images are affected with a scattered light problem that hampers interpretation of subtle color contrasts even after a rigorous remediation to constrain interpretations of the msi color data we characterize this residual scattered light and demonstrate how complete correction would affect derived color ratios results of our comprehensive study are consistent with previous mapping confirming that bright streaks average regolith and dark soils fall on a mixing line consistent with space weathering effects we find that the ponded deposits do not fall on this putative mixing line the color and reflectance of the ponded deposits are consistent with some combination of compositional grain size and maturity variations from the average regolith additionally we show that spectral separation of the four units on ratio plots would only increase with full removal of residual scattered light especially for features that are small in terms of pixels global analysis of the eros color units illustrates complex regolith processes and grain sorting that may hold clues to understanding space weathering processes and the link between asteroids and meteorites

new constraints on the thermal history of north east greenland from apatite fission track analysis apatite fission track analyses from the area north of jameson land east greenland indicate that the region has undergone at least three phases of cooling during the mesozoic and cenozoic two major periods of cooling during the tertiary have been identified a middle tertiary episode in which cooling began between 40 and 30 ma and a late tertiary episode in which cooling began between 10 and 5 ma the middle tertiary event is synchronous with emplacement of major intrusive bodies associated with continental rifting and may be due either to uplift and erosion or hydrothermal effects the late tertiary event appears to be related to erosion associated with uplift resulting from changes in the north atlantic spreading direction and associated events no paleothermal effects have been identified related to the onset of rifting in the early tertiary results from samples farthest from the continental margin reveal an earlier event in which cooling began between 225 and 165 ma the origin of this event is not clear but it may reflect uplift and erosion associated with recognized unconformities within the jurassic section

geothermal reservoir characterization using distributed temperature sensing at brady geothermal field nevada abstract distributed temperature sensing dts systems provide near real time data collection that captures borehole spatiotemporal temperature dynamics temperature data were collected in an observation well at an active geothermal site for a period of eight days under geothermal production conditions collected temperature data showcase the ability of dts systems to detect changes to the location of the steam water interface visualize borehole temperature recovery following injection of a cold water slug and identify anomalously warm and or cool zones the high sampling rate and spatial resolution of dts data also shows borehole temperature dynamics that are not captured by traditional pressure temperature survey tools inversion of thermal recovery data using a finite difference heat transfer model produces a thermal diffusivity profile that is consistent with laboratory measured values and correlates with identified lithologic changes within the borehole used alone or in conjunction with compl

a reassessment of the role of ice sheet glaciation in the long term evolution of the east greenland fjord region abstract the long term evolution of the east greenland fjord region is investigated using geomorphological and stratigraphical evidence to 1 assess the nature of landscape modification caused by late cenozoic ice sheet glaciation and 2 relate patterns of glacial landscape modification to first order i e continent margin scale topography and geology geomorphological and stratigraphical evidence demonstrates evolution of the first order topography and incision of at least part of the present first order fjord system by 55 ma this hypothesis is tested using apatite u th he ages for samples from two bedrock profiles near kong oscar fjord the thermochronology supports landscape evolution before 55 ma followed by relative tectonic stability because it indicates rapid denudation around the time of rifting that occurred prior to continental breakup i e between 75 and 55 ma the nature of landscape modification caused by late cenozoic glacial erosion appears to have been controlled by first order topography and geology with selective ice sheet erosion in areas of high elevation caledonian basement and apparently little glacial erosion of low elevation mesozoic sedimentary strata nevertheless fjord morphometry demonstrates systematic evolution of the first order fjord system from confined and overdeepened fjords in caledonian basement to wider and disproportionately larger fjords in mesozoic strata the latter indicates that changes in lithological strength enabled the development of more efficient fjord morphology under full glacial conditions that may have promoted fast ice flow

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

palaeothermal and compaction studies in the mochras borehole nw wales reveal early cretaceous and neogene exhumation and argue against regional palaeogene uplift in the southern irish sea the north atlantic continental margins have been subject to widespread exhumation although the timing magnitude and causes of this uplift and erosion are debated exhumation is thought to be most severe across the irish sea basin system western uk and recent years have seen an increasing emphasis on the role of palaeogene underplating as the primary mechanism of uplift we present a study of palaeothermal and compaction data from the mochras borehole nw wales located near the presumed locus of exhumation mochras penetrated thick successions of lower jurassic and oligo miocene sediments our results indicate that both these successions experienced considerably deeper burial prior to early cretaceous and neogene exhumation respectively apatite fission track analysis afta and vitrinite reflectance data from the borehole reveal evidence for exhumation related cooling episodes beginning during the cretaceous 150 80 ma and cenozoic 50 0 ma regional afta results and stratigraphic constraints refine the timing estimates to the early cretaceous 120 115 ma and neogene 20 0 ma estimates of exhumation magnitudes during these episodes based on palaeothermal and compaction data are c 2 5 km and c 1 5 km respectively palaeothermal data provide no evidence for elevated palaeogene palaeotemperatures indicative of deeper burial and thus question the basis of palaeogene exhumation

fission track dating of phosphate minerals and the thermochronology of apatite several phosphate minerals have been investigated for their usefulness in geochronology and thermochronology by the fission track method of these apatite ca5 po4 3 f cl oh has proved pre eminently suitable for this purpose for reasons discussed below apatite was one of the first minerals amongst many others to be investigated for fission track dating by fleischer and price 1964 and has subsequently become by far the most important of all the minerals used for dating by this method the usefulness of apatites for fission track dating arises from their near universal tendency to concentrate uranium within their structure at the time of crystallization and their widespread occurrence in all of the major rock groups price and walker 1963 first recognized the possibility that the accumulation of radiation damage tracks in natural minerals from the spontaneous nuclear fission of 238u within their lattices could be used for geological dating they also demonstrated that a simple chemical etching procedure served to enlarge these fission tracks to optical dimensions so that they could be observed and measured under an ordinary optical microscope price and walker 1962b 1963 this simple procedure quickly opened the way for a wide range of nuclear particle track studies in natural minerals and glasses e g fleischer et al 1975 the most important of which was fission track dating fleischer et al 1964 also showed that spontaneous or fossil fission tracks provided an explanation for various anomalous etch pits in apatite which had puzzled crystallographers over many years the essence of a fission track age determination involves measuring the number of tracks that have accumulated over the lifetime of the mineral along with an estimate of the amount of uranium that is present knowing the rate of spontaneous fission decay a geological age can be calculated detailed

near at eros imaging and spectral results eros is a very elongated 34 kilometers by 11 kilometers by 11 kilometers asteroid most of the surface of which is saturated with craters smaller than 1 kilometer in diameter the largest crater is 5 5 kilometers across but there is a 10 kilometer saddle like depression with attributes of a large degraded crater surface lineations both grooves and ridges are prominent on eros some probably exploit planes of weakness produced by collisions on eros and or its parent body ejecta blocks 30 to 100 meters across are abundant but not uniformly distributed over the surface albedo variations are restricted to the inner walls of certain craters and may be related to downslope movement of regolith on scales of 200 meters to 1 kilometer eros is more bland in terms of color variations than gaspra or ida spectra 800 to 2500 nanometers are consistent with an ordinary chondrite composition for which the measured mean density of 2 67 0 1 grams per cubic centimeter implies internal porosities ranging from about 10 to 30 percent

an inverse method of modeling thermal histories from apatite fission track data abstract apatite fission track ft ages and track length distributions are important sources of information about the thermal histories of rocks recent advances in the understanding of track annealing in apatite provide a solution to the forward problem of predicting ft ages and track length distributions that result from a given thermal history in this paper a method is presented to address the inverse problem estimation of the thermal history from ft data the inverse method uses an iterative approach the downhill simplex to systematically modify a starting thermal history to achieve satisfactory statistical agreement between the predicted and observed ft age and track length distribution however because of analytical uncertainties a unique thermal history does not exist monte carlo simulations are used to take into account the uncertainties in the data and yield a spectrum of possible thermal histories the results are based on the isothermal annealing model of laslett et al 1 chem geol isot geosci sect vol 65 but because the method uses forward predictions and not an analytical formula specific to a single annealing model alternative annealing models could be used within the same framework this method is an improvement in interpreting fission track data because the range of thermal histories permitted by the data can be evaluated to demonstrate the method it is applied to several sets of test data created by forward modeling of idealized thermal histories the results show that the age at which the sample cooled through its closure temperature and the most general features of the thermal history are revealed however data from partially annealed samples have wide spectra that reflect large uncertainties in the form of the thermal history for such samples ft data alone are not likely to provide strong tests of geologic hypotheses conversely geologic information may play a crucial role in constraining the thermal history spectrum in application to uplift related cooling this inverse method can provide much more realistic assessments of the cooling rate and its uncertainty than are otherwise possible

regolith transport in craters on eros abstract images of eros from the near shoemaker spacecraft reveal bright and dark albedo features on steep crater walls unlike markings previously observed on asteroids these features have been attributed to the downslope movement of space weathered regolith exposing less weathered material science 292 2001 484 meteor planet sci 36 2001 1617 icarus 155 2002 145 here we present observations of the interiors of large craters 1 km in diameter to test this hypothesis and constrain the origin of the features we find that bright regions in these craters correspond to steep slopes consistent with previous work the geographic distribution of craters with albedo variations shows no pattern and does not resemble the distribution of ponds another phenomenon on eros attributed to regolith movement shadows and other indications of topography are not observed at feature boundaries implying that the transported layer is 1 m thick the presence of multiple bright and dark units on long slopes with sharp boundaries between them suggests that mobilized regolith may be halted by frictional or other effects before reaching the foot of the slope features on crater walls should darken at the same rate as bright ejecta deposits from crater formation the lack of observed morphologically fresh craters with bright interiors or ejecta suggests that the albedo patterns are younger than the most recently formed craters greater than about 100 m in diameter smaller or micrometeorite impacts which would not necessarily leave evident deposits of bright ejecta remain possible causes of albedo patterns although their effectiveness is difficult to assess electrostatic processes and thermal creep are also candidates

thermotectonic evolution of a rifted continental margin fission track evidence from the kangerlussuaq area se greenland fission track analyses of apatites from sediments precambrian gneisses and caledonian to tertiary intrusive rocks from the kangerlussuaq region reveal its post caledonian thermotectonic history inland the history involves cooling to temperatures within the high temperature part of the apatite annealing interval and slow cooling or reheating continued in cretaceous times through this interval apatites from coastal areas between kangerlussuaq and tasiilaq reveal only tertiary cooling in tertiary times cooling accelerated after the main intrusive phase in the tertiary the evolution is taken as evidence for a general uplift erosion since caledonian times probably disturbed by basin formation and sedimentation and reheating due to magmatic activity thermal subsidence of the rift shoulders following the opening of the adjacent oceanic basin is not indicated annealing patterns inland of the plume centre in the kangerlussuaq provide no evidence for the earlier movement of the plume from a westerly direction

crestal unconformities on an exposed jurassic tilted fault block wollaston forland east greenland as an analogue for buried hydrocarbon traps abstract the stratigraphy of successions exposed in footwall crests of tilted fault blocks is commonly highly complex crestal stratigraphy and structure are particularly difficult to unravel in the subsurface due to poor seismic resolution across fault zones footwall collapse and coalescing syn and post rift unconformities crestal ridges are important elements in basin evolution as they form drainage divides and sediment sources for aprons along footwall scarps and hangingwall deltas a middle jurassic lowermost cretaceous footwall crest is exceptionally well exposed in the mountain stratumbjerg in wollaston forland east greenland rifting and block tilting was initiated in the bajocian intensified in the oxfordian kimmeridgian culminated in latest jurassic volgian time and faded out in the earliest cretaceous the main border faults of the westward tilted blocks trend roughly n s the first early syn rift block was formed in the middle late jurassic and was 40 km wide during rift climax in the latest jurassic it was fragmented into three blocks each 10 15 km wide the early syn rift succession rests on thin upper permian evaporites and carbonates or directly on peneplaned crystalline basement it is composed of the stepwise backstepping marine pelion jakobsstigen and bernbjerg formations deposited in progressively deeper water reflecting the combined effects of increased rifting and long term eustatic rise the rift climax and late syn rift succession was deposited along the main western basin margin fault scarp up to several kilometres thick it consists of coalesced mainly conglomeratic deep marine slope apron fans over the block crest this succession unconformably overlies early syn rift strata whereas in the deeper parts of the halfgraben the base of the succession is conformable a post rift unconformity was formed in the late hauterivian probably during early post rift emergence and has an irregular stratigraphically and structurally controlled erosional topography the eroded early syn rift rift climax and late syn rift successions were subsequently draped by deep marine barremian and younger post rift strata the outcrop example highlights the interplay between large scale block faulting minor synthetic intra block faulting crestal degradation and development of rift climax and post rift unconformities with pronounced erosional topography it provides an excellent structural sedimentological field analogue to deeply buried marine halfgraben settings which are key elements in many hydrocarbon reservoirs its tectonic and stratigraphic development is thus highly similar to a number of large oil fields in the north sea and the norwegian shelf

re os and 40ar 39ar ages of porphyry molybdenum deposits in the east greenland volcanic rifted margin precise re os dating of molybdenite from the malmbjerg and flammefjeld rift related porphyry molybdenum deposits indicates that they are among the youngest magmatic events 25 8 0 1 and 39 7 0 2 ma in their respective areas of the east greenland rifted continental margin an 40 ar 39 ar age for biotite from the malmbjerg granite stock 25 7 0 3 ma demonstrates that molybdenite mineralization is essentially concurrent with granite emplacement further the identical ages obtained by argon and re os geochronology suggest that for the youngest events in a region re os and argon based methods produce similar age results whereas this is generally not the case for older ore forming events that have been thermally overprinted in the latter case disturbance of argon systematics produces ages younger than those determined by re os both deposits postdate continental breakup and the associated flood volcanism episode at 56 to 54 ma we suggest that the malmbjerg and flammefjeld molybdenum deposits formed during later periods of lithospheric uplift which at least in the case of malmbjerg may have been related to plate tectonic reorganization of the northeast atlantic ocean basin this uplift may have caused decompression mantle melting and renewed generation of mafic magma that led to crustal anatexis and the establishment of major hydrothermal systems the suggestion that molybdenum mineralization occurred at times of late uplift of a volcanic rifted margin may be useful in prospecting

passive margins getting squeezed in the mantle convection vice 1 passive margins often exhibit uplift exhumation and tectonic inversion we speculate that the compression in the lithosphere gradually increased during the cenozoic as seen in the number of mountain belts found at active margins during that period less clear is how that compression increase affects passive margins in order to address this issue we design a 2 d viscous numerical model wherein a lithospheric plate rests above a weaker mantle it is driven by a mantle conveyor belt alternatively excited by a lateral downwelling on one side an upwelling on the other side or both simultaneously the lateral edges of the plate are either free or fixed representing the cases of free convergence and collision or slab anchoring respectively this distinction changes the upper mechanical boundary condition for mantle circulation and thus the stress field between these two regimes the flow pattern transiently evolves from a free slip convection mode toward a no slip boundary condition above the upper mantle in the second case the lithosphere is highly stressed horizontally and deforms for a constant total driving force compression increases drastically at passive margins if upwellings are active conversely if downwellings alone are activated compression occurs at short distances from the trench and extension prevails elsewhere these results are supported by earth like models that reveal the same pattern where active upwellings are required to excite passive margins compression our results substantiate the idea that compression at passive margins is in response to the underlying mantle flow that is increasingly resisted by the cenozoic collisions

preliminary remediation of scattered light in near msi images abstract during a failed eros orbit insertion maneuver on 20 december 1998 more than 28 kg of hydrazine were expended by attitude control jets on the near shoemaker spacecraft deposition of burn products on the outer optic of the multispectral imager or msi resulted in a wavelength dependent degradation of the system point spread function psf the scattered light is progressively worse in the shortest and longest wavelength filters especially at 450 and 1050 nm the degraded psf was characterized using numerous images of canopus acquired subsequent to the anomaly there is no evidence for temporal change in the psf since the burn abort incident a fast fourier transform based image restoration method using the optimal filter recovers most of the spatial resolution of the original images while preserving radiometric accuracy for the 550 to 1000 nm images this procedure has enabled nearly unimpeded monochrome imaging of asteroid morphology and select 5 color measurements at a scale of 5 pixels

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

fundamentally distinct outcomes of asteroid collisional evolution itokawa and eros 1 the outcomes of asteroid collisional evolution are presently unclear are most asteroids larger than 1 km size gravitational aggregates reaccreted from fragments of a parent body that was collisionally disrupted while much smaller asteroids are collisional shards that were never completely disrupted the 16 km mean diameter s type asteroid 433 eros visited by the near mission has surface geology consistent with being a fractured shard the hayabusa spacecraft visited an s asteroid smaller than 1 km namely 25143 itokawa here we report the first comparative analyses of itokawa and eros geology itokawa lacks a global lineament fabric and its blocks craters and regolith are inconsistent with formation and evolution as a fractured shard unlike eros itokawa is not a scaled down eros but formed by a distinct process of catastrophic disruption and reaccumulation

imaging of small scale features on 433 eros from near evidence for a complex regolith on 25 october 2000 the near earth asteroid rendevous near shoemaker spacecraft executed a low altitude flyover of asteroid 433 eros making it possible to image the surface at a resolution of about 1 meter per pixel the images reveal an evolved surface distinguished by an abundance of ejecta blocks a dearth of small craters and smooth material infilling some topographic lows the subdued appearance of craters of different diameters and the variety of blocks and different degrees of their burial suggest that ejecta from several impact events blanketed the region imaged at closest approach and led to the building up of a substantial and complex regolith consisting of fine materials and abundant meter sized blocks

near surface characterization using a roadside distributed acoustic sensing array abstract due to the broadband nature of distributed acoustic sensing das measurement a roadside section of the stanford das 2 array can record seismic signals from various sources for example

eros shape topography and slope processes stereogrammetric measurement of the shape of eros using images obtained by near s multispectral imager provides a survey of the major topographic features and slope processes on this asteroid this curved asteroid has radii ranging from 3 1 to 17 7 km and a volume of 2535 20 km3 the center of figure is within 52 m of the center of mass provided by the navigation team this minimal difference suggests that there are only modest variations in density or porosity within the asteroid three large depressions 10 8 and 5 3 km across represent different stages of degradation of large impact craters slopes on horizontal scales of 300 m are nearly all less than 35 although locally scarps are much steeper the area distribution of slopes is similar to those on ida phobos and deimos regions that have slopes greater than 25 have distinct brighter markings and have fewer large ejecta blocks than do flatter areas the albedo patterns that suggest downslope transport of regolith have sharper boundaries than those on phobos deimos and gaspra the morphology of the albedo patterns their lack of discrete sources and their concentration on steeper slopes suggest transport mechanisms different from those on the previously well observed small bodies perhaps due to a reduced relative effectiveness of impact gardening on eros regolith is also transported in talus cones and in connected sinuous paths extending as much as 2 km with some evident as relatively darker material talus material in at least one area is a discrete superposed unit a feature not resolved on other small bodies flat floored craters that apparently contain ponded material also suggest discrete units that are not well mixed by impacts

the geology of 433 eros the global high resolution imaging of asteroid 433 eros by the near earth asteroid rendezvous near shoemaker spacecraft has made it possible to develop the first comprehensive picture of the geology of a small s type asteroid eros displays a variety of surface features and evidence of a substantial regolith large scale facets grooves and ridges indicate the presence of at least one global planar structure directional and superposition relations of smaller structural features suggest that fracturing has occurred throughout the object as with other small objects impact craters dominate the overall shape as well as the small scale topography of eros depth diameter ratios of craters on eros average 0 13 but the freshest craters approach lunar values of 0 2 ejecta block production from craters is highly variable the majority of large blocks appear to have originated from one 7 6 km crater shoemaker the interior morphology of craters does not reveal the influence of discrete mechanical boundaries at depth in the manner of craters formed on lunar mare regolith and on some parts of phobos this lack of mechanical boundaries and the abundant evidence of regolith in nearly every high resolution image suggests a gradation in the porosity and fracturing with depth the density of small craters is deficient at sizes below 200 m relative to predicted slopes of empirical saturation this characteristic which is also found on parts of phobos and lunar highland areas probably results from the efficient obliteration of small craters on a body with significant topographic slopes and a thick regolith eros displays a variety of regolith features such as debris aprons fine grained ponded deposits talus cones and bright and dark streamers on steep slopes indicative of efficient downslope movement of regolith these processes serve to mix materials in the upper loose fragmental portion of the asteroid regolith in the instance of ponded materials and crater wall deposits there is evidence of processes that segregate finer materials into discrete deposits the near observations have shown us that surface processes on small asteroids can be very complex and result in a wide variety of morphologic features and landforms that today seem exotic future missions to comets and asteroids will surely reveal still as yet unseen processes as well as give context to those discovered by the near shoemaker spacecraft

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

quantification of the magnitude of net erosion in the southwest barents sea using sonic velocities and compaction trends in shales and sandstones abstract during specific intervals within mesozoic and cenozoic times several areas of the southwestern barents sea were subjected to uplift and erosion areas with missing shallow stratigraphic interval sections and major erosion can be seen at several places along interpreted regional profiles in the southwestern barents sea a new normal compaction trend nct for two selected shale and sandstone dominated lithologies has been constructed based on sonic logs in the southwestern barents sea the shale dominated nct is calibrated to the cretaceous shales in the northern north sea and norwegian sea and applied to the cretaceous shales of the barents sea the sandstone dominated nct is calibrated to the lower jurassic are formation of the norwegian sea and applied to the lower jurassic upper triassic coastal plain section in the barents sea by utilising the nct model the study estimates net apparent erosion in 28 selected barents sea wells based on comparison of sonic log velocities a net apparent erosion map of the study area was constructed by gridding of the well values the accuracy of the map is limited in areas with little well control such as in the northwest where the east west transition into the southwestern barents sea region is poorly constrained with that in mind the map clearly shows two regional trends which dominate the erosion pattern in the study area an increasing amount of erosion towards the north and a sharp decrease of erosion westwards of the hinge zone into the southwestern barents sea the highest erosion estimates are observed towards svalbard with values up to 2500 m the results of this study can be further utilized in petroleum system studies in the eroded areas

the evolution of the east greenland margin as revealed from fission track studies abstract a comprehensive dataset of fission track analyses mainly of apatite covers the east greenland margin between ca 73 n geographical society island and ca 63 n skjoldungen it consists of data from archaean and caledonian basement post caledonian sedimentary rocks and magmatic rocks the studied areas represent different aspects of the east greenland evolution we report new apatite fission track ft analyses from the east greenland gneissic basement south of scoresby sund to skjoldungen and put them into context with existing data a regional pattern along the east greenland continental margin south of 73 n of deeply eroded shorelines and highstanding slowly eroding hinterland with remnants of old peneplain surfaces is overprinted in the central kangerlussuaq area by tertiary magmatic activity to the northeast the thermal evolution is dominated by a domal structure shown by apatite fission track ft ages to have cooled in the neogene this pattern may result from rapid erosion of the locally uplifted basaltic pile in the area and heating caused by late sill intrusions possibly enhanced on a regional scale by climatic deterioration in the hinterland to the south and west of kangerlussuaq the data restrict the basalt cover to

diagenesis and reservoir properties of middle jurassic sandstones traill o east greenland the influence of magmatism and faulting the c 500 m thick middle jurassic sandstones of the fluvial bristol elv and marine pelion formations of the east greenland basin are evaluated here in order to improve the understanding of the processes that influenced the diagenetic evolution the study may help to predict the reservoir properties of sandstones affected by magmatism and faulting both in general and specifically in undrilled areas on and offshore east greenland and in the voring basin on the mid norwegian shelf the study shows a variety of authigenic mineral phases dominated by quartz cement carbonate cement illite and iron oxide one of the clear differences between the two formations is the presence of early carbonate cemented horizons in the marine sandstones these horizons are inferred to reflect a primary concentration of biogenic clasts and fossil shells intense quartz cementation occurs primarily in the fluvial sandstones but the marine sandstones are also highly quartz cemented two episodes of burial and uplift are recorded in the diagenetic sequence and widespread grain crushing in coarse grained intervals is believed to result from overpressure and subsequent compaction due to sudden pressure release along major faults maximum burial depths may only have been around 2000 2500 m cathodoluminescence analyses show that grain crushing was followed by intense quartz cementation the quartz cement is to a great deal believed to have formed due to increased surface area from crushing of detrital quartz grains creating fresh nucleation sites for the quartz cathodoluminescence investigations also show that only minor pressure dissolution has taken place between detrital quartz grains and that the ubiquitous quartz cementation displays several growth zones and was thus in part the result of the introduction of silica rich extra formational fluids related to the flow of hot fluids along reactivated faults and increased heat flow and temperature due to magmatism this interpretation is supported by fluid inclusion homogenization temperatures between 117 and 158 c in quartz cements in one of the two study areas the development of macroscopic stylolites has significantly enhanced quartz cementation probably in connection with thermal convection flow as a result of the magmatic and fault related quartz cementation and illitization the reservoir quality of the sandstone formations deteriorated and changed drastically

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

shoemaker crater as the source of most ejecta blocks on the asteroid 433 eros the loose material regolith on the surfaces of asteroids is thought to represent ballistically emplaced ejecta from impacts but the identification of source craters and the detailed study of the regolith modification have been hampered by the limited spatial resolution and area coverage of the few asteroids imaged by spacecraft here we report the results of global mapping of the asteroid 433 eros from high resolution images obtained by the near shoemaker spacecraft based on the images and ejecta emplacement models we suggest that most large ejecta blocks on eros originate from a relatively young 7 6 km diameter crater a large fraction of the ejecta from impacts pre dating that crater has apparently been buried or eroded the images also show evidence for the action of a variety of sorting environments for regolith particles after they are deposited on the surface

response of marine palynomorphs to neogene climate cooling in the iceland sea odp hole 907a abstract the present study on odp leg 151 hole 907a combines a detailed analysis of marine palynomorphs dinoflagellate cysts prasinophytes and acritarchs and a low resolution alkenone based sea surface temperature sst record for the interval between 14 5 and 2 5 ma and allows to investigate the relationship between palynomorph assemblages and the paleoenvironmental evolution of the iceland sea a high marine productivity is indicated in the middle miocene and palynomorphs and ssts both mirror the subsequent long term neogene climate deterioration the diverse middle miocene palynomorph assemblages clearly diminish towards the impoverished assemblages of the late pliocene parallel with a somewhat gradual decrease of ssts being as high as 20 c at 13 5 ma to around 8 c at 3 ma superimposed palynomorph assemblages not only reflect middle to late miocene climate variability partly coinciding with the short lived global miocene isotope events mi events but also the initiation of a proto thermohaline circulation across the middle miocene climate transition which led to increased meridionality in the nordic seas last occurrences of species cluster during three events in the late miocene to early pliocene and are ascribed to the progressive strengthening and freshening of the proto east greenland current towards modern conditions a significant high latitude cooling between 6 5 and 6 ma is depicted by the supraregional decahedrella event coeval with lowest miocene productivity and a sst decline in the early pliocene a transient warming is accompanied by surface water stratification and increased productivity that likely reflects a high latitude response to the global biogenic bloom the succeeding crash in palynomorph accumulation and a subsequent interval virtually barren of marine palynomorphs may be attributed to enhanced bottom water oxygenation and substantial sea ice cover and indicates that conditions seriously affecting marine productivity in the iceland sea were already established well before the marked expansion of the greenland ice sheet at 3 3 ma