evidence for excavation of deep crustal material of a vesta like body from ca compositional gradients in pyroxene abstract recent discovery of basaltic achondrite asteroids in the main belt has provided a link between basaltic achondrites howardite eucrite and diogenite and asteroid 4 vesta a spectral study suggests that these asteroids are fragments ejected from vesta and that vesta s eucritic crust is of substantial thickness we computed the cooling rate and burial depth of the moore county cumulate eucrite on the basis of ca compositional gradients and the width of augite lamella in pyroxene to obtain information on the early evolution of the parent body our calculations show that 1 moore county cooled initially at a rate of 0 00016 c yr which corresponds to a burial depth of about 8 km 2 after this cooling a sudden temperature rise occurred probably due to an impact and finally 3 moore county cooled down again at a rate of 0 35 c yr the latter events may correspond to the excavation of crustal material the burial depth of moore county is consistent with the result of a recent spectral study in which the largest observed eucritic fragment 10 km sets a lower limit on the thickness of the eucritic crust reheating and excavation of a deep crustal material imply impact events which are supported by spectral observations

fluid inclusion evidence for a cretaceous palaeogene petroleum system kangerlussuaq basin east greenland abstract petrographic and fluid inclusion studies of sandstone samples from the cretaceous palaeogene kangerlussuaq basin reveal the presence of oil inclusions as secondary trails across grains fluid inclusion petrographic and microthermometric investigations suggest that oil was trapped at temperatures in excess of about 108 c although due to deep burial in excess of 6 km and subsequent exhumation the kangerlussuaq basin itself cannot be considered as prospective for petroleum it provides a useful analogue for nearby basins on the north atlantic margin given the fact that no sediments older than aptian albian are present in the basin a conventional upper jurassic source rock can be ruled out oil may have been generated from an aptian albian estuarine mudstone whose potential as a regional source rock needs to be assessed oil inclusions also occur in injected sandstones that cross cut the whole sedimentary section and these sandstones may have acted as conduits for petroleum migration their presence in offshore north atlantic basins underneath the tertiary basalts also needs to be considered in play concepts

40ar 39ar ages of intrusions in east greenland rift to drift transition over the iceland hotspot abstract sixteen 40 ar 39 ar ages are presented for alkaline intrusions to appraise prolonged post breakup magmatism of the central east greenland rifted margin the chronology of rift to drift transition and the asymmetry of magmatic activity in the northeast atlantic igneous province the alkaline intrusions mainly crop out in tectonic and magmatic lineaments orthogonal to the rifted margin and occur up to 100 km inland the area south of the kangerlussuaq fjord includes at least four tectonic lineaments and the intrusions are confined to three time windows at 56 54 ma 50 47 ma and 37 35 ma in the kangerlussuaq fjord which coincides with a major tectonic lineament possibly the failed arm of a triple junction the alkaline plutons span from 56 to 40 ma to the north and within the continental flood basalt succession alkaline intrusions of the north south trending wiedemann fjord kronborg gletscher lineament range from 52 to 36 ma we show that post breakup magmatism of the east greenland rifted margin can be linked to reconfiguration of spreading ridges in the northeast atlantic northwards propagation of the proto kolbeinsey ridge rifted the jan mayen micro continent away from central east greenland and resulted in protracted rift to drift transition the intrusions of the wiedemann fjord kronborg gletscher lineament are interpreted as a failed continental rift system and the intrusions of the kangerlussuaq fjord as off axis magmatism the post breakup intrusions south of kangerlussuaq fjord occur landward of the greenland iceland rise and are explained by mantle melting caused first by the crossing of the central east greenland rifted margin over the axis of the iceland mantle plume 50 47 ma and later by uplift associated with regional plate tectonic reorganization 37 35 ma the iceland mantle plume was instrumental in causing protracted rift to drift transition and post breakup tholeiitic and alkaline magmatism on the east greenland rifted margin and asymmetry in the magmatic history of the conjugate margins of the central northeast atlantic

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

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

weathering of meteorites from oman correlation of chemical and mineralogical weathering proxies with 14c terrestrial ages and the influence of soil chemistry fifty four fragments of ordinary chondrites from 50 finds representing all searched areas in central oman and all weathering stages were selected to compare the physical chemical and mineralogical effect of terrestrial weathering with 14c terrestrial ages 14c ages range from 2 0 to 49 kyr with a median value of 17 9 kyr the peak of the age range which is between 10 20 kyr falls in an arid climate period a comparison of the chemical composition of omani chondrites with literature data for unweathered h and l chondrites demonstrates a strong enrichment in sr and ba and depletion in s during weathering water contents in h chondrites increase with terrestrial age whereas l chondrites show a rapid initial increase followed by nearly constant water content correlating sr ba and h2o with age indicates two absorption trends i an initial alteration within the first 20 kyr dominated by h2o uptake mainly reflecting fe ni metal alteration and ii a second baand sr dominated stage correlated with slower and less systematic weathering of troilite that starts after h2o reaches 2 wt sulfur released from troilite partly combines with ba and sr to form sulfate minerals other parameters correlated with 14c age are degree of weathering color of powdered meteorites and the ni fe ratio chemical analyses of 145 soils show a high degree of homogeneity over the entire interior oman desert indicating large scale mixing by wind soil samples collected from beneath meteorite finds typically are enriched in ni and co confirming mobilization from the meteorites high cr and ni concentrations in reference soil samples which decrease from ne to sw are due to detrital material from ultramafic rocks of the oman mountains

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

basin evolution in southern east greenland an outcrop analog for cretaceous paleogene basins on the north atlantic volcanic margins the cretaceous paleogene kangerlussuaq basin in southern east greenland represents a unique outcrop analog for the frontier petroleum provinces along the deep water volcanic margins of the northern north atlantic the 1 km thick sedimentary succession comprises six facies associations 1 alluvial plain and shallow marine late aptian 2 fluvio estuarine late aptian early albian 3 offshore marine late cretaceous early paleocene 4 submarine fan and channel levee early paleocene 5 fluvial mid paleocene and 6 volcanic late paleocene sedimentation was terminated in the late paleocene by extrusion of flood basalts related to continental breakup the basin fill is divided into two depositional megasequences related to regional tectonic events and sea level changes the oldest megasequence sq1 spans the late aptian to the earliest paleocene with sea level rise in the late aptian and maximum flooding in the late albian cenomanian followed by sea level highstand in the late cretaceous early paleocene sq1 is truncated by a basin wide unconformity related to regional uplift and basin reorganization in the mid paleocene the upper megasequence sq2 spans the mid to late paleocene and comprises sediments deposited during early sea level rise extensive volcanic deposits and continental flood basalts overlie it deep burial 6 km and middle eocene early oligocene uplift excludes the kangerlussuaq basin as a petroleum basin in itself however to evaluate the petroleum potential of similar volcanic influenced offshore basins such as the west shetland faeroe more and voring basins we discuss three conceptual play models based on the kangerlussuaq basin 1 early albian stratigraphic trap 2 early paleocene structural trap and 3 paleocene stratigraphic trap

apatite fission track analysis of oligocene strata in south texas u s a testing annealing models analysis of apatite fission track data from forty seven surface and subsurface samples of fine grained sandstone to pebbly conglomerate from the oligocene catahoula gueydan frio and vicksburg formations documents the response of fission track ages and track length distributions to simple post depositional thermal histories characterized by monotonic heating data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from 120 to 50 c during the early tertiary the apatite population is characterized by a log normal chlorine distribution mean 0 3 wt 0 3 wt consisting predominantly of low cl apatites 80 is 0 5 wt mean track lengths from core samples decrease systematically with increasing depth and temperature the decrease in apatite fission track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition no tracks were observed in apatite from samples at temperatures above 130 c mean track lengths for the south texas data agree well with those for a similar data set from the otway basin southeastern australia for present day temperatures of 70 c at higher temperatures mean lengths are 1 to 9 m longer than those observed from the otway basin this discrepancy is interpreted to reflect up to 40 ma longer residence times at maximum burial temperatures for the otway basin samples standard deviations about mean lengths are also lower than observed in the otway basin study consistent with the wider variation of cl contents mean 0 8 wt 0 7 wt that characterize apatite from the otway basin recently published apatite fission track annealing models predict significantly different mean track length vs present day temperature profiles for thermal histories believed to be representative of those experienced by sampled south texas strata because of the large uncertainties attributed to present day temperatures 10 c the predicted mean length vs temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend residuals of predicted minus observed mean lengths suggest that the previously published carlson composite parameter model using an initial mean length of 15 8 m instead of 16 5 m or the crowley et al model for track length reduction down to 11 m provide the best estimates of mean track length reduction over geologic time scales for near end member f apatite populations

oxygen isotope exchange and mineral alteration in gabbros of the lower layered series kap edvard holm complex east greenland multiple intrusions of gabbros mafic dikes and syenites in the kap edvard holm complex gave rise to prolonged circulation of meteoric hydrothermal solutions and extreme isotope exchange and mineral alteration in the 3600 m thick lower layered series gabbros in the lower layered series 18o of plagioclase varies from 0 3 to 5 8 and it decreases with an increase in the volume of secondary talc chlorite and actinolite in the same gabbros pyroxenes have a more restricted range in 18o from 5 0 to 3 8 and values of 18opyroxeneare independent of the abundance of secondary minerals which ranges from 14 to 30 these relations indicate that large amounts of water continued to flow through the rocks at temperatures of 500 600 c altering the gabbros to assemblages of talc chlorite actinolite epidote albite and causing significant oxygen isotope exchange in plagioclase but not in pyroxene the extensive low temperature secondary mineralization and 18o depletion of plagioclase in the lower layered series are associated with the later emplacement of dikes and gabbros and syenites which created new fracture systems and provided heat sources for hydrothermal fluid circulation this produced subsolidus mineral alteration and isotope exchange in the lower layered series that are distinct from those in the skaergaard and cuillin gabbros of the north atlantic tertiary province but are similar to those observed in some oceanic gabbros

oxygen isotope evidence for rapid mixing of the hed meteorite parent body abstract the 16 o 17 o and 18 o abundances of howardites eucrites and diogenites have been used to assign them to a single hed parent body thought to be asteroid 4 vesta we report the first evidence of oxygen isotopic heterogeneity among hed meteorites indicating incompletely mixed sources new high precision oxygen isotope measurements of 34 hed meteorites reveal that most have the same 17 o consistent with a very rapid early history of large scale mixing on vesta however howardites are on average very slightly enriched in 16 o whereas ibitira caldera pasamonte and alha78132 are 16 o depleted compared to other investigated eucrites the 17 o of ibitira is completely different from all other heds measured some of the results for eucrites and diogenites can be explained by partial melting and rapid mixing of the interior of vesta others require a separate parent body or indicate that parts of the outer layer of vesta retained some primary isotopic heterogeneity the oxygen isotopic composition of howardites provides an upper limit for the amount of admixed carbonaceous chondritic material into the hed parent body regolith

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

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

pre break up palaeostress state along the east greenland margin this paper describes intraplate deformation and the palaeostress state along the east greenland margin during the paleocene between 65 and 55 myr ago prior to the onset of the ne atlantic spreading it is shown that the pre break up deformation is the result of dip oblique strike slip tectonics in the se and compressive tectonics in the north the reduced palaeostress tensors derived from inversion of the fault slip data show that the maximum horizontal stress 1 is compressive and the orientations of 1 change from ene wsw in the south to nne ssw in the north the reconstructed palaeostress trajectory map demonstrates that the 1 orientations reflect the plate motion path and define small circles whereas the trends of the minimum horizontal stress 3 converge and cluster around an area in the arctic that is interpreted as the rotation pole of greenland the intraplate deformation folding and uplift that affected the greenland and european margins the barents sea and the north sea during the paleocene can be explained by the counter clockwise rotation of greenland the present paper calculates the pole of rotation of greenland using the kinematics of brittle faults along the plate margin and the palaeostress derived from inversion of fault slip data analysis as an indicator of motion path

petrology and geochemistry of the unbrecciated achondrite northwest africa 1240 nwa 1240 an hed parent body impact melt nwa 1240 is an unusual eucrite recently recovered in morocco as a single stone of 98 g it is an unbrecciated greenish brown rock nearly devoid of fusion crust it displays porphyritic texture consisting of skeletal hollow low ca pyroxene phenocrysts set in a variolitic fan spherulitic mesostasis of fine elongate pyroxene and plagioclase crystals minor phases are skeletal chromite iron silica troilite ilmenite and minute amounts of phosphate and fayalite pyroxenes are unequilibrated and show one of the widest ranges of composition so far described for a eucrite from en 76 0 wo 1 9 fs 22 1 to compositions nearly devoid of mg unusual ferrosilite and fe augite symplectites and possibly pyroxferroite plagioclase crystals contain significant amounts of fe and mg which are possibly controlled by the ca mg fe2 si3o8 plagioclase component

petrology and geochemistry of the fine grained unbrecciated diogenite northwest africa 4215 we report on the petrology and geochemistry of northwest africa nwa 4215 an unbrecciated diogenite recovered in the sahara this single stone weighing 46 4 g displays a wellpreserved cumulative texture it consists of zoned xenomorphic orthopyroxene grains on the order of 500 m in size along with a few large chromite crystals 5 vol up to 3 mm accessory olivine and scarce diopside grains occur within the groundmass usually around the chromite crystals minor phases are cristobalite troilite and metal unlike other diogenites orthopyroxenes en76 2wo1 1fs22 7 to en68 6wo5 5fs25 9 olivines fo76 to fo71 and chromites mg 14 3 44 0 cr 42 2 86 5 are chemically zoned the minor element behavior in orthopyroxenes and the intricate chemical profiles obtained in chromites indicate that the zonings do not mirror the evolution of the parental melt we suggest that they resulted from reaction of the crystals with intercumulus melt in order to preserve the observed zoning profiles nwa 4215 clearly cooled significantly faster than other diogenites indeed the cooling rate determined from the diffusion of cr in olivine abutting chromite is in the order of 10 50 c a suggesting that nwa 4215 formed within a small shallow intrusion the bulk composition of nwa 4215 has been determined for major and trace elements this meteorite is weathered and its fractures are filled with calcite limonite and gypsum typical of hot desert alteration in particular the feo cao abundances and most of the trace element concentrations sr ba pb and ree among others are high and indicate a significant contribution from the secondary minerals to remove the terrestrial contribution we have leached with hcl a subsample of the meteorite the residue made essentially of orthopyroxene and chromite has similar major and trace element abundances to diogenites as shown by the shape of its ree pattern or by its high al ga ratio the connection of nwa 4215 with diogenites is confirmed by its o isotopic composition 17o 1 431 0 102 18o 3 203 0 205 17o 0 248 0 005

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

a case study on the behavior of shield tunneling in sandy cobble ground this study investigates the behavior of shield tunneling based on a complete case record of an excavation in sandy cobble ground both numerical and analytical analyses were conducted to estimate the surface displacement along the tunnel axis and the surface zone affected by the shield tunneling this paper presents the performance of the peck method in forecasting the transversal surface settlement trough caused by the shield tunneling in a sandy cobble layer in particular this study has made a comparison with the vertical surface displacement monitored during the advancing excavation to the settlements estimated by using the peck method and by conducting a three dimensional finite element analysis the effective measures to provide the necessary face support pressure and to reduce the formation of sinkholes and ground settlements in sandy cobble ground were also investigated and discussed

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

the e greenland rifted continental margin an examination of the coastal flexure the structure of the e greenland coastal flexure a major structure developed during continental break up is interpreted on the basis of field observations an earlier model which involves normal inland dipping antithetic faulting and seaward rotation of fault blocks is confirmed and amplified this model requires that regional dips are very much less than dips measured on bedding planes thus leading to considerably reduced thicknesses for the tertiary volcanic succession in e greenland detailed mapping confirms the validity of these thickness estimates and leads to the conclusion that the volcanic extrusion rate was similar to that of present day iceland thus obviating the need for special mechanisms of magma generation comparable structures occur in other regions of continental break up and voluminous basalt discharge and it is suggested that the flexure developed by collapse of the attenuated crust subsequent to the massive extrusion of plateau basalts

structure and stratigraphy of the early tertiary basalts of the blosseville kyst east greenland the central part of the 65 000 km 2 lava plateau in east greenland between kangerlussuaq and scoresby sund has been investigated by multi model photogrammetry and profile sampling and a three dimensional framework for the lava plateau has been established post volcanic movements have divided the region into several structural blocks with dips varying from 1 2 n ne in the inland areas to 12 se at the coast a major n s trending fracture zone may reflect an underlying caledonian structure early volcanic and sedimentary rocks are overlain by widespread plateau basalts locally with an angular unconformity of 8 the basalt stratigraphy established in the scoresby sund area has been extended over most of the region the plateau basalts were erupted over a zone more than 150 km wide from the present coast and inland the succession attains a vertical thickness of more than 5 5 km in the central coastal areas and thins inland to 2 3 km a differential sagging of the coastal areas by at least 2 3 km took place during the emplacement of the lavas accelerating with time the features suggest increasing focusing of the magmatic production into a developing rift zone close to the present coast

reaction relationships of chrome spinels in igneous rocks further evidence from the layered intrusions of rhum and mull inner hebrides scotland compositions of chrome spinels in peridotites from the layered igneous rocks of rhum and of the ben buie intrusion mull show evidence of post depositional reaction relationships with the cumulus olivine and or the intercumulus liquid some seam forming spinels in the ben buie intrusion are highly aluminous more so than those in the rhum intrusion occasional zoned spinels in both intrusions show enrichment in al towards their rims the evidence suggests that the spinel reaction trend involving cr al exchange proceeds in the direction of al enrichment equilibrium between chrome spinel and cumulus olivine appears to have been attained rarely thus limiting the application of the olivine spinel geothermometer

metamorphic diogenite grosvenor mountains 95555 mineral chemistry of orthopyroxene and spinel and comparisons to the diogenite suite abstract grosvenor mountains gro 95555 is a relatively newly discovered and unique metamorphic diogenite it does not show the usual brecciated appearance of other diogenites or wide compositional variability of orthopyroxene or spinel electron microprobe analysis empa and secondary ion mass spectrometer sims analysis of orthopyroxene and empa of spinel show limited compositional variability compositions for orthopyroxene for fe fe mg atomic al zr y and yb fall in the middle of the compositional ranges of the diogenite suite apparently gro 95555 formed at sufficient depth or location to escape brecciation by meteorite bombardment and in a thermal regime that led to high grade metamorphism resulting in homogeneous mineral compositions the believed introduction howardite eucrite and diogenite hed lithologies are to have originated on asteroid 4 vesta during an extensive melting event at 4 6 ga consolmagno and drake

petrology and geochemistry of the elephant moraine a79002 diogenite a genomict breccia containing a magnesian harzburgite component the elephant moraine a79002 eeta79002 diogenite is a fragmental breccia with a subtle lightdark structure it is composed of orthopyroxene with minor olivine chromite and ubiquitous inhomogeneously distributed approximately 5 500 m sized troilite and metal grains these latter are present in the matrix and as inclusions in and as symplectic intergrowths with orthopyroxene and olivine trace amounts of silica and diopside are also present most orthopyroxene compositions typical orthopyroxenes are in the narrow range wo2 1 2 7en74 1 75 6fs22 2 23 8 like those of most diogenites a few magnesian orthopyroxenes are present with compositions of wo1 7 2 5en77 5 80 2 fs18 2 20 3 these are among the most magnesian orthopyroxenes known from diogenites a few ferroan orthopyroxenes have compositions of wo2 1 2 9en71 7 73 7fs24 2 25 5 differences in al2o3 tio2 and cr2o3 between the different orthopyroxene groups are inconsistent with a simple igneous fractionation relationship between them olivine compositions are fo75 0 76 9 the olivines could be in equilibrium with the magnesian orthopyroxenes but not with the typical or ferroan orthopyroxenes that form the bulk of eeta79002 metal grains exhibit a range of ni and co contents and ni co ratios their compositions indicate that they are primary igneous metal metal and troilite grains are more prevalent in the dark samples the trace incompatible lithophile element contents of 16 samples are remarkably uniform their yb concentrations are all within their 2s analytical uncertainties of the mean the uniformity and low content of light rare earth elements in eeta79002 indicate that negligible amounts of a trapped liquid component or foreign material mixed in the breccia could be present the siderophile and chalcophile element data show that the light dark structure is due to the distribution of metal and troilite grains dark samples contain higher ni co and se compared to light samples meteorite eeta79002 appears to contain material from three or more related plutons a magnesian harzburgite and two orthopyroxenites and is a genomict breccia

a method of estimating surface settlement above tunnels constructed in soft ground a technique suitable for the analysis of lined tunnels constructed in soft soil is described this technique permits consideration of the soil lining interaction lining weight and plastic failure within the soil particular attention is given to the simulation of loss of ground including the annular void created by the difference between the tunnelling machine and lining diameters the analysis is used in a parametric study to identify potentially significant factors affecting the prediction of surface settlement due to tunnel construction consideration is given to the effects of elastic modulus the distance between the tunnel and the underlying rigid base stratum plastic failure initial stresses ground loss including the annular void and the injection of clay grout into the tailpiece void the results of this analysis indicate that elastic anisotropy ground loss and clay grout injection are all important factors that are not usually considered in analyses in particular a parameter called th

computational homogenization for mechanical properties of sand cobble stratum based on fractal theory abstract sandy cobble strata is one of the most commonly encountered engineering geological body a further research into the stability of ground and underground structure demands for precise modeling of actual formation in this paper a meso scale numerical method for modelling sandy cobble strata is presented which considers rock blocks and soil matrix as separate constituents in the approach the particle size distribution and spatial distribution of rock blocks are two crucial points for the first point i e the particle size distribution of rocks the fractal scaling theory is included in particle size distribution description and design in the log log plots 60 sets of particle size distributions of sandy cobble soil in beijing are examined for fractal behavior for the second point i e the spatial distribution of rocks the monte carlo principle is used to generate random spatial distribution of rocks in soil matrix while the rock shape is assumed to be circular in two dimension or sphere in three dimension based on the compassion of rock volume content between the numerical model and theoretical calculation value it is validated that the meso scale method could basically be used to establish the meso model of sandy cobble strata then the present sandy cobble strata model is extended to investigate tunnel excavation in such a formation based on the simulation results the deformation characteristics on transverse section and longitudinal profile are explored respectively and their variations with fractal dimension or the maximum rock size are discussed subsequently

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

tertiary faulting and pseudotachylytes in the east greenland volcanic rifted margin seismogenic faulting during magmatic construction volcanic rifted margins have voluminous magmatic constructions at continent ocean transitions including thick sequences of flood basalts dike swarms and mafic plutons developed in crustal scale flexures in the tertiary east greenland volcanic rifted margin upper crustal dilation and flexure were accommodated by extensive faulting locally pervasive cataclastic deformation and pseudotachylyte generation the widespread distribution and large volumes of pseudotachylyte suggest that regional seismogenic faulting was vigorous during rapid crustal subsidence dike intrusion and the start of sea floor spreading

shrimp u pb zircon geochronology of the late archaean ruinnaesset syenite skjoldungen alkaline province southeast greenland abstract a sample of the ruinnaesset syenite of the southeast greenland skjoldungen alkaline province contains a homogeneous population of zircons up to 1 mm diameter that are devoid of new overgrowths and old inherited cores u pb isotopic analyses of these zircons form a single population with weighted mean 207 pb 206 pb and 206 pb 238 u ages of 2699 4 ma and 2690 20 ma 2 respectively these dates are interpreted as giving the time of crystallisation of the syenite

widespread magma oceans on asteroidal bodies in the early solar system our solar system formed about 4 6 billion years ago and within 4 million years small planetary bodies had formed some melting to form volcanic and related rocks two families of meteorites the heds and angrites are thought to have originated from asteroids that melted at this time new oxygen isotope measurements confirm that these meteorites are from two distinct asteroids that underwent large scale melting in the early solar system these new results show that early global scale melting was a feature of all the differentiated planets earth moon and mars and asteroids so far sampled immediately following the formation of the solar system small planetary bodies accreted1 some of which melted to produce igneous rocks2 3 over a longer timescale 15 33 myr the inner planets grew by incorporation of these smaller objects4 5 through collisions processes operating on such asteroids strongly influenced the final composition of these planets4 including earth5 currently there is little agreement about the nature of asteroidal igneous activity proposals range from small scale melting to near total fusion and the formation of deep magma oceans2 here we report a study of oxygen isotopes in two basaltic meteorite suites the heds howardites eucrites and diogenites which are thought to sample the asteroid 4 vesta6 and the angrites from an unidentified asteroidal source our results demonstrate that these meteorite suites formed during early global scale melting 50 per cent events we show that magma oceans were present on all the differentiated solar system bodies so far sampled magma oceans produced compositionally layered planetesimals the modification of such bodies before incorporation into larger objects can explain some anomalous planetary features such as earth s high mg si ratio

variability of apatite fission track annealing kinetics ii crystallographic orientation effects a method is presented that permits the length of any horizontal confined fission track inclined at a specified angle to the crystallographic c axis in apatite to be converted to an equivalent track length parallel to the crystallographic c axis the model is based on the results of annealing experiments for six selected apatites five calcian fluorapatites and durango apatite representing a subset of the 15 total apatite specimens studied an iterative process of calculation is required to project fission track lengths onto the c axis and computer source code implementing the solution to this problem is presented this method of projecting apatite fission track lengths onto the crystallographic c axis is shown to remove effectively fission track length variation within single fission track populations due to anisotropic track length reduction for all 15 apatites studied in addition a model is developed that offers predictions that closely reproduce published experimental data concerning the relationship between fission track density etched fission tracks per unit area of apatite surface and the arithmetic mean fission track length finally it is shown that natural fission track populations exhibit fission track length anisotropy similar to that of fission track populations created and annealed in the laboratory this observation implies that the same process by which apatite fission tracks anneal in the laboratory is responsible for annealing of apatite fission tracks in the geological environment

young ages of two diogenites and their genetic implications the achondrite meteorites known as eucrites and diogenites are thought to be igneous rocks derived from the crust and mantle respectively of a common parent planet or asteroid1 2 several eucrites have been dated at 4 5 4 6 gyr by the rb sr method4 6 and a rb sr age of 4 45 0 18 gyr 1 42x 10 11yr 1 has been reported3 for three diogenites from these data one cannot judge whether diogenites and eucrites are the same age here we present precise rb sr data for two diogenites tatahouine and johnstown that yield an age of 4 394 0 011 gyr significantly younger than our age of 4 52 0 15 gyr for the juvinas eucrite the low initial 87sr 86sr ratio of these diogenites and their rare earth element abundance patterns are inconsistent with the interpretation that the young ages reflect secondary metamorphism we suggest that our data raise doubts about a genetically close relationship between eucrites and these diogenites and that there exist groups of diogenites that are genetically distinct from one another our results also suggest that igneous activity in the assumed parent body continued for about one hundred million years after its formation 4 52 gyr ago the parent body may thus have had a complicated evolutionary history

the erosional and uplift history of ne atlantic passive margins constraints on a passing plume new apatite fission track analyses from nw britain indicate that a maximum of 2 5 km of erosion has occurred there during the cenozoic similar to values for se greenland and the east greenland coast north of scoresby sund the erosion may have been facilitated by magmatic underplating during break up however at kangerdlugssuaq east greenland 4 6 km of erosion is measured since 45 ma lower mid eocene marine sedimentary rocks overlying the lavas on the blosseville coast indicate that magmatic underplating on the central greenland coast substantially post dated flood volcanism and break up behaviour not predicted by simple plume rift models subsidence reconstructions of the hebrides shelf and the east and west greenland coasts show that rapid dynamic uplift was effectively synchronous at 63 ma and preceded volcanism by c 400 m is compatible with a mantle temperature anomaly of c 100 c these data suggest very rapid lateral flow of the impacting iceland plume head the predicted crossing of the plume by the east greenland coast in the mid late eocene would account for post rift magmatic underplating and dynamic support on the greenland but not the european side of the north atlantic basin

chemical alteration and ree mobilization in meteorites from hot and cold deserts the effects of terrestrial weathering on ree mobilization are evaluated for a variety of uncommon meteorites found in antarctica and in hot deserts the meteorites analyzed include 7 non cumulate eucrites 10 shergottites 3 nakhlites 2 lunar meteorites 4 angrites 10 acapulcoites 1 winonaite and 1 brachinite in situ concentration measurements of lanthanides and selected other minor and trace elements were made on individual grains by secondary ion mass spectrometry sims in antarctic meteorites oxidation converts ce 3 to ce 4 which is less soluble than the trivalent ree resulting in ce anomalies the mineral most affected is low ca pyroxene however not all grains of a given mineral are and distinct analyses of a single grain can even yield ree patterns with and without ce anomalies the effect is most pronounced for antarctic eucrites in which ce anomalies are observed not only in individual minerals but also in whole rock samples although ce anomalies are observed in meteorites from hot deserts as well the most characteristic signs of chemical alteration in this environment are a lree enrichment with a typical crustal signature as well as sr ba and u contaminations these can modify the whole rock ree patterns and disturb the isotope systematics used to date these objects the lree contamination is highly heterogeneous affecting some grains and not others of a given mineral mainly olivine and low ca pyroxene the two minerals with the lowest ree concentrations the major conduit for ree movement is through shock induced cracks and defects and the highest levels of contamination are found in altered material filling such veins and cracks meteorites that experienced low shock levels and those that are highly recrystallized are the least altered copyright 2003 elsevier ltd

comparative study of equilibrated and unequilibrated eucrites subsolidus thermal histories of haraiya and pasamonte thermal histories of non cumulate eucrites pasamonte and haraiya were determined from ca ca fe mg profiles of host lamellae pyroxene pairs from compositional profiles of pyroxene rims affected by metasomatism and from lamellae thicknesses using a rate law for lamellar coarsening pasamonte a type 2 eucrite experienced partial equilibration during a relatively short period of thermal annealing this equilibration is expressed texturally by metasomatized rims in mg rich and fe rich pyroxene grains and by coarsening of nanometer scale exsolution lamellae a cooling rate of 10 2 c day corresponds to post impact mixing and reburial of the polymict pasamonte assemblage to a depth similar to that of the initial lava flow haraiya a type 7 eucrite has experienced a complex thermal history involving multiple brecciation events and mixing of a single flow to produce a monomict assemblage containing clasts of variable grain size and texture a period of thermal annealing 50000 years in duration at temperatures between 1000 and 700 c corresponding to a cooling rate of 10 4 to 10 5 c day produced augite exsolution up to 3 m thick in pigeonite rapid burial by successive flows during a period of high magma productivity and high heat flow due to 2 6 al decay in the crust and mantle was a possible source of heat for metamorphism in the lower crust however cooling rates during relaxation of the lower crustal thermal gradient are much less than the mineralogically determined cooling rates heat derived from impact or from mid to upper crustal level intrusions is a plausible heat source for metamorphism and is consistent with observed cooling rates

aubrites and diogenites trace element clues to their origin we have analyzed by rnaa 25 aubrite and 9 diogenite samples for 13 to 29 siderophile volatile and lithophile trace elements both meteorite classes show a typically igneous siderophile element pattern with ir os re ge more depleted than au ni pd sb but aubrites tend to have about 10 higher abundances 10 3 10 4 cl for the first 4 and 10 2 10 3 cl for the last 4 siderophiles apparently reflecting smaller metal silicate distribution coefficients at lowerf o2 or less complete segregation of metal se is surprisingly abundant in aubrites up to 0 4 cl but te is less so sete 5 cl apparently due to its stronger siderophile character other volatiles ag zn in cd bi t1 show depletions intermediate between lunar dunite and the earth s mantle of 7 aubrites analyzed for ree ce nd eu tb yb lu 6 are depleted in ree 0 08 0 5 cl and 5 show negative eu anomalies the exceptions are bishopville and mt egerton silicate this supports an igneous origin as already noted by boynton and schmitt 1972 no samples of the complementary basaltic and feldspathic rocks have been found thus far but one of our samples of khor temiki dark is a candidate for the basalt it is 5 7 enriched in ree and only slightly less so in rb cs and u though shocked and enriched in siderophiles to 0 05 cl it apparently represents a new meteorite class three diogenites analyzed for ree show very diverse patterns from strongly depleted in light ree for tatahouine ce 0 01 cl to flat for garland 2 5 cl the data confirm the trends found by fukuokaet al 1977 as well as their interpretations factor analysis shows several parallel groupings for aubrites and diogenites siderophiles re ir os pd ge chalcophiles se te volatiles ag in tl and incompatibles u ree and cs or rb but there are some differences for elements such as ni sb cd bi au and zn most of which behave more sensibly in aubrites than in diogenites several element pairs that differ greatly in volatility cs u ge ir correlate closely in aubrites in approximately cl chondrite proportions these correlations and other lines of evidence suggest strongly that aubrites originated by igneous processes in their parent body not by direct nebular condensation the source material may have resembled el chondrites in oxidation state and depletion of refractories metal and volatiles

low temperature thermochronology of the southern east greenland continental margin evidence from apatite u th he and fission track analysis and implications for intermethod calibration abstract the southern coast of east greenland is characterized by high topographic relief and deep fjords but the evolution of the landscape and the low temperature thermochronology of the region is not well understood here we present apatite fission track and u th he ages that suggest several important features of the long term geomorphic history of this region but which also illustrate an important discrepancy in the thermal histories derived from each technique apatite from bedrock of the southern coast of east greenland between 62 n and 67 n has fission track ages ranging from 60 to 840 ma and u th he ages ranging from 21 to 250 ma the ages generally increase with elevation and distance from the coast and fission track analyses show significant differences in thermal histories for the different regions in the kangertittivatsiaq area c 66 67 n apatite fission track data and models suggest two separate periods of slow cooling prior to c 200 ma and between c 160 ma and the late cenozoic more recently than c 20 ma each of which was followed by a period of rapid cooling and inferred exhumation apatite he data in the kangertittivatsiaq region including crystal size age correlations in low elevation samples are most simply interpreted as recording an incision event of at least 1 5 km later than 20 ma near the coast this may have been caused by glacial erosion the u th he data also indicate an earlier phase of rapid exhumation at c 250 ma in the skjoldungen kap mosting area c 62 64 n approximately 200 km south of the kangertittivatsiaq apatite fission track data suggest slow exhumation from c 200 ma into the neogene followed by fast exhumation the similarity of fission track ages 200 ma at sea level in the fjords in the skjoldungen area c 62 64 n do not suggest tilting in the hinterland related to the breakup of the east greenland continental margin furthermore the cenozoic fission track ages and modeling fission track data suggest that pre breakup basins may have covered the outer coast despite the broadly similar topographic implications of the fission track and u th he data the thermal histories derived from these systems are inconsistent fission track data require thermal histories that predict he ages younger than observed and he data require thermal histories that predict fission track ages older than observed similar discrepancies have also been observed in other settings characterized by long term low temperature thermal histories and may reflect changes in annealing or diffusion behavior or both that either develop or become more apparent in such cases

post orogenic tectonic and thermal history of a rifted continental margin the scoresby sund area east greenland abstract fission track ft analysis of zircon sphene and apatite from crystalline basement in the scoresby sund area east greenland and ft modelling reveal information about the cooling and uplift paths for individual tectonic blocks since the caledonian orogeneny up to c 325 ma the area cooled and behaved as a single unit however it subsequently broke into several fault bounded blocks each block moving independently of adjacent blocks net uplift since 325 ma was of a similar magnitude 8 km assuming a geothermal gradient of 30 c km along the crest of the devonian fault zone for the southern blocks but about 9 km for the stauning alper and these blocks were probably tilted away from the rifted continental margin the relief evolution accompanying uplift in the caledonian basement is closely related to mesozoic basin formation subsidence and infilling in the area ft modelling reveals fast cooling from c 70 c to surface temperatures during the last 55 m y probably as a result of tertiary rifting and magmatic activity in the area

global crustal metamorphism of the eucrite parent body abstract we conducted a petrologic study of 18 equilibrated eucrites with the goal of understanding the formation and evolution of the crust of asteroid 4 vesta the likely source of eucrite meteorites their textures indicate that eucrites were basaltic igneous rocks but modified by postcrystallization brecciation recrystallization and impact melting recrystallized rocks are the most common among clasts in the eucrites impact melt breccias are rare equilibration temperatures of the metamorphic clasts range from 700 to 1000 c with most in the 800 900 c range complex exsolution and recrystallization textures in pyroxenes suggest that eucrites cooled very slowly from high peak temperatures after reheating this extended period of thermal metamorphism requires a high interior temperature in a vesta sized body this metamorphism could have taken place during and shortly after crust formation we suggest the crust of vesta evolved through the eruption rapid cooling and subsequent burial and reheating of lava flows as the crust grew in thickness the depth of burial increased causing temperatures to rise and leading to global metamorphism this resulted in only a small percentage of unequilibrated eucrites only the last few percent of basalts erupted would not be metamorphosed and a wide range of metamorphic temperatures and durations for the equilibrated eucrites

thermal and deformational histories of diogenites as inferred from their microtextures of orthopyroxene abstract orthopyroxenes of bronzite composition from three diogenites johnstown ibbenburen and allan hills alpha 77256 were examined by transmission electron microscopy to find microtextures suggestive of their origin subboundaries decorated with thick augite lamellae up to 100 m in length were found in all three orthopyroxenes and suggest either dislocation recovery processes during mild deformation or annealing at high subsolidus temperature the ibbenburen orthopyroxene has augite exsolution lamellae up to 0 4 m wide with the 100 plane in common the augite is semicoherent with the host as was found in those of the terrestrial layered intrusions of bushveld both textures are consistent with a deep seated origin in their parent body the johnstown orthopyroxene with the bulk chemical compositions ca 3 4 mg 71 0 fe 25 6 is similar to ibbenburen and contains coherent 100 augite lamellae only several unit cell wide and abundant guinier preston zones in addition the presence of untwinned pigeonite lamellae up to 0 1 m in width with remnant antiphase boundaries which are interpreted to have been produced by stress induced transformation at high temperature suggest shock deformation processes due to meteoritic impacts and excavation of its parental mass resulting in rapid cooling at high temperature

the tatahouine diogenite mineralogical and chemical effects of sixty three years of terrestrial residence comparison between clasts of the tatahouine diogenite collected the day of the fall in 1931 and 63 years later in 1994 allows the evaluation of mineralogical and chemical effects of terrestrial residence on meteorites secondary minerals are found in the 1994 samples iron stains and carbonate rosettes major and trace element abundances have been determined on fallen and found clasts no significant differences have been observed for most elements with the exception of rb sr and in a single case the light rare earth elements lree in this case the ree pattern of a 1994 clast displays a weak positive ce anomaly probably linked to the presence of iron hydroxide the contents of rb and sr are significantly higher in the 1994 samples than in the 1931 clasts and reflect the formation of calcite inside some of the clast fractures these results demonstrate that weathering processes may change the chemistry of meteorites in a very short time

constraints on the evolution of the east greenland margin evidence from detrital apatite in offshore sediments we test a new approach to understanding the tectonic evolution of passive margins by using fission track analysis on detrital apatites from sediments deposited offshore east greenland these apatites have not undergone postdepositional track annealing and therefore reflect provenance the apatites preserve a component of the source rocks thermal history that otherwise may not be retainedwithinthepresent dayoutcrop fission track deriveddenudational histories from samples at ocean drilling program drill sites offshore east greenland at lat 63 n are compared with data fromtheonshoresingertatcomplex previousapatitefission track studies and geomorphic mapping of the east greenland coast have shown that locally up to 6 km of denudation may have occurred implying significant tectonic or magmatic activity starting as much as30m y afterbreakupat56ma incontrast apatitefission track datapresentedhererecord 2kmofcenozoicdenudationinsoutheast greenland probably driven by magmatic underplating at the time of breakup large magnitude postrift denudation of east greenland is restricted to the area around kangerdlugssuaq 68 n thetiming 40 50ma andmagnitudeareinaccordwith revised plume track models suggesting that the iceland plume crossed the margin here during the late eocene

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

presidential address presented 2000 august 28 chicago illinois usa the eucrite vesta story many lines of evidence indicate that meteorites are derived from the asteroid belt but in general identifying any meteorite class with a particular asteroid has been problematical one exception is asteroid 4 vesta where a strong case can be made that it is the ultimate source of the howardite eucrite diogenite hed family of basaltic achondrites visible and near infrared reflectance spectra first suggested a connection between vesta and the basaltic achondrites experimental petrology demonstrated that the eucrites the relatively unaltered and unmixed basaltic achondrites were the product of approximately a 10 melt studies of siderophile element partitioning suggested that this melt was the residue of an asteroidal scale magma ocean mass balance considerations point to a parent body that had its surface excavated but remains intact modern telescopic spectroscopy has identified kilometer scale vestoids between vesta and the 3 1 orbit orbit resonance with jupiter dynamical simulations of impact into vesta demonstrate the plausibility of ejecting relatively unshocked material at velocities consistent with these astronomical observations hubble space telescope images show a 460 km diameter impact basin at the south pole of vesta it seems that nature has provided multiple free sample return missions to a unique asteroid major challenges are to establish the geologic context of the hed meteorites on the surface of vesta and to connect the remaining meteorites to specific asteroids

inversion of apatite fission track data for thermal history information apatite fission track length distributions and ages provide an integrated record of the low temperature 20 150 c thermal history of the host rock over geologic time scales the information content of these data is quantified by applying a stochastic optimization technique simulated annealing to determine the range of thermal histories compatible with synthetic apatite fission track data given a mathematical description of fission track annealing the goodness of fit between the observed and predicted data parameters and a slowly decreasing control parameter are treated as analogous to the free energy and temperature respectively of a thermodynamic system on this basis a boltzmann type probability distribution is defined and used to accept or reject random thermal history perturbations a priori information used to constrain the model space may include the temperature range in which the solutions are sought present day temperature the complexity of the thermal history and the maximum duration of the data sensitive thermal history this approach allows determination of the range of thermal histories compatible with an observed confined track length distribution and associated fission track age and it provides an estimate of the probability distribution of temperatures at a specific time results for synthetic data sets for diverse model thermal histories suggest that the resolution of thermal history is generally poor parts of the thermal history to which the data are most sensitive can be resolved to no better than about 10 c for ideal data bounds on acceptable time temperature space are sensitive to the assumed complexity of the thermal history but are relatively insensitive to typical uncertainties associated with the data application of this approach to real data is fundamentally limited by the uncertainty associated with extrapolating annealing models to geologic conditions