valles marineris dune sediment provenance and pathways abstract although low albedo sand is a prevalent component of the martian surface sources and pathways of the sands are uncertain as one of the principal present day martian sediment sinks the valles marineris vm rift system hosts a diversity of dune field populations associated with a variety of landforms that serve as potential sediment sources including spur and gully walls interior layered deposits ilds and landslides here we test the hypothesis that vm dune fields are largely derived from a variety of local and regional intra rift sediment sources results show several dune fields are superposed on ancient wall massifs and ilds that are topographically isolated from extra rift sand sources spectral analysis of dune sand reveals compositional heterogeneity at the basinal dune field and dune scales arguing for discrete relatively unmixed sediment sources in coprates and melas chasmata mapping is consistent with the principle sand source for dunes being noachian aged upper and lower wall materials composed of primary igneous minerals and glasses some of which show evidence for alteration in contrast dune fields in capri juventae and ganges chasmata show evidence for partial sediment derivation from adjacent early hesperian aged hydrated sulfate bearing ild units this finding indicates that these ilds act as secondary sand sources dunes containing soft secondary minerals e g monohydrated sulfate are unlikely to have been derived from distant sources due to the physical weathering of sand grains during transport isolated extra rift dune fields sand sheets and sand patches are located on the plateaus surrounding vm and the adjoining areas but do not form interconnected networks of sand pathways into the rift if past wind regimes with respect to directionality and seasonality were consistent with more recent regimes inferred from morphological analysis i e dune slip faces wind streaks and were sufficient in strength and duration small dune populations within aurorae chaos and north of eastern vm might have resulted from extended sand pathways into vm however we favor local and regional derivation of dune sand from a variety of intra rift lithologic sources for most cases dune sand sources and the mechanism by which the sand is liberated are discussed in the context of findings described herein but are broadly applicable to analysis of sediment production elsewhere on mars

palaeomagnetic data suggest link between the archaean proterozoic boundary and inner core nucleation it is generally believed that the earth s magnetic field arises from dynamo action in the convecting outer core1 3 thus the geomagnetic field and especially its strength can provide information about core processes recent determinations of the geomagnetic palaeointensity using archaean and early proterozoic samples from the kaapvaal and superior cratons are consistent with a sharp increase in the magnitude of the geomagnetic field between 2 7 and 2 1 gyr analysis of published late archaean and early proterozoic apparent polar wander paths shows that an abrupt change in the rate and style of continental motion occurred at about 2 5 2 6 gyr ago if this change is also interpreted to be related to the growth of an inner core then an intriguing conjecture arises that the archaean proterozoic transition is related to inner core nucleation

definitive evidence of hesperian basalt in acidalia and chryse planitiae 1 the surface materials of acidalia and chryse planitiae mars have been variably interpreted morphologically as basalt and compositionally as andesite or altered basalt a thorough survey using the compact reconnaissance imaging spectrometer for mars crism near infrared spectrometer reveals olivine and high calcium pyroxene signatures in the shallow subsurface exposed by impact craters these signatures indicate that the near surface of these regions are primarily basaltic in nature and are similar to other regions of hesperian volcanism across mars e g syrtis major previous spectroscopic studies using coarser resolution data sets have failed to identify these mafic signatures due to obscuration of the underlying material in addition to the relatively small scale exposures in impact craters the nature of the surficial obscuration material is likely multifaceted and includes the deposition of latitude dependent mantling material and the presence of alteration rinds this observation shows that the northern plains of mars are basaltic and must be factored into the thermal and surficial evolution of mars

composition morphology and stratigraphy of noachian crust around the isidis basin definitive exposures of pristine ancient crust on mars are rare and the finding that much of the ancient noachian terrain on mars exhibits evidence of phyllosilicate alteration adds further complexity we have analyzed high resolution data from the mars reconnaissance orbiter in the well exposed noachian crust surrounding the isidis basin we focus on data from the compact reconnaissance imaging spectrometer for mars as well as imaging data sets from high resolution imagine science experiment and context imager these data show the lowermost unit of noachian crust in this region is a complex brecciated unit of diverse compositions breccia blocks consisting of unaltered mafic rocks together with rocks showing signatures of fe mg phyllosilicates are commonly observed in regions of good exposure layered or banded phyllosilicate bearing breccia rocks are observed suggestive of pre isidis sedimentary deposits in places the phyllosilicate bearing material appears as a matrix surrounding mafic blocks and the mafic rocks show evidence of complex folded relationships possibly formed in the turbulent flow during emplacement of basin scale ejecta these materials likely include both pre isidis basement rocks as well as the brecciated products of the isidis basin forming event at 3 9 ga a banded olivine unit capped by a mafic unit covers a large topographic and geographic range from northwest of nili fossae to the southern edge of the isidis basin this olivine mafic cap combination superimposes the phyllosilicate bearing basement rocks and distinctly conforms to the underlying basement topography this may be due to draping of the topography by a fluid or tectonic deformation of a previously flatter lying morphology we interpret the draping superposed olivine mafic cap combination to be impact melt from the isidis basin forming event while some distinct post isidis alteration is evident carbonate kaolinite and serpentine the persistence of olivine from the time of isidis basin suggests that large scale aqueous alteration processes had ceased by the time this unit was emplaced

valles marineris tectonic and volcanic history inferred from dikes in eastern coprates chasma magmatic dikes have been proposed to have weakened and fractured the crust allowing the formation of valles marineris hence dikes were studied in the region of eastern coprates chasma in an area that includes a major transition between hesperian aged volcanic deposits in the western walls and pristine noachian crust in the eastern walls over a hundred dikes were identified dike widths are 13 m on average estimation of magma eruption rates are comparable with previous estimates for hesperian lava flows on mars 105 to 106 m3 s 1 dikes dips range from 55 to 90 orientations record two distinct main tectonic stress fields 90 and 70 different from the chasmata dikes striking 90 are only observed at elevations below 1500 m dikes striking 70 are observed at elevation below 0 m and are therefore considered older however linear features are also observed on the late noachian early hesperian surrounding plateaus and could be related to the 70 dike group in the western part of our study area dikes 10 of the total amount of dikes mapped strike 110 sub parallel to valles marineris and suggests a relationship between dike emplacement and graben formation the presence of pre existing faults in the two directions 90 and 70 could explain the shape of eastern valles marineris and chaotic terrains which have a different general orientation than the valles marineris main rift our results suggest a complex relationship between dike emplacement and the formation of valles marineris

the structure and driving mechanisms of the baltic intrusions abstract data from closely spaced ctd profiling performed in the eastern gotland basin after the 1993 inflow event are used to study thermohaline intrusions in the baltic sea two ctd cross sections display abundant intrusive layers in the permanent halocline despite the overwhelming dominance of the salinity stratification diffusive convection is shown to work in the baltic halocline enhancing diapycnical mixing to understand the driving mechanisms of observed intrusions these are divided into different types depending on their structural features only two types of observed intrusions are suggested to be strongly influenced by diffusive convection 1 relatively thin 3 5 m and long up to 8 km intrusions inherent to high baroclinicity regions and 2 relatively thick 10 m and short 2 5 km intrusions inherent to low baroclinicity regions to verify this hypothesis the linear stability models of 3d and 2d double diffusive interleaving in approximation of a finite width front were used it is sh

geochronology of the belmont lake metavolcanic complex and implications for crustal development in the central metasedimentary belt grenville province ontario u pb analyses of zircon and titanite were carried out on eight rocks from the belmont lake metavolcanic complex a volcano sedimentary sequence in the central metasedimentary belt of the grenville province of southeastern ontario the ages of concordant supracrustal rocks within the complex do not accord with stratigraphic position the youngest volcanic age is from a rhyolite near the base of the sequence the oldest age is from a dacite in the middle this is overlain by a rhyolite in age a rhyolite at the top of the sequence appears to contain zircon inherited from a source about 1870 ma old the complex is therefore interpreted as comprising a lithotectonic sequence composed of structurally interleaved segments of contrasting age tectonic emplacement of these segments was most likely along previously unrecognized thrust faults the supracrustal rocks were subjected to at least two major deformational events as well as a late metamorphism the earliest event was probably associated with thrusting t

post tectonic magnetizations from the cordova gabbro ontario and palaeozoic reactivation in the grenville province summary the cordova gabbro of southern ontario intrudes 1300 myr old volcanic rocks of the hastings lowlands in the grenville structural province three distinct vector magnetizations a b and c have been isolated using a combination of stable endpoints subtracted vectors from orthogonal vector plots and converging remagnetization circles the a magnetization with mean direction d 294 i 55 5 k 42 ag5 5 5 n 18 sites is a high coercivity high blocking temperature remanence recorded by 49 samples the b magnetization was isolated in 33 samples and has a mean direction d 305 5 1 1 5 k 24 ag5 9 5 n 11 sites b has lower coercivities and blocking temperatures than a where the two are superimposed the a and b palaeopoles 151 e 10 5 s dp 6 dm 8 and 165 5 e 24 n dp so dm 9 5 fall on the grenville track around 900 and 820 ma respectively the a and b magnetizations thus date from uplift and cooling following the grenvillian orogeny the third magnetization the c component has been isolated in 23 samples its mean direction is d 180 i 27 5 k 18 ag5 10 5 n 12 sites the c is a low coercivity low blocking temperature overprint of a and b its palaeopole 102 e 31 n dp 6 5 dm 12 is unlike post 1300 precambrian poles for cratonic north america but matches silurian and late ordovician poles 40ar 39ar plateau ages of 446 and 447 ma determined by lopez martinez and york for plagioclases from one of the cordova samples confirm this age assignment the c magnetization therefore records a previously unrecognized mild thermal or hydrothermal event that occurred in palaeozoic time long after the grenvillian orogeny

paleointensity determination on the late precambrian tudor gabbro ontario paleointensity determination by the coe modified thellier method was carried out on the 1100 ma tudor gabbro of southern ontario the tudor has a bivectorial natural remanent magnetization nrm the c nrm is a grenvillian uplift thermoviscous remagnetization which overprints the a nrm the surviving primary thermoremanent magnetization trm of the tudor intrusion a sharp junction at 530 c between the a and c vectors in laboratory thermal demagnetization matches the peak metamorphic reheating temperature of 480 500 c in nature when the difference in time scales is taken into account the unblocking temperature distributions of the a nrm and of laboratory trm also match a is carried by single domain or small pseudo single domain grains probably magnetite rods exsolved in plagioclase or pyroxene at temperatures above 580 c arai plots of nrm versus partial trm are linear from 520 c or 530 c to 580 c for 45 specimens of 19 samples from 9 sites the 45 reliable paleointensity values from these specimens give a virtual axial dipole moment vadm of 4 6 0 8 1022 a m2 around 1100 ma this is about one half of the modern field intensity but is similar to the mean cretaceous cenozoic intensity and to most archean and proterozoic vadms keweenawan rocks whose ages are within 20 myr of the tudor gabbro have a vadm of 11 4 1022 a m2 the difference between the tudor and keweenawan vadms is similar to differences recorded over similar time intervals in the cretaceous and seems to represent normal variation in geomagnetic field strength throughout earth s history

multivectorial paleointensity determination from the cordova gabbro southern ontario abstract we report geomagnetic field intensities for the a 1000 ma and b 850 ma natural remanent magnetizations of the cordova gabbro of southern ontario we interpret a and b to be secondary thermal overprints produced during regional uplift and cooling following the grenvillian orogeny multivectorial a b paleointensity data were analyzed using pairs of arai diagrams for the separated a and b vectors from 18 reliable a results and 15 reliable b results we find paleofield values of 18 1 2 1 t and 7 1 1 5 t respectively the corresponding virtual axial dipole moments vadms are 3 12 0 36 and 1 82 0 38 10 22 a m 2 about 70 and 40 of the average phanerozoic dipole moment based on data from 0 3 300 ma the cordova data and other precambrian paleointensities are generally within a range of approximately 0 5 1 5 times the phanerozoic mean vadm three sets of paleofield values as a function of paleolatitude including the cordova data support a dipole configuration for the earth s field in 25 150 ma time windows around 2700 ma 1100 ma and 850 ma

olivine and pyroxene diversity in the crust of mars datafromthe observatoire pour la mineralogie l9eau les glaces et l9activite omega on the mars express spacecraft identify the distinct mafic rock forming minerals olivine low calcium pyroxene lcp and high calcium pyroxene hcp on the surface of mars olivine and hcp rich regions are found in deposits that span the age range of geologic units however lcp rich regions are found only in the ancient noachian aged units which suggests that melts for these deposits were derived from a mantle depleted in aluminum and calcium extended dark regions in the northern plains exhibit no evidence of strong mafic absorptions or absorptions due to hydrated materials

high geomagnetic intensity during the mid cretaceous from thellier analyses of single plagioclase crystals recent numerical simulations have yielded the most efficient geodynamo having the largest dipole intensity when reversal frequency is low reliable paleointensity data are limited but heretofore have suggested that reversal frequency and paleointensity are decoupled we report data from 56 thellier thellier experiments on plagioclase crystals separated from basalts of the rajmahal traps 113 to 116 million years old of india that formed during the cretaceous normal polarity superchron these data suggest a time averaged paleomagnetic dipole moment of 12 5 1 4 1022 amperes per square meter three times greater than mean cenozoic and early cretaceous late jurassic dipole moments when geomagnetic reversals were frequent this result supports a correlation between intervals of low reversal frequency and high geomagnetic field strength

the effect of remanence anisotropy on paleointensity estimates a case study from the archean stillwater complex paleomagnetism of archean rocks potentially provides information about the early development of the earth and of the geodynamo precambrian layered intrusive rocks are good candidates for paleomagnetic studies such complexes are commonly relatively unaltered and may contain some single domain magnetite armored by silicate mineral grains however layered intrusives often have a strong petrofabric that may result in a strong remanence anisotropy magnetic anisotropy can have particularly disastrous consequences for paleointensity experiments if the anisotropy is unrecognized and if its effects remain uncorrected here we examine the magnetic anisotropy of an anorthosite sample with a well developed magmatic foliation the effect of the sample s remanence fabric on paleointensity determinations is significant paleointensities estimated by the method of thellier and thellier range from 17 to 55 t for specimens magnetized in a field of 25 t we describe a technique based on the remanence anisotropy tensor to correct paleointensity estimates for the effects of magnetic fabric and use it to estimate a paleointensity for the stillwater complex mt usa of 32 t adjusted for the effects of slow cooling

a regional paleomagnetic study of lithotectonic domains in the central gneiss belt grenville province ontario abstract we have made a regional paleomagnetic study of lithotectonic domains in the central gneiss belt of the grenville province in ontario along ten n s and e w traverses up to 200 km in length although originally intended to clarify the tectonic mechanism by which these exotic terranes were assembled and welded to the archean superior craton during the 1150 ma grenvillian orogeny we actually learned much more about the timing of post orogenic uplift of the various domains around 1000 900 ma as they stabilized and became part of the rodinia supercontinent the normal n and reverse r natural remanent magnetizations nrms of all domains as well as those of reactivated regions flanking the grenville front gf the superior grenville boundary to the north and south have paleomagnetic poles falling on the 980 920 ma 40ar 39ar calibrated portion of the grenville apparent polar wander track for laurentia there is a general tendency for paleopoles to young with increasing distance of domains from the gf implying that more southerly domains were uplifted and magnetized later but two of the domains do not fit this pattern previously reported younging trends away from the gf based on k ar thermochron maps and paleomagnetic zone poles are untrustworthy because of hydrothermal alteration which causes chemical remagnetization and anomalously old k ar ages near the gf another trend in our data is a regular increase in the r n ratio with increasing distance south of the gf in the reactivated zones flanking the gf nrms are overwhelmingly of n polarity whereas well away from the gf r n is close to 50 50 also nrm intensities and susceptibility values increase 100 fold away from the gf peaking 10 km south of the front with a pulse like pattern similar to that documented in anomalously high 40ar 39ar dates in the same region both the magnetic and ar ar results are likely due to a wave of hydrothermal alteration and remagnetization during which fluids were driven away from the gf since the remagnetized nrm near the gf has approximately the same direction as nrms in domains away from the gf hydrothermal activity along fault systems south of the gf must have continued until 1000 ma long after the collisional orogeny itself

the anatomy of a wrinkle ridge revealed in the wall of melas chasma mars wrinkle ridges are among the most common tectonic structures on the terrestrial planets and provide important records of the history of planetary strain and geodynamics the observed broad arches and superposed narrow wrinkles are thought to be the surface manifestation of blind thrust faults which terminate in near surface volcanic sequences and cause folding and layer parallel shear however the subsurface tectonic architecture associated with the ridges remains a matter of debate here we present direct observations of a wrinkle ridge thrust fault where it has been exposed by erosion in the southern wall of melas chasma on mars the thrust fault has been made resistant to erosion likely due to volcanic intrusion such that later erosional widening of the trough exposed the fault plane as a 70 km long ridge extending into the chasma a plane fit to this ridge crest reveals a thrust fault with a dip of 13 8 7 between 1 and 3 5 km depth below the plateau surface with no evidence for listric character in this depth range this dip is significantly lower than the commonly assumed value of 30 which if representative of other wrinkle ridges indicates that global contraction on mars may have been previously underestimated

calcite graphite isotope thermometry a test for polymetamorphism in marble tudor gabbro aureole ontario canada graphitization and coarsening of organic material in carbonate bearing metasedimentary rocks is accompanied by carbon isotope exchange which is the basis of a refractory pressure independent geothermometer comparison of observed isotopic fractionations between calcite and graphite a13ccal gr with independent petrological thermometers provides the following empirical calibration over the range 400 800 c a13ccal gr 5 81 x lo6 x t k 2 61 this system has its greatest potential in marbles where calcite graphite is a common assemblage and other geothermometers are often unavailable the temperature dependency of this empirical calibration differs from theoretical calibrations reasons for this are unclear but the new empirical calibration yields temperature estimates in better agreement with independent thermometry from several terranes and is preferred for geological applications both calcite graphite isotopic thermometry and calcite dolomite solvus thermometry are applied to marble adjacent to the tudor gabbro in the grenville province of ontario canada the marble has undergone two metamorphic episodes early contact metamorphism and later regional metamorphism values of a13cca gr decrease regularly from c 8 0 in samples over 2 km from the pluton to values of 3 4 within 200m of the contact these samples appear to preserve fractionations from the early thermal aureole with the empirical geothermometer and indicate temperatures of 450 500 c away from the intrusion and 700 750 c near the gabbro this thermal profile around the gabbro is consistent with conductive heat flow models in contrast the distribution of mg between calcite and dolomite has been completely reset during later regional metamorphism and yields uniform temperatures of c 500 c even at the contact graphite textures are important for interpreting the results of the calcite graphite thermometer coarsening of graphite approaching the tudor gabbro correlates with the decrease in isotopic fractionations and provides textural evidence that graphite crystallization took place at the time of intrusion in contrast to isotopic exchange during prograde metamorphism which is facilitated by graphitization retrogressive carbon isotopic exchange appears to require recrystallization of graphite which is sluggish and easily recognized texturally resistance of the calcite graphite system to resetting permits thermometry in polymetamorphic settings to see through later events that have disturbed other systems

assessing martian bedrock mineralogy through windows in the dust using near infrared and thermal infrared remote sensing abstract much of mars surface is mantled by bright dust which masks the spectral features used to interpret the mineralogy of the underlying bedrock despite the wealth of near infrared nir and thermal infrared tir data returned from orbiting spacecraft in recent decades the detailed bedrock composition of approximately half of the martian surface remains relatively unknown due to dust cover to address this issue and to help gain a better understanding of the bedrock mineralogy in dusty regions dust cover index results from the mars global surveyor thermal emission spectrometer tes and analysis of images from the mars reconnaissance orbiter mars color imager marci were used to identify 63 small localized areas within the classical bright dusty regions of arabia terra elysium planitia and tharsis montes as potential windows through the dust that is areas where the dust cover is thin enough to permit infrared remote sensing of the underlying materials the mineralogy of each candidate window was inferred using spectra from the mars express observatoire pour la mineralogie l eau les glaces et l activite omega nir spectrometer and where possible tes twelve areas of interest returned spectra that are consistent with mineral species expected to be present at the regional scale such as high and low calcium pyroxene olivine and iron bearing glass distribution maps were created using previously defined index parameters for each species present within an area high quality tes spectra if present within an area of interest were deconvolved to estimate modal mineralogy and to support nir interpretations omega data from arabia terra and elysium planitia are largely similar and indicate the presence of high calcium pyroxene with significant contributions of glass and olivine while tes data suggest an intermediate between the established compositions of the southern highlands and syrtis major limited data from tharsis are consistent with low calcium pyroxene mixed with lesser amounts of glass and high calcium pyroxene tes data from southern tharsis correlate well with the previously inferred compositions of the aonium and mare sirenum highlands immediately to the south of particular note is the detection of iron bearing glass as a significant component of all three analyzed regions especially in tharsis overall the underlying compositions of the classically dust covered regions of mars appear consistent with the compositions of adjacent and other low albedo not dust covered regions of the planet identified in previous studies with the noted contribution from iron bearing glass

revised crism spectral parameters and summary products based on the currently detected mineral diversity on mars the investigation of hyperspectral data from the mars reconnaissance orbiter compact reconnaissance imaging spectrometer for mars crism and the observatoire pour la mineralogie l eau les glaces et l activitie omega on mars express has revealed an increasingly diverse suite of minerals present on the martian surface a revised set of 60 spectral parameters derived from corrected spectral reflectance at key wavelengths in crism targeted observations and designed to capture the known diversity of surface mineralogy on mars is presented here as summary products some of the summary products have strong heritage to omega spectral parameter calculations this paper also presents newly derived parameters that highlight locations with more recently discovered spectral signatures type locations for the diversity of currently identified mineral spectral signatures have been compiled into a library presented in this work our analysis indicates that the revised set of summary products captures the known spectral diversity of the surface and successfully highlights and differentiates between locations with differing spectral signatures the revised spectral parameter calculations and related products provide a useful tool for scientific interpretation and for future mission landing site selection and operations

an improved methodology for thellier type paleointensity determination in igneous rocks and its usefulness for verifying primary thermoremanence we propose a new methodology for thellier type paleointensity experiments in standard paleointensity experiments the blocking temperatures of most stable remanences are often not reached before thermal alteration of magnetic mineralogy begins and subsequent data have to be discarded we emphasize that when alteration begins at low temperature and continues throughout the experiment which then fails in standard analyses the resulting unblocking temperature tub spectrum of the alteration product does not necessarily overlap with the whole tub spectrum of natural remanent magnetization nrm because tub depends on physical characteristics of the new grains not the temperatures at which they were formed nrm may survive in an uncontaminated higher tub window if alteration remanence only has low tub then partial thermoremanent magnetization ptrm checks at temperature step tj 1 can be used to correct for alteration that has occurred at tj and furthermore thermal demagnetization of a full trm acquired in the laboratory at the end of the progressive thellier thellier experiment should reveal the true uncontaminated tub spectrum of the nrm in higher temperature intervals we propose a new experimental sequence which allows monitoring and correction of alteration and provides two semi independent estimates of palaeointensity in the circumstances described above we illustrate the issues involved through new experimental work on igneous rocks from a paleozoic charnockitic syenite where we unravel trm from multidomain isothermal remanence despite massive alteration during laboratory heating finally we point out the value of these experiments for verifying primary trm in igneous rocks indicating properties that distinguish trm from other remanence

mars a review and synthesis of general environments and geological settings of magma h2o interactions the advent of a global cryosphere likely occurred very early in the history of mars and much of the available water and related volatiles co 2 clathrates etc were sequestered within and below the cryosphere this means that magmatism plutonism and volcanism as a geological process throughout the history of mars cannot be fully understood without accounting for the interaction of magma and water and related species in both solid and liquid form we review and outline the probable configuration of water and ice deposits in the history of mars describe environments and modes of magma h 2o interaction and provide specific examples from the geological record of mars magma and water ice interactions have been interpreted to have formed 1 massive pyroclastic deposits 2 large scale ground collapse and chaotic terrain 3 major outflow channels 4 mega lahars dwarfing terrestrial examples 5 sub ice sheet eruptions and edifices 6 pseudocraters 7 landslides on volcanic edifice flanks and 8 hydrothermal sites the global nature of the cryosphere its longevity and the diversity of environments means that mars is an excellent laboratory for the study of magma h 2o interactions and the role of related volatile species

layered megablocks in the central uplifts of impact craters abstract a database of bedrock exposed in crater central uplifts has been compiled from multiple orbital datasets in this study we focus on uplifts which show decameter scale layers within the exposed megablocks derived from the bedrock of the preexisting target this distinctive morphology found in 41 craters globally occurs mostly in regions mapped as hesperian plains material generally interpreted as regions of extensive flood lavas the association with volcanic units coupled with morphology and mineralogy that is consistent with flood lava emplacement suggests that the layers are stacks of dense lava interbedded with weaker materials estimates for the uplift of stratigraphic sections coupled with morphologic and morphometric analyses lead to estimated thicknesses of the layered unit these estimates indicate hesperian flood lavas are 23 thicker than a previous minimum estimate with a volume of 5 5 10 7 km 3 this increases the known extrusive volcanic production for the history of mars and volatile release to past martian atmospheres

evidence for extensive olivine rich basalt bedrock outcrops in ganges and eos chasmas mars 1 several localized outcrops of olivine enriched bedrock have been previously identified in the ganges and eos chasma area on the eastern end of valles marineris with the thermal emission imaging system multispectral images these outcrops form a layer in the walls of ganges chasma and appear to be the remnants of a once continuous unit which was mapped over 100 km in this study we further characterize the composition forsterite content of 0 68 olivine abundance 10 to 15 thermal inertia 600 jk 1 m 2 s 1 2 consistent with in place rocky material vertical dimension 60 to 220 m extent 1100 km laterally volume 9 9 104 km3 dip 0 013 ne and continuity of this layer utilizing thermal emission spectrometer hyperspectral thermal emission imaging system multispectral and mars orbiter laser altimeter elevation data morphologic data from high resolution imagery display a relatively unmantled rough and pitted surface associated with the olivine enriched material consistent with thermal inertia data four possibilities for the origin of the olivine enriched unit are 1 volcanism associated with tectonic rifting of the valles marineris system 2 a volcaniclastic flow deposit 3 an intrusive mafic sill or 4 a discrete episode in martian history during which flood lavas were erupted onto the surface the most likely origin is an eruptive event consisting of compositionally uniform flood lavas originating from a primitive mantle source region possibly associated with the initiation of tharsis volcanism this unit is one of the largest continuous compositional units found on mars and is strikingly similar to other olivine enriched deposits identified in previous studies where compositional morphologic and thermophysical similarities are observed these similarities may indicate that there was a period in early martian history where compositionally uniform and extensive olivine enriched flood basalts were erupted on the martian surface

mesoscale thermohaline variability in the eastern gotland basin following the 1993 major baltic inflow high horizontal resolution data from a tow yo conductivity temperature depth profiling system are analyzed to examine the mesoscale and fine scale response of the gotland basin to the 1993 major baltic inflow the permanent halocline in the basin is characterized by intensive thermohaline intrusions a well defined front of the intrusive region was found to be propagating north from the stolpe channel to the gotland deep with a speed of 2 cm s 1 or more a substantial horizontal intermittency of intrusion intensity related to mesoscale eddies was observed behind the front a strongly nonlinear cyclonic eddy undetectable on the sea surface was found in the halocline the cyclone contributed to the transport of salty water after the inflow the combined effect of the mesoscale eddies and thermohaline intrusions is shown to be one of the mechanisms responsible for the deep water ventilation by major baltic inflows

quantitative compositional analysis of martian mafic regions using the mex omega reflectance data 1 methodology uncertainties and examples of application abstract the mars express observatoire pour la mineralogie l eau les glaces et l activite omega collected an unprecedented visible and near infrared hyperspectral dataset covering the low albedo regions of mars we investigate the ability to infer modal abundance of surfaces of these regions from a radiative transfer model developed by shkuratov et al shkuratov y starukhina l hoffmann h arnold g 1999 icarus 137 235 246 and adapted to basaltic surfaces by poulet and erard poulet f erard s 2004 j geophys res 109 e2 doi 10 1029 2003je002179 from omega measurements of mafic surfaces we develop several sensitivity tests to assess the extent to which the model can be applied to predict pyroxene composition high calcium phase and low calcium phase abundance of almost neutral components plagioclase in the near infrared wavelength as well as grain sizes by using a library of selected end members results of the sensitivity tests indicate that the scattering model can estimate both abundances and grain sizes of major basaltic materials of low albedo regions within uncertainties 5 to 15 vol the model is then applied to data from dissected cratered terrains located in terra meridiani the derived grain size including uncertainties is in the 50 500 m range this is consistent with the thermal inertia and albedo of this region which indicates a fine sand sized surface with little dust the abundances of plagioclase 43 57 and pyroxenes 35 45 10 including 11 5 of low calcium phase are in good agreement with previous basalt like compositions of low albedo regions from thermal infrared spectral measurements the method presented in this paper will provide a valuable tool for evaluating the modal mineralogy of other mafic regions of mars observed in the near infrared wavelength range

the formation of valles marineris 2 stress focusing along the buried dichotomy boundary 1 although valles marineris is widely regarded as an extensional tectonic feature the source of stress responsible for its formation remains unknown this study argues that the tensile stresses that triggered valles marineris tectonism are a result of its location south of and subparallel to the buried crustal dichotomy boundary beneath tharsis the emplacement of the tharsis volcanic load straddling the pre existing topographic step of the crustal dichotomy boundary would have resulted in an abrupt change in the thickness of the load causing differential subsidence and extension across the boundary thin shell flexural models predict a narrow belt of focused tensile stresses south of the buried dichotomy boundary coinciding with the location of present day valles marineris the interaction of these boundary generated stresses with the competing stress fields associated with tharsis loading can explain the formation of noctis labyrinthus in the west and the deflection of the valles marineris troughs away from the buried boundary toward the east finite element models demonstrate that the magnitudes and vertical variations of stress at valles marineris are sensitive to the timing of loading and flexure in tharsis the incremental loading and flexure expected for a large volcanic rise results in the maximum tensile stress at valles marineris occurring at depth with tensile stresses through the majority of the lithospheric column dikes forming within this tensile stress belt would propagate through the full vertical extent of the lithosphere due to the stress release associated with the dilation of the dikes playing a crucial role in the formation of the valles marineris troughs

generation of subsurface cyclonic eddies in the southeast baltic sea observations and numerical experiments 1 closely spaced ctd transects performed in the summertime reveal simultaneous downward upward bendings of temperature salinity contours in the seasonal thermocline permanent halocline of the stolpe channel and the gulf of gdansk which may be interpreted as geostrophically balanced cyclonic eddies in the intermediate layer to examine processes capable of forming the observed cyclonic eddies a numerical simulation based on the princeton ocean model pom has been initiated the subsurface cyclones in the stolpe channel were satisfactory simulated in model runs under easterly northerly wind conditions their formation was shown to result from the adjustment of the high potential vorticity pv outflow from the bornholm basin via the stolpe sill to low potential vorticity environment by vortex stretching so called the pv outflow hypothesis by spall and price 1998 in accordance with the real wind conditions a cyclonic eddy observed in the intermediate layer of the gulf of gdansk was satisfactorily reproduced in a model run with the westerly wind shutdown which implies westward transport throughout the stolpe channel and thereby excludes the pv outflow hypothesis the subsurface cyclone simulated in the gulf of gdansk was traced to form in the course of relaxation of the coastal downwelling baroclinic jet

identification distribution and possible origins of sulfates in capri chasma mars inferred from crism data crism is a hyperspectral imager onboard the mars reconnaissance orbiter mro nasa 2005 which has been acquiring data since november 2006 and has targeted hydrated minerals previously detected by omega mars express esa 2003 the present study focuses on hydrated minerals detected with crism at high spatial resolution in the vicinity of capri chasma a canyon of the valles marineris system crism data were processed and coupled with mro and other spacecraft data in particular hirise high resolution science experiment mro images detections revealed sulfates in abundance in capri especially linked to the interior layered deposits ild that lie in the central part of the chasma both monohydrated and polyhydrated sulfates are found at different elevations and are associated with different layers monohydrated sulfates are widely detected over the massive light toned cliffs of the ild whereas polyhydrated sulfates seem to form a basal and a top layer associated with lower albedo deposits in flatter areas hydrated silicates phyllosilicates or opaline silica have also been detected very locally on two mounds about a few hundred meters in diameter at the bottom of the ild cliffs we suggest some formation models of these minerals that are consistent with our observations

vertical mixing in the baltic sea and consequences for eutrophication a review abstract in the transition area between the north sea and the baltic sea entrainment processes dominate the vertical mixing in the inflowing saline bottom water the hot spots of these processes are located at the darss sill and the bornholm channel in the western baltic sea in the central baltic sea the horizontal advection of saline water in deep layers below the permanent halocline dominate the temporal changes and associated transports this is accompanied by the turbulent vertical transport through the halocline into the surface layers the related vertical salt transport into the entire surface mixed layer estimated by various methods is slightly above 30 kg m 2 a during stagnation periods the residence time of the deep water in the eastern gotland basin increases roughly by a factor of five vertical mixing through the halocline is drastically reduced when inflows are lacking the potential processes of diapycnal mixing are discussed to the present knowledge the turbulent motion resulting from breaking internal waves is capable of turbulent transports through the halocline corresponding to the estimates of the salt transport into the surface mixed layer the actual knowledge about boundary mixing due to internal waves in the baltic sea is poor mesoscale eddies may contribute to the vertical mixing but it is not known whether they really do and which of the possible direct and indirect mixing mechanisms is most effective near bottom currents induced by inflow events likely enhance vertical mixing coastal upwelling certainly contributes to the vertical transport but the depth of its origin and the volume transport are hard to determine for large scale quantifications the short spatiotemporal scale of turbulent transports through the halocline resulting in a weakening of the halocline during summer together with the mixing of the entire surface layer down to the halocline in winter form a consistent description of the vertical salt transport it is hypothesised that the longer residence time of the deep water during stagnation periods results from the lack of energy imported by the inflows and directly or indirectly feeding the diapycnal mixing processes the vertical transport of nutrients such as the phosphate is quantitatively not sufficiently understood and needs further interdisciplinary research activities

cold intermediate layer of the baltic sea hypothesis of the formation of its core abstract a hypothesis for the formation of the core the coldest water of the cold intermediate layer cil of the baltic proper is proposed it is based on a joint analysis of previously published research on shallow spring thermocline development and pycnocline formation and on a recent field monitoring of the transition from winter to summertime vertical stratification in the gdansk basin the simultaneous appearance of numerous field observations of i warmer slightly fresher water at the surface and ii anomalously cold and slightly more saline plus 0 1 0 3 intrusions in the lower portion of the upper mixed layer 40 60 m in early april suggest that they are parts of a single whole horizontal exchange process within the baltic proper we suggest that this exchange is driven by the early spring release of gravitational energy excess which was maintained during winter by vertical mixing when mixing ceases the 500 km long vertically homogeneous layer with longitudinal salinity gradient relaxes to a more gravitationally stable stratification this exchange forces winter cold 1 5 4 c in different years surface waters of moderate salinity 7 5 8 to penetrate rather quickly into intermediate layers where they are then effectively conserved throughout the warmer period as the core of the cil such a temperature salinity index is characteristic of waters of the upper mixed layer in the bornholm basin in march the hypothesis is verified against published works on mean climatic data intrusion activity in the baltic proper numerical simulations of thermohaline conveyor and laboratory experiments

identification and mapping of dikes with relatively primitive compositions in thaumasia planum on mars implications for tharsis volcanism and the opening of valles marineris 1 we have identified several exposed dikes in thaumasia planum mars using themis ctx hirise and crism data these dikes extend from tens to 100 kilometers in length with average widths of 50 m they display classic en echelon patterns while cross cutting preexisting geologic features including extensive wrinkle ridges both the dikes and associated fissure eruption products have very blocky morphologies with 38 higher thermal inertia than the surrounding regions the dikes are all enriched in mg rich olivine relative to surrounding terrain and a subset also contains elevated high calcium pyroxene both of which indicate relatively primitive magma compositions we propose that these dikes might have served as feeders for the olivine enriched flood basalts in this region and may be derived from the tharsis plume these observations provide further evidence that the opening of valles marineris was facilitated by tectonic stresses following paths of preferential weakness along preexisting structures such as fractures and faults like those indicated by these dikes

spectrally distinct ejecta in syrtis major mars evidence for environmental change at the hesperian amazonian boundary analysis of visible and near infrared vnir imaging spectrometer data of the syrtis major volcanic complex on mars shows spectrally distinct ejecta sde around a subset of the region s impact craters we explore the nature of this spectral difference with the intention of constraining the physical cause of the distinction and the significance of their near random spatial distribution crater counting performed by baratoux et al 2007 indicated that the craters with sde are systematically younger than craters without sde extensive crater counts of the craters with sde show that they fit a consistent hartmann 2005 isochron indicting that they represent temporally continuous population this population was dated near 2 ga consistent with the counts of baratoux et al 2007 this modeled age corresponds to just after the hesperian amazonian boundary indicating that it may be related to a global event we explore possible explanations for the lack of sde around older craters including atmospheric changes significant but brief regional emplacement of materials and volcanic activity we conclude that the preferred explanation is that the sde represent the true composition of the syrtis major volcanics and that surfaces older than 2 ga were altered by interactions with water vapor or volcanic gases under different hesperian climatic and atmospheric conditions leading to all craters formed after this alteration event to display sde

igneous dikes on mars revealed by mars orbiter laser altimeter topography the origin of martian grabens has remained controversial for decades given the nonuniqueness of graben morphology and conflicting interpretations of dike induced or faultingbased formation processes we use measurements from the mars orbiter laser altimeter to identify the characteristic topographic signature at the surface of an igneous dike beneath a martian graben our results suggest that this subtle but diagnostic signature can be used to test competing interpretations of the formation of grabens and associated fissures and collapse depressions

dike indicators in the hadriaca patera promethei terra region mars abstract the eastern hellas basin rim has been highly modified by a multitude of both volcanic and fluvial processes it is covered by a large part of the circum hellas volcanic province consisting of the volcanic plains of hesperia planum and western promethei terra as well as the two central volcanoes hadriaca and tyrrhena patera and their associated lava flows large outflow channels of dao niger harmakhis reull and teviot valles dissect the wrinkle ridged plains postdating the major volcanic events the origin of these outflow channels is still ambiguous as the mobilization mechanism for the underground volatile reservoirs has yet to be revealed due to the proximity of the volcanic structures many previous studies have suggested via models that the released ice or ground water was mobilized due to endogenic heating from magmatic activity in the region to find evidence of this we conducted a systematic search for any magmatic intrusions at 50 m pixel resolution this paper provides detailed mapping of several areas where we found features which we interpret to be dikes and shows the overall distribution of such structures in the eastern hellas rim region the hadriaca patera volcano flanks exhibit a concentric pattern of linear ridges and fractures indicative of a vast ring dike system the dikes occupy mostly the area near the summit and the hellas facing flank extending there for over 400 km away from the caldera a hadriaca radial dike swarm pattern is observed extending southwards from the volcano composed of isolated parallel linear ridge group outcrops and cut by the valles canyons an additional isolated dike ridge group exists south of lower reull valles possibly controlled by the tyrrhena patera volcano some 1300 km away all dikes within the study region are roughly late hesperian in age either predating the valles formation or being roughly concurrent with them in total 500 dike segments were identified with a combined length of 2500 km since 90 of the dikes are ridges they suggest that the entire region has undergone large scale erosion of at least a few tens of meters to expose the dikes the dike orientations were most probably controlled by the volcanic centers and possibly partly by a hellas concentric fracture pattern

formation erosion and exposure of early amazonian dikes dike swarms and possible subglacial eruptions in the elysium rise utopia basin region mars hundreds of narrow linear ridge segments are found in the transition zone between the elysium rise and the utopia basin occurring as both single and multiple ridges the ridges are distinctive because of their very linear steep sided nature their often sharp ridge crest which sometimes is fractured their association with stubby flows their continuity over long distances and their cross cutting of different terrain the linear ridges are interpreted to be single dikes and dike swarms either emplaced as normal dikes or as dikes emplaced subglacially feeding an explosive or effusive eruption five dike swarms are identified having lengths ranging from 10 45 km and being between 1 7 km wide while single ridges are up to 20 km long and 100 500 m wide in the areas of dike swarms crustal dilatation is estimated to vary from 15 60 dikes emplaced en echelon suggest that variations in the local stress field caused rotation during dike emplacement and dikes crosscutting flow units imply that dike emplacement can account for some of the observed linear fractures in the area the ridges both modify and constrain early amazonian flows and flood plain deposits suggesting intense dike emplacement in the early amazonian the association with different stages of inverted craters as well as some features of ice related origin possible ice cauldron and tindar like features indicate that the dikes may have been exposed due to eolian erosion and loss of volatile rich units subsequent to their emplacement

40ar 39ar dating of the thanet gabbro ontario looking through the grenvillian metamorphic veil and implications for paleomagnetism in this first dating study of the thanet gabbro complex from the hastings basin area we have obtained k ar evidence to support the geological contention that this pluton and by inference others nearby has escaped the severity of the grenvillian metamorphic overprint specifically a reliable date of 1200 ma for a hornblende demonstrates that this body was emplaced at least 100 ma earlier than the peak of metamorphism in the adjacent haliburton highlands from considerations of possible cooling histories and a proposed grenville apparent polar wander apw curve we deduce that only the thanet magnetization component with the lowest laboratory blocking temperatures th3 was likely acquired as a thermoremanent magnetization whereas the other two components were probably acquired as low temperature chemical remanent magnetizations furthermore the th3 component was likely set before 1 0 ga consistent with our earlier proposed grenville loop

further thermochronometric unravelling of the age and palaeomagnetic record of the southwest grenville province the cordova gabbro in the hastings basin of the southwestern grenville province has been studied thermochronometrically to see if the anomalous c magnetic pole was actually acquired prior to 1200 ma ago resetting of the plagioclase argon clock very strongly indicates that in fact the c pole was acquired during a mild siluro ordovician event and does not record the existence of a pre grenville small ocean between a grenville plate and interior laurentia such a hypothesized mild event is consistent with the magnetic isotopic and fluid inclusion record finally it is noted that the age and blocking temperature points for the two hornblendes analyzed are consistent with the cooling curve derived for the thanet gabbro another hastings basin intrusive

the tectonic architecture of wrinkle ridges on mars abstract the geodynamic history of mars is written largely in the form of its tectonic structures a global population of compressional structures records a history of interior cooling and contraction in combination with volcanic loading and flexure of the lithosphere the most common of these structures are wrinkle ridges interpreted as having formed by folding of near surface layered volcanic materials above blind thrust faults topographic profiles of wrinkle ridges are found to dominantly fall into three classes symmetric ridges arch style ridges characterized by broad convex upward backlimbs and double ridges characterized by a broad arch and narrow ridge a monte carlo boundary element model was used to constrain the underlying geometry of faults associated with the different ridge types symmetric ridges are pop up structures formed between quasi symmetric thrust and backthrust faults in some cases above a horizontal decollement or low angle fault at depth arch style ridges formed above a dominant primary thrust fault of near constant dip with a secondary backthrust playing a lesser role in generating subtle inflections in the backlimb double ridges require two backthrust faults to localize strain within the narrow ridge at the ridge crest and to generate the secondary antiform on the backlimb in these ridges both the upper primary thrust and backthrust are contained within the layered volcanic materials while the lower portions of the primary thrust can extend deep into the crust or upper mantle a shallower depth of fault penetration in areas of thicker crust is consistent with the depth of faulting being limited by the brittle ductile transition dips vary widely but are typically steep in the upper faults and quite gentle in the lower faults thus while wrinkle ridges do provide important records of tectonic and geodynamic processes on mars as well as other bodies the associated tectonic structures are more complex and varied than previously considered

paleomagnetism and upb geochronology of volcanic rocks from michipicoten island lake superior canada precise calibration of the keweenawan polar wander track abstract paleomagnetic poles have been determined for normally magnetized samples of late proterozoic volcanic rocks from 23 sites on michipicoten island lake superior canada the results are in general accord with an earlier less precise study by one of the authors and indicate a small polar shift between rocks of the mamainse point formation 186 e 38 n and the michipicoten island formation 175 e 26 n a quartz feldspar porphyry intruding the lower mamainse point formation but unconformably overlain by the michipicoten island formation was sampled for u pb zircon dating the zircons define an age of emplacement of 1086 5 1 3 3 0 ma this age and the pole positions are consistent with and supplement ages previously determined for the keweenawan paleomagnetic polar wander curve these data define an apparent polar wander rate of 14 cm a 1 this age combined with previously published u pb ages indicates a time span of 22 ma for most keweenawan igneous activity in addition the time of the keweenawan paleomagnetic reversal is constrained to be between 1086 5 1 3 3 0 and 1097 6 3 6 ma the age of the upper part of the reversely magnetized osler group the zircon population contained an inherited component from a source 1403 50 ma old this suggests that the porphyry magma was at least partly derived by melting of an anorogenic pluton emplaced during the mid proterozoic

volcanic rifting at martian grabens 1 a large fraction of surface extension on mars occurred at segmented grabens having width length ratios akin to oceanic rifts on earth association with volcanic landforms such as pit craters clearly suggests interconnection between tectonic and magmatic processes a martian rift evolution model is proposed on the basis of new geomorphological and structural interpretations of imagery high resolution digital elevation models dems scaled experimental modeling and three dimensional boundary element modeling of magmatic and tectonic processes and a comparison with terrestrial rifts the dems were obtained from mars observer laser altimeter viking orbiter stereo images or a combination of both comparison of terrestrial rifts included afar iceland and the east pacific rise the ambient extensional stress field induced by regional body forces is combined at depth with decompression melting and mantle plume thermal anomaly resulting in emplacement of elongated magma reservoirs along the grabens injection of dikes above the reservoirs and flood basalt eruption result in a reservoir underpressurization of up to hundreds of mpa and induces surface collapse each collapse event is associated with an eruption of volcanic volumes akin to those of individual flow eruptions in large terrestrial igneous provinces the geometry and mechanisms of graben formation and surface collapse are described and used to infer reservoir depth and width we conclude from this study that giant dike swarms akin to typical giant terrestrial dike swarms are unlikely to underlie the volcanic martian grabens on the basis one graben one dike rather every volcanic graben segment appears to own a local dike swarm perhaps analogous to the dike swarms in the icelandic fissure zones index terms 5475 planetology solid surface planets tectonics 8149 5480 planetology solid surface planets volcanism 8450 6225 planetology solar system objects mars 8121 tectonophysics dynamics convection currents and mantle plumes 8010 structural geology fractures and faults keywords rifting graben pit crater magma chamber dyke

pristine noachian crust and key geologic transitions in the lower walls of valles marineris insights into early igneous processes on mars abstract valles marineris is a unique vertical section through the uppermost kilometers of the martian crust its location east of the tharsis bulge and its water related history fuel a great diversity of rock types in this area carr m h head j w 2010 earth planet sci lett 294 185 203 hirise and crism data available over the walls of the canyon were analyzed to infer the importance of magmatic and sedimentary processes through time this contribution provides a complete morphologic and mineralogic characterization of the cross section of rocks exposed in the canyon walls low calcium pyroxene and olivine are detected in the lower portion of the walls in association with morphologically distinct outcrops leading to the idea that pristine noachian crust might be exposed phyllosilicates are also present within the walls but they appear to correspond to an alteration product no proper sedimentary layers were observed within the walls of valles marineris at the resolution available today all these detections are limited to the eastern portion of valles marineris especially juventae coprates capri and ganges chasmata preserved noachian crustal material is rare on the martian surface and is rarely exposed in its pristine geologic context such detections lend precious information about early igneous processes this survey also supports observations from the nearby impact crater central peaks quantin et al 2009 quantin et al 2011 and suggests that the western part of valles marineris may be cut into another material consistent with lavas or volcanic sediments

density and lithospheric thickness of the tharsis province from mex mars and mro gravity data 1 radio science tracking of mars express mars experiment and mars reconnaissance orbiter produced high resolution martian gravity data applying localized spectral analysis on the new gravity data sets we study the surface density and lithospheric elastic thickness in the tharsis province the gravity signal is predicted with geophysical models either including bottom loading top bottom model or taking into account the loading history top top model volcanic shields are mainly composed of high density lava but their construction could have begun with lower density lava with the exception of ascraeus mons which has a top of lower density buoyant bottom loading may have been present in the form of a mantle plume under olympus mons the elastic thickness was much larger at olympus mons than at other volcanoes suggesting large spatial variations of heat flux during the hesperian alternatively small elastic thicknesses could be artifacts reflecting the presence of very localized high density crustal intrusions beneath the volcanoes thaumasia highlands were probably supported by a mantle plume at the time of formation in valles marineris top bottom models predict low densities and large elastic thicknesses in conflict with the basaltic rock composition and hesperian age of the valley dense mafic dikes underlie the western part of the valley the top top model serves to test another scenario in which the trough is formed with sedimentary infilling removed much later by erosion the elastic thickness increasing in between at the large volcanoes the relation between gravity and topography is anisotropic probably because of density variations

dikes of distinct composition intruded into noachian aged crust exposed in the walls of valles marineris 1 valles marineris represents the deepest natural incision in the martian upper crust previous studies showed that the upper parts of the walls were made of finely layered probable basalts in most of the chasmata while the base of the stratigraphy reveals primary noachian crustal blocks exposures of pristine noachian bedrock are rare on mars and mostly observed outside of their geological context the occurrence of well preserved and extended outcrops of pristine material in this giant rift could bring valuable information on the early processes that took place at the surface of mars analyses of high resolution data over the best exposures of lower walls in coprates chasma central valles marineris revealed the presence of multiple magmatic intrusions interpreted as dikes these dikes intrude an old massive fractured bedrock interpreted as being preserved ancient noachian crust their composition determined using crism data and distribution limited to this ancient crust at the bottom walls indicate that they might have formed early in the rift formation and therefore represent exceptionally well preserved outcrops of the early history of mars

compositional and structural constraints on the geologic history of eastern tharsis rise mars abstract identification and mapping of distinct compositional units using high resolution orbital imagery of the walls of valles marineris mars provide key structural and environmental constraints on the geologic history of the eastern tharsis rise our results corroborate an overall vertical structure of the upper crust consistent with that inferred from previous studies an upper unit spectrally consistent with basalt that has variable thickness is overlain on an early to possibly pre noachian substrate the pre early noachian material is heterogeneous dominated by low calcium pyroxene rich material but ranging locally from feldspathic to and olivine rich aqueous alteration of pre early noachian rock to dominantly fe mg smectite is widespread and observed along the chasma walls from 4 to 1 km however phyllosilicates outcrop discontinuously suggesting that they were emplaced via impact excavation of even older altered material or formed by non uniform alteration driven by impact or magma related hydrothermal activity a distinct higher temperature alteration assemblage identified by the presence of chlorite zeolite and associated carbonate serpentine occurs on both the north and south walls of eastern coprates chasma in a confined longitudinal band where the eastern margin of the thaumasia plateau intersects valles marineris these secondary minerals are concentrated within a heavily fractured band exposed at a regional tectonic boundary along the margin of the thaumasia plateau and likely record a regional zone of elevated crustal heat flow and fluid circulation the generally north south trending band exhibiting this distinct assemblage serves as a tracer for tectonic deformation its continuity across valles marineris is incongruous with previously suggested lateral slip along the margin of a megaslide and constrains left lateral transtensional faulting to less than 25 50 km mapping of compositionally distinct outcrops to the west also reveals localized uplift in western coprates chasma suggesting thrust faults underlying wrinkle ridges in western valles marineris the upper basalt layer thickens dramatically supporting either occurrence of a large infilled basin to the west or down dropping and volcanic burial of material near melas candor chasma the latter consistent with a constructional origin of the tharsis rise

an algorithm to detect isolated anomalies in three dimensional stratified data fields with an application to density fields from four deep basins of the baltic sea 1 a new approach to describe the mesoscale variability caused by eddies in terms of the integral properties of all eddies contained in a certain ocean volume is suggested for this purpose a pattern recognition algorithm to detect isolated anomalies in three dimensional stratified data fields was developed and is introduced in detail an application to 12 eddy resolving density fields acquired in the framework of the german russian project mesodyn in four deep basins of the baltic sea namely the arkona basin the bornholm basin the stolpe furrow and the eastern gotland basin demonstrates that the algorithm works properly the most remarkable finding of this application is that the volume fraction occupied by the isolated anomalies or eddies is constant it amounts to about 12 of the total volume for each data field no matter whether the stratification corresponds to a summer or a winter situation many possible applications of the pattern recognition are proposed to document its general usefulness finally the main features of the algorithm and possible extensions are discussed extensively

evidence for an early archean geomagnetic field a paleomagnetic study of the komati formation barberton greenstone belt south africa 3 5 ga old peridotitic komatiites of the komati formation barberton greenstone belt south africa have a characteristic nrm natural remanent magnetization that is stable during alternating field and thermal demagnetization the thermal nature of this remanence is demonstrated by successful thellier type paleo intensity determinations on some samples in the temperature range 350 to 575 c the characteristic nrm is an almost total thermal overprint acquired during unroofing and cooling following pervasive greenschist metamorphism at 3470 20 ma the mean direction of magnetization after cleaning is d 326 i 81 k 60 95 8 n 7 sites with a paleopole at 11 s 21 e p m 15 the paleopole falls in southern africa ancestral southern africa was therefore in polar latitudes around 3 5 ga the same position it occupied in the late archean and early proterozoic paleofield intensities are about one half present day intensities for polar latitudes a vigorous earth s magnetic field was already in existence in the early archean implying that the core had a suitable size composition and convective flow to support dynamo action

northeast trending early proterozoic dykes of southern superior province multiple episodes of emplacement recognized from integrated paleomagnetism and u pb geochronology integrated paleomagnetic and u pb geochronologic studies have been conducted to establish the paleomagnetic directions and ages of early proterozoic tholeiitic dykes of northeast trend in the southern superior province previously referred to collectively as preissac dykes it is demonstrated that they are readily separated on the basis of paleomagnetism into subsets referred to as the biscotasing and senneterre swarms in addition a pair of unnamed dykes may be associated with the north and northwest trending matachewan swarm farther west biscotasing dykes have a down west magnetization of single polarity with a corresponding paleopole at 27 8 n 136 7 w dm 12 3 and dp 9 4 senneterre dykes carry an up north or occasionally down south direction with corresponding paleopole at 15 3 s 75 7 w dm 7 0 dp 4 4 the senneterre direction is indistinguishable from the primary n1 remanence direction that dominates the magnetization of nipissing sills of the southern province paleomagnetic fiel

archeomagnetism of ontario potsherds from the last 2000 years an archeomagnetic study was carried out on potsherds samples from sites in ontario with ages ranging from a d 90 to a d 1640 as determined by 14c dating thellier double heating paleointensity experiments were performed in air on 65 specimens of 52 samples from seven sample sets reliable paleointensity estimates were obtained for 49 specimens alternating field and thermal demagnetization temperature dependence of weak field susceptibility and hysteresis measurements indicate that magnetite of pseudo single domain grain size is the carrier of natural remanent magnetization the paleointensity results follow a half cycle sine curve with a steady decrease from 54 0 5 9 t to 37 6 5 7 t between a d 90 and a d 885 and a monotonic increase from 52 0 6 1 t to 59 4 1 7 t between a d 1200 and a d 1900 the paleointensities determined yield virtual axial dipole moments vadms of the earth s magnetic field that agree well with those from other parts of north america except between a d 900 and a d 1400 when they are systematically lower this discrepancy is probably caused by a substantial non dipole field in southwestern north america from the tenth to the fifteenth century since secular variation studies using potsherds from arizona and lake sediments from minnesota show different inclination variations during that period

surface deformation and shallow dike intrusion processes at inyo craters long valley california the inyo craters are the two largest of four phreatic craters that lie within a 2 5 km long 500 to 700 m wide n s trend of faults and fissures at the south end of the inyo volcanic chain in eastern california the alignment of these features with dike fed silicic volcanic centers of the same age a few kilometers to the north suggests that they were produced during intrusion of a dike at about 650 550 yr b p e w extension south of south inyo crater is ten to several tens of meters suggesting that the dike is at least that thick to understand how the faults and fissures developed we mapped and studied the fault and fissure pattern used a theoretical boundary element model to determine the surface strain profile above a shallow dike in a purely elastic medium and conducted physical model experiments of fault and fissure growth results of the field studies and experiments indicate that deformation develops according to the following sequence 1 extension fractures and perhaps other inelastic deformation develop immediately above the dike top and on the limbs of a shallow syncline which forms above the dike 2 fissures form along two parallel trends at the surface on opposite sides of the dike plane leaving a relatively unfractured region in between 3 dip slip movement on subsurface fractures and linkage of these fractures with surface fissures produces inward facing normal fault scarps that bound a nested graben above the dike experimental graben widths are up to several times narrower than predicted from the locations of theoretical strain maxima above a dilating crack in a linearly elastic medium this fact is apparently due to the growth of a zone of inelastic deformation above the experimental dike top in the subsurface if the ratio between the depth to the dike top and the distance between the outermost surface fissures at inyo craters is within the range of ratios measured experimentally then the depth to the dike top is between 250 m and several times that a slant hole drilled in the summer of 1987 by the department of energy office of basic energy sciences intersected three breccia bodies of possibly intrusive origin directly below the center of south inyo crater between 550 m and 610 m below the crater rim no intact juvenile igneous rock was intersected suggesting that the hole passed above the magma filled dike top perhaps passing through the zone of inelastic deformation which is inferred to exist from our model results

the central uplift of ritchey crater mars abstract ritchey crater is a 79 km diameter complex crater near the boundary between hesperian ridged plains and noachian highland terrain on mars 28 8 s 309 0 e that formed after the noachian high resolution imaging science experiment hirise images of the central peak reveal fractured massive bedrock and megabreccia with large clasts compact reconnaissance imaging spectrometer for mars crism spectral analysis reveals low calcium pyroxene lcp olivine ol hydrated silicates phyllosilicates and a possible identification of plagioclase bedrock we mapped the ritchey crater central uplift into ten units with 4 main groups from oldest and originally deepest to youngest 1 megabreccia with large clasts rich in lcp and ol and with alteration to phyllosilicates 2 massive bedrock with bright and dark regions rich in lcp or ol respectively 3 lcp and ol rich impactites draped over the central uplift and 4 aeolian deposits we interpret the primitive martian crust as igneous rocks rich in lcp ol and probably plagioclase as previously observed in eastern valles marineris we do not observe high calcium pyroxene hcp rich bedrock as seen in argyre or western valles marineris the association of phyllosilicates with deep megabreccia could be from impact induced alteration either as a result of the richey impact or alteration of pre existing impactites from argyre basin and other large impacts that preceded the ritchey impact or both

two years in the life of a mediterranean salt lens abstract a lens of mediterranean water meddy was tracked in the eastern north atlantic for two years with sofar floats the meddy was first found between the canary islands and the azores in october 1984 it center moved in an irregular pattern at speeds of a few cm s 1 and translated 1100 km to the south in two years this meddy was surveyed four times by ctd and velocity profilers and once with the microstructure profiler epsonde when observed during the first two surveys the meddy had a core that was stably and smoothly stratified in both salinity and temperature nearly uniform in the horizontal and was saltier than the surrounding ocean by 0 65 psu the meddy was eroded from its edges top and bottom and lost salt and hat with an e folding time of about one year the salinity at the center remained at its original value during the first year and decreased during the second year evidence was seen for mixing by lateral intrusions double diffusion and turbulence the intrusions are thought to