lunar global shape and polar topography derived from kaguya lalt laser altimetry a global lunar topographic map with a spatial resolution of finer than 0 5 degree has been derived using data from the laser altimeter lalt on board the japanese lunar explorer selenological and engineering explorer selene or kaguya in comparison with the previous unified lunar control network ulcn 2005 model the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers spherical harmonic analysis of global topographic data for the moon earth mars and venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales however simple rigid support is suggested to dominate for the moon venus and mars for smaller scales which may indicate a drier lithosphere than on earth especially for the moon and venus

the shape and internal structure of the moon from the clementine mission global topographic and gravitational field models derived from data collected by the clementine spacecraft reveal a new picture of the shape and internal structure of the moon the moon exhibits a 16 kilometer range of elevation with the greatest topographic excursions occurring on the far side lunar highlands are in a state of near isostatic compensation whereas impact basins display a wide range of compensation states that do not correlate simply with basin size or age a global crustal thickness map reveals crustal thinning under all resolvable lunar basins the results indicate that the structure and thermal history of the moon are more complex than was previously believed

stratigraphy and paleomagnetism of a 3 km thick miocene lava pile in the mjoifjordur area eastern iceland we have carried out stratigraphic mapping in the upper miocene basalt lava pile around the fjords mjoifjordur and seydisfjordur eastern iceland the mapping is based on conventional methods including the use of interbasaltic clastic horizons and petrographically distinct lava groups these units are also used to provide correlations with the nordfjordur area south of mjoifjordur we present a 3 km composite stratigraphic column for the area between mjoifjordur and seydisfjordur the geology of this area shows some differences from the classical model of walker for the structure of eastern iceland partly due to the fact that most of mjoifjordur is not in the vicinity of central volcanoes detailed laboratory measurements of remanent magnetization were carried out on oriented core samples from 363 lavas in 10 selected profiles the local paleomagnetic polarity stratigraphy supports correlations made on the basis of other criteria over 20 geomagnetic reversals are recorded in the eastern iceland lava pile in a period approximately 13 10 ma ago the geomagnetic field during this period averages to a central axial dipole field and its overall statistical properties resemble those obtained in earlier surveys in iceland

major lunar crustal terranes surface expressions and crust mantle origins in light of global remotely sensed data the igneous crust of the moon can no longer be viewed as a simple globally stratified cumulus structure composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual melt kreep sandwich horizon near the base of the lower crust instead global geochemical information derived from clementine multispectral data and lunar prospector gamma ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique 1 the procellarum kreep terrane pkt 2 the feldspathic high lands terrane fht and 3 the south pole aitken terrane spat the pkt is a mafic province coincident with the largely resurfaced area in the procellarum imbrium region whose petrogenesis relates to the early differentiation of the moon here some 40 of the th in the moon s crust is concentrated into a region that constitutes only about 10 of the crustal volume this concentration of th average 5 ppm and by implication the other heat producing elements u and k led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust lower crustal materials within the pkt likely interacted with underlying mantle materials to produce hybrid magmatism leading to the magnesian suite of lunar rocks and possibly kreep basalt although rare in the apollo sample collection widespread mare volcanic rocks having substantial th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources the fht is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation basin impacts into this region do not excavate significantly more mafic material suggesting a thickness of tens of kilometers of anorthositic crust the feldspathic lunar meteorites may represent samples from the anorthositic central region of the fht ejecta from deep penetrating basin impacts outside of the central anorthositic region however indicate an increasingly mafic composition with depth the spat a mafic anomaly of great magnitude may include material of the upper mantle as well as lower crust thus it is designated a separate terrane whether the spa basin impact simply uncovered lower crust such as we infer for the fht remains to be determined

lunar polar topography derived from clementine stereoimages clementine stereoimagery has been used to produce digital elevation models of the moon at a scale of 1 km pixel these models cover regions poleward of 60 in both hemispheres and reveal topography beyond that covered by the clementine laser altimeter or earth based radar by combining these polar terrain models with the current clementine laser altimeter data we have produced a global topographic map of the lunar surface several topographic features in the new polar topographic data set are described including three previously unrecognized pre nectarian impact basins several known basins have also been mapped including the southern extent of the south pole aitken basin and other previously suspected basins have been verified

the tidal rotational shape of the moon and evidence for polar wander analysis of the moon s topography reveals that when its largest basins are removed the lunar shape is consistent with processes controlled by early earth tides and implies a reorientation of the moon s principal shape axes attempts to assess the various theories for the formation of the moon and to determine its true shape are complicated by the presence of several large basins on its surface that formed after the crust solidified here ian garrick bethell et al concentrate on the topography and gravity outside these basins and propose that the long wavelength shape of the moon has evolved through a combination of two early tidal processes first a crust building process controlled by early tidal heating throughout the moon and second the later development of a frozen tidal rotational bulge the authors also infer that an uneven distribution of internal density eventually reoriented the moon s polar axis by about 36 to the configuration that we see today the origin of the moon s large scale topography is important for understanding lunar geology1 lunar orbital evolution2 and the moon s orientation in the sky3 previous hypotheses for its origin have included late accretion events4 large impacts5 tidal effects6 and convection processes7 however testing these hypotheses and quantifying the moon s topography is complicated by the large basins that have formed since the crust crystallized here we estimate the large scale lunar topography and gravity spherical harmonics outside these basins and show that the bulk of the spherical harmonic degree 2 topography is consistent with a crust building process controlled by early tidal heating throughout the moon the remainder of the degree 2 topography is consistent with a frozen tidal rotational bulge that formed later at a semi major axis of about 32 earth radii the probability of the degree 2 shape having both tidal heating and frozen shape characteristics by chance is less than 1 we also infer that internal density contrasts eventually reoriented the moon s polar axis by 36 4 to the configuration we observe today together these results link the geology of the near and far sides and resolve long standing questions about the moon s large scale shape gravity and history of polar wander

lunar surface geochemistry global concentrations of th k and feo as derived from lunar prospector and clementine data abstract accurate estimates of global concentrations of th k and feo have an important bearing on understanding the bulk chemistry and geologic evolution of the moon we present empirical ground truth calibrations transformations for lunar prospector gamma ray spectrometer data k and th and a modified algorithm for deriving feo concentrations from clementine spectral reflectance data that incorporates an adjustment for tio 2 content the average composition of soil samples for individual landing sites is used as ground truth for remotely sensed data among the apollo and luna sites apollo 12 and 14 provide controls for the incompatible element rich compositions apollo 16 and luna 20 provide controls for the feldspathic and incompatible element poor compositions and apollo 11 15 and 17 and luna 16 and 24 provide controls for fe rich compositions in addition to these apollo and luna sample data we include the composition of the feldspathic lunar meteorites as a proxy for the northern farside highlands to extend the range of the calibration points thus providing an additional anorthositic end member composition these empirical ground truth calibrations for lunar prospector th and k provide self consistency between the existing derived data and lunar sample data clementine spectral reflectance data are used to construct a tio 2 sensitive feo calibration that yields higher feo concentrations in areas of high fe low ti mare basalt rich surfaces than previous feo algorithms the data set so derived is consistent with known sample compositions and regolith mixing relationships

small scale density variations in the lunar crust revealed by grail abstract data from the gravity recovery and interior laboratory grail mission have revealed that 98 of the power of the gravity signal of the moon at high spherical harmonic degrees correlates with the topography the remaining 2 of the signal which cannot be explained by topography contains information about density variations within the crust these high degree bouguer gravity anomalies are likely caused by small scale 10 s of km shallow density variations here we use gravity inversions to model the small scale three dimensional variations in the density of the lunar crust inversion results from three non descript areas yield shallow density variations in the range of 100 200 kg m 3 three end member scenarios of variations in porosity intrusions into the crust and variations in bulk crustal composition were tested as possible sources of the density variations we find that the density anomalies can be caused entirely by changes in porosity characteristics of density anomalies in the south pole aitken basin also support porosity as a primary source of these variations mafic intrusions into the crust could explain many but not all of the anomalies additionally variations in crustal composition revealed by spectral data could only explain a small fraction of the density anomalies nevertheless all three sources of density variations likely contribute collectively results from this study of grail gravity data combined with other studies of remote sensing data and lunar samples show that the lunar crust exhibits variations in density by 10 over scales ranging from centimeters to 100 s of kilometers

the lunar mascons revisited the entire spectra of the surface topography and gravity field of lunar mascons are well presented by the high resolution clementine data the negative correlation between the topography and gravitational potential of the mascons suggests that they are dynamically supported both elastic support and viscous decay models are examined for the elastic support models the spectral characteristics and the lateral variations of the thickness of the elastic layer are determined on the basis of the thin spherical shell flexure formulation and using only the antivarying harmonics of the topography and potential an elastic layer thickness of about 50 km is required to support imbrium serenitatis and nectaris mascons about 35 km for crisium mascon and about 30 km for smythii and humorum mascons a layer of about 20 km thickness can support orientale mascon the strength envelopes of the upper 100 km of the moon within 4 3 gyr ago show that the elastic layer was not thick enough to support the mascons in the early history they decayed through viscous deformation of the lunar interior a lower limit of 6 1024 pa s is estimated for the lunar viscosity within 3 6 3 gyr ago we also determine the thicknesses of the crust and mare flows of the mascon basins on the basis of the assumption that the basins were isostatically compensated prior to the mascon formation the crust beneath the mascon basins is about 30 40 km except for crisium and orientale where the crust is about 20 km the mare flows of about 3 6 km are obtained for almost all of the mascon basins the topography and gravitational potential of aitken basin shows that the basin is compensated at 52 54 km depth the mantle beneath the basin has rebounded upward by about 20 30 km and is overlain by about 20 25 km of a mixture of the excavated crustal and mantle material the lack of a mascon and pervasive mare flows in the basin brings into question the current models of the mascon formation

no evidence for strong fields during the r3 n3 icelandic geomagnetic reversal a previous study of the r3 n3 icelandic reversal which corresponds probably to the matuyama reunion reversal provided relatively large virtual dipole moments when the pole is close to equator to check these former results obtained using the shaw paleointensity method we resampled the very same sections and flows and reanalysed the samples using the thellier method 38 lava units and one baked horizon from 4 sections provide intermediate r3 n3 paleofield directions most of them possibly related to a single eruption display similar directions corresponding to the near equator vgp cluster unfortunately most of the intermediate lava flows are thermally unstable as attested by the irreversibility of the susceptibility versus temperature k t curves which precludes their use for paleointensity purpose the rest of the units provide fairly reversible k t curves and a near magnetite tc due to fe rich titanomagnetite resulting from oxyexsolution at high temperature 25 baked units or lava flows of this kind yield reliable thellier paleointensity data average paleostrengths of 44 7 14 9 t and 32 5 22 9 t were found for the reversed r3 and the normal n3 polarity zones respectively combining these non transitional paleostrengths with other thellier data from over the world indicates that the pliocene dipole moment was close to 8 1022 a m2 the average paleostrength is reduced to 11 3 3 0 t during the r3 n3 transition we find no indication for the strong fields 20 4 to 38 6 t previously obtained by the shaw method thus our results do not confirm the existence of large virtual dipole moments when the pole approaches the equator

the myth of the pacific dipole window the angular dispersion of virtual geomagnetic poles vgp from lava flows is often cited as having been anomalously low in the pacific during the brunhes epoch because the dispersion from hawaiian lavas is said to be much lower than measured elsewhere this led to the concept of the pacific dipole window or pacific non dipole low because lavas tend to be erupted in bursts of activity many of the hawaiian data are serially correlated and thus cannot necessarily be treated as independent observations geochronological controls as are available for hawaii have been used in a previous analysis to thin the data to try to avoid repeated sampling of the same geomagnetic field unfortunately in that analysis the angular dispersion of vgps was calculated about the mean vgp instead of about the spin axis and thus underestimated the dispersion we have therefore reanalyzed the relevant data using the following criteria 1 only those lavas with 95 10 have been considered 2 a latitude dependent cut off angle is used to eliminate those vectors that are not part of the normal secular variation 3 we have developed a statistical method to rationalise those flows that have repeatedly sampled the same geomagnetic field vector because suitable geochronological controls are rarely available application of this new method to the hawaiian data shows excellent agreement with the results from using geochronological controls where possible we have therefore included this method in our overall analysis as expected the resulting global data are compatible with a fisher distribution about the spin axis brunhes age data from hawaii n 96 independent measurements give a vgp angular dispersion about the spin axis of sf 12 4 and for the pacific region as a whole sf 12 5 n 190 between latitudes 15 and 30 north or south these values are the same as sf 12 4 n 160 calculated for the rest of the world in the same latitude range this clearly demonstrates that the hypothesis of the pacific dipole window may confidently be rejected

on the origin of mascon basins on the moon and beyond 1 mascon basins on the moon are large craters that display significant positive free air and bouguer gravity anomalies an important question is why is not every large crater a mascon as less than half have been previously determined to be we detrend the free air topographic and bouguer gravity anomalies and find that most large basins 28 of 41 display mascon characteristics e g strong positive bouguer anomalies narrower than the surface rims negative free air gravity annuli surrounding the central highs generally are absent in the bouguer gravity implicating surface topography we propose that beneath a forming large basin the relatively narrow transient crater drives mantle uplift while upward and inward collapse forms the surface topography furthermore the nonmascon basins are all ancient and heavily degraded indicating a postimpact evolutionary process our results suggest that mascon formation is the standard for large impacts on the moon and by extension on other terrestrial planets

the evolution of impact basins viscous relaxation of topographic relief we evaluate the hypothesis that viscous relaxation has been an important process for modifying the topographic profiles of ancient large impact basins on the moon we adopt a representative topographic profile of the orientale basin the youngest large impact basin on the moon as an estimate of the initial topography of older basins of similar horizontal dimensions and we predict the topographic profiles that would result from viscous relaxation according to a number of simple analytical representations of the rheological response of the moon to surface topography at wavelengths greater than the thickness of a high viscosity lithosphere both a decrease in viscosity with depth and the partial to complete isostatic compensation of topographic relief have pronounced effects on the wavelength dependent relaxation times and must be considered in modeling viscous relaxation for features as large as impact basins the effect of a decrease in viscosity with depth is to enhance the rate of viscous relaxation at long wavelengths while the rate of relaxation decreases substantially for the fraction of long wavelength topography which is isostatically compensated as an initial condition these models are applied to two pre nectarian basins on the moon the tranquillitatis basin on the lunar nearside and the much larger and older south pole aitken basin on the farside the topographic profile of tranquillitatis after correcting for the effect of mare basalt fill is consistent with significant viscous relaxation of relief prior to the oldest episode of mare volcanism preserved as a surface unit the large topographic relief of the larger farside basin on the contrary is not consistent with significant viscous relaxation and implies a mean crustal viscosity at least a factor of 10 higher than for the central nearside over the time interval during which substantial viscous relaxation of older nearside basins such as tranquillitatis probably occurred a difference in typical crustal temperature profiles between the farside and nearside is the most likely explanation of such a viscosity difference such a nearside farside asymmetry in near surface temperature may date from the time of crust mantle differentiation and may have persisted because of the different histories of late stage impact basin formation and mare volcanism on the two hemispheres

density and porosity of the lunar crust from gravity and topography 1 newly obtained gravity and topography data of the moon combined with a lithospheric flexure model that considers both surface and subsurface loading are used to place constraints on the density of the upper crust from a localized spectral admittance analysis subsurface loads are found to be relatively unimportant in the highlands and when subsurface loads are neglected the best fitting bulk densities for a number of highland regions are found to vary from 2590 to 2870 kg m 3 with a mean value of 2691 kg m 3 crustal rock densities estimated from geochemical considerations and global iron and titanium abundances imply somewhat greater densities which we interpret as porosity affecting the gravity derived bulk density estimates the average porosity in the upper few kilometers of crust is calculated to be about 7 7 which is consistent with porosity estimates of impact fractured meteorites and terrestrial impact craters

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

precise dating of the holmatindur cooling event in eastern iceland evidence for mid miocene bipolar glaciation a succession of basaltic lavas volcaniclastic sediments and lignite beds in the holmatindur region of eastern iceland provides the means for wing magnetic reversal stratigraphy and a record of major north atlantic cooling to a precise radiometric timescale a prominent part of the section is the holmatindur clastic bed which is up to 66 m thick and can be traced 80 km along strike the geological significance of this unit lies in its composition and associated thin lignite seams the volcaniclastic composition is basaltic in contrast to the common rhyolitic dacitic composition of tuff units in the area and hyaloclastic material is dominant hydroexplosive volcanism most likely produced the hyaloclastite through subglacial eruptions within the paleovolcanic zone pollen assemblages from the lignite beds indicate a dramatic climatic deterioration from subtropical to cool temperate conditions through these sediments feldspar crystals separated from the holmatindur clastic bed were determined to be from 10 72 0 16 ma from 4oar 39ar incremental heating experiments we correlate the holmatindur cooling event with a relative maximum in benthic foraminiferal bso zone mi6 of miller et al 1991 which has been interpreted as an episode of ice accumulation within the mid miocene cooling period as well as with pulses in ice rafted debris supplied to deep water sites in the north atlantic ocean a global sea level drop of 70 m and submarine canyon cutting all of which occurred within the early part of magnetic anomaly 5 normal c5n while strong evidence exists for mid miocene ice sheets in antarctica northern hemisphere glaciation is thought to have started much later the iceland sites studied here demonstrate that significant ice accumulation occurred albeit intermittently as early as late middle miocene time in the north atlantic ocean from radiometric dating of tertiary lavas that lie below and above the well established lower boundary c5n we conclude that the onset of this long normal polarity period occurred at 10 94 0 16 ma the new data are compatible with the cande and kent 1995 interpolated estimate for this boundary 10 95 ma but are significantly older or more precise than previous direct dating by conventional k ar methods

stratigraphy and paleomagnetism of a 2 9 km composite lava section in eyjafjordur northern iceland a reconnaissance study eight mountainside profiles in lava flows south of the fjord eyjafjordur northern iceland were sampled for paleomagnetic studies the sampling was concurrent with pilot stratigraphic mapping of the lava sequences in these and several supplementary profiles the eight profiles are correlated with minor overlaps so that they form a composite section of 2 9 km thickness estimated to cover the age range between about 9 and 5 million years ago hardarson et al 1999 paleomagnetic measurements made on 319 lavas generally yield primary remanence directions of high stability and within unit consistency evidence for at least 17 reversals of the geomagnetic field is seen as well as numerous field excursions frequent clustering of directions in successive lavas indicates that the volcanism was episodic

the lunar crust global structure and signature of major basins new lunar gravity and topography data from the clementine mission provide a global bouguer anomaly map corrected for the gravitational attraction of mare fill in mascon basins most of the gravity signal remaining after corrections for the attraction of topography and mare fill can be attributed to variations in depth to the lunar moho and therefore crustal thickness the large range of global crustal thickness 20 120 km is indicative of major spatial variations in melting of the lunar exterior and or significant impact related redistribution the 61 km average crustal thickness constrained by a depth to moho measured during the apollo 12 and 14 missions is preferentially distributed toward the farside accounting for much of the offset in center of figure from the center of mass while the average farside thickness is 12 km greater than the nearside the distribution is nonuniform with dramatic thinning beneath the farside south pole aitken basin with the global crustal thickness map as a constraint regional inversions of gravity and topography resolve the crustal structure of major mascon basins to half wavelengths of 150 km in order to yield crustal thickness maps with the maximum horizontal resolution permitted by the data the downward continuation of the bouguer gravity is stabilized by a three dimensional minimum slope and curvature algorithm both mare and non mare basins are characterized by a central upwarped moho that is surrounded by rings of thickened crust lying mainly within the basin rims the inferred relief at this density interface suggests a deep structural component to the surficial features of multiring lunar impact basins for large 300 km diameter basins moho relief appears uncorrelated with diameter but is negatively correlated with basin age in several cases it appears that the multiring structures were out of isostatic equilibrium prior to mare emplacement suggesting that the lithosphere was strong enough to maintain their state of stress to the present

high northern geomagnetic field behavior and new constraints on the gilsa event paleomagnetic and 40ar 39ar results of 0 5 3 1 ma basalts from jokuldalur iceland abstract recent paleomagnetic results of extrusive rocks from high southern latitudes 60 s and high northern latitudes 60 n have been suggested to reflect a hemispheric asymmetry of the geomagnetic field on time scales of 105 to 106 yrs with higher and more stable fields in the north this interpretation however is based on only a few modern standard paleodirectional data sets and on high northern stable field paleointensity data of rocks that are mainly younger than 100 kyr the sparsity of modern standard data questions the validity and age range of this potential geomagnetic asymmetry in 2013 and 2014 we sampled basaltic lava flows in jokuldalur north eastern iceland to obtain high standard paleodirectional and paleointensity data at relatively high northern latitudes 65 2 n on average we sampled 15 cores per site at 51 sites of predominantly matuyama age complete demagnetization was carried out on all samples using af or thermal demagnetization we present 45 distinct paleomagnetic directions based on overall n 10 chrms per site and 95 3 5 we obtain a mean direction of d 355 7 i 76 3 and 95 3 2 for n 45 sites that is not significantly different from a gad field the resulting 45 vgps distribute around the north pole and the global mean paleomagnetic pole 87 8 224 3 is coincident with the north pole within the 95 confidence limit we calculate a vgp dispersion s b m a t 20 5 23 3 17 8 and an average inclination anomaly i 0 91 2 94 4 88 for our 38 matuyama age data the dispersion s b overall supports the interpretation of a dependence of s b on latitude during the matuyama while the negligible i suggests little deviation from a gad field based on relatively strict cut off criteria we also present six new field strength estimates from the time interval 1 2 1 83 ma thus filling a large data gap of the high northern stable field behavior we obtain a median vadm of 57 3 zam 2 vdm of 60 5 am 2 which is higher than the median vadm of 16 intensity estimates from antarctica 39 7 zam2 from the same period a higher northern field is also found when using less strict cut off criteria resulting in 14 field estimates from jokuldalur i e we find support for higher field strength in the northern hemisphere as compared to the southern hemisphere during the matuyama finally we deliver a revised magneto chronostratigraphic model of jokuldalur and conduct an investigation of the type sections of the so called gilsa normal polarity event around 1 62 ma our revised model is based on 11 new 40ar 39ar ages no evidence is found of the existence of the gilsa event in jokuldalur instead we find that the normal polarity intervals in the type sections can both be correlated to olduvai subchron

lunar impact basins and crustal heterogeneity new western limb and far side data from galileo multispectral images of the lunar western limb and far side obtained from galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution the data reveal that the ejecta from the orientale impact basin 900 kilometers in diameter lying outside the cordillera mountains was excavated from the crust not the mantle and covers pre orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts the inside of the far side south pole aitken basin 2000 kilometers in diameter has low albedo red color and a relatively high abundance of iron and magnesium rich materials these features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta

on low latitude virtual geomagnetic poles in icelandic basalt lava sequences abstract in two paleomagnetic studies from the neogene lava sequences of iceland published in 1977 of the order of 10 of the reliably determined remanence directions corresponded to virtual pole positions below 40 latitude this was a larger proportion than found in most other volcanic locations to explain it harrison harrison c g a 1980 secular variation and excursions of the earth s magnetic field j geophys res 85 3511 3522 suggested that some 10 of the observed virtual geomagnetic poles vgp from iceland might be distributed at random over the globe these random poles can be envisaged as dating from periods when the geomagnetic field is weak and dominated by variable non dipole terms much additional data on remanence directions and intensities has been collected since then and the present study analyses results from over 3500 lava flows in iceland the relative frequency and strength of virtual dipoles in this collection vary with the pole latitude in a similar way as in the collection studied by harrison normalizing of remanence intensity data by the use of anhysteretic remanence arm may improve the resolution of this type of analysis

a 70th degree lunar gravity model glgm 2 from clementine and other tracking data a spherical harmonic model of the lunar gravity field complete to degree and order 70 has been developed from s band doppler tracking data from the clementine mission as well as historical tracking data from lunar orbiters 1 5 and the apollo 15 and 16 subsatellites the model combines 361 000 doppler observations from clementine with 347 000 historical observations the historical data consist of mostly 60 s doppler with a noise of 0 25 to several mm s the clementine data consist of mostly 10 s doppler data with a data noise of 0 25 mm s for the observations from the deep space network and 2 5 mm s for the data from a naval tracking station at pomonkey maryland observations provided clementine provide the strongest satellite constraint on the moon s low degree field in contrast the historical data collected by spacecraft that had lower periapsis altitudes provide distributed regions of high resolution coverage within 29 of the nearside lunar equator to obtain the solution for a high degree field in the absence of a uniform distribution of observations we applied an a priori power law constraint of the form 15 10 5 l2 which had the effect of limiting the gravitational power and noise at short wavelengths coefficients through degree and order 18 are not significantly affected by the constraint and so the model permits geophysical analysis of effects of the major basins at degrees 10 12 the glgm 2 model confirms major features of the lunar gravity field shown in previous gravitational field models but also reveals significantly more detail particularly at intermediate wavelengths 103 km free air gravity anomaly maps derived from the new model show the nearside and farside highlands to be gravitationally smooth reflecting a state of isostatic compensation mascon basins including imbrium serenitatis crisium smythii and humorum are denoted by gravity highs first recognized from lunar orbiter tracking all of the major mascons are bounded by annuli of negative anomalies representing significant subsurface mass deficiencies mare orientale appears as a minor mascon surrounded by a horseshoe shaped gravity low centered on the inner and outer rook rings that is evidence of significant subsurface structural heterogeneity although direct tracking is not available over a significant part of the lunar farside glgm 2 resolves negative anomalies that correlate with many farside basins including south pole aitken hertzsprung korolev moscoviense tsiolkovsky and freundlich sharonov

new analysis of lunar prospector radio tracking data brings the nearside gravity field of the moon with an unprecedented resolution abstract a new analysis of the doppler tracking data from the lunar prospector mission in 1999 revealed a number of previously unseen gravity anomalies at spatial scales as small as 27 km over the nearside the tracking data at low altitudes 50 km or below were better analyzed to resolve the nearside features without dampening from a power law constraint by partitioning the gravity parameters concentrated on either the nearside or farside the resulting model presents gravity anomalies correlated with topography with a correlation coefficient of 0 7 or higher from degree 50 to 150 the widest bandwidth yet the gravity topography admittance of 70 mgal km is found from numerous craters of which diameters are 60 km or less in addition the new model produces orbits that fit to independent radio tracking data from the lunar reconnaissance orbiter and kaguya selene better than previous gravity models this high resolution model can be of immediate use to geophysical analysis of small craters our technique could be applied to an upcoming mission the gravity recovery and interior laboratory and useful to extract short wavelength signals from the messenger doppler data

young mare volcanism in the orientale region contemporary with the procellarum kreep terrane pkt volcanism peak period 2 billion years ago 1 the crater retention ages of the mare deposits within the orientale multi ring impact basin are investigated using 10 m resolution images obtained by the selene kaguya spacecraft in order to constrain the volcanic history of the moon around the nearside farside boundary precise crater counting analyses reveal that mare deposits in the orientale region are much younger than previously estimated 2 9 ga mare basalt in the eastern part of mare orientale and 1 8 2 2 ga mare deposits in lacus veris and lacus autumni maria along the northeastern rings of the basin the latter age estimates indicate that the orientale region experienced volcanic activities 2 billion years after the basin formation impact the dominance of a uniform surface age across the mare deposits in the peripheral regions strongly suggests that these volcanic eruptions are contemporary with the elevated volcanic activity episode proposed for the procellarum kreep terrane on the lunar nearside at 2 ga and that this activity peak is much more widespread than previously estimated the longevity of mare volcanism in the orientale region further suggests high initial temperatures and or high content of heat producing elements in the underlying mantle of this region

gravitational spreading of mountain ridges coeval with late weichselian deglaciation impact on glacial landscapes in trollaskagi northern iceland abstract during the late weichselian deglaciation the coastal mountains of northern central iceland have experienced significant paraglacial readjustment processes in the form of conspicuous rock slope failures and deep seated gravitational slope deformation dsgsd local topographic slopes and ridges were deeply reshaped by these large scale paraglacial processes located on the eastern side of skagafjor ur one of the largest fjords of northern iceland the oslandshli arfjoll and hnjukar ridges 65 49n 19 14w exhibit geomorphic evidence of spectacular dsgds several series of dsgsd induced landforms such as crestal graben and troughs initiated by ridge top splitting were investigated over a 30 km 2 area on the basis of geomorphological mapping we recognized i a ridge top splitting event mainly controlled by glacial debuttressing induced by a minimal 300 m lowering of the glacier surface in the deildardalur valley ii a rapid late weichselian deglaciation of the deildardalur valley spanning a few thousands of years ice free stage probably reached around 14 000 years cal bp iii ridge top splitting having an influence on large scale glacial patterns by guiding and facilitating glacial erosion along ridge top grabens resulting in accelerated trough widening based on these interpretations we propose an evolutionary sequence of both the kinematic stages of the dsgsd and the late weichselian deglaciation at the valley scale this work provides new insights into i the patterns of the late weichselian deglaciation in the skagafjor ur area especially in tributary valleys of the fjord ii the timing of large scale paraglacial ridge top deformations in relation to the post lgm deglaciation and iii the influence of paraglacial dsgsd features on large scale glacial erosional patterns

feldspathic lunar meteorites and their implications for compositional remote sensing of the lunar surface and the composition of the lunar crust we present new compositional data for six feldspathic lunar meteorites two from cold deserts yamato 791197 and 82192 and four from hot deserts dhofar 025 northwest africa 482 and dar al gani 262 and 400 the concentrations of feo or al2o3 and th or any other incompatible element together provide first order compositional information about lunar polymict samples breccias and regoliths and regions of the lunar surface observed from orbit concentrations of both elements on the lunar surface have been determined from data acquired by orbiting spacecraft although the derived concentrations have large uncertainties and some systematic errors compared to sample data within the uncertainties and errors in the concentrations derived from orbital data the distribution of feo and th concentrations among lunar meteorites which represent 18 source regions on the lunar surface is consistent with that of 18 random samples from the surface approximately 11 of the lunar meteorites are low feo and low th breccias consistent with large regions of the lunar surface particularly the northern farside highlands almost all regoliths from apollo sites on the other hand have larger concentrations of both elements because they contain fe rich volcanic lithologies from the nearside maria and th rich lithologies from the high th anomaly in the northwestern nearside the feldspathic lunar meteorites thus offer our best estimate of the composition of the surface of the feldspathic highlands and we provide such an estimate based on the eight most well characterized feldspathic lunar meteorites the variable but high on average mg fe ratio of the feldspathic lunar meteorites compared to ferroan anorthosites confirms a hypothesis that much of the plagioclase at the surface of the feldspathic highlands is associated with high mg fe feldspathic rocks such as magnesian granulitic breccia not ferroan anorthosite geochemically the high mg fe breccias appear to be unrelated to the mafic magnesian suite rocks of the apollo collection models for the formation of the upper lunar crust as a simple flotation cumulate composed mainly of ferroan anorthosite do not account for the complexity of the crust as inferred from the feldspathic lunar meteorites

a detailed palaeomagnetic study of the oldest 15 myr lava sequences in northwest iceland summary we have determined the directions of primary remanence in over 400 lava flows in the northwestern peninsula of iceland near 66 1 n 23 3 w these lavas were sampled in 16 profiles spread across 75 km at the stratigraphic level of the oldest approximately 15 myr in age of several distinctive lignite bearing sediments in the peninsula we find that the pattern of polarity reversals in the lava pile is broadly similar in these profiles but it is generally not possible to trace short polarity zones and excursions over more than a few kilometres laterally our results which also include measurements on the lignite sediments at three sites are consistent with previous suggestions that these sediment beds represent a time gap of the order of 0 2 myr between the lavas above and below the mean virtual geomagnetic pole of this collection is far sided by approximately 7 and the scatter of individual poles is greater than that in palaeomagnetic surveys on younger lava series in iceland

optical measurements of small deeply penetrating bubble populations generated by breaking waves in the southern ocean bubble size distributions ranging from 0 5 to 125 m radius were measured optically during high winds of 13 m s 1 and large scale wave breaking as part of the southern ocean gas exchange experiment very small bubbles with radii less than 60 m were measured at 6 9 m depth using optical measurements of the near forward volume scattering function and critical scattering angle for bubbles 80 the bubble size distributions generally followed a power law distribution with mean slope values ranging from 3 6 to 4 6 the steeper slopes measured here were consistent with what would be expected near the base of the bubble plume bubbles likely stabilized with organic coatings were present for time periods on the order of 10 100 s at depths of 6 9 m here relatively young seas with an inverse wave age of approximately 0 88 and shorter characteristic wave scales produced lower bubble concentrations shallower bubble penetration depths and steep bubble size distribution slopes conversely older seas with an inverse wave age of 0 70 and longer characteristic wave scales produced relatively higher bubble concentrations penetrating to 15 m depth larger bubble sizes and shallower bubble size distribution slopes when extrapolated to 4 m depth using a previously published bubble size distribution our estimates suggest that the deeply penetrating small bubbles measured in the southern ocean supplied 36 of the total void fraction and likely contributed to the transfer and supersaturation of low solubility gases