quantitative bedrock geology of alaska and canada 1 we quantitatively analyze the area age distribution of sedimentary igneous and metamorphic bedrock on the basis of data from the most recent geologic maps of alaska beikman 1980 1 2 500 000 and canada douglas 1969 updated 1 5 000 000 made available in digital form by the u s geologic survey and the geologic survey of canada national resources canada respectively sediments cover 72 9 and 52 4 of the surface of alaska and canada volcanic rocks comprise 11 6 and 6 of the surface area in alaska and canada respectively whereas intrusive rocks cover 6 6 and 24 of the surface respectively ultramafic rocks account for 0 20 and 0 08 of the bedrock area whereas metamorphic rocks cover 3 4 and 16 1 the average ages of major lithologic units weighted according to bedrock area are significantly younger in alaska than in canada marine sediments stratigraphic age of 206 myr in alaska versus 599 myr in canada continental sediments stratigraphic age of 81 myr versus 150 myr volcanic rocks 126 myr versus 1377 myr intrusive rocks 114 myr versus 2109 myr ultramafic rocks 261 myr versus 874 myr and metamorphic rocks 474 myr versus 2545 myr this age difference reflects the contrast between the young active margin influence on the geology of alaska and the old cratonic nature of much of the bedrock exposed in canada glacial erosion and the resulting exposure of precambrian bedrock primarily in canada contributes to this age contrast the average temporal and spatial resolution of the digital data is sufficiently high to perform age area analyses on individual river basins larger than 20 000 km2 and to evaluate the relationship between bedrock geology and river chemistry

true polar wander in mantle convection models with multiple mobile continents a b s t r a c t a r t i c l e i n f o the geologic record supports numerous instances during which continents apparently moved at speeds signi cantly faster than any of today s tectonic plates while the time dependence of convective driving forces likely explains some such observations rapid motions of large continents in particular are often attributed to true polar wander tpw in order to gauge the potential for connections between continents mantle temperature anomalies and polar motion we present the rst calculations of tpw derived from models that couple mantle convection with multiple mobile continents we nd that the aggregation and dispersal of supercontinents can lead to two types of tpw driven either by a well developed hot upwelling axis that creates a stable maximum moment of inertia or by the homogenization of mantle thermal structure following continent dispersal that leads to destabilization of the principal axis and possible large magnitude polar wander these supercontinent modulated thermal heterogeneities drive model tpw events as large as 90 at rates of up to 2 5 ma 1 such magnitudes and speeds are greater than those attained in similar models lacking continents but comparable to those for episodes inferred from paleomagnetic data for some large continents in the past published by elsevier b v on behalf of international association for gondwana research

temporal record of osmium concentrations and 187os 188os in organic rich mudrocks implications for the osmium geochemical cycle and the use of osmium as a paleoceanographic tracer the final publication is available at elsevier via https doi org 10 1016 j gca 2017 06 046 2017 this manuscript version is made available under the cc by nc nd 4 0 license http creativecommons org licenses by nc nd 4 0

quantitative bedrock geology of the continents and large scale drainage regions we quantitatively analyze the area age distribution of sedimentary extrusive volcanic and endogenous plutonic and or metamorphic bedrock on the basis of data from the most recent digital geological map of the world at a scale of 1 25 000 000 the spatial resolution of the digital bedrock data averages 13 905 km2 per polygon comparison of certain regions of the world previously analyzed at higher spatial resolution with the low resolution world data reveals general consistency in the areal exposure of major rock types as well as a minor systematic bias toward older average bedrock ages in the global data set application of the global bedrock data to 19 large scale drainage regions and three large internally drained regions reveals considerable regional variability of earth s bedrock geology that is consistent with the dominant geotectonic setting of the respective drainage region

the miniature radio frequency instrument s mini rf global observations of earth s moon abstract radar provides a unique means to analyze the surface and subsurface physical properties of geologic deposits including their wavelength scale roughness the relative depth of the deposits and some limited compositional information the nasa lunar reconnaissance orbiter s lro miniature radio frequency mini rf instrument has enabled these analyses on the moon at a global scale mini rf has accumulated 67 coverage of the lunar surface in s band 12 6 cm radar with a resolution of 30 m pixel here we present new mini rf global orthorectified uncontrolled s band maps of the moon and use them for analysis of lunar surface physical properties reported here are readily apparent global and regional scale differences in lunar surface physical properties that suggest three distinct terranes namely a 1 nearside radar dark region 2 orientale basin and continuous ejecta and the 3 highlands radar bright region integrating these observations with new data from lro s diviner radiometer rock abundance maps as well clementine and lunar prospector derived compositional values show multiple distinct lunar surface terranes and sub terranes based upon both physical and compositional surface properties previous geochemical investigations of the moon suggested its crust is best divided into three to four basic crustal provinces or terranes feldspathic highlands terrane an and outer procellarum kreep terrane and south pole aitken terrane that are distinct from one another however integration of these geochemical data sets with new geophysical data sets allows us to refine these terranes the result shows a more complex view of these same crustal provinces and provides valuable scientific and hazard perspectives for future targeted human and robotic exploration

a revised algorithm for calculating tio2 from clementine uvvis data a synthesis of rock soil and remotely sensed tio2 concentrations 1 investigating mare basalt compositions at both the sample and remote sensing level for the apollo and luna mare sites reveals the need for a more complex regression procedure than previously proposed in order to extract accurate tio2 concentrations from clementine spectral reflectance csr data the tio2 algorithm of lucey and coworkers is modified by using two different sets of regression parameters to relate measured regolith compositions from sampling locations to the csr properties of these sites one regression trend fits the majority of apollo data and the second regression is a fit to the apollo 11 luna 16 and luna 24 data which were considered to be anomalous in previous tio2 calibrations these three sites have unusually low albedo compared to other mare landing sites and some 32 of nearside mare regions appear to share this characteristic possible reasons for these differences related to proximity of the other sites to mare highland boundaries are discussed using the dual regression method we find 1 that tio2 concentrations calculated for the basaltic landing sites faithfully reproduce a bimodal distribution as seen in the sample data 2 that when coupled with the effects of other thermal neutron absorbers ti concentrations are more consistent with observed epithermal to thermal neutron flux ratios than are previous clementine based derivations of tio2 for basaltic regions and 3 that basalts of intermediate tio2 concentrations occur most frequently in the oceanus procellarum region and that these intermediate concentrations appear to be inherent to the flows underlying the regolith and presumably to the basalt source regions

ages and stratigraphy of mare basalts in oceanus procellarum mare nubium mare cognitum and mare insularum accurate estimates of mare basalt ages are necessary to place constraints on the duration and the flux of lunar volcanism as well as on the petrogenesis of lunar mare basalts and their relationship to the thermal evolution of the moon we performed new crater size frequency distribution measurements in order to investigate the stratigraphy of mare basalts in oceanus procellarum and related regions such as mare nubium mare cognitum and mare insularum we used high resolution clementine color data to define 86 spectrally homogeneous units within these basins which were then dated with crater counts on lunar orbiter iv images our crater size frequency distribution measurements define mineralogical and spectral surface units and offer significant improvements in accuracy over previous analyses our data show that volcanism in the investigated region was active over a long period of time from 3 93 to 1 2 b y a total of 2 7 b y volumetrically most of the basalts erupted in the late imbrian period between 3 3 and 3 7 b y and we see evidence that numerous units have been resurfaced during the eratosthenian period significantly less basalt was erupted depending on the absolute model ages that one can assign to the lunar chronostratigraphic systems five units might be of copernican age younger basalts are generally exposed in the center of the investigated area that is closer to the volcanic centers of the aristarchus plateau and marius hills older basalts occur preferentially along the northwestern margin of oceanus procellarum and in the southeastern regions of the studied area i e in mare cognitum and mare nubium combining the new data with our previously measured ages for basalts in mare imbrium serenitatis tranquillitatis humorum australe and humboldtianum we find that the period of active volcanism on the moon lasted 2 8 b y from 4 b y to 1 2 b y on the basis of the basalts dated so far which do not yet include the potentially young basalts of mare smythii e g schultz and spudis 1983 we conclude that oceanus procellarum not only exhibits the widest range of ages of all investigated basins but probably also is the location of some of the youngest basalts on the lunar surface

mars mapping with delay doppler radar mars radar imaging results from arecibo 12 6 cm observations are presented the images were derived from delay doppler mapping using a coded long pulse technique to mitigate the effects of echo overspreading images of the depolarized echo are used to identify regions of high decimeter scale roughness some of the strongest echo features are located on the major shield volcanoes or on relatively young off shield flows such as the olympus and pavonis lava aprons the shields themselves have highly irregular radar signatures suggesting complex volcanic histories some mars radar features have twice the depolarized brightness of the roughest terrestrial lava flows apparently due to higher levels of multiple scattering from surfaces of spectacular roughness or from volume scattering low brightness smooth areas are associated with older surfaces such as fractured and highland terra as well as with terrain interpreted to be debris lobes ash flows and aureoles in particular a close connection was found between the 12 6 cm counterpart of the stealth feature and the medusae fossae formation postulated to be deep ignimbrite deposits marte valus is anomalous in being the only outflow channel showing strongly enhanced echoes which supports the idea that this channel and the elysium basin that it drained are filled with lava flows a weak radar feature was found for the south polar residual ice cap comparisons with goldstone 3 5 cm data show that the south polar enhancement is much weaker at 12 6 cm than at 3 5 cm indicating that the southern ice cap becomes optically thin at the longer wavelength a north polar enhancement has also been found which is comparable in strength to the 12 6 cm south polar feature

slab pull mantle convection and pangaean assembly and dispersal two global scale mantle convection cells presently exist on earth centred on upwelling zones in the south pacific ocean and northeast africa one cell panthalassan contains only oceanic plates the other pangaean contains all the continental plates they have remained fixed relative to one another for 400 ma a transverse rheic tethyian subduction system splits the pangaean cell poloidal plate motion in the oceanic cell reflects circumferential pull of panthalassan slabs but toroidal flow in the pangaean cell reflected by vortex type motion of continents toward the altaids of central east asia throughout the phanerozoic has resulted from the competing slab pull forces of both cells the combined slab pull effects from both cells also controlled pangaean assembly and dispersal assembly occurred during palaeozoic clockwise toroidal motion in the pangaean cell when gondwana was pulled into pangaea by the ne trending rheic subduction zone forming the appalachian variscide altaid chain pangaean dispersal occurred when the rheic trench re aligned in the jurassic to form the nw trending tethyside subduction system which pulled east gondwanan fragments in the opposite direction to form the cimmerian himalayan alpine chain this re alignment also generated a new set of indian mid ocean ridge systems which dissected east gondwana and facilitated breakup 100 200 myr long phanerozoic wilson cycles reflect rifting and northerly migration of gondwanan fragments across the pangaean cell into the rheic tethyian trench pangaean dispersal was amplified by retreat of the panthalassan slab away from europe and africa which generated mantle counterflow currents capable of pulling the americas westward to create the atlantic ocean thermal blanketing beneath pangaea and related hotspot activity were part of a complex feedback mechanism that established the breakup pattern but slab retreat is considered to have been the main driving force the size and longevity of the two cells organised and maintained by long lived slab pull forces favours deep mantle convection as the dominant circulation process during the phanerozoic

focused 70 cm wavelength radar mapping of the moon we describe new 70 cm wavelength radar images of the lunar near side and limb regions obtained via a synthetic aperture radar patch focusing reduction technique the data are obtained by transmitting a circularly polarized pulsed waveform from the arecibo telescope in puerto rico and receiving the echo in both senses of circular polarization with the robert c byrd green bank telescope in west virginia the resultant images in both polarizations have a spatial resolution as fine as 320 m 450 m near the lunar limb the patch focusing technique is a computationally efficient method for compensating for range migration and doppler azimuth smearing over long coherence times i e 983 s which is needed to achieve the required doppler resolution three to nine looks are averaged for speckle reduction and to improve the signal to noise ratio at this long wavelength the radar signal penetrates up to several tens of meters into the dry lunar surface materials thus revealing details of the bulk loss properties and decimeter scale rock abundance not evident in multispectral and other remote sensing data application of the new radar images to the analysis of basalt flow complexes in mare serenitatis shows that the long wavelength radar data are sensitive to differences in both flow age and composition and may be particularly useful for studies of smaller deposits that do not have robust crater statistics the new 70 cm lunar radar data are archived at the national aeronautics and space administration planetary data system

slabs in the lower mantle results of dynamic modelling compared with tomographic images and the geoid abstract the recent increase in resolution of tomographic images of the earth s interior has enabled us to see slabs in the lower mantle on the other hand the distribution of slabs can be inferred from subduction history using a dynamical model of mantle flow comparison of tomographic images with model results can help to distinguish between alternative models of subduction history tomographic models and mantle flow models and thus improve our understanding of the earth here a simple dynamic model of subduction is used and some results are presented amounts and locations of subduction are inferred from published models of plate motion and plate boundaries for the past 120 ma the latter have been interpolated on 2 ma time intervals mantle flow driven by the density anomalies corresponding to subducted slabs is calculated with the method of hager and o connell for a viscosity structure that features an increase in viscosity from 4 10 20 pa below the lithosphere to 4 10 22 pa in the lower part of the lower mantle slabs are advected in the flow field in the model slabs sink on average about 1700 km through the mantle during 100 ma however the calculated average horizontal motion of slabs throughout most of the mantle is only about 600 700 km for slabs that have sunk to the lowermost mantle it is about 1000 km this is in accordance with the previously observed good correlation between subduction locations and lowermost mantle heterogeneities slabs sink fastest in regions with abundant subduction and little trench migration e g below east asia in the lowermost mantle predicted slab locations tend to lie in areas with high seismic velocities however there are large areas of fast seismic velocities where no slabs are predicted and which therefore presumably correspond to earlier subduction in some regions e g below japan our model approximately reproduces the observed shape of the slab in other regions where the agreement is poor the results can help to further constrain models of subduction history and associated mantle flow additionally the predicted geoid is computed and compared with the actual geoid predicted and observed geoid have similar magnitude and a number of features in common however an optimization of the fit is not attempted here since in order to do this also the hot upwellings from the lower boundary layer presumably in the form of plumes would have to be included

quantitative bedrock geology of the conterminous united states of america 1 we quantitatively analyze the area age distribution of bedrock based on data from the most recent geologic map of the conterminous united states of america king and beikman 1974a 1974b made available in digital form by the united states geologic survey the area age distribution agrees surprisingly well with older data higgs 1949 but provides much higher temporal resolution the mean stratigraphic age of all sedimentary bedrock is 134 myr that of tertiary cambrian sediments is 104 myr the analysis also reveals area coverage of some minor lithologies such as ultramafic rocks that cover 0 15 of the conterminous united states area coverage of 162 lithostratigraphic units is made available as an excel data sheet

stratigraphy and evolution of basalts in mare humorum and southeastern procellarum we have studied the mare basalts of mare humorum and southeastern procellarum 30w 50w 0 40s one hundred and nine basaltic units have been identified from differences in their feo wt and tio2 wt content and variations in crater densities crater counting and reference to isotopically dated apollo samples have provided an age for 33 major units some evidence for three distinct periods of volcanic activity has been found we found that the large unit in the middle of mare humorum is the oldest in the basin this supports the suggestion that the oldest central unit sank causing the lithosphere to bend and create dykes through which lava flowed to produce the outer units no evidence of a trend in feo wt and tio2 wt content against time is found within mare humorum there appears to be no lateral trend of basalts in terms of feo and tio2 wt over the entire area with time an increase in feo content with time is found in the 33 major units and there is some evidence for an increase in tio2 in the same units a correlation between feo wt and tio2 wt content is evident when all 109 units are compared a notable feature of this correlation is a sharp increase in gradient of tio2 wt content when the feo wt content rises above about 17

regolith composition and structure in the lunar maria results of long wavelength radar studies radar measurements at 70 cm and 7 5 m wavelengths provide insight into the structure and composition of the upper 5 100 m of the lunar regolith and crust we combine high resolution 3 5 km 70 cm radar data for the nearside with earlier calibrated full disk observations at the same wavelength to provide a reasonable estimate of the lunar backscatter coefficient these data are tested against models for echoes from a buried substrate and mie scattering from surface and buried rocks these mechanisms are expected to dominate the 70 cm radar echo with their relative importance determined by the rock population regolith depth substrate roughness and the loss tangent of the soil results indicate that the 70 cm radar echo for the maria comes largely from mie scattering by rocks buried within the fine soil radar scattering from a buried substrate is not likely to greatly affect the observed return we also compared the 70 cm and 7 5 m radar images to infrared eclipse temperature maps crater population age estimates for the maria and to tio2 and feo abundances inferred from earth based telescopic and clementine multispectral observations these data imply that 1 the tio2 ilmenite content of the regolith controls variations in 70 cm depolarized echo strength among mare units with higher titanium abundance leading to lower echoes 2 changes in the average 70 cm return for a given tio2 abundance between maria of different ages do occur but uncertainties in the current radar data do not allow us to uniquely distinguish between variations in rock population with age and calibration effects 3 the 7 5 m radar echoes are controlled by the age of the mare basalt flows with older deposits having a greater degree of fracturing and higher backscatter future mapping at 12 6 cm and 70 cm wavelengths will help to resolve some of the issues raised here

earth based 12 6 cm wavelength radar mapping of the moon new views of impact melt distribution and mare physical properties abstract we present results of a campaign to map much of the moon s near side using the 12 6 cm radar transmitter at arecibo observatory and receivers at the green bank telescope these data have a single look spatial resolution of about 40 m with final maps averaged to an 80 m four look product to reduce image speckle focused processing is used to obtain this high spatial resolution over the entire region illuminated by the arecibo beam the transmitted signal is circularly polarized and we receive reflections in both senses of circular polarization measurements of receiver thermal noise during periods with no lunar echoes allow well calibrated estimates of the circular polarization ratio cpr and the four element stokes vector radiometric calibration to values of the backscatter coefficient is ongoing radar backscatter data for the moon provide information on regolith dielectric and physical properties with particular sensitivity to ilmenite content and surface or buried rocks with diameter of about one tenth the radar wavelength and larger average 12 6 cm circular polarization ratio cpr values for low to moderate tio 2 mare basalt deposits are similar to those of rough terrestrial lava flows we attribute these high values to abundant few centimeter diameter rocks from small impacts and a significant component of subsurface volume scattering an outflow deposit inferred to be impact melt from glushko crater has cpr values near unity at 12 6 cm and 70 cm wavelengths and thus a very rugged near surface structure at the decimeter to meter scale this deposit does not show radar brightness variations consistent with levees or channels and appears to nearly overtop a massif suggesting very rapid emplacement deposits of similar morphology and or radar brightness are noted for craters such as pythagoras rutherfurd theophilus and aristillus images of the north pole show that despite recording the deposition of orientale material byrd and peary craters do not have dense patterns of radar bright ejecta from small craters on their floors such patterns in amundsen crater near the south pole were interpreted as diagnostic of abundant impact melt so the fraction of orientale derived melt in the north polar smooth plains 1000 km farther from the basin center is inferred to be much lower

geophysics of the pitman fracture zone and pacific antarctic plate motions during the cenozoic multibeam bathymetry and magnetometer data from the pitman fracture zone fz permit construction of a plate motion history for the south pacific over the past 65 million years reconstructions show that motion between the antarctic and bellingshausen plates was smaller than previously hypothesized and ended earlier at chron c27 61 million years ago the fixed hot spot hypothesis and published paleomagnetic data require additional motion elsewhere during the early tertiary either between east antarctica and west antarctica or between the north and south pacific a plate reorganization at chron c27 initiated the pitman fz and may have been responsible for the other right stepping fracture zones along the ridge an abrupt 8 clockwise rotation in the abyssal hill fabric along the pitman flowline near the young end of chron c3a 5 9 million years ago dates the major change in pacific antarctic relative motion in the late neogene

polar wandering of a dynamic earth summary the rotational behaviour of a stratified visco elastic planet submitted to changes in its inertia tensor is studied in a viscous quasi fluid approximation this approximation allows for large displacements of the earth rotation axis with respect to the entire mantle but is only valid for mass redistribution within the planet occurring on the time scale of a few million years such a motion called true polar wander tpw is detected by palaeomagneticiens assuming that the earth s magnetic field remains on average aligned with the spin axis our model shows that a downgoing cold slab induces a tpw which quickly brings this slab to the pole for a mantle of uniform viscosity the same slab is slowly moved toward the equator when a large viscosity increase with depth takes place in the mantle our model is also suitable to investigate the effects of a non steady state convection on the earth s rotation we discuss these effects using a simple mass redistribution model inspired by the pioneering paper of goldreich toomre 1969 it consists of studying the tpw induced by a random distribution of slabs sinking into the mantle for such a mass redistribution only a strongly stratified mantle can reduce the earth s pole velocity below l ma which is the upper bound value observed by palaeomagnetic investigations for the last 200 ma our model also shows that when corrected for the hydrostatic flattening the earth s polar inertia generally corresponds to the maximum inertia as it is presently observed however this may not be the case during some short time periods we also discuss the amount of excess polar flattening that can be related to tidal deceleration this frozen component is found to be negligible

tectonism and exhumation in convergent margin orogens insights from ore deposits abstract three widespread and abundant types of ore deposits epithermal silver gold ag au porphyry copper cu and orogenic gold au form by hydrothermal activity during tectonic convergence along continental margins and their preservation provides new insights into rates of those processes that form and destroy ore deposits as well as overlying rock ages for each of the three deposit types define lognormal age frequency distributions that are nearly identical in form but differ in their modal ages epithermal ag au porphyry cu and orogenic au deposits exhibit age modes at 3 11 and 199 ma respectively these ore types form at depths of 0 5 1 9 and 10 km respectively such that modal age increases with depth of ore emplacement qualitatively the dearth of deposits younger than their modal age reflects the fact that ore deposits form at depth within the crust and time is required for exhumation to expose them continued erosion serves to destroy ore bodies giving rise to fewer deposits

surface morphology of domes in the marius hills and mons rumker regions of the moon from earth based radar data 1 clusters and coalesced complexes of domes represent a relatively rare landform within the extensive low relief lunar maria while they are typically spectroscopically similar to mare basalts emplaced by high volume low viscosity eruptions the large scale morphology of the domes is more consistent with slower emplacement and or more viscous magma we use new earth based radar data to study the decimeter to meter scale rock abundance at the surface and buried within the probing range of the radar signal of domes in the marius hills and mons rumker regions domes of the marius hills are characterized by high circular polarization ratio cpr values at 12 6 cm and 70 cm wavelength similar to the near rim ejecta deposits of young lunar craters like tycho areas of large ejecta fragments near the rim of meteor crater and blocky lavas such as sp flow in arizona we infer that a very rugged flow surface morphology associated with the original dome forming eruption rather than postemplacement modification exists beneath at most a few meters of regolith magmas with greater silica content than sampled lunar basalts are unlikely so the blocky structure of the dome forming lava must arise from some combination of compositional change effusion rate and or cooling effects not typically observed in basaltic landforms on the earth much of the 80 km diameter mons rumker has low backscatter and cpr at 12 6 cm wavelength relative to nearby mare terrain at 70 cm wavelength the northern and most of the southern parts of the complex are radar dark but there is a radar bright feature that extends from the central region eastward into oceanus procellarum we conclude that much of mons rumker is mantled by rock poor fine grained pyroclastic material the radar bright feature in the 70 cm map is detectable owing to some combination of greater roughness like the marius domes and thinner mantling cover

quantitative bedrock geology of east and southeast asia brunei cambodia eastern and southeastern china east timor indonesia japan laos malaysia myanmar north korea papua new guinea philippines far eastern russia singapore south korea taiwan thailand vietnam 1 we quantitatively analyze the area age distribution of sedimentary igneous and metamorphic bedrock based on data from the most recent digital geologic maps of east and southeast asia coordinating committee for coastal and offshore geosciences programmes in east and southeast asia ccop and the geologic survey of japan 1997 1 2 000 000 published as digital geoscience map g 2 by the geological survey of japan sedimentary rocks volcanic rocks plutonic rocks ultramafic rocks and metamorphic rocks cover 73 3 8 5 8 8 0 9 and 8 6 of the surface area respectively the average ages of major lithologic units weighted according to bedrock area are as follows sedimentary rocks average stratigraphic age of 123 myr median age of 26 myr volcanic rocks 84 myr 20 myr intrusive rocks 278 myr 195 myr ultramafic rocks unknown and metamorphic rocks 1465 myr 1118 myr the variability in lithologic composition and age structure of individual countries reflects the complex tectonic makeup of this region that ranges from precambrian cratons e g northeast china and north korea to mesozoic cenozoic active margins e g japan the philippines indonesia and new guinea the spatial resolution of the data varies from 44 km2 per polygon japan to 1659 km2 per polygon taiwan and is on average 490 km2 polygon similar to our previous analyses of the united states of america and canada the temporal and spatial resolution is sufficiently high to perform age area analyses of individual river basins larger than 10 000 km2 and to quantitatively evaluate the relationship between bedrock geology and river chemistry as many rivers draining tropical mountainous islands of east and southeast asia have a disproportionate effect on the dissolved and particulate load delivered to the world oceans bedrock geology in such river drainage basins disproportionately affect ocean chemistry

arecibo radar imagery of mars the major volcanic provinces abstract we present earth based radar images of mars obtained with the upgraded arecibo s band 12 6 cm radar during the 2005 2012 oppositions the imaging was done using the same long code delay doppler technique as for the earlier pre upgrade imaging but at a much higher resolution 3 km and for some regions a more favorable sub earth latitude this has enabled us to make a more detailed and complete mapping of depolarized radar reflectivity a proxy for small scale surface roughness over the major volcanic provinces of tharsis elysium and amazonis we find that vast portions of these regions are covered by radar bright lava flows exhibiting circular polarization ratios close to unity a characteristic that is uncommon for terrestrial lavas and that is a likely indicator of multiple scattering from extremely blocky or otherwise highly disrupted flow surfaces all of the major volcanoes have radar bright features on their shields although the brightness distribution on olympus mons is very patchy and the summit plateau of pavonis mons is entirely radar dark the older minor shields paterae and tholi are largely or entirely radar dark which is consistent with mantling by dust or pyroclastic material other prominent radar dark features include the fan shaped deposits possibly glacial associated with the three major tharsis montes shields various units of the medusae fossae formation a region south and west of biblis patera where stealth deposits appear to obscure tharsis flows and a number of dark halo craters with radar absorbing ejecta blankets deposited atop surrounding bright flows several major bright features in tharsis are associated with off shield lava flows these include the olympus mons basal plains volcanic fields east and south of pavonis mons the daedalia planum flows south of arsia mons and a broad expanse of flows extending east from the tharsis montes to echus chasma the radar bright lava plains in elysium are concentrated mainly in cerberus and include the fluvio volcanic channels of athabasca valles grjota valles and marte valles as well as an enigmatic region at the southern tip of the cerberus basin some of the cerberus bright features correspond to the distinctive platy ridged flows identified in orbiter images the radar bright terrain in amazonis planitia comprises two distinct but contiguous sections a northern section formed of lavas and sediments debouched from marte valles and a southern section whose volcanics may derive in part from local sources this south amazonis region shows perhaps the most complex radar bright structure on mars and includes features that correspond to platy ridged flows similar to those in cerberus

ages of mare basalts on the lunar nearside the chronology of lunar volcanism is based on radiometric ages determined from apollo and luna landing site samples regional stratigraphic relationships and crater degradation and size frequency distribution data for units largely defined prior to the end of the apollo program here we report on new crater size frequency distribution data for 139 spectrally and morphologically defined basalt units which are exposed in six nearside impact basins australe tranquillitatis humboldtianum humorum serenitatis and imbrium crater size frequency distribution measurements are a statistically robust and accurate method to derive absolute model ages of unsampled regions of the moon compared to crater degradation ages crater size frequency ages performed on spectrally defined units offer significant improvements in accuracy our investigation showed that 1 in the investigated basins lunar volcanism was active for at least 1 5 2 0 b y starting at about 3 9 4 0 b y and ceasing at 2 0 b y 2 most basalts erupted during the late imbrian period at about 3 6 3 8 b y 3 significantly fewer basalts were emplaced during the eratosthenian period 4 basalts of copernican age were not found in any of the investigated basins 5 lunar basin filling volcanism probably started within 100 m y after the formation of the individual basins we also assessed the relationship between impact basin age and the history of mare basalt emplacement in these basins we found that 1 in all pre nectarian basins australe and tranquillitatis as well as in the humboldtianum basin which is of nectarian age the distribution of surface ages is clearly dominated by only a single peak in the number of erupted units at 3 6 3 8 b y 2 in the younger basins humorum serenitatis and imbrium a second peak at 3 3 3 5 b y is observed 3 basalt eruptions younger than 2 6 b y occur only intermittently and 4 in the youngest basins serenitatis and imbrium we see an extended period of active basin filling volcanism 1 5 1 6 b y which is 500 m y longer than in the australe and humorum and even 1 0 b y longer than in tranquillitatis and humboldtianum

the origin of ina evidence for inflated lava flows on the moon 1 ina is an enigmatic volcanic feature on the moon known for its irregularly shaped mounds the origin of which has been debated since the apollo missions three main units are observed on the floor of the depression 2 9 km across 64 m deep located at the summit of a low shield volcano irregularly shaped mounds up to 20 m tall a lower unit 1 to 5 m in relief that surrounds the mounds and blocky material analyses of lunar reconnaissance orbiter camera images and topography show that features in ina are morphologically similar to terrestrial inflated lava flows comparison of these unusual lunar mounds and possible terrestrial analogs leads us to hypothesize that features in ina were formed through lava flow inflation processes while the source of the lava remains unclear this new model suggests that as the mounds inflated breakouts along their margins served as sources for surface flows that created the lower morphologic unit over time mass wasting of both morphologic units has exposed fresh surfaces observed in the blocky unit ina is different than the terrestrial analogs presented in this study in that the lunar features formed within a depression no vent sources are observed and no cracks are observed on the mounds however lava flow inflation processes explain many of the morphologic relationships observed in ina and are proposed to be analogous with inflated lava flows on earth

excitation of true polar wander by subduction true polar wander the global motion of the mantle relative to the earth s rotation axis is known from the analysis of palaeomagnetic data hotspot tracks and plate motions to have occurred at velocities of up to 0 5 myr 1 since the late cretaceous period1 4 we address here the longstanding question of how fast episodes of true polar wander tpw can be excited5 by analysing the impact of the distribution and activity of subduction zones on polar motion using nonlinear liouville equations which allow us to treat large excursions of the polar axis we show that unrealistically fast tpw is excited by subduction episodes unless the lower mantle has a viscosity at least 10 times that of the upper mantle this need for a viscosity increase with depth in the mantle reinforces the conclusions of previous studies on post glacial rebound and geoid anomalies theoretical creep laws and some preliminary results on tpw induced by density anomalies embedded in the mantle6 10 the lower viscosity in the upper mantle means that upper mantle density anomalies are most effective in exciting tpw changes in the pattern of subduction through time may be responsible for both episodes of fast tpw and times of quiescence in polar motion

rugged lava flows on the moon revealed by earth based radar 1 basaltic volcanism is widespread on the lunar nearside and returned samples suggest that the mare forming magmas had low viscosity that led to primarily sheet like deposits new 70 cm wavelength radar observations that probe several meters beneath the lunar surface reveal differences in mare backscatter properties not explained by age or compositional variations we interpret areas of high backscatter and high circular polarization ratio in maria serenitatis imbrium and crisium as having an enhanced abundance of decimeter scale subsurface rocks relative to typical mare forming flows the 3 5 b y survival of these differences implies an initial platy blocky or ridged lava flow surface layer with thickness of at least 3 5 m such rugged morphology might arise from episodic changes in magma effusion rate as observed for disrupted flood basalt surfaces on the earth and mars very high flow velocities or increased viscosity due to a number of factors significant information on lunar mare eruption conditions may thus be obtained from long wavelength radar probing of the shallow subsurface

phase transition and density of subducted morb crust in the lower mantle abstract phase relations mineral chemistry and density of a natural mid oceanic ridge basalt morb composition were investigated up to 134 gpa and 2300 k by a combination of in situ x ray diffraction measurements and chemical analyses using transmission electron microscope tem results demonstrate that the morb composition consists of mgsio 3 rich perovskite stishovite casio 3 perovskite and cafe 2 o 4 type al phase in the upper part of the lower mantle the most abundant mineral of mgsio 3 rich perovskite undergoes phase transition to a cairo 3 type post perovskite phase above 110 gpa and 2500 k post perovskite phase is similar in composition to perovskite except considerably high na 2 o content stishovite transforms to cacl 2 type sio 2 phase above 62 gpa and 2000 k and further to pbo 2 type phase above 110 gpa pbo 2 type sio 2 phase includes large amount of al 2 o 3 which significantly expands its stability relative to cacl 2 type phase phase transition of casio 3 perovskite from tetragonal to cubic was also observed with increasing temperature cafe 2 o 4 type al phase is stable to the bottom of the mantle the density of morb crust was calculated using volume data combining with measured chemical compositions and calculated mineral proportions the former morb crust is denser than the average lower mantle at all depths greater than 720 km contrary to earlier predictions the subducted basaltic crust may have accumulated at the base of the mantle

mantle dynamics geoid inertia and tpw since 120 myr abstract we investigate the effect of internal masses redistributions on the position of the earth rotational pole for the last 120 myr we use a geodynamic model based on plate reconstructions that estimates the location and rate of subducted slabs under the assumption that they sink vertically into the mantle ricard et al 1993b our model also takes into account the effect of large scale upwellings domes derived from an analysis of seismic tomography their location is assumed to remain stable with time we then compute the geoid associated with the time dependent mantle density heterogeneities in order to reconcile the computed and observed geoids we investigate the influence of the depth down to which the subducted pacific plates beneath the americas present a significant density contrast with respect to the surrounding mantle on the present day geoid and propose a plate model in which we obtain a variance reduction greater than 0 9 for the degree 2 we show that the vertical oscillation of domes within mantle only modulates the amplitude of the associated geoid the temporal variation of the mantle density heterogeneities is consequently essentially due to changes in the subduction history the temporal evolution of the principal inertia axis pia of the earth derived from our model the rotational axis is aligned to the maximum pia is then investigated and finally compared to estimations of tpw both the maximum and intermediate pias have moved in a plane perpendicular to africa along a circle corresponding to the low of geoid induced by subduction around the pacific the minimum pia seems to be relatively stable since 120 myr and close to the maximum degree 2 geoid high under africa this can account for observed tpw or african apw in the last 200 myr

the 125 150 ma high resolution apparent polar wander path for adria from magnetostratigraphic sections in umbria marche northern apennines italy timing and duration of the global jurassic cretaceous hairpin turn a new high resolution apparent polar wander path apwp segment has been obtained from the magnetostratigraphy of four kimmeridgian to lower aptian sections in the northern apennines italy the use of paleomagnetic data for determination of the adria apwp was hampered by the large local rotations linked to apennine tectonics characterized by folds and thrusts developed during the neogene to overcome this problem we have computed relative rotations between time overlapping sections and realigned them in a common declination reference frame namely the bosso section we synthesized a new high resolution 150 to 125 ma apwp for adria which has a similar shape to the time equivalent segment of the synthetic apwp of africa of besse and courtillot j besse v courtillot apparent and true polar wander and the geometry of the geomagnetic field over the last 200 myr j geophys res 107 b11 2002 doi 10 1029 200jb000050 a 26 clockwise rotation of our combined adria apwp places it in almost perfect overlap with african data of same age confirming that the adria promontory moved coherently with africa during this time span whereas the counterclockwise rotation of adria with respect to africa was introduced later most probably during apennines orogenesis finally we discuss in relation with worldwide plate evolution the peculiar shape of our apwp which displays a hairpin turn during berriasian time and dates the main late jurassic early cretaceous change in plate motion at around anomaly m16

an explanation for earth s long term rotational stability paleomagnetic data show less than approximately 1000 kilometers of motion between the paleomagnetic and hotspot reference frames that is true polar wander during the past 100 million years which implies that earth s rotation axis has been very stable this long term rotational stability can be explained by the slow rate of change in the large scale pattern of plate tectonic motions during cenozoic and late mesozoic time provided that subducted lithosphere is a major component of the mantle density heterogeneity generated by convection therefore it is unnecessary to invoke other mechanisms such as sluggish readjustment of the rotational bulge to explain the observed low rate of true polar wander

radar remote sensing of pyroclastic deposits in the southern mare serenitatis and mare vaporum regions of the moon 1 we use polarimetric radar observations to study the distribution depth and embedded rock abundance of nearside lunar pyroclastic deposits radar images were obtained for mare vaporum and the southern half of mare serenitatis the imaged areas contain the large rima bode mare vaporum sulpicius gallus and taurus littrow pyroclastic deposits potential pyroclastic deposits at rima hyginus crater the tacquet formation and a dome in mare vaporum are also included data were acquired at s band 12 6 cm wavelength using arecibo observatory and the green bank telescope in a bistatic configuration the s band images have resolutions between 20 and 100 m pixel the pyroclastic deposits appear dark to the radar and have low circular polarization ratios at s band wavelengths because they are smooth easily penetrable by radar waves and generally contain few embedded blocks changes in circular polarization ratio cpr across some of the pyroclastic deposits show areas with increased rock abundance as well as deposits that are shallower radar backscatter and cpr maps are used to identify fine grained mantling deposits in cases where optical and near infrared data are ambiguous about the presence of pyroclastics the tacquet formation in southern serenitatis areas near hyginus crater and a dome in mare vaporum have lower backscatter cross sections than would be expected for mare basalts of similar estimated titanium content combined with very low cpr values this is strong evidence that these areas are covered in fine grained pyroclastic mantling material

the relationship between radar scattering and surface roughness of lunar volcanic features lunar roughness measurements derived from the lunar orbiter laser altimeter are compared to 12 6 cm wavelength radar data collected by the miniature radio frequency instrument and 70 cm wavelength radar data collected by the arecibo observatory these data are compared to assess how surface and subsurface roughness are correlated and affected by parameters including age and composition at length scales between 0 1 and 100 m a range of features are analyzed including volcanic domes marius hills rumker hills gruithuisen and mairan domes mare imbrium serenitatis and oceanus procellarum pyroclastic dark mantle deposits sinus aestuum sulpicius gallus and mare vaporum and two young craters copernicus and tycho statistically significant positive correlations exist between topographic roughness and both p and s band circular polarization ratios the strongest correlation is observed at the longest length scales correlations weaken as length scales become less similar potentially due to distinct processes controlling surface modification roughness is not significantly correlated with local slope although the marius hills are compositionally distinct from the gruithuisen and mairan domes they are indistinguishable in roughness characteristics conversely the rumker hills mare and dark mantle deposits are smoother at the length scales examined possibly due to fine grained mantling of regolith or pyroclastic deposits the floor and ejecta of tycho are the roughest surfaces measured in this study while the floor and ejecta of copernicus overlap the roughness distribution of the volcanic features this study shows that many factors control the evolution of roughness over time on various length scales

toroidal poloidal partitioning of plate motions since 120 ma changes in plate motions and plate configurations during the cenozoic and mesozoic have been investigated extensively but most geodynamical models have concentrated on present day plate motions we have investigated the recent evolution of plate tectonics by examining the history of toroidal poloidal partitioning of plate motions taking into account estimated errors our results suggest a significant increase in the ratio of toroidal to poloidal motions postdating the hawaiian emperor h e bend at 43 ma corresponding to an overall decrease in global plate motions these changes may reflect greater mantle plume activity in the mesozoic but a causal mechanism is not obvious in general observed cenozoic and mesozoic plate motions do not appear to be random which implies that they are correlated we also find perhaps three significant changes in net rotation of the lithosphere with respect to hotspots since 120 ma

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

global geologic maps are tectonic speedometers rates of rock cycling from area age frequencies relations among ages and present areas of exposure of volcanic sedimentary plutonic and metamorphic rock units lithosomes record a complex interplay between depths and rates of formation rates of subsequent tectonic subsidence and burial and or rates of uplift and erosion thus they potentially serve as efficient deep time geologic speedometers providing quantitative insight into rates of material transfer among the principal rock reservoirs processes central to the rock cycle areal extents of lithosomes exposed on all continents from two map sources geological survey of canada gsc and the food and agricultural organization fao of the united nations educational scientific and cultural organization unesco indicate that volcanic sedimentary plutonic and metamorphic rocks occupy 8 73 7 and 12 of global exposures respectively plots of area versus age of all mapped rock types display a power law relation where 6 5 of continental area is resurfaced with younger 10 volcanic 90 sedimentary units every million years and where areas of rock exposure decrease by 0 86 for each 1 increase in outcrop age r 2 0 90 area age relations for volcanic and sedimentary lithosomes are similar to the power law distribution defined by all rock units because 81 of mapped area consists of these two lithologies and reflect progressive decrease in amount of exposure with increasing age over the long term continental surfaces are blanketed by new volcanic rocks and sediments at rates of 1 5 and 12 1 10 6 km 2 ma respectively in contrast to power law distributed volcanic and sedimentary rocks that form at the earth9s surface age frequency distributions for plutonic and metamorphic rocks exhibit lognormal relations with modes at ca 154 and 697 ma respectively a dearth of younger exposures of plutonic and metamorphic rocks reflects the fact that these rock types form at depth and some duration of tectonism is therefore required for their exposure increasing modal ages from quaternary for volcanic and sedimentary successions to early mesozoic for intrusive rocks to neoproterozoic for metamorphic rocks demonstrate that greater amounts of geologic time are required for uplift to bring more deeply formed rocks to the earth9s surface the two different age frequency distributions observed for these major rock types a general power law age distribution for volcanic and sedimentary rocks and a lognormal distribution for plutonic and metamorphic rock ages reflect the interplay between depths of formation and mean rates of vertical tectonic displacement age frequency distributions for each of the major rock types are closely replicated by a model that presumes that individual crustal elements behave as a large population of random walks in geologic time and crustal depth and where the processes of surficial erosion associated with tectonic uplift serve to impose an absorbing boundary on this random walk space comparisons between model predicted age frequencies and those apparent in global map data suggest that mean rates of crustal subsidence and uplift are approximately equal in magnitude with mean rates of vertical tectonic diffusion of lithosomes from crustal depths of formation of about half a kilometer per million years rates of uplift and subsidence are strongly dependent on durations of tectonic dispersion lithosome ages however mean rates on the order of hundreds of meters per million years suggested by map age frequencies are the same as would be anticipated on the basis of hundreds of published rates of erosional uplift and exhumation determined by more conventional geochronometers this agreement suggests that geologic maps serve as effective deep time speedometers for the geologic rock cycle

quantitative bedrock geology of brazil 1 we quantitatively analyze the area age distribution of sedimentary igneous metamorphic and ultramafic bedrock on the basis of data from the digital geologic map of brazil published as a gis map by the brazilian geological survey bedrock units exclusively encompassing sedimentary rocks igneous rocks or metamorphic rocks cover 40 4 31 5 and 17 7 respectively of the total bedrock area these numbers have to be considered minimum estimates of the areal abundance of sedimentary igneous and metamorphic bedrock because polygons defined by mixed lithologies cover 8 5 9 5 of the total bedrock area these mixed units are sedimentary rocks with igneous and or metamorphic contributions 1 4 metamorphic rocks with sedimentary contributions 1 2 metamorphic rocks with igneous contributions 1 5 igneous rocks with sedimentary and or metamorphic contributions 4 4 and ultramafic units with sedimentary igneous and or metamorphic contributions 1 2 the average ages of major lithologic units weighted according to bedrock area are as follows sedimentary rocks average stratigraphic age of 248 5 1 myr median stratigraphic age of 87 5 myr igneous rocks 1153 13 1 myr metamorphic rocks 1678 30 1 myr and ultramafic rocks 1227 25 1 myr the average bedrock age of brazil is 946 7 1 myr the range in lithologic composition and age structure of the various bedrock units reflects the complex tectonic makeup of brazil that ranges from neogene sedimentary cover in the amazon basin to precambrian cratons guyana and brazilian shields and transamazonian greenstone belts the average spatial resolution of the data is 232 km2 polygon 1 and is sufficient to perform area age analyses of individual river drainage basins larger than 5 000 km2

lunar iron and titanium abundance algorithms based on final processing of clementine ultraviolet visible images the clementine mission to the moon returned global imaging data collected by the ultraviolet visible uvvis camera this data set is now in a final state of calibration and a five band multispectral digital image model dim of the lunar surface will soon be available to the science community we have used observations of the lunar sample return sites and stations extracted from the final dim in conjunction with compositional information for returned lunar soils to revise our previously published algorithms for the spectral determination of the feo and tio2 content of the lunar surface the algorithms successfully normalize the effects of space weathering so that composition may be determined without regard to a surface s state of maturity these algorithms permit anyone with access to the standard archived dim to construct high spatial resolution maps of feo and tio2 abundance such maps will be of great utility in a variety of lunar geologic studies

improved discrimination of volcanic complexes tectonic features and regolith properties in mare serenitatis from earth based radar mapping radar images at 70 cm wavelength show 4 5 db variations in backscatter strength within regions of relatively uniform spectral reflectance properties in central and northern mare serenitatis delineating features suggesting lava flow margins channels and superposition relationships these backscatter differences are much less pronounced at 12 6 cm wavelength consistent with a large component of the 70 cm echo arising from the rough or blocky transition zone between the mare regolith and the intact bedrock such deep probing is possible because the ilmenite content which modulates microwave losses of central mare serenitatis is generally low 2 3 by weight modeling of the radar returns from a buried interface shows that an average regolith thickness of 10 m could lead to the observed shifts in 70 cm echo power with a change in tio2 content from 2 to 3 this thickness is consistent with estimates of regolith depth 10 15 m based on the smallest diameter for which fresh craters have obvious blocky ejecta the 70 cm backscatter differences provide a view of mare flow unit boundaries channels and lobes unseen by other remote sensing methods a localized pyroclastic deposit associated with rima calippus is identified based on its low radar echo strength radar mapping also improves delineation of units for crater age dating and highlights a 250 km long east west trending feature in northern mare serenitatis that we suggest is a large graben flooded by late stage mare flows

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

geoid pangea and convection abstract we show that the present geoid has a simple low order configuration with an axis of symmetry in the equatorial plane we show further that it is a tennis ball pattern with an equatorial high belt and a polar low one which is clearly controlled by the rotation of the earth finally we show that the outline of pangea between at least 200 ma and 125 ma ago lay along a great circle passing through the paleo poles of rotation thus it also had an axis of symmetry in the equatorial plane this hemispheric super continent configuration ended in middle cretaceous time during a major geologic catastrophe which was accompanied by high rates of spreading hotspot outbreaks and high sea level stands we interpret this evidence in terms of separate steady state lower mantle convection responsible for the present geoid weakly coupled to the upper mantle one this weak coupling leads to the hemispheric continent configuration which ends when excessive heating of the upper mantle due to the insulating continental cap leads to continent dispersal the complete cycle from one supercontinent to the next might be of the order of 400 ma

terrestrial analogues for lunar impact melt flows abstract lunar impact melt deposits have unique physical properties they have among the highest observed radar returns at s band 12 6 cm wavelength implying that they are rough at the decimeter scale however they are also observed in high resolution optical imagery to be quite smooth at the meter scale these characteristics distinguish them from well studied terrestrial analogues such as hawaiian p hoehoe and a lava flows the morphology of impact melt deposits can be related to their emplacement conditions so understanding the origin of these unique surface properties will help to inform us as to the circumstances under which they were formed in this work we seek to find a terrestrial analogue for well preserved lunar impact melt flows by examining fresh lava flows on earth we compare the radar return and high resolution topographic variations of impact melt flows to terrestrial lava flows with a range of surface textures the lava flows examined in this work range from smooth hawaiian p hoehoe to transitional basaltic flows at craters of the moon cotm national monument and preserve in idaho to rubbly and spiny p hoehoe like flows at the recent eruption at holuhraun in iceland the physical properties of lunar impact melt flows appear to differ from those of all the terrestrial lava flows studied in this work this may be due to a differences in post emplacement modification processes or b fundamental differences in the surface texture of the melt flows due to the melts unique emplacement and or cooling environment information about the surface properties of lunar impact melt deposits will be critical for future landed missions that wish to sample these materials