the central anomaly magnetic high implications for ocean crust construction and evolution the central anomaly magnetic high camh is a long lineated short wavelength 10 km wide at the sea surface magnetic anomaly overlying many of the world s midocean spreading centers this anomaly is particularly well developed over the northern juan de fuca ridge including the northern symmetrical and endeavour segments the ubiquitous presence of this zone of high magnetic contrast directly in the zone of active oceanic plate formation is a key to our understanding of near axis crustal plate evolution recently obtained deep tow magnetometer data from segments of the juan de fuca spreading center have caused us to revise the present models of the source of the camh and to review the implications the new model would have on our understanding of the evolution of the magnetic structure of oceanic plates in this model we attribute the near axis magnetization contrast to tectonically controlled low temperature alteration of the upper vertical section of extrusive basement extensive and systematic fissuring of the upper extrusive rocks allows penetration of sea water and rapid alteration of the magnetic minerals in fissured areas approximately 3 km off axis the correlation between fissured crustal blocks and near bottom magnetic lows and unfissured crustal blocks with magnetic highs which is observed at the axis is also seen in a single off axis tow over an outer flanking ridge

models of the distribution and abundance of hydrogen at the lunar south pole 1 permanently shadowed locations at the lunar poles are potential sites for significant concentrations of cold trapped volatiles including water ice hydrogen enhancements are seen at the poles but the physical form abundance and distribution of this hydrogen remains controversial using a pixon based image reconstruction algorithm to effectively improve spatial resolution we derive maps of the lunar south polar water equivalent hydrogen concentration that are fully consistent with the orbital neutron measurements with abundances greater than 0 5 wt in some permanently shadowed locations this is much greater than the highest solar wind hydrogen abundance in returned lunar samples and may indicate ice between regolith grains if the hydrogen distribution is inhomogeneous within a permanently shadowed crater then even higher abundances are implied in shackleton crater for example the derived count rates are consistent with 10 of the crater floor area having 20 wt water equivalent hydrogen and the remainder at 0 25 wt

holocene water levels at rice lake ontario canada sediment pollen and plant macrofossil evidence four cores taken along a transect from the western basin and four cores from the middle basin of rice lake ontario provide evidence for shoreline transgression during the early holocene for low

why are marine magnetic anomalies suppressed over sedimented spreading centers the absence of lineated marine magnetic anomalies over sedimented recent spreading centers has been observed in several areas we propose that magnetic anomalies can be suppressed as a result of pervasive hydrothermal reactions underneath thick blankets of sediment the relatively impermeable sediment cover produces comparatively closed hydrothermal systems which increase the residence time of the hot fluids in basaltic layer 2 causing more thorough leaching of the remanence carrying iron titanium oxides and diminishing the marine magnetic anomalies this contrasts with lesser alteration at sparsely or unsedimented zones of extension with more open circulation conversely spreading ridges and oceanic crust characterized by absent or subdued lineated anomalies may signal sites of extensive hydrothermal mineralization this process might also provide an explanation for some magnetic quiet zones such as in the gulf of california the gulf of aden and the northern red sea

hydrothermal manganese plumes in the mid atlantic ridge rift valley the concentration of dissolved manganese in sea water can be used as a chemical tracer of hydrothermal activity on the underlying sea floor here we present vertical profiles of seawater manganese concentrations above the rift valley of the mid atlantic ridge mar the values obtained indicate the presence of plumes that are presently active generated by hydrothermal vents in the rift valley these plumes are confined to the rift valley and do not spill over into the adjacent deep ocean basins differences between them suggest that there are at least five hydrothermal sources along this 1 700 km long section of mid ocean ridge

unravelling the mystery of lunar anomalous craters using radar and infrared observations in miniature radio frequency mini rf radar images anomalous craters are those having a high circular polarization ratio cpr in their interior but not exterior to their rims previous studies found that most cpr anomalous craters contain permanently shadowed regions psrs and that their population is overabundant in the polar regions however there is considerable controversy in the interpretation of these signals both water ice deposits and rocks surface roughness have been proposed as the source of the elevated cpr values to resolve this controversy we have systematically analyzed 4000 impact craters with diameters between 2 5 and 24 km in the mini rf radar image and diviner rock abundance ra map we first constructed two controlled orthorectified global mosaics using 6818 tracks of mini rf raw data and then analyzed the correlations between radar cpr and surface slope rock abundance and depth diameter ratios of impact craters our results show that cpr anomalous craters are distributed relatively uniformly across the lunar surface with no apparent difference in cpr between the polar potentially icy and non polar not icy craters most cpr anomalous craters are relatively young with a large depth diameter ratio and they actually represent an intermediate stage of crater evolution comparison with a two component radar scattering model suggests that rocks and surface roughness are major contributors to the observed cpr values using craters of 4 7 22 km in diameter with known ages we find that craters spend up to 120 ma with a high exterior ra and 3 ga in the cpr anomalous phase

source of marine magnetic anomalies some results from dsdp leg 83 leg 83 of the deep sea drilling project represents the deepest penetration of undisturbed marine crust yet achieved providing samples from the lower part of the extrusive layer and the upper 300 m of the sheeted dike complex we present here measurements of the magnetic properties of rocks from leg 83 and address the question of their suitability as sources for marine magnetic anomalies we find that due to extensive hydrothermal alteration the extrusive part of the leg 83 section is insufficiently magnetized to be part of the magnetic source layer the sheeted dike complex on the other hand does have sufficient magnetization and contrary to recent models of marine magnetization based on ophiolite studies may be a contributor to magnetic anomalies the strong dependence of magnetic properties on the alteration history of the rocks however makes extension of these results to other regions problematical

relict hydrothermal zones in the tag hydrothermal field mid atlantic ridge 26 n 45 w two relict hydrothermal zones were delineated between water depths of 3400 and 3500 m at the lower part of the east wall of the rift valley of the mid atlantic ridge in the tag hydrothermal field using a deep towed side scan sonar tow and a camera temperature tow along the northern 3 km of the wall and a submersible transect named the north and mir relict zones they are located about 4 km and 2 km northeast respectively of the known active high temperature sulfide mound between water depths of 3625 and 3670 m on the rift valley floor near the base of the east wall the north zone extends about 2 km along the northern end of the lower east wall the zone includes two moundlike features up to 30 m high by 200 m in diameter imaged by side scan sonar within a 2 km long line of discontinuous hydrothermal deposits comprising inactive toppled and standing chimneys layered material and patchy dark stains on sediment photographed by the camera temperature tow several other moundlike features were imaged with the side scan sonar outside of the photographic coverage the mir relict hydrothermal zone 2 km south of the north zone named after the mir submersible used to investigate it consists of three subzones 1 a 200 m wide area of diverse types of hydrothermal materials exposed by normal faulting at its western margin 2 a 400 m wide by 700 m long central area of discrete groups of toppled and standing inactive sulfide chimneys up to 25 m high on a substrate of red metalliferous sediment and carbonate lutite spires sampled on the highest chimneys are composed of coarse grained recrystallized sulfides dominated by pyrite and chalcopyrite which contain the first primary free gold grains 2 3 m diameter found at a hydrothermal site on a mid ocean ridge and 3 a 150 m wide hummocky area of layered hydrothermal material with the appearance of low temperature precipitates and carbonate lutite with patchy dark stains at its eastern margin the active sulfide mound the north zone and the mir zone are each located on the fractured western margins of gentle dome shaped areas of pillow flows typically 500 m in diameter interpreted as summits of volcanic centers that may have supplied heat to drive adjacent hydrothermal activity the distribution and size of the active and inactive hydrothermal zones of the tag field the chronology and the characteristics of relict samples recovered indicate a history of at least 100 103 years of high temperature hydrothermal episodes with multiple overprinting stages of mineralization accompanied by alteration

analyzing the ages of south polar craters on the moon implications for the sources and evolution of surface water ice abstract surface water ice in the permanently shadowed polar regions of the moon has a patchy surficial distribution and is not found within all available cold trapping areas to date it is not well understood when the ice was delivered which has important implications for the surficial characteristics of the ice as well as for possible delivery mechanisms here we present absolute model ages for 20 south polar craters that host surface water ice providing maximum estimates of the ages of surface ice contained within these craters we quantify the amount of available cold trapping surface area that is occupied by water ice in order to examine the relationship between the patchiness of ice within each crater and the age of each host crater the majority of surface ice is contained in old craters 3 1 gyr where the majority of cold trapping area on the pole exists the ice is these ancient craters is very patchy in surficial distribution occupying siegler et al 2016 if true polar wander did occur on the moon then the ages of ice bearing craters presented here set an upper limit for the age of post true polar wander hydrogen emplacement of 4 1 0 1 gyr

active and relict sea floor hydrothermal mineralization at the tag hydrothermal field mid atlantic ridge the tag hydrothermal field is a site of major active and inactive volcanic hosted hydrothermal mineralization in the rift valley of the slow spreading mid atlantic ridge at 26 degree n the axial high is the principal locus of present magmatic intrusions the tag field contains three main areas of present and past hydrothermal activity 1 an actively venting high temperature sulfide mound 2 two former high temperature vent areas 3 a zone of low temperature venting and precipitation of fe and mn oxide deposits the volcanic centers occur at the intersections between ridge axis parallel normal faults and projected axis transverse transfer faults the intersections of these active fault systems may act as conduits both for magmatic intrusions from sources beneath the axial high that build the volcanic centers and for hydrothermal upwelling that taps the heat sources radiometric dating of sulfide samples and manganese crusts in the hydrothermal zones and dating of sediments intercalated with pillow lava flows in the volcanic center adjacent to the active sulfide mound indicate multiple episodes of hydrothermal activity throughout the field driven by heat supplied by episodic intrusions over a period of at least 140 times 10 sup 3 yr the sulfide deposits are built by juxtaposition and superposition during relatively long residence times near episodic axial heat sources counterbalanced by mass wasting in the tectonically active rift valley of the slow spreading oceanic ridge hydrothermal reworking of a relict hydrothermal zone by high temperature hydrothermal episodes has recrystallized sulfides and concentrated the first visible primary gold reported in a deposit at an oceanic ridge

radar imaging of the lunar poles long wavelength measurements reveal a paucity of ice in the moon s polar craters we have used a radio telescope at arecibo observatory puerto rico to map features of the lunar poles some as small as 300 metres across by collecting long wavelength radar images that can penetrate several metres of lunar dust we find that areas of the crater floors at the poles that are in permanent shadow from the sun which are potential cold traps for water or other volatiles do not give rise to strong radar echoes like those associated with thick ice deposits in the polar craters on mercury any lunar ice present within regions visible to the arecibo radar must therefore be in the form of distributed grains or thin layers

dielectric properties of asteroid vesta s surface as constrained by dawn vir observations abstract earth and orbital based radar observations of asteroids provide a unique opportunity to characterize surface roughness and the dielectric properties of their surfaces as well as potentially explore some of their shallow subsurface physical properties if the dielectric and topographic properties of asteroid s surfaces are defined one can constrain their surface textural characteristics as well as potential subsurface volatile enrichment using the observed radar backscatter to achieve this objective we establish the first dielectric model of asteroid vesta for the case of a dry volatile poor regolith employing an analogy to the dielectric properties of lunar soil and adjusted for the surface densities and temperatures deduced from dawn s visible and infrared mapping spectrometer vir our model suggests that the real part of the dielectric constant at the surface of vesta is relatively constant ranging from 2 3 to 2 5 from the night to day side of vesta while the loss tangent shows slight variation as a function of diurnal temperature ranging from 6 10 3 to 8 10 3 we estimate the surface porosity to be 55 in the upper meter of the regolith as derived from vir observations this is 12 higher than previous estimation of porosity derived from previous earth based x and s band radar observation we suggest that the radar backscattering properties of asteroid vesta will be mainly driven by the changes in surface roughness rather than potential dielectric variations in the upper regolith in the x and s band

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

evidence for water ice near the lunar poles improved versions of lunar prospector thermal and epithermal neutron data were studied to help discriminate between potential delivery and retention mechanisms for hydrogen on the moon improved spatial resolution at both poles shows that the largest concentrations of hydrogen overlay regions in permanent shade in the north these regions consist of a heavily cratered terrain containing many small less than 10 km diameter isolated craters these border circular areas of hydrogen abundance h that is only modestly enhanced above the average equatorial value but that falls within large flat bottomed and sunlit polar craters near the south pole h is enhanced within several 30 km scale craters that are in permanent shade but is only modestly enhanced within their sunlit neighbors we show that delivery by the solar wind cannot account for these observations because the diffusivity of hydrogen at the temperatures within both sunlit and permanently shaded craters near both poles is sufficiently low that a solar wind origin cannot explain their differences we conclude that a significant portion of the enhanced hydrogen near both poles is most likely in the form of water molecules

craters hosting radar bright deposits in mercury s north polar region areas of persistent shadow determined from messenger images 1 radar bright features near mercury s poles were discovered in earth based radar images and proposed to be water ice present in permanently shadowed areas images from messenger s one year primary orbital mission provide the first nearly complete view of mercury s north polar region as well as multiple images of the surface under a range of illumination conditions we find that radar bright features near mercury s north pole are associated with locations persistently shadowed in messenger images within 10 of the pole almost all craters larger than 10 km in diameter host radar bright deposits there are several craters located near mercury s north pole with sufficiently large diameters to enable long lived water ice to be thermally stable at the surface within regions of permanent shadow craters located farther south also host radar bright deposits and show a preference for cold pole longitudes thermal models suggest that a thin insulating layer is required to cover these deposits if the radar bright material consists predominantly of long lived water ice many small 10 km diameter and low latitude extending southward to 66 n craters host radar bright material and water ice may not be thermally stable in these craters for 1 gy even beneath an insulating layer the correlation of radar bright features with persistently shadowed areas is consistent with the deposits being composed of water ice and future thermal modeling of small and low latitude craters has the potential to further constrain the nature source and timing of emplacement of the radar bright material

the clementine bistatic radar experiment during the clementine 1 mission a bistatic radar experiment measured the magnitude and polarization of the radar echo versus bistatic angle beta for selected lunar areas observations of the lunar south pole yield a same sense polarization enhancement around beta 0 analysis shows that the observed enhancement is localized to the permanently shadowed regions of the lunar south pole radar observations of periodically solar illuminated lunar surfaces including the north pole yielded no such enhancement a probable explanation for these differences is the presence of low loss volume scatterers such as water ice in the permanently shadowed region at the south pole

nrm irm s demagnetization plots of intrusive rocks and the origin of their nrm abstract alternating field demagnetization characteristics of laboratory induced thermal remanence trm and saturation isothermal remanence irm s have been determined for a collection of samples representing the major intrusive rock types these results are compared to nrm irm s curves for the same intrusive specimens and for a smaller number of extrusive and high grade metamorphic rocks samples a number of the intrusive rock specimens which contained primary magnetic mineralogies display nrm irm s curves which are similar in character to their trm irm s counterparts the nrms of these samples are generally unidirectional and resistant to thermal demagnetization suggesting their thermal origin intrusive samples with dissimilar nrm irm s and trm irm s curves are often directionally unstable or contain secondary or altered magnetic mineralogies in contrast to the mixed behavior of the intrusive samples the nrms for a collection of extrusive rock samples are generally trm like whereas the nrms of high grade metamorphic rock samples more often display characteristics which are inconsistent with a simple thermal origin of nrm this study suggests that nrm irm s curves may be useful in evaluating whether the remanent magnetization of crystalline rocks is predominantly of primary or secondary origin

the 3 d geological model around chang e 3 landing site based on lunar penetrating radar channel 1 data high frequency lunar penetrating radar lpr data from an instrument on the lunar rover yutu from the chang e 3 ce 3 robotic lander were used to build a three dimensional 3 d geological model of the lunar subsurface structure the ce 3 landing site is in the northern mare imbrium more than five significant reflection horizons are evident in the lpr profile which we interpret as different period lava flow sequences deposited on the lunar surface the most probable directions of these flows were inferred from layer depths thicknesses and other geological information moreover the apparent imbrian paleoregolith homogeneity in the profile supports the suggestion of a quiescent period of lunar surface evolution similar subsurface structures are found at the nasa apollo landing sites indicating that the cause and time of formation of the imaged phenomena may be similar between the two distant regions

magnetic properties and opaque mineralogy of rocks from selected seafloor hydrothermal sites at oceanic ridges magnetic properties natural remanent magnetization nrm susceptibility curie point temperature tc saturation isothermal remanent magnetization irms and koenigsberger ratio q and opaque mineralogy were determined for basalts diabases gabbros peridotites and serpentinites collected by dredging and submersible from the rift valley at five hydrothermal sites 15 n 17 n 23 n the snake pit hydrothermal field 26 n the tag hydrothermal field on the mid atlantic ridge and 42 n the sea cliff hydrothermal field on the northern gorda ridge the magnetomineralogy is interpreted in terms of deuteric hydrothermal metasomatic and ambient seawater alteration evidence for unequivocal magnetic mineral modification by hydrothermal action is present only in a small percentage of extrusive basalts but is pervasive in diabases gabbros and ultramafic rocks this lithologiec distribution suggests a progressive increase in alteration intensity with depth in the oceanic crust and upper mantle from minor low temperature alteration in young surface basalts to more pervasive high temperature alteration in diabases gabbros and peridotites the studies reveal distinct correlations between magnetization intensity thermomagnetic behavior and magnetic mineralogy grain size style and intensity of alteration and rock type basalts have the highest nrm intensities and the lowest curie points 105 294 c basalts with nrm irms ratios less than 10 2 may have been remagnetized and have nrm intensities and q values much lower one third and one half respectively than basalts with nrm irms ratios of 10 2 or greater in the oceanic lithospheric suite examined remanent q 1 magnetization is present in basalts and induced magnetization q 1 occurs in metabasalts and the other rock types layer 2a basalts are the source of median valley magnetic anomalies the magnetic source may shift from the surface to deeper horizons with progressive seafloor aging and enhanced deuteric oxidation in layer 2b dikes and layer 3 gabbros and the formation of magnetite in serpentinized peridotites this shift is influenced by fluctuations in the curie isotherm related to the duration of active magma chambers and convective hydrothermal cells the magnetic and mineralogie properties of oceanic rocks determined show the effects of a wide range of alteration processes that are variously related to depth in oceanic lithosphere magmatic cooling history and hydrothermal circulation

age constraints of mercury s polar deposits suggest recent delivery of ice abstract surface ice at the poles of mercury appears as several m thick deposits that are composed of nearly pure water we provide new age estimates of the surfaces of mercury s polar deposits from combined analyses of poisson statistics and direct observations of crater densities within permanently shadowed radar bright regions imaged by the messenger spacecraft these age estimates conservatively suggest that ice was delivered to mercury within the last 330 myr the geologically young ages suggest that the surfaces have been recently refreshed and this may be accomplished by the delivery of ice in a young impactor or impactors a single recent impactor is more consistent with the relative purity of the ice as suggested by the earth based radar observations in contrast to ice on mercury observations of the lunar poles are suggestive of a highly patchy distribution of surface frost the patchiness of lunar polar deposits is consistent with long exposure times to the space weathering environment given enough time the polar deposits on mercury may age into a more heterogeneous spatial distribution similar to that on the moon

reduced crustal magnetization beneath the active sulfide mound tag hydrothermal field mid atlantic ridge at 26 n abstract a detailed near bottom magnetic field survey was carried out by the submersiblealvin over the actively venting mound located within the tag trans atlantic geotraverse hydrothermal field on the mid atlantic ridge at 26 08 n 44 49 w three dimensional analysis of these data clearly shows a distinct zone of reduced magnetization directly beneath the active mound this magnetization low is consistent with the highly altered upflow zone of a hydrothermal vent system that feeds the actively venting mound structure in contrast the sea surface magnetic anomaly is associated with a broad 2 8 km magnetization low elongated along the axis that includes both the active and inactive mounds the short wavelength 250 m near bottom magnetic anomaly over the active mound is far too small to produce the long wavelength 8 km sea surface magnetic anomaly at tag however and even a collection of mounds with similar magnetic structure cannot produce the magnetic moment needed to generate the sea surface anomaly other hypotheses including reversely magnetized crust and structurally thinned crust could account for the sea surface anomaly but are considered unlikely the existence of vigorous hydrothermal activity at tag and the lack of microseismic activity in the tag area suggests that thermal demagnetization is the prime contributor to the sea surface anomaly the thermal halo associated with a largely solid but still hot intrusion would provide sufficient demagnetization on a kilometer scale to produce the long wavelength sea surface anomaly pervasive alteration at depth would also be an important factor in the destruction of crustal magnetization and is the only way that such a long wavelength magnetic signal could be preserved in the crust the overall model of crustal magnetization at a hydrothermal field with discrete zones of demagnetization in the upper crust and a broader zone of demagnetization at depth is consistent with studies of hydrothermal systems in ophiolite suites these studies show narrow alteration pipes in the upper crust feeding the exhalative seafloor deposits and pervasive alteration at depth which commonly have associated late stage intrusive bodies 1 while detailed magnetic surveys may provide some clues to the location of oceanic hydrothermal upflow zones only drilling will ultimately test these hypotheses

an explanation of bright areas inside shackleton crater at the lunar south pole other than water ice deposits 1 whether water molecules of cometary and or solar wind origin migrated to and accumulated in cold permanently shadowed areas at the lunar poles has long been debated from the perspective of scientific interest and expectations for future utilization recently high reflectance condition was observed inside the lunar south pole shackleton crater for the 1064 4 nm of the lunar orbiter laser altimeter on the lunar reconnaissance orbiter and the high reflectance was explained to perhaps be due to a surface frost layer in excess of 20 water ice here we investigate the crater with the selenological engineering explorer multi band imager that has nine bands in the visible to near infrared range including a 1050 nm band 62 m pixel resolution part of the illuminated inner wall of shackleton crater exhibits high reflectance at 1050 nm but also exhibits the diagnostic 1250 nm spectral absorption a signature that is consistent with naturally bright purest anorthosite

microflint in archaeological sediments from boker tachtit israel a new method for quantifying concentrations of small flint fragments abstract flint is one of the most common rock types used for producing stone tools during flint knapping huge amounts of microscopic sized flint particles are produced thus the presence of high concentrations of microflint in a sedimentary layer could be a good indication that flint was knapped at that location we have developed and tested a method for quantification of microflint concentrations in sediments the method involves concentrating the microflints in specific density fractions and then counting a representative proportion of the flint fragments using a polarized light microscope we show that the method successfully identifies a knapping layer in an initial upper palaeolithic level at the site of boker tachtit israel this level also contains macroscopic flint debitage including refitted artifacts microflint quantification can aid in identifying knapping areas and be useful for better understanding site formation processes

quartz flakes in lakes microdebitage evidence for submerged great lakes prehistoric late paleoindian early archaic tool making sites exploration for submerged prehistoric archaeological sites in the great lakes north america is a major challenge due to difficulties in locating scant cultural artifacts in lake bottom sediments stone tool microfragments microdebitage 10 6 per tool and more dispersed around tool making sites but have not been identified previously in an underwater context to evaluate their use as a submerged site indicator microdebitage analysis was conducted on five lake sediment cores from a shallow lagoon adjacent to a long occupied prehistoric site mcintyre site rice lake ontario we identified 155 microdebitage fragments within a distinctive muddy peat horizon 2 2 5 m depth using light microscopy and scanning electron microscopy methods the microdebitage consisted of angular to very angular quartz fragments 400 1000 m with characteristic conchoidal fractures and flake scars produced by mechanical percussion the microdebitage horizon had a distinctive bimodal particle size peak and contained a low diversity soil thecamoebian assemblage phryaginella bullinularia sp indicative of a wetland environment that formed during an early holocene shoreline transgression accelerator mass spectrometry 14 c dating of wood fragments yielded ages of 9470 8760 50 yr b p 11 070 9560 cal calibrated yr b p indicating a late paleoindian early archaic age for the deposit results demonstrate that coring and microdebitage analysis are effective tools in the search for underwater prehistoric sites and can be employed more broadly in exploration of submerged landscapes in the great lakes basins

circular polarization ratio characteristics of impact craters from mini rf observations and implications for ice detection at the polar regions of the moon 1 in an attempt to reduce the ambiguity on radar detection of water ice at the permanently shadowed regions near the lunar poles radar echo strength and circular polarization ratio cpr of impact craters are analyzed using the miniature radio frequency mini rf radar data from the lunar reconnaissance orbiter mission eight typical craters among over 70 craters are selected and classified into four categories based on their locations and cpr characteristics polar anomalous polar fresh nonpolar anomalous and nonpolar fresh the influences on cpr caused by surface slope rocks and dielectric constant are analyzed quantitatively using high resolution topography data and optical images a two component mixed model for cpr that consists of a normal surface and a rocky surface is developed to study the effect of rocks that are perched on lunar surface and buried in regolith our analyses show that inner wall of a typical bowl shaped crater can give rise to a change of about 30 in local incidence angle of radar wave which can further result in a cpr difference of about 0 2 there is a strong correlation between mini rf cpr and rock abundance that is obtained from high resolution optical images and predictions from the two component mixed model match well with the observed cprs and the estimated rock abundances statistical results show that there is almost no apparent difference in cpr characteristics between the polar and nonpolar anomalous craters or between the polar and nonpolar fresh craters the enhanced cpr in the interior of anomalous craters is most probably caused by rocks that are perched on lunar surface or buried in regolith instead of ice deposits as suggested in previous studies

reduced crustal magnetization beneath relict hydrothermal mounds tag hydrothermal field mid atlantic ridge 26 n submersible magnetic profiles over the mir and alvin relict hydrothermal zones of the tag hydrothermal field on the mid atlantic ridge at 26 n show magnetic anomalies that are consistent with the presence of reduced crustal magnetization these magnetic anomalies are similar to the anomaly found associated with the tag active sulfide mound and suggests that hydrothermal alteration rather than thermal demagnetization is responsible for these reduced magnetization zones magnetic field mapping thus can be useful in determining the subsurface extent of upflow zones and alteration pipes of midocean ridge hydrothermal systems

spreading rate dependent magnetization of the oceanic lithosphere inferred from the anomalous skewness of marine magnetic anomalies summary the anomalous skewness of marine magnetic anomalies decreases with increasing spreading rate and becomes negligible above a spreading rate of about 50 km myr i previous magnetization models of the oceanic lithosphere fail to explain this observation we propose a new model in which the magnetic structure of the oceanic lithosphere is dependent on spreading rate anomalous skewness measurements for anomalies 33 reversed and 25 reversed at various spreading rates are in agreement with a magnetization model in which layer 3 and the uppermost mantle bear a similar saturation magnetization and the ratio of layer 3 over layer 2a saturation magnetizations varies linearly from about 0 4 at a spreading rate of 10kmmyr to about 0 at 55kmmyr i for spreading rates higher than 55 km myr layer 3 and uppermost mantle magnetizations are negligible recent advances concerning accretionary processes at mid ocean ridges suggest that the combined effect of variations with spreading rate of magma fractionation alteration of layer 2a and serpentinization of layer 3 and the uppermost mantle may account for the proposed variation of magnetization with spreading rate

magnetic properties of the bay of islands ophiolite suite and implications for the magnetization of oceanic crust rock magnetic properties opaque mineralogy and degree of metamorphism were determined for 101 unoriented samples from the north arm and blow me down massifs of the bay of islands ophiolite complex newfoundland the weathered and metamorphosed extrusive basalt samples have a weak secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin the initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation the magnetic intensity of the gabbroic samples increases as the degree of alteration increases with the highly altered upper metagabbros having an average intensity of 3 10 3 emu c3 because magnetization of the metagabbro samples is related to nonpervasive variable alteration these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies a compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer roughly 600 m thick with no contribution from a deeper source layer recognizable from these bay of islands data

serpentinized ultramafics and hydrothermal activity at the mid atlantic ridge crest near 15 n the initial occurrence of serpentinized ultramafic rocks at the nontransform intersection of a wall of a rift valley with the wall of a fracture zone is described from a site at the fifteen twenty fracture zone the ultramafics crop out in block faulted terrain on the upper portion of the eastern intersection between the rift valley and fracture zone walls in water depths between 2910 and 3300 m they comprise cumulate harzburgites pyroxenites iherzolites and wehrlites as well as gabbronorites olivine gabbronorites gabbropegmatites and alteration products including serpentinites bastite serpentinites and asbestos the ti zr y relations and relatively constant zr ti ratio in basalts recovered with the ultramafic rocks indicate a cogenetic relation from a common magmatic source that has undergone a late stage differentiation in the lower crust ongoing hydrothermal activity is indicated by chemical anomalies 3he mn in the near bottom water at the ultramafic outcrop the upwelling hydrothermal circulation apparently follows crust penetrating faults that may have controlled the diapiric ascent of the serpentinites and that continue to tap degassing magma and or mantle the observations presented indicate that ultramafic cumulates form beneath the rift valley adjacent to long offset 100 km ridge ridge transform faults where they are serpentinized by hydrothermal processes within the initial 1 106 years of generation of lithosphere at a slow spreading axis the corners formed by the intersections of the walls of a rift valley with both the transform rt corner and the nontransform rn corner portions of these fracture zones are principal loci of diapiric emplacement of serpentinized ultramafics

lunar polar craters icy rough or just sloping abstract circular polarisation ratio cpr mosaics from mini sar on chandrayaan 1 and mini rf on lro are used to study craters near to the lunar north pole the look direction of the detectors strongly affects the appearance of the crater cpr maps rectifying the mosaics to account for parallax also significantly changes the cpr maps of the crater interiors it is shown that the cprs of crater interiors in unrectified maps are biased to larger values than crater exteriors because of a combination of the effects of parallax and incidence angle using the lola digital elevation map dem the variation of cpr with angle of incidence has been studied for fresh craters cpr 0 7 with only a weak dependence on angle of incidence or position interior or just exterior to the crater consistent with dihedral scattering from blocky surface roughness for anomalous craters the cpr interior to the crater increases with both incidence angle and distance from the crater centre central crater cprs are similar to those in the crater exteriors cpr does not appear to correlate with temperature within craters furthermore the anomalous polar craters have diameter to depth ratios that are lower than those of typical polar craters these results strongly suggest that the high cpr values in anomalous polar craters are not providing evidence of significant volumes of water ice rather anomalous craters are of intermediate age and maintain sufficiently steep sides that sufficient regolith does not cover all rough surfaces

crustal structure interpreted from magnetic anomalies this review discusses publications during the last quadrennium 1987 1990 that used aeromagnetic data marine magnetic data satellite magnetic data and rock magnetic and petrologic data to provide information on the sources of magnetic anomalies the publications reviewed reflect increased integration of rock magnetic property and petrologic studies with magnetic anomaly interpretation studies particularly in deep crustal magnetization exploration for hydrocarbons and inversion of marine magnetic anomalies interpretations of aeromagnetic data featuring image display techniques and using the horizontal gradient method for locating magnetization boundaries became standard

paleomagnetism of the samail ophiolite oman 1 the sheeted dike complex at ibra we have studied the rock magnetism and paleomagnetism of 200 oriented samples from the middle cretaceous sheeted dike sequence of the samail ophiolite oman the samples are from 28 sites spanning a cross strike distance of 30 km most of the dikes have undergone green schist metamorphism the natural remanent magnetization nrm of the samples is about 1 a m and qn is also near 1 thermal and alternating field demagnetization treatment resolves both normal north and reversed south polarities about one third of the samples have low median destructive fields mdf less than 100 oe 7 96 103 a turn m these low mdf samples have scattered directions and are classified as undetermined polarities u hysteresis measurements show pseudo single domain carriers predominate in all samples although the low mdf samples are suggested to have the largest grains in the samples studied thermomagnetic curves show both magnetite and minor maghemite thermal demagnetization and microscopic study reveals that hematite is abundant and is the carrier of the r remanence in addition several dikes exhibit both n and r polarities these facts coupled with the degree of metamorphism indicate that part of the remanence is secondary and could be due to hydrothermal metamorphism below the seafloor we suggest that the n polarity is primary and resides in exsolved magnetite while the r polarity is secondary and resides primarily in metamorphic origin hematite several short r events observed in the albian through cenomanian magnetostratigraphic record are candidates for the r event in the ophiolite if the r polarity originated near the spreading center alternately nonreproducible self reversal is another possible origin for the r polarity regardless of whether the reversal originated at the spreading center secondary magnetization in the dikes considerably increases the directional dispersion another major factor affecting dispersion is viscous remanent magnetization vrm in the larger magnetite grains this extreme dispersion disallows the samail ophiolite dike layer as a significant source for marine magnetic anomalies regardless of the strength of the nrm or the value of q the stable n and r directions yield a paleomagnetic pole which is far sided suggesting northward movement of the ophiolite however the paleomagnetic pole is not as far sided as the contemporaneous africa pole which suggests a component of north south closure between the ophiolite and africa prior to northward movement

drilling the snake pit hydrothermal sulfide deposit on the mid atlantic ridge lat 23 sup 0 22 n a major high temperature hydrothermal area has been discovered in the mid atlantic ridge rift valley about 25 km south of the kane fracture zone the vent field consists of a wide area 40 000 m sup 2 of dark hydrothermal deposits numerous sulfide chimneys and mounds some up to 11 m high and high temperature black smoker vents ten shallow holes the first ever drilled in an active submarine hydrothermal area recovered friable unconsolidated fe cu fe and zn sulfides and several large fragments of massive sulfide mainly chalcopyrite from the locally thick 13 m hydrothermal deposits the vents are also associated with an unusual biological community of smaller more mobile organisms than reported from the east pacific rise

identification of experimental quartz microdebitage from rock engravings many aboriginal rock engravings in australia have been pecked or abraded into sandstone outcrops the engraving process produces some fine 1 mm diameter sediment or microdebitage which is derived both from the outcrop surface and the stone pecking tool quartz grains constitute a relatively durable component of microdebitage comparisons were made between quartz grains derived from experimental microdebitage and those occurring naturally in sediments in the arid broken hill area australia and in coastal dunes and weathered building stone in sydney warm temperate climate visual assessment of the roundness of quartz grains was made from scanning electron micrographs experimental microdebitage was angular in shape contrasting with the subrounded grains in the original sandstone in the nearby soil and in coastal dunes near sydney quartz grains from sandstone in a sydney building weathered in the city environment into angular to very angular grains surface features usually associated with mechanically crushed grains and microdebitage were recognized in experimental microdebitage but not in quartz grains derived from other sources if quartz microdebitage could be identified in natural sediments and dated using single grain optically stimulated luminescence information would be gained about periods of engraving activity copyright 2001 john wiley sons ltd

multi proxy lake sediment record of prehistoric paleoindian archaic archaeological paleoenvironments at rice lake ontario canada abstract the arrival of paleoindian peoples in the lower great lakes ca 11 5 ka cal bp coincided with a phase of lowstand lakes and rapid environmental change in southern ontario at rice lake an archaeologically rich area north of lake ontario rising early holocene water levels inundated wetland areas exploited by paleoindian and archaic peoples in order to better understand the distribution of submerged archaeological sites and the water level history of rice lake a detailed multi proxy study was conducted on two vibracores extracted from the open lake and a shallow the basin stratigraphy consisted of holocene organic rich muds gyttja laminated marls and peats overlying glacial lake iroquois sands and clay deposits two erosional hiatuses indicating lowstand phases eh 1 ca 12 5 11 ka cal bp eh 2 ca 6 3 ka cal bp were identified by rapid shifts in particle size and thecamoebian abundance and assemblages the dominant thecamoebian species in the open lake basin were arcella vulgaris and centropyxis constricta aerophila indicating the trophic status of the lake has remained stable throughout the holocene in the mcintyre lagoon the eh 1 lowstand was associated with a unique bog and wetland species bullinularia and phryganella sp along with the recovery of microdebitage indicating that paleoindian peoples were likely exploiting wetland resources such as plants fish and waterfowl we show that the study of lacustrine paleoenvironments using a multi proxy approach provides additional information for identifying areas of archaeological potential and gaining additional understanding of settlement patterns and resource procurement strategies of paleoindian and archaic peoples in southern ontario

high resolution near bottom vector magnetic anomalies over raven hydrothermal field endeavour segment juan de fuca ridge high resolution near bottom vector magnetic data were collected by remotely operated vehicle jason over the raven hydrothermal vent field 47 57 3 n 129 5 75 w located north of main endeavour vent field on the endeavour segment of the juan de fuca ridge the survey was part of a comprehensive heat flow study of the raven site using innovative thermal blanket technology to map the heat flux and crustal fluid pathways around a solitary hydrothermal vent field raven hydrothermal activity is presently located along the western axial valley wall while additional inactive hydrothermal deposits are found to the nw on the upper rift valley wall magnetic inversion results show discrete areas of reduced magnetization associated with both active and inactive hydrothermal vent deposits that also show high conductive heat flow higher spatial variability in the heat flow patterns compared to the magnetization is consistent with the heat flow reflecting the currently active but ephemeral thermal environment of fluid flow while crustal magnetization is representative of the static time averaged effect of hydrothermal alteration a general nw to se trend in reduced magnetization across the raven area correlates closely with the distribution of hydrothermal deposits and heat flux patterns and suggests that the fluid circulation system at depth is likely controlled by local crustal structure and magma chamber geometry magnetic gradient tensor components computed from vector magnetic data improve the resolution of the magnetic anomaly source and indicate that the hydrothermally altered zone directly beneath the raven site is approximately 15 106 m3 in volume

crustal magnetization in the south atlantic from inversion of magnetic anomalies a method for inverting magnetic anomalies in the presence of topography parker and huestis 1974 is used to analyze and describe crustal magnetization along 12 profiles in the south atlantic the profiles are approximately 2000 km long and are almost perpendicular to the trend of the magnetic anomalies a bandpass filter is used to remove long wavelength anomalies unassociated with seafloor spreading processes a filter that passes only wavelengths between 200 and 3 km produces a magnetization that approximates the positive and negative aspects of the geomagnetic reversal sequence the positive aspects originating from normally magnetized portions of the crustal source and negative aspects originating from reversely magnetized portions of the crustal source a 6 km thick crust is assumed in order to produce magnetizations consistent with dredged oceanic rocks a long wavelength pattern is evident in the magnetization solutions the highest magnetizations are associated with the ridge crest 1 35 1 74 a m within the western section of the study area a sharp decrease in magnetization occurs within 100 km of the ridge crest 4 5 ma a minimum in magnetization is reached at 400 km from the axis or at 18 ma 0 51 0 57 a m the magnetization then gradually increases out to 1100 km from the ridge axis or 50 ma 0 91 0 93 a m and dramatically decreases to 1900 km or 86 ma 0 34 0 43 a m within the eastern section of the study area a sharp decrease in magnetization occurs within the first 100 km of the ridge crest 5 ma a minimum in the magnetization occurs at approximately 400 km from the ridge axis or at 20 ma 0 54 0 56 a m the magnetization then gradually increases out to 1200 km from the ridge axis or to 60 ma 1 15 1 24 a m an overall pronounced decrease occurs to 1900 km from the ridge axis or to 95 ma 0 36 0 40 a m in order to explain this behavior the field intensity may have changed with a time scale of several millions of years alternatively the higher magnetizations at 50 60 ma could be explained by a uniform intensity of magnetization in a thicker crust

the characteristics and significance of secondary magnetite in a profile through the dike component of the troodos cyprus ophiolite secondary magnetite sm is the dominant fe ti oxide over a 3 4 km thick vertical interval in a profile through the troodos cyprus ophiolite sm is important in dikes and flows where dike density exceeds about 30 within the transition from extrusives to sheeted dikes and remains important until dike density falls below about 30 in the transition from sheeted dikes to plutonics the association of sm with high dike density suggests that it is a product of the thermal metamorphism of hydrothermally metamorphosed dikes and flows the most common occurrence of sm is at the site of primary titanomagnetites that had been altered earlier through deuteric low temperature and regional hydrothermal alteration processes sm often closely pseudomorphs the form of primary magnetite pm grains but it can be distinguished from pm using a series of criteria sm is low in tio2 and other impurities estimated and observed curie temperatures are undistinguishable which combined with optical evidence indicates tha

initial observations from the lunar orbiter laser altimeter lola as of june 19 2010 the lunar orbiter laser altimeter an instrument on the lunar reconnaissance orbiter has collected over 2 0 10 9 measurements of elevation that collectively represent the highest resolution global model of lunar topography yet produced these altimetric observations have been used to improve the lunar geodetic grid to 10 m radial and 100 m spatial accuracy with respect to the moon s center of mass lola has also provided the highest resolution global maps yet produced of slopes roughness and the 1064 nm reflectance of the lunar surface regional topography of the lunar polar regions allows precise characterization of present and past illumination conditions lola s initial global data sets as well as the first high resolution digital elevation models dems of polar topography are described herein

variations in magnetization intensity and low temperature titanomagnetite oxidation of ocean floor basalts the remanent magnetization of the oceanic crust exhibits a systematic long term variation which correlates with the amplitudes of marine magnetic anomalies after a sharp initial decrease of natural remanent magnetization intensity a minimum is reached at 20myr followed by a gradual increase up to ages of 120 myr the progressive sea floor alteration of the magnetic minerals carrying the crustal magnetism is proposed as a cause for this behaviour

a geologic model for lunar ice deposits at mining scales abstract water ice has been detected at the lunar poles but existing and near future orbital datasets do not have the capabilities to determine its horizontal and vertical distribution at meter to hundred meter scales relevant for mining operations additionally there has not yet been a coherent geologic model put forward for how ice deposits have formed and evolved that can be used to assist in planning prospecting campaigns or developing relevant hardware here we propose a system model for understanding these deposits at scales of meters to hectares the model considers sources of water ice capture at and below the surface and retention it focuses heavily on impact gardening as a modifying process that drives changes in how ice is distributed 3 dimensional stochastic impact simulations are then used to test the system model and explore how ice deposits might evolve over an area the size of a potential mining outpost the simulation results showed ice concentrations should eventually become fairly homogeneous at meter to hectare scales due to impact gardening and high concentrations are distributed randomly rather than clustered in earth like ore bodies we found the best ice deposits for extracting likely exist 10s of cm deep or more even in locations where ice is currently stable at the very surface terrestrial mining software was then used to create block models and grade tonnage curves that can inform future in situ resource utilization demonstration missions and future mining operations planning

the iceland research drilling project crustal section variation of magnetic properties with depth in icelandic type oceanic crust an attempt has been made to identify the processes that give rise to a number of depth trends in the magnetization of a 3 1 km vertical section of icelandic type oceanic crust and to assess the possibility that similar processes act and depth trends occur in typical oceanic crust the depth trends in the icelandic section consist of a general increase in saturation and induced magnetization to 2 km crustal depth below which flow magnetization decreases while dike magnetization remains constant and of large changes in flow magnetization that occur on a scale of a few hundred metres below 3 km crustal depth increase in saturation and induced magnetization with depth in the upper 2 km is thought to be the result of two processes a decrease in low temperature oxidation from the original lava surface to 700 800 m crustal depth thence an increase in hydrothermal alteration with depth this interpretation is based on oxide petrography and curie temperatures which show a weakly defined minimum in the 700 8

paleomagnetism of the samail ophiolite oman 2 the wadi kadir gabbro section four stratigraphic vertical transects were obtained from the gabbroic and ultramafic section of the samail ophiolite middle cretaceous age the transect through wadi kadir was the most detailed 65 independent oriented cores were obtained from 22 sites on a 14 km traverse from field mapping we infer that this traverse corresponds to a vertical section of 6 0 km which includes sheeted dikes plagiogranites isotropic high level gabbro transitional gabbro cumulate gabbros cumulate ultramafics and ultramafic rocks there are some noticeable variations in magnetic mineralogy with depth 1 primary exsolved magnetite is found mainly in the late stage high level gabbro and 2 secondary magnetite is found mainly in the upper 3 5 km of the cumulate gabbros and in the cumulate ultramafics most of the gabbros have a stable magnetization direction that is almost horizontal and slightly west of north the median natural remanent magnetization nrm intensity for the cumulate gabbros is 0 93 a m the median qn value is 3 0 with most values falling in the range of 1 to 5 the ultramafic rocks below the gabbroic layer are more strongly magnetized due to higher concentrations of secondary magnetite and their magnetization is more stable to af demagnetization than that of the overlying gabbros it is not clear what fraction of their magnetization was acquired beneath the seafloor because some of the serpentinization is thought to be of subaerial origin hysteresis measurements on the gabbros suggest that the magnetic carriers in the gabbros are a few tenths of microns in diameter pseudo single domain the magnetic properties of the cumulate gabbro section divide it into an upper intensely magnetized layer 3 5 km thick and a lower weak layer 2 km thick this was also found for the point sal ophiolite california the low intensities below 2 km are in agreement with petrological observations of a minimum in the concentration of secondary magnetite the upper intense layer can contribute over one half of the amplitude of any marine magnetic anomaly which might have existed when the ophiolite was submarine the serpentinized rocks also are possible contributors to anomaly amplitude consideration of the probable variations in the magmatic and hydrothermal history of the ocean crust and comparison of our results to other studies indicate that it may not be possible to specify a generalized magnetic source model for the plutonic section of the ocean crust

predynastic human presence discovered by core drilling at the northern nile delta coast egypt a small but significant find made during a geological survey provides evidence of the oldest human presence yet discovered along the northernmost margin of egypt9s nile delta a manuport a rock fragment carried by human agency to the site was discovered in a sediment core section north of burullus lagoon near the mediterranean coast accelerator mass spectrometry ams radiocarbon analysis of plant rich matter in the mud surrounding the object provides a date calibrated to 3350 3020 b c the late predynastic period this long thin manuport formed of dolomite had not been deposited by the nile or the sea but was collected and transported from an outcrop exposure positioned at least 160 km south of the core site the fragile manuport used for an undetermined function lay buried at a depth of 7 4 m in dark olive gray mud deposited in a shallow brackish lagoon setting close to a marsh this fortuitous find documents an early human presence in the middle holocene wetlands along the delta9s paleocoast a sector where traditional excavation and augering are normally incapable of reaching occupation levels or zones of activity at considerable subsurface depths core drilling provides a means to help archaeologists locate undetected and potentially important sites

an upper limit for ice in shackleton crater as revealed by lro mini rf orbital radar 1 although diverse measurements have indicated h oh or h2o species in the lunar polar regions pinpointing its location form and abundance in specific reservoirs has proven elusive here we report on the first orbital radar measurements of shackleton crater near the lunar south pole mini rf observations indicate a patchy heterogeneous enhancement in cpr circular polarization ratio on the crater walls whose strength decreases with depth toward the crater floor a result that is most consistent with a roughness effect due to less mature regolith present on the crater wall slopes however the results do not rule out a modest ice contribution and an upper limit of 5 10 wt h2o ice up to 30 vol present in the uppermost meter of regolith is also consistent with the observations

nrm irm s demagnetization plots an aid to the interpretation of natural remanent magnetization af demagnetization of thermoremanent magnetization trm and saturation isothermal remanent magnetization irm s are used to establish diagnostic criteria for primary trm and for secondary magnetization in igneous rocks in applying the approach to the interpretation of natural remanent magnetization nrm the demagnetization of irm s documents the nature of the magnetic phases in the rock while the demagnetization of the nrm gives information about the process of magnetization the ratio of nrm irm s measures the efficiency of the magnetization process

black smokers massive sulphides and vent biota at the mid atlantic ridge the discovery of black smokers massive sulphides and vent biota in the rift valley of the mid atlantic ridge demonstrates that this assemblage of hydrothermal phenomena is not limited to intermediate to fast spreading oceanic ridges hydrothermal exchange processes may thus be important at the ridges which extend through the atlantic ocean and western indian ocean comprising more than half of the 55 000 km global length of seafloor spreading centres

subsurface migration of h2o at lunar cold traps 1 permanently shaded areas near the poles of the moon and mercury may harbor water ice we develop a physical model for migration of water molecules in the regolith and discover two pathways that can lead to accumulation of h2o in the subsurface a small fraction of water molecules delivered either continuously or abruptly to permanently cold areas diffuses into the regolith and can remain there longer than on the surface higher temperatures lead to deeper burial at constant temperature this diffusive migration produces less than one molecular layer of volatile h2o on grains because it is driven by differences in surface concentrations the water is therefore expected to be in adsorbed form and the amount stored in this fashion could be at most a few hundred ppm of h2o a second pathway is pumping by diurnal temperature oscillations from a transient ice cover that may have formed during a large comet impact it can lead to high ground ice densities but the ground ice layer lasts not long beyond the disappearance of the ice cover both types of subsurface charging mechanism work best for temperatures typical of permanently shaded areas with sunlit surfaces in their field of view

no evidence for thick deposits of ice at the lunar south pole the rim of the shackleton crater at the lunar south pole is a candidate crash site for nasa s lcross probe lunar crater observation and sensing satellite due to launch in 2008 the plume of debris kicked up by the crash is to be analysed in the hope that it will reveal the water thought to be there suggestions of lunar ice date from 1996 when data from the clementine spacecraft gave some indications of the presence of ice on crater walls at the south pole now using high resolution radar imagery the radar scattering parameter thought indicative of thick ice deposits has been found also to match radar echoes from the rock strewn walls and ejecta of young impact craters at all lunar latitudes there is no evidence for thick ice though there could be grains of water ice spread more thinly through the lunar soil shackleton crater at the moon s south pole has been suggested as a possible site of concentrated deposits of water ice on the basis of modelling of bi static radar polarization properties and interpretations of earlier earth based radar images1 2 this suggestion and parallel assumptions about other topographic cold traps is a significant element in planning for future lunar landings hydrogen enhancements have been identified in the polar regions3 but these data do not identify the host species or its local distribution the earlier earth based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties cold traps in permanently shadowed areas and local terrain features such as the walls and ejecta of small craters here we present new 20 m resolution 13 cm wavelength radar images that show no evidence for concentrated deposits of water ice in shackleton crater or elsewhere at the south pole the polarization properties normally associated with reflections from icy surfaces in the solar system4 5 6 were found at all the observed latitudes and are strongly correlated with the rock strewn walls and ejecta of young craters including the inner wall of shackleton there is no correlation between the polarization properties and the degree of solar illumination if the hydrogen enhancement observed by the lunar prospector orbiter3 indicates the presence of water ice then our data are consistent with the ice being present only as disseminated grains in the lunar regolith

bistatic radar observations of the moon using mini rf on lro and the arecibo observatory the miniature radio frequency mini rf instrument aboard nasa s lunar reconnaissance orbiter lro is a hybrid dual polarized synthetic aperture radar sar that operated in concert with the arecibo observatory to collect bistatic radar data of the lunar nearside from 2012 to 2015 the purpose of this bistatic campaign was to characterize the radar scattering properties of the surface and near surface as a function of bistatic angle for a variety of lunar terrains and search for a coherent backscatter opposition effect indicative of the presence of water ice a variety of lunar terrain types were sampled over a range of incidence and bistatic angles including mare highland pyroclastic crater ejecta and crater floor materials responses consistent with an opposition effect were observed for the ejecta of several copernican aged craters and the floor of the south polar crater cabeus the responses of ejecta material varied by crater in a manner that suggests a relationship with crater age the response for cabeus was observed within the portion of its floor that is not in permanent shadow the character of the response differs from that of crater ejecta and appears unique with respect to all other lunar terrains observed analysis of data for this region suggests that the unique nature of the response may indicate the presence of near surface deposits of water ice

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

drowned forests and archaeology on the continental shelf of british columbia canada we have used high resolution digital terrain imaging and sea floor sampling to reveal drowned late glacial to early postglacial terrestrial landscapes at water depths as great as 150 m in situ tree stumps and shellfish rich paleobeaches are present on these drowned landscapes a stone tool encrusted with barnacles and bryozoa was recovered from a drowned delta flood plain now 53 m below mean sea level this is the first tangible evidence that the formerly subaerial broad banks of the western north american continental shelf may have been occupied by humans in earliest holocene and possibly late glacial time analyses 14 c of the drowned terrestrial and intertidal deposits were used to refine the local sea level curve which shows very rapid change within this glacio isostatically dynamic region

reconstruction of post iroquois shoreline evolution in western lake ontario when lake iroquois drained between 11 7 and 11 4 ka bp lake level in the ontario basin fell from a high of more than 40 m above present lake level to a minimum close to the then existing sea level which was approximately 40 m below present sea level since that time lake level has been rising at an exponentially decreasing rate in the western portion of the basin as a result of postglacial and neotectonic uplift of the outlet near kingston at the eastern end the published lake level history has been combined with other less well known parameters the post iroquois regional topography erosion deposition rates and distribution of resistive shore materials to reconstruct the evolution of the western lake ontario shoreline borehole long piston core and other subsurface data sources primarily from the western portion of the lake near hamilton harbour provide most of the physical constraints time references were provided by radiocarbon dates on shallow water organics in the subsurface sediments

holocene paleoshorelines water levels and submerged prehistoric site potential of rice lake ontario canada abstract rice lake located in the eastern great lakes of north america has a high density of prehistoric 11 0 5 ka bp terrestrial archaeological sites it has been speculated that a large number of sites are submerged on the lakebed as lake levels have risen 9 m since the arrival of early paleoindian peoples 11 ka bp in order to better understand the submerged landscape and its archaeological potential a detailed bathymetric survey and sediment coring program was conducted across a 30 km 2 area of northeastern rice lake changes in holocene water levels and shoreline positions were reconstructed by integrating core data with a digital elevation and bathymetric model debm that accounted for differential isostatic uplift and basin sedimentation the debm was used to generate a series of maps showing changes in the lake paleobathmetry and paleogeography and areas of prehistoric archaeological potential isostatic uplift of the eastern basin outlet 30 m had a dramatic influence on water levels and shoreline positions since the inception of rice lake 12 ka bp during the early paleoindian occupation phase 11 10 5 ka bp water levels were at a maximum lowstand 10 m bpl and much of the present lakebed was an exposed lake plain with extensive wetlands at the time of the late paleoindian early archaic occupation 9 5 8 7 ka bp 11 150 9560 cal bp the lake was about half its modern extent and during the second lowstand phase 4 m bpl and the lake became hydrologically closed after 4000 cal bp water levels recovered and the lake approached its modern extents an archaeological potential map based on the reconstructed paleoshorelines identified four areas with archaeological potential these include drowned river mouths submerged wetlands and an area of uplifted early holocene lakebed in northeast rice lake the results illustrate that isostatically driven changes in lake paleobathymetry can be substantial and must be accounted for when attempting to reconstruct paleoshoreline positions the approach can be applied more broadly to other basins within the great lakes and elsewhere to assess prehistoric site archaeological potential

drowned coastal deposits with associated archaeological remains from a sea level slowstand northwestern gulf of maine usa drowned terrestrial wetland environments such as lakes marshes and beaches were thought to be rare in formerly glaciated regions like the gulf of maine united states in the northwestern gulf of maine postglacial relative sea level changes include a slowstand between 11 5 ka and 7 5 ka when the ocean rose 5 m this period of sea level stability permitted erosion of glacial materials and concomitant construction of spits and sheltered wetland habitats attractive to human occupation between 17 m and 22 m below modern sea level this work underscores the importance of a well constructed sea level chronology to predict the location of drowned terrestrial environments and associated cultural resources

lack of exposed ice inside lunar south pole shackleton crater the inside of shackleton crater at the lunar south pole is permanently shadowed it has been inferred to hold water ice deposits the terrain camera tc a 10 meter resolution stereo camera onboard the selenological and engineering explorer selene spacecraft succeeded in imaging the inside of the crater which was faintly lit by sunlight scattered from the upper inner wall near the rim the estimated temperature of the crater floor based on the crater shape model derived from the tc data is less than 90 kelvin cold enough to hold water ice however at the tc s spatial resolution the derived albedo indicates that exposed relatively pure water ice deposits are not on the crater floor water ice may be disseminated and mixed with soil over a small percentage of the area or may not exist at all

microdebitage analysis initial considerations abstract microdebitage is defined as all stone flaking residue less than 1 mm in maximum dimension experimental replication indicates that it is produced in great quantities by stone tool manufacture and can permeate site matrices as a permanent signature of past cultural activity initial sampling studies suggest that microdebitage analysis may have considerable utility as a means of lithic site surveying

magnetic modeling near selected areas of hydrothermal activity on the mid atlantic and gorda ridges sea surface magnetic and bathymetric data from two areas of observed high temperature hydrothermal activity in the atlantic trans atlantic geotraverse or tag hydrothermal field and pacific sea cliff hydrothermal field and two areas of inferred hydrothermal activity in the atlantic mid atlantic ridge mar at 15 n and 17 n were studied to determine the effect of vent activity on magnetization of the oceanic crust all of the sites examined show a low in the magnetic anomaly in varying degrees magnetization lows within the axial marine magnetic anomaly have been associated with some areas of active and relict high temperature hydrothermal venting a three dimensional magnetic inversion was performed on magnetic and bathymetric data from the tag hydrothermal area on the mid atlantic ridge 26 n and two dimensional magnetic inversions were done on individual profiles from the other study sites the map from the tag area shows a negative in the crustal magnetization solution just to the east of the median valley axis which encompasses the active hydrothermal area a low in magnetization continues up the eastern wall which suggests alteration of the crust a distinct low in magnetization is present within the axial anomaly at the sea cliff hydrothermal field located on the eastern wall of the gorda ridge the magnetization low becomes less pronounced farther south of the known vent field profiles from 15 n and 17 n on the mid atlantic ridge show magnetization lows over areas of inferred hydrothermal activity these lows are present over the the eastern and western walls of the median valley respectively the lows observed in the axial marine magnetic anomaly in these four study sites all occur slightly off axis on crust that is at least 200 000 years old on the mid atlantic ridge and at least 100 000 years old on the gorda ridge on the basis of magnetic modeling and measurements of rock magnetic properties the most probable cause of the low in the magnetization is alteration of the oceanic crust with other subsidiary contributing factors which vary from site to site the magnetization low over tag is most probably due to high temperature hydrothermal alteration of the crust and a thinner layer 2 with possible contributions from reversal events and magma chamber curie isotherm effects the low near the sea cliff hydrothermal field on the gorda ridge is probably the product of tectonically controlled low temperature nonhydrothermal alteration high temperature hydrothermal alteration and magnetic reversal events at 15 n and 17 n on the mar the lows may be produced by alteration of the crust due to possible hydrothermal activity

the iceland research drilling project crustal section stable remagnetization below 3 km crustal depth a section at below 3 1 km depth in icelandic crust sampled in the 1978 icelandic research drilling project drill hole contains a number of subaerially deposited lava flows showing both downwards and probably original upwards inclinations of cleaned stable remanent magnetization such mixed polarities are inconsistent with an initial cooling thermoremanent origin for the magnetization an attempt is made to identify the factors involved in producing these mixed polarities and to consider the possible wider importance of the results the mixed polarity flows have experienced intense hydrothermal alteration followed by the widespread deposition of secondary magnetite secondary magnetite which is formed in relatively anhydrous conditions associated with dike intrusion dominates primary magnetite volumetrically where dike density locally exceeds about 30 where secondary magnetite is very dominant or is the only type of magnetite present directional remagnetization appears to be uniform and complete

magnetic structure of the upper kilometer of the marine crust at deep sea drilling project hole 504b eastern pacific ocean deep sea drilling project hole 504b is located in 5 9 m y crust in the eastern pacific ocean about 200 km south of the costa rica rift at 1076 m subbasement it is the deepest penetration of marine crust yet achieved we present here magnetic data from this hole especially from the recently cored leg 83 section which constitutes the lowermost 500 m these data when combined with those of other studies yield not only the deepest but also the most detailed and comprehensive picture of marine magnetic structure at a single site currently available the basement rocks from hole 504b can be divided into three major magnetic units the upper units the top 500 m or so of basement are essentially similar to other shallow marine basement sections consisting of a mixture of various types of extrusive basalt low temperature altered titanomagnetite is the dominant magnetic carrier and the magnetic properties of these rocks are comparable to other shallow marine basalts below the upper units is a 200 m transition zone consisting of a mixture of extrusives and dikes high temperature hydrothermal alteration much of it greenschist facies grade has caused oxidation exsolution of primary titanomagnetite as well as its partial or total replacement by silicates the dominant magnetic carrier is an fe rich titanomagnetite magnetically indistinguishable from pure magnetite the combination of oxidation exsolution and silicate replacement results in a very low natural remanent magnetization nrm the remaining 300 m are in the upper portion of the sheeted dike complex primary titanomagnetite is exsolved but alteration is less intense than in the transition zone nrm values are substantially higher than those of the transition zone due to less silicate replacement of primary titanomagnetite coupled with an uncertain contribution from secondary magnetite which occurs as a silicate alteration product the nrm magnitude is sufficiently high that the sheeted dike complex in this location at least may make a significant if not substantial contribution to the magnetic anomaly overall the magnetic properties of this hole especially the lower 500 m are strongly influenced by postemplacement alteration and may bear little or no resemblance to their values upon initial cooling as hydrothermal temperatures do not appear to have exceeded 400 c the nrm in the lower two sections is apparently a chemical rather than a thermal remanence as such models of marine magnetic structure that combine cooling models of the crust with the assumption that magnetic remanence is purely of thermal origin do not appear sufficient to adequately predict the properties of the deeper crust a better understanding of the nature of postemplacement alteration in the marine crust is required especially its characteristics at high temperatures and its effects on magnetic properties

magnetic effects of maghemitization of oceanic crust both theoretical considerations and available experimental results indicate that magnetic effects of maghemitization are strongly dependent on the grain size of the originally unoxidized titanomagnetite maghemitization of single domain titanomagnetite results in a decrease in coercivity an increase in susceptibility and a large decrease in q ratio maghemitization of multidomain titanomagnetite results in an increase in coercivity a decrease in susceptibility and no large changes in q ratio single domain titanomagnetite is probably resistant to the development of a chemical remanent magnetization crm whereas multidomain titanomagnetite can acquire a crm during maghemitization the behavior of pseudo single domain titanomagnetite which is the main carrier of remanence in submarine extrusive rocks is investigated by comparing the magnetic properties of the french american mid ocean undersea study famous less than 0 1 m y old and the leg 37 3 5 m y old pillow basalts recovered from the mid atlantic ridge near 37 n combining electron microprobe analyses curie temperature measurements and cell edge determinations we find that the famous rocks are already oxidized z 0 38 possibly as a result of some high temperature maghemitization during cooling of the magma comparison with the more highly oxidized z 0 7 leg 37 pillow basalts indicates that low temperature maghemitization of such rocks does not result in appreciable changes of coercivity and susceptibility although the q ratio does decrease and crm seems to be acquired such a crm could account for the anomalously low magnetic inclinations observed at most of the leg 37 sites

evidence for water ice on the moon results for anomalous polar craters from the lro mini rf imaging radar 1 the mini rf radar instrument on the lunar reconnaissance orbiter spacecraft mapped both lunar poles in two different rf wavelengths complete mapping at 12 6 cm s band and partial mapping at 4 2 cm x band in two look directions removing much of the ambiguity of previous earth and spacecraft based radar mapping of the moon s polar regions the poles are typical highland terrain showing expected values of radar cross section albedo and circular polarization ratio cpr most fresh craters display high values of cpr in and outside the crater rim the pattern of these cpr distributions is consistent with high levels of wavelength scale surface roughness associated with the presence of block fields impact melt flows and fallback breccia a different class of polar crater exhibits high cpr only in their interiors interiors that are both permanently dark and very cold less than 100 k application of scattering models developed previously suggests that these anomalously high cpr deposits exhibit behavior consistent with the presence of water ice if this interpretation is correct then both poles may contain several hundred million tons of water in the form of relatively clean ice all within the upper couple of meters of the lunar surface the existence of significant water ice deposits enables both long term human habitation of the moon and the creation of a permanent cislunar space transportation system based upon the harvest and use of lunar propellant

constraints on the volatile distribution within shackleton crater at the lunar south pole shackleton crater is nearly coincident with the moon s south pole its interior receives almost no direct sunlight and is a perennial cold trap making shackleton a promising candidate location in which to seek sequestered volatiles however previous orbital and earth based radar mapping and orbital optical imaging have yielded conflicting interpretations about the existence of volatiles here we present observations from the lunar orbiter laser altimeter on board the lunar reconnaissance orbiter revealing shackleton to be an ancient unusually well preserved simple crater whose interior walls are fresher than its floor and rim shackleton floor deposits are nearly the same age as the rim suggesting that little floor deposition has occurred since the crater formed more than three billion years ago at a wavelength of 1 064 nanometres the floor of shackleton is brighter than the surrounding terrain and the interiors of nearby craters but not as bright as the interior walls the combined observations are explicable primarily by downslope movement of regolith on the walls exposing fresher underlying material the relatively brighter crater floor is most simply explained by decreased space weathering due to shadowing but a one micrometre thick layer containing about 20 per cent surficial ice is an alternative possibility