apollo 16 impact melt splashes petrography and major element composition we made petrographic and major element chemical analyses of 50 impact melt splash ims samples from the apollo 16 landing site to assess their origin and the nature of their subregolith source these melts possess volumes that are significantly larger than those of agglutinates but smaller than those represented by fragments of generally holocrystalline melt sheets most of these melts occur as splashes that drape various host rocks the majority appear to have been deposited onto their hosts inside growing crater cavities or during ballistic flight and subsequently piggy backed to their collection site s macroscopically ims s exhibit a glassy appearance but display varied crystallinity under the microscope schlieren rich glasses dominate the holohyaline areas most ims s contain generally feldspathic monomineralic and lithic clasts while purely regolithic materials i e agglutinates are absent crystalline portions are predominately spherulitic but definitive criteria to distinguish between crystallization from a melt or solid state devitrification are lacking more than half of the ims s possess a distinct crystallization front that we attribute to devitrification chemically most ims s are fairly homogeneous on the scale of a thin section variation among samples is much greater e g al2o3 varied from 24 to 32 wt feo from 2 to 6 wt such a wide range of melt compositions suggests that more than one impact generated these 50 ims s the chemistry of most ims s is unlike the local regolith and appears to represent varied mixtures of vha impact melt breccias and anorthosite i e are dimict like the host rocks are predominantly dimict breccias 70 or one of their component lithologies vha impact melt breccias and anorthosite because of the short surface residence times for these samples determined from microcrater populations on all samples and absolute exposure ages of 10 specimens many ims s might be associated with south ray and baby ray craters in the absence of absolute chronological ages for melt formation we cannot distinguish between a young scenario in which the melts were formed during excavation of south ray and or baby ray craters and an old scenario in which previously formed melts were exposed as part of the discontinuous ejecta of either or both of these craters we prefer the former in part because of the tight compositional cluster of most ims s in either case we conclude that most of these samples or their progenitors resided at depth within the south ray and or baby ray targets furthermore the cayley formation in the southern part of the apollo 16 landing site is a polymict deposit predominantly composed of vha impact melt breccias and anorthosites both lithologies must be intimately mixed as they are in dimict breccias and large coherent units of individual lithologies appear to be limited to 50 m in dimensions

an integrated approach to understanding apollo 16 impact glasses chemistry isotopes and shape the major and minor element abundances were determined by electron microprobe in 1039 glasses from regoliths and regolith breccias to define the compositional topology of lunar glasses at the apollo 16 landing site in the central highlands of the moon while impact glasses with chemical compositions similar to local materials i e apollo 16 rocks and regoliths are abundant glasses with exotic compositions i e transported from other areas of the moon account for up to 30 of the population a higher proportion of compositionally exotic angular glass fragments exists when compared to compositionally exotic glass spherules ratios of non volatile lithophile elements i e al ti mg have been used to constrain the original source materials of the impact glasses this approach is immune to the effects of open system losses of volatile elements e g si na k four impact glasses from one compositionally exotic group low mg high k fra mauro lmhkfm were selected for 40ar 39ar dating the individual fragments of lmhkfm glass all yielded ages of 3750 50 ma for the time of the impact event based on the petrography of these individual glasses we conclude that the likely age of the impact event that formed these 4 glasses as well as the possible time of their ballistic arrival at the apollo 16 site from a large and distant cratering event perhaps in the procellarum kreep terrain zeigler et al 2004 is 3730 40 ma close to the accepted age for imbrium

apollo 16 impact melt sheets contrasting nature of the cayley plains and descartes mountains and geologic history apollo 16 stations 4 and 5 rake samples were examined petrographically and by electron microprobe and inaa results were combined with published information major and trace element compositions petrologic information and age determinations for nonrake samples from stations 4 and 5 and some other apollo 16 sample localities lithologic abundances support the idea korotev 1981 that the variation of soil compositions at apollo 16 is a result of mixing between a component represented by station 5 soil and components much like either the dimict breccias station 4 soils or feldspathic fragmental breccias stations 1 2 and 11 in composition dimict breccias because of their restricted occurrence are apparently not a constituent of either the cayley or descartes formations they were contributed to the surface materials by south ray crater and were probably excavated from beneath both formations by this event pyroxene olivine and coexisting plagioclase compositions from within the anorthosite portions of dimict breccias bridge the gap between the mg rich and ferroan anorthosite fields analyses from associated cumulate and granulitic clasts indicate that they are the source of the intermediate material dimict breccia anorthosites are thus polymict rocks not pristine ferroan anorthosite compositions of apollo 16 impact melt rocks suggest a number of compositional clusters discriminant and cluster analyses of compositional data confirm the existence and strength of these clusters as do age determinations and ir au ratios within each group each of three clusters represents an impact event in the apollo 16 region petrologic information and age determinations indicate that dimict breccias formed approximately 3 92 b y ago the nectaris event occured between 3 84 and 3 92 b y ago and the cayley plains were deposited as a result of the imbrium event sometime later than 3 84 b y

discussion of an interpretation of the variscan structures of sw england discussion concernant un article publie dans le j geol soc london vol 139 4eme partie 1982 pp 533 541

comparative geochemistry of apollo 16 surface soils and samples from cores 64002 and 60002 through 60007 new data are presented for the concentrations of 23 to 27 elements in nine apollo 16 surface soil samples two subsplits each of 12 splits of core 60002 7 and one subsplit each of 10 splits of drive tube 64002 the surface soils are generally similar to other surface soils collected at their respective stations all ten 64002 samples are similar to each other and to the station 4 surface soils and distinctly different from soils at other stations high iron concentrations previously reported for these same subsplits of 60002 7 result primarily from meteoritic metal one sample from each core is contaminated by stainless steel the recently proposed ferroan anorthositic norites are required to explain the soil compositions a yet uncharacterized component with high concentrations of na sr and eu is also needed

petrologic comparisons of cayley and descartes on the basis of apollo 16 soils from stations 4 and 11 petrologic aspects of the cayley and descartes formations are reviewed in the light of new data on apollo 16 soils specific comparison of the modal abundances of lithic fragments in drive tube sample 64001 2 from the slopes of stone mountain station 4 and in soil 67941 from the north ray crater rim station 11 shows that melt rocks especially poikilitic rocks are more abundant at station 4 than at station 11 the reverse is true for fragmental breccias such lithologic differences suggest that stations 4 and 11 do not belong to the same geologic formation metamorphosed breccias are pervasive in both the formations and may represent a local component that has been reworked and diluted as fresh materials were added lithologic compositions inferred from the study of soil samples are different from lithologic compositions inferred from the study of rake samples or breccia clasts this difference may be related to a mixing of material of different grain size distributions the petrology of soils at the apollo 16 site may not accurately reflect original material associated with either the descartes or the cayley formation because of extensive mixing with local material

composition of the cayley formation at apollo 16 as inferred from impact melt splashes chemical data for impact melt splashes ims collected at the apollo 16 landing site show that ni concentrations and feo ni cr ni and co ni correlations are consistent with a chondritic meteoritic component present at levels between approximately 1 5 and 11 wt like apollo 16 soils the ims are intermediate in composition to apollo 16 rocks the chemical data for the ims are consistent with two main compositional groups the group a ims 28 samples are chemically distinct from local apollo 16 soils and are very similar to mixtures of anorthosite and low sc vha lscvha impact melt rocks calculated to a meteorite free basis their average sc concentration la sc mgo sc and tio2 mgo ratios and mg value are 6 1 ug g 1 94 9800 0 066 and 0 74 respectively the group b ims seven samples have chemical equivalents among the soils five samples are chemically very similar to mature apollo 16 soils from the central and southern parts of the landing site two are more similar to soils 67601 and 67941 from north ray crater generally the group b ims and soils are enriched in a composition similar to anorthositic norite 67215 or mixtures thereof with anorthosite as compared to the group a ims the average sc concentration la sc mgo and tio2 mgo ratios and mg value for the subgroup of five are 9 3 ug g 1 41 5780 0 124 and 0 66 respectively the corresponding values for the subgroup of two are 7 5 ug g 1 04 7400 0 090 and 0 71 respectively the group b ims and most soils have a minor high ti component not present in the group a ims if this component is high ti mare basalt its average concentration is approximately 1 6 wt the seven group a ims that have been dated by rare gas methods all have approximately 2 m y exposure ages an age generally associated with south ray crater these seven and potentially most group a ims are likely quenched samples of the melt volume produced by the south ray impact the chemical signature of the impacting projectile is chondritic and its average concentration for the group a ims is 7 3 wt like large coherent melt sheets from terrestrial impacts the impact melt volume of the south ray impact as represented by the group a ims is homogeneous with respect to target lithologies target lithologies at south ray crater which are represented by the host rocks for the ims include anorthosite lscvha impact melt rocks hscvha impact melt rocks and dimict breccias with the exception of 61016 the melt portion of analyzed dimict breccias has the hscvha composition implying that the dimensional scales of lscvha type of rocks and anorthosite in the south ray target do not extend to the 1 10 cm scale observed for the hscvha dimict breccias the compositional difference between group a ims and surface soils from the southern part of the landing site implies stratigraphic variation in the dominant type of vha impact melt rock within the cayley formation chemical data and mixing model results are consistent with a model in which hscvha rocks dominate lscvha rocks in the surface layer the lscvha rocks dominate hscvha rocks in the layer beneath the south ray impact penetrated both layers as both types of vha impact melt rocks are traceable as ejecta material its impact melt volume was formed primarily from the lower layer to give the observed composition of the group a ims that the north ray impact also sampled the lower layer is indicated by the chemical affinities of soils 67601 and 67941 with the lscvha composition away from north ray crater most soils have chemical affinities with the hscvha composition reflecting soil development primarily from the surface layer estimated average compositions give tio2 mgo sc and la concentrations of 0 69 and 7 1 wt and 10 5 and 21 2 ug g respectively for the surface cayley layer and 0 38 and 5 9 wt and 6 1 and 11 8 ug g respectively for the subsurface cayley layer an average composition estimated for the descartes formation from soil compositions has tio2 mgo sc and la concentrations of 0 25 and 3 5 wt and 7 7 and 2 2 ug g respectively the cayley formation is more kreepy more magnesian and less aluminous than the descartes formation

examining the compositions of impactors striking the moon using apollo impact melt coats and anorthositic regolith breccia meteorites abstract impactors striking the moon since the formation of its crust have left an indelible imprint on the lunar surface in the guise of craters and associated impact rocks the lunar crust has low intrinsic abundances of the highly siderophile elements hse re os ir ru pt rh pd au at greater than 3000 times lower than in chondrite meteorites consequently during impact bolides with chondritic or differentiated iron rich compositions should impart elevated hse signatures to the lunar crust here we examine glassy lunar impact melt coats imc from the outside rims of apollo 16 cataclastic anorthosites 60015 65325 and breccias 65035 as well as both fragments and powders of antarctic anorthositic regolith breccia arb meteorites miller range 090034 36 70 75 and macalpine hills 88105 for their petrography mineral chemistry and bulk rock compositions the hse concentrations for imc range from 0 001 to 0 1 ci chondrite with measured 187os 188os between 0 1189 and 0 1366 anorthositic regolith breccia meteorites which have components with 2 6 4 1 ga ages have similar hse concentrations to imc but typically have lower 187os 188os 0 1164 0 1284 these latter os ratios are generally less radiogenic than those measured in 3 8 3 9 ga apollo impact melt breccias the apollo 16 imc are not well dated but their kreepy trace element signatures and associated ages of 3 7 to 3 8 ga for apollo 16 glasses might imply at least in part an origin from the imbrium or serenitatis basin forming impacts within the imc metal schreibersite troilite assemblages record significant inter element hse fractionation which is also reflected in bulk hse patterns for both imc and arb meteorites variations in relative and absolute hse compositions directly reflect the control of metal and sulfide segregation within and between impact melt and breccia lithologies collectively imc and arb meteorites exhibit approximately 50 of the variation in ru ir and 187os 188os observed in lunar impact melt breccias these results imply that significant variations in inter element compositions can occur during impact brecciation and melting and so some impact melt rock hse compositions may not record the compositions of impactors that struck the moon with fidelity nonetheless the generally low 187re 188os of lunar impact melt rocks means that osmium isotope ratios provide evidence for impact composition and a change from ordinary to carbonaceous like impactors either with time or location striking the moon

identifying impact events within the lunar cataclysm from 40ar 39ar ages and compositions of apollo 16 impact melt rocks abstract lunar impact melt breccias provide a unique record of the timing and frequency of collisional events during the early history of the inner solar system prior to the development of a significant rock record on earth the predominance of ages clustering between 3 8 and 4 0 ga was a major unexpected discovery obtained from geochronological studies of lunar impact melts and is the basis of the concept that a cataclysmic bombardment of large planetesimals struck the earth and moon and possibly the entire inner solar system about 3 85 0 10 billion years ago as a test of the cataclysm hypothesis we measured high resolution 20 50 steps 40 ar 39 ar age spectra on 25 samples of apollo 16 impact melt breccias using a continuous laser heating system on sub milligram fragments twenty one of these 25 breccias produced multi step plateaus that we interpret as crystallization ages with 20 of these ages falling in the range 3 75 3 96 ga we propose that at least four different melt producing impact events can be distinguished based on the ages bulk compositions and petrographic characteristics of apollo 16 melt breccias the recognition of multiple impact events within the apollo 16 melt breccia suite shows that numerous impact events occurred on the lunar surface within a relatively narrow time interval providing additional evidence of a heavy bombardment of the moon during the early archean

composition and evolution of the lunar crust in the descartes highlands apollo 16 samples from the north ray crater ejecta blanket apollo 16 were investigated by petrographic microscope electron microprobe instrumental neutron activation and xray fluorescence analyses and 40ar 39ar and rb sr dating techniques nine major groups of monomict and polymict breccias were defined on the basis of microscopic texture and these were further subdivided into chemical subgroups on the basis of characteristic elements such as al mg fe cr ree ni and co the polymict breccias fragmental breccias granulitic breccias and impact melt breccias are the result of multiple impact induced mechanical mixing and melting and of thermal and impact metamorphism of rock and mineral clasts derived from primordial igneous crustal rocks for calculations of mixing models it was found that end members consisting of the pristine igneous rock components present as discrete samples at the apollo 16 site and supplemented by kreep dunite and a meteoritic component yield the best fits for the composition of polymict breccias the end member rocks a re ferroan anorthosite various magnesian gabbronorites including sodic ferrogabbro and feldspathic lherzolite and spinei troctolite the following model is proposed for the composition and stratigraphy of the target for north ray crater the lower section of the stratigraphy is composed of a megabreccia with clasts of highly feldspathic polymict breccias kreep free old eastern highland rock suite interpreted as nectaris ejecta descartes formation the top section contains kreep bearing polymict breccias kreep bearing young western highland rock suite and appears to be similar to the lithologies found in the cayley plains this material interpreted as cayley formation may be a distant facies of imbrium basin ejecta deposits of the imbrium basin the petrographic differences between these two major selenographic units the descartes and the cayley formations in the apollo 16 area are more distinct than the chemical differences the petrographic and chemical composition of the primordial igneous upper crust in the regions of the nectaris and imbrium basins has been calculated by subtraction of the kreep and meteoritic components from the bulk composition of the descartes and cayley materials the nectaris crust which is better constrained consists of 86 87 a northosite 4 sodic ferrogabbro 0 5 1 3 feldspathic lherzolite 6 8 regular magnesian gabbronorite 1 8 2 8 dunite and 0 1 spinel troctolite a model for the evolution of the upper lunar crust in the descartes highlands is proposed on the basis of isotope ages and clast matrix relationships of polymict breccias essential features of this model in sequenial order are 1 development of multiple layers of kreep free early feldspathic fragmental megabreccias and impact melt sheets on the primordial crust in the time period from 4 4 aeons to the time of the nectaris impact which could have occurred as late as 3 85 aeons ago 2 excavation of these megabreccias by the nectaris event and deposition of a nectarian feldspathic fragmental megabreccia in the descartes area 3 introduction of kreep basaltic material into the upper crust mainly west and northwest of the descartes site and formation of kreepy impact melt sheets most probably from 4 05 to 3 80 aeons ago 4 imbrium impact at 3 8 aeons ago and deposition of kreep bearing imbrian feldspathic fragmental breccias at the descartes site which form the cayley formation and 5 redeposition mixing and melting of all preexisting breccias yielding kreep bearing and kreep poor post cayley fragmental breccias and melt ejecta glass bombs as the result of small impacts craters 1 5 km in diameter in the cayley plains and the descartes mountains respectively

moderate velocity oblique impact sliding production of shocked meteorite textures and palaeomagnetically important metallic spherules in planetary regoliths we detail the production of metallic spherules in laboratory oblique shock impact experiments and their applicability 1 to textures in a partly shock melted chondritic meteorite and 2 to the occurrence of palaeomagnetically important fine iron or iron alloy particles in the lunar regolith samples recovered from 29 44 gpa 800 ns experiments revealed melting and textures reminiscent of metallic spherules in the yanzhuang h chondrite including dumbbell forms and other more complex morphologies our experiments demonstrate that metallic spherules can be produced via oblique impact sliding at lower velocities 1 85 km s 1 than are generally assumed in previous work associated with bulk shock melting and that oblique impact sliding is a viable mechanism for producing spherules in shock induced veins in moderately shocked meteorites significantly our experiments also produced fine metallic iron alloy spherules within the theoretical narrow size range a few tens of nanometers for slightly ellipsoidal particles for stable single domain ssd particles which are the most important palaeomagnetically since they can record lunar and planetary magnetic fields over geological time periods the experiments also produced spherules consistent with superparamagnetic sp and multidomain md particle sizes the fine ssd and sp particles on the lunar surface are currently thought to have been formed predominantly by space weathering processes our experiments suggest that oblique shock impact sliding may be a further means of producing the ssd and sp iron or iron alloy particles observed in the lunar regolith and which are likely to occur in the regoliths of mercury and other planetary bodies

characterization of melt and ejecta deposits of kepler crater from remote sensing data we used moon mineralogy mapper m3 arecibo and mini rf radar and diviner radiometer data with lunar reconnaissance orbiter lro camera and kaguya terrain camera images to characterize the target ejecta and impact melt rich lithologies in and around lunar central peak crater kepler m3 data indicate the impact melt rocks of crater floor to be high ca pyroxene dominated distinct from the low ca pyroxene dominated crater wall the central uplift is high ca pyroxene dominated and has higher albedo these observations are consistent with thin mare basalts underlain by noritic imbrium ejecta underlain by gabbroic crustal material m3 data reveal an enigmatic splash like feature of melt rich material on the southeastern uprange crater wall and flank m3 data also highlight halos around kepler in detail the halos are slightly variable but in broad terms they define a consistent feature offset to the inferred downrange direction and interpreted to reflect the distribution of glass bearing impact breccia the radar data sets show most of the proximal ejecta to be radar bright however diviner rock abundance data do not indicate the presence of blocks on the surface nor can they be seen using lro narrow angle camera images thus the blocks giving rise to the enhanced radar signal are buried beyond the radar bright zone a subtle radar dark halo emerges coincident with a region of very low rock abundance in diviner data this multidisciplinary approach provides a robust analysis of the main characteristics of a lunar complex crater and reveals previously unidentified features related to the distribution of impact melt

geochemical studies of feldspathic fragmental breccias and the nature of north ray crater ejecta major and trace element analyses of clasts and matrix from feldspathic fragmental breccias show that these breccias are not all alike but vary widely in their bulk compositions and clast assemblages these studies together with analyses of other north ray crater large rocks reveal the major components to be anorthosites ferroan anorthositic norites magnesian granulites feldspathic melt rocks and vha impact melts the ferroan anorthositic norites are important lunar crustal rocks identified here for the first time the kreepy vha melts are found to be much more important in north ray crater ejecta than was previously assumed sodic ferrogabbro is an important minor component the compositional characteristics of bulk breccias and feldspathic melt rocks are modeled quantitatively as mixtures of two to five components anorthosites ferroan anorthositic norites magnesian granulites sodic ferrogabbros and vha melt rocks breccia 67455 is unique in consisting wholly of ferroan kreep free components

petrology and geochemistry of lunar dimict breccia 61015 dimict breccia 61015 consists dominantly of granulated anorthosite and impact melt rock of vha very high alumina basalt composition the anorthosite is a typical apollo 16 ferroan anorthosite except that it is slightly more augite rich than most other ferroan anorthosites the breccia probably formed in the floor of an expanding crater cavity by the following process impact melt generated within the cavity was injected into underlying anorthositic bedrock and solidified rapidly and the anorthosite and melt rock were then fragmented by deformation in the later stages of the impact all the apollo 16 dimict breccias except perhaps 61016 appear to have formed in the same impact the source crater cannot yet be identified but it may be an intermediate sized 50 150 km diameter crater within a few hundred kilometers of the apollo 16 site in the direction of the imbrium basin of either pre nectarian or post nectarian pre imbrian age the breccia has been affected by at least one and perhaps as many as four recent small impacts the most recent was probably the south ray impact the recent impact s produced internal shock induced melting of the breccia and injected and coated the rock with externally derived impact melts the coating glass is heterogeneous its average composition is similar to the compositions of other apollo 16 coating glasses except that its tio2 content is lower the vein glass is unusually mafic and has very low tio2 for its al2o3 content the tio2 contents of these glasses establish that they cannot be melted soils their compositions require a mafic low tio2 protolith component that has not yet been identified among the large rock samples perhaps a very mafic member of the ferroan anorthosite suite

galileo observations of post imbrium lunar craters during the first earth moon flyby copernican age craters are among the most conspicuous features seen on the far side and western limb of the moon in the galileo multispectral images acquired in december 1990 among the new morphologic observations of far side craters are bright rays continuous ejecta deposits and dark rings associated with probable impact melt veneers these observations suggest that the mapped age assignments of several large far side craters ohm robertson and possibly lowell and lenz need revision new crater size frequency measurements on lunar orbiter images suggest the following age reassignments hausen 170 km diameter pythagoras 120 km and bullialdus 61 km from eratosthenian to upper imbrian and carpenter 60 km and harpalus 39 km from copernican to eratosthenian colors and albedos of craters away from impact melt veneers are correlated with their geologic emplacement ages as determined from counts of superposed craters these age color relations are used to estimate the emplacement age time since impact event for other copernican age craters these age color relations indicate a probable copernican age for 27 far side or western limb craters larger than 10 km diameter that were not previously mapped as copernican the apparent deficiency of copernican craters on the far side compared with the near side in published geologic maps is not present in our data age color trends differ between mare and highland regions and between the interiors and continuous ejecta of the craters similar trends are established for color and albedo versus soil maturity indices for the returned lunar samples with distinct trends for mare and highland soils however the mare versus highland offsets are reversed in the two comparisons these relations can be explained by variations in regolith thicknesses and rates of mixing with relatively fresh crystalline ejecta therefore the soil maturity trends represent longer geologic time periods in regions with thinner regoliths such as the maria

on the origin of impact glass in the apollo 16 regolith this study addresses the issue of what fraction of the impact glass in the regolith of a lunar landing site derives from local impacts those within a few kilometers of the site as opposed to distant impacts 10 or more kilometers away among 10 323 fragments from the 64 210 lm grain size fraction of three apollo 16 regolith samples 14 are impact glasses that is fragments consisting wholly or largely of glass produced in a crater forming impact another 16 are agglutinates formed by impacts of micrometeorites into regolith we analyzed the glass in 1559 fragments for major and minor element concentrations by electron probe microanalysis and a subset of 112 of the fragments that are homogeneous impact glasses for trace elements by secondary ion mass spectrometry of the impact glasses 75 are substantially different in composition from either the apollo 16 regolith or any mixture of rocks of which the regolith is mainly composed about 40 of the impact glasses are richer in fe mg and ti as well as k p and sm than are common rocks of the feldspathic highlands these glasses must originate from craters in maria or the procellarum kreep terrane of the feldspathic impact glasses some are substantially more magnesian greater mgo feo or have substantially lower concentrations of incompatible elements than the regolith of the apollo 16 site many of these however are in the range of feldspathic lunar meteorites most of which derive from points in the feldspathic highlands distant from the procellarum kreep terrane these observations indicate that a significant proportion of the impact glass in the apollo 16 regolith is from craters occurring 100 km or more from the landing site in contrast the composition of glass in agglutinates on average is similar to the composition of the apollo 16 regolith consistent with local origin 2010 elsevier ltd all rights reserved

modern sedimentary processes at the heads of martinez channel and steffen fjord chilean patagonia abstract chilean fjord sediments constitute high resolution archives of climate and environmental change in the southern andes to interpret such records accurately it is crucial to understand how sediment is transported and deposited within these basins this issue is of particular importance in glaciofluvial martinez channel and steffen fjord 48 s due to the increasing occurrence of glacial lake outburst floods glofs originating from outlet glaciers of the northern patagonian icefield hence the bathymetry of the head of martinez channel and steffen fjord was mapped at high resolution and the grain size and organic carbon content of grab sediment samples were examined results show that the subaquatic deltas of baker and huemules rivers at the head of martinez channel and steffen fjord respectively are deeply incised up to 36 m by sinuous channels the presence of sediment waves and coarser sediments within these channels imply recent activity and sediment transport by turbidity currents although several triggering mechanisms are possible we argue that elevated river discharge and the associated relatively high suspended sediment loads is the main cause of the occurrence of turbidity currents at the head of these fjords and are of key importance in shaping the fjord s subaquatic morphology this study shows that the heads of martinez channel and steffen fjord are dynamic sedimentary environments with rapidly migrating channels it highlights the importance of site selection and multi coring in any future project aimed at reconstructing environmental change using the sediments of either fjord

lunar meteorite queen alexandra range 94281 glass compositions and other evidence for launch pairing with yamato 793274 abstract lunar meteorite queen alexandra range 94281 is remarkably similar to yamato 793274 pairing in the conventional earth entry sense is difficult to reconcile with the 2500 km separation between the find locations for these two samples nonetheless both of these regolith breccias are dominated by very low ti vlt mare basalt the pyroxenes of which feature exsolution lamellae on a remarkably coarse scale typical lamella width 0 5 1 m by mare standards the pyroxenes also show similar compositional variations e g fe vs ti trends which confirm parentage from vlt mare basalt plots using al2o3 or feo as a tracer of the highland component indicate indistinguishable internal mare highland geochemical mixing trends the same two distinctive glass types dominate the mare glass populations of both breccias glass type yq1 features 0 37 0 63 wt tio2 10 17 wt mgo and 9 11 wt al2o3 glass type yq2 features higher tio2 0 99 1 22 wt which is inversely correlated with mgo 12 6 13 8 wt and nearly constant 8 8 wt al2o3 all of these similarities suggest that y 793274 and que 94281 are a launch pair which we designate yq most of these similarities also extend to another mare breccia meteorite elephant moraine 87521 however the eet 87521 mare basalt is unusually v poor 88 g g whereas the yq mare component contains 166 g g queen alexandra range 94281 features a variety of textural domains discrete patches of dark matrix material appear to represent clods of mature regolith that have been mixed with a coarser relatively immature material interior to a frothy fusion crust are areas of massive glass that probably formed as a splash coating on que 94281 when it was still on the moon the coarse yq and eet 87521 pyroxene exsolution features imply relatively slow cooling in either a very shallow sill or an unusually thick ponded lava and or later annealing within a cryptomare mare pyroclastic glasses including the two yq varieties are systematically mgo rich compared to crystalline mare basalts this disparity may be a consequence of limited survival of graphite the main fuel for explosive volcanism during formation of the mare source regions as magma ocean cumulates graphite 2 2 g cm3 survived preferentially in regions that avoided extensive early melting and thus remained mgo rich an apparent bimodality in the tio2 contents of mare volcanics especially the pyroclastic glasses also seems a plausible consequence of petrogenesis by remelting of magma ocean cumulates cumulates deposited after the magma ocean evolved to ilmenite saturation had vastly higher tio2 contents than cumulates deposited shortly before the yq regolith s subequal proportions of mare and highland matter are consistent with derivation from a terrain close to a mare highland boundary however a similar mixture might also develop through vertical mixing in a cryptomare or a region of thin mare coverage thus unfortunately the yq bulk composition is not a very useful clue to the identity of the source crater

thermal annealing of experimentally shocked feldspar crystals single crystals of sanidine orthoclase microcline oligoclase and labradorite as well as polycrystalline bytownite were shocked experimentally to peak pressures as high as 45 gpa and subsequently annealed under dry conditions for various times at 800 c 900 c and 1000 c these experiments reveal that alkali feldspars do not change their al si distribution due to shock alone but when subjected to shock pressures 22 gpa and then annealed microcline and orthoclase rapidly transform to sanidine displaying a highly disordered al si distribution high diffusivity of k na and ca was observed in a labradorite sample shocked to 26 gpa subsequent annealing may thus disturb chemical structural and isotopic characteristics of shocked minerals and rocks more easily than of unshocked specimens this is of considerable importance for the interpretation of isotopic age data of impact breccias recrystallization textures of annealed diaplectic plagioclase glasses are very distinctive and may be used as a relative measure of the shock pressure experienced by the samples