global survey of lunar regolith depths from lroc images abstract we performed the first global survey of lunar regolith depths using lunar reconnaissance orbiter camera lroc data and the crater morphology method for determining regolith depth we find that on both the lunar farside and in the nearside non mare regions the regolith depth is twice as deep as it is within the lunar maria our data compare favorably with previous studies where such data exist we also find that regolith depth correlates well with density of large craters 20 km diameter this result is consistent with the gradual formation of regolith by rock fracture during impact events

a note on the impact factor of gondwana research with a view towards understanding the evolutionary history of the complex south indian shield several geological and geophysical studies have been carried out recent geophysical studies include magnetotelluric mt deep seismic sounding dss gravity magnetic and deep resistivity soundings drs in the present study mt results along 140 km andiyur turaiyur east west profile is presented the data are subjected to groom bailey decomposition and static shift correction before deriving a 2 d model the 2 d modeling results have shown that the upper crust up to about 15 km towards western part of the profile have exhibited high resistive character of about 40 000 ohm m as compared to the eastern part less than 5 000 ohm m the mid lower crust has shown a decrease in resistivity in western part of the profile the order of resistivity being 2 000 ohm m an anomalous steep conductive feature less than 100 ohm m is observed near sankari at mid lower crustal depths 20 km towards middle part of the profile this feature is spatially correlatable with the well known moyar bhavani shear zone mbsz the features obtained in the present study are consistent with earlier mt studies in this region and correlatable with other geophysical studies dss studies near the study region gave an evidence for differing crustal structure on either side of mbsz variation in geoelectric character along the profile both in the upper crust and mid lower crust indicate a block structure in the sgt with shear zones acting as boundaries the new evidence in the form of distinct geoelectric structure and also variation in seismic structure indicate a continent continent collision zone in this region and plays an important role for the gondwana reconstruction models of south indian shield

numerical simulations of impact crater formation with dilatancy impact induced fracturing creates porosity that is responsible for many aspects of the geophysical signature of an impact crater this paper describes a simple model of dilatancy the creation of porosity in a shearing geological material and its implementation in the isale shock physics code the model is used to investigate impact induced dilatancy during simple and complex crater formation on earth simulations of simple crater formation produce porosity distributions consistent with observations dilatancy model parameters appropriate for low quality rock masses give the best agreement with observation more strongly dilatant behavior would require substantial postimpact porosity reduction the tendency for rock to dilate less when shearing under high pressure is an important property of the model pressure suppresses impact induced dilatancy in the shock wave at depth beneath the crater floor and in the convergent subcrater flow that forms the central uplift consequently subsurface porosity distribution is a strong function of crater size which is reflected in the inferred gravity anomaly the bouguer gravity anomaly for simulated craters smaller than 25 km is a broad low with a magnitude proportional to the crater radius larger craters exhibit a central gravity high within a suppressed gravity low lower crustal pressures on the moon relative to earth imply that impact induced dilatancy is more effective on the moon than earth for the same size impact in an initially nonporous target this difference may be mitigated by the presence of porosity in the lunar crust

a strain based porosity model for use in hydrocode simulations of impacts and implications for transient crater growth in porous targets numerical modelling of impact cratering has reached a high degree of sophistication however the treatment of porous materials still poses a large problem in hydrocode calculations we present a novel approach for dealing with porous compaction in numerical modelling of impact crater formation in contrast to previous attempts e g p alpha model snowplow model our model accounts for the collapse of pore space by assuming that the compaction function depends upon volumetric strain rather than pressure our new e alpha model requires only four input parameters and each has a physical meaning the model is simple and intuitive and shows good agreement with a wide variety of experimental data ranging from static compaction tests to highly dynamic impact experiments our major objective in developing the model is to investigate the effect of porosity and internal friction on transient crater formation we present preliminary numerical model results that suggest that both porosity and internal friction play an important role in limiting crater growth over a large range in gravity scaled source size

differentiating between anthropogenic calcite in plaster ash and natural calcite using infrared spectroscopy implications in archaeology abstract infrared spectroscopy provides information not only on the type of calcium carbonate polymorph but also on the extent of atomic order in calcite three major infrared absorption peaks are identified 3 2 and 4 it was shown that the ratio between 2 and 4 bands reflects the order of the calcite crystal structure in this paper we analyse this ratio in geologically formed calcites archaeological plasters modern plasters and experimentally prepared plasters for the geological calcite the values of the 2 4 ratio are around 3 whereas for the experimentally prepared plasters the values are around 6 5 the 2 4 ratio for archaeological plasters varies from 3 to 6 this shows that a high ratio is indicative of disorder in the crystal and implies that the calcite was formed from calcium oxide at high temperatures it also implies that this disorder can be preserved for at least 14 000 years the 2 4 ratio of calcite from archaeological sites can thus be used to differentiate between anthropogenic calcite such as in plaster mortar and wood ash from geogenic calcite such as in limestone the ratio may also be used to identify plaster or ash that still retains its original crystals and therefore carbon 14 content

ultra high temperature metamorphism and multistage decompressional evolution of sapphirine granulites from the palni hill ranges southern india sapphirine granulites from a new locality in the palni hill ranges southern india occur in a small enclave of migmatitic highly magnesian metapelites mg 85 72 within massive enderbitic orthogneiss they show a variety of multiphase reaction textures that partially overprint a coarse grained high pressure assemblage of bt opx ky grt pl qtz the sequence of reactions as deduced from the corona and symplectite assemblages together with petrogenetic grid considerations records a clockwise p t evolution with four distinct stages 1 equilibration of the initial high p assemblage in deep overthickened crust 12 kbar 800 900 c was followed by a stage of near isobaric heating presumably as a consequence of input of extra heat provided by the voluminous enderbitic intrusives during heating kyanite was converted to sillimanite and biotite was involved in a series of vapour phase absent melting reactions which resulted in the ultra high temperature assemblage opx crd kfs spr sil grt qtz bt coexisting with melt equilibration at c 950 1000 c 11 10 kbar 2 subsequently as a result of decompression of the order of 4 kbar at ultra high temperature a sequence of symplectite assemblages opx sil spr spr crdopx spr crdopx crdopx crd spl crd spl developed at the expense of garnet orthopyroxene and sillimanite this stage of near isothermal decompression implies rapid ascent of the granulites into mid crustal levels possibly due to extensional collapse and erosion of the overthickened crust 3 development of late biotite through back reaction of melt with residual garnet indicates a stage of near isobaric cooling to c 875 c at 7 8 kbar i e relaxation of the rapidly ascended crust to the stable geotherm 4 a second period of near isothermal exhumation up to c 6 5 kbar 850 c is indicated by the partial breakdown of late biotite through volatile phase absent melting reactions available isotope data suggest that the early part of the evolutionary history stages 1 3 is presumably coeval with the early proterozoic metamorphism in the extended granulite terrane of the nilgiri biligirirangan and shevaroy hills to the north while the exhumation of the granulites from mid crustal levels stage 4 occurred only during the pan african thermotectonic event which led to the accretion of the kerala khondalite belt to the south

lunar regolith thickness deduced from concentric craters in the ce 5 landing area abstract lunar regolith is the layer of fragmented and unconsolidated rock material that is repeatedly stirred and overturned on the lunar surface it can provide critical information about lunar geologic processes e g impact volcanism and the space environment china s chang e 5 ce 5 mission which will be launched in 2019 will land on the lunar near side surface and return at least 2 kg of lunar regolith through surface collection and by boring a hole no

climate of the supercontinent pangea numerous climate models predict that the geography of the supercontinent pangea was conducive to the establishment of a megamonsoonal circulation in general geologic evidence supports the hypothesis of a megamonsoon that reached maximum strength in the triassic pangea in the late carboniferous had widespread peat formation in what is now central and eastern north america and europe and relatively dry conditions on the colorado plateau the equatorial region of the continent became drier through the end of the carboniferous by the permian the equatorial region of pangea was dry and indicators of aridity and rainfall seasonality became more widespread wind directions from colorado plateau eolian sandstones are consistent with an increasing influence of monsoonal circulation at this time in the triassic climate in the colorado plateau region became relatively wet though still seasonal and the few eolian sandstones indicate a major shift in wind direction at that time in addition sedimentation

crater degradation on the lunar maria topographic diffusion and the rate of erosion on the moon landscape evolution on the moon is dominated by impact cratering in the post maria period in this study we mapped 800 m to 5 km diameter craters on 30 of the lunar maria and extracted their topographic profiles from digital terrain models created using the kaguya terrain camera we then characterized the degradation of these craters using a topographic diffusion model because craters have a well understood initial morphometry these data provide insight into erosion on the moon and the topographic diffusivity of the lunar surface as a function of time the average diffusivity we calculate over the past 3 ga is 5 5 m2 myr with this diffusivity after 3 ga a 1 km diameter crater is reduced to approximately 52 of its initial depth and a 300 m diameter crater is reduced to only 7 of its initial depth and craters smaller than 200 300 m are degraded beyond recognition our results also allow estimation of the age of individual craters on the basis of their degradation state provide a constraint on the age of mare units and enable modeling of how lunar terrain evolves as a function of its topography

application of stable carbon isotopes to early biochemical evolution on earth the emergence and early evolution of life on earth have long been intriguing subjects for scientific inquiry and a continuous source of intel lectual excitement current work at this frontier proceeds along a number of different avenues and comprises a variety of disciplinary approaches that together strongly suggest that the earth was inhabited by life as early as almost 4 gyr ago the present state of the field as inferred from the results of a broad interdisciplinary approach has recently been summarized by j w schopf and coworkers cf schopf 1 983 it is with the advantage of such a synoptic view that the present review addresses a single facet of the theme namely the potential isotopic infer ences of the presence of co2 fixing autotrophic organisms for the carbon cycle of the early earth with biologically derived organic carbon as well as carbonates limestone dolomite etc abundantly preserved in sediments relevant isotopic evidence should have been encoded in the geologic record from its onset about 3 8 gyr ago it has been known since the pioneering studies by nier gulbransen 1939 murphey nier 1941 and rankama 1948 that the trans formation of inorganic carbon into living matter entails a marked bias in favor of the light isotope c2c with the heavy species l3c retained in the inorganic reservoir subsequent work performed by many investigators e g craig 1953 park epstein 1960 has confirmed that all common

distinguishing between calcites formed by different mechanisms using infrared spectrometry archaeological applications infrared spectrometry is a well established method for the identification of minerals due to its simplicity and the short time required to obtain a result it can be practiced on site during excavation using portable infrared spectrometers however the identification of a mineral may not be sufficient for example a lime plaster floor and a crushed chalk surface have a similar appearance and are composed of the same mineral calcite here we exploit differences in the infrared spectra of geogenic biogenic and pyrogenic calcites for the identification of each calcite type the infrared calcite spectrum has three characteristic peaks in the region of 400 4000 cm 1 designated 2 3 and 4 when a calcite sample is ground as part of the measurement preparation procedure some grinding dependent changes will be revealed in the infrared spectrum with additional grinding the 3 peak narrows and the heights of the 2 and 4 peaks decrease when both are normalized to the 3 height by plotting the normalized heights of the 2versus the 4 of several grindings of the same sample a characteristic trend line is formed for each calcite type the trend lines of geogenic calcites have the shallowest slopes and highest 4 values when compared to pyrogenic calcites which can be further divided to ash and plaster mortar samples this method can assist in distinguishing between the various calcites and provide insights into homogeneity and preservation state of the calcitic materials in question

regolith thickness over sinus iridum results from morphology and size frequency distribution of small impact craters high resolution optical images returned from recent lunar missions provide a new chance for estimation of lunar regolith thickness using morphology and the size frequency distribution of small impact craters in this study regolith thickness over the sinus iridum region is estimated using lunar reconnaissance orbiter camera lroc narrow angle cameras nacs images a revised relationship between crater geometry and regolith thickness is proposed based on old experimental data that takes into considering the effect of the illumination angle of the images in total 227 high resolution lroc nac images are used and 378 556 impact craters with diameters from 4 2 to 249 8 m are counted and their morphologies are identified our results show that 50 of the sinus iridum region has a regolith thickness between 5 1 and 10 7 m and the mean and median regolith thicknesses are 8 5 and 8 0 m respectively there are substantial regional variations in the regolith thickness with its median value varying from 2 6 to 12 0 m for most regions local variations of regolith thickness are found to be correlated with the lunar surface age the older the surface the greater the thickness in addition sporadically distributed impact ejecta and crater rays are associated with relatively larger regolith thickness which might result from excavation and transport of materials during the formation of the secondaries of copernican aged craters our estimated regolith thickness can help with future analysis of chang e 3 lunar penetrating radar echoes and studies of the subsurface stratigraphic structure of the moon

a primary analysis of microwave brightness temperature of lunar surface from chang e 1 multi channel radiometer observation and inversion of regolith layer thickness abstract in china s first lunar exploration project chang e 1 ce 1 a multi channel microwave radiometer was aboard the satellite with the purpose of measuring microwave brightness temperature tb from lunar surface and surveying the global distribution of lunar regolith layer thickness in this paper the primary 621 tracks of swath data measured by ce 1 microwave radiometer from november 2007 to february 2008 are collected and analyzed using the nearest neighbor interpolation to collect the tb data under the same sun illumination global distributions of microwave brightness temperature from lunar surface at lunar daytime and nighttime are constructed based on the three layer media modeling the top dust soil regolith and underlying rock media for microwave thermal emission of lunar surface the ce 1 measured tb and its dependence upon latitude frequency and feo tio2 content etc are discussed the ce 1 tb data at apollo landing sites are especially chosen for validation and calibration on the basis of available ground measurements using the empirical dependence of physical temperature upon the latitude verified by the ce 1 multi channel tb data at apollo landing sites the global distribution of regolith layer thickness is further inverted from the ce 1 brightness temperature data at 3 ghz channel those inversions at apollo landing sites and the characteristics of regolith layer thickness for lunar maria are well compared with the apollo in situ measurements and the regolith thickness derived from the earth based radar data finally the statistical distribution of regolith thickness is analyzed and discussed

constraints on the depth and variability of the lunar regolith knowledge of regolith depth structure is important for a variety of studies of the moon and other bodies such as mercury and asteroids lunar regolith depths have been estimated using morphological techniques i e quaide and oberbeck 1968 shoemaker and morris 1969 crater counting techniques shoemaker et al 1969 and seismic studies i e watkins and kovach 1973 cooper et al 1974 these diverse methods provide good first order estimates of regolith depths across large distances tens to hundreds of kilometers but may not clearly elucidate the variability of regolith depth locally 100 m to km scale in order to better constrain the regional average depth and local variability of the regolith we investigate several techniques first we find that the apparent equilibrium diameter of a crater population increases with an increasing solar incidence angle and this affects the inferred regolith depth by increasing the range of predicted depths from 7 15 m depth at 100 m equilibrium diameter to 8 40 m at 300 m equilibrium diameter second we examine the frequency and distribution of blocky craters in selected lunar mare areas and find a range of regolith depths 8 31 m that compares favorably with results from the equilibrium diameter method 8 33 m for areas of similar age 2 5 billion years finally we examine the utility of using clementine optical maturity parameter images lucey et al 2000 to determine regolith depth the resolution of clementine images 100 m pixel prohibits determination of absolute depths but this method has the potential to give relative depths and if higher resolution spectral data were available could yield absolute depths

analysis of impact crater populations and the geochronology of planetary surfaces in the inner solar system analyzing the density of impact craters on planetary surfaces is the only known technique for learning their ages remotely as a result crater statistics have been widely analyzed on the terrestrial planets since the timing and rates of activity are critical to understanding geologic process and history on the moon the samples obtained by the apollo and luna missions provide critical calibration points for cratering chronology on mercury venus and mars there are no similarly firm anchors for cratering rates but chronology models have been established by extrapolating from the lunar record or by estimating their impactor fluxes in other ways this review provides a current perspective on crater population measurements and their chronological interpretation emphasis is placed on how ages derived from crater statistics may be contingent on assumptions that need to be considered critically in addition ages estimated from crater populations are somewhat different than ages from more familiar geochronology tools e g radiometric dating resurfacing processes that remove craters from the observed population are particularly challenging to account for since they can introduce geologic uncertainty into results or destroy information about the formation age of a surface regardless of these challenges crater statistics measurements have resulted in successful predictions later verified by other techniques including the age of the lunar maria the existence of a period of heavy bombardment in the moon s first billion years and young volcanism on mars

upb geochronology of the sri lankan basement abstract u pb ages of zircons and monazites from ortho and paragneisses representing the major crystalline basement units of sri lanka establish a new geochronological framework which is consistent with previously published work on sm nd model ages rb sr whole rock ages and u pb mineral ages in the highland complex three newly dated orthogneisses one previously dated by baur et al 1991 and one dated by kroner and williams 1992 all intruded 1 85 to 1 9 ga ago this widespread intrusion event occurred soon after the end of sediment deposition which is estimated at 1 9 to 2 0 ga using upper intercept ages of zircons from metapelites in the highland complex within the boundaries of this complex established by sm nd model age mapping milisenda et al 1994 only one orthogneiss has been found which is substantially younger than 1 8 ga this is the metatonalite from polonnaruwa which intruded 670 ma ago baur et al 1991 three orthogneisses from the vijayan complex which lies to the east of the highland complex yield similarly consistent crystallization ages of 1023 8 1016 28 and 1033 121 ma in the wanni complex which lies to the west of the highland complex a sillimanite bearing gneiss which is apparently of metasedimentary origin but contains zircons of igneous appearance yields a primary crystallization age of 793 4 ma consistent with a previously dated orthogneiss from kurunegala of 770 ma baur et al 1991 in addition single zircon data by kroner et al 1994 indicate primary crystallization ages of 1 0 to 1 1 ga for orthogneisses from the vavuniya charnockite province which is considered to be part of the wanni complex these results confirm the age contrast between the highland complex on the one hand and the vijayan complex and wanni complex on the other as previously inferred from sm nd model ages milisenda et al 1988 1994 post tectonic granitoids and pegmatites intruded throughout all three complexes 550 ma ago the age of regional high grade metamorphism mostly granulite facies in the highland complex mostly amphibolite facies in the vijayan complex and both granulite and amphibolite facies in the wanni complex is constrained to be less than 670 ma the primary crystallization age of the polonnaruwa metatonalite it is more closely defined by lower intercept zircon ages which include one concordant age of 608 4 ma and one discordant but well defined age of 611 23 ma and by a nearly concordant monazite age of 592 2 ma this indicates that peak metamorphic conditions occurred 610 ma ago numerous other lower intercept ages between 590 and 550 ma and post tectonic intrusion ages of 550 ma set a lower age limit for high grade conditions and deformation the temperature history between 610 and 550 ma is not yet well resolved and it is not clear whether there was a separate thermal event 550 ma ago previously published whole rock rb sr and sm nd isochrons for gneisses from the highland complex yielding ages of 2 ga and greater and previously interpreted to date the time of granulite grade metamorphism must be reinterpreted in the light of the new data presented here as well as other recently published results e g burton and o nions 1990b baur et al 1991 and in view of the accumulated evidence for very limited element mobility during high grade metamorphism these whole rock ages are in fact identical or close to the ages of primary granitoid emplacement rather than the age of granulite facies metamorphism

structural framework of deolapar area central india and its implications for proterozoic nappe tectonics abstract a controversial nappe like structure deolapar nappe in the intensely deformed and polymetamorphosed precambrian rocks of the sausar fold belt around the deolapar area of central india has remained the subject of a long standing unresolved debate while some workers interpreted it as the inverted limb of a large scale recumbent fold which has been thrusted onto the adjoining part of the supracrustal sequence sausar group others discounted the very existence of the nappe because of the lack of structural evidence in favour of the recumbent fold thrust structure recent structural study by the present authors around the deolapar area and also in the adjoining parts of the sausar fold belt has looked back into the controversy surrounding the deolapar nappe the study reveals that the deolapar nappe is constituted of an allochthonous block of metasedimentary rocks and crystalline gneiss migmatites placed over the metacalcareous rocks lohangi formation of the sausar group along a low angle thrust plane marked by a sheared fibrolite biotite schist the whole thrust sheet has been folded by later f2 upright folds however careful structural mapping confirmed that there is no evidence of any map scale f1 recumbent fold in the whole area although small scale thrust related reclined f1 folds are occasionally found also there is not enough field evidence suggesting regional inversion of stratigraphic succession so as to indicate the lower limb of a recumbent fold the deolapar nappe can therefore be best interpreted as a thrust nappe details of the existing controversy the new observations and a new tectonic model of the deolapar nappe is presented here

the density and porosity of lunar rocks 1 accurate lunar rock densities are necessary for constructing gravity models of the moon s crust and lithosphere most apollo era density measurements have errors of 2 5 or more and few include porosity measurements we report new density and porosity measurements using the bead method and helium pycnometry for 6 apollo samples and 7 lunar meteorites with typical grain density uncertainties of 10 30 kg m 3 0 3 0 9 and porosity uncertainties of 1 3 comparison between igneous grain densities and normative mineral densities show that these uncertainties are realistic and that the helium fully penetrates the pore space basalt grain densities are a strong function of composition varying over at least 3270 kg m 3 high aluminum basalt to 3460 kg m 3 high titanium basalt feldspathic highland crust has a bulk density of 2200 2600 kg m 3 and porosity of 10 20 impact basin ejecta has a bulk density of 2350 2600 kg m 3 and porosity of 20

the global effects of impact induced seismic activity on fractured asteroid surface morphology abstract impact induced seismic vibrations have long been suspected of being an important surface modification process on small satellites and asteroids in this study we use a series of linked seismic and geomorphic models to investigate the process in detail we begin by developing a basic theory for the propagation of seismic energy in a highly fractured asteroid and we use this theory to model the global vibrations experienced on the surface of an asteroid following an impact these synthetic seismograms are then applied to a model of regolith resting on a slope and the resulting downslope motion is computed for a full range of impactor sizes next this computed downslope regolith flow is used in a morphological model of impact crater degradation and erasure showing how topographic erosion accumulates as a function of time and the number of impacts finally these results are applied in a stochastic cratering model for the surface of an eros like body same volume and surface area as the asteroid with craters formed by impacts and then erased by the effects of superposing craters ejecta coverage and seismic shakedown this simulation shows good agreement with the observed 433 eros cratering record at a main belt exposure age of 400 200 myr including the observed paucity of small craters the lowered equilibrium numbers loss rate production rate for craters less than 100 m in diameter is a direct result of seismic erasure which requires less than a meter of mobilized regolith to reproduce the near observations this study also points to an upper limit on asteroid size for experiencing global surface modifying seismic effects from individual impacts of about 70 100 km depending upon asteroid seismic properties larger asteroids will experience only localized regional seismic effects from individual impacts

age of metamorphism in the high grade rocks of sri lanka controversy concerning the age of regional granulite grade metamorphism in sri lanka stems from the fact that different isotopic systems apparently record different events published isotopic data show that zircons from igneous and sedimentary protoliths experienced considerable pb loss at 550 ma and that new growth of zircon monazite rutile and garnet between 539 pm 6 and 608 pm 3 ma probably dates near peak metamorphic conditions upper concordia intercept ages between 670 and 1950 ma for magmatic zircons from high grade orthogneisses and charnockites date igneous emplacement and also support the occurrence of granulite metamorphism after 670 ma a granulite of igneous origin from the kataragama klippe in southern sri lanka yielded discordant ion microprobe data that suggest emplacement of the protolith at 1770 1880 ma thus a rb sr whole rock age of 1930 pm 130 ma from the same suite is unlikely to reflect isotopic homogenization during granulite formation and we interpret this and oth

mass wasting features on the moon how active is the lunar surface abstract mass wasting features have long been noticed on the moon but there has been no systematic studies for their morphological geometrical or distribution characteristics the effect of mass wasting on topographic evolution and surface erosion on the moon is not fully understood using high resolution image and topography data obtained from the lunar reconnaissance orbiter spacecraft we found that mass wasting has been globally and continuously occurring on the moon meteor impacts and moonquakes are the two major triggering mechanisms in forming lunar mass wasting features we selected over 300 examples of lunar mass wasting features and classified them as falls flows slides slumps and creeps after studying their morphology potential mode of emplacement and sizes of displaced materials the slope and age distributions for their host terrains are studied to estimate the topographic evolutionary sequence of the lunar surface under the effect of mass wasting due to continuous reshaping by mass wasting surface topographies on the moon tend to become smoother with time with fewer mass wasting events occurring on older surfaces pre nectarian surfaces may represent the final stage of surface topographic evolution on slope angles regarding the effect of mass wasting crater densities on lunar surfaces vary with slope angles because the surface erosion rate and regolith production rate on slopes are larger than those on flat areas

stable carbon and oxygen isotopic compositions of wood ash an experimental study with archaeological implications abstract wood ash composed mainly of the mineral calcite is an important component in many archaeological sites identification of wood ash in the archaeological record is often difficult due to mixing of ash with other calcitic components of geogenic origin and or due to diagenetic changes a recent empirical study using the stable isotope compositions of carbon 13 c and oxygen 18 o in wood ash enabled the identification of mixtures of wood ash with geogenic calcite and to follow diagenetic changes due to partial dissolution and re precipitation of ash in two prehistoric cave sites in israel little however is known about the processes responsible for the isotopic compositions of wood ash in relation to formation at various temperatures and the influence on isotopic composition of ash from a variety of plant species here we present an experimental study of wood ash formed by burning three c3 tree species and one c4 desert bush at different temperatures the results indicate that there are significant differences in the isotopic compositions of carbon and oxygen between wood ash that forms by combustion at a relatively low temperature 500 c and at a higher temperature 900 c in addition we show that the isotopic composition of carbon and oxygen in high temperature wood ash approaches equilibrium over a period of several months and that the carbon isotopic composition of low temperature wood ash may reflect the photosynthetic pathway of the burnt woody species lastly we show that the isotopic compositions obtained from wood ash prepared at different temperatures do not reflect a temperature dependent fractionation process but a mixing line between calcite that formed by low temperature combustion and calcite formed by high temperature combustion which later underwent re carbonation with atmospheric co 2 in addition we suggest that exchange processes may possibly occur during combustion between decomposing calcium oxalate and atmospheric o 2 co 2 and co the archaeological implications of this study are discussed in relation to identification of wood ash in the archaeological record identification of fuel sources and burning temperatures and diagenetic changes expected in karstic cave environments the method presented here can be applied at any archaeological site

small lunar craters at the apollo 16 and 17 landing sites morphology and degradation abstract new analysis and modeling approaches are applied to high resolution images and topography of the apollo 16 and 17 landing sites to investigate the morphology and estimate degradation of small lunar craters slcs 35 to 250 m diameter we find slcs at the two sites are mostly degraded with an average depth diameter ratio d d 0 1 resulting in a landscape dominated by shallow inverted cone shaped craters an improved standardized morphological classification and a novel set of quantitative shape indicators are defined and used to compare slcs between the two sites our classification methodology allows morphological class populations to be designated with minimal and measurable ambiguity simplifying the study of slc degradation at different target regions slc shape indicators are computationally obtained from topography further facilitating a quantitative and repeatable comparison across study areas our results indicate that the interior slopes of slcs evolve faster and through different processes relative to larger craters 500 m assuming slcs are formed with large initial depth to diameter ratio d d 0 2 our observation that even the fresher slcs are relatively shallow imply that a faster mass wasting process post formation stabilizes the crater walls and eventually slows down degradation we also found that the apollo 16 cayley plains have a higher percentage of fresh craters than the apollo 17 taurus littrow tl plains a combination of a less cohesive target material and or seismic shaking resulting from moonquakes or the impact of tycho crater secondaries was likely responsible for a higher degradation rate in the tl plains compared to the cayley plains this study explores the relationship between the symmetry and probability densities of key morphological traits like d d mean wall slope and rate of degradation we show that the shape of d d probability density function of slcs in a study area encodes their rate of degradation comparison of power law fitting and probabilistic modeling of depth diameter relations shows that probabilistic methods complement regression models and are necessary for robust prediction of slc depths from diameter and vice versa for different geological targets

ultrahigh temperature stability of sapphirine and kornerupine in ganguvarpatti granulite madurai block southern india

deformation of a high grade gondwana fragment sri lanka abstract the sri lankan gondwana fragment is a high grade gneiss terrain consisting of at least three crustal units namely the wanni complex wc the highland complex hc and the vijayan complex vc which were juxtaposed during the pan african collision at least six phases of ductile deformation were recognized in the smallest gondwana fragment sri lanka there is microscopic and mesoscopic evidence for a first deformation d 1 which occurred during prograde metamorphism but before the main granulite facies metamorphism this first deformation is represented by straight to curved and crenulated inclusion trails in garnet porphyroblasts microfolds in some metapelites and quartzo feldspathic gneisses and by a s 1 foliation preserved in crenulation folds and some rootless intrafolial folds d 2 has two main stages of which the second phase is the most intense and dominant deformation which produced most part of the major composite and transposed compositional layering as well as the prominent stretching lineation l 2 the first stage of d 2 may have been responsible for the formation of a crenulation cleavage of s 1 as seen in garnet porphyroblasts in some metapelites the compositional layering s 2 in metapelites and metasemipelites appears to have formed through the development of a crenulation cleavage f 2 folds are mesoscopic isoclinal rootless and occur as intrafolial folds and their limbs are highly attenuated major part of the deformation during the latter stage of d 2 was non coaxial many minor and large scale recumbent isoclinal folds f 3 were produced during d 3 both d 2 and d 3 were coeval with the peak conditions of granulite facies metamorphism d 4 produced very large gentle nearly e w upright folds probably during the beginning of uplift of the entire high grade assemblage from deeper crustal levels still under granulite facies conditions d 5 is the second strongest deformation and was responsible for the large scale upright folds f 5 which control the present map pattern of sri lanka the superimposition of d 5 folds on d 4 folds gave rise to a large scale type i fold interference pattern of ramsay 1967 d 6 deformation caused local refolding of the f 5 folds and was accompanied by amphibolite facies conditions during uplift the deformation represented by the majority of vein type structures such as patchy charnockite veins cordierite bearing veins and graphite veins clearly post date d 5 it is argued that the wc the hc and the vc in sri lanka may be three distinctly different proterozoic crustal units brought into contact by tectonism in late proterozoic at two different stages

crustal trajectory of sapphirine bearing granulites from ganguvarpatti south india evidence for an isothermal decompression path abstract ganguvarpatti is part of a precambrian terrane characterized by granulite facies rocks including charnockites mafic granulites sapphirine bearing granulites leptynites and gneisses a sequence of reactions deduced from the multiphase reaction textures provide information on the metamorphic history of this area as they formed in response to decompression during uplift geothermobarometry and constraints from reaction textures define a segment of a p t path traversed by the granulites of ganguvarpatti near peak metamorphic conditions of c 800 c and 8 kbar were succeeded by a symplectitic stage at a significantly lower pressure c 700 c and 4 5 kbar documenting a nearly isothermal decompression p t path and rapid uplift c 12 km followed by cooling the presence of many fluid inclusions of extremely low density in the charnockites is consistent with a nearly isothermal uplift path attainment of a maximum pressure of c 8 kbar indicates c 27 km depth of burial during metamorphism this would imply a total crustal thickness of c 65 70 km at 2 6 2 5 ga such a profound crustal thickness and a clockwise decompressive p t path is interpreted as a consequence of tectonic thickening of crust accomplished by collision tectonics of the southern granulite terrane against the dharwar craton along the palghat cauvery shear zone via northward subduction

the effect of target properties on transient crater scaling for simple craters the effects of the coefficient of friction and porosity on impact cratering are not sufficiently considered in scaling laws that predict the crater size from a known impactor size velocity and mass we carried out a systematic numerical study employing more than 1000 two dimensional models of simple crater formation under lunar conditions in targets with varying properties a simple numerical setup is used where targets are approximated as granular or brecciated materials and any compression of porous materials results in permanent compaction the results are found to be consistent with impact laboratory experiments for water low strength and low porosity materials e g wet sand and sands using this assumption we found that both the friction coefficient and porosity are important for estimating transient crater diameters as is the strength term in crater scaling laws i e the effective strength the effects of porosity and friction coefficient on impact cratering were parameterized and incorporated into group scaling laws and predict transient crater diameters within an accuracy of 5 for targets with friction coefficients f 0 4 and porosities 0 30 moreover 90 crater scaling relationships are made available and can be used to estimate transient crater diameters on various terrains and geological units with different coefficient of friction porosity and cohesion the derived relationships are most robust for targets with 10 15 applicable for a lunar environment and could therefore yield significant insights into the influence of target properties on cratering statistics

pb loss patterns in zircons from a high grade metamorphic terrain as revealed by different dating methods upb and pbpb ages for igneous and metamorphic zircons from northern sri lanka abstract we report u pb and 207 pb 206 pb ages for multigrain fractions single grains and grain domains in zircons from highgrade igneous and sedimentary rocks of the vavuniya charnockite province vcp in northern sri lanka using the ionmicroprobe shrimp a new vapour digestion technique vdt and evaporation charnockitic enderbitic and mangeritic gneisses are derived from i type tonalitic syenitic granodioritic and granitic precursors for which the u pb systematics of zircons as determined by shrimp suggest crystallization ages between 1000 and 1100 ma many translucent round and multifacetted zircons in these rocks are not of metamorphic but of igneous origin and acquired their shape through partial zircon dissolution and recrystallization the large majority of zircons exhibit severe and variable pb loss some 540 580 ma ago which we ascribe to granulite grade metamorphism almost immediately followed by local retrogression most of the zircons lost pb from the entire grain with no domains remaining that reflect the original pb isotopic composition it was therefore impossible to obtain meaningful 207 pb 206 pb evaporation ages for such grains and this cautions against use of this method in zircons that experienced severe pb loss however zircons formed during high grade metamorphism apparently retain their primary pb isotopic composition and were dated successfully by the evaporation technique yielding ages between 553 26 and 560 30 ma conventional multigrain analysis and small fractions following vdt for two samples although much more precise than the shrimp data yielded only strongly discordant data points with patterns reflecting variable pb loss these data alone would not have made it possible to obtain reliable primary zircon crystallization ages 207 pb 206 pb evaporation ages for detrital zircons from two garnetiferous gneiss samples of sedimentary origin in the centre of the vcp revealed a maximum age of 1329 18 ma whereas a metaquartzite near the southern margin of the vcp contained zircons with 207 pb 206 pb ages between 1857 14 and 2543 14 ma we interpret the latter rock as belonging to the highland complex which occurs adjacent to the vcp our zircon data in combination with nd model ages milisenda et al 1994 suggest the vcp to be part of the wanni complex a distinct crustal domain in northern sri lanka characterized by relatively young ages in comparison with much older ages in the adjacent highland complex

dependence of secondary crater characteristics on downrange distance high resolution morphometry and simulations on average secondary impact craters are expected to deepen and become more symmetric as impact velocity vi increases with downrange distance l we have used high resolution topography 1 2 m pixel to characterize the morphometry of secondary craters as a function of l for several well preserved primary craters on mars the secondaries in this study n 2 643 span a range of diameters 25 m d 400 m and estimated impact velocities 0 4 km s vi 2 km s the range of diameter normalized rim to floor depth d d broadens and reaches a ceiling of d d 0 22 at l 280 km vi 1 1 2 km s whereas average rim height shows little dependence on vi for the largest craters h d 0 02 d 60 m populations of secondaries that express the following morphometric asymmetries are confined to regions of differing radial extent planform elongations l 110 160 km taller downrange rims l 280 km and cavities that are deeper uprange l 450 500 km populations of secondaries with lopsided ejecta were found to extend to at least l 700 km impact hydrocode simulations with isale 2d for strong intact projectile and target materials predict a ceiling for d d vs l whose trend is consistent with our measurements this study illuminates the morphometric transition from subsonic to hypervelocity cratering and describes the initial state of secondary crater populations this has applications to understanding the chronology of planetary surfaces and the long term evolution of small crater populations

modeling damage and deformation in impact simulations numerical modeling is a powerful tool for investigating the formation of large impact craters but is one that must be validated with observational evidence quantitative analysis of damage and deformation in the target surrounding an impact event provides a promising means of validation for numerical models of terrestrial impact craters particularly in cases where the final pristine crater morphology is ambiguous or unknown in this paper we discuss the aspects of the behavior of brittle materials important for the accurate simulation of damage and deformation surrounding an impact event and the care required to interpret the results we demonstrate this with an example simulation of an impact into a terrestrial granite target that produces a 10 km diameter transient crater the results of the simulation are shown in terms of damage a scalar quantity that reflects the totality of fragmentation and plastic strain both total plastic strain the accumulated amount of permanent shear deformation regardless of the sense of shear and net plastic strain the amount of permanent shear deformation where the sense of shear is accounted for damage and plastic strain are both greatest close to the impact site and decline with radial distance however the reversal in flow patterns from the downward and outward excavation flow to the inward and upward collapse flow implies that net plastic strains may be significantly lower than total plastic strains plastic strain in brittle rocks is very heterogeneous however continuum modeling requires that the deformation of the target during an impact event be described in terms of an average strain that applies over a large volume of rock large compared to the spacing between individual zones of sliding this paper demonstrates that model predictions of smooth average strain are entirely consistent with an actual strain concentrated along very narrow zones furthermore we suggest that model predictions of total accumulated strain should correlate with observable variations in bulk density and seismic velocity

impact induced seismic activity on asteroid 433 eros a surface modification process high resolution images of the surface of asteroid 433 eros revealed evidence of downslope movement of a loose regolith layer as well as the degradation and erasure of small impact craters less than 100 meters in diameter one hypothesis to explain these observations is seismic reverberation after impact events we used a combination of seismic and geomorphic modeling to analyze the response of regolith covered topography particularly craters to impact induced seismic shaking applying these results to a stochastic cratering model for the surface of eros produced good agreement with the observed size frequency distribution of craters including the paucity of small craters

paleoclimate of the kimmeridgian tithonian late jurassic world i results using a general circulation model abstract the kimmeridgian tithonian 154 7 145 6 ma middle and late late jurassic was a time of expanded continental rifting increased sea floor spreading and a relatively high eustatic sea level stand these processes collectively caused the fragmentation and flooding of the megacontinent pangea as well as the alteration of the global paleoclimate using a version of the community climate model ccm from the national center for atmospheric research we report two kimmeridgian tithonian paleoclimate seasonal simulations with geologically inferred paleotopography one using a co 2 concentration of 280 ppm pre industrial level and the other 1120 ppm increasing the co 2 four fold warms virtually the entire planet the greatest warming occurs over the higher latitude oceans and the least over the equatorial and subtropical regions simulation of a warmer planet with an elevated greenhouse effect fits the distribution of paleoclimatically sensitive faunas floras and sedimentary rocks model results indicate that sea ice was restricted to the high latitudes of the boreal and austral seas making landfall only in restricted areas the trade winds bring heavy rainfall in december january february to eastern gondwana and in june july august to the tethys sea margins a strong june july august monsoon occurs over southeast asia the distribution of coals correlates to precipitation sufficient to maintain gymnosperm forests and coastal areas where water saturated sediments are a result of eustatic high stands of sea level evaporites are localized to areas of negative precipitation evaporation runoff is restricted to regions of intense precipitation overall the 1120 ppm co 2 simulation provides a reasonable paleoclimate for the kimmeridgian tithonian and provides a standard until a ccm with oceanic heat transport a coupled atmospheric oceanic model or one with a finer grid cell configuration is available the results need further scrutiny in areas with more detailed geologic information

the morphology of small fresh craters on mars and the moon the depth diameter ratio for new meter to decameter scale martian craters formed in the last 20 years averages 0 23 only slightly deeper than that expected for simple primary craters on rocky surfaces large variations in depth diameter d d between impact sites indicate that differences between the sites such as target material properties impact velocity angle and physical state of the bolide s are important in determining the depth of small craters in the strength regime on the moon the d d of random fresh small craters with similar diameters averages only 0 10 indicating that either the majority of them are unrecognized secondaries or some proportion are degraded primaries older craters such as these may be shallower due to erosional infilling which is probably not linear over time but more effective over recently disturbed and steeper surfaces processes that are not yet acting on the new martian craters brand new meter to decameter scale craters such as the martian ones studied here are statistically easily distinguishable as primaries but the origins of older craters of the same size such as the lunar ones in this study are ambiguous

stable carbon isotope ratios and their relevance to the determination of accurate radiocarbon dates for lime mortars abstract attempts have been made to date mortar by radiocarbon analysis potential problems are discussed and the possible use of stable carbon isotopes to detect contamination by geological carbonates is investigated

u pb isotopic systematics of zircons from prograde and retrograde transition zones in high grade orthogneisses sri lanka we present u pb zircon isotopic data from locally restricted prograde arrested in situ charnockitization and retrograde metamorphic transition zones which are well exposed in proterozoic orthogneisses tectonically interbanded with granulite facies supracrustal rocks of the highland group in sri lanka these granitoid rocks yield apparent ages of 1942 pm 22 ma 770 ma 660 ma and 560 ma all samples show severe pb loss some 550 560 ma ago the main phase of granulite formation could not be dated unambiguously but is bracketed between 660 ma and 550 ma the pervasive pb loss event around 550 560 ma reflects the end of this period of high grade metamorphism and was associated with widespread igneous activity and retrogression this is constrained by the 550 pm 3 ma intrusion age for a post tectonic granite we relate this late phase of thermal activity to crustal uplift of the sri lankan granulites our data unambiguously prove the high grade history of the sri lanka gneisses to be a late

sapphirine bearing granulites and related high temperature metamorphic rocks from the higo metamorphic terrane west central kyushu japan the higo metamorphic unit in west central kyushu island southwest japan is an imbricated crustal section in which a sequence of units with increasing metamorphic grade from high northern part to low southern part structural levels is exposed the basal part of the metamorphic sequence representing an original depth of 23 24 km consists mainly of garnet cordierite biotite gneiss garnet orthopyroxene gneiss orthopyroxene bearing amphibolite and orthopyroxene bearing s type tonalite these metamorphic rocks underwent high amphibolite facies up to granulite facies metamorphism with peak p t conditions of 720 mpa 870 c in addition sapphirine bearing granulites and related high temperature metamorphic rocks also occur as tectonic blocks in a metamorphosed peridotite intrusion the sapphirine bearing granulites and their related high temperature metamorphic rocks can be subdivided into five types of mineral assemblages reflecting their bulk chemical compositions as follows 1 sapphirine corundum spinel cordierite 2 corundum spinel cordierite 3 garnet corundum spinel cordierite 4 garnet spinel gedrite corundum and 5 orthopyroxene spinel gedrite these metamorphic rocks are characterized by unusually high al2o3 and low sio2 contents which could represent a restitic nature remaining after partial melting of pelitic granulite under the ultra high temperature contact metamorphism at the peak metamorphic event of the higo metamorphic unit the metamorphic conditions are estimated to be about 800 mpa and above 950 c which took place at about 250 ma as a result of the thermal effect of the regional gabbroic rock intrusions

a geometric model for excavation and modification at terrestrial simple impact craters a geometric model for the excavation and modification of simple crater development is presented modification is modelled by considering the relative dimensions and geometries of the final crater and the transient cavity formed by excavation and displacement the input parameters required are the rim crest diameter of the final crater the depth to autochthonous basement the rim crest height and the outer rim slope the model calculates the diameter of the final crater at the original ground plane the dimensions of the transient cavity and the rim crest volume difference between the final and transient cavities this volume is considered to be the material which slumped off the unstable overheightened transient cavity wall during modification and corresponds to the observed volume of the breccia lens within the final crater excavation is approximated by a steady state z model with the diameter of excavation equivalent to the previously modelled diameter of the transient cavity at the original ground plane the center of flow taken as 1 projectile diameter and z 2 5 3 0 the z model predicts such parameters as the depth and volume of excavation which can be compared with observational data the applicability of the model has been tested with data from meteor and brent craters in the case of meteor the modelled final crater diameter at the original ground plane is within 26 m of the observed value and the modelled breccia lens and the rim crest volumes of the final true crater are within 9 5 and 2 5 respectively of observed values the results of the z model for meteor crater with z 2 8 0 1 give results consistent with observational data on the depth and volume of excavation the correspondence for the more degraded brent crater is less precise as there is greater uncertainty in the input parameters it is possible however to match the model parameters with the breccia lens volume and published estimates of original dimensions the modelled excavated volumes for meteor and brent are 58 and 55 respectively of the transient cavity volume below the original ground plane in the absence of additional observational data for further testing it is concluded that the model may provide first order spatial information on the formation of simple craters

stable carbon and oxygen isotope investigation in historical lime mortar and plaster results from field and experimental study abstract lime mortar and plaster were sampled from roman medieval and early modern buildings in styria the historical lime mortar and plaster consist of calcite formed in the matrix during setting and various aggregates the stable c and o isotopic composition of the calcite matrix was analyzed to get knowledge about the environmental conditions during calcite formation the 13 c matrix and 18 o matrix values range from 31 to 0 and 26 to 3 vpdb respectively obviously such a range of isotope values does not represent the local natural limestone assumed to be used for producing the mortar and plaster in an ideal case the calcite matrix in lime mortar and plaster is isotopically lighter in the exterior vs the interior mortar layer according to the relationship 18 o matrix 0 61 13 c matrix 3 3 vpdb calcite precipitation by uptake of gaseous co 2 into alkaline ca oh 2 solutions shows a similar relationship 18 o calcite 0 67 13 c calcite 6 4 vpdb both relationships indicate that the 13 c 12 c and 18 o 16 o values of the calcite reflect the setting behaviour of the lime mortar and plaster initially co 2 from the atmosphere is fixed as calcite which is accompanied by kinetic isotope fractionation mostly due to the hydroxylation of co 2 13 c matrix 25 and 18 o matrix 20 as calcite formation continued the remaining gaseous co 2 is subsequently enriched in 13 c and 18 o causing later formed calcite to be isotopically heavier along the setting path in the matrix deviations from such an ideal isotopic behaviour may be due to the evolution of h 2 o e g evaporation the source of co 2 e g from biogenic origin relicts of the natural limestone and secondary effects such as recrystallization of calcite the results of the field and experimental study suggest that isotope values can be used as overall proxies to decipher the origin of carbonate and the formation conditions of calcite in the matrix of ancient and recent lime mortar and plaster moreover these proxies can be used to select calcite matrix from historical lime mortar and plaster for 14 c dating