timing of crystallization of the lunar magma ocean constrained by the oldest zircon the primitive moon was covered with a thick layer of melt known as the lunar magma ocean whose crystallization resulted in the moon s surface as it is observed today dating of the oldest zircon so far in lunar rocks indicates that much of the magma was probably crystallized within 100 million years of the moon s formation

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

active fault related folding in the epicentral area of the december 25 1222 io ix mcs brescia earthquake northern italy seismotectonic implications abstract a dense grid of petroleum industry seismic reflection profiles coupled with field mapping exploratory trenching and geomorphic and structural analysis are used to characterize the quaternary growth history of the capriano del colle fault system one of several inferred active buried thrusts that extend across the po plain in northern italy shortening is characterized here by a deeply buried south vergent forethrust and an associated north vergent backthrust whose upward propagation is expressed by fault propagation folding near the surface structural interpretation based on seismic data suggests that strain is accommodated at very shallow levels by secondary flexural slip thrusts and reverse faults developed on synclinal flanks that emanate from active axial surfaces analysis of syntectonic growth strata document maximum rates of dip slip of 3 45 0 66 mm yr 1 6 myr 1 2 myr and 0 47 0 22 mm yr during a more recent time period 0 89 myr present a quarry excavation at capriano del colle allows a preliminary paleoseismologic analysis of coseismic surface faulting and liquefaction exposed near the core of an active mid pleistocene to holocene anticline these features are interpreted to be generated during strong local earthquakes consistent with the environmental effects and ground motions of an event similar to the december 25 1222 brescia earthquake io ix mcs this indicates for the first time that compressive folds and blind thrusts in the po plain are currently accommodating slow rates of modern contraction in an active zone of the southern alps that extends from lake garda to varese we thus argue that earthquakes similar to the december 25 1222 brescia event are likely to occur in this region and pose a direct threat to such a densely populated and developed area

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

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

persistent solar influence on north atlantic climate during the holocene surface winds and surface ocean hydrography in the subpolar north atlantic appear to have been influenced by variations in solar output through the entire holocene the evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon 14 and beryllium 10 and centennial to millennial time scale changes in proxies of drift ice measured in deep sea sediment cores a solar forcing mechanism therefore may underlie at least the holocene segment of the north atlantic9s 1500 year cycle the surface hydrographic changes may have affected production of north atlantic deep water potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally

argon 40 argon 39 age spectra of apollo 17 highlands breccia samples by laser step heating and the age of the serenitatis basin we have obtained high resolution 21 63 steps 40ar 39ar age spectra using a continuous laser system on 19 submilligram samples of melt rocks and clasts from apollo 17 samples collected from the pre imbrian highlands in the easternmost part of the serenitatis basin the samples include poikilitic melt rocks inferred to have been formed in the serenitatis basin forming impact aphanitic melt rock whose compositions vary and whose provenance is uncertain and granulite gabbro and melt clasts three of the poikilitic melts have similar age spectrum plateau ages 72395 96 3893 16 ma 2 72535 7 3887 16 ma 76315 150 3900 16 ma with a weighted mean age of 3893 9 ma which we interpret as the best age for the serenitatis basin forming impact published 40ar 39ar age spectrum ages of apollo 17 poikilitic melts are consistent with our new age but are much less precise two poikilitic melts did not give plateaus and the maxima in their age spectra indicate ages of 3869 ma 72558 7 and 3743 ma 77135 178 plateau ages of two poikilitic melts and two gabbro clasts from 73155 range from 3854 16 ma to 3937 16 ma and have probably been affected by the ubiquitous older clasts and by post formation heating impact events plateau ages from two of the aphanitic melt blobs and two granulites in sample 72255 fall in the narrow range of 3850 16 ma to 3869 16 ma with a weighted mean of 3862 8 ma two of the aphanitic melt blobs from 72255 have ages of 3883 16 ma and 3894 ma whereas a poikilitic melt clast of different composition from the serenitatis melts has an age of 3835 16 ma which is the upper limit for the accretion of 72255 these data suggest that either the aphanitic melts vary in age as is also suggested by their varying chemical compositions or they formed in the 72255 accretionary event about 3 84 3 85 ga and older relict material is responsible for the dispersion of ages in any case the aphanitic melts do not appear to be serenitatis products our age for the serenitatis impact shows on the basis of the isotopic age evidence alone that serenitatis is 20 25 ma and probably 55 60 ma older than imbrium 3870 ma and probably 3836 ma dalrymple and ryder 1993 noritic granulite sample 78527 has a plateau age of 4146 17 ma representing a minimum age for cooling of this sample in the early lunar crust so far there is no convincing evidence in the lunar melt rock record for basin forming impacts significantly older than 3 9 ga

petrological and thermal histories of a lunar breccia 73217 as inferred from pyroxene crystallization sequences exsolution phenomena and pyroxene geothermometry electron probe microanalyses x ray diffraction studies and pyroxene geothermometry of blue gray breccia 73217 indicate a record of an early plutonic period and a later thermal event the breccia contains two domains one breccia a contains coarse orthopyroxene clasts whereas the other breccia b contains coarse pigeonite clasts pyroxene trends deduced from pyroxene clasts from breccias a and b are analogous to the early and late fractionation stages respectively of terrestrial basic layered intrusions minor element compositions of both augite and ca poor pyroxenes from breccias a and b vary continuously with feo mgo feo ratio optical and x ray observations reveal that pyroxene clasts show a great variety of exsolution textures but that individual pyroxene grains show relatively simple and less intensive exsolution patterns there is no overlap in mineral compositions of pyroxenes as well as plagioclase and ilmenite clasts between breccias a and b these characteristics are consistent with a model that the coarse mineral clasts of both breccias a and b possibly originated from the same relatively small layered intrusion i e breccia a being derived from an early stage 1100 1060 c 20 c and b from a later stage of fractionation 1060 1050 c both breccias experienced a later common annealing event 1040 1070 c

holocene and eemian climatic optima in the korean peninsula based on textural and carbon isotopic records from the stalagmite of the daeya cave south korea abstract textural and stable isotopic records from the absolute dated stalagmite of the daeya cave dy 1 provide new insights into the climatic evolution of the korean peninsula during the holocene and eemian climatic optima the stalagmite yielded ages of 8572 227 to 5907 158 and 1 23 456 535 to 1 19 837 1089 years which coincide with the holocene and eemian climatic optima respectively the stalagmite s 13 c record closely resembles previously reported chinese speleothem 18 o data thus it can be suggested that textural and geochemical results of the dy 1 reflect east asian monsoon intensity which is forced by summer insolation patterns in the northern hemisphere lighter carbon isotopic compositions well developed fibrous calcite crystals and their relatively faster growth rate in the stalagmite sample are interpreted to reflect the warmest and wettest climate conditions of the holocene and eemian interglacials both climatic optima took place when insolation was decreasing from its maximum level temperature in greenland was highest and sea level approached its maximum level these climatic optima also coincide with decreasing antarctic temperatures compared the dy 1 data to other proxies it is suggested that the holocene and eemian climatic optima developed through a balance among boreal insolation monsoon intensity and sea level also continental ice volume which are the main climatic forcing factors in the northern hemisphere these trends also follow the bi polar seesaw mechanism as previously described

characteristics of deep marine dolomite abstract deep marine sediment has not been subjected to the influences of meteoric waters deep burial or tectonic stress that have profoundly altered most rocks available to us in continental exposures hence it preserves the record of formation and early development of its dolomite evaluation of the dsdp x ray and smear slide data files indicates that dolomite is a common component in deep marine sediments it averages 1 and is found in all sampled ocean basins throughout post jurassic time dolomite abundance is not related to the abundance of any other detrital authigenic or alteration mineral except aragonite petrographic examination of 48 samples suggests that deep marine dolomite crystal size and appearance are similar to the size and appearance in modern supratidal deposits do omite does not increase in abundance or in crystal size downhole nor does crystal size increase with increasing age the dolomite is commonly nonstoichiometric avg 56 caco3 and poorly ordered globally it does not change in stoichiometry or order with depth or age dolomite in deep marine sediments does not originate from unusual or regionally important conditions it entered the sediments early most probably as a chemical precipitate from pore waters an uncertain amount estimated to be 10 is detrital

el nino as a mediator of the solar influence on climate 1 using a climate model of intermediate complexity we simulate the response of the el nino southern oscillation enso system to solar and orbital forcing over the holocene solar forcing is reconstructed from radiocarbon production rate data using various scaling factors to account for the conflicting estimates of solar irradiance variability as estimates of the difference since the maunder minimum range from 0 05 to 0 5 of the solar constant we consider these two extreme scenarios along with the intermediate case of 0 2 we show that for large or moderate forcings the low pass filtered east west sea surface temperature gradient along the equator responds almost linearly to irradiance forcing with a short phase lag about a decade wavelet analysis shows a statistically significant enhancement of the century to millennial scale enso variability for even a moderate irradiance forcing in contrast the 0 05 case displays no such enhancement orbitally driven insolation forcing is found to produce a long term increase of enso variability from the early holocene onward in accordance with previous findings when both forcings are combined the superposition is approximately linear in the strong scaling case overall the sea surface temperature response is of the magnitude required and is persistent enough to induce important climatic perturbations worldwide the results suggest that enso may plausibly have acted as a mediator between the sun and the earth s climate a comparison to key holocene climate records from the northern hemisphere subtropics and midlatitudes shows support for this hypothesis

the complex stratigraphy of the highland crust in the serenitatis region of the moon inferred from mineral fragment chemistry large impact basins are natural drill holes into the moon and their ejecta carries unique information about the rock types and stratigraphy of the lunar crust we have conducted an electron microprobe study of mineral fragments in the poikilitic melt breccias collected from the taurus mountains at the apollo 17 landing site these breccias are virtually unanimously agreed to be impact melt produced in the serenitatis impact event they contain lithic fragments and much more abundant mineral fragments of crustal origin we have made precise microprobe analyses of minor element abundances in fragments of olivine pyroxene and plagioclase to provide new information on the possible source rocks and the crustal stratigraphy in the serenitatis region these data were also intended to elucidate the nature of the cryptic geochemical component in breccias such as these with low k fra mauro basalt compositions we chose the finest grained i e most rapidly quenched breccias for study to avoid reacted and partly assimilated fragments as much as possible most of the mineral fragments appear to have been derived from rocks that would fall into the pristine igneous mg suite as represented by lithic fragments in the apollo collection or reasonable extensions of it gabbroic rocks were more abundant in the target stratigraphy than is apparent from the apollo sample collection some pyroxene and plagioclase but probably not much olivine could be derived from feldspathic granulites which are metamorphosed polymict breccias some mineral fragments are from previously unknown rocks these include highly magnesian olivines up to fo94 possibly volcanic in origin that exacerbate the difficulty in explaining highly magnesian rocks in the lunar crust it appears that some part of the lunar interior has an mg 100 mg mg fe atomic greater than the conventional bulk moon value of 80 84 other volcanic rocks including mare basalts and rapidly cooled impact melt rocks do not contribute significantly to the fragment population nor do ferroan anorthosites contribute more than a tiny part of even the plagioclase fragment population a few mineral fragments that are consistent with the cryptic low k fra mauro chemical component were found and these appear to be from gabbroic sources the mineral fragment populations cannot be mixed in their observed proportions to produce the whole rock composition because the fragments are more refractory and deficient in ti p and alkalis a preferential contribution to the melt from a rock similar to sodic ferrogabbro can partly resolve the discrepancy the population of mineral fragments requires a very diverse population of igenous rocks that are not all related to each other demonstrating the existence of a complex crust built of numerous separate igneous plutons many of these plutons may have crystallized at shallow depths the chemical composition of the melt breccias in combination with the mineral fragment data and an understanding of the cratering process suggests that the deepest crust sampled by the serenitatis impact not necessarily the deepest crust was basaltic in composition including kreep and gabbroic rocks like sodic ferrogabbro and lacking abundant olivine rich material these were overlain by mg suite rocks of varied types including norites and troctolites that supplied most of the olivine mineral fragments granulites which are metamorphosed and more feldspathic breccias were abundant near the surface remote sensing indicates that the entire serenitatis region lacks ferroan anorthosite consistent with the results of our study

sixth foray for pristine nonmare rocks and an assessment of the diversity of lunar anorthosites eleven nonmare samples are characterized generally both compositionally and petrographically five are almost certainly pristine ferroan anorthosite 10056c alkali anorthosite 14047c ferroan anorthosite 14312c anorthositic troctolite 14321c3 and granite 14321c4 and four are probably pristine norite 14318c noritic anorthosite 67215 quasi pristine ferroan anorthosite 73217c and norite 78527 five are unique anorthosites extending the diversity of lunar anorthosites considerably alkali anorthosites particularly 14047c are extremely rich in incompatible elements the first anorthosite from apollo 11 with manifestations of pristinity 10056c appears to be a normal member of the ferroan group however the first pristine ferroan anorthosites from apollo 14 and 17 to be studied in detail 14312c and 73217c both have unusually sodic plagioclase by ferroan standards with only 75 plagioclase 67215 is the first large 273 g probably pristine ferroan sample with less than 83 plagioclase the nature of the correlations between longitude and such parameters as eu and sm concentrations and sc sm ti sm and ca na ratios among pristine ant samples has been elucidated because five of the new pristine samples are from a western site apollo 14 interestingly ferroan anorthosite 14312c has ca na sc sm and ti sm ratios close to the normal ferroan values but significantly displaced in the direction of the nonferroan western pristine rocks this suggests that the composition longitude relationships are as old as the late stages of the crystallization of the putative magma ocean

the case for an imbrium origin of the apollo thorium rich impact melt breccias abstract mafic th rich impact melt breccias most of which are identified with the composition known as low k fra mauro lkfm are the most common rock type in the nonmare regoliths of the apollo lunar landing sites the origin of mafic impact melt breccias bears on many lunar problems the nature of the late meteoroid bombardment cataclysm the spatial distribution of kreep both near the surface and at depth the ages of the major basins and the composition of the early crust of the nearside lunar highlands thus it is crucial that the origin of mafic impact melt breccias be accurately understood because of both intra and intersite differences in compositions of mafic impact melt breccia samples apparent differences in crystallization age and differences in siderophile element ratios previous studies have argued that either 1 most mafic impact melt breccias are the products of several large craters local to the site at which they were found but that some are of basin origin or that 2 they are all from the imbrium apollos 14 and 15 nectaris apollo 16 and serenitatis apollo 17 basins here we reconsider the hypothesis that virtually all of the th rich mafic impact melt breccias from the apollo missions are products of the imbrium impact ejecta deposit modeling based on modern crater scaling indicates that the imbrium event produced ejecta deposits that average hundreds of meters thick or more at all apollo highland sites which is thicker than some previous estimates substantial amounts of imbrium ejecta should have been sampled at every apollo highland site we suggest that the mafic impact melt breccias may be the principal form of those ejecta the imbrium projectile impacted into th rich material that we regard as part of a unique mafic lunar geochemical province we call the high th oval region based on the surface distribution of th only basins within the high th oval region excavated th rich material the th concentrations of the highlands as observed by the apollo orbiting ray experiments are consistent with the estimates from ejecta modeling of the younger basin forming impacts only imbrium was large enough to produce the copious amount of melt required by the ubiquitous presence of mafic impact melt breccias in the apollo sampled regolith the high th oval region still may have been molten or hot at shallow depths 4 ga ago when the imbrium projectile struck we reason that compositional heterogeneity of ejected melt breccia is to be expected under these circumstances we argue that siderophile element fingerprints of mafic impact melt breccias are not inconsistent with production of all common types by a single projectile we suggest that the narrow range of ages of 3 7 4 0 ga for all successfully dated mafic impact melt breccias may reflect a single event whose age is difficult to measure precisely rather than a number of discrete impact events closely spaced in time such that reported age variations among mafic impact melt breccias reflect the ability to measure 40ar 39ar ages with greater precision than the accuracy with which measured portions of mafic impact melt breccias have recorded the time of their formation

diagenesis of silica rich mound bedded chalk the coniacian arnager limestone denmark abstract the coniacian arnager limestone formation is exposed on the danish island of bornholm in the baltic sea it is composed of mound bedded siliceous chalk and x ray diffraction and scanning electron microscopy indicate a content of 30 70 insoluble minerals including authigenic opal ct quartz clinoptilolite feldspars calcite dolomite and barite opal ct and clinoptilolite are the most common and constitute 16 53 and 2 9 respectively the content of insoluble minerals varies laterally both within the mounds and in planar beds and the opal ct content varies by up to 10 vertically the mounds consist of two microfacies spiculitic wackestone and bioturbated spiculitic wackestone containing 10 22 and 7 12 moulds after spicules respectively subsequent to deposition and shallow burial dissolution of siliceous sponge spicules increased the silica activity of the pore water and initiated precipitation of opal ct the opal ct formed at temperatures around 17 c the precipitation lowered the silica activity and the si al ratio of the pore water resulting in precipitation of clinoptilolite feldspar and smectite calcite formed synchronously with the latest clinoptilolite minor amounts of quartz precipitated in pore water with low silica activity during maximum burial probably to depths of 200 250 m the dissolution of sponge spicules and decomposition of the sponge tissue also resulted in the release of ba2 sr2 mg2 ca2 and co32 facilitating precipitation of barite and dolomite precipitation of especially opal ct reduced the porosity to an average of 40 and cemented the limestone the study highlights the diagenetic pathways of bio siliceous chalk and the effects on preservation of porosity and permeability

a terrestrial perspective on using ex situ shocked zircons to date lunar impacts deformed lunar zircons yielding u pb ages from 4333 ma to 1407 ma have been interpreted as dating discrete impacts on the moon however the cause of age resetting in lunar zircons is equivocal as ex situ grains in breccias they lack lithologic context and most do not contain microstructures diagnostic of shock that are found in terrestrial zircons detrital shocked zircons provide a terrestrial analog to ex situ lunar grains for both identifying diagnostic shock evidence and also evaluating the feasibility of dating impacts with ex situ zircons electron backscatter diffraction and sensitive high resolution ion microprobe u pb analysis of zircons eroded from the ca 2020 ma vredefort impact structure south africa show that complete impact age resetting did not occur in microstructural domains characterized by microtwins planar fractures and low angle boundaries which record ages from 2890 ma to 2645 ma an impact age of 1975 39 ma was detected in neoblasts within a granular zircon that also contains shock microtwins which link neoblast formation to the impact however we show that granular texture can form during regional metamorphism and thus is not unique to impact environments these results demonstrate that dating an impact with ex situ shocked zircon requires identifying diagnostic shock evidence to establish impact provenance and then targeting specific age reset microstructures with the recognition that zircon can deform plastically in both impact and magmatic environments age resetting in lunar zircons that lack diagnostic shock deformation may record magmatic processes rather than discrete impacts identifying shock microstructures that record complete age resetting for geochronological analysis is thus crucial for constructing accurate zircon based impact chronologies for the moon earth or other planetary bodies

contributions of la nina and el nino to middle holocene drought and late holocene moisture in the american southwest eolian landforms in estancia basin central new mexico record two episodes of extreme drought and low groundwater levels during the middle holocene 7000 5400 1 4 c yr b p followed by a rise in the water table throughthe late holocene blowouts and associated lunettes formed when water levels fell below the desiccated floor of pluvial lake estancia allowing widespread deflation elevation of the water table in the basin is regulated by a balance between evaporation from playas that occupy the blowouts and recharge of aquifers in the adjacent manzano mountains isotopic analyses of modern precipitation and groundwater reveal that recharge originates primarily as winter moisture which is amplified during el ninos and diminished during la ninas thus changes in the elevation of a reconstructed holocene water table may reflect systematic changes in el nino southern oscillation enso circulation

apollo 12 breccia 12013 impact induced partial pb loss in zircon and its implications for lunar geochronology abstract apollo 12 breccia 12013 is composed of two portions one grey in colour the other black the grey portion of the breccia consists mainly of felsite thought to have formed during a single crystallisation event while the black part is characterized by presence of lithic fragments of noritic rocks and individual plagioclase crystals in this study u pb analyses of ca phosphate and zircon grains were conducted in both portions of the breccia the zircon grains within the grey portion yielded a large range of ages 4154 7 to 4308 6 ma 2 and show decreasing u and th concentrations within the younger grains moreover some grains exhibit recrystallisation features and potentially formation of neoblasts the latter process requires high temperatures above 1600 1700 c leading to the decomposition of the primary zircon grain and subsequent formation of new zircon occurring as neoblasts as a result of the high temperatures the u pb system of the remaining original zircon grains was most likely open for pb diffusion causing partial resetting and the observed range of 207pb 206pb ages the event that led to the pb loss in zircon could potentially be dated by the u pb system in ca phosphates which have a weighted average 207pb 206pb age across both lithologies of 3924 3 ma 95 conf this age is identical within error to the combined average 207pb 206pb age of 3926 2 ma that was previously obtained from ca phosphates within apollo 14 breccias zircon grains in apollo 12 impact melt breccias and the lunar meteorite sau 169 this age was interpreted to date the imbrium impact the zircon grains located within the black portion of the breccia yielded a similar range of ages 4123 13 to 4328 14 ma 2 to those in the grey portion given the brecciated nature of this part of the sample the interpretation of these ages as representing igneous crystallisation or resetting by impact events remains ambiguous since there is no direct link to their source rocks via textural relationships or crystal chemistry similarly the currently available zircon data set for all lunar samples may be distorted by partial pb loss resulting in meaningless and misleading age distribution patterns therefore it is crucial to fully understand and recognize the processes and conditions that may lead to partial resetting of the u pb system in zircon in order to better constrain the magmatic and impact history of the moon

a young solidification age for the lunar magma ocean abstract the time at which the lunar magma ocean solidified can be determined from the lu hf isotope systematics of lunar rocks derived from magma sources that formed during crystallization of the lunar magma ocean the final magma ocean crystallization product termed urkreep is enriched in incompatible elements including k ree and p we have determined the initial hf isotopic compositions of four samples two kreep basalts and two mg suite norites the incompatible trace element compositions of these samples are controlled by an urkreep component and therefore the initial hf isotopic compositions of these samples represent the hf isotopic evolution of urkreep in order to correct the effects of neutron irradiation on the hf isotopic compositions of these samples we have developed a model that uses the stable hf and sm isotopic compositions measured on an irradiated sample to determine and correct for the thermal and epithermal neutron fluence that has modified the hf isotopic composition of the sample we use our corrected results to calculate a 176 lu 176 hf urkreep model age of 4353 37 ma and the 176 lu 177 hf of urkreep to be 0 0153 0 0033 the lu hf model age is concordant with the re calculated sm nd urkreep model age of 4389 45 ma and we take the average of these ages 4368 29 ma to represent the time at which urkreep formed this age is concordant with the age of the most reliably dated ferroan noritic anorthosite as well as 142 nd model ages for the formation or re equilibration of mare basalt sources taken together these ages indicate that the moon experienced a widespread large scale magmatic event around 4370 ma most plausibly attributed to solidification of the lunar magma ocean

correlated δ 18 o and ti in lunar zircons a terrestrial perspective for magma temperatures and water content on the moon zircon grains were separated from lunar regolith and rocks returned from four apollo landing sites and analyzed in situ by secondary ion mass spectrometry many regolith zircons preserve magmatic 18o and trace element compositions and although out of petrologic context represent a relatively unexplored resource for study of the moon and possibly other bodies in the solar system the combination of oxygen isotope ratios and ti provides a unique geochemical signature that identifies zircons from the moon the oxygen isotope ratios of lunar zircons are remarkably constant and unexpectedly higher in 18o 5 61 0 07 vsmow than zircons from earth s oceanic crust 5 20 0 03 even though mare basalt whole rock samples are nearly the same in 18o as oceanic basalts on earth 5 6 thus the average fractionation of oxygen isotopes between primitive basalt and zircon is smaller on the moon 18o wr zrc 0 08 0 09 than on earth 0 37 0 04 the smaller fractionations on the moon suggest higher temperatures of zircon crystallization in lunar magmas and are consistent with higher ti in lunar zircons phase equilibria estimates also indicate high temperatures for lunar magmas but not specifically for evolved zircon forming melts if the solidus temperature of a given magma is a function of its water content then so is the crystallization temperature of any zircon forming in that melt the systematic nature of o and ti data for lunar zircons suggests a model based on the following observations many of the analyzed lunar zircons are likely from k rare earth elements p kreep zr rich magmas zircon does not saturate in normal mafic magmas igneous zircons in mafic rocks are typically late and formed in the last most evolved portion of melts even if initial bulk water content is moderately low the late zircon forming melt can concentrate water locally in general water lowers crystallization temperatures in which case late igneous zircon can form at significantly lower temperatures than the solidus inferred for a bulk rock composition although lunar basalts could readily lose h2 to space during eruption lowering water fugacity the morphology large size and presence in plutonic rocks suggest that many zircons crystallized at depths that retarded degassing in this case the crystallization temperatures of zircons are a sensitive monitor of the water content of the parental magma as well as the evolved zircon forming melt if the smaller 18o zircon mare basalt values reported here are characteristic of the moon then that would suggest that even highly evolved zircon forming magmas on the moon crystallized at higher temperature than similar magmas on earth and that magmas though not necessarily water free were generally drier on the moon

occurrence and formation of dolomite in organic rich continental margin sediments dolomite is presently forming throughout a large part of the oceans in continental margin marine sediments accumulating at rates less than 500 m m y and having organic carbon contents greater than 0 5 wt at higher sedimentation rates the dolomite content of the sediments is greatly diluted at lower organic carbon content the porewater chemistry precludes dolomite formation the reactants for dolomite formation have the following sources magnesium supplied from overlying seawater calcium supplied by the dissolution of calcium carbonate and carbon supplied from carbonate dissolution and organic carbon oxidation the rate of dolomite formation appears to be limited by the rate of calcium carbonate dissolution this rate can be quantitatively calculated from the magnesium diffusional and advective fluxes conversely in ancient sediments the depth and timing of dolomite formation can be calculated from the amount of dolomite and the sedimentation rate in dolomite rich sediments these calculations demonstrate that most of the dolomite formed within a few tens of meters of the sea floor within the zone of microbial sulfate reduction such dolomites have ne ative values of dgr13c dolomite in dolomite poor sediments may form at greater burial depth below the zone of sulfate reduction resulting in positive values of dgr13c the distribution coefficient of strontium in dolomite has been determined to have an average value of 0 06 using this value predicted strontium contents for submarine dolomites range from 150 ppm in dolomite rich sections to 1 290 ppm in dolomite poor sections

strong coherence between solar variability and the monsoon in oman between 9 and 6 kyr ago variations in the amount of solar radiation reaching the earth are thought to influence climate but the extent of this influence on timescales of millennia to decades is unclear a number of climate records show correlations between solar cycles and climate1 but the absolute changes in solar intensity over the range of decades to millennia are small2 and the influence of solar flux on climate is not well established the formation of stalagmites in northern oman has recorded past northward shifts of the intertropical convergence zone3 whose northward migration stops near the southern shoreline of arabia in the present climate4 here we present a high resolution record of oxygen isotope variations for the period from 9 6 to 6 1 kyr before present in a th u dated stalagmite from oman the 18o record from the stalagmite which serves as a proxy for variations in the tropical circulation and monsoon rainfall allows us to make a direct comparison of the 18o record with the 14c record from tree rings5 which largely reflects changes in solar activity6 7 the excellent correlation between the two records suggests that one of the primary controls on centennial to decadal scale changes in tropical rainfall and monsoon intensity during this time are variations in solar radiation

sims u pb study of zircon from apollo 14 and 17 breccias implications for the evolution of lunar kreep abstract we report the results of a sims u pb study of 112 zircons from breccia samples from the apollo 14 and 17 landing sites zircon occurs in the breccia matrices as rounded irregular shaped broken and rarely euhedral grains and as constituent minerals in a variety of lithic clasts ranging in composition from ultra mafic and mafic rocks to highly evolved granophyres crystallisation of zircon in magmatic rocks is governed by the zirconium saturation in the melt as a consequence the presence of zircon in mafic rocks on the moon implies enrichment of their parent melts in the kreep component our sims results show that the ages of zircons from mafic to ultramafic clasts range from ca 4 35 ga to ca 4 00 ga demonstrating multiple generations of kreepy mafic and ultramafic magmas over this time period individual zircon clasts in breccia matrices have a similar age range to zircons in igneous clasts and all represent zircons that have been incorporated into the breccia from older parents the age distributions of zircons from breccias from both the apollo 14 and apollo 17 landing sites are essentially identical in the range 4 35 4 20 ga however whereas apollo 14 zircons additionally show ages from 4 20 to 3 90 ga no zircons from apollo 17 samples have primary ages less than ca 4 20 ga also in contrast to previous suggestions that the magmatism in the lunar crust is continuous our results show that the zircon age distribution is uneven with distinct peaks of magmatic activity at ca 4 35 ga ca 4 20 ga in apollo 14 and 17 and a possible third peak in zircons from apollo 14 at ca 4 00 ga to explain the differences in the zircon age distributions between the apollo 14 and 17 landing sites we propose that episodes of kreep magmatism were generated from a primary reservoir and that this reservoir contracted over time towards the centre of procellarum kreep terrane we attribute the peaks in kreep magmatism to impact induced emplacement of kreep magma from a primary mantle source or to a progressive thermal build up in the mantle source until the temperature exceeds the threshold for generation of kreep magma which is transported into the crust by an unspecified possibly plume like process

the sudbury structure controversial or misunderstood the origins of the sudbury structure and associated igneous complex have been controversial most models call for a major impact event followed by impact induced igneous activity although totally igneous models are still being proposed much of the controversy is due in our opinion to a misunderstanding of the size of the original sudbury structure by analogy with other terrestrial impact structures the spatial distribution of shock features and huronian cover rocks at the sudbury structure suggest that the transient cavity was 100 km in diameter which places the original final structural rim diameter in the range of 150 200 km theoretical calculations and empirical relationships indicate that the formation of an impact structure of this size will result in 104 km3 of impact melt more than sufficient to produce a melt body the size of the igneous complex present volume 4 8 103 km3 for the igneous complex to be an impact melt sheet it must have a composition similar to that of the target rocks evidence for this has been presented previously for sr and nd isotopic data which suggest a crustal origin here we also present new evidence from least squares mixing models that the average composition of the igneous complex corresponds to a mix of archean granite greenstone terrain with possibly a small component of huronian cover rocks this is a geologically reasonable mix based on the interpreted target rock geology and the geometry of melt formation in an impact event of this size the igneous complex is differentiated which is not a characteristic of previously studied terrestrial impact melt sheets this can be ascribed however to its great thickness and slower cooling that large impact melt sheets can differentiate has important implications for how the lunar samples and the early geologic history of the lunar highlands are interpreted if this working hypothesis is accepted namely that both the sudbury structure and the igneous complex are impact in origin then previous hybrid impact igneous hypotheses can be discarded and the sudbury structure can be studied specifically for the constraints it provides to large scale cratering and the formation of basin sized multiring impact structures

geomorphic expression of abrupt climate change in southwestern north america at the glacial termination eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern north america drying of pluvial lake estancia central new mexico occurred after ca 12 000 14c yr b p thereafter eolian landforms on the old lake floor constructed of gypsum sand were overridden by rising lake water modified by subaqueous processes and organized into beach ridges along the lake s eastern shore preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the younger dryas yd stade the beach ridges provide information about lake surface area which was 45 of the lake area reached during the maximum highstands of the late pleistocene a similar proportional response has been reported for yd climate changes outside the north atlantic region

paleohydrology of the santiaguillo basin mexico since late last glacial and climate variation in southern part of western subtropical north america abstract stratigraphy geochemistry and radiocarbon dating of a succession of sediment in the santiaguillo basin central northern mexico help reconstruct the millennial scale dynamics of hydrological variability that occurred in the southern part of western subtropical north america since the late last glacial runoff was generally above average during the late last glacial from 27 to 18 ka following this interval runoff decreased and deposition of authigenic carbonate and aeolian transported sediment increased until 4 ka heinrich 1 and 2 and younger dryas were intervals of reduced runoff and increased aeolian activity the wetter climate of central northern mexico and arid conditions in north northwestern mexico during the late last glacial were probably related to formation of tropical cyclones in the eastern north pacific during the autumn with restricted rainfall swaths and an absent weaker north american monsoon enhanced north american monsoon and tropical cyclones with expanded rainfall swaths brought more summer and autumn precipitation to a broader region extending from the central northern mexico to the continental interiors of southwestern us during the early holocene

origin of the lunar highlands mg suite an integrated petrology geochemistry chronology and remote sensing perspective the mg suite represents an enigmatic episode of lunar highlands magmatism that presumably represents the first stage of crustal building following primordial differentiation this review examines the mineralogy geochemistry petrology chronology and the planetary scale distribution of this suite of highlands plutonic rocks presents models for their origin examines petrogenetic relationships to other highlands rocks and explores the link between this style of magmatism and early stages of lunar differentiation of the models considered for the origin of the parent magmas for the mg suite the data best fit a process in which hot solidus temperature at 2 gpa 1600 to 1800 c and less dense 3100 kg m3 early lunar magma ocean cumulates rise to the base of the crust during cumulate pile overturn some decompressional melting would occur but placing a hot cumulate horizon adjacent to the plagioclase rich primordial crust and kreep rich lithologies at temperatures of 1300 c would result in the hybridization of these divergent primordial lithologies producing mg suite parent magmas as urkreep primeval kreep is not the petrologic driver of this style of magmatism outside of the procellarum kreep terrane pkt mg suite magmas are not required to have a kreep signature evaluation of the chronology of this episode of highlands evolution indicates that mg suite magmatism was initiated soon after primordial differentiation 10 m y alternatively the thermal event associated with the mantle overturn may have disrupted the chronometers utilized to date the primordial crust petrogenetic relationships between the mg suite and other highlands suites e g alkali suite and magnesian anorthositic granulites are consistent with both fractional crystallization processes and melting of distinctly different hybrid sources

evidence for pacific modulated precipitation variability during the late holocene from the southwestern usa 1 the mechanisms driving late holocene drought cycles in the western united states are not well known due to the general scarcity of long term high resolution absolutely dateable proxies for precipitation in continental interiors here we show that late holocene precipitation variability in the southwestern united states has been caused by changes in the pacific ocean we present a stalagmite based annually resolved moisture record that indicates large shifts from pluvial to drought conditions alternating with periods of dampened near average precipitation over the last 3000 years significant spectral peaks at decadal scale 20 50 70 80 year frequencies likely correspond to modern frequencies of the pacific decadal oscillation or a low frequency component of the el nino southern oscillation and are dominant during episodes of large precipitation shifts overall pluvial conditions punctuated by severe droughts may have challenged the adaptive capacities of emerging agrarian communities of ancestral americans

the dolomite nodules enclosing fossil marine vertebrates in the east pisco basin peru field and petrographic insights into the lagerstatte formation abstract the mio pliocene pisco formation peru is a world famous marine vertebrate lagerstatte several fossil specimens are wrapped up in dolomitic nodules some others lie in the sediment displaying dolomite only in bone cavities e g mesorostral canal and endocranium with the aim to understand whether the precipitation of the dolomitic nodules influenced the formation of the lagerstatte we collected field data on a high number of fossil vertebrates and conducted petrographic and mineralogical analyses on samples representative of the variable development of concretions our results revealed positive relationships between size completeness and articulation of skeletons and the presence of an external nodule clear evidence of chemoautotrophic communities that thrived on the carcasses is scarce microborings are often found in the cortical bone tissues together with iron oxides the former are left by microorganisms feeding on the carcass the latter are traces of former fe sulphides a product of organic matter degradation we suggest that an early burial of the skeletons was a determinant factor in the development of dolomite concretions since it allowed methanogenesis and anaerobic sulphate reduction exploiting the lipids in the bones and the organic matter dispersed in the sediments dolomite precipitation was driven by the same bacteria operating during the suphophilic stage of whale fall communities textural observations imply that dolomite precipitated shortly after the burial of carcasses the increase of alkalinity generated by sulphate reduction and methanogenesis caused a rapid precipitation of the dolomite within skeletal cavities and prevented the degradation of the bones and diagenetic compression of skeletons the nodules themselves prevented erosion of fossils after exhumation therefore nodule formation had a crucial role in the development of the pisco lagerstatte

d h variations of meteoric waters in albuquerque new mexico u s a abstract meteoric waters in the vicinity of albuquerque new mexico u s a exhibit a wide range of d values local precipitation sampled on a monthly basis over a 2 yr period had d values ranging between 158 and 6 with the most negative values in the winter months and the most positive in the summer waters of the rio grande at albuquerque ranged in d from 103 to 79 over the same 2 yr period however for about half the sample period rio grande d values were within 2 of a baseline value of 92 the most negative rio grande d values were produced by the contribution of spring meltwater while runoff from summer rain produced positive shifts in the river water d values the principal components of local groundwater recharge have significantly different d values 1 average rio grande water with d of 92 and 2 recharge from the sandia and manzano mountains with d values of 83 to 70 groundwater d values in the local aquifer the upper tertiary santa fe formation vary from 104 to 77 over a horizontal distance of 20 km the d data suggest that there are distinct domains of groundwater within the santa fe formation which retain their isotopic identities over relatively long time scales isotopic differences between these domains seem to reflect the differences in their respective local sources of recharge the most negative d values appear to characterize deeper groundwater in the domain of rio grande recharge and may reflect climatic conditions different from those at present

sea land oxygen isotopic relationships from planktonic foraminifera and speleothems in the eastern mediterranean region and their implication for paleorainfall during interglacial intervals the oxygen and carbon stable isotope compositions of cave speleothems provide a powerful method for understanding continental climate change here we examine the question of the regionality of this isotopic record and its linkage with the marine isotopic record in the eastern mediterranean em region the study presents a new accurately dated 250 kyr 18o and 13c record determined from speleothems of the peqiin cave northern israel its comparison with the continuous 185 kyr isotopic record of the soreq cave speleothems from central israel reveals striking similarities thus a strong regional climatic signal brought about by variations in temperature and rainfall amount is reflected in both cave records low 18o minima in the peqiin profile for the last 250 to 185 kyr period interglacial marine isotopic stage 7 match the timing of sapropels 9 to 7 and are indicative of high rainfall in the em region at these times the combined soreq and peqiin 18o record for the last 250 kyr excellently matches the published globigerinoides ruber g ruber marine 18o record for the em sea with the isotopic compositional difference g ruber speleothems remaining relatively constant at 5 6 0 7 thus establishing for the first time a robust exploitable link between the land and the marine isotopic records the correspondence of low 18o speleothem values and high cave water stands with low g ruber 18o values during interglacial sapropel events indicates that these periods were characterized by enhanced rainfall in the em land and sea regions by use of sea surface temperatures derived from alkenone data as a proxy for land temperatures at the soreq cave we calculate the paleorainfall 18o values and its amounts maximum rainfall and lowest temperature conditions occurred at the beginning of the sapropel events and were followed by decrease in rainfall and increase in temperatures leading to arid conditions the record for the last 7000 yr shows a trend toward increasing aridity and agrees well with climatic and archeological data from north africa and the middle east

solar forcing of holocene climate new insights from a speleothem record southwestern united states holocene climate change has likely had a profound infl uence on ecosystems and culture a link between solar forcing and holocene climate such as the asian monsoon has been shown for some regions although no mechanism for this relationship has been suggested here we present the fi rst high resolution complete holocene climate record for the north american monsoon region of the southwestern united states southwest in order to address the nature and causes of holocene climate change we show that periods of increased solar radiation correlate with decreased rainfall the opposite to that observed in the asian monsoon and suggest that a solar link to holocene climate is through changes in the walker circulation and the pacifi c decadal oscillation and el nino southern oscillation systems of the tropical pacifi c ocean given the link between increased warming and aridity in the southwest additional warming due to greenhouse forcing could potentially lead to persistent hyperarid conditions similar to those seen in our record during periods of high solar activity

climate history of the southwestern united states based on estancia basin hydrologic variability from 69 to 10 ka abstract newly acquired u th dates on gypsum sands contained within pleistocene lake sediments allow us to extend the record of climatic change in the estancia basin of central new mexico back to 69 ka from a previous limit of 29 ka using a hydrologic balance index hbi that reflects variations in sediment mineralogy and bedding characteristics we find strong similarities to speleothem oxygen isotopic records for the southwestern united states as well as to isotopic variations in greenland ice cores intervals of wetter climate in the estancia basin generally appear to correlate to colder conditions in the north atlantic and conversely the existence of a pronounced dry period from 18 1 to 17 ka matches in timing the extrapolar climate reversal of asmerom et al 2017 at fort stanton cave in southern new mexico and confirms a different origin for this stadial like event furthermore the new u th dates support the existing estancia basin interpretation of a dry bolling allerod followed by a wet younger dryas a result consistent with speleothem and wet meadow evidence from new mexico and arizona asmerom et al 2010 2017 polyak et al 2004 hall et al 2012 wagner et al 2010 but in conflict with an interpretation of speleothem evidence from central texas feng et al 2014

osmium isotope and highly siderophile element constraints on ages and nature of meteoritic components in ancient lunar impact rocks abstract the concentrations of highly siderophile elements hse re os ir ru pt rh pd au and 187os 188os isotope compositions have been determined for 67 subsamples of six lunar impact rocks from the apollo 14 16 and 17 landing sites and the lunar meteorite dar al gani dag 400 using inductively coupled plasma mass spectrometry icp ms and negative thermal ionization mass spectrometry n tims we report the first re os isochron age on a lunar impact melt rock 187re 187os isotope systematics for apollo 16 sample 67935 define an isochron age of 4 21 0 13 ga mswd 1 5 which is interpreted to reflect localized partitioning processes between solid metal liquid metal as this rock melted the new age adds further constraints on the significance of pre 4 0 ga basin forming impacts on the moon and possible mixing of ancient impactor compositions in lunar impact rocks linear correlations displayed by subsamples of a given impact rock in plots of hse versus ir concentrations are explained by dilution processes through essentially hse free anorthositic lunar crustal target rocks or binary mixing between a high hse meteoritic end member and a low hse end member composition slope derived hse ratios and 187os 188os of the meteoritic component in granulitic impactites 67915 67955 and 79215 are similar to slightly volatile element depleted carbonaceous chondrites suprachondritic ratios of ru ir pt ir rh ir and pd ir for apollo 14 impact melt rock 14310 are similar to ratios observed for other apollo 14 samples and apollo 17 poikilitic impact melt rocks apollo 16 poikilitic and subophitic impact melt rocks 60315 and 67935 show slightly subchondritic os ir and suprachondritic ratios of 187os 188os ru ir pt ir rh ir pd ir and au ir their strongly fractionated hse compositions are similar to some members of the iva iron meteorite group and provide further evidence for an iron meteorite impactor component in apollo 16 impact melt rocks the range of chondritic to suprachondritic ratios of 187os 188os ru ir pt ir pd ir and chondritic to slightly subchondritic os ir of apollo 17 and 14 impact melt rocks may be explained by variable mixing of a carbonaceous chondrite like hse composition as in granulitic impactites with a suprachondritic iron meteorite like impactor composition as inferred from 67935 and 60315 and subsequent homogenization by younger impact events the inferred dispersal of these two components across the lunar nearside and their antiquity 4 2 ga suggest at least two basin forming impacts that predate the 3 9 3 8 ga basin forming era the hse composition of the silicate earth can be matched by a late veneer comprised of 80 volatile depleted carbonaceous chondrite like material and 20 differentiated meteoritic metal similar to what has been identified in ancient lunar impact rocks

chemical model for the origin of minor limestone shale cycles by anaerobic methane oxidation chemical and isotopic studies of jurassic carbonate concretions indicate an origin by anaerobic methane oxidation concretion growth occurred within the top 1 m of sediment in a thin zone where methane was consumed to stimulate a late rejuvenated phase of sulfate reduction similar chemical and isotopic characteristics are shown by diagenetic carbonate in several limestone shale sequences and an origin by anaerobic methane oxidation is proposed for these sequences also the evolution of isolated concretions into diagenetic limestones depends on the extent of and depth variations in carbonate supersaturation arising from anaerobic methane oxidation and the persistence of a reduced sedimentation rate or a depositional hiatus diagenetic limestones formed in this way can often be recognized by their association with a later pyrite phase that is more abundant and has more positive sup 34 s values than the adjacent shales

a 4 2 billion year old impact basin on the moon u pb dating of zirconolite and apatite in lunar melt rock 67955 abstract a sharp rise in the flux of asteroid size bodies traversing the inner solar system at 3 9 ga has become a central tenet of recent models describing planetary dynamics and the potential habitability of early terrestrial environments the prevalence of 3 9 ga crystallization ages for lunar impact melt breccias and u pb isotopic compositions of lunar crustal rocks provide the primary evidence for a short lived cataclysmic episode of late heavy bombardment at that time here we report u pb isotopic compositions of zirconolite and apatite in coarse grained lunar melt rock 67955 measured by ion microprobe that date a basin scale impact melting event on the moon at 4 22 0 01 ga followed by entrainment within lower grade ejecta from a younger basin approximately 300 million yr later significant impacts prior to 3 9 ga are also recorded by lunar zircons although the magnitudes of those events are difficult to establish other isotopic evidence such as 40 ar 39 ar ages of granulitic lunar breccias regolith fragments and clasts extracted from fragmental breccias and re os isotopic compositions of lunar metal is also suggestive of impact related thermal events in the lunar crust during the period 4 1 4 3 ga we conclude that numerous large impactors hit the moon prior to the canonical 3 9 ga cataclysm that some of those pre cataclysm impacts were similar in size to the younger lunar basins and that the oldest preserved lunar basins are likely to be significantly older than 3 9 ga this provides sample based support for dynamical models capable of producing older basins on the moon and discrete populations of impactors an extended period of basin formation implies a less intense cataclysm at 3 9 ga and therefore a better opportunity for preservation of early habitable niches and hadean crust on the earth a diminished cataclysm at 3 9 ga suggests that the similarity in the age of the oldest terrestrial continental crust with the canonical lunar cataclysm is likely to be coincidental with no genetic significance

a permian triassic boundary section at quinn river crossing northwestern nevada and implications for the cause of the early triassic chert gap on the western pangean margin the upper permian lower triassic quinn river formation in northwestern nevada was previously thought to represent an incomplete permian triassic boundary sequence owing to an inferred disconformable relationship between permian radiolarian and spicule rich chert and overlying triassic siltstone petrographic and geochemical studies demonstrate that the siltstone is in fact a radiolarian bearing early authi genic dolomicrite with both the chert and dolomicrite deposited conformably in deep water chert production declined or ceased in the late permian and reappeared in the spathian forming a widespread chert gap in permian triassic sequences given the conformable lithofacies relationships deep water depositional setting new radiolarian data extending ranges of key taxa and the presence of the global chert gap sedimentation in the quinn river formation was apparently continuous across the permian triassic boundary this represents the first permian triassic boundary section in the united states portion of the north american cordillera and one of the few deep water sections worldwide organic carbon isotope stratigraphy of the quinn river formation displays multiple excursions through sediments of wuchiapingian anisian age with a negative excursion 1 54 m above the chert shale transition likely representing the permian triassic boundary the multiple excursions in the organic carbon record verify studies of the carbonate carbon record in china that suggest instability in the isotopic record throughout the early triassic and demonstrate that the permian triassic boundary isotope excursion was not an isolated event stratigraphic variation in redox sensitive trace metals indicates that seawater became less oxic slightly before the chert shale transition in turn impacting siliceous sponge communities and creating the widespread chert gap the distinctive dolomicrites in the quinn river formation represent a widespread lithofacies deposited in many localities during the late permian early triassic and express early authigenic formation of dolomite via microbial sulfate reduction in organic rich low oxygen environments

a review of lunar chronology revealing a preponderance of 4 34 4 37 ga ages in this study data obtained from sm nd and rb sr isotopic measurements of lunar highlands samples are renormalized to common standard values and then used to define ages with a common isochron regression algorithm the reliability of these ages is evaluated using five criteria that include whether 1 the ages are defined by multiple isotopic systems 2 the data demonstrate limited scatter outside uncertainty 3 initial isotopic compositions are consistent with the petrogenesis of the samples 4 the ages are defined by an isotopic system that is resistant to disturbance by impact metamorphism and 5 the rare earth element abundances determined by isotope dilution of bulk of mineral fractions match those measured by in situ analyses from this analysis it is apparent that the oldest highlands rock ages are some of the least reliable and that there is little support for crustal ages older than 4 40 ga a model age for ur kreep formation calculated using the most reliable mg suite sm nd isotopic systematics in conjunction with sm nd analyses of kreep basalts is 4389 45 ma this age is a good match to the lu hf model age of 4353 37 ma determined using a subset of this sample suite the average modelmore age of 4353 25 ma determined on mare basalts with the 146sm 142nd isotopic system with a peak in pb pb ages observed in lunar zircons of 4340 20 ma and the oldest terrestrial zircon age of 4374 6 ma the preponderance of ages between 4 34 and 4 37 ga reflect either primordial solidification of a lunar magma ocean or a widespread secondary magmatic event on the lunar nearside the first scenario is not consistent with the oldest ages reported for lunar zircons whereas the second scenario does not account for concordance between ages of crustal rocks and mantle reservoirs less

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

a dolomitized diatomite in an oligocene miocene deep sea fan succession gonfolite lombarda group northern italy abstract an unique 5 10 cm thick layer of a dolomitized diatomite which contains traces of volcanic material occurs intercalated between terrigenous mudstones thin bedded turbidites and pebbly mudstones of the montana member burdigalian of the oligocene miocene gonfolite lombarda group south alpine molasse dolomite formation took place during early diagenesis under conditions of sulfate reduction as suggested by the strongly negative 13 c values 13 pdb stereoscan electron microscope observations show that the dolomite grew as a pore filling cement enveloping deeply corroded diatom frustules the dolomitized diatomite can be correlated with coeval occurrences of biosiliceous tripoli and cineritic deposits in the northern apennines and the southern alps its preservation as a unique and distinct layer in the deep sea fan facies of the gonfolite lombarda group appears to reflect a particular event and suggests that it was deposited rapidly rather than during a longer time interval of slow pelagic sedimentation

high velocity collisions from the lunar cataclysm recorded in asteroidal meteorites lunar samples suggest that the inner solar system was bombarded by asteroids about 4 gyr ago radiometric ages of meteorites suggest an unusual number of high velocity asteroids at this time consistent with a dynamical origin of the bombardment in which the asteroids were pushed by outer planet migration onto highly eccentric orbits

146sm 142nd formation interval for the lunar mantle now extinct 146sm t1 2 103ma was present in the early solar system and lunar basalts might be expected to have inherited small anomalies in 142nd abundances from mantle sources with variable sm nd ratios established during the early global differentiation of the moon 142nd 144nd ratios were measured for several lunar basalts and values of nd142 deviations from terrestrial 142nd 144nd in parts in 104 calculated for them the nd142 values show very small variations attributable to 146sm decay neutron capture near the lunar surface also modified both the samarium and neodymium isotopic compositions of the basalt samples the calculated neutron fluences range from 0 to 7 8 1016 n cm2 both thermal and epithermal neutron fluences were calculated from the sm isotopic compositions of the basalts and used to correct the nd142 values for neutron capture by neodymium well resolved radiogenic enrichments nd142 and 0 17 0 08 2 respectively were measured for lunar meteorite asuka 881757 and apollo 17 basalt 74255 respectively for which the neutron fluences were nil basalts 70135 and 75075 which were exposed to small measureable neutron fluences of 2 5 1015 and 7 7 1015 n cm2 respectively have neutron corrected nd142 values of 0 25 0 15 and 0 29 0 11 respectively the average value of radiogenic nd142 for the three high ti basalts from apollo 17 is 0 22 0 06 neutron capture effects were greater for the other basalts but can be corrected using the measured neutron fluences derived from the samarium isotopic data the neutron corrected nd142 for apollo 12 ilmenite basalt 12056 consistent with its derivation from a highly depleted mantle source also three low ti basalts from apollo 12 and apollo 15 12038 15076 15555 have neutron corrected nd142 which are not resolved from zero and average 0 04 0 06 a fourth low ti basalt 12039 has neutron corrected nd142 but is subject to the largest neutron correction of 0 32 e units kreep basalt 14078 was exposed to only a small neutron fluence of 6 4 1015 n cm2 and has a small deficit of 142nd corresponding to nd142 the average neutron corrected nd142 of three kreep basalts is 0 05 0 04 the nd142 values of the basalts correlate with 147sm 144nd values for their source regions as calculated from their ages and initial nd142 values 147sm 143nd and 146sm 142nd systematics were combined in a three stage model yielding an isochron equation for the lunar mantle formation interval which was calculated to be 238 40 56 ma 2 sm nd ratios for the source regions also are derived from the model and compare favorably with values from conventional geochemical models of mare basalt petrogenesis if the moon were formed by impact of a large mars sized planetesimal with the earth the impact was early enough that the lunar mantle cooled to neodymium isotopic closure by 4 32 ga ago the bulk lunar moon142 evaluated from the mantle isochron at 147sm 144nd chur 0 1967 is 0 01 0 03 2 consistent with derivation of lunar and terrestrial neodymium from a common reservoir

the fluvial record of climate change fluvial landforms and sediments can be used to reconstruct past hydrological conditions over different time scales once allowance has been made for tectonic base level and human complications field stratigraphic evidence is explored here at three time scales the later pleistocene the holocene and the historical and instrumental period new data from a range of field studies demonstrate that croll milankovitch forcing dansgaard oeschger and heinrich events enhanced monsoon circulation millennial to centennial scale climate variability within the holocene probably associated with solar forcing and deep ocean circulation and flood event variability in recent centuries can all be discerned in the fluvial record although very significant advances have been made in river system and climate change research in recent years the potential of fluvial palaeohydrology has yet to be fully realized to the detriment of climatology public health resource management and river engineering

geochemical and mineralogical criteria for the identification of ash layers in the stratigraphic framework of a foredeep the early miocene mt cervarola sandstones northern italy abstract dacitic rhyodacitic and rhyolitic talc alkaline volcaniclastic sediments forming lithified ash layers have been found within the mt cervarola sandstones in two turbidite systems torre amorotti and scoltenna of upper aquitanian lower burdigalian age mount cervarola sandstones have undergone intense diagenetic alteration leading to the complete recrystallization of glass shards in the lithified ash layers the volcanic origin of some sediments has been determined by means of petrographical observations whereas mineralogy and geochemistry were used to recognize other lithified ash layers and to discriminate between volcaniclastic and non volcaniclastic normal sediments the most significant parameters are the occurrence of interstratified illite smectite and of almost stoichiometric diagenetic calcite in lithified ash layers whereas in normal sediments illite and more abundant carbonates are observed distribution of first row transition metals v cr ni was originally different between the two sediment types but significantly diagenetically depleted in lithified ash layers compared with both non volcaniclastic sediments and unaltered northern ash layers v cr and ni were particularly efficient when used in the geochemical discrimination between volcaniclastic and normal sediments coupled with immobile elements zr and to the possibility of rapidly distinguishing volcaniclastic sediments including also those that underwent deep diagenesis and burial has been tested using a wider data set including sediments of different tectonic environments and with variable diagenetic histories lithified ash layers occur in five distinct stratigraphic positions within the mt cervarola sandstones and may be traced over a distance of 65 k km these ash layers represent a new regional constraint for the correlation and the regional modelling of this complex foredeep turbidite system hemipelagic facies and thin bedded turbidite environments are demonstrated to favour the preservation of volcaniclastic sediments

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

interpreting u pb data from primary and secondary features in lunar zircon in this paper we describe primary and secondary microstructures and textural characteristics found in lunar zircon and discuss the relationships between these features and the zircon u pb isotopic systems and the significance of these features for understanding lunar processes lunar zircons can be classified according to i textural relationships between zircon and surrounding minerals in the host breccias ii the internal microstructures of the zircon grains as identified by optical microscopy cathodoluminescence cl imaging and electron backscattered diffraction ebsd mapping and iii results of in situ ion microprobe analyses of the th u pb isotopic systems primary zircon can occur as part of a cogenetic mineral assemblage lithic clast or as an individual mineral clast and is unzoned or has sector and or oscillatory zoning the age of primary zircon is obtained when multiple ion microprobe analyses across the polished surface of the grain give reproducible and essentially concordant data a secondary set of microstructures superimposed on primary zircon include localised recrystallised domains localised amorphous domains crystal plastic deformation planar deformation features and fractures and are associated with impact processes the first two secondary microstructures often yield internally consistent and close to concordant u pb ages that we interpret as dating impact events others secondary microstructures such as planar deformation features crystal plastic deformation and micro fractures can provide channels for pb diffusion and result in partial resetting of the u pb isotopic systems

complex history of a zircon aggregate from lunar breccia 73235 abstract results are reported of an investigation of the age and origin of the exceptional zircon aggregate in an anorthositic clast from lunar breccia 73235 cathodoluminescence and birefringence images show that the aggregate consists of numerous angular fragments of sector zoned primary zircon in a matrix of secondary zircon with an overall texture that resembles a pseudotachylite sims u pb analyses of the primary fragments and the matrix yielded two clearly defined ages an age of 4 315 0 015 ga and initial th u ratio of 0 21 0 35 for the primary zircon and an age of 4 187 0 011 ga and th u of 0 04 0 17 for the secondary zircon matrix a raman spectroscopic study the secondary matrix zircon was undertaken to investigate its structure results showed that the matrix has a zircon structure but there is also evidence for the presence of an amorphous component implications of the structural and u pb age data are discussed in terms of the origin and evolution of the aggregate and the history of lunar events it is proposed that an original single millimetre sized sector zoned zircon formed at 4 31 ga was subjected to a severe shock event at 4 18 ga this event resulted in the fracturing of the zircon the displacement and rotation of fragments the compression of the aggregate to a lensoid shape and the shock reduction of zircon to sub micron sized and amorphous granules in crush zones in the mosaic of fractures volatilisation loss of pb and the addition of u to the secondary zircon is attributed to processes activated by the extreme thermal pulse which accompanied the 4 18 ga shock event shock effects are seen in some of the primary fragments but raman spectra of the primary and secondary zircon show no evidence for pressure induced transformation of zircon to a scheelite structure the zircon u pb system has not been affected by the ca 3 95 ga thermal pulse that accompanied formation of the host breccia although this event has largely reset the k ar systems

the effect of 1 9 and 1 4 ga impact events on 4 3 ga zircon and phosphate from an apollo 15 melt breccia 1 zircon and phosphate grains from matrix and quartz monzodiorite qmd clasts in two thin sections of apollo 15 impact melt breccia 15405 were investigated using optical microscopy scanning electron microscopy raman spectroscopy and ion microprobe u pb analyses u pb results for zircon grains with well defined cathodoluminescence zoning define the primary i e magmatic crystallization age as 4330 6 ma 2 one zircon consists of a preserved inner part surrounded by a porous polycrystalline granular mixture of zircon and baddeleyite indicating incomplete reaction of the zircon with melt previous work showed that this microstructure could form at pressures above 60 gpa and a temperature close to 1700 c and is evidence of an impact related melting event the u pb system of this grain indicates a resetting event at 1940 10 ma interpreted as the age of this impact impact 1 other zircon and phosphate grains also have disturbed u pb systems showing an even younger reset event impact 2 at 1407 57 ma evidence of impact is supported by microstructures of zircon and baddeleyite such as secondary rims these impacts are tentatively identified as those having formed autolycus and aristillius craters

effects of crystallographic anisotropy on fracture development and acoustic emission in quartz 1 transgranular microcracking is fundamental for the initiation and propagation of all fractures in rocks the geometry of these microcracks is primarily controlled by the interaction of the imposed stress field with the mineral elastic properties however the effects of anisotropic elastic properties of minerals on brittle fracture are not well understood this study examines the effects of elastic anisotropy of quartz on the geometry of brittle fracture and related acoustic emissions ae developed during indentation experiments on single crystals at ambient pressure and temperature a hertzian cone crack developed during blunt indentation of a single crystal of flawless brazilian quartz parallel to the c axis shows geometric deviation away from predictions based on the isotropic case consistent with trigonal symmetry the visible cone crack penetration depth varies from 3 to 5 mm and apical angle from 53 to 40 electron backscatter diffraction ebsd mapping of the crack tip shows that fracturing initiates along a 40 m wide process zone comprising damage along overlapping en echelon high index crystallographic planes shown by discrete bands of reduced electron backscatter pattern ebsp quality band contrast coalescence of these surfaces results in a stepped fracture morphology monitoring of ae during indentation reveals that the elastic anisotropy of quartz has a significant effect on ae location and focal mechanisms ninety four ae events were recorded during indentation and show an increasing frequency with increasing load they correspond to the development of subsidiary concentric cracks peripheral to the main cone crack the strong and complex anisotropy in seismic velocity 28 vp 43 vs with trigonal symmetry resulted in inaccurate and high uncertainty in ae locations using geiger location routine with an isotropic velocity model this problem was overcome by using a relative master event location algorithm that only requires a priori knowledge of the velocity structure within the source volume the ae location results correlate reasonably well to the extent of the observed cone crack decomposition of ae source mechanisms of the geiger relocated events shows dominantly end member behavior between tensile and compressive vector dipole events with some double couple dominated events and no purely tensile or compressive events the same events located by the master event algorithm yield greater percentage of vector dipole components and no double couple events indicating that ae source mechanism solutions can depend on ae location accuracy and therefore relocation routine that is utilized calculations show that the crystallographic anisotropy of quartz causes apparent deviation of the moment tensors away from double couple and pure tensile compressive sources consistent with the observations preliminary modeling of calcite anisotropy shows a response distinct from quartz indicating that the effects of anisotropy on interpreting ae are complex and require detailed further study

the monterey event in the mediterranean a record from shelf sediments of malta oligo miocene carbonate platform and shelf sediments outcropping on the maltese islands provide an excellent archive of the paleoceanography of the central mediterranean a sequence of shallow water limestones than shelf limestones and marls followed again by shallow water limestones reflects drowning of a carbonate platform the establishment of a shelf environment and in the late miocene renewed progradation and aggradation of shallow water carbonates the sequence recording the deepening of the maltese platform contains several phosphorite hardgrounds and phosphorite pebble beds these phosphorites were dated with strontium isotopes major episodes of phosphogenesis occurred between 25 and 16 ma and they are coeval with those phosphorite events reported from florida and north carolina a miocene carbon isotope and oxygen isotope stratigraphy was established on planktic and benthic foraminifera and on bulk samples a major carbon isotope excursion with an amplitude of up to l between 18 and 12 5 ma can be correlated with the globally recognized monterey carbon isotope excursion this is the first record of this event both in shallow water sediments and in the mediterranean the carbon isotope excursion precedes an oxygen isotope excursion which also was recognized in deep sea records major episodes of phosphogenesis and platform drowning preceded the carbon isotope excursion by up to millions of years

compositional variation in apollo 16 impact melt breccias and inferences for the geology and bombardment history of the central highlands of the moon abstract high precision data for the concentrations of a number of lithophile and siderophile elements were obtained on multiple subsamples from 109 impact melt rocks and breccias mostly crystalline from the apollo 16 site compositions of nearly all apollo 16 melt rocks fall on one of two trends of increasing sm concentration with increasing sc concentration the eastern trend lower sm sc mg fe and sm yb ratios consists of compositional groups 3 and 4 of previous classification schemes these melt rocks are feldspathic poor in incompatible and siderophile elements and appear to have provenance in the descartes formation to the east of the site the western trend higher sm sc mg fe and sm yb ratios consists of compositional groups 1 and 2 these relatively mafic kreep bearing breccias are a major component 35 of the cayley plains west of the site and are unusual compared to otherwise similar melt breccias from other sites in having high concentrations of fe ni metal 1 2 the metal is the carrier of the low ir au 0 3 chondritic siderophile element signature that is characteristic of the apollo 16 site four compositionally distinct groups 1m 1f 2db and 2nr of western trend melt breccias occur that are each represented by at least six samples compositional group 1 of previous classification schemes the poikilitic or lkfm melt breccias can be subdivided into two groups group 1m represented by six samples including 60315 is characterized by lower al2o3 concentrations higher mgo and alkali concentrations and higher mg fe and cr sc ratios than group 1f represented by fifteen samples including 65015 group 1m also has siderophile element concentrations averaging about twice those of group 1f and ir au and ir ni ratios that are even lower than those of other western trend melt rocks ir au 0 24 0 03 ci normalized at the mafic extreme of group 2 vha melt breccias the melt lithology occurring as clasts in feldspathic fragmental breccias from north ray crater group 2nr is compositionally distinct from the melt lithology of dimict breccias from the cayley plains group 2db in having higher concentrations of sc cr and heavy rare earth elements and lower concentrations of siderophile elements the distinct siderophile element signature high absolute abundances low ir au ratio suggest that the four groups of mafic melt breccia are all somehow related ratios of some lithophile elements also suggest that they are more closely related to each other than they are to melt breccias from other apollo sites however none of the breccia compositions can be related to any of the others by any simple process of igneous fractionation or mixing involving common lunar materials thus the origin of the four groups of mafic melt breccia is enigmatic if they were produced in only one or two impacts then a mechanism exists for generating regimes of impact melt breccia in a single impact that are substantially different from each other in composition for various reasons including the problem of delivering large volumes of four different types of melt to the apollo 16 site it is unlikely that any of these breccias were produced in basin forming impacts if they were produced in as many as four crater forming impacts then the unusual siderophile element signature is difficult to explain possible explanations are 1 1 the four groups of melt breccia all contain metal from a single earlier impact 2 2 they were each formed by related metal rich meteoroids or 3 3 some common postimpact process has resulted in metal of similar composition in each of four melt pools within a compositional group most intrasample and intersample variation in lithophile element concentrations is caused by differences among samples in the proportion of a component of normative anorthosite or noritic anorthosite in most cases this compositional variation probably reflects variation in clast abundance for group 2db and probably 2nr differences in abundance of a component of ferroan anorthosite estimated al2o3 32 accounts for the compositional variation for groups 1m and 1f the anorthositic component is more mafic estimated al2o3 26 some group 2 samples may be related by a troctolitic component of varying abundance

thermal history of apollo 12 granite and kreep rich rock clues from pb pb ages of zircon in lunar breccia 12013 abstract with the mafic to ultramafic petrology of the moon the presence of granite appears anomalous however fragments of rocks with a definite granitic textures and mineralogy have been recovered from the maria where their ages point to an ultimate origin in the highlands apollo 12 mare breccia 12013 is one of these unique lunar rocks containing abundant granitic components it consists of a black portion composed mainly of fragments of plagioclase and noritic rock with minor fragments of granitic rock and a gray portion that is dominated by an overall granitic component zircon grains from this breccia were studied by combining cathodoluminescence cl imaging and micron scale ion microprobe dating techniques zircon grains from the black portion have a large age variation 4 0 4 3 ga a few of them exhibit complex age zoning within individual grains corresponding to cl zoning zircon grains from the gray portion show no cl zoning features but also have a large age variation between different grains 4 2 4 3 ga in this study we suggest that the large age variations of zircon in 12013 among different grains and within individual grains were caused by post crystallization impact events and most of them are not original crystallization ages the 4 3 ga zircon age probably represents the minimum crystallization age of the granitic component in 12013 similar to lunar granites from the apollo 14 and 17 landing sites this old crystallization age also implies that various ree patterns of lunar granites might not be entirely related to their crystallization ages based on comparison with the 207pb 206pb ages for zircon from the apollo 12 14 and 17 landing sites we suggest that there was at least one pre 3 9 ga major impact event on the moon at 4 2 ga

the formation and evolution of the moon s crust inferred from the sm nd isotopic systematics of highlands rocks abstract ages determined for magnesian and ferroan anorthosite crustal rock suites overlap suggesting they formed contemporaneously about 4 3 4 5 ga a notable exception is the sm nd age previously determined on mg suite gabbronorite 67667 which is at least 100 ma younger than the youngest ferroan anorthosite new chronologic measurements of 67667 presented here yield concordant sm nd and rb sr mineral isochron ages of 4349 31 ma and 4368 67 ma suggesting the sample is older than previous estimates furthermore a whole rock sm nd isochron of mg suite rocks from the apollo 14 15 16 and 17 landing sites yields an age of 4348 25 ma indicating that mg suite magmatism was widespread and roughly contemporaneous on the lunar nearside analysis of sm nd internal isochron ages confirms that mg suite magmatism was restricted to a period between about 4 33 and 4 35 ga at the apollo 14 15 16 and 17 landing sites and was synchronous with magmatism at the apollo 16 site associated with the ferroan anorthosite suite between 4 35 and 4 37 ga magnesian and ferroan anorthosite suite rocks with ages younger than 4 33 ga appear to have experienced slow cooling in the deep lunar interior so that the ages record when the samples cooled below the closure temperature of the sm nd isotopic system and not the time they crystallized the ages determined for mg suite and ferroan anorthosite suite rocks are concordant with the age determined for the formation of urkreep of 4350 34 ma using the sm nd isotopic systematics of 67667 and measurements completed on norite 78238 troctolite 76535 kreep basalt 15386 and gabbronorite nwa 773 crystallization ages of mg suite and fas are also concordant with the average of 146sm 142nd ages previously determined for the formation of the mare basalt source region of 4333 30 ma the similarity of ages for mg suite magmatism ferroan anorthosite suite magmatism urkreep formation and formation of the mare basalt source regions implies the processes that produced these rocks were petrogenetically linked it also implies that both early stage and late stage lunar magma ocean cumulates formed over a relatively short duration of

dolomite formation in the dynamic deep biosphere results from the peru margin early diagenetic dolomite beds were sampled during the ocean drilling programme odp leg 201 at four reoccupied odp leg 112 sites on the peru continental margin sites 1227 684 1228 680 1229 681 and 1230 685 and analysed for petrography mineralogy 13c 18o and 87sr 86sr values the results are compared with the chemistry and 13c and 87sr 86sr values of the associated porewater petrographic relationships indicate that dolomite forms as a primary precipitate in porous diatom ooze and siliciclastic sediment and is not replacing the small amounts of precursor carbonate dolomite precipitation often pre dates the formation of framboidal pyrite most dolomite layers show 87sr 86sr ratios similar to the composition of quaternary seawater and do not indicate a contribution from the hypersaline brine which is present at a greater burial depth also the 13c values of the dolomite are not in equilibrium with the 13c values of the dissolved inorganic carbon in the associated modern porewater both petrography and 87sr 86sr ratios suggest a shallow depth of dolomite formation in the uppermost sediment 30 m below the seafloor a significant depletion in the dissolved mg and ca in the porewater constrains the present site of dolomite precipitation which co occurs with a sharp increase in alkalinity and microbial cell concentration at the sulphate methane interface it has been hypothesized that microbial hot spots such as the sulphate methane interface may act as focused sites of dolomite precipitation varying 13c values from 15 to 15 for the dolomite are consistent with precipitation at a dynamic sulphate methane interface where 13c of the dissolved inorganic carbon would likewise be variable a dynamic deep biosphere with upward and downward migration of the sulphate methane interface can be simulated using a simple numerical diffusion model for sulphate concentration in a sedimentary sequence with variable input of organic matter thus the study of dolomite layers in ancient organic carbon rich sedimentary sequences can provide a useful window into the palaeo dynamics of the deep biosphere

modeling speleothem δ13c variability in a central sierra nevada cave using 14c and 87sr 86sr abstract carbon isotopes in speleothems can vary in response to a number of complex processes active in cave systems that are both directly and indirectly related to climate progressing downward from the soil zone overlying the cave these processes include soil respiration fluid rock interaction in the host limestone degassing of co2 and precipitation of calcite upflow from the speleothem drip site and calcite precipitation at the drip site here we develop a new approach to independently constrain the roles of water rock interaction and soil processes in controlling stalagmite 13c this approach uses the dead carbon proportion dcp estimated from coupled 14c and 230th u measurements in conjunction with sr isotope analyses on stalagmite calcite from a central sierra nevada foothills cave in california a region characterized by a highly seasonal mediterranean type climate to determine the roles of water rock interaction and soil processes in determining stalagmite 13c increases in stalagmite dcp between 16 5 and 8 8 ka are coincident with decreased 13c indicating a varying yet substantial contribution from the soil organic matter som reservoir likely due to significantly increased average age of som in the soil veneer above the cave during wet climatic intervals we use geochemical and isotope mixing models to estimate the host carbonate contribution throughout the 13c time series and determine the degree of degassing and calcite precipitation that occurred prior to precipitation of stalagmite calcite the degree of degassing and prior calcite precipitation we calculate varies systematically with other climate indicators with less degassing and prior calcite precipitation occurring during wetter climatic intervals and more during drier intervals modeled 13c values and degassing calculations suggest that some degree of prior calcite precipitation is necessary at all time intervals to explain measured stalagmite 13c values even during relatively wet intervals these results illustrate the importance of constraining degassing and prior calcite precipitation in the interpretation of speleothem 13c records particularly those from caves that formed in seasonal semi arid to arid environments

complex magmatic and impact history prior to 4 1 ga recorded in zircon from apollo 17 south massif aphanitic breccia 73235 abstract sample 73235 is one of several aphanitic impact melt breccias collected by the apollo 17 mission at stations 2 and 3 on the slopes of the south massif this study presents a detailed investigation of internal structures and u pb ages of large zircon grains from this breccia sample new data combined with the results of previous studies of zircon grains from the same location indicate that most zircon clasts in breccias from stations 2 and 3 formed during multiple magmatic events between 4 37 and 4 31 ga although the oldest zircon crystallized at about 4 42 ga and the youngest at 4 21 ga in addition zircons from the aphanitic breccias record several impact events prior to the 3 9 ga late heavy bombardment the results indicate that the zircons probably crystallized at different locations within the procellarum kreeep terrane and were later excavated and modified by several impacts and delivered to the same locality within separate ejecta blankets this locality became a source of material that formed the aphanitic impact melt breccias of the south massif during a 3 9 ga impact however the zircons showing old impact features are not modified by this 3 9 ga impact event suggesting that i this common source area was located at the periphery of excavation cavity and ii the 3 9 ga ages recorded by the zircon grains could date large basin forming events as significant as major later 3 9 ga collisions such as imbrium and serenitatis

uranium lead ages for lunar zircons evidence for a prolonged period of granophyre formation from 4 32 to 3 88 ga the ages of a number of small fragments of lunar granophyre have been determined by the in situ u th pb isotopic analysis of zircon using a sensitive high mass resolution ion microprobe shrimp i the zircon from lunar granophyre is characterized by consistently high u and th contents most 200 500 ppm and 100 300 ppm respectively compared to zircon from mafic lunar rocks some fragments of lunar granophyre are found to be as old as 4 32 ga supporting other evidence that the original lunar magma ocean crystallized completely within 200 ma of the formation of the moon itself other fragments are as young as 3 88 ga which is much later than the time of formation of most of the lunar crust the older lunar granophyres have rare earth element ree patterns that are similar to lunar kreep whilst the younger granophyres have bow shaped ree patterns that feature a greater relative enrichment in the heavy ree the wide range of ages of numerous lunar zircons lunar granophyres and other rocks indicates that zircon forming magmatism in the lunar highlands was most active prior to 4 3 ga but continuous until at least 3 88 ga the u pb isotopic composition of much lunar zircon is near concordant but the effects of isotopic disturbance as late as 1 0 ga are observed in some zircon both within granophyre fragments recrystallized by reheating and within fragments in which the original delicate silica k feldspar granophyric intergrowth is well preserved it is therefore essential to make multiple analyses of individual zircon grains and preferably analyses of suites of zircons from lunar igneous rocks if they are to be dated reliably by the u pb method it is possible that some of the younger lunar granophyres are the product of large scale silicate liquid immiscibility within late stage differentiates but this remains unproven until remnants of demonstrably cogenetic fe rich immiscible liquid are positively identified

a protracted timeline for lunar bombardment from mineral chemistry ti thermometry and u pb geochronology of apollo 14 melt breccia zircons new zircon u pb and trace element investigations from apollo 14 lunar impact breccia sample 14311 reveal at least three distinct concordia 2 age populations at 4334 10 4245 10 and 3953 10 ma titanium in zircon thermometry tixln results correlated with u pb ages range from 800 1200 oc lattice strain models used to infer zircon versus whole rock rare earth element contents and partitioning calculations against lunar impact breccia component compositions quantitatively constrain formation conditions for the different age populations a compilation of new data with published work shows that apollo 14 zircons older than ca 4300 ma formed by igneous processes associated with lunar crust formation compositional variability in the ca 4240 ma zircon age population is interpretable however via a mixture of inherited and melt generated components from one or more large impacts perhaps related to a marked increase in bombardment flux ages from the youngest zircon group at ca 3950 ma coincide with the classical late heavy bombardment lhb as documented from previous lunar geochronologies these results lend support to the idea that instead of a simple unimodal lhb scenario or a monotonic decline in impacts the moon was battered by multiple cataclysms since ca 4240 ma such a picket fence like bombardment to the moon best describes the mode and tempo of impacts that accompanied the late stages of solar system formation and giant planet migration

holocene forcing of the indian monsoon recorded in a stalagmite from southern oman a high resolution oxygen isotope record from a thorium uranium dated stalagmite from southern oman reflects variations in the amount of monsoon precipitation for the periods from 10 3 to 2 7 and 1 4 to 0 4 thousand years before the present ky b p between 10 3 and 8 ky b p decadal to centennial variations in monsoon precipitation are in phase with temperature fluctuations recorded in greenland ice cores indicating that early holocene monsoon intensity is largely controlled by glacial boundary conditions after approximately 8 ky b p monsoon precipitation decreases gradually in response to changing northern hemisphere summer solar insolation with decadal to multidecadal variations in monsoon precipitation being linked to solar activity

prolonged wet period in the southwestern united states through the younger dryas the younger dryas was one of the more dramatic climatic transitions ever recorded how these types of climatic shifts are expressed in continental interiors is of primary scientific interest and of vital societal concern here we present a speleothem based absolutely dated record using uranium series data of climate change for the southwestern united states from growth chronology of multiple speleothems the stalagmite growth represents the onset of wetter climate 12 500 yr b p soon after the start of the younger dryas the wetter climate persisted a millennium beyond the termination of the younger dryas this wet cycle is likely related to a more southern positioning of the polar jet stream in response to cooler northern hemisphere climate the end of the wet period coincides with the peak of the holocene summer insolation maximum ca 10 500 yr b p the allerod prior to the younger dryas which corresponds to clovis occupation in the southwestern united states was drier in comparison and seems in line with a climatic contribution to megafauna extinction

flocculent layers and bacterial mats in the mudstone interbeds of the primary lower gypsum unit tertiary piedmont basin nw italy archives of palaeoenvironmental changes during the messinian salinity crisis abstract the recognition of peculiar laminated layers atypically rich in a biogenic intrabasinal component in the mudstone intervals from the messinian late miocene primary lower gypsum unit 5 97 5 60 ma of the piedmont basin nw italy provides information on the palaeoenvironmental evolution at precessional insolation maxima these cyclic layers consist of irregular alternation of cm thick grey terrigenous laminae and whitish composite packets the latter is in turn composed of sub mm thick wrinkled dolomite rich laminae that alternate with terrigenous ones two types of layers can be distinguished i peloidal layers composed of faecal pellets and irregular diatom rich aggregates interpreted as marine snow floccules and ii filament bearing layers composed of interwoven filaments up to 150 m across corresponding to remains of beggiatoa like giant sulphide oxidising bacteria by comparison with present day settings the peloidal layers are interpreted as flocculent layers deposited on anoxic sea bottoms following episodes of phytoplankton bloom in the upper water column the filament bearing layers are considered as chemotrophic microbial mats growing on dysaerobic sea bottoms the uncommon preservation of both kinds of layers is the result of extensive dolomite precipitation in the shallow subsurface induced by bacterial sulphate reduction the laminated layers are the first reported example of a high frequency climate driven cyclicity in the non evaporitic portion of the primary lower gypsum unit their stacking pattern within the mudstone intervals reflects the gradual increase of the oxygen content of bottom waters during the humid precessional hemicycle culminating with gypsum deposition at the onset of the arid phase

resolution of impact related microstructures in lunar zircon a shock deformation mechanism map abstract the microstructures of lunar zircon grains from breccia samples 72215 73215 73235 and 76295 collected during the apollo 17 mission have been characterized via optical microscopy cathodoluminescence imaging and electron backscatter diffraction mapping these zircon grains preserve deformation microstructures that show a wide range in style and complexity planar deformation features pdfs are documented in lunar zircon for the first time and occur along 001 110 and 112 typically with 0 1 25 m spacing the widest pdfs associated with 112 contain microtwin lamellae with 65 misorientation relationships deformation bands parallel to 100 planes and irregular low angle misorientation axes this geometry is consistent with a dislocation glide system with 010 during dislocation creep nonplanar fractures recrystallized domains with sharp irregular interfaces and localized annealing textures along fractures are also observed no occurrences of reidite were detected shock deformation microstructures in zircon are explained in terms of elastic anisotropy of zircon pdfs form along a limited number of specific hkl planes that are perpendicular to directions of high young s modulus suggesting that pdfs are likely to be planes of longitudinal lattice damage twinned 112 pdfs also contain directions of high shear modulus a conceptual model is proposed for the development of different deformation microstructures during an impact event this shock deformation mechanism map is used to explain the relative timing conditions and complexity relationships between impact related deformation microstructures in zircon

cratering history and lunar chronology the moon is exceptional and important because it is the only planetary body besides the earth for which we have both a detailed stratigraphic history and datable rock samples that can be related to specific geomorphologic units fig 5 1 the moon has preserved much of its magmatic and impact record of at least the last 4 billion years while its endogenic history is of great interest for the fundamentals of planetary interiors and surfaces the moon has become a calibration plate for the cratering record of the earth moon system and by extrapolation of the entire inner solar system if one assumes a heliocentric origin for impactor populations these populations range from asteroids through long and short period comets to interplanetary dust and cover a size range from hundreds of kilometers to micrometers figure 5 1 telescopic view of the nearside of the earth s moon with landing sites of the apollo and luna missions this chapter reviews the presently available data sets in support of this paradigmatic assumption as follows 1 the phenomenology of lunar impact craters 2 the terrestrial record of the impact cratering process and the interpretation of terrestrial impactites as far as this ground truth is relevant for the interpretation of lunar impact craters and datable lunar impact breccias and melt rocks 3 the theory and numerical simulation of the cratering process and the characteristics of the earth moon crossing population of impactors asteroids and comets 4 the principles of relative age dating of lunar surface units and the general lunar stratigraphy 5 the stratigraphic significance and ages of lunar samples impactites and basalts and based on this data set the absolute ages of lunar surface units 6 the cratering rate of the moon as a function of time and 7 the time calibration of this cratering rate based on the

large holocene lakes and climate change in the chihuahuan desert lake level variations preserved as beach ridges in the laguna el fresnal and laguna santa maria subbasins northern mexico record millennially spaced episodes of increased precipitation during the holocene epoch we find that the early middle and late holocene were punctuated by periods wet enough to establish large pluvial lakes in currently dry basins in the chihuahuan desert the largest dated pluvial lake covered 5650 km2 during the early holocene constructional beach ridges in these subbasins are 221 33 14c yr b p little ice age equivalent 3815 52 to 4251 59 14c yr b p early neoglacial 6110 80 to 6721 68 14c yr b p mid holocene and 8269 64 to 8456 97 14c yr b p early holocene dates that correlate with other millennially spaced wet or cold events in the northern hemisphere we attribute these wet episodes to increased precipitation cooler temperatures and reduced evaporation following southward shifts in winter storm tracks which are related to long term el nino southern oscillation variability during the holocene

climatic and environmental controls on speleothem oxygen isotope values variations in speleothem oxygen isotope values d 18 o result from a complicated interplay of environmental controls and processes in the ocean atmosphere soil zone epikarst and cave system as such the controls on speleothem d 18 o values are extremely complex an understanding of the processes that control equilibrium and kinetic fractionation of oxygen isotopes in water and carbonate species is essential for the proper interpretation of speleothem d 18 o as paleoclimate and paleoenvironmental proxies and is best complemented by study of site specific cave processes such as infiltration flow routing drip seasonality and saturation state and cave microclimate among others this review is a process based summary of the multiple controls on d 18 o in the atmosphere soil epikarst and speleothem calcite illustrated with case studies primary controls of d 18 o in the atmosphere include temperature and relative humidity through their role in the multiple isotope effects variability and modifications of water d 18 o values in the soil and epikarst zones are dominated by evaporation mixing and infiltration of source waters the isotopically effective recharge into a cave system consists of those waters that participate in precipitation of caco3 resulting in calcite deposition rates which may be biased to time periods with optimal dripwater saturation state recent modeling experimental and observational data yield insight into the significance of kinetic fractionation between dissolved carbonate phases and solid caco3 and have implications for the hendy test to assist interpretation of speleothem d 18 o time series quantitative and semi quantitative d 18 o climate calibrations are discussed with an emphasis on some of the difficulties inherent in using modern spatial and temporal isotope gradients to interpret speleothems as paleoclimate proxy records finally several case studies of globally significant speleothem paleoclimate records are discussed that show the utility of d 18 o to reconstruct past climate

an enhanced role for the tropical pacific on the humid pleistocene holocene transition in southwestern north america abstract climate effects on landscape evolution during the late pleistocene holocene transition 14 6 8 ka in southwestern north america traditionally are linked to the activity of the north american monsoon and to vegetation change related to a decrease in winter precipitation acting in response to orbital cyclicity we performed an integrated analysis of regional alluvial fan lacustrine and paleobotanical records for the area comparing them with hemispheric and regional paleoclimate proxies our focus was on the potential role the tropical pacific has as a synoptic pattern modulator and moisture source for hydrogeomorphic activity in the region our analysis indicates that the onset of alluvial fan aggradation in most of the region at 13 5 ka could have been a response to semi permanent el nino like conditions in the tropical pacific which enhanced the frequency of winter frontal storms as well as increased penetration of tropical cyclones in the region the north american monsoon was restricted in extent and intensity until 7 ka and probably was not a major factor in alluvial fan aggradation a second stage of alluvial fan aggradation from 11 5 to 9 ka was dominated by hyper concentrated flows and sheet flood sedimentation along with deposition in fluvial settings storms were probably were linked to landfall of enhanced water vapor bands in the leading edge of winter extra tropical cyclones with moisture advected directly from the tropical pacific at 8 ka favorable conditions for the occurrence of these storms waned and storm tracks shifted northward analysis of modern analogs for storm types described above as prevalent during this period indicates that changes in circulation patterns across the tropical pacific can affect storm properties enough to explain the observed geomorphic effects regardless of other factors traditionally considered of large impact like vegetation change our results suggest that the tropical pacific plays a larger role than currently thought in landscape evolution of the region

early miocene tephra in the apennine pelagic sequence an inferred sardinian provenance and implications for western mediterranean tectonics during the tertiary period the northeastern apennines of italy functioned as a quiet depositional basin for fine grained volcanic ashfalls from distant explosive volcanism accompanying the alpine apennine orogenesis these ashes have been dated by several authors with different radioisotopic methods in the past decade k ar 40ar 39ar and rb sr on biotite separates 40ar 39ar single crystal laser fusion on plagioclase and sanidine and u pb on zircon and provide the means for a precise accurate age calibration of the tertiary magnetostratigraphic and biostratigraphic timescales however the provenance of these tephras has remained uncertain to resolve this problem we have carried out detailed grain size analysis of the so called livello raffaello a feldspar bearing bentonite recognized in numerous outcrops throughout the region at the very base of the aquitanian to burdigalian bisciaro formation the raffaello stratigraphically located in the upper part of planktonic foraminiferal zone n4 and calcareous nannofossil zone nnl upper chron 6a r middle aquitanian yielded an isochron age of 21 2 0 5 ma 2 from 27 40ar 39ar dates by laser fusion on plagioclase we measured the mean grain size m of the 63 m felsic fraction i e feldspar and quartz of the raffaello in 11 representative outcrops in the region and compared the grain size against distance from two possible volcanic sources the venetian province northern provenance and the sardinian province western provenance while the venetian source shows no distinct trend of the m distribution the sardinian plot exhibits a very clear linear grain size decrease with distance after having tentatively established a sardinian source no other volcanoes of aquitanian age are known west of the apennine basin we revised the m distribution through palinspastic restoration including the post aquitanian anticlockwise rotation of the sardinian microplate and consequent orogenic shortening of the northeastern apennine fold and thrust belt for this we have used the thick skinned model of lavecchia et al 1984 which envisions a shortening for the northeastern apennines of 3 to 30 km and the thin skinned model of bally et al 1986 which assumes a variable shortening of 50 to 250 km we have also modeled the distribution of the m of felsic crystals for modern analogue stratospheric westerly winds blowing in this region from fall to spring at speeds of 10 to 30 m s and altitudes ranging from 25 km to 40 km which account for distal 400 km transport of fine tephra cornell et al 1983 in addition we have calculated the m of felsic crystals from six representative sites of the quaternary y 5 ash which was produced 38 000 years ago by an explosive volcanic event in the neapolitan area and was distributed downwind throughout the eastern mediterranean basin our results indicate that restoration by the thick skinned model yields a crystal size distribution gradient incompatible with that predicted by the computed model and overall m values much finer than those observed in the y 5 sample at a comparable distance from the source on the other hand restoration using the thin skinned structural setting yields good agreement with that of the computed model and with the observed m distribution of the y 5 ash

thermal history recorded by the apollo 17 impact melt breccia 73217 abstract lunar breccia 73217 is composed of plagioclase and pyroxene clasts originating from a single gabbronorite intrusion mixed with a silica rich glass interpreted to represent an impact melt a study of accessory minerals in a thin section from this breccia 73217 52 identified three different types of zircon and anhedral grains of apatite which represent distinct generations of accessory phases and provide a unique opportunity to investigate the thermal history of the sample equant anhedral zircon grains that probably formed in the gabbronorite referred to as type 1 have consistent u pb ages of 4332 7 ma a similar age of 4335 5 ma was obtained from acicular zircon type 2 grains interpreted to have formed from impact melt a polycrystalline zircon aggregate type 3 occurs as a rim around a baddeleyite grain and has a much younger age of 3929 10 ma similar to the 3936 17 ma age of apatite grains found in the thin section a combined apatite type 3 zircon age of 3934 12 ma is proposed as the age of the serenitatis impact event and associated thermal pulse x ray mapping and electron probe analyses showed that ti is inhomogeneous in the zircon grains on the sub micrometer scale however model temperatures estimated from shrimp analyses of ti concentration in the 10 m diameter spots on the polished surfaces of type 1 and type 2 zircons range between about 1300 and 900 c respectively whereas ti concentrations determined for the type 3 zircon are higher at about 1400 1500 c a combination of u pb ages ti concentration data and detailed imaging and petrographic studies of the zircon grains shows that the gabbronorite parent of the zircon clasts formed shortly before the 4335 5 ma impact which mixed the clasts and the felsic melt and projected the sample closer to the surface where fast cooling resulted in the crystallization of acicular zircon type 2 the 3934 12 ma serenitatis event resulted in partial remelting of the glass and formation of polycrystalline zircon type 3 this event also reset the u pb system of apatite formed merrillite coronas around some apatite grains and probably re equilibrated some pyroxenes in the clasts although there have been arguments for pre 3 9 ga impacts based on other types of samples the age of the acicular zircon at 4335 5 ma provides the first evidence of impact melt significantly predating the lunar cataclysm our data combined with other chronological results demonstrate the occurrence of pre 3 9 ga impacts on the moon and suggest that the lunar impact history consisted of a series of intense bombardment episodes interspersed with relatively calm periods of low impact flux

electron backscatter diffraction analysis of zircon a systematic assessment of match unit characteristics and pattern indexing optimization quantitative microstructural analysis of zircon using electron backscatter diffraction ebsd requires a comparison of empirically collected electron backscatter patterns with theoretical patterns or match units derived from known crystallographic parameters there are 23 possible crystallographic data sets for zircon and associated match units derived from natural and synthetic zircon and from theoretical calculations over a range of pressures and different rare earth element ree compositions a systematic assessment of these match units has been undertaken by ebsd analysis of each of four zircons from a range of geological environments combined with principal components analysis and self organizing map networks comparison of the different match units shows a systematic relationship across all samples that are related to changes in unit cell dimensions associated with pressure and compositional variations systematic variations in the data generated from 96 ebsd maps each comprising 10 000 electron backscatter patterns indicate that match units associated with increasing pressure or ree dopants yield poorer quality ebsd data the match units from low pressure undoped natural zircon consistently yield the best ebsd results and are recommended for natural zircon ebsd studies irrespective of the zircon source or u content the results provide a clear strategy for optimizing the acquisition and analysis of ebsd data from zircon from both crustal and mantle sources in addition the developed approach to match unit analysis may be applied to all other crystalline materials potentially optimizing ebsd analyses from a range of materials