nominally hydrous magmatism on the moon for the past 40 years the moon has been described as nearly devoid of indigenous water however evidence for water both on the lunar surface and within the lunar interior have recently emerged calling into question this long standing lunar dogma in the present study hydroxyl as well as fluoride and chloride was analyzed by secondary ion mass spectrometry in apatite ca5 po4 3 f cl oh from three different lunar samples in order to obtain quantitative constraints on the abundance of water in the lunar interior this work confirms that hundreds to thousands of ppm water of the structural form hydroxyl is present in apatite from the moon moreover two of the studied samples likely had water preserved from magmatic processes which would qualify the water as being indigenous to the moon the presence of hydroxyl in apatite from a number of different types of lunar rocks indicates that water may be ubiquitous within the lunar interior potentially as early as the time of lunar formation the water contents analyzed for the lunar apatite indicate minimum water contents of their lunar source region to range from 64 ppb to 5 ppm h2o this lower limit range of water contents is at least two orders of magnitude greater than the previously reported value for the bulk moon and the actual source region water contents could be significantly higher

the oxygen isotope composition petrology and geochemistry of mare basalts evidence for large scale compositional variation in the lunar mantle to investigate the formation and early evolution of the lunar mantle and crust we have analysed the oxygen isotopic composition titanium content and modal mineralogy of a suite of lunar basalts our sample set included eight low ti basalts from the apollo 12 and 15 collections and 12 high ti basalts from apollo 11 and 17 collections in addition we have determined the oxygen isotopic composition of an apollo 15 kreep k potassium ree rare earth element and p phosphorus basalt sample 15386 and an apollo 14 feldspathic mare basalt sample 14053 our data display a continuum in bulk rock delta o 18 values from relatively low values in the most ti rich samples to higher values in the ti poor samples with the apollo 11 sample suite partially bridging the gap calculation of bulk rock delta o 18 values using a combination of previously published oxygen isotope data on mineral separates from lunar basalts and modal mineralogy determined in this study match with the measured bulk rock delta o 18 values this demonstrates that differences in mineral modal assemblage produce differences in mare basalt delta o 18 bulk rock values differences between the low and high ti mare basalts appear to be largely a reflection of mantle source heterogeneities and in particular the highly variable distribution of ilmenite within the lunar mantle bulk delta o 18 variation in mare basalts is also controlled by fractional crystallisation of a few key mineral phases thus ilmenite fractionation is important in the case of high ti apollo 17 samples whereas olivine plays a more dominant role for the low ti apollo 12 samples consistent with the results of previous studies our data reveal no detectable difference between the delta o 17 of the earth and moon the fact that oxygen three isotope studies have been unable to detect a measurable difference at such high precisions reinforces doubts about the giant impact hypothesis as presently formulated

the petrology geochemistry and age of lunar regolith breccias miller range 090036 and 090070 insights into the crustal history of the moon meteorites ejected from the surface of the moon as a result of impact events are an important source of lunar material in addition to apollo and luna samples here we report bulk element composition mineral chemistry age and petrography of miller range mil 090036 and 090070 lunar meteorites mil 090036 and 090070 are both anorthositic regolith breccias consisting of mineral fragments and lithic clasts in a glassy matrix they are not paired and represent sampling of two distinct regions of the lunar crust that have protoliths similar to ferroan anorthosites 40ar 39ar chronology performed on two subsplits of mil 090070 33 a pale clast impact melt and a dark glassy melt component shows that the sample underwent two main degassing events one at 3 88 ga and another at 3 65 ga the cosmic ray exposure data obtained from mil 090070 are consistent with a short 8 9 ma exposure close to the lunar surface bulk rock feo tio2 and th concentrations in both samples were compared with 2 degree lunar prospector gamma ray spectrometer lp grs data sets to determine areas of the lunar surface where the regolith matches the abundances observed on the sample we find that mil 090036 bulk rock is compositionally most similar to regolith surrounding the procellarum kreep terrane whereas mil 090070 best matches regolith in the feldspathic highlands terrane on the lunar farside our results suggest that some areas of the lunar farside crust are composed of ferroan anorthosite and that the samples shed light on the evolution and impact bombardment history of the ancient lunar highlands

antarctic lunar meteorites yamato 793169 asuka 881757 mil 05035 and met 01210 yamm launch pairing and possible cryptomare origin abstract the antarctic lunar meteorite meteorite hills met 01210 is a polymict regolith breccia dominantly composed of mare basalt components one relatively large 2 7 4 7 mm basalt clast in met 01210 met basalt shows remarkable mineralogical similarities to the lunar meteorite crystalline mare basalts yamato y 793169 asuka a 881757 and miller range mil 05035 all four basalts have similar rock texture mineral assemblage mineral composition pyroxene crystallization trend and pyroxene exsolution lamellae the estimated tio 2 contents 2 0 wt of the met basalt and mil 05035 are close to the bulk rock tio 2 contents of y 793169 and a 881757 these similarities suggest that y 793169 a 881757 mil 05035 and the met basalt came from the same basalt flow which we designate the yamm basalt the source basalt pairing of the yamm is also supported by their similar ree abundances crystallization ages approx 3 8 3 9 ga and isotopic compositions low u pb low rb sr and high sm nd the pyroxene exsolution lamellae which are unusually coarse up to a few microns by mare standards imply a relatively slow cooling in an unusually thick lava and or subsequent annealing within a cryptomare reported noble gas and cre data with close launch ages 1 ma and ejection depths deeper than several meters among the four meteorites further indicate their simultaneous ejection from the moon despite the marginally close terrestrial ages pairing in the conventional earth entry sense seems unlikely because of the remote recovery sites among the yamm meteorites the high abundance 68 of mare components in met 01210 estimated from a two component mixing model calculation could have resulted from either lateral mixing at a mare highland boundary or vertical mixing in a cryptomare the proportion of mare materials in met 01210 is greater than in apollo core samples at the mare highland boundary the burial depth several meters deep inferred from the lack of surface irradiation of met 01210 exceeds the typical mare regolith thickness a few meters thus the source of the yamm meteorites is likely a terrain of locally high mare highland mixing within a cryptomare we searched for a possible source crater of the yamm meteorites within the well defined cryptomare based on the multiple constraints obtained from this study and published data an unnamed 1 4 km diameter crater 53 w 44 5 s on the floor of the schickard crater is the most suitable source for the yamm meteorites the 238 u 204 pb value of the yamm basalts is extremely low relative to those of the apollo mare basalts but comparable to those of the luna 24 very low ti basalts the low source indicates a derivation from a less differentiated mantle with a lack of kreep components although the chemical sources of materials and heat source of melting might be independent the heat source that generated the source magma of the yamm and luna 24 basalts may not be related to kreep unlike the case of the apollo basalts the distinct chemical and isotopic compositions of mantle sources between the apollo basalts and the yamm lunar 24 basalts imply differences in mantle composition and thermal evolution between the procellarum kreep terrane pkt and non pkt regions of the nearside

hydrous melting of the martian mantle produced both depleted and enriched shergottites the search for water in our solar system is one of the primary driving forces for planetary science and exploration because water plays an important role in many geologic processes and is required for biologic processes as we currently understand them excluding earth mars is the most promising destination in the inner solar system to find water as it is undoubtedly responsible for shaping many geomorphologic features observed on the present day martian surface however the water content of the martian interior is currently unresolved much of our information about the martian interior comes from studies of the basaltic martian meteorites shergottites in this study we examined the water contents of magmatic apatites from a geochemically enriched shergottite the shergotty meteorite and a geochemically depleted shergottite the queen alexandria range 94201 meteorite from these data we determined that there was little difference in water contents between the geochemically depleted and enriched shergottite magmas the water contents of the apatite imply that shergottite parent magmas contained 730 2870 ppm h 2 o prior to degassing furthermore the martian mantle contains 73 290 ppm h 2 o and underwent hydrous melting as recently as 327 ma in the absence of plate tectonics the presence of water in the interior of mars requires planetary differentiation under hydrous conditions this is the first evidence of significant hydrogen storage in a planetary interior at the time of core formation and this process could support elevated h abundances in the interiors of other terrestrial bodies like the moon mercury venus large differentiated asteroids and earth

distinguishing high alumina mare basalts using clementine uvvis and lunar prospector grs data mare moscoviense and mare nectaris 1 high alumina ha mare basalts are a unique group of the lunar sample collection sample geochemistry indicates that these basalts are derived from sources composed of late stage cumulates from the lunar magma ocean lmo their aluminous nature suggests their sources contained significant plagioclase which has implications regarding the efficiency of plagioclase separation from earlier forming mafic cumulates in the lmo to form the anorthositic lunar crust and hence the heterogeneity of the lunar mantle the apollo and luna missions sampled ha basalts from four different locations that are separated by 80 equatorial degrees 2400 km radiometric age dating of these samples demonstrates aluminous basaltic volcanism spanned over 1 billion years suggesting ha basalts may be more prevalent on the moon than implied by the sample population knowing their global occurrence would ultimately enhance our understanding of lunar evolution aluminous mare basalts occupy a unique location in th feo compositional space that suggests they can be identified using global remote sensing data of the moon we present our approach for distinguishing exposures of ha basalts using clementine ultraviolet visible infrared uvvis and lunar prospector gamma ray spectrometer lp grs data with constraints based on the feo tio2 and th abundances of apollo and luna ha samples we identified 34 regions of interest rois where ha basalts could be a prominent component of the lunar surface by analyzing the rims and proximal ejecta from small impacts 0 4 4 km in diameter into the mare surface we characterized compositionally distinct basaltic units that make up the mare and thus determined which units represent ha basalt lavas the results were used to generate maps that depict discrete mare units and classify their general basalt type here we focus on two rois mare moscoviense and mare nectaris mare moscoviense is composed of four basaltic units two of which are ha candidates clementine uvvis data of mare nectaris show evidence of up to three mare basalt units one is the remnants of a mid ti unit that capped earlier low ti flows the majority of the basin is filled by a compositionally indistinguishable low fe low ti basalt however spectral profiles suggest there are two units regardless the units both fit the criteria for a ha basalt

in situ sims u pb dating of phanerozoic apatite with low u and high common pb abstract apatite is a common accessory mineral in various igneous metamorphic and sedimentary rocks it has strong potential to provide important information for geochronology and petrogenesis however precise u th pb dating of apatite especially young samples is difficult due to low abundances of u and less radiogenic pb posing significant challenges for accurate common pb correction an additional issue is the lack of suitable apatite to serve as a standard for in situ analyses here we present both analytical and data reduction protocols for sims in situ u pb analyses on apatite with low u and high common lead with nw 1 apatite as the u pb age standard which was separated from 1160 ma carbonatite in the prairie lake complex in canada apatites from the kovdor carbonatite in the kola peninsula which contains low u mostly 2 5 ppm and high common pb 20 80 yielded weighted average 207pb corrected u pb ages of 375 13 ma kv 8 and kv 18 and 377 11 ma kv a respectively apatites from the quruqtagh ultramafic intrusion in nw china containing low u 2 3 ppm and high common pb 70 yield 207pb corrected u pb age of 805 21 ma the cenozoic durango apatite was dated at 31 2 ma all these new apatite u pb ages are indistinguishable from independently known age constraints to within 2 4 our results demonstrate that a u pb age can be accurately and precisely measured for apatite with low u 50 by sims with a suitable standard and a careful choice of common pb composition

the origin of young mare basalts inferred from lunar meteorites northwest africa 4734 032 and lapaz icefield 02205 northwest africa nwa 4734 is an unbrecciated basaltic lunar meteorite that is nearly identical in chemical composition to basaltic lunar meteorites nwa 032 and lapaz icefield lap 02205 we have conducted a geochemical petrologic mineralogic and sm nd rb sr and ar ar isotopic study of these meteorites to constrain their petrologic relationships and the origin of young mare basalts nwa 4734 is a low ti mare basalt with a low mg 36 5 and elevated abundances of incompatible trace elements e g 2 00 ppm th the sm nd isotope system dates nwa 4734 with an isochron age of 3024 27 ma an initial end of 0 88 0 20 and a source region 147sm 144nd of 0 201 0 001 the crystallization age of nwa 4734 is concordant with those of lap 02205 and nwa 032 nwa 4734 and lap 02205 have very similar bulk compositions mineral compositions textures and ages their source region 147sm 144nd values indicate that they are derived from similar but distinct source materials they probably do not sample the same lava flow but rather are similarly sourced but isotopically distinct lavas that probably originate from the same volcanic complex they may have experienced slightly different assimilation histories in route to eruption but can be source crater paired nwa 032 remains enigmatic as its source region 147sm 144nd definitively precludes a simple relationship with nwa 4734 and lap 02205 despite a similar bulk composition their high ti sm low la yb n and cl poor apatite compositions rule out the direct involvement of kreep rather they are consistent with low degree partial melting of late formed lmo cumulates and indicate that the geochemical characteristics attributed to urkreep are not unique to that reservoir these and other basaltic meteorites indicate that the youngest mare basalts originate from multiple sources and suggest that kreep is not a prerequisite for the most recent known melting in the moon

the longevity of lunar volcanism implications of thermal evolution calculations with 2d and 3d mantle convection models abstract lunar volcanism as is generally accepted started well before the emplacement of the mare fill at 3 1 3 9 ga b p and likely extended well into the eratosthenian 3 1 1 1 ga b p the early volcanism is relatively easily understood the extension of the activity to possibly 1 5 ga b p albeit at a decreasing rate poses a problem since a relatively small body such as the moon may be expected to cool rapidly and freeze a partially molten mantle layer quickly we present thermal history models in which a region of partial melt forms in the mantle underneath the lithosphere almost immediately after the start of the model at depths between 300 and 700 km depending on the chosen initial depth of the magma ocean to calculate the thermal histories we use axisymmetric 2d and fully 3d spherical shell convection codes with viscosity depending on the azimuthally averaged temperature the thermal evolution of the moon is found to be characterized by the growth of a massive 700 to 800 km thick lithosphere while the lower mantle and core cool only by 100 200 k the partial melt zone decreases in thickness with time from top to bottom until it vanishes at times between 3 4 and 2 2 ga b p the maximum degree of partial melting is between roughly 10 and 20 the partial melt layer is initially global and is disrupted by cold downwellings as cooling proceeds the melt zone freezes from above due to the thickening of the lithosphere which implies that the source region of volcanic rock proceeds to increasing depth with time this corresponds nicely with the variation of titanium with age of lunar mare basalts mixing of the melt zone with the underlying mantle chemically rejuvenates the melt zone to some degree and thus the source region of the mare basalts

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

feldspathic lunar meteorites pecora escarpment 02007 and dhofar 489 contamination of the surface of the lunar highlands by post basin impacts abstract pca pecora escarpment 02007 and dhofar 489 are both meteorites from the feldspathic highlands of the moon pca 02007 is a feldspathic breccia consisting of lithified regolith from the lunar surface it has concentrations of both incompatible and siderophile elements that are at the high end of the ranges for feldspathic lunar meteorites dhofar 489 is a feldspathic breccia composed mainly of impact melted material from an unknown depth beneath the regolith concentrations of incompatible and siderophile elements are the lowest among brecciated lunar meteorites among 19 known feldspathic lunar meteorites all of which presumably originate from random locations in the highlands concentrations of incompatible elements like sm and th tend to increase with those of siderophile elements like ir feldspathic meteorites with high concentrations of both suites of elements are usually regolith breccias iridium derives mainly from micrometeorites that accumulate in the regolith with duration of surface exposure micrometeorites have low concentrations of incompatible elements however so the correlation must reflect a three component system we postulate that the correlation between sm and ir occurs because the surface of the feldspathic highlands terrane has become increasingly contaminated with time in sm rich material from the procellarum kreep terrane that has been redistributed across the lunar surface by impacts of moderate sized post basin impacts the most sm rich regolith breccias among feldspathic lunar meteorites are about 3 enriched compared to the most sm poor breccias but this level of enrichment requires only a few percent sm rich material typical of the procellarum kreep terrane the meteorite data suggest that nowhere in the feldspathic highlands are the concentrations of k rare earths and th measured by the lunar prospector mission at the surface representative of the underlying bedrock all surfaces covered by old regolith as opposed to fresh ejecta are at least slightly contaminated dhofar 489 is one of 15 paired lunar meteorite stones from oman total mass of meteorite 1037 g on the basis of its unusually high mg fe ratio the meteorite is likely to have originated from northern feldspathic highlands

early loss fractionation and redistribution of chlorine in the moon as revealed by the low ti lunar mare basalt suite abstract the relative abundances of chlorine isotopes measured in low ti basalts from the moon appear to reflect mixing between two reservoirs one component representing the urkreep the final product of the crystallization of the lunar magma ocean with 37 cl 25 relative to standard mean ocean chlorine the other representing either a mare basalt reservoir or meteoritic materials with 37 cl 0 using the abundances of other kreep enriched elements as proxies for the abundance of cl in low ti mare basalts which is difficult to constrain due to magmatic processes such as fractional crystallization and degassing we find that the urkreep contains 28 times higher cl abundance 25 170 ppm cl as compared to the low 37 cl end member in the observed mixing relationship chlorine with an urkreep c i ratio of 0 2 to 1 5 is 500 to 3400 times less enriched than refractory incompatibles such as u and th and is consistent with incomplete loss of cl species taking place during or prior to the magma ocean phase the preservation of multiple isotopically distinct reservoirs of cl can be explained by 1 incomplete degassing pre or syn giant impact with preservation of undegassed chondritic cl and subsequent formation of an enriched and isotopically fractionated reservoir or 2 development of both high concentration high 37 cl and low concentration low 37 cl reservoirs during the degassing and crystallization of the lunar magma ocean a range of model bulk lunar cl abundances from 0 3 0 6 ppm allows us to place cl in the context of the rest of the elements of the periodic table and suggests that cl behaves as only a moderately volatile element during degassing chlorine isotope fractionation resulting from loss syn or pre magma ocean is characterized by 1000 ln 3 96 to 4 04 abundance and isotopic constraints are consistent with the loss of cl being limited by vaporization of mixtures of cl salts such as hcl zncl2 fecl2 and nacl these new constraints on the chlorine abundance and isotopic values of urkreep make it a well constrained target for dynamic models aiming to test plausible conditions for the formation of the earth moon system

chlorine isotopic compositions of apatite in apollo 14 rocks evidence for widespread vapor phase metasomatism on the lunar nearside 4 billion years ago abstract compared to most other planetary materials in the solar system some lunar rocks display high 37cl signatures loss of cl in a h cl environment has been invoked to explain the heavy signatures observed in lunar samples either during volcanic eruptions onto the lunar surface or during large scale degassing of the lunar magma ocean to explore the conditions under which cl isotope fractionation occurred in lunar basaltic melts five apollo 14 crystalline samples were selected 14053 19 14072 13 14073 9 14310 171 along with basaltic clast 14321 1482 for in situ analysis of cl isotopes using secondary ion mass spectrometry cl isotopes were measured within the mineral apatite with 37cl values ranging from 14 6 1 6 to 40 0 2 9 these values expand the range previously reported for apatite in lunar rocks and include some of the heaviest cl isotope compositions measured in lunar samples to date the data here do not display a trend between increasing rare earth elements contents and 37cl values reported in previous studies other processes that can explain the wide inter and intra sample variability of 37cl values are explored magmatic degassing is suggested to have potentially played a role in fractionating cl isotope in these samples degassing alone however could not create the wide variability in isotopic signatures our favored hypothesis to explain small scale heterogeneity is late stage interaction with a volatile rich gas phase originating from devolatilization of lunar surface regolith rocks 4 billion years ago this period coincides with vapor induced metasomastism recorded in other lunar samples collected at the apollo 16 and 17 landing sites pointing to the possibility of widespread volatile induced metasomatism on the lunar nearside at that time potentially attributed to the imbrium formation event

petrogenesis and chronology of lunar meteorite northwest africa 4472 a kreepy regolith breccia from the moon northwest africa nwa 4472 is a polymict lunar regolith meteorite the sample is kreep rich high concentrations of potassium rare earth elements and phosphorus and comprises a heterogeneous array of lithic and mineral fragments these clasts and mineral fragments were sourced from a range of lunar rock types including the lunar high magnesian suite the high alkali suite kreep basalts mare basalts and a variety of impact crater environments the kreep rich nature of nwa 4472 indicates that the sample was ejected from regolith on the nearside of the moon in the procellarum kreep terrane and we have used lunar prospector gamma ray remote sensing data to show that the meteorite is most similar to and most likely sourced from regoliths adjacent to the imbrium impact basin u pb and pb pb age dates of nwa 4472 phosphate phases reveal that the breccia has sampled pre nectarian 4 35 ga rocks related to early episodes of kreep driven magmatism some younger phosphate u pb and pb pb age dates are likely indicative of impact resetting events at 3 9 4 ga consistent with the suggested timing of basin formation on the moon our study also shows that nwa 4472 has sampled impact melts and glass with an alkali depleted incompatible trace element rich high sc low rb th ratios low k compositional signature not related to typical apollo high k kreep or that sampled by kreepy lunar meteorite sayh al uhaymir sau 169 this provides evidence that there are numerous sources of kreep rich protoliths on the moon

crustal thickness of the moon implications for farside basin structures 1 based on the latest selene lunar gravity and topography model obtained by kaguya mission we compute the lunar crustal thickness map to investigate differences between farside basin structures the thickest crust is located in the southern rim of the dirichlet jackson basin and the thinnest crust at the moscoviense basin the thickest crust corresponds to the highest topography and is consistent with airy isostasy the thinnest crust is due to an abnormally large mantle plug the crustal thicknesses at apollo 12 14 sites of our crustal thickness model are 45 1 and 49 9 km the crustal thickness map indicates that the differences between recently proposed type i and type ii basins are probably controlled by the ratio between pre impact crustal thickness and impact scale

an ancient reservoir of volatiles in the moon sampled by lunar meteorite northwest africa 10989 abstract northwest africa nwa 10989 is a recently found lunar meteorite we used to elucidate the history of volatiles h and cl in the moon through analysis of its phosphates the petrology bulk geochemistry and mineralogy of nwa 10989 are consistent with it being a lunar meteorite with intermediate iron bulk composition composed of 40 of mare basaltic material and 60 non mare material but with no obvious kreep rich basaltic components it is probable that the source region for this meteorite resides near a mare highlands boundary possibly on the farside of the moon analyses of chlorine and hydrogen abundances and isotopic composition in apatite and merrillite grains from nwa 10989 indicate sampling of at least two distinct reservoirs of volatiles one being similar to those for known mare basalts from the apollo collections while the other potentially represents a yet unrecognized reservoir in situ th u pb dating of phosphates reveal two distinct age clusters with one ranging from 3 98 0 04 to 4 20 0 02 ga similar to the ages of cryptomare material and the other ranging from 3 32 0 01 to 3 96 0 03 ga closer to the ages of mare basalts known from the apollo collections this lunar breccia features mixing of material among which a basaltic d poor volatile reservoir which doesn t appear to have been recorded by apollo samples

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

phosphate halogen metasomatism of lunar granulite 79215 impact induced fractionation of volatiles and incompatible elements in the last decade it has been recognized that the moon contains significant proportions of volatile elements h f cl and that they are transported through the lunar crust and across its surface here we document a significant segment of that volatile cycle in lunar granulite breccia 79215 impact induced remobilization of volatiles and vapor phase transport with extreme elemental fractionation 79215 contains 1 volume of fluorapatite ca 5 po 4 3 f cl oh in crystals to 1 mm long which is reflected in its analyzed abundances of f cl and p the apatite has a molar f cl ratio of 10 and contains only 25 ppm oh and low abundances of the rare earth elements ree the chlorine in the apatite is isotopically heavy at 37 cl 32 7 1 6 hydrogen in the apatite is heavy at d 1060 180 much of that d came from spallogenic nuclear reactions and the original d was lower between 350 and 700 unlike other p rich lunar rocks e g 65015 79215 lacks abundant k and ree and other igneous incompatible elements characteristic of the lunar kreep component here we show that the p and halogens in 79215 were added to an otherwise normal granulite by vapor phase metasomatism similar to rock alteration by fumarolic exhalations as observed on earth the ultimate source of the p and halogens was most likely kreep it being the richest reservoir of p on the moon and 79215 having h and cl isotopic compositions consistent with kreep a kreep rich rock was heated and devolatilized by an impact event this vapor was fractionated by interaction with solid phases including merrillite a volatile free phosphate mineral a fe ti oxide and a zr bearing phase these solids removed ree th zr hf etc from the vapor and allowed the vapor to transport primarily p f and cl with lesser proportions of ba and u into 79215 vapor deposited crystals of apatite to 30 m are known in some lunar regolith samples but lunar vapor has not before this been implicated in significant mass transfer it seems unlikely however that phosphate halogen metasomatism is related to the high th sm abundance ratios of this and other lunar magnesian granulites the metasomatism of 79215 emphasizes the importance of impact heating in the lunar volatile cycle both in mobilizing volatile components into vapor and in generating strong elemental fractionations

a 7000 year sea surface temperature record from ca sri 147 santa rosa island california usa california mussels mytilus californianus excavated from archaeological site ca sri 147 on the southern side of santa rosa island california provided a discontinuous environmental record spanning about 7000 years an earlier report of the midden remains at this site found a weak inverse correlation between changes in mussel shell length and sea surface temperature sst but not productivity and a decline in mussel size from 5800 to 5100 calendar years before present during a period of low productivity and increasing sst this study uses oxygen isotopes from the site to directly compare environmental change to shifts in faunal assemblage four intervals of low temperatures are revealed in the nearshore environmental data each corresponding to a significant change in faunal assemblage at the site the first occurs c 6600 calendar years before present cal bp and coincides with the greatest amount of mussel shell mass and size in the site the second c 5500 cal bp occurs during an interval of variable mussel contribution and increasing red abalone haliotis rufescens contribution the third c 4800 cal bp occurs during a time when platform mussels septifer bifurcatus exceed california mussels in meat weight while the final interval c 3700 cal bp occurs prior to a period of probable site hiatus the overall pattern of decreasing shell contribution and size at the site is not found in the mollusk isotope data suggesting that environmental change had a profound impact on short term variability while human predation of key resources provided the long term primary stress on nearshore biota

lunar ferroan anorthosites mineralogy compositional variations and petrogenesis detailed petrologic study of a suite of lunar ferroan anorthosites indicates that their mineral compositional variations are generally consistent with derivation of these anorthosites from a common parent magma there are continuous compositional variations in major elements and smooth trends in minor elements mg fe in plagioclase al ti cr in pyroxene relict textures zoning and possible primary trends of mineral compositional variations are preserved in many of the anorthosites the presence of heterogeneous bimodal and or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks however they are composed entirely of ferroan anorthosite suite lithologies some aspects of the mineral composition data suggest that complex processes operated during formation of the ferroan anorthosites the lack of a well defined positive or negative trend of pyroxene mg mg fe versus plagioclase anorthite content the homogenization of mineral compositions in some anorthosites and the varied and apparently enriched mn contents of pyroxenes in some anorthosites suggest that original igneous compositional characteristics have been altered during and or after crystallization processes operative during anorthosite formation may have included some mixing of different melts trapping of variable amounts of intercumulus liquid postcrystallization redistribution of elements or perturbations both during adcumulus growth and subsequent to crystallization by impact events feo and mgo contents of the highly calcic plagioclase typical of these anorthosites suggest that the plagioclase melt distribution coefficients for these elements need to be reassessed

early degassing of lunar urkreep by crust breaching impact s current models for the moon s formation have yet to fully account for the thermal evolution of the moon in the presence of h2o and other volatiles of particular importance is chlorine since most lunar samples are characterised by unique heavy 37cl values significantly deviating from those of other planetary materials including earth for which 37cl values cluster around 0 in order to unravel the cause s of the moon s unique chlorine isotope signature we performed a comprehensive study of high precision in situ cl isotope measurements of apatite from a suite of apollo samples with a range of geochemical characteristics and petrologic types the cl isotopic compositions measured in lunar apatite in the studied samples display a wide range of 37cl values reaching a maximum value of 36 which are positively correlated with the amount of potassium k rare earth element ree and phosphorous p kreep component in each sample using these new data integrated with existing h isotope data obtained for the same samples we are able to place these findings in the context of the canonical lunar magma ocean lmo model the results are consistent with the urkreep reservoir being characterised by a 37cl 30 such a heavy cl isotope signature requires metal chloride degassing from a cl enriched urkreep lmo residue a process likely to have been triggered by at least one large crust breaching impact event that facilitated the transport and exposure of urkreep liquid to the lunar surface

geochemistry and petrology of lunar meteorite queen alexandra range 94281 a mixed mare and highland regolith breccia with special emphasis on very low titanium mafic components queen alexandra range que 94281 a lunar meteorite recently discovered in antarctica is a glassy matrix clast rich regolith breccia containing a mixture of mafic volcanic glass and gabbroic constituents and a diverse set of highland constituents in thin section the clast assemblage is dominated by coarse mineral debris from a shallow intrusive or hypabyssal setting or from deep within a thick mare flow abundant coarse grained pyroxene clasts have fine scale exsolution lamellae and compositions similar to pyroxenes of known lunar very low ti vlt basalts and other lunar meteorites of basaltic composition pyroxene compositions follow fe enrichment extending to hedenbergite which is associated with fayalite and cristobalite indicating slow cooling we refer to the protolith of the crystalline vlt component as vlt gabbro fragments of pyroclastic glasses that have high fe and low ti concentrations similar to the pyroclastic green glasses known from apollo samples are common lithic clasts include abundant subrounded glassy to cryptocrystalline aluminous 17 30 wt al2o3 kreep poor melt breccias of highland origin and a variety of other feldspathic impactites on the basis of composition of our subsamples que 94281 consists of 54 wt mafic or mare components and 46 wt feldspathic or highland components the bulk composition of que 94281 is similar to that of yamato y 793274 but que 94281 has slightly greater concentrations of some siderophile elements and slightly lower concentrations of those elements contributed mainly by mafic constituents differences in siderophile element concentrations are consistent with longer surface exposure of que 94281 minor differences in trace element variations of subsamples of the two meteorites suggest subtle differences in the composition of their highland constituents nonetheless the overall similarity of compositions supports the possibility that they were ejected from the same source region on the moon the crystalline vlt component of que 94281 differs from those known from apollo 17 and luna 24 vlt lithologies and from that of basaltic breccia elephant moraine eet 87521 the vlt gabbro component and the ferroan vlt volcanic glasses in que 94281 have compositions that may be petrogenetically related by derivation from a common picritic parent composition represented by an ultramafic glass found in que 94281

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

mare volcanism in the lunar farside moscoviense region implication for lateral variation in magma production of the moon 1 accurate estimates of the duration and volume of extrusive volcanism of the moon are essential for understanding the lunar thermal evolution here using new high resolution images obtained by the selene terrain camera we determined the thicknesses and ages of basalts in mare moscoviense one of the most prominent mare deposits on the farside mare volcanism in mare moscoviense was active for at least 1 5 ga following the formation of the moscoviense basin mare basalts are estimated to be at least 600 m thick corresponding to a total volume of 9 500 16 000 km 3 the long duration and large volume of extrusive volcanism are plausibly attributed to the thinner crust of the moscoviense basin relative to those of other farside basins from a comparison with mare volume within a same sized nearside basin we concluded that a magma production in the farside mantle was 3 10 times less than that of the nearside

asymmetrical distribution of rayed craters on the moon the synchronous rotation of the satellite ought to cause a spatial variation in the cratering rate over its surface the crater density is expected to be maximum at the apex of the orbital motion and decrease with the increase of the angular distance from the apex the ratio of the density at the apex maximum to that of the antapex minimum depends on the average encounter velocity of impactors to the satellite although the moon is also in a state of the synchronous rotation it has been supposed that the asymmetry in the crater density on the moon can be hardly observed we report here a spatial variation in the density of rayed craters on the moon which may be associated with the synchronous rotation since the lifetime of a ray is relatively short 0 8 billion years the results provide information on recent impacts rayed craters are identified on clementine 750 nm mosaic images we investigate craters in a lower latitude zone from 42 n to 42 s to avoid an effect of material difference on the ray preservation we analyze craters on the highland from 70 e to 290 e in east longitude a total of 222 rayed craters larger than 5 km in diameter are identified in the study area of about 1 4 107 km2 the average density of rayed craters on the leading side is substantially higher than that on the trailing side the crater density decreases as a sinusoidal function of the angular distance from the apex the observed ratio of the density at the apex to that at the antapex is about 1 5 the ratio suggests that recent craters on the moon are formed mainly by near earth asteroids rather than comets with higher encounter velocities

h and cl isotope systematics of apatite in brecciated lunar meteorites northwest africa 4472 northwest africa 773 sayh al uhaymir 169 and kalahari 009 we have investigated the h and cl systematics in apatite from four brecciated lunar meteorites in northwest africa nwa 4472 most of the apatites contain 2000 6000 ppm h2o with d between 200 and 0 except for one grain isolated in the matrix which contains 6000 ppm h2o with d of 500 900 this low d apatite contains 2500 7500 ppm cl associated with 37cl of 15 20 while the high d grain contains 2500 ppm cl with 37cl of 7 15 in nwa 773 apatites in a first group contain 700 2500 ppm h2o with d values averaging around 0 100 while apatites in a second group contain 5500 16500 ppm h2o with d 250 50 in sayh al uhaymir sau 169 and kalahari kal 009 apatites are similar in terms of their h2o contents 600 3000 ppm and d values 100 to 200 in sau 169 apatites contain 6000 10 000 ppm cl characterized by 37cl of 5 12 overall most of the analyzed apatite grains have d within the range reported for carbonaceous chondrites similar to apatite analyzed in ancient 3 9 ga lunar magmatic one grain in nwa 4472 has h and cl isotope compositions similar to apatite from mare basalts with an age of 4 35 ga this grain could be a representative of the oldest known lunar volcanic activity finally since numerous evolved clasts in nwa 773 formed through silicate liquid immiscibility the apatite grains with extremely high h2o contents reaching pure hydroxylapatite composition could provide insights into the effects of such process on the evolution of volatiles in lunar magmas

shock metamorphism of enstatite chondrites abstract we have extended the shock metamorphism classification scheme of stoffler et al 1991 to account for shock effects in orthopyroxene and applied it to sixty enstatite chondrites orthopyroxene exhibits the following sequence of progressive shock effects shock stage s1 unshocked sharp optical extinction s2 very weakly shocked undulose extinction s3 weakly shocked development of clinoenstatite lamellae parallel to 100 s4 moderately shocked weak mosaicism s5 strongly shocked strong mosaicism as in the stoffler et al 1991 scheme stage s5 is characterized principally by the solid state transformation of crystalline plagioclase into maskelynite most el3 chondrites exhibit foliations caused by impact deformation of chondrules and metal particles el5 and el6 chondrites are all shock stage s2 because opaque veins are rare in s2 ordinary chondrites it is plausible that the centimeter size kamacite veins in atlanta and blithfield and the 1 6 cm long oldhamite rich vein in jajh deh kot lalu all el6 formed when their hosts were shocked to s3 s5 levels because removal of shock stage s3 s5 features including repair of shock damaged orthopyroxene requires levels of metamorphism comparable to those experienced by petrologic type 5 to 6 chondrites we infer that proto el6 material was shocked to s3 s5 levels prior to peak metamorphism and shocked again to stage s2 after metamorphism overall enstatite chondrites appear to have suffered greater shock damage than ordinary and carbonaceous chondrites

evolved mare basalt magmatism high mg fe feldspathic crust chondritic impactors and the petrogenesis of antarctic lunar breccia meteorites meteorite hills 01210 and pecora escarpment 02007 antarctic lunar meteorites meteorite hills 01210 and pecora escarpment 02007 are breccias that come from different regolith lithologies on the moon met 01210 is composed predominantly of fractionated low ti basaltic material and is classified as an immature predominantly basaltic glassy matrix regolith breccia pca 02007 is a predominantly feldspathic regolith breccia consisting of metamorphosed feldspathic noritic troctolitic and noritic anorthosite clasts agglutinate and impact glasses as well as a number of basaltic clasts with mare and possible non mare affinities the basalt clasts in met 01210 have undergone fenner trend enrichments in iron and may also have witnessed late stage crystallization of zircon or a zirconium rich mineral some of the features of met 01210 are similar to other basaltic lunar breccia meteorites e g northwest africa 773 elephant moraine 87521 96008 yamato 793274 981031 but it is not paired with them the presence of metamorphic anorthositic clasts as well as agglutinates indicates a small regolith component similarities with previously discovered evolved e g lapaz icefield 02205 northwest africa 032 and ferroan e g asuka 881757 yamato 793169 basaltic lunar meteorites suggest a similar mare source region for met 01210 despite lack of evidence for pairing pca 02007 shares many features with other feldspathic regolith breccias e g yamato 791197 queen alexandra range 94281 including a high mg fe whole rock composition glass spherules agglutinate fragments and a diverse clast inventory spanning the range of ferroan anorthosite and high magnesium suite rocks some of the basalt fragments in this sample are fractionated and have an igneous origin however the majority of the basalt fragments are impact melt clasts pca 02007 supports previous studies of feldspathic lunar meteorites that have suggested an aluminous crust for the moon with compositions more similar to magnesium granulite breccias than ferroan anorthosites a chondrule like fragment found in pca 02007 and unlike any previously described lunar material is described and tentatively identified as the remnants of a chondritic lunar impactor this clast is porphyritic with equant olivines that have forsterite rich cores fo 98 extreme normal zonation to more fayalitic rims fo 44 and a mineral assemblage with rare earth element abundances distinct from described lunar material and more similar to chondrules found in ordinary or carbonaceous chondrites its discovery and description is significant for understanding the composition of lunar impactors previously the main evidence for chondritic lunar impactors was from chondritic relative abundances and near chondritic ratios of highly siderophile elements in lunar impact melt breccias however the presence of this clast along with two other chondritic clasts from apollo soils 12037 and 15602 provides clues to the identity of ancient meteorite impactors on the moon

oxygen isotope constraints on the origin and differentiation of the moon we report new high precision laser fluorination three isotope oxygen data for lunar materials terrestrial silicates with a range of 18 o values 0 5 to 22 9 were analyzed to independently determine the slope of the terrestrial fractionation line tfl 0 5259 0 0008 95 confidence level this new tfl determination allows direct comparison of lunar oxygen isotope systematics with those of earth values of 17 o for apollo 12 15 and 17 basalts and luna 24 soil samples average 0 01 and are indistinguishable from the tfl the 18 o values of high and low ti lunar basalts are distinct average whole rock 18 o values for low ti lunar basalts from the apollo 12 5 72 0 06 and apollo 15 landing sites 5 65 0 12 are identical within error and are markedly higher than apollo 17 high ti basalts 5 46 0 11 evolved low ti lapaz mare basalt meteorite 18 o values 5 67 0 05 are in close agreement with more primitive low ti apollo 12 and 15 mare basalts modeling of lunar mare basalt source composition indicates that the high and low ti mare basalt mantle reservoirs were in oxygen isotope equilibrium and that variations in 18 o do not result from fractional crystallization instead these differences are consistent with mineralogically heterogeneous mantle sources for mare basalts and with lunar magma ocean differentiation models that result in a thick feldspathic crust an olivine pyroxene rich mantle and late stage ilmenite rich zones that were convectively mixed into deeper portions of the lunar mantle higher average 18 o wr values of low ti basalts compared to terrestrial mid ocean ridge basalts 0 18 suggest a possible oxygen isotopic difference between the terrestrial and lunar mantles however calculations of the 18 o of lunar mantle olivine in this study are only 0 05 higher than terrestrial mantle olivine these observations may have important implications for understanding the formation of the earth moon system 2006 elsevier b v all rights reserved

the meteoritical bulletin no 102 meteoritical bulletin 102 contains 3141 meteorites including 12 falls boumdeid 2003 boumdeid 2011 braunschweig chelyabinsk dongyang draveil heyetang indian butte katol ladkee ouadangou xining with 2611 ordinary chondrites 264 hed achondrites 124 carbonaceous chondrites 30 ureilites 20 martian meteorites 16 primitive achondrites 16 rumuruti chondrites 15 mesosiderites 12 iron meteorites 10 lunar meteorites 9 enstatite chondrites 4 enstatite achondrites 4 pallasites 4 ungrouped achondrites and 2 angrites and with 1708 from antarctica 956 from africa 294 from south america 126 from asia 47 from north america 6 from europe including russia and 4 from oceania information about approved meteorites can be obtained from the meteoritical bulletin database mbd available on line at http www lpi usra edu meteor

an interdisciplinary study of weathering effects in ordinary chondrites from the acfer region algeria weathering effects on meteorite finds from the acfer region were studied by various analytical techniques and in dependence on the depth of sampling in thin sections of weathered meteorites weathering effects usually decrease from the outside to the interior of the meteorite the results of evolved gas analysis indicate that variation in weathering between surface and core is not significant in respect to the formation of fe oxyhydroxides the secondary alteration effects in the noble gases are distributed unevenly throughout the specimens as seen in the nonsystematic differences observed for the heavy noble gases chemical analyses show significant enrichment of ba and sr in the outer parts of the weathered samples due to element contamination through aqueous solution iron ni and co are partly flushed from the system as the metal oxidation proceeds oxygen isotopes show increases in d180 and d17o with increasing terrestrial age for a set of h3 chondrites the degree of weathering determined from the water content was correlated with terrestrial ages and is discussed with respect to possible weathering mechanisms

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

kreepy lunar meteorite dhofar 287a a new lunar mare basalt dhofar 287 dho 287 is a new lunar meteorite found in oman on january 14 2001 the main portion of this meteorite dho 287a consists of a mare basalt while a smaller portion of breccia dho 287b is attached on the side dho 287a is only the fourth crystalline mare basalt meteorite found on earth to date and is the subject of the present study the basalt consists mainly of phenocrysts of olivine and pyroxene set in a finer grained matrix which is composed of elongated pyroxene and plagioclase crystals radiating from a common nucleii the majority of olivine and pyroxene grains are zoned from core to rim in terms of fe and mg accessory minerals include ilmenite chromite ulvaspinel troilite and feni metal chromite is invariably mantled by ulvaspinel this rock is unusually rich in late stage mesostasis composed largely of fayalite si k ba rich glass fluorapatite and whitlockite in texture and mineralogy dho 287a is a low ti mare basalt with similarities to apollo 12 a 12 and apollo 15 a 15 basalts however all plagioclase is now present as maskelynite and its composition is atypical for known low ti mare basalts the fe to mn ratios of olivine and pyroxene the presence of feni metal and the bulk rock oxygen isotopic ratios along with several other petrological features are evidence for the lunar origin for this meteorite whole rock composition further confirms the similarity of dho 287a with a 12 and a 15 sam ples but requires possible kreep assimilation to account for its rare earth element ree contents cooling rate estimates based on fo zonation in olivine yield values of 0 2 0 8 c hr for the lava typical for the center of a 10 20 m thick flow the recalculated major element concentrations after removing 10 15 modal olivine are comparable to typical a 15 mare basalts crystallization mod eling of the recalculated dho 287a bulk composition yields a reasonable fit between predicted and observed mineral abundances and compositions

compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration we present new compositional data for 30 lunar stones representing about 19 meteorites most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites 3 7 feo and the basaltic lunar meteorites 17 23 feo all but one are polymict breccias some as implied by their intermediate composition are mainly mixtures of brecciated anorthosite and mare basalt with low concentrations of incompatible elements such as sm 1 3 g g these breccias likely originate from points on the moon where mare basalt has mixed with material of the fht feldspathic highlands terrane others however are not anorthosite basalt mixtures three 17 75 g g sm consist mainly of nonmare mafic material from the nearside pkt procellarum kreep terrane and a few are ternary mixtures of material from the fht pkt and maria some contain mafic nonmare lithologies like anorthositic norites norites gabbronorites and troctolite these breccias are largely unlike breccias of the apollo collection in that they are poor in sm as well as highly feldspathic anorthosite such as that common at the apollo 16 site several have high th sm compared to apollo breccias dhofar 961 which is olivine gabbronoritic and moderately rich in sm has lower eu sm than apollo samples of similar sm concentration this difference indicates that the carrier of rare earth elements is not kreep as known from the apollo missions on the basis of our present knowledge from remote sensing among lunar meteorites dhofar 961 is the one most likely to have originated from south pole aitken basin on the lunar far side

petrogenesis of lunar highlands meteorites dhofar 025 dhofar 081 dar al gani 262 and dar al gani 400 the petrogenesis of four lunar highlands meteorites dhofar 025 dho 025 dhofar 081 dho 081 dar al gani 262 dag 262 and dar al gani 400 dag 400 were studied for dho 025 measured oxygen isotopic values and fe mn ratios for mafic minerals provide corroboratory evidence that it originated on the moon similarly fe mn ratios in the mafic minerals of dho 081 indicate lunar origin lithologies in dho 025 and dho 081 include lithic clasts granulites and mineral fragments a large number of lithic clasts have plagioclase an and coexisting mafic mineral mg that plot within the gap separating ferroan anorthosite suite fan and high magnesium suite hms rocks this is consistent with whole rock ti sm ratios for dho 025 dho 081 and dag 262 which are also intermediate compared to fan and hms lithologies although ion microprobe analyses performed on dho 025 dho 081 dag 262 and dag 400 clasts and minerals show far stronger fan affinities than whole rock data suggest most clasts indicate admixture of 12 hms component based on geochemical modeling in addition coexisting plagioclase pyroxene ree concentration ratios in several clasts were compared to experimentally determined plagioclase pyroxene ree distribution coefficient ratios two dho 025 clasts have concordant plagioclase pyroxene profiles indicating that equilibrium between these minerals has been sustained despite shock metamorphism one clast has an intermediate fan hms composition these lunar meteorites appear to represent a type of highland terrain that differs substantially from the kreep signatured impact breccias that dominate the lunar database from remote sensing data it is inferred that the lunar far side appears to have appropriate geochemical signatures and lithologies to be the source regions for these rocks although the near side cannot be completely excluded as a possibility if these rocks are indeed from the far side their geochemical characteristics may have far reaching implications for our current scientific understanding of the moon

ancient volcanism on the moon insights from pb isotopes in the mil 13317 and kalahari 009 lunar meteorites abstract lunar meteorites provide a potential opportunity to expand the study of ancient 4000 ma basaltic volcanism on the moon of which there are only a few examples in the apollo sample collection secondary ion mass spectrometry sims was used to determine the pb isotopic compositions of multiple mineral phases ca phosphates baddeleyite k feldspar k rich glass and plagioclase in two lunar meteorites miller range mil 13317 and kalahari kal 009 these data were used to calculate crystallisation ages of 4332 2 ma 95 confidence level for basaltic clasts in mil 13317 and 4369 7 ma 95 confidence level for the monomict basaltic breccia kal 009 from the analyses of the mil 13317 basaltic clasts it was possible to determine an initial pb isotopic composition of the protolith from which the clasts originated and infer a 238u 204pb ratio value of 850 130 2 uncertainty for the magmatic source of this basalt this is lower than values determined previously for kreep rich an acronym for k rare earth elements and p basalts although analyses of other lithological components in the meteorite suggest the presence of a kreep component in the regolith from which the breccia was formed and therefore a more probable origin for the meteorite on the lunar nearside it was not possible to determine a similar initial pb isotopic composition from the kal 009 data but previous studies of the meteorite have highlighted the very low concentrations of incompatible trace elements and proposed an origin on the farside of the moon taken together the data from these two meteorites provide more compelling evidence for widespread ancient volcanism on the moon furthermore the compositional differences between the basaltic materials in the meteorites provide evidence that this volcanism was not an isolated or localised occurrence but happened in multiple locations on the moon and at distinct times in light of previous studies into early lunar magmatic evolution these data also imply that basaltic volcanism commenced almost immediately after lunar magma ocean lmo crystallisation as defined by nd hf and pb model ages at about 4370 ma

basalt thickness in mare humorum the crater excavation method basalt thicknesses in mare basins have been determined using assumptions about the premare topography of partly buried craters and by comparison to the orientale basin differences in those assumptions have led to a factor of 4 difference in mare thickness estimates further knowledge of thickness is restricted to areas in which buried craters are present using mixing models applied to multispectral images acquired by the clementine spacecraft we have shown that craters in the mare sometimes excavate highland material from below the mare cover using such craters and assumptions about their depth of excavation we obtain independent estimates of basalt thickness our results are in agreement with the lowest of previous thickness estimates we derive a volume of 40 000 km 3 for basalts in mare humorum considerably less than the 110 000 km 3 from previous estimates we also confirm a diameter of 425 km for thc humorum multiring basin based on the clementine gridded global topography assuming an original morphology like orientale

potential anomalies on a sphere applications to the thickness of the lunar crust a new technique for calculating potential anomalies on a sphere due to finite amplitude relief has been developed we show that by raising the topography to the nth power and expanding this field into spherical harmonics potential anomalies due to topography on spherical density interfaces can be computed to arbitrary precision using a filter for downward continuing the bouguer anomaly we have computed a variety of crustal thickness maps for the moon assuming both a homogeneous as well as a dual layered crust the crustal thickness maps for the homogeneous model give plausible results but this model is not consistent with the seismic data petrologic evidence and geoid to topography ratios all of which suggest some form of crustal stratification several dual layered models were investigated and it was found that only models with both upper and lower crustal thickness variations could satisfy the gravity and topography data these models predict that the entire upper crust has been excavated beneath the major nearside multiring basins additionally significant amounts of lower crustal material was excavated from these basins especially beneath crisium this model also predicts that mantle material should not have been excavated during the south pole aitken basin forming event and that lower crustal material should be exposed at the surface in this basin

petrogenesis of mare basalts a record of lunar volcanism returned rock and soil samples from our nearest planetary neighbor have provided the basis for much of our understanding of the origin and evolution of the moon of particular importance are the mare basalts which have revealed considerable information about lunar volcanism and the nature of the mantle as well as post magma generation processes this paper is a critical review of the petrogenetic models for the generation of mare basalts formulated over the last twenty years we have used all available mare basalt analyses to define a six fold classification scheme using tio2 contents as the primary division i e 1 wt very low ti or vlt 1 6 wt low ti 6 wt high ti a secondary division is made using al2o3 contents i e 11 wt low al 11 wt high al and a tertiary division is defined using k contents i e 2000 ppm low k 2000 ppm high k such divisions and subdivisions yield a classification containing twelve categories of which six are accounted for by the existing apollo and luna collections therefore we present our discussions in the form of six mare basalt rock types 1 1 high ti low al low k referred to as high ti low k 2 2 high ti low al high k referred to as high ti high k 3 3 low ti low al low k referred to as low ti 4 4 low ti high al low k referred to as high alumina 5 5 low ti high al high k referred to as vhk 6 6 vlt low al low k basalts referred to as vlt a variety of post magma generation processes have been invoked such as fractional crystallization either alone or combined with wallrock assimilation to explain the compositional ranges of the various mare basalt suites in order to evaluate these proposed petrogenetic processes this review is by rock type and is non site specific but for each rock type reference to particular lunar sample return missions is brought forth this permits a comparison of similarities and differences of broadly similar rock types correlated with geography on the moon which in turn allows a more thorough petrogenetic evaluation high ti mare basalts i e high ti low al low k are found at apollo 11 and apollo 17 sites however the a 11 basalts contain lower tio2 abundances a considerably larger range in trace element contents and the only occurrence of high ti high k mare basalts fractional crystallization and source heterogeneity within each site are the keys to understanding the petrogenesis of the high ti basalts low ti basalts including both low al k and high al k varieties are found at apollo 12 14 and 15 and luna 16 sites the low ti basalts exhibit a wide range of major and trace element compositions and require source heterogeneity fractional crystallization and some assimilation the high alumina mare basalts i e low ti high al low k are found at apollo 14 and luna 16 sites and exhibit a wide range of major and trace element compositions however in these examples source heterogeneity is not a major factor indeed fractional crystallization coupled with kreep assimilation particularly for the apollo 14 variants can explain the compositional ranges of these high alumina basalts the vhk mare basalts i e low ti high al high k have been sampled only at the apollo 14 locale and are products of a parental highalumina magma assimilating lunar granite very low ti vlt mare basalts i e vlt low al low k are found at apollo 17 and luna 24 sites fractional crystallization has had a major influence upon the range in vlt compositions but luna 24 vlt basalts have been derived from a source slightly different in composition from that for apollo 17 vlt varieties for example the luna 24 vlt basalts generally exhibit positive eu anomalies a unique property for mare basalts which almost always have negative eu anomalies the concept of a lunar magma ocean lmo is generally accepted and source modelling of all basalts invokes a mafic lmo cumulate source this is the only unifying model for mare basalt petrogenesis but the semantics and logistics of it are and will be debated for many years for example major convective overturn of the lmo appears plausible but whether this occurred on a local or planet wide scale to produce source heterogeneity remains to be determined

d poor hydrogen in lunar mare basalts assimilated from lunar regolith apatite grains in lunar mare basalts contain hydrogen that ranges in d h ratio by more than a factor of two for most of these basalts the d h ratios in their apatite grains decrease with measures of the host basalts time spent at elevated temperature specifically the fe mg homogenization of their pyroxenes most basalts with homogeneous pyroxenes i e with constant fe mg ratio have apatite grains with low d h d 100 whereas most basalts with heterogeneous pyroxenes i e varying or zoned fe mg have apatite with high d h d up to 1100 this relationship suggests that low d h values were acquired during thermal processing i e during fe mg chemical equilibration during or after emplacement this light hydrogen is likely derived from solar wind implanted into the lunar regolith with d from 125 to 800 and could enter basalts either by assimilation of regolith or by vapor transport from regolith heated by the flow if a basalt could not interact with regolith rich in solar wind e g it was emplaced onto other fresh basalts its apatite could retain a magmatic d h signature the high d h component in the apatites of unequilibrated basalts is most reasonably that indigenous magmatic hydrogen i e representing hydrogen in the basalt s source mantles or magmatic hydrogen that was residual after partial degassing of h 2

cryptomare magmatism 4 35 gyr ago recorded in lunar meteorite kalahari 009 the origin and evolution of the moon remain controversial one notable point of controversy being the timing of the beginning and end of basaltic volcanism in the lunar mares or plains lunar research over the past three decades has suggested that mare volcanism occurred mainly after the late heavy bombardment that ended 3 9 billion years ago because most of known mare basalts lunar meteorites and returned apollo and luna samples and remote sensing data indicate crystallization ages younger than 3 9 billion years but a new u pb dating of minerals in the lunar meteorite kalahari 009 gives an age of roughly 4 35 billion years for a lunar basalt this suggests that the volcanism started as early as 4 35 billion years ago relatively soon after lunar formation and differentiation and that kalahari 009 is our first sample of a cryptomare from the moon the result of u pb dating of minerals in a lunar meteorite kalahari 009 is reported analyses of five grains associated with basaltic clasts give an age of 4 35 0 15 billion years these are thought to represent the crystallization ages of parental basalt magma making kalahari 009 one of the oldest known mare basalt this suggests that mare basalt volcanism on the moon started as early as 4 35 billion years ago the origin and evolution of the moon remain controversial1 2 with one of the most important questions for lunar evolution being the timing and duration of basaltic mare magmatism1 3 4 5 6 7 8 here we report the result of ion microprobe u pb dating of phosphates in a lunar meteorite kalahari 009 which is classified as a very low ti mare basalt breccia in situ analyses of five phosphate grains associated with basaltic clasts give an age of 4 35 0 15 billion years these ancient phosphate ages are thought to represent the crystallization ages of parental basalt magma making kalahari 009 one of the oldest known mare basalts we suggest that mare basalt volcanism on the moon started as early as 4 35 gyr ago relatively soon after its formation and differentiation and preceding the bulk of lunar volcanism which ensued after the late heavy bombardment around 3 8 3 9 gyr refs 7 and 8 considering the extremely low abundances of incompatible elements such as thorium and the rare earth elements in kalahari 009 ref 9 and recent remote sensing observations illustrating that the cryptomaria tend to be of very low ti basalt type10 11 12 we conclude that kalahari 009 is our first sample of a very low ti cryptomare from the moon

geochronology of the martian meteorite zagami revealed by u pb ion probe dating of accessory minerals abstract the precise chronology of geological events on mars is hampered by the lack of absolute ages for the martian timescale and the significant uncertainties that result from the extrapolation of the lunar timescale to mars hartmann and neukum 2001 martian meteorites represent the only samples of mars currently available attempts to identify source craters for the meteorites have thus far proven inconclusive hamilton et al 2003 lang et al 2009 mouginis mark and boyce 2012 precluding their use in constraining the absolute martian timescale the majority of the known martian meteorites are basalts shergottites all dated shergottites have mineral separate rb sr or sm nd ages of borg et al 2005 here we report a 238u 206pb age of 182 7 6 9 ma by ion microprobe analysis of baddeleyite zro2 grains in the zagami shergottite there is no correlation between discordancy and baddeleyite grain location relative to shock metamorphism mineral petrography demonstrates that baddeleyite is the result of late stage igneous crystallization and raman spectroscopy shows that baddeleyite has not been transformed by shock into preservable high pressure polymorphs supported by an age of 153 81 ma for phosphate grains obtained using the same method we conclude that zagami crystallized at 180 ma in agreement with previous results from mineral separate geochronology therefore the shergottites represent igneous rocks preferentially ejected from young terrains on mars in a small number of ejection events

lunar meteorite regolith breccias an in situ study of impact melt composition using la icp ms with implications for the composition of the lunar crust dar al gani dag 400 meteorite hills met 01210 pecora escarpment pca 02007 and macalpine hills mac 88104 88105 are lunar regolith breccia meteorites that provide sampling of the lunar surface from regions of the moon that were not visited by the us apollo or soviet luna sample return missions they contain a heterogeneous clast population from a range of typical lunar lithologies dag 400 pca 02007 and mac 88104 88105 are primarily feldspathic in nature and met 01210 is composed of mare basalt material mixed with a lesser amount of feldspathic material here we present a compositional study of the impact melt and impact melt breccia clast population i e clasts that were generated in impact cratering melting processes within these meteorites using in situ electron microprobe and la icp ms techniques results show that all of the meteorites are dominated by impact lithologies that are relatively ferroan mg 10 and have low incompatible trace element ite concentrations i e typically 10 ppm sm high magnesium suite typically 70 mg or high alkali suite high ites sc sm ratios 2 target rocks instead the meteorite mafic melts are more ferroan kreep poor and sc rich and represent mixing between feldspathic lithologies and low ti or very low ti vlt basalts as pca 02007 and mac 88104 05 were likely sourced from the outer feldspathic highlands terrane our findings suggest that these predominantly feldspathic regions commonly contain a vlt to low ti basalt contribution

the nature of the meteoritic components of apollo 16 soil as inferred from correlations of iron cobalt iridium and gold with nickel concentrations of co ni ir and au in small samples of submature and mature soil from apollo 16 are highly variable correlations of fe co ir and au with ni indicate that the variation in siderophile element concentrations results from variation in the concentration of fe ni metal from these correlations the mean composition of the metal is inferred to be 5 6 ni and 0 36 co for a ni co ratio of 15 5 0 7 i e dissimilar to the chondritic ratio of 20 21 the fe ni metal is also characterized by low ir ni and ir au ratios compared to metal in ordinary chondrites metal with a similar composition is also found in metal rich noritic impact melt breccias that occur as discrete rocks as well as small clasts in ancient regolith breccias at apollo 16 mass balance models using lithophile element concentrations indicate that about 35 of the soil is noritic impact melt the fe ni metal associated with this component is sufficient to supply virtually all the ancient fe ni metal found in the typical apollo 16 soil 0 4 0 5 i e no other source is required the soil also contains 1 2 carbonaceous chondrite the concentration of this component appears to be relatively constant from sample to sample and does not contribute significantly to the variation in siderophile element abundances these two meteoritic components contribute nearly equal concentrations of ni to the typical apollo 16 soil

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

four lunar mare meteorites crystallization trends of pyroxenes and spinels we studied crystallization trends of pyroxene and spinel in four antarctic meteorites known to be derived from mare regions of the moon y 793169 and a 881757 ya meteorites are unbrecciated igneous basalts eet 87521 is a fragmental breccia and y 793274 is a regolith breccia all have relatively low bulkrock tio2 content and the ya meteorites are uncommonly ancient our electron probe microanalysis epma data indicate that the ya meteorites and the dominant mare components of y 793274 and eet 87521 conform to a general trend for ti poor low ti and very low ti mare basalts their pyroxenes show a strong correlation between fe fe mg fe and ti ti cr ti both ratios typically increasing from core to rim these trends presumably reflect local crystallization differentiation of interstitial melt previous studies m j drake and coworkers have suggested that the detailed configurations of such fe vs ti trends may reflect the bulk tio2 contents of the parent magmas basalts as a more systematic approach to this problem we plot bulk rock tio2 as a function of the fe 0 50 intercept of each rock s pyroxene fe vs ti trend we call this intercept the fe normalized ti based on our data for eet 87521 the ya meteorites and apollo 12 basalts 12031 and 12064 plus literature data for several other ti poor mare basalts we find a strong correlation between fe normalized ti and the bulk tio2 content of the parent basalt this correlation confirms that fragmental breccia eet 87521 is nearly pure very low ti vlt basalt and that the ya meteorites for which bulk rock tio2 results scatter due to unusually coarse grain size a 881757 or scarcity of available sample y 793169 are pieces of an uncommonly ti poor but not quite vlt variety of low ti mare basalt extrapolating from this correlation the dominant mare component of regolith breccia y 793274 is probably of vlt affinity besides the normal mare pyroxene trend of strong correlation between fe and ti y 793274 includes two additional pyroxene compositional trends both showing a wide range of ti despite relatively constant and low by mare standards fe the most magnesian of these trends consists of a single clast with a mode of orthopyroxene mgo rich ilmenite these two trends are of uncertain origin possibly one or both represents the highland component of this regolith breccia although unlike most highland pyroxenes these appear relatively unaltered by impact brecciation and metamorphism compositions of spinels in the coarse grained a 881757 show an extraordinary distribution chromite and ulvospinel components vary among grains but are nearly constant within grains despite its old age and unusually coarse grain sizes mineralogical evidence i e heterogeneity within both pyroxene and spinel typical pyroxene exsolution scale very coarse by mare standards but exceeded by the pyroxenes of eet 87521 and y 793274 indicates that a 881757 was cooled only slightly more slowly than typical mare basalts and may have formed near the center of an uncommonly thick lava flow both of the vlt basaltic lunar meteorite breccias eet 87521 and y 793274 are composed dominantly of pyroxenes with exsolution coarser than normal for mare basalts possibly vlt basalt flows tend to be systematically thicker and thus more slowly cooled than more ti rich flows

lunar feldspathic meteorites constraints on the geology of the lunar highlands and the origin of the lunar crust abstract the composition of the lunar crust provides clues about the processes that formed it and hence contains information on the origin and evolution of the moon current understanding of lunar evolution is built on the lunar magma ocean hypothesis that early in its history the moon was wholly or mostly molten this hypothesis is based on analyses of apollo samples of ferroan anorthosites 90 plagioclase molar mg mg fe mg 75 and the assumption that they are globally distributed however new results from lunar meteorites which are random samples of the moon s surface and remote sensing data show that ferroan anorthosites are not globally distributed and that the apollo highland samples used as a basis for the model are influenced by ejecta from the imbrium basin in this study we evaluate anorthosites from all currently available adequately described lunar highland meteorites representing a more widespread sampling of the lunar highlands than apollo samples alone and find that 80 of them are significantly more magnesian than apollo ferroan anorthosites interestingly luna mission anorthosites collected outside the continuous imbrium ejecta are also highly magnesian if the lunar highland crust consists dominantly of magnesian anorthosites as suggested by their abundance in samples sourced outside imbrium ejecta a reevaluation of the lunar magma ocean model is a sensible step forward in the endeavor to understand lunar evolution our results demonstrate that lunar anorthosites are more similar in their chemical trends and mineral abundance to terrestrial massif anorthosites than to anorthosites predicted in a lunar magma ocean this analysis does not invalidate the idea of a lunar magma ocean which seems a necessity under the giant impact hypothesis for the origin of the moon however it does indicate that most rocks now seen at the moon s surface are not primary products of a magma ocean alone but are products of more complex crustal processes

heterogeneous distribution of water in the moon the discovery of water in lunar samples in 2008 challenged the notion that the moon s interior had lost all its volatiles since then analyses of the water concentrations and isotopic compositions in lunar samples taken together suggest that the moon is heterogeneously wet which may lend clues to its origin

hydrogen isotope ratios in lunar rocks indicate delivery of cometary water to the moon water has been found in many lunar rock samples but its sources are unknown isotopic analyses of apollo samples of lunar mare basalts and highlands rocks suggest that a significant volume of water was delivered to the moon by comets shortly after its formation by giant impact