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Arguably, the most striking geochemical distinction between Earth and the Moon has been the virtual lack of water (hydrogen) in the latter. This conclusion was recently challenged on the basis of geochemical data from lunar materials that suggest that the Moon's water content might be far higher than previously believed. We measured the chlorine isotope composition of Apollo basalts and glasses and found that the range of isotopic values [from -1 to +24 per mil ([per thousand]) versus standard mean ocean chloride] is 25 times the range for Earth. The huge isotopic spread is explained by voiatilization of metal halides during basalt eruption--a process that could only occur if the Moon had hydrogen concentrations tower than those of Earth by a factor of [~10.sup.4] to [10.sup.5], implying that the lunar interior is essentially anhydrous. 10.1126/science.1192606

Quantifying atmospheric C[O.sub.2] concentrations ([[C[O.sub.2]].sub.atm]) during Earth's ancient greenhouse episodes is essential for accurately predicting the response of future climate to elevated C[O.sub.2] levels. Empirical estimates of [[C[O.sub.2]].sub.atm] during Paleozoic and Mesozoic greenhouse climates are based primarily on the carbon isotope composition of calcium carbonate in fossil soils. We report that greenhouse [[C[O.sub.2]].sub.atm] have been significantly overestimated because previously assumed soil C[O.sub.2] concentrations during carbonate formation are too high. More accurate [[C[O.sub.2]].sub.atm], resulting from better constraints on soil C[O.sub.2], indicate that large (1,000s of ppmV) fluctuations in [[C[O.sub.2].sub.atm] did not characterize ancient climates and that past greenhouse climates were accompanied by concentrations similar to those projected for A.D. 2100. paleosol barometer | carbon isotopes | pedogenic carbonate | Phanerozoic | climate sensitivity www.pnas.org/cgi/doi/10.1073/pnas.0902323106

Carbonatite lavas are highly unusual in that they contain almost no Si[O.sub.2] and are >50 per cent carbonateminerals. Although carbonatite magmatism has occurred throughout Earth's history, Oldoinyo Lengai, in Tanzania, [...]

In order to better calibrate pedogenic carbonate as a proxy for past environments, we compared the stable isotopic composition of soil C[O.sub.2], soil water, and pedogenic carbonate in young soils from central New Mexico, USA. Seasonal changes in the [delta][sup.13]C value of soil C[O.sub.2], the [delta][sup.18]O value of soil water, and the soil temperature were monitored to establish the timing of isotopic equilibrium with the carbonate. Calcite solubility was calculated from measured temperatures and C[O.sub.2] concentrations in the soil. This approach allowed us to determine the conditions associated with pedogenic carbonate formation. Carbon isotope equilibrium, oxygen isotope equilibrium, and minimum calcite solubility all occurred simultaneously during warm, dry conditions in May 2008 when soil C[O.sub.2] concentrations were low. It is therefore concluded that pedogenic carbonate forms during warm, dry periods and does not record mean growing season conditions as typically assumed. The seasonal bias in pedogenic carbonate formation may explain the occurrence of pedogenic carbonate in monsoon climates and its absence in regions where annual precipitation is more uniformly distributed. The implications of the seasonal bias for stable isotope--based paleoenvironmental reconstructions are that paleoelevations may have been previously over- or underestimated, paleoatmospheric C[O.sub.2] concentrations likely have been significantly overestimated, and pedogenic carbonate provides a [C.sub.4]-biased record of paleovegetation, especially in dry soils.

Oxygen and C isotope compositions of C[O.sub.2] gas released by thermal decomposition of siderite, calcite, and dolomite were measured using a new 'real-time' continuous-flow technique to determine whether fractionation associated with simple thermal decarbonation could explain the large isotopic variations and mineralogy such as those found in the ALH84001 meteorite. Oxygen and C isotope fractionation between calcite or dolomite and evolved C[O.sub.2] gas during thermal decarbonation in a 3 bar He pressure environment is very small. The [delta][sup.13]C and [delta][sup.8]O values of evolved C[O.sub.2] gas are nearly identical to those of the carbonate, very different from the calculated equilibrium [DELTA][sup.18] [O.sub.calcite-C[O.sub.2]] value of -4 to -5 [per thousand] at 800-900[degrees] C or from previous experimental results of decarbonation in vacuum. The kinetic [DELTA][sup.18][O.sub.siderite-C[O.sub.2]] values are ~-2 [per thousand], whereas [DELTA][sup.13][C.sub.siderite-C[O.sub.2]] values increase logarithmically with time, from ~1 [per thousand] for the earliest stages of decarbonation to >5 [per thousand] in the final stages. Incomplete siderite decomposition produces both magnetite ([delta][sup.18]O = 3.5 [per thousand] SMOW) and minor graphite. CO and [O.sub.2] were detected during the decarbonation process. The data can be explained by simultaneous oxidation and reduction by the reaction: 6FeC[O.sub.3] [right arrow] 2[Fe.sub.3][O.sub.4] + 2x CO + 4y C[O.sub.2] + (6 - 2x - 4y) C + (5 - x - 4y) [O.sub.2], where x and y are between 0 and 1. Siderite decomposition in the presence of [H.sub.2] gas produces wustite and Fe metal in place of oxidized Fe minerals. The experiments in this study are not a perfect analog for possible decarbonation conditions that might have occurred to the carbonates in ALH84001. Nevertheless, the large [delta][sup.13]C and [delta][sup.18]O variations observed in ALH84001 (>10 [per thousand] for O) are significantly larger than those expected by thermal decarbonation, suggesting instead a low-temperature mechanism for their formation.

Research concerning the measurement of different types of Middle Triassic material used to evaluate the effect of diagenesis on oxygen isotope composition of preserved biogenic phophates is presented.

Isotope analysis of a bulk fossil tooth gives a 'snapshot' impression of paleoclimatic conditions - a single point in time. However, hypsodont teeth grow over a period of a year or more, so that stable carbon and oxygen isotope variations along their length are a 'tape recorder' of short-term seasonal variations from the distant past. We have used a new in situ micro-laser sampling method to determine submillimeter carbon and oxygen isotope variations in the enamel of individual fossil horse teeth to assess ancient annual meteoric water variations and feeding patterns. The [[Delta].sup.18]O values from a 6.8 Ma fossil horse tooth (Astrohippus ansae) from Texas vary cyclically along the 6 cm length of the tooth with a smoothed amplitude of >4[per thousand], similar to the monthly averaged amplitude measured in modern meteoric waters from the region. The seasonal [[Delta].sup.18]O values are [approximately]3[per thousand] to 4[per thousand] higher than those calculated from modern meteoric water data, suggesting either a higher local meteoric water value in the Miocene of Texas, or that the animal received a high proportion of its dietary water from plants or highly evaporated water. A Holocene horse tooth from the shores of Glacial Lake Agassiz, North Dakota (Equus sp.), also has isotopic variations with the same 35 mm periodicity, but a smoothed amplitude of only 2[per thousand]. This horse most likely had a buffered drinking supply. The calculated [[Delta].sup.18]O of the water in equilibrium with this tooth is the same as the modern measured annual average. The variations within a single tooth can be as large as those generally observed in entire stratigraphic sections of fossil teeth analyzed by bulk methods. The new method provides an important technique for evaluating fossil disgenesis; conventional bulk analyses of teeth fragments may not be representative of the whole tooth, thus explaining analytical scatter that has been previously attributed to diagenesis.

To examine the potential for volatile fluxing of magma chambers by in situ degassing of hydrous minerals, we obtained complete chemical analyses for biotite separates from silicic lavas. The separates exhibit unusually low [H.sub.2]O contents that inversely correlate with host lava temperatures, high [Fe.sup.3+]/[Fe.sup.2+] ratios that inversely correlate with host lava oxygen fugacities, and the highest [Delta]D values yet reported for biotite from any silicic igneous rock (up to -19[per thousand]). These results are direct evidence for selective loss of protium (1H) from biotite during dehydrogenation in magma chambers heated from below by intrusion of marie magma. The maximum P[Delta]V energy generated from dehydrogenation alone can approach 2 x [10.sup.3] joules per kilogram of magma. This finding provides support for the concept that injection of mafic magma coupled with sudden degassing of hydrous minerals in a volatile-rich magma chamber can increase pressure, and thus enhance the possibility of initiating a volcanic eruption.

Equilibrium fractionation factors for A12SiO5 polymorphs were derived using o calibrate new phases for stable isotope thermometry. Samples from a wide variety of metamorphic rock types were used. A12SiO5 polymorphs in mantle xenoliths, amphibolite, granulites, eclogites and blueschists were found to have the same oxygen isotope properties. For a number of samples, the oxygen isotope temperatures are much higher than the regional metamorphic temperatures, which may indicate early, high temperature contact metamorphic effects preserved only in the most refractory phases.

O-isotopic study of annealed porphyroclastic meta-anorthosite helps determine the extent of postpeak-metamorphic and postshearing reequilibration. Peak Grenville granulite facies metamorphism precedes the infiltration of a 18O- and CO2-rich fluid in the Whitestone anorthosite and ductile shearing occurs during and after peak metamorphism. Analysis of delta 18O values of minerals helps determine the isotopic equilibration accompanying fluid infiltration and at different stages of the rock's history. Rapid diffusion of 18O/16O makes the plagioclase porphyroclasts isotopically homogeneous. Whitestone data suggest the presence of a hydrous fluid during cooling.

A study was conducted in Dora Maira Massif, western Alps, to determine temperatures by oxygen isotope thermometry. Accurate data about peak metamorphic pressure, temperature and fluid composition of the whiteschists enables the understanding of the metamorphic processes in the deeper crustal regimes. The intimate and enigmatic connections between the whiteschists and the hosting orthogneiss, the deprivation of the rock's iron content and the enhancement of magnesium content in the whiteschists can be determied from the metasomatism of the orthogneiss protolith by a slab-derived fluid.

In situ, laser microprobe analyses of millimetre-wide quartz veins has revealed the largest delta18-O gradients (90 0/00/mm) yet documented in terrestrial samples. The systematic isotopic variations indicate a crack-seal growth mechanism that variably interleaved 18O-enriched quartzite porphyroclasts with newly precipitated, 18O-depleted vein quartz. The isotopically light quartz requires open-system infiltration of meteoric fluids into the quartzite during its incorporation into the Ruby Gap duplex (central Australia). Documentation of the fluid source in these small veins would not be possible without submillimetre isotopic sampling capabilities. Application of this laser-based technology to other geologic problems should result in similar documentation of large isotopic gradients and provide new insight into fluid-rock interactions.

The oxygen isotope compositions of mineral separates from a ultra-high pressure-temperature coesite-bearing grospydite are measured in order to estimate temperatures of formation. Results show that the oxygen isotope thermometric estimates are the highest measured to date due to the extremely refractory behavior of the grospydite mineral assemblage combined with a rapid cooling from ultra-high temperatures.

The oxygen isotope composition of magnetite grains, hosted in a calcite marble from the Bancroft terrane of the Ontario Grenville province, vary systematically with grain size. The [[delta].sup.18.O] values of magnetite and corresponding closure temperatures ([T.sub.c]) based on [[Delta].sub.calcite-magnetite] range from [[delta].sup.18.O] = [2.6.sup.0/.sub.00], [T.sub.c.] = 505 [degrees] C for a grain radius of 0.075 mm, to [[delta].sup.18.O] = [5.5.sup.0/.sub.00], [T.sub.c] = 660 [degrees] C for a grain radius of 1.15 mm. The [[delta].sup.18.O] of the calcite is constant within a scale of 100 [mu]m at a value of [12.3.sup.0/.sub.00]. The observed isotopic variations can be be fit to be diffusion model of Dodson by the method of least squares (r=0.98) to yield an activation energy (Q) = 211 ([= or -]20) kJ/mole and a pre-exponential factor ([D.sub.o] = 4.3 (+3.3, -1.9) x [10.sup.-7] [cm.sup.2]/s for a cooling rate of 4 [degrees] C/m.y. The activation energy estimate is independent of the assumed cooling rate, but the calculated pre-exponential factor varies as follows: [D.sub.0] ([cm.sup.2/s]) = (dt/dt) x (-1.08 x [10.sup.-7]). (Note: dT/dt is in [degrees] C/m.y.) The activation energy is identical to an experimental determination by Giletti and Hess, but the pre-exponential factor is 100 times lower. The difference is attributed to the water-rich conditions in the experiments and the absence of fluid in the slowly cooled marbles investigated in this study. The strong dependence of diffusion rate on water presence, or [f.sub.H.sub.2.O,] may be used as a sensor for water-rich fluids during cooling in natural systems.

Quartz veins ranging in size from less than 50 cm length and 5 cm width to greater than 10 m in length and 5 m in width are found throughout the Central Swiss Alps where they are either completely filled with milky quartz or contain void-filling quartz crystals. A mechanism of differential pressure and silica diffusion, combined with pressure solution, is proposed for early vein formation.

Research was conducted to examine the synorogenic, mid-crustal hydrogeology of the Helvetic Alps, Switzerland. Based on the results of previous studies, new isotopic data for numerous thrust faults are presented with an emphasis on the basal thrust of the lowest Nappe, the Morcles/Doldenhorn nappe. There is little isotopic evidence to prove that large quantities of fluids passed through most of the carbonate-hosted thrusts in the Helvetic Alps.