Large sulfur isotope fractionations in Martian sediments at Gale crater

Variability in the sulfur isotopic composition in sediments can reflect atmospheric, geologic and biological processes. Evidence for ancient fluvio-lacustrine environments at Gale crater on Mars and a lack of efficient crustal recycling mechanisms on the planet suggests a surface environment that was once warm enough to allow the presence of liquid water, at least for discrete periods of time, and implies a greenhouse effect that may have been influenced by sulfur-bearing volcanic gases. Here we report in situ analyses of the sulfur isotopic compositions of SO2 volatilized from ten sediment samples acquired by NASA’s Curiosity rover along a 13 km traverse of Gale crater. We find large variations in sulfur isotopic composition that exceed those measured for Martian meteorites and show both depletion and enrichment in 34S. Measured values of δ34S range from −47 ± 14‰ to 28 ± 7‰, similar to the range typical of terrestrial environments. Although limited geochronological constraints on the stratigraphy traversed by Curiosity are available, we propose that the observed sulfur isotopic signatures at Gale crater can be explained by equilibrium fractionation between sulfate and sulfide in an impact-driven hydrothermal system and atmospheric processing of sulfur-bearing gases during transient warm periods

Three-Dimensional Spatially Constrained Sulfur Isotopes Highlight Processes Controlling Sulfur Cycling in the Near Surface of the Iheya North Hydrothermal System, Okinawa Trough

Abstract Modern seafloor hydrothermal systems are unique environments in which many of the Earth's reservoirs, including the hydrosphere, biosphere, and geosphere, dynamically interact. Analysis of spatially constrained sulfur isotope compositions from fluids and hydrothermal precipitates within the discharge zone of a volcanogenic system can be used to trace the interactions between the various isotopically distinct sulfur reservoirs that result in the formation of hydrothermal massive sulfide deposits. Here we present in situ sulfur isotope results from laterally and vertically constrained euhedral hydrothermal pyrite from the Iheya North hydrothermal system in the Okinawa Trough, which was investigated during the Integrated Ocean Drilling Program Expedition 331. Hydrothermal pyrite at the North Big Chimney yields δ34S values of ~+11.9 ± 1.1‰ (1σ), which are near identical to the δ34S composition of the vent fluid. Outward, ~150 and ~450 m from North Big Chimney, hydrothermal pyrite within drill core yields δ34S equal to +10.9 ± 1.3‰ (1σ) and +7.0 ± 3.8‰ (1σ), respectively, showing a shift in isotopic composition away from the main vent site. This evolution to a lighter and more scattered isotopic signature of hydrothermal pyrite (which is easily identifiable from biogenic pyrite) is interpreted to indicate that the hydrothermal fluid leached sulfides (formed previously by biogenic processes) from the surrounding sedimentary strata. As the most significant metal enrichments (Fe, Zn, Cu, Bi, Tl, and Cd) are associated with samples that contain average hydrothermal pyrite δ34S values similar to δ34S of the vent fluid, we demonstrate that sulfur isotopes can vector toward metals in seafloor massive sulfide deposits

An Archean Biosphere Initiative

The search for life on extrasolar planets will necessarily focus on the imprints of biolgy on the composition of planetary atmospheres. The most notable biological imprint on the modern terrestrial atmosphere is the presence of 21 % O2, However, during most of the past 4 billion years, life and the surface environments on Earth were profoundly different than they are today. It is therefore a major goal of the astrobiology community to ascertain how the O2 content of the atmosphere has varied with time. and to understand the causes of these variations. The NAI and NASA Exobiology program have played critical roles in developing our current understanding of the ancient Earth's atmosphere, supporting diverse observational, analytical, and computational research in geoscience, life science, and related fields. In the present incarnation of the NAI, ongoing work is investigating (i) variations in atmospheric O2 in the Archean to the Cambrian, (ii) characterization of the redox state of the oceans shortly before, during and after the Great Oxidation Event (GOE), and (iii) unraveling the complex connections between environmental oxygenation, global climate, and the evolution of life

Sulfur isotope evolution in sulfide ores from Western Alps: Assessing the influence of subduction-related metamorphism

Sulfides entering subduction zones can play an important role in the release of sulfur and metals to the mantle wedge and contribute to the formation of volcanic arc-associated ores. Fractionation of stable sulfur isotopes recorded by sulfides during metamorphism can provide evidence of fluid-rock interactions during metamorphism and give insights on sulfur mobilization. A detailed microtextural and geochemical study was performed on mineralized samples from two ocean floor-related sulfide deposits (Servette and Beth-Ghinivert) in high-pressure units of the Italian Western Alps, which underwent different metamorphic evolutions. The combination of microtextural investigations with d34S values from in situ ion probe analyses within individual pyrite and chalcopyrite grains allowed evaluation of the effectiveness of metamorphism in modifying the isotopic record and mobilizing sulfur and metals and have insights on fluid circulation within the slab. Textures and isotopic compositions inherited from the protolith are recorded at Beth-Ghinivert, where limited metamorphic recrystallization is attributed to limited interaction with metamorphic fluids. Isotopic modification by metamorphic processes occurred only at the submillimeter scale at Servette, where local interactions with infiltrating hydrothermal fluid are recorded by metamorphic grains. Notwithstanding the differences recorded by the two deposits, neither underwent intensive isotopic reequilibration or records evidence of intense fluid-rock interaction and S mobilization during metamorphism. Therefore, subducted sulfide deposits dominated by pyrite and chalcopyrite are unlikely to release significant quantities of sulfur to the mantle wedge and to arc magmatism sources at metamorphic grades below the lower eclogite facies

Measurement of the Associated γ+μ±\gamma + \mu^\pm Production Cross Section in ppˉp \bar p Collisions at s=1.8\sqrt{s} = 1.8 TeV

We present the first measurement of associated direct photon + muon production in hadronic collisions, from a sample of 1.8 TeV $p \bar p$ collisions recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from the Compton scattering process $cg \to c\gamma$, with the final state charm quark producing a muon. Hence this measurement is sensitive to the charm quark content of the proton. The measured cross section of $29\pm 9 pb^{-1}$ is compared to a leading-order QCD parton shower model as well as a next-to-leading-order QCD calculation.Comment: 12 pages, 4 figures Added more detailed description of muon background estimat

Measurement of the top quark mass and top-antitop production cross section from dilepton events at the Collider Detector at Fermilab

We present an analysis of dilepton events originating from top-antitop production in proton-antiproton collisions at sqrt{s}=1.8 TeV at the Fermilab Tevatron Collider. The sample corresponds to an integrated luminosity of 109+-7 pb^{-1}. We observe 9 candidate events, with an estimated background of 2.4+-0.5 events. We determine the mass of the top quark to be M_top = 161+-17(stat.)+-10(syst.) GeV/c^2. In addition we measure a top-antitop production cross section of 8.2+4.4-3.4 pb (where M_top = 175 GeV/c^2 has been assumed for the acceptance estimate).Comment: 6 pages of text, 3 figure

Search for the Supersymmetric Partner of the Top-Quark in ppˉp \bar{p} Collisions at s=1.8TeV\sqrt{s} = 1.8 {\rm TeV}

We report on a search for the supersymmetric partner of the top quark (stop) produced in $t \bar{t}$ events using $110 {\rm pb}^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.8 {\rm TeV}$ recorded with the Collider Detector at Fermilab. In the case of a light stop squark, the decay of the top quark into stop plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with Standard Model $t \bar{t}$ production and decay. Hence, we set limits on the branching ratio of the top quark decaying into stop plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 {\rm GeV/c}$^{2}$.Comment: 11 pages, 4 figure