Nigel J.F. Blamey

Evidence for methane in Martian meteorites

The putative occurrence of methane in the Martian atmosphere has had a major influence on the exploration of Mars, especially by the implication of active biology. The occurrence has not been borne out by measurements of atmosphere by the MSL rover Curiosity but, as on Earth, methane on Mars is most likely in the subsurface of the crust. Serpentinization of olivine-bearing rocks, to yield hydrogen that may further react with carbon-bearing species, has been widely invoked as a source of methane on Mars, but this possibility has not hitherto been tested. Here we show that some Martian meteorites, representing basic igneous rocks, liberate a methane-rich volatile component on crushing. The occurrence of methane in Martian rock samples adds strong weight to models whereby any life on Mars is/was likely to be resident in a subsurface habitat, where methane could be a source of energy and carbon for microbial activity.

Follow the methane: the search for a deep biosphere, and the case for sampling serpentinites, on Mars

If life occurs elsewhere in the Solar System, there is a strong likelihood that it occurs in a deep biosphere beneath the planetary surface. The evidence for methane in the martian atmosphere has drawn attention to the possible role of serpentinites in fuelling a deep biosphere through the generation of hydrogen and/or methane. Serpentinites represent a good target for the search for biosignatures in a range of reaction products. Isotopic measurements in each of methane, sulphide and carbonate in serpentinites can help determine evidence of biological activity. We show that ancient terrestrial serpentinites retain methane that could be subject to the measurement of carbon and hydrogen isotopes. There is, therefore, potential to sample serpentinites on Mars and test for evidence of life in the deep geological record of Mars.

Paradigm shift in determining Neoproterozoic atmospheric oxygen

ACKNOWLEDGMENTS We thank the Geological Survey of Australia for permission to sample the Empress 1A and Lancer 1 cores, the Natural Sciences and Engineering Research Council of Canada for financial support (grant #7961–15) of U. Brand, and the National Natural Science Foundation of China for support of F. Meng and P. Ni (grants 41473039 and 4151101015). We thank M. Lozon (Brock University) for drafting and constructing the figures. We thank the editor, Brendan Murphy, as well as three reviewers (Steve Kesler, Erik Sperling, and an anonymous reviewer), for improving the manuscript into its final form.

Sampling methane in basalt on Earth and Mars

If confirmed, the extremely low concentrations of methane (CH4) detected in the Martian atmosphere may represent reservoirs and emission processes that would normally be considered negligible on Earth. One such process is the release of ancient volatiles from fluid inclusions and interstitial sites in rocks and minerals during erosion or geothermal activity. Using a highly sensitive rock-crushing and mass-spectrometry technique previously shown to detect CH4 in serpentinites and hydrothermal mineral deposits, we have demonstrated that CH4 and other ancient volatiles can be recovered from basalt, the dominant rocktype on the Martiansurface. Basalt samples fromawide range of ages and geological systems were tested, all of which released CH4 when crushed. Oxidative weathering was associated with lower quantities of CH4. Otherwise, CH4 recoverability showed no relationship with age or geological context. Mineral veins, cross-cutting one locality were found to share the volatile composition of the basalt. In general, the results suggest that CH4-release from ancient basalts could be a significant process on Mars, which could be further investigated by Martian rovers using a similar rock-crushing and mass spectrometry technique in situ. Received 13 April 2012, accepted 1 November 2012, first published online 2 January 2013

Hydrocarbon migration in the Porcupine Basin, offshore Ireland: evidence from fluid inclusion studies

ABSTRACT A petrographic and microthermometric study of fluid inclusions in Jurassic and Cretaceous sandstones from the Porcupine Basin, offshore Ireland was integrated with innovative fluorescence lifetime measurements of hydrocarbon-bearing fluid inclusions to determine the compositions of the fluids associated with diagenesis and post-diagenetic fluid migration and the extent of hydrocarbon and aqueous fluid migration pathways. Petrographic analyses indicate that Jurassic strata were the main fluid migration pathways for hydrocarbon fluids and that hydrocarbon migration occurred relatively late in the diagenetic history of these sandstones. UV fluorescence and fluorescence lifetime measurements have recognized at least two chemically distinct hydrocarbon groups (Types 1a and 1b) with dissimilar lifetime-wavelength (τ-λ) profiles, consistent with at least two petroleum charges derived from different sources. Primary aqueous inclusions in authigenic cements show that cementation in Cretaceous sandstones occurred at relatively shallow levels at low temperatures (<50°C), while inclusions in authigenic cements in Jurassic sandstones were trapped at higher temperatures (70–120°C) and deeper levels. Aqueous fluid inclusions in intergranular trails indicate that post-cementation fluid migration occurred at high temperatures (up to 175°C). These high temperature fluid migrations are interpreted to be associated with plume-related activity during the opening of the North Atlantic.

Detection of reduced carbon in a basalt analogue for martian nakhlite: a signpost to habitat on Mars

C. W. Taylor and J. Still are thanked for skilled technical support. J. Parnell, H.G.M. Edwards, I. Hutchinson and R. Ingley acknowledge the support of the UKSA and the STFC Research Council in the UK ExoMars programme. L. V. Harris and S. McMahon acknowledge STFC studentship funding.

Sampling methane in hydrothermal minerals on Earth and Mars

The source of Martian atmospheric methane is unknown. On Earth, hydrothermal mineral deposits contain ancient methane together with a host of chemical and geological lines of evidence for the mechanism of gas production. Such deposits are therefore potentially attractive sampling sites on Mars. In order to evaluate this potential, hydrothermal calcite veins were sampled across the Caithness region of Scotland and analysed for methane by an incremental-crushing mass spectrometry technique that may be adaptable to Mars rovers. Methane was detected in all samples. Variations in the quantity of methane released were found to relate directly to the geological history of the localities. Calcite particle size was found to affect measurements in a systematic and informative way. Oxidative weathering had no discernable effect on methane recoverability. These results suggest that the technique is sensitive and informative enough to deserve consideration for missions to Mars.

Evidence for Seismogenic Hydrogen Gas, a Potential Microbial Energy Source on Earth and Mars

UNLABELLED The oxidation of molecular hydrogen (H2) is thought to be a major source of metabolic energy for life in the deep subsurface on Earth, and it could likewise support any extant biosphere on Mars, where stable habitable environments are probably limited to the subsurface. Faulting and fracturing may stimulate the supply of H2 from several sources. We report the H2 content of fluids present in terrestrial rocks formed by brittle fracturing on fault planes (pseudotachylites and cataclasites), along with protolith control samples. The fluids are dominated by water and include H2 at abundances sufficient to support hydrogenotrophic microorganisms, with strong H2 enrichments in the pseudotachylites compared to the controls. Weaker and less consistent H2 enrichments are observed in the cataclasites, which represent less intense seismic friction than the pseudotachylites. The enrichments agree quantitatively with previous experimental measurements of frictionally driven H2 formation during rock fracturing. We find that conservative estimates of current martian global seismicity predict episodic H2 generation by Marsquakes in quantities useful to hydrogenotrophs over a range of scales and recurrence times. On both Earth and Mars, secondary release of H2 may also accompany the breakdown of ancient fault rocks, which are particularly abundant in the pervasively fractured martian crust. This study strengthens the case for the astrobiological investigation of ancient martian fracture systems. KEY WORDS Deep biosphere-Faults-Fault rocks-Seismic activity-Hydrogen-Mars. Astrobiology 16, 690-702.

Origin of vein-graphite derived from metamorphic fluids in Moine (Glenfinnan Group) rocks, NW Scotland

Synopsis Proterozoic metasediments at Glen Strathfarrar, Inverness-shire, host a deposit of vein-graphite that is unique within the Moinian stratigraphic sequence. Carbon isotopic analysis, Raman microspectroscopy, fluid inclusion studies and volatile gas analysis were used to constrain the origin of the vein-graphite. Carbon isotopic analysis shows that the carbon is heavier than that expected for sedimentary material (δ13C value of −14.35‰), suggesting that fractionation has taken place since sedimentation. Graphitization of sedimentary carbon in the Glenfinnan Group pelitic gneiss occurred in response to changes in both temperature and pressure arising from a series of regional metamorphic events. Scavenging of carbon by metamorphic fluids generated during amphibolite-grade metamorphism associated with the youngest, possibly Caledonian, event is the most probable source of the vein-graphite at Glen Strathfarrar. Similarities in gas composition with quartz veins occurring in Dalradian rocks show that carbonaceous sedimentary sequences consistently generate fluids rich in CO2 and N2, making volatile gas analysis a valuable tool in determining the history of metamorphic fluids. The occurrence of crystalline graphite in the pelitic gneiss at Glen Strathfarrar makes it highly likely that the carbon-rich fluids have been generated from within the Glenfinnan Group sediments rather than from Lewisian rocks at depth. Despite the assertion that graphite is uncommon in Moine rocks, the high ammonium content of biotite in these metasediments and the consistently high N2 values of fluid inclusions within the siliceous schist and quartz veins suggest that, prior to metamorphism, the sediments contained more organic matter than their present composition suggests. Supplementary material: The results of incremental crush analysis of vein samples from localities within the Moine, Dalradian and Old Red Sandstone are available at http://www.geolsoc.org.uk/SUP18499.

High-resolution signatures of oxygenation and microbiological activity in speleothem fluid inclusions

*nblamey@ees.nmt.edu Citation: