Compositional End Members in Gale Crater, Mars

Geochemical data returned from the Mars Science Laboratory’s Curiosity rover over 1296 sols, has revealed a previously unforeseen martian geochemical complexity. Before Curiosity landed in Gale Crater, Martian SNC meteorite studies along with previous orbiter, rover and lander data showed Mars as being a predominantly basaltic planet with little magmatic differentiation. But through using ChemCam density contour plots to collate compositional data obtained by that instrument, we can identify 4 compositional end members in Gale sedimentary and igneous samples

Thermochemical Modelling of Fluid-Rock Reactions in Vera Rubin ridge, Gale Crater, Mars.

Vera Rubin Ridge (VRR) in Gale Crater, Mars, is a ~200 m wide ~6.5 km long northeast- southwest resistant geomorphological feature on the northern slopes of Aeolis Mons (Mt. Sharp). Analysis of Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) orbital data showed that VRR has strong hematite spectral signatures. Hematite was confirmed in-situ at VRR with the Curiosity rover and has been shown to be present throughout the Mur- ray formation. VRR is stratigraphically continu-ous with the underlying Murray formation. Previous thermochemical modelling showed how hematite at VRR could have formed as the result of open-system weathering at high water/rock ratios. Here we use thermochemical modelling to investigate possible reaction pathways for the hematite-clay- bearing assemblage observed at VRR, starting from an identified least-altered (minimum clay content) Murray composition, and a Mars basal brine

Enhanced groundwater flow on and below Vera Rubin ridge, the Murray Formation, Gale Crater: Evidence from thermochemical modeling

NASAs Mars Science Laboratory Curiosity rover has been exploring Vera Rubin ridge (VRR), part of the Murray formation in Gale crater, Mars, between sol 1809 and 2302. Evidence for Fe-oxides and phyllosilicates in mineralogical and geochemical data for this region was returned by Curiosity [1-5]. We applied thermochemical modeling to con-strain the formation conditions of the phyllosilicate-hematite assemblage identified on and below VRR. Average alteration compositions for the Murray formation on and below VRR were derived using CheMin and APXS data. These compositions were reacted with Gale Portage Water (GPW) between 25100 C and for 10% and 50% Fe3+/Fetot of the host rock [6]. Here we summarize models run at 50 C and 10% Fe3+/Fetot for alteration compositions derived from Murray host rock compositions

The Spectrum of the Dirac Operator in the Linear Sigma Model with Quarks

We derive the spectrum of the Dirac operator for the linear sigma-model with quarks in the large N_c approximation using renormalization group flow equations. For small eigenvalues, the Banks-Casher relation and the vanishing linear term are recovered. We calculate the coefficient of the next to leading term and investigate the spectrum beyond the low energy regime.Comment: 15 pages, 6 figures, to appear in Phys. Rev.

Rochechouart 2017-Drilling Campaign: First Results

No abstract available

Igneous Differentiation of the Martian Crust

Our understanding about the differentiation of the Mars crust is increasing rapidly as a result of the combination of 129 distinct SNC meteorites, lander and orbiter data. Recent debates have centred on the existence of alkaline versus tholeiitic and silicic magmatism, crystal fractionation versus partial melting controls on melt composition, and the oxidation state of mantle source regions. Recently we have used MSL ChemCam data to show the presence of trachybasalt float rocks, of tholeiitic affinity, in Gale Crater [1]. Other igneous components recorded in Gale sediments suggest the presence of alkaline and silica oversaturated magmatism as well [2,3,4]. When we compare martian datasets, it is apparent that a key primary melt composition in the ancient highlands is basalt with SiO2 45 wt%, Na2O + K2O 3.5 wt%, and high Fe, low Al. Crystal fractionation from this has led to trachybasalt and possibly in extreme cases to rhyolites [4]. The juxtaposition with some likely alkaline source regions is analogous to intraplate magmatism on Earth. Although one martian meteorite (a regolith breccia) shows clasts of alkaline affinity [5,6], the 112 shergottites are silica saturated. We classify them on the basis of their REE abundances, reflecting mantle source compositions rather than crustal contamination [7]. Bulk compositions indicate that their source regions – probably under Tharsis and the Northern Lowlands - were alkali-poor compared to the Ancient Highlands’ basalts. Limited evidence for crystal fractionation has been identified. Here we present the results of new work comparing shergottites, Gale, MER and terrestrial analogue igneous rocks to determine the key controls on martian magmatism. [1] Edwards P.H. et al. (2017) MAPS. DOI: 10.1111/maps.1295. [2] Bedford C. et al. GCA (in rev.). [3] Treiman et al. (2016) doi: 10.1002/2015JE004932. [4] Morris et al. (2016) doi: 10.1073/pnas.1607098113. [5] Santos A. et al. (2015) doi.org/10.1016/j.gca.2015.02.02. [6] MacArthur J. et al. (2017) MetSoc. #6108. [7] Bridges J.C. and Warren P.H. (2006) doi:10.1144/0016-764904-501

Igneous compositions preserved in Gale crater's geological record

Gale crater’s geological record has two stratigraphic groups deposited in an early Hesperian fluviolacustrine system[1, 2]. The Bradbury Group (sols 1-750) is dominated by fluvial conglomerate and sandstone with lacustrine mudstone in Yellowknife Bay[1,2]. The Mt Sharp Group (Murray formation) is mainly well laminated lacustrine mudstone[2]. We have analysed NASA Curiosity rover ChemCam[3] observation point compositions for targets up to sol 1482 that have hit in situ host rock lacking obvious diagenetic features. ChemCam data are plotted on scatter and density contour plots for their associated stratigraphic units to replicate whole rock composition[4]. Our results show that coarse grained (>1 mm) targets are dominated by trachybasalt[5] and subalkaline basalt[5] igneous endmembers. Sandstone (0.062 – 1 mm) targets indicate a mixture of subalkaline basalt[5], trachybasalt[5] and potassic igneous[6] sources. Finally, mudstone units are dominated by the subalkaline basalt[5] at Yellowknife Bay, and a relatively silica-rich, subalkaline basalt endmember in most of the Murray formation[4], with an even more silica-rich volcanic component at Marias Pass[7]. This demonstrates that Gale crater sediments record a variety of igneous compositions, with subalkaline basalts dominant, but also including lesser amounts of alkaline and silica oversaturated igneous components. References: [1] Grotzinger et al. (2014) doi:10.1126/science.1242777, [2] Grotzinger et al. (2015) doi:10.1126/science.aac7575. [3] Wiens et al. (2012) doi:10.1007/s11214-012-9902-4. [4] Bedford et al. (subm.) GCA. [5] Edwards et al., (2017) MAPS, doi:10.1111/maps.12953. [6] Treiman et al. (2016) doi: 10.1002/2015JE004932. [7] Morris et al. (2016) doi: 10.1073/pnas.1607098113

Noble gases in two shergottites and one nakhlite from Antarctica: Y000027, Y000097, and Y000593

We have investigated secondary influences on the noble gas budget in rim and interior pairs of three Martian meteorites from Antarctica: the lherzolitic shergottites Y000027 and Y000097, and the nakhlite Y000593. Three factors have been found to influence the original Martian noble gas budget: shock metamorphic overprint, cosmic irradiation, and terrestrial weathering. The 3He/4He ratio of the shergottites is between 0.189 and 0.217, which indicates almost complete loss of radiogenic 4He. This is expected from the high shock pressure observed in the shergottite samples. The concentration of 4He in these shergottite samples ranges from 33.8 to 39.4 × 10−8 ccSTP/g. 22Ne in the shergottites is on the order of 14 × 10−9 ccSTP/g. The nakhlite has 800 × 10−8 ccSTP/g 4He and 26 × 10−9 ccSTP/g 22Ne. An indication for solar cosmic ray contribution to the neon budget can be found in the shergottites. As Y000027 and Y000097 are reported to be paired we conclude the cosmic ray exposure (CRE) age T(3+21) of this shergottite to be 4.41 ± 0.54 Ma. For the nakhlite Y000593 T(3+21) is 11.8 ± 0.3 Ma. Heavy noble gas concentrations show large differences between rim and interior samples with the rim samples having 1.3–2.9, 1.7–38, and 1.4–20 times as much 36Ar, 84Kr, and 132Xe, respectively. The enrichment of heavy noble gases in the rim samples indicates severe terrestrial contamination. The relation between 129Xe/132Xe and 84Kr/132Xe in the rim samples shows that the incorporation mechanism caused elemental fractionation of Kr and Xe to the extent that in the Y000027 shergottite samples any Martian signature is completely masked by terrestrial contamination, if the total is taken. Only the 1400 °C steps show clear evidence for Martian atmosphere. The Y000593 nakhlite interior sample, on the other hand, shows low 84Kr/132Xe in relation to 129Xe/132Xe, which is characteristic for fractionated Martian atmosphere observed in nakhlites