We report on fractionated noble gases in the Martian meterorites - a literature survey and new data

Bart, G. D.

Bridges, J. C.

Bullock, M. A.

Chaves, C.

Crowther, S. A.

Filiberto, J.

Gilmour, J. D.

Herrmann, S.

Hicks, L. J.

Kelley, S. P.

Miller, M. A.

Mohapatra, R.

Moore, J. M.

Ott, U.

Schwenzer, S. P.

Seidel, R.

Smith, H.

Swindle, T. D.

Treiman, A. H.

English

Open Research Online (The Open University)

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsFractionated Martian Atmosphere – the Case of theNakhlites, Revisited with ExperimentsConference or Workshop ItemHow to cite:Schwenzer, S. P.; Ott, U.; Hicks, L. J.; Bridges, J. C.; Filiberto, J.; Bart, G. D.; Swindle, T. D.; Miller, M.A.; Treiman, A. H.; Crowther, S. A.; Gilmour, J. D.; Herrmann, S.; Mohapatra, R.; Seidel, R.; Kelley, S. P.; Bullock,M. A.; Chaves, C.; Smith, H. and Moore, J. M. (2018). Fractionated Martian Atmosphere – the Case of the Nakhlites,Revisited with Experiments. In: 49th Lunar and Planetary Science Conference, 19-23 Mar 2018, The Woodlands,Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: Version of RecordLink(s) to article on publisher’s website:https://www.hou.usra.edu/meetings/lpsc2018/pdf/1561.pdfCopyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukFRACTIONATED MARTIAN ATMOSPHERE – THE CASE OF THE NAKHLITES, REVISITED WITH EXPERIMENTS.  S. P. Schwenzer1,2,3, Ott2,4, U., Hicks5, L. J., Bridges5, J. C., Filiberto6,1, J., Bart7,8, G. D., Swin-dle8, T. D., Miller9, M. A., Treiman3, A. H., Crowther10, S. A., Gilmour10, J. D., Herrmann2, S., Mohapatra2,10, R., Seidel11, R. G. W., Kelley1,12, S. P., Bullock10, M. A., Chavez14, C., Smith14, H., Moore14, J. M. – 1The Open Univer-sity, School of Environment, Earth and Ecosystem Sciences, Walton Hall, Milton Keynes MK7 5AA, UK; Su-sanne.schwenzer@open.ac.uk; 2Max-Planck Institute for Chemistry, 55128 Mainz, Germany, 3Lunar and Planetary Institute, USRA, Houston, TX 77058, USA; 4MTA Atomki, 4026 Debrecen, Hungary; 5University of Leicester, Leicester LE1 7RH, UK; 6Southern Illinois University, Carbondale, US; 7University of Idaho, Moscow, Idaho, USA; 8Lunar and Planetary Laboratory, University of Arizona, Tucson AZ, U.S.A.; 9Southwest Research Institute, San Antonio, USA; 10University of Manchester, Manchester, UK; 11The Open University, School of Physical Sciences, Milton Keynes, UK; 12University of Edinburgh, Endinburgh, UK; 13Southwest Research Institute, Boulder, CO USA; 14NASA Ames Research Center, Moffett Field, CA, USA.  Introduction:  Noble gases in Martian meteorites have three endmembers. First, the Martian atmosphere as measured by Viking [1,2] and found in the sher-gottites [3]. This component, more specifically its match between in situ measurements on Mars and data from the shergottite meteorites, established the link between the SNC meteorites and Mars. The second component, found in Chassigny [4], is considered to be Martian interior. The third component has atmospheric 129Xe/132Xe but lower Kr/Xe elemental ratios than Mar-tian atmosphere (as seen in 84Kr/132Xe on the plot 129Xe/132Xe vs 84Kr/132Xe [4]). For reviews on the com-ponents see [5-7]. The fractionated Martian atmosphere is the subject of this abstract. Formation hypotheses:  There are four ways to explain elemental fractionation of atmospheric noble gases in the nakhlites: a) an internal (possibly crustal) gas reservoir, with its host rocks melted or assimilated into the meteorites’ parent magmas [8]; b) elementally fractionated Martian atmosphere in the rocks’ aqueous alteration minerals [9]; c) fractional adsorption of at-mospheric noble gases onto mineral surfaces [10]; and d) incorporation of an unfractionated ancient Martian atmosphere, which was significantly different from today’s [11]; see also [7, 12]. Terrestrial samples and alteration experiments have demonstrated that ele-mental noble gas fractionation in hot and cold desert environments is the rule rather than the exception [13-15], and that elemental fractionation is replicable in the laboratory environment [16].  Data sets:  In this study of nakhlites we use a lit-erature compilation of existing noble gas data [7,12], PhD thesis [17] and unpublished data from MPI Mainz, unpublished data from LPL [18], unpublished data from University of Manchester [19-21], and data from our experimental study [22-26].  Mainz data.  At MPI, we measured mineral sepa-rates and bulk rock using an MAP215-50 noble gas mass spectrometer. All separates and bulk rocks showed a tendency towards 84Kr/132Xe ratios lower than expected from a mixture of Martian interior and un-fractionated Martian atmosphere. The most fractionat-ed 84Kr/132Xe ratios were observed in olivine and mesostasis (Fig. 1), in which the 1200°C T-step of ‘Nakhla olivine (a)’ shows the highest 129Xe/132Xe (2.4±0.1) and the largest fractionation (84Kr/132Xe = 0.9±0.9) from the unfractionated atmospheric 84Kr/132Xe ratio (of 20.5). The 136Xe/132Xe ratio of this T-step also has Martian atmospheric signatures of 0.373±0.011, indicating that the sample is not contami-nated by terrestrial air (136Xe/132Xe= 0.3294±0.0004).  Tucson data.  Governador Valadares (GV) and Na-khla samples were analyzed in a VG5400. Most sam-ples returned many T-steps with low 129Xe/132Xe, sug-gesting air contamination. 136Xe/132Xe confirmed the assumption that low 129Xe/132Xe data are a good indica-tion for terrestrial air contamination, but also demon-strated that GV gases were not significantly affected by contamination. The highest 129Xe/132Xe ratio of 1.884±0.016 was measured in the 1000°C T-step of GV bulk (Fig. 2). Manchester data. Samples were analyzed on the RELAX mass spectrometer [22,23]. The highest 129Xe/132Xe of 2.282±0.061 was found in mesostasis, accompanied by a Martian atmospheric 129Xe/136Xe. Experimental data.  We tested the fluid hypothesis (b) by experimentally altering minerals analogous to those found in Martian meteorites [24-28]. The exper-imental apparatus was a daisy chain of vessels, with CO2-headspace gas flow containing 2 vol.% Ar, 30 ppm Kr, and 8 ppm Xe.  We calculated a generalized solution to the differential equation for this daisy chain problem and found that the peak concentration of gas exiting the third vessel would be achieved after 50 min, while that exiting the 30th vessel would be realized after 700 min when each vessel is 250 mL and the vol-umetric gas flow is 10 standard cm3/min. This has, however, not been achieved for the reason of limited gas throughput (i.e., excess unfractionated gas mixture) compared to the system size, which in addition to the experimental complexities also shows the difficulties we face when investigating natural systems. However, 1561.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)comparing the elementally fractionated gas signature measured in olivine from the first vessel (84Kr/132Xe=1.77±0.11; 1000 °C T-step) to the head-space gas (84Kr/132Xe=7.9) shows considerable ele-mental fractionation.   Figure 1.  Olivine and mesostasis data measured at MPI Mainz [17] and unpublished data.  Figure 2. Bulk and mineral separate data from Tucson [18]. 136Xe/132Xe0.30 0.32 0.34 0.36129Xe/132Xe1.01.21.41.61.82.02.22.42.6MAChair-S -Esf136Xe/132Xe0.30 0.32 0.34 0.361.01.21.41.61.82.02.22.42.6MACh-S -E airIdd1Idd2MstPx2Px1OL(b)(a)sfMstPx2IDD2IDD1Px1OL Figure 3. Bulk and mineral separate data from Manchester [19-21]. Summary and conclusions: Elemental fractiona-tion occurs in all nakhlites with the highest fractiona-tion factors (α=[(84Kr/132Xe)frac/(84Kr/132Xe)atm]) ob-served in the 1200°C step of Nakhla olivine (MZ data, α = 0.04). Reported here is an α of 0.1 for the 1000 °C step from AZ corresponding to the highest 129Xe/132Xe ratio of this data set; however, we note that the 1400 °C step of GV from AZ has a similarly low α (0.03). For comparison, air noble gases dissolved in terrestrial water are fractionated with α ≈ 0.5 (depending on T and salinity), but much greater fractionation occurs upon incorporation into terrestrial alteration minerals [13-15] and in our experiments (α =0.22).  The wide range of α in Martian, terrestrial, and ex-perimental systems demonstrates that more experi-mental and terrestrial analog data are required to un-derstand the complexity of noble gas incorporation into secondary alteration minerals. Especially important experimental issues to address are the differences be-tween a static and a dynamic flow regime – and the influence of mineral surface changes. The Martian sys-tem has the added complexity that the Kr/Xe ratio at the time of incorporation is not known, thus the exper-imental and terrestrial data are vital to narrow the num-ber of possible hypotheses for the incorporation of fractionated Martian atmosphere into the nakhlites.  References: [1] Owen, T., et al. (1977) JGR, 82: 4635–4639. [2] Conrad, P.G. et al. 2016) EPSL, 454, 1-9. [3] Bogard, D.D., and Johnson, P. (1983) Science 221, 651–654. [4] Ott, U. (1988) GCA 52, 1937–1948. [5] Swindle, T.D. (2002) Rev. Mineral. Geochem. 47, 171-190. [6] Ott, U., et al. (2017) In: Filiberto, J. and Schwenzer, S.P., Volatiles in the Martian Interi-or; Elsevir, May 2018. [7] Schwenzer, S.P. et al. (in prep.) Re-evaluating elementally fractionated Martian atmosphere in the nakhlite Martian meteorites. [8] Gilmour, J.D., et al. (1999) EPSL 166, 139–147. [9] Swindle, T.D., et al. (2000) MAPS 35, 107-116. [10] Gilmour, J.D., et al. (2000) LPSC XXXI, abstr. #1513. [11] Swindle, T.D., et al. (2009) LPSC XL, Abstr. #1660. [12] Schwenzer, S.P. et al. (2016) http://heli-um.crpg.cnrs-nancy.fr/DINGUE-4/abstracts/Schwenzer.pdf. [13] Schwenzer, S.P., et al. (2007) LPSC XXXVIII, Abstr. #1150. [14] Schwen-zer, S.P., et al. (2007) LPSC XXXVIII, Abstr. #1143. [15] Schwenzer, S.P., et al. (2013) MAPS, 48: 929–954. [16] Schwenzer, S.P., et al. (2012) MAPS, 47: 1049–1061. [17] Schwenzer, S.P. (2004) PhD thesis, Univ. Mainz. [18] Bart, G.D., et al. (2001) LPSC XXXII, Abstr. #1363. [19] Mohapatra, R.K., et al. (2005) LPSC XXXVI, abstr. #1757. [20] Mohapatra, R.K., et al. (2004) Second Conference on Early Mars, abstr. #8015. [21] Mohapatra, R.K., et al., (2004) MAPS, 39, A71. [22] Gilmour, J. D. et al. (1994) Rev. scientific instruments, 65, 617-625. [23] Crowther, S. A. (2008) J. Anal. Atomic Spectrom. 23, 938-947. [24] Bullock, M.A., et al. (2015) LPSC XXXXVI, abstr. #1235. [25] Schwenzer, S.P., et al. (2016) 47th LPSC, abstr. #1889. [26] Schwenzer, S.P., et al. (2017) 48th LPSC, abstr. # 1344. [27] Miller, M.A. (2018) this confernece. [28] Bridges, J.C. (2018) this confererence.  Acknowledgement:  We acknowledge funding through NASA MFRP grant Grant NNX14AJ94G.  1561.pdf49th Lunar and Planetary Science Conference 2018 (LPI Contrib. No. 2083)

Fractionated Martian Atmosphere – the Case of the Nakhlites, Revisited with Experiments

Fractionated Martian Atmosphere – the Case of the Nakhlites, Revisited with Experiments

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