We report Fe isotopic composition of seven martian meteorites and other terrestrial materials that may be considered Martian analogues

Anand, M.

Blackhurst, R.

Grady, M. M.

Russell, S. S.

English

Open Research Online

Open Research OnlineThe Open University’s repository of research publicationsand other research outputsFe isotopic composition of Martian meteorites andsome terrestrial analoguesConference or Workshop ItemHow to cite:Anand, M.; Russell, S. S.; Blackhurst, R. and Grady, M. M. (2006). Fe isotopic composition of Martianmeteorites and some terrestrial analogues. In: 37th Lunar and Planetary Science Conference, 13-17 Mar 2006,Houston, Texas, USA.For guidance on citations see FAQs.c© [not recorded]Version: [not recorded]Link(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1824.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.ukFE ISOTOPIC COMPOSITION OF MARTIAN METEORITES & SOME TERRESTRIAL ANALOGUES M. Anand1 (M.Anand@open.ac.uk), S.S. Russell2, R. Blackhurst3, M.M. Grady4 1Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK 2Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD, UK 3Department of Earth Science and Engineering, Imperial College, London, SW7 2AZ, UK 4Planetary Science & Space Research Institute, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK  Introduction Recent Spacecraft and Lander missions have rein-forced the earlier suggestions that Mars was once a warmer and wetter place [e.g., 1]. These missions have also highlighted the presence of diverse rock types on the surface of Mars. Martian landscape is increasingly thought to have been shaped by processes similar to those operating on our own Earth. Such developments have highlighted the importance of sample return mis-sions to fully understand the Martian petrologic and hydrologic (biologic?) processes. However, until such return sample missions from Mars take place, one of the ways to look for past evidence of aqueous activity on Mars is through mineral, chemical and isotopic studies of primary and secondary minerals in Martian meteorites. The present study is the continuation of our Fe isotope work to understand the action and effects of water on Mars by using fractionation of iron isotopes, which can be significant during low-temperature altera-tion processes. Methodology and Samples:  The goals of the pro-ject are to study bulk, elemental and isotopic composi-tion of components within Martian meteorites. Iron is an important constituent of the rock-forming minerals that are produced at elevated temperatures experienced during magma genesis. Iron has four stable isotopes (54, 56, 57 and 58) and is also an important constituent of secondary minerals produced by alteration of pri-mary minerals, occurring in clay minerals and carbon-ates. Kinetic, equilibrium and nuclear processes frac-tionate the isotopes, in the same way as is commonly observed for other stable isotopes. Iron isotopes have also been shown to be fractionated by biological proc-esses, and thus have potential in providing bio-signatures in a sample [2].  Previous to this study, a suite of 8 Martian meteorites were analysed for their whole-rock Fe isotope composition using an MC-ICP-MS technique, which indicated limited but distinct fractionation patterns compared to terrestrial and lunar samples [3]. In the present work, we have measured iron isotope compositions of a group of Martian mete-orites to ascertain variation in δ56Fe and δ57Fe. Previ-ously, we reported our first Fe isotope results [4] on six Martian meteorites (Shergotty, Zagami, Los Angeles, Sah Al Uhaymir 005, Nakhla and Chassigny). We have further analyzed 7 more Martian meteorites (Gover-nador Valadares, Lafayette, MIL 03346, Y000593, Y980459, Dar Al Gani (DaG) 476), a range of terres-trial samples including basalts, granites and Antarctic sandstones which may be considered Martian ana-logues. The sample preparation and ion-exchange chromatography methods are same as in [5]. Fe-isotope compositions (δ56Fe and δ57Fe) were measured on a fixed resolution (m/ m = 500) MC-ICP-MS (IsoProbe, GV Instruments, U.K.) with respect to the Fe-isotope standard IRMM-014, using the sample-standard brack-eting method [5]. Correction for 54Cr on 54Fe is made by monitoring the 53Cr signal and applying an on-line mathematical correction at mass 54. Blank subtraction is undertaken off-line. The effect of 40Ar16OH back-ground at mass 57 is reduced by analyzing solutions at approximately 5-10ppm concentration and sample and standard solutions are concentration matched to within 5%. Typical errors are less than 0.1 per mil (2 sigma) in most cases.  Fe-isotope Fractionation: All of the Martian me-teorites analysed so far plot within a restricted range on a 3-isotope plot (diamond symbols in Fig. 1). The Fig-ure 2 shows the spread in the measured δ56Fe and δ57Fe ratios in our samples with 2 sigma error bars. The grey circles in Figure 1 represent Fe isotope data available on various planetary materials that have been compiled from various sources [2-14]. The majority of Martian meteorites display a restricted range in Fe-isotopic composition between -0.01 to 0.04 ‰ for δ56Fe and from -0.02 to 0.07 ‰ for δ57Fe (Table 1, Fig 1), with a mean value only slightly lighter than the average of 9 Proterozoic basalts from Southern India analyzed in this study. However, Martian meteorite, Y 000593, has significantly heavier Fe isotope signature compared to other Martian samples and terrestrial basalts. However, the precision on Fe isotope measurement in this sample is bit poor, making it difficult to reliably assess the cause of its heavier Fe isotopic signature. The two Pre-cambrian granite samples (SiO2 – 69-70% and MgO – 0.9-1.6%) have the heaviest Fe isotope values, similar to those reported by [15]. The two Antarctic sand-stones, MM45 and VH-59 (both are feldspathic sand-stones), analyzed have different Fe isotopic signatures. Fe isotopic composition of MM45 is similar to the mean of Martian meteorite values whereas VH-59 has heavier isotopic values (Table 1, Fig. 2). Furthermore, the Fe-isotope data for all the samples analyzed in this study fall on the mass fractionation line already de-scribed for a range of other solar system samples [2-14] Lunar and Planetary Science XXXVII (2006) 1824.pdf(Fig 1). The mean of δ56Fe and δ57Fe values from the 13 Martian meteorites appear to be slightly lighter than the mean of terrestrial basalts analyzed in our study. However, given the uncertainty of 0.1 per mil on our measurements, it is not possible to conclusively estab-lish the difference between the Martian and terrestrial basalts. References: [1] Squyres et al. (2004), Science, 306, 1698-1703. [2] Beard et al (1999), Science, 285, 1889‐1892. [3] Poitrasson et al., (2004) Earth Planet. Sci. Lett. 223, 253‐266. [4] Anand et al., (2005) LPSC XXXVI, Abs. #1859. [5] Mullane et al. (2003) In: Holland & Tanner  (Eds.) Plasma Source Mass Spec., Royal Soc. Chem. 351‐361.  [6] Mullane et al. (2003) LPSC XXXIV, Abs. #1027. [7] Zhu et al. (2001) Nature 412: 311. [8] Mullane et al. (2004) LPSC XXXV,  Abs.  #1015.  [9]  Mullane  et  al.  (2004)  Met  Soc,  Abs. #5147. [10] Mullane et al. (2004) Met Soc, Abs. #5148. [11] Mul‐lane  et  al.  (2003)  LPSC XXXIV, Abs.  #1027.  [12] Wiesli  et  al. (2003) Earth Planet. Sci. Lett. [13] Zhu et al. (2000) Earth Planet. Sci. Lett. 200, 47‐62.  [14] Beard   et al  (2003) Chem. Geol., 195, 87‐117. [15] Poitrasson et al. (2005) Chem. Geol., 222, 132‐147.   Lunar and Planetary Science XXXVII (2006) 1824.pdf

Fe isotopic composition of Martian meteorites and some terrestrial analogues

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Fe isotopic composition of Martian meteorites and some terrestrial analogues

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