Dissolution possibly assisted by the presence of organic material is evident at the glass-gel palagonite interfaces. In the pore layers, varying cation concentrations seem to relate to ion mobility, with Ti cations precipitating in the bottom gel layers, followed by Fe cations and finally Mg2+ in the top smectite layer. In the nakhlites, the composition of the gel layers may have had some dependence on local transport of cations from surrounding host grains which may explain the Fe enrichment at the gel-phyllosilicate Lafayette interface. Some putative organic material has been identified in the nakhlites [8]. cavities at the silicate-gel interfaces where aqueous and OM based fluid may have filled in these locations could also be localities in the meteorites to find organic material. H. G. Changela 1 , C. C. Cockell 2 , C. Bryce 2 and A. J. Brearley 1 1 University of New Mexico, Dept. Earth & Planetary Sciences, Albuquerque, NM87131, USA. 2 UK Centre for Astrobiology, University of Edinburgh, Edinburgh, EH9 3JZ UK. (Email:[email protected]) SEM-TEM Study of Icelandic Palagonite: Application to Hydrated Silicate Gel Interfaces in the Nakhlite Meteorites and Secondary Processes on Mars References:[1] Stronik N. A. & Schmincke H. (2002) Int J. Earth Sci (Geol Rundsch) 91,680–697 [2] Changela and Bridges (2010) MaPs. 45(12), 1847- 1867. [3] Trieman (2005) Chemie der Erde 65 203–270. [4] Ming-Shan Sun (1957) American Mineralogist, 42, 525-533. [5] Cockell et al. (2009) Geomicrobiology J. 26(7) 491-507. [6] Benzerara K. et al. (2007) EPSL 260(1- 2): 187-200. [7] Changela H.G. & Bridges J. C. (2010) 73 rd MetSoc #5300. [8] White L. M et al. (2014) Astrobiology 14(2):170-181. 300 μm Palagonite is a collective term for altered volcanic glass. Rapidly quenched volcanic glasses in a variety of environments ranging from hydrothermal vents, sub marine and sub glacial environments can form palagonite [1]. Palagonite typically contains an assemblage of primary basaltic glass that has been altered into amorphous hydrated silicate ‘gel-palagonite’ and phyllosilicate (usually smectite) [1]. Although the nakhlite martian meteorites and their secondary alteration assemblages may have very different petrogeneses to palagonite, the types of alteration within them, namely the hydrated silicate assemblages (the most abundant form of alteration in the nakhlites), are also found in palagonite. Of particular interest in the nakhlites is the zoned olivine fracture filling material which dominates them - an Fe-Mg-Al hydrated silicate lacking any detectable crystalline structure by electron diffraction and deemed as a gel [2]. A collective term, iddingsite, has been used to describe these olivine based alteration assemblages [3]. As well as ‘iddingsite’ based terrestrial rocks [4], palagonite may also provide insights into the formation mechanisms of the structurally complex, hydrated and perhaps metastable hydrated silicate assemblages in the nakhlites. The interaction of organic material (OM) with these hydrated assemblages by possible biotic and abiotic processes could also be investigated, with palagonite shown to have strong affinities with them on Earth [5,6]. We have been using FIB/SEM-TEM analysis to explore distinctive features in Icelandic palagonite and at silicate-gel interfaces. Pores Basaltic Glass Gel-palagonite 500 μm Alteration Layers 50 μm Glass 0.5 μm Gel Phyl Phyl 0.9 nm Phyl 1 μm Phyl Gel Gel Fe Kα Mg Kα Ti Kα Ti-Rich Fe-Rich Mg-Rich Mg + Fe-Rich Oli Glass Interface Left: TEM of extracted altered pore marked in the BSE image of the pore above (marked a.). DF STEM montage. A 1-2 μm top phyllosilicate (smectite) layer in pore transitions to the gel layers which are Fe rich-Ti rich. Bright bands are rich in the high Z (Fe and Ti) cations. Below the montage is A STEM-EDX map of the region in red dashed rectangle in the montage. SAD of gel and phyllosilicate regions show the difference in structure between them. Dark blebs of carbonaceous material under are arrowed. Right: A phosphate inclusion in the gel-phyllosilicate region (blue rectangle from montage) is margined with carbonaceous material. left: SEM-EDX of the primary glass (blue spectra). STEM- EDX of the layer closest to the glass interface in the pore (region 1) the smectite top layer (region 2) from the STEM DF montage top left. Note the depleted Mg at the interface and the presence of Ti. Also note the higher carbon peak in this texturally more heterogeneous layer than the smooth gel layers. BSE Images of Icelandic Palagonite. Above: Low Mag image showing the generic phases. Bright region is sideromelane - primary glass. Darker material is gel-palagonite. Left: An altered pore lined with the alteration zones in gel- palagonite. Note the inset which shows the layers of alteration that were sectioned through with the FIB in the pores. Left & Below: Extraction across the gel--glass interface attached to the altered pore (marked b.) The interface as shown by TEM below is filled with carbonaceous material which feeds into the gel layer. Note the textural similarity between the heterogeneous, broken down gel layer and the bottom layer of the extracted pores at their glass interface. Gel-glass interface Extracted pore Nakhlites: BF TEM image of olivine fracturevphyllosilica te-gel assemblage in the Lafayette nakhlite [7]. Dark regions in the gel are high Z, Fe rich layers. Similar 2:1 phyllosilicatee(sme ctite) fringes were found in palagonite. The phyllosilicate-gel assemblages differ by containing Fe enriched bands between the gel-phyllosilicate interface rather than a gradual Mg enrichment in the palagonite. 1 2 1 2 3 4 5 6 7 8 0 Energy (eV) SEM-EDX GLASS Bright Field TEM 100 μm 1 μm 15 μm Pore Gel-Palagonite Glass Gel Gel Phyl. Glass Interface 0 1 2 3 4 5 6 7 0 100 200 300 400 Energy (eV) 1 2 Counts (10 3 ) Counts Fe Kα Ti Kα Ca Kα Si Kα Al Kα Mg Kα Na O Kα Fe Kα Ca Kα Ti Kα Si Kα Al Mg C TEM-EDX Gel-Palagonite Layers a. a. b. Glass Gel Pore Na 500 nm b. Gel Glass Carbonaceous Material 1 μm Carbonaceous b. Pt Cap Pt Cap BSE STEM Dark Field Gel Carbon