2nd International Mars Sample Return 2018 (LPI Contrib. No. 2071) 6047.pdf

CLUES ON PAST CLIMATIC ENVIRONMENTS AND SUBSURFACE FLOW IN MARS FROM AQUEOUS ALTERATION MINERALS FOUND IN NAKHLA AND ALLAN HILLS 84001 METEORITES J.M. Trigo-Rodríguez1,2, C.E. Moyano-Cambero1,2, J.A. Donoso1,2, M.I. Benito-Moreno3, and J. Alonso-Azcárate4. 1Institute of Space Sciences (ICE, CSIC), Campus UAB, c/Can Magrans s/n. 08193 Cerdanyola del Vallés, Barcelo- na, Catalonia, Spain, e-mail: [email protected] 2Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2-4, Ed. Nexus, desp. 201, 08034 Barcelona, Catalonia, Spain, 3Departamento de Estratigrafía-IGEO, Facultad de Cien- cias Geológicas, Universidad Complutense de Madrid-CSIC, José Antonio Nováis, 12, 28040 Madrid, Spain, 4Universidad de Castilla-La Mancha (UCLM) Campus Fábrica de Armas, 45071 Toledo, Spain

Introduction: Until sample-return missions from host rock of ALH 84001, and it was affected by chemi- Mars are achieved, the achondrite meteorites are the cal variations probably associated with atmospheric only Martian rocks available for study in our laborato- changes and volcanic outgassing. ries. Some of them contain evidence of water interac- On the other hand, Nakhla achondrite is dominated tion at different times, and provide valuable infor- by olivine and augite, but also contains metallic inclu- mation about current and ancient environmental condi- sions that often contain magnetite, and iddingsite, two tions on the red planet [1]. Martian meteorites are so products of aqueous alteration. valuable because they have different crystallization Conclusions: Given the well-known geochemical ages and relevant information about their formation processes that formed both meteorites, we can say that regions, although many of them remain unknown [1-2]. they were significantly affected by water. The presence Here we focus in Allan Hills 84001 meteorite (hereaf- of aqueous alteration minerals in Nakhla reveals that it ter ALH 84001) and Nakhla, which can be used for was affected by water during or shortly after its crystal- constraining conditions on early Mars because they lization age. Then, it is evidence for quasi- formed 4 and 1.3 Ga ago, respectively. Due to their contemporaneous presence of water in Mars’ crust. No long exposure to the Martian environment, both mete- surprising given the detection of salty fluids emanating orites recorded processes of interaction with water. In from permafrost-like layers in crater borders [4]. the case of ALH 84001 we concentrate in Fe-Mg-Ca Having into account that the crystallization age of carbonates [2], and in Nakhla in the presence of id- Nakhlites and Chassignites can be rounded to 1.3 Ga, dingsite and magnetite. and that both types of meteorites are somehow related, Instrumental procedure: We have used a comparison with crater count chronology of different SEM+EDX techniques to obtain X-Ray mappings to regions suggested that Nakhlites formed on the large establish the mineralogical composition of the samples volcanic construct of either Tharsis Elysium, or Syrtis and identifying aqueous alteration minerals, particular- Major Planum, being ejected from Mars around 10.75 ly focusing here in the carbonate globules in NASA million years ago by an asteroid impact [5]. The sub- thin section ALH 84001,82 and magnetite in Nakhla. surface of some of these regions could be significantly Quantitative chemical analyses were obtained using a affected by hydrothermal processes. JEOL JXA-8900 electron microprobe equipped with Conclusions: The presence of distinctive aqueous five wavelength-dispersive spectrometers at the UCM. alteration minerals in Mars like e.g. carbonates and Nakhla’s sample is a fresh appearance section with no magnetite, could be of great interest to distinguish wa- evidence of rusting, being currently part of the IEEC- ter sources and identify potential habitats for human exploration and sample-return. Remote-sensing studies CSIC meteorite collection repository. could concentrate in rocks with similar mineralogy to Results: The petrographic features and composi- obtain valuable clues on the long-standing action of tional properties of these two Martian meteorites pro- water on the Martian environment. vide clear evidence for continuous action of water in References: [1] Moyano-Cambero C.E. et al. Martian subsurface. A clear example are the complex carbonates that we have studied in ALH 84001, which (2013) In The Early Evolution of the Atmospheres of are consequence of pervasive action of water. Detailed Terrestrial Planets, J.M. Trigo-Rodríguez, F. Raulin, mineralogical growing patterns indicate that a Mg- and C. Muller and C. Nixon (eds.), Springer, New York, Fe-rich solution saturated the rock, leading to their 165–172, 2013. [2] Moyano-Cambero C.E. et al., precipitation in at least 2 or 3 different episodes [2-4]. (2017) MAPS 52, 1030-1047. [3] Trigo-Rodríguez J. This is supported by the presence of distinct chemical M., et al. (2018) LPS XLIX, Abstract #1448. [4] trends indicating that these carbonates grew in two or Michalski J.R. et al. (2013) Nature Geoscience 6, 133- more stages. In conclusion, about 4 Ga ago carbonate 138 [5] Treiman, A.H (2005) Chemie der Erde- globule formation occurred when a fluid soaked the Geochemistry 65.3, 203–270.