Craddock, R. A.

Helbert, Jörn

Jaumann, Ralf

Maturilli, Alessandro

Platz, Thomas

Spengler, Daniel

Tirsch, Daniela

English

Institute of Transport Research:Publications

Mineralogical Analyses of Basaltic Dune Sands from Ka’u Desert(Hawaii) - Comparison with Martian Dark DunesD. Tirsch (1), R. A. Craddock (2), A. Maturilli (1), T. Platz (3), D. Spengler (4), J. Helbert (1) and R. Jaumann (1,3)(1) Institute of Planetary Research, German Aerospace Center (DLR), Berlin, Germany (2) Center for Earth and PlanetaryStudies, National Air and Space Museum, Smithsonian Institution, Washington D.C. (3) Institute of Geological Sciences, FreeUniversity Berlin, Berlin, Germany (4) Section 1.4 Remote Sensing, Helmholtz Centre Potsdam - GFZ German ResearchCentre for Geosciences, Potsdam, Germany. (daniela.tirsch@dlr.de / Fax: +49-30-67055402)AbstractSamples of tephra collected in Hawaii’s Ka’u Desertare investigated by means of different laboratory meth-ods in order to examine their detailed mineral assem-blages and chemistries. The analyses involve spectral,microscopic, and microporobe investigations. Spectralanalyses reveal similar mineral assemblages as Mar-tian dark dunes pointing to a similar volcanic origin ofthe material.1. IntroductionDark basaltic dunes are the dominant of aeolian bed-forms on Mars. On Earth basaltic dunes occur in thevicinity of volcanic regions such as Hawaii, Iceland,New Zealand, and the western United States [1]. Dueto the correlation of volcanic processes and dune de-velopment, the terrestrial dark dunes are promisingstudy objects as analogue for Martian dark dunes asthe latter are supposed to consist of ancient volcanicashes (e.g. [2]). We want to determine (i) if thedune sands originate from the stripping of Keanakakoitephra or from local reworked tephra emplaced bylarger phreatic eruptions, (ii) the change of grain sizeand composition with transport distance, and (iii) thematerial’s transport mechanisms (i.e. fluvial and/or ae-olian) [3]. The results will be used for an analogy stud-ies between dark dune sands on Mars and Earth whichaims to shed light on the sediment source, transportmechanism, and development of the dune material.2. MethodologyDifferent tephra samples were collected during a fieldtrip to Ka’u Desert in summer 2009. Dune sand sam-ples were collected from 3 different dark dunes in Ka’uDesert: A large, dark vegetated parabolic dune (Fig.1A, sample 6), a falling dune (Fig. 1B, sample 1), anda large dark climbing dune (Fig. 1C, sample 2). Airfallashes (Fig.2) were collected over one year in severalbins placed at different locations downwind of Kilaueacaldera in summer 2008 in order to catch fresh tephraof the small phreatic eruption that started on March 19,2008 (cf. [3]).Figure 1: Comparison of terrestrial (A, B, C) and Martian(D) dark sands. Note different image width and grain sizes.A, B, C: Photographs of the sand samples collected in Ka’uDesert, Hawaii (A=sample 6, B=sample1, C=sample2, cf.Fig. 2, 3, 4, and 9). Grain size ranges between fine- tocoarse-grained sand; image width is about 65 cm. D: Viewof Microscopic Imager (MI) onboard the Mars ExplorationRover "Spirit" of very fine dark sand on Mars; image widthis about 15 mm (image from [4]).Figure 2: Microscopic view of airfall ash samples collectedin sample bins downwind of Kilauea caldera (A,B,C), and adune sand sample collected ~6.2 km from Kilauea caldera(D). Magnification is 20x, field of view 9.3 mm.2.1. Spectral AnalysesReflectance spectra of the airfall tephra and two dunesand samples were acquired at the Planetary Emissiv-ity Laboratory (PEL) [5] of the DLR Institute of Plane-tary Research using a Bruker IFS 88 FTIR spectrome-ter for the VIS/NIR spectral range from 0.4 to 1.2 µm.The near-infrared measurements from 1.2 to 2.5 µmwere obtained by means of a Bruker Vertex 80V FTIRspectrometer. Sample preparation involved the thecomminution of the coarse-grained samples and theEPSC AbstractsVol. 5, EPSC2010-482, 2010European Planetary Science Congress 2010c© Author(s) 2010separation into four different grain size ranges. Thereflectance spectra of further dune sand samples wereacquired from 0.5 to 2.5 µm at the German ResearchCentre for Geosciences by using an Analytical Spec-tral Device (ASD) FieldSpec Pro spectrometer, whichwas installed in a laboratory. Here, we measured thesamples in their original constitution, no special sam-ple preparation has been performed. For each sample,we took average reflection spectra from 0.5 to 2.5 µm,which best reflect the mineralogical composition.2.2. Laboratory AnalysesFor these analyses, the samples have been preparedto thin-sections enabling to investigate the tephra ona grain scale. Microscope analyses will be accom-plished to determine the individual minerals and fora characterization of grain size and shape. We willanalyse how grain size changes with transport dis-tance. The grain shape information will shed light onthe transport mechanisms of the material. We supposemost of the material to be aeolian transported, whichmight be evidenced by a high amount of angular min-eral grains. However, fluvial channels in Ka’u Desertalso indicate the involvement of fluvial processes inthat region. The amount of rounded mineral grains inthe samples will indicate the proportion of this alter-native transport mechanism. The microprobe analysiswill be accomplished in order to determine the exactconcentration of the individual elements of a mineralwith high accuracy. The results will be used to cross-check the interpretation of the spectra and to determinethe initiators of the individual absorption bands.3. Preliminary ResultsSpectral analyses reveal an initial aqueous alterationof the Hawaiian samples, probably related to hydratedamorphous silica (Fig. 3). Water absorptions mightalso be caused by molecular water in the glass frag-ments. The overall spectral shape of all samples indi-cates a mineralogical correlation between Martian andterrestrial dune sands pointing to a similar volcanicorigin of the material.First microscopic analyses revealed a high amountof volcanic glass fragments in the samples, followedby feldspars, olivine and pyroxene. Figure 4 providesan impression of the different proportions of rock frag-ments and glasse shards. For example, sand sam-ple 2 (climbing dune) consists of a high amount ofrock fragments. This may indicate that a considerableamount of this dune sand originates from reworkedlava.Figure 3: Comparison of Terrestrial (ASD) and Martian re-flectance spectra of dark dune sands. Olivine and pyroxeneare represented in all spectra by the 1 and ~2 µm bands.Aqueous alteration is indicated by the 1.9 and 2.2 µm bands.Figure 4: Microscopic view of thin sections of (A) a sam-ple collected from a climbing dune dominated by rock frag-ments, and (B) a dark ripple dominated by volcanic glassfragments. Field of view is about ~3.5 mm.AcknowledgmentsThis research has been supported by NASA’s Mars Funda-mental Research Program, Grant NNX09AC27G (Smithso-nian Institution) and by the Helmholtz Association throughthe research alliance ’Planetary Evolution and Life’.References[1] Edgett, K.S. and N. Lancaster, J. Arid Env., 25, pp. 271-297, 1993.[2] Tirsch, D., PhD thesis, Free University Berlin, Berlin, 2009,http://www.diss.fu-berlin.de/diss/receive/FUDISS_thesis_000000008848.[3] Craddock, R. A., et al., LPSC 2010, #2164.[4] Sullivan, R., et al., JGR, 113, doi: 10.1029/2008JE003101, 2008.[5] Maturilli, A., EPSC 2010, this issue.

EPSC 2010, this issue.

Mineralogical Analyses of Basaltic Dune Sands from Ka’u Desert (Hawaii) - Comparison with Martian Dark Dunes

Mineralogical Analyses of Basaltic Dune Sands from Ka’u Desert (Hawaii) - Comparison with Martian Dark Dunes

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