ArticlePDF Available

Abstract and Figures

A large fraction of clay minerals detected on Mars by infrared remote sensing represent materials exhumed from the subsurface by meteor impact, begging the question of whether the infrared features used to detect the clays are affected by shock associated with the impacts. We used X-ray diffraction and infrared and Mössbauer spectroscopy to evaluate the mineralogy of five clay minerals after experimentally shocking them to six shock pressures from ~10 to 40 GPa. The shocked clays exhibit three main relevant shock effects: (1) an overall decrease in infrared spectral contrast in the impact-fragmented materials, (2) oxidation of Fe in ferrous clays, and (3) loss of some spectral structure in relatively well-ordered clays such as kaolinite. Other than the widespread oxidation of ferrous clays, shock metamorphism likely has little effect on the accurate interpretation of clay mineralogy on Mars from remote sensing data. However, we are able to identify rare cases of extreme shock in some Martian clay deposits.
Content may be subject to copyright.
Shock metamorphism of clay minerals
on Mars by meteor impact
Joseph R. Michalski
1
, Timothy D. Glotch
2
, Lonia R. Friedlander
3
, M. Darby Dyar
4
,
David L. Bish
5
, Thomas G. Sharp
6
, and John Carter
7
1
Department of Earth Sciences and Laboratory for Space Research, University of Hong Kong, Pokfulam, Hong Kong,
2
Department of Geosciences, State University of New York at Stony Brook, Stony Brook, New York, USA,
3
Blaustein Institutes
for Desert Research, Ben- Gurion University of the Negev, Beersheba, Israel,
4
Mount Holyoke College, South Hadley,
Massachusetts, USA,
5
Department of Earth and Atmospheric Sciences, University of Indiana, Bloomington, Bloomington,
Indiana, USA,
6
School of Earth and Space Exploration, Arizona State University, Tempe, Arizona,USA,
7
Institut dAstrophysique
Spatiale, Université de Paris, Paris, France
Abstract A large fraction of clay minerals detected on Mars by infrared remote sensing represent
materials exhumed from the subsurface by meteor impact, begging the question of whether the infrared
features used to detect the clays are affected by shock associated with the impacts. We used X-ray diffraction
and infrared and Mössbauer spectroscopy to evaluate the mineralogy of ve clay minerals after
experimentally shocking them to six shock pressures from ~10 to 40 GPa. The shocked clays exhibit three
main relevant shock effects: (1) an overall decrease in infrared spectral contrast in the impact-fragmented
materials, (2) oxidation of Fe in ferrous clays, and (3) loss of some spectral structure in relatively well-ordered
clays such as kaolinite. Other than the widespread oxidation of ferrous clays, shock metamorphism likely has
little effect on the accurate interpretation of clay mineralogy on Mars from remote sensing data. However,
we are able to identify rare cases of extreme shock in some Martian clay deposits.
Plain Language Summary One of the most signicant achievements in planetary sciences in the
last 20 years has been the identication and mapping of Martian surface mineralogy by infrared remote
sensing. Of major interest is the characterization of clay minerals that formed in ancient habitable
environments on Mars >3.5 Ga ago. Because most of these deposits are extremely ancient, they exist within
crustal materials that have experienced numerous meteor impacts and therefore could have been affected
by heat and pressure associated with those events. The paper contains three main points: (1) the main
features that are used to interpret clay mineralogy from infrared data remain intact despite shock
metamorphic effects up to pressures of ~40 GPa, (2) shocked clays display some key features that can be used
to identify effects of shock remotely, and (3) we describe some of the global-scale spectral biases in
interpretation of clays on Mars that are likely to arise from shock effects and we show some concrete
examples of shocked Martian clays in certain cases. We believe that this would be the rst publication of clear
evidence for shocked minerals detected by remote sensing on any planet.
1. Introduction
Over a decade of near-infrared remote sensing exploration of Mars has revealed thousands of deposits of
clay minerals, a large fraction of which occur in materials exhumed from the subsurface by impact craters
[Ehlmann et al., 2011]. Clay minerals detected by near-infrared spectroscopy (λ13μm) occur within
igneous rocks, sedimentary strata, and hydrothermal deposits in the central peaks [Sun and Milliken,
2015], uplifted rims, and ejecta of impact craters [Carter et al., 2013] (Figure 1). Given this context, it
stands to reason that clay minerals exhumed from subsurface environments could be affected by shock
metamorphism associated with meteor impacts [Boslough et al., 1986; Johnson et al., 2002]. While litho-
static pressures in the shallow Martian crust (<50 km) only are <1 GPa, meteor impacts result in large
parts of impacted crust experiencing shock pressures of 1050 GPa, with heterogeneous, local peak
pressures reaching an order of magnitude higher[French, 1998]. The question is whether shock-induced
pressure [Kraus et al., 2013] or temperature effects [Gavin and Chevrier, 2010; Che et al., 2011] would
confound attempts to interpret clay mineralogy [Weldon et al., 1982; Boslough et al., 1986] of Mars from
remote sensing data.
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6562
PUBLICATION
S
Geophysical Research Letters
RESEARCH LETTER
10.1002/2017GL073423
Key Points:
Five clay minerals known to exist on
Mars were experimentally shocked
from 10 to 40 GPa and products were
analyzed with infrared spectroscopy
At 10 GPa, chlorite exhibits
impact-induced oxidation of Fe, and
at 2030 GPa, kaolinite exhibits signs
of structural disorder
Laboratory results are applied to
infrared remote sensing of clays
on Mars
Supporting Information:
Supporting Information S1
Correspondence to:
J. R. Michalski,
jmichal@hku.hk
Citation:
Michalski, J. R., T. D. Glotch,
L. R. Friedlander, M. Darby Dyar,
D. L. Bish, T. G. Sharp, and J. Carter
(2017), Shock metamorphism of clay
minerals on Mars by meteor impact,
Geophys. Res. Lett.,44, 65626569,
doi:10.1002/2017GL073423.
Received 14 MAR 2017
Accepted 19 JUN 2017
Accepted article online 20 JUN 2017
Published online 12 JUL 2017
©2017. The Authors.
This is an open access article under the
terms of the Creative Commons
Attribution-NonCommercial-NoDerivs
License, which permits use and distri-
bution in any medium, provided the
original work is properly cited, the use is
non-commercial and no modications
or adaptations are made.
Not all clay minerals associated with craters were necessarily uplifted/exposed by the impact, and clay miner-
als could be formed by impacts themselves [Tornabene et al., 2013]. Undoubtedly, impact-induced clay for-
mation must have happened on Mars [Marzo et al., 2010]. However, most clay minerals associated with
impact craters occur within units that appear to be uplifted from the subsurface in fractured but intact
clay-bearing terranes [e.g., Michalski and Niles, 2010], rather than postimpact hydrothermally altered rocks
(Figure 1). Impact craters are also the most common type of sedimentary basin on Mars. Therefore, it is impor-
tant to differentiate between rocks exhumed by the impact and rocks that formed later in the basin, many of
which could contain clays and other hydrated phases detectable by infrared remote sensing (Figure 1).
Understanding the mineralogy of clay minerals exhumed by meteor impact on Mars is important for several
reasons. The detailed mineralogy and crystal chemistry of the clays trace the chemical conditions of ancient
aqueous processes within the crust [Ehlmann et al., 2013]. These include diagenetic and metamorphic pro-
cesses relevant to understanding the nature of the planets crust and overall water budget. Also, life could have
formed and been sustained within deep crustal hydrothermal systems [Michalski et al., 2013]. But to truly under-
stand the 3-D composition of the crust and subsurface alteration, as indicated by clay minerals exhumed by
impact, it is important to determine how shock affects those interpretations of clay mineralogy. Some recent
studies have investigated the effects of shock on clay mineralogy at low shock pressures (<20 GPa) [Gavin et al.,
2013] and described some detailed relationships between shock and clay spectroscopy at higher pressures
[Friedlander et al., 2015, 2016]. Here we summarize the results of a series of shock experiments carried out on
clay minerals in the laboratory and relate those results to the spectroscopically observed mineralogy of Mars.
2. Experimental Setup and Analytical Methods
The <2μm size fraction of each of ve well-characterized phyllosilicate samples was separated, dried, and
gently ground with mortar and pestle into loose powder. In an effort to decrease porosity, which can
Figure 1. Clay minerals are found in several different contexts associated with impact craters on Mars. (a) Some contexts
represent preimpact clays that have been exhumed by the impact event (e.g., central peaks, ejecta, and uplifted rims) and
might contain shocked materials. Other contexts include clays deposited postimpact into crater basins. A global map shows
alteration minerals associated with impact craters on Mars. (b) The green stars show all hydrated minerals occurring in
impact craters [Carter et al., 2013], and the white stars show only clay minerals associated with crater central peaks [Sun and
Milliken, 2015]. Both maps include many examples of exhumed clay minerals and some examples of postimpact clays.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6563
result in increased shock melting during experimental impacts, ~150 mg samples of each powder were
pressed at ~70 MPa into disks ~2 mm thick using a hydraulic hand press. Each pellet was loaded into a sample
container precisely milled to t the pellet, minimizing void space. These samples were then shocked experi-
mentally using the at plate accelerator (FPA) at NASAs Johnson Space Center.
At the FPA, stainless steel or fansteel yer plate projectiles were launched horizontally at the secured sample
containers. Lasers mounted in the ight path were used to determine the projectile velocity and mounted
cameras were positioned to characterize projectile tilt (experiments with tilt >3° were rerun). Velocities of
0.8721.349 km/s were converted to pressure using one-dimensional shock-stress relationships [Gault and
Heitowit, 1963].
The experimental setup was designed to produce six runs resulting in six peak shock pressures ofapproximately
10, 20, 25, 30, 35, and 40 GPa for each of ve clay samples; achieved shock pressures differed by up to a few
percent. Recovery was nearly 100% for most runs, although the highest-pressure experiments resulted in some
sample loss because the sample holder was highly deformed. Samples chosen for shock experiments include
ve important phyllosilicates known to exist on Mars from infrared remote sensing: two dioctahedral clay
minerals (kaolinite and nontronite) and three trioctahedral clay minerals (serpentine, chlorite, and saponite).
Of primary interest in this work were the near-infrared reectance (NIR) (λ=13μm) spectra because these
data are directly relevant to measurements of clay minerals made on Mars by orbital remote sensing instru-
ments. In addition to NIR analyses, the unshocked and shocked samples were analyzed by Mössbauer spec-
troscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). We provide a brief summary of
analytical methods here. Additional details are available in Friedlander et al. [2016].
Bidirectional NIR data were collected under a nitrogen-purged environment from λ= 0.352.5 μm with a sam-
pling interval of 1.42 nm at the Center for Planetary Exploration at Stony Brook University. Mössbauer spec-
tra were acquired using a source of ~60 mCi
57
Co in Rh on a WEB Research Co. (now SEE Co.) model WT302
spectrometer (Mount Holyoke College) at 295 K. Spectra were calibrated against an Fe metal foil and tted
using standard methods [Cuadros et al., 2013]. XRD analyses were carried out using a Bruker D8 diffract-
ometer at Indiana University, with Cu Kαradiation and a SolX solid-state point detector. All samples were ana-
lyzed before shock experiments using random-powder cavity mounts, and run products were mounted on
zero-backgroundquartz plates. The clay particles were examined by TEM using a Philips CM200FEG
S/TEM instrument in the LeRoy-Eyring Center for Solid State Science at Arizona State University. Bright eld
images were used to characterize particle size and morphology, and selected area electron diffraction (SAED)
patterns were collected to determine crystallinity and disorder.
3. Effects of Shock on Near-Infrared Spectroscopy of Clay Minerals
The most important result of this work is the demonstration that shock effects generally do not obfuscate
identication or interpretation of clay minerals from NIR spectra even if they are shocked to pressures up
to ~40 GPa. Major absorptions used to identify and characterize clay minerals with NIR remote sensing
remain intact despite shock effects [Gavin et al., 2013], although interesting and important modications
to some of those spectral features occur. The conservation of most NIR spectral features upon exposure to
high shock pressures stands in contrast to the midinfrared spectral characteristics, which, depending on
the species, typically begin to resemble amorphous silicates between 20 and 40 GPa [Friedlander et al., 2016].
Essentially all clay minerals exhibit some similar spectral features related to basic phyllosilicate mineralogy
[Farmer, 1968] (Figure 2). Absorptions located near 1.4 μm result from OH stretching overtones. H
2
O
adsorbed onto surfaces and between layers within the phyllosilicate structure result in infrared absorption
at ~1.9 μm. Metal-OH deformations within the octahedral sheets produce diagnostic absorptions located
from 2.2 to 2.35 μm, where the position of this feature is an important indication of octahedral chemistry.
Absorption at 2.2 μm is indicative of AlOH in kaolinite (the nontronite has a kaolinite contaminant in it).
FeOH in nontronite absorbs at ~2.282.29 μm. MgOH in saponite, serpentine, and chlorite absorbs at approxi-
mately 2.32, 2.33, and 2.34 μm, respectively. Absorptions at 2.352.5 μm are less diagnostic, resulting from
complex combination absorptions in the octahedral and tetrahedral sheets. Lastly, a broad absorption
located between 1 and 2 μm results from electronic crystal eld effects in Fe within Fe
2+
-bearing samples.
This is most pronounced in the chlorite sample, which contains signicant amounts of Fe
2+
.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6564
NIR spectra of shocked clays are affected by both physical and mineralogical changes. Physical changes result
from intense fragmentation of the sample during shock decompression. Such changes are evident in the XRD
analyses, which show peak broadening of the 001, 02 , and 06 peaks in all shocked samples, consistent with
a decrease in crystallite size in the shocked samples relative to the unshocked samples.
Changes in crystallite sizes and physical particle sizes are known to affect NIR spectral shape and contrast.
Here we quantify the effects of impact-induced changes on spectral contrast for the most diagnostic of
the NIR absorptions for clays, the
metal-OH feature located from (λ=)
2.17 to 2.35 μm (see supporting infor-
mation for details). For each mineral,
we created a simple spectral index
dened as
BD ¼1Rλ12ðÞ=Rλ2þRλ3
ðÞ;
where BD is the band depth, R
λ1
is the
reectance at the metal-OH absorp-
tion center, and R
λ2
and R
λ3
are the
continuum reectance values on
either side of the absorption. Using
kaolinite as an example, R
λ1
corre-
sponds to 2.210 μm, R
λ2
corresponds
to 2.127 μm, and R
λ3
corresponds to
2.231 μm. The result of this analysis
shows that the band depth of the
metal-OH feature decreased by an
average of ~40% due to shock
effects for all samples (Figure 3).
However, the effects are more pro-
nounced for dioctahedral clays (aver-
age R
2
= 0.74) than for trioctahedral
clays (average R
2
= 0.40). The band
depth for saponite (trioctahedral) is
essentially unaffected.
Figure 3. Shock metamorphism and fragmentation result in decreased
spectral contrast in the diagnostic metal-OH features used to identify clay
minerals on Mars with NIR data. The effect is more pronounced for diocta-
hedral clays (e.g., kaolinite and nontronite) (dashed lines) than for triocta-
hedral clays (e.g., chlorite, serpentine, and saponite).
Figure 2. NIR spectra are presented for shocked clay minerals, as well as for the corresponding unshocked samples. MOH
corresponds to metal-OH features for each mineral located from 2.2 to 2.35 μm. HOHcorresponds to vibrational over-
tones in adsorbed H
2
O. Fe
2+
corresponds to a spectral slope located from 1 to 2 μm related to electronic transitions in Fe.
OHcorresponds to hydroxyl deformation overtones located near 1.4 μm. GPacorresponds to the shock pressure
calculated for each experimentally altered mineral.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6565
Changes in the spectral slope of
chlorite between λ= 1 and 2 μm sug-
gest that Fe-oxidation is related to
shock, as has been observed in
igneous minerals [McCanta and
Dyar, 2017]. Mössbauer spectroscopy
results relating the amount of oxi-
dized Fe to total Fe show that even
relatively low amounts of shock pres-
sure (1020 GPa) have a profound
effect on Fe oxidation for chlorite
(Figure 4). The trend is nonlinear
and incremental increases in shock
pressure above 20 GPa do not pro-
duce a proportional increase in Fe
oxidation (Figure 4). We interpret this
to result from heterogeneous distri-
bution of peak heating within the
samples likely due to collapse of resi-
dual pore space.
In fact, the TEM data of kaolinite sam-
ples show strong evidence for het-
erogeneous distribution of shocked
Figure 4. The amount of oxidized iron (Fe
3+
) versus total Fe is plotted
against experimental shock pressure for chlorite. Even minor amounts of
shock (10 GPa) dramatically affect oxidation of Fe. The effect is nonlinear at
high shock pressures (>20 GPa). Estimated error bars of ±3% are shown for
Fe
3+
data derived from Mössbauer spectroscopy.
Figure 5. Bright-eld TEM images and inset selected area electron diffraction (SAED) patterns of (a) unshocked kaolinite
and kaolinite shocked to (b) 10, (c) 20, (d) 29, (e) 36, and (f) 40 GPa. These are examples of the most deformed materials
that show a progression from ordered pseudo hexagonal plates (Figure 5a) through nearly amorphous material at 40 GPa.
At 10 GPa (Figure 5b), the crystals show minor deformation and rotational disorder in the SAED pattern. At 20 GPa
(Figure 5c), the plate-like morphology is reduced and the SAED shows a prominent and sharp ring pattern indicative of
rotational disorder. At 29, 36, and 40 GPa, the fragments have lost their plate-like morphology and the SAED patterns show
progressively more diffuse and weakening diffraction intensity.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6566
material. The unshocked kaolinite crystals are relatively coarsely crystalline, with hexagonal plates ~12μmin
diameter and tens of nanometer thickness (Figure 5). Like the unshocked sample, the 10 GPa shock material
was generally composed of large crystals and displays SAED patterns indicative of well-ordered material.
Signicant changes are observed at 20 GPa where the material contains both amorphous domains and rela-
tively undeformed domains. This trend continues up to 25, 30, and 36 GPa, where the proportion of highly
deformed and disordered material steadily increases. The 40 GPa material that is nearly completely amor-
phous, but even in this highly shocked sample, domains of crystalline kaolinite exist (Figure 5).
These progressive shock effects in kaolinite result in discernible changes to NIR spectral structure of the sam-
ples (Figure 2). The NIR spectra of unshocked and low-shock (10 GPa) samples show spectral structure in the
2.172.21 μm region diagnostic of the AlAlOH vibrations in relatively well-ordered kaolinite-group minerals
[Crowley and Vergo, 1988]. With increasing shock, these overlapping features are broadened and merged into
a single spectral absorption centered at ~2.22.21 μm. Similar impact-induced disorder is observed in the loss
of the doublet spectral structure of the OH overtone absorptions located at 1.41 μm in shock pressures
above 20 GPa.
Figure 6. CRISM spectra show evidence for shocked kaolinite on Mars. (a and b) The blue-green colors in the CRISM images
correspond to kaolinite-bearing surfaces. (c) The central peak of Leighton crater (Figure 6a) and ejecta of an unnamed
crater located at 158.9°E, 25.83°S (Figure 6b) show systematic changes in their spectral features that could be related to
shock. Specically, variations in the spectral structure of AlOH overtones at 2.17 and 2.21 μm are consistent with the
observed trends in experimentally shocked kaolinite. Some spectra within the kaolinite unit in Leighton crater show
extreme spectral changes (gray-black lines in Figure 6c). (d) The surface bearing these spectra appears brecciated and
possibly melted in HiRISE data, and therefore, the features observed with CRISM in these surfaces could correspondto melt
or altered melt rocks. CRISM false color images display I/F at 1.08 μm as blue, 1.51 μm as green, and 2.53 μm as red.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6567
Nontronite and chlorite exhibit slightly more complex behavior in the 2.22.35 μm spectral region. Just as in
the pure kaolinite sample, the admixed kaolinite contaminant in the nontronite sample loses its spectral
structure at ~20 GPa [Friedlander et al., 2015], but a strong 2.2 μm AlOH feature persists to high pressures.
Over the same pressure range, the FeOH absorption at 2.28 μm becomes weaker and broader to the point
that it is unrecognizable against the dominant, stronger AlOH absorption prole. Similarly, chlorite contains
two metal-OH absorptions relating to AlMgOH at lower wavelength (~2.26 μm) and FeMgOH at higher wave-
length (2.35 μm). With increasing shock, the 2.35 μm feature is lost, potentially due in part to oxidation of Fe,
which destabilizes MgFeOH bonds in the octahedral sheet. The AlMgOH bonds are less affected, and there-
fore, the 2.26 μm absorption persists to high shock pressures.
4. Detection of Shocked Clays on Mars
Impact-driven fragmentation of the Martian crust would have resulted in the decrease in lithic particle size
and clay crystallite size in ancient, phyllosilicate-bearing materials. Some of the record of ancient Martian
clays is likely, as a result, either spectrally undetectable or spectroscopically similar to amorphous materials
[Friedlander et al., 2016]. However, some particular features of shocked clays allow for remote infrared detec-
tion of shock effects in some cases on Mars.
Spectra from the Compact Reconnaissance Imaging Spectrometer for Mars, of the ejecta of an unnamed cra-
ter located at 158.9°E, 25.83°S, and the uplifted central peak of Leighton crater (57.76°E, 3.16°N) both show
spectral trends consistent with shock metamorphism of kaolinite (Figure 6) (see supporting information for
data processing details). NIR spectra of kaolinite in crater ejecta (Figure 6c) show a decrease in spectral struc-
ture and increasing breadth. Spectra of kaolinite in the central peak of Leighton display systematic changes
to the AlOH spectral structure, as is observed in lab data of shocked kaolinite (Figure 6). Breccia observed
within the kaolinite unit in high-resolution visible images exhibits interesting spectral features that might
represent melted bedrock or altered melted bedrock. While neither of these examples demonstrates the
detection of shocked clays beyond a shadow of a doubt, both show trends consistent with shock processes
in appropriate geologic contexts. Shock effects might be more widespread on Mars, but the effects are more
easily detectable as they pertain to kaolinite, which is why these two examples were chosen.
5. Conclusions
Most of the Martian surface has been modied by impact cratering. Clay minerals that formed on early Mars
at the surface and in the subsurface have been affected by impact processes, potentially including shock
metamorphism. Given the importance of Martian clay mineralogy for understanding ancient climate and
early habitability of the planet [Bibring et al., 2006], the questions of if and how shock processes inuence
our interpretation of the mineralogy of clay minerals on Mars are both interesting and necessary.
Importantly, our results show that most of the essential aspects of clay mineral identication by infrared
remote sensing of Mars are not obfuscated by shock effects. This result is important not only for remote sen-
sing of Mars but also for other impacted bodies with clay minerals such as asteroids and Ceres [Ammannito
et al., 2016].
Effects of shock up to 40 GPa do not dominate the NIR spectral features of clay minerals, but some effects are
useful, interesting, and important for Mars. On a global scale, impact fragmentation has reduced the spectral
contrast of impacted clays, and therefore, it is important to recognize that the current assessment of clay dis-
tribution and abundance on Mars is an underestimate. Second, impact-induced shock could affect the detec-
tion of Fe
2+
-rich clays and our analysis of the oxidation state under which early clays formed on Mars.
Therefore, it is likely that our interpretation clay mineralogy in the ancient, heavily impacted Martian crust
is biased against ferrous clays, which might have been abundant on early Mars.
References
Ammannito, E., et al. (2016), Distribution of phyllosilicates on the surface of Ceres, Science,353(6303), aaf4279.
Bibring, J. P., et al. (2006), Global mineralogical and aqueous Mars history derived from OMEGA/Mars Express data, Science,312(5772),
400404, doi:10.1126/science.1122659.
Boslough, M. B., E. L. Venturini, B. Morosin, R. A. Graham, and D. L. Williamson (1986), Physical properties of shocked and thermally altered
nontronite: Implications for the Martian surface, J. Geophys. Res.,91(B13), E207E214, doi:10.1029/JB091iB13p0E207.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6568
Acknowledgments
HiRISE and CRISM spectral data used in
this work are available through the
Planetary Data System (https://pds.nasa.
gov). Near-infrared spectra of shocked
clays will be made available through the
following URL in the event of
publication: http://www.clays.space.
Carter, J., F. Poulet, J. P. Bibring, N. Mangold, and S. Murchie (2013), Hydrous minerals on Mars as seen by the CRISM and OMEGA imaging
spectrometers: Updated global view, J. Geophys. Res. Planets,118, 831858, doi:10.1029/2012JE004145.
Che, C., T. D. Glotch, D. L. Bish, J. R. Michalski, and W. Xu (2011), Spectroscopic study of the dehydration and/or dehydroxylation of phyllo-
silicate and zeolite minerals, J. Geophys. Res.,116, E05007, doi:10.1029/2010JE003740.
Crowley, J. K., and N. Vergo (1988), Near-infrared reectance spectra of mixtures of kaolin-group minerals: Use in clay mineral studies, Clays
Clay Miner.,36(4), 310316, doi:10.1346/CCMN.1988.0360404.
Cuadros, J., J. R. Michalski, V. Dekov, J. Bishop, S. Fiore, and M. D. Dyar (2013), Crystal-chemistry of interstratied Mg/Fe-clay minerals from
seaoor hydrothermal sites, Chem. Geol.,360361, 142158, doi:10.1016/j.chemgeo.2013.10.016.
Ehlmann, B. L., J. F. Mustard, R. N. Clark, G. A. Swayze, and S. L. Murchie (2011), Evidence for low-grade metamorphism, hydrothermal
alteration, and diagenesis on Mars from phyllosilicate mineral assemblages, Clays Clay Miner.,59(4), 359377, doi:10.1346/
CCMN.2011.0590402.
Ehlmann, B. L., G. Berger, N. Mangold, J. R. Michalski, D. C. Catling, S. W. Ruff, E. Chasseere, P. B. Niles, V. Chevrier, and F. Poulet (2013),
Geochemical consequences of widespread clay mineral formation in Marsancient crust, Space Sci. Rev.,174(14), 329364, doi: 10.1007/
S11214-012-9930-0.
Farmer, V. C. (1968), Infrared spectroscopy in clay mineral studies, Clay Miner.,7(4), 373387, doi:10.1180/claymin.1968.007.4.01.
French, B. M. (1998), Traces of Catastrophe: A Handbook of Shock-Metamorphic Effects in Terrestrial Meteorite Impact Structures, 120 pp., Lunar
and Planetary Institute, Houston, Tex.
Friedlander, L. R., T. D. Glotch, D. L. Bish, M. D. Dyar, T. G. Sharp, E. C. Sklute, and J. R. Michalski (2015), Structural and spectroscopic changes to
natural nontronite induced by experimental impacts between 10 and 40 GPa, J. Geophys. Res. Planets,120, 888912, doi:10.1002/
2014JE004638.
Friedlander, L. R., T. D. Glotch, B. L. Phillips, J. S. Vaughn, and J. R. Michalski (2016), Examining structural and related spectral change in Mars-
relevant phyllosilicates after experimental impacts between 1040 GPa, Clays Clay Miner.,64(3), 189209.
Gault, D. E., and E. D. Heitowit (1963), The partition of en ergy for hypervelocity impact craters formed in rock, Proc. Sixth Hypervelocity Impact
Symp.,37, doi:10.1190/1.1437716.
Gavin, P., and V. Chevrier (2010), Thermal alteration of nontronite and montmorillonite: Implications for the Martian surface, Icarus,208(2),
721734, doi:10.1016/j.icarus.2010.02.027.
Gavin, P., V. Chevrier, K. Ninagawa, A. Gucsik, and S. Hasegawa (2013), Experimental investigation into the effects of meteoritic impacts on
the spectral properties of phyllosilicates on Mars, J. Geophys. Res. Planets,118,6580, doi:10.1029/2012JE004185.
Johnson, J. R., F. Hörz, P. G. Lucey, and P. R. Christensen (2002), Thermal infrared spectroscopy of experimentally shocked anorthosite and
pyroxenite: Implications for remote sensing of Mars, J. Geophys. Res.,107(E10), 314, doi:10.1029/2001JE001517.
Kraus, R. G., S. T. Stewart, M. G. Newman, R. E. Milliken, and N. J. Tosca (2013), Uncertainties in the sho ck devolatilization of hydrated minerals:
A nontronite case study, J. Geophys. Res. Planets,118, 21372145, doi:10.1002/jgre.20147.
Marzo, G. A., A. F. Davila, L. L. Tornabene, J. M. Dohm, A. G. Fairen, C. Gross, T. Kneissl, J. L. Bishop, T. L. Roush, and C. P. Mckay (2010), Evidence
for Hesperian impact-induced hydrothermalism on Mars, Icarus,208(2), 667683, doi:10.1016/j.icarus.2010.03.013.
McCanta, M. C., and M. D. Dyar (2017), Impact-related thermal effects on the redox state of Ca-pyroxene, Meteorit. Planet. Sci.,52(2), 320332,
doi:10.1111/maps.12793.
Michalski, J. R., and P. B. Niles (2010), Deep crustal carbonate rocks exposed by meteor impact on Mars, Nat. Geosci.,3(11), 751755,
doi:10.1038/ngeo971.
Michalski, J. R., J. Cuadros, P. B. Niles, J. Parnell, A. D. Rogers, and S. P. Wright (2013), Groundwater activity on Mars and implications for a deep
biosphere, Nat. Geosci.,6(2), 133138, doi:10.1038/Ngeo1706.
Sun, V. Z., and R. E. Milliken (2015), Ancient and recent clay formation on Mars as revealed from a global survey of hydrous minerals in crater
central peaks, J. Geophys. Res. Planets,120, 22932332, doi:10.1002/2015JE004918.
Tornabene, L. L., G. R. Osinski, A. S. McEwen, J. J. Wray, M. A. Craig, H. M. Sapers, and P. R. Christensen (2013), An impact origin for hydrated
silicates on Mars: A synthesis, J. Geophys. Res. Planets,118, 9941012, doi:10.1002/jgre.20082.
Weldon, R. J., W. M. Thomas, M. B. Boslough, and T. J. Ahrens (1982), Shock-induced color changes in nontronite: Implications for the Martian
nes, J. Geophys. Res.,87(B12), 10,10210,114, doi:10.1029/JB087iB12p10102.
Geophysical Research Letters 10.1002/2017GL073423
MICHALSKI ET AL. SHOCKED CLAYS ON MARS 6569
... We focused on exposing nontronite to Mars-like surface conditions of atmospheric pressure and composition, and progressively heated the samples to temperatures up to 300 • C. This complements several previous studies which were conducted under different conditions and/or over different temperature intervals or periods of heating (e.g., Boslough et al., 1980;Weldon et al., 1982;Cloutis et al., 2007;Gavin and Chevrier, 2010;Morris et al., 2010;Che and Glotch, 2012;Gavin et al., 2013;Friedlander et al., 2015;Michalski et al., 2017). We also spectrally characterized a suite of 5 nontronite samples to assess any spectral variability of natural samples and assessed whether grain size variations can mimic spectral variations associated with low-pressure CO 2 environments and heating. ...
... Friedlander et al. (2015) found that dioctahedral smectites were more susceptible to structural deformation than trioctahedral smectites, likely due to the site vacancies in the former. Michalski et al. (2017) also conducted shock experiments on finegrained (<2 nm) nontronite powders pressed into pellets. The shock experiments were conducted in air, with pressures between 10 and 40 GPa (Table 5). ...
... It is difficult to directly compare the results of the impact experiments to the heating experiments, as the shock experiments result in a range of temperatures (e.g., Gavin et al., 2013), and temperature estimates are not provided in the other cited studies (Friedlander et al., 2015;Michalski et al., 2017). Nevertheless, the major spectral differences relate to the preservation of 1400 and 1900 nm bands in the shock experiments over a wide range of shock pressures. ...
... In clays, impact-altered features occur from deformation of the Si-O fundamental bending and stretching vibrations of the tetrahedral sheet, seen in the MIR, and from octahedral sheet vibrations, seen in the VNIR (Gavin et al. 2011;Michalski et al. 2017;Friedlander et al. 2015). Illustrations of these features for nontronite are provided in Fig. 4 at NIR and MIR wavelengths. ...
... Impact-induced structural disorder in the octahedral and tetrahedral sheets of smectites produces noticeable spectral changes in the MIR and the VNIR in the Fig. 4 Examples of IR spectral changes in nontronite with increasing shock pressure, between ~ 20 and 40 GPa, after undergoing experimental shock, at a NIR and b MIR ranges. a NIR reflectance spectra of nontronite are shown at the pressures indicated in GPa (Michalski et al. 2017). OH corresponds to hydroxyl deformation overtones located near 1.4 μm, HOH corresponds to vibrational overtones in adsorbed H 2 O, and Fe-OH features for nontronite are located at ~ 2.28-2.29 μm (Michalski et al. 2017). ...
... a NIR reflectance spectra of nontronite are shown at the pressures indicated in GPa (Michalski et al. 2017). OH corresponds to hydroxyl deformation overtones located near 1.4 μm, HOH corresponds to vibrational overtones in adsorbed H 2 O, and Fe-OH features for nontronite are located at ~ 2.28-2.29 μm (Michalski et al. 2017). b MIR emissivity spectra of nontronite are shown at the pressures indicated in GPa (Friedlander et al. 2015). ...
Article
Full-text available
The Perseverance rover (Mars 2020) mission, the first step in NASA’s Mars Sample Return (MSR) program, will select samples for caching based on their potential to improve understanding Mars’ astrobiological, geological, geochemical, and climatic evolution. Geochronologic analyses will be among the key measurements planned for returned samples. Assessing a sample’s shock history will be critical because shock metamorphism could influence apparent sample age. Shock effects in one Mars-relevant mineral class, plagioclase feldspar, have been well-documented using various spectroscopy techniques (thermal infrared reflectance, emission, and transmission spectroscopy, Raman, and luminescence). A subset of these data will be obtained with the SuperCam and SHERLOC (Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals) instruments onboard Perseverance to inform caching decisions for MSR. Here, we review shock indicators in plagioclase feldspar as revealed in Raman, luminescence, and IR spectroscopy lab data, with an emphasis on Raman spectroscopy. We consider how this information may inform caching decisions for selecting optimal samples for geochronology measurements. We then identify challenges and make recommendations for both in situ measurements performed with SuperCam and SHERLOC and for supporting lab studies to enhance the success of geochronologic analyses after return to Earth.
... A key question is what structural changes does kaolinite undergo to facilitate such intercalation at high pressures? So far only a few studies examined the structural changes of kaolinite and its structural polytypes at high pressures (Johnston et al., 2002;Dera et al., 2003;Welch and Crichton, 2010;Welch et al., 2012;Hwang et al., 2017;Michalski et al., 2017;Basu and Mookherjee, 2021;Hong et al., 2022). The high-pressure studies based on X-ray diffraction have proposed polytypic transformations (Dera et al., 2003;Welch and Crichton, 2010). ...
Article
Kaolinite is formed by weathering of continental crustal rocks and is also found in marine sediments in the tropical region. Kaolinite and other layered hydrous silicate minerals are likely to play a vital role in transporting water into the Earth's interior via subducting slabs. Recent studies have experimentally documented the expansion of the interlayer region by intercalation of water molecules at high pressures i.e., pressure-induced hydration. This is counter-intuitive since the interlayer region in the layered silicates is quite compressible, so it is important to understand the underlying mechanism that causes intercalation and expansion of the interlayer region. To address this, we explore the high-pressure behavior of natural kaolinite from Keokuk, Iowa. This sample is free of anatase impurities and thus helps to examine both low-energy (0–1200 cm−1) and high-energy hydroxyl (3000–4000 cm−1) regions using Raman spectroscopy and synchrotron-based powder X-ray diffraction. Our results show that the pressure dependence of the hydroxyl modes exhibits discontinuities at ∼3 GPa and ∼ 6.5 GPa. This is related to the polytypic transformation of Kaolinite from K-1 to K-II and K-II to K-III phase. Several low-energy Raman modes' pressure dependence also exhibits similar discontinuous behavior. The synchrotron-based powder X-ray diffraction results also indicate discontinuous behavior in the pressure dependence of the unit-cell volume and lattice parameters. The analysis of the bulk and the linear compressibility reveals that kaolinite is extremely anisotropic and is likely to aid its geophysical detectability in subduction zone settings. The K-I to K-II polytypic transition is marked by the snapping of hydrogen bonds, thus at conditions relevant to the Earth's interior, water molecules intercalate in the interlayer region and stabilize the crystal structure and help form the super-hydrated kaolinite which can transport significantly more water into the Earth's interior.
... An intriguing finding is that many clay minerals in martian sediments are relatively unaffected by the thermal shock of impacts. Only in the most altered zones, at P > 40 GPa and T > 600°C, do clay minerals display partial dehydroxylation and oxidation of Fe 2+ to Fe 3+ Michalski, Glotch, et al., 2017). Amphiboles, by contrast, may display significant shock dehydroxylation (Giesting et al., 2015). ...
Article
Full-text available
A systematic survey of 161 known and postulated minerals originating on Mars points to 20 different mineral‐forming processes (paragenetic modes), which are a subset of formation modes observed on Earth. The earliest martian minerals, as on Earth, were primary phases from mafic igneous rocks and their ultramafic cumulates. Subsequent primary igneous minerals were associated with products of limited fractional crystallization, including alkaline and quartz‐normative lithologies. Significant mineral diversification occurred via precipitation of primary phases from aqueous and atmospheric fluids, including authigenesis, hydrothermal and cryogenic precipitation, and evaporites, including freeze drying during eras of low atmospheric pressures. In particular, hydrothermal mineral formation associated with both volcanic fluids and sustained hydrothermal activity in impact fracture zones may have triggered significant mineral diversification, though as yet undocumented. At least 65 such primary minerals have been identified by flown missions to Mars and from martian meteorites. A host of secondary martian minerals were produced by near‐surface processes related to water/rock interactions, including hydration/dehydration, oxidation/reduction, serpentinization, metasomatism, and a variety of diagenetic alterations. Additional mineral diversity resulted from metamorphic events, including thermal and shock metamorphism, lightning, and bolide impacts. However, several dominant sources of mineral diversity on Earth, including (a) extensive fluid/rock interactions and element concentration associated with plate tectonics; (b) high‐pressure regional metamorphism associated with plate tectonics; and (c) biologically mediated mineralization—are not known to be in play on Mars. Consequently, we estimate the total mineral diversity of Mars to be an order of magnitude smaller than on Earth.
... In addition, impact-induced shock could affect the detection of Fe(II)-rich clays that might have been abundant on early Mars (Friedlander et al., 2016). However, Michalski et al. (2017b) found that, although shocked clays exhibit an overall decrease in infrared spectral contrast, oxidation of Fe in ferrous clays and loss of some spectral features in well-ordered clays such as kaolinite, most of the essential aspects of clay mineral identification by infrared remote sensing are not obfuscated by shock effects even if they are shocked to pressures up to ~40 GPa. Besides high pressure, impacts also bring high temperature, which may result in the dehydration and/or dehydroxylation of clay minerals. ...
Article
Clay minerals, or analogously phyllosilicates, are some of the most astonishing minerals ever discovered on Mars due to their roles as indicators of water-rock interaction. Their types, abundances, and locations provide hints to ancient environmental conditions of Mars and to the possible places where present-day mineral-bound water and/or biosignatures are likely to be detected. In this contribution, the definition, structures, and hydrated states, the global distribution and formation mechanisms, the significance of occurrence, and the developing detection techniques of clay minerals on Mars are summarized and discussed. The definition and structure-based classification of martian clay minerals build upon their Earth analogues; some martian clay minerals contain less water in their structure and thus exhibit smaller interlayer spacings. Clay minerals on Mars have been widely detected in ancient terrains of Noachian and Early Hesperian age (>3.5 Ga) across the planet. They have been formed mainly by chemical weathering, sedimentation, and hydrothermal alteration, at the surface or in the subsurface. Many techniques, including telescopic observations from Earth, remote sensing from Mars orbiters, in-situ characterizations by Mars landers/rovers, and lab studies of martian meteorites and terrestrial analogues and geochemical modeling, have been developed to detect, identify and further understand clay minerals on Mars. Among these techniques, visible and near-infrared reflectance spectroscopy onboard orbiters is the most powerful at global or regional scales while in-situ X-ray diffraction is the most definitive at a much smaller scale. The occurrence of clay minerals on Mars provides evidence for the presence of liquid water, the evolving geological alterations under varied environments and climates, and the potential habitability. Clay minerals on their own can serve as water sources for rocket fuel, human exploration, and immigration. Although many revolutionary advances have been made on martian clay minerals, many intriguing questions remain, including but not limited to the precise identification and quantification of clay minerals, the effects of impact on the detection of clay minerals, the formation and preservation of short-range ordered clay minerals, the co-occurrence of clay minerals and other secondary minerals, and the detection of clay minerals beyond Earth and Mars.
... Shock processes can result in numerous types of changes to impacted phases ranging from deformation to melting. Shock metamorphism can also cause oxidation or reduction of multivalent elements like Fe and S within target materials depending on the bulk composition of the system, the physicochemical conditions of metamorphism, and the time over which those conditions persist (e.g., Bauer, 1979;Michalski et al., 2017;Rao et al., 2021;Taylor et al., 2004). ...
Article
Full-text available
Apatite can incorporate sulfur in its reduced form (S²⁻) when apatite equilibrates with a silicate melt under reducing conditions. Incorporation of sulfate (S⁶⁺) has been observed in terrestrial apatite under oxidizing conditions. Thus, it has been suggested that the proportions of S⁶⁺/S²⁻ in apatite may record the oxygen fugacity (fO2) during the formation and/or equilibration of apatite grains with a silicate melt in a wide variety of igneous and metamorphic rocks, including from Earth, Mars, the Moon, and in materials from the asteroid belt. Martian rocks, which record fO2 values intermediate between those recorded by rocks from the Moon and Earth, may have apatite that contains only S²⁻ or mixtures of S⁶⁺ and S²⁻. Here, we present new measurements of the oxidation state of sulfur in apatite grains in the basaltic shergottite, Shergotty, which exhibits spectral features consistent with the presence of sulfide (S²⁻) structurally bound in apatite, and no evidence for the presence of sulfite (S⁴⁺) or sulfate (S⁶⁺). The presence of sulfide‐only apatite in Shergotty is consistent with other mineralogical records of fO2 in this meteorite, which are calculated from other late‐stage crystallizing phases like Fe‐Ti oxides as well as from early crystallizing phases like clinopyroxene (DEuCpx/melt) of ΔIW + 1.9 to ΔIW + 3.5. At these fO2 values, S is present in silicate melts as only S²⁻, and this suggests that the oxidation state of sulfur records and preserves the fO2 during the igneous crystallization of apatite reinforcing the idea that sulfur in apatite can be used as an igneous oxybarometer.
... Accordingly, impact related alteration of rocks and minerals plays a role on Mars (Newsom, 1980;Allen et al., 1982;Hellevang et al., 2013). A few recent studies focus on the influence of impact processes and shock metamorphism in relation to the post-impact formation of hydrated materials Cannon and Mustard, 2015;Michalski et al., 2017). The relationship may be two-fold, water-bearing minerals are most susceptible for damage as result of shock metamorphism (e.g. ...
Article
Full-text available
The Planetary Terrestrial Analogues Library (PTAL) is a dedicated lithological collection that currently consists of 102 terrestrial rock samples selected to be possible Mars analogues. The ultimate goal is improving future remote mineralogical and petrological analysis on Mars and other planetary bodies based on selected analysis such as Near- Infrared Reflectance Spectroscopy (NIR), Raman spectroscopy, Laser Induced Breakdown Spectroscopy (LIBS) and X-ray diffraction (XRD). Most international standards applied in the remote martian mineralogical and petrological analysis have so far been based on single, pure mineral analysis, with minimal interferences from other naturally occurring minerals. Here we present detailed lithological sample evaluations based on field appearance along with optical and XRD analysis of key terrestrial rock types. The detailed mineralogical and petrological descriptions give good basis for more complete lithological understanding. In combination with NIR, LIBS and Raman analysis of the very same samples PTAL aims at improving mineralogical and petrographical information from future rovers on Mars e.g. NASA's Mars2020-Perseverance and ESA and Roscosmos's ExoMars - Rosalind Franklin. The PTAL sample collection covers exclusively collected volcanic, magmatic and various sedimentary rocks and regoliths from well-known locations all over the world. These samples have a general composition comparable to what is currently known from Mars. The strength of this sample collection is its origin as common whole rock samples, in which minerals occur in their natural settings. It thereby allows studying possible detection interferences and a comparison of the sensitivity of the different techniques. The collection, in addition, forms the base for various alteration studies to better understand and explain alteration and weathering conditions on Mars. The complete results and sample preparations will be available to all scientists interested.
Article
Full-text available
The NASA Perseverance rover discovered light-toned float rocks scattered across the surface of Jezero crater that are particularly rich in alumina ( ~ 35 wt% Al2O3) and depleted in other major elements (except silica). These unique float rocks have heterogeneous mineralogy ranging from kaolinite/halloysite-bearing in hydrated samples, to spinel-bearing in dehydrated samples also containing a dehydrated Al-rich phase. Here we describe SuperCam and Mastcam-Z observations of the float rocks, including the first in situ identification of kaolinite or halloysite on another planet, and dehydrated phases including spinel and apparent partially dehydroxylated kaolinite. The presence of spinel in these samples is likely detrital in origin, surviving kaolinitization, pointing to an ultramafic origin. However, the association of low hydration with increased Al2O3 abundances suggests heating-induced dehydration which could have occurred during the lithification or impact excavation of these rocks. Given the orbital context of kaolinite-bearing megabreccia in the Jezero crater rim, we propose an origin for these rocks involving intense aqueous alteration of the parent material, followed by dehydration/lithification potentially through impact processes, and dispersion into Jezero crater through flood or impact-related processes.
Article
Clay minerals are widespread in the Martian crust. Over the last few decades, accumulating data and research into the type, crystallinity, quantity, and distribution of Martian clay minerals (MCMs) has remarkably advanced the understanding of Martian geology, paleoclimate, environment, and the question of whether water, organic matter, and life exist there. Meanwhile, some issues remain enigmatic and arguable. To date, mineralogical data from orbiters and rovers have provided information regarding the distribution, composition, age, and geological evolution of MCMs. Several models for interpreting the formation of MCMs, including weathering, hydrothermal alteration, magmatic precipitation, and diagenesis, have been proposed. Nevertheless, the exact formation mechanism of MCM, remains unclear, primarily because of the lack of sufficient information on the chemical reactions and element cycles involved in the formation of clay minerals. Examination on the type, crystallinity, quantity, and distribution of MCMs indicates that Mars possibly had a warm and wet climate during the Noachian period. Since clay minerals possess abundant -OH groups in the layered structure and can host H2O in the interlayer space, MCMs are thought to be potentially large water reservoirs. Studies of MCMs and their interaction with organic matter are possibly conducive to finding answers to the question of whether or not on Mars life exists as clay minerals can preserve and enrich organic matter, catalyze the formation of biotic molecules, such as RNA oligomers, ribose, and amino acids, and even contribute to the assembly of vesicles. Future missions to Mars are recommended to set studies on MCMs with the key issues above and are expecting to lead to more exciting findings.
Article
X-ray diffraction patterns of Martian mudstones acquired by Chemistry & Mineralogy X-Ray Diffraction (CheMin) aboard Mar Science Laboratory (MSL) suggest that the smectites detected in Gale crater have poor crystallinity. This finding poses an urgent question about the structural ordering of phyllosilicates found globally by Visible/Near-Infrared (VIS-NIR) spectroscopic orbital remote sensing on Mars, linked to their formation conditions. In this study, we synthesized saponite (Nz+x/z[M6][Si8-xAlx]O20(OH)4·nH2O, where M and N correspond to the divalent octahedral cations and the interlayer cations, respectively) with variable crystallinity, which bear structural similarities to the smectite discovered at Gale crater. Synthetic saponite was characterized using Field Emission Scanning Electron Microscopy (FE-SEM), powder X-ray diffraction (XRD), then studied the spectral features of these samples using nuclear magnetic resonance spectroscopy (NMR),Raman spectroscopy, and VIS-NIR reflectance spectroscopy. Our study revealed that the crystallinity of these saponite samples increased (as shown in the FWHM of XRD (060) peak), and is accompanied by (1) improved T-O-T layer stacking along the c axis (specified by the intensity and width of the XRD (001) peak); (2) increased uniformity of the SiO4 unit in tetrahedral sheets (based on the peak widths of Raman spectra and the well-resolved ²⁹Si NMR peaks); (3) improved regularity in the distribution of Mg²⁺ in octahedral sites and thus the regularity of metal-OH bonds in octahedral sheet (based on the resolution of the NIR 2.2–2.4 μm band and the peak width of the XRD (060,330) peak); and (4) the increased Al in tetrahedral sites and decrease of Al in octahedral sites (the width of ²⁷Al NMR peak), the crystallinity of saponite raised. Based on experimental observations, the first derivative spectra of metal-OH absorptions were proposed as a crystallinity index for smectite on Mars. Our results indicate that different vibration spectroscopy techniques can constrain the structural ordering of smectite on Mars and provide insight into their formation conditions.
Article
Full-text available
Global mineralogical mapping of Mars by the Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activité (OMEGA) instrument on the European Space Agency’s Mars Express spacecraft provides new information on Mars’ geological and climatic history. Phyllosilicates formed by aqueous alteration very early in the planet’s history (the ‘‘phyllocian’’ era) are found in the oldest terrains; sulfates were formed in a second era (the ‘‘theiikian’’ era) in an acidic environment. Beginning about 3.5 billion years ago, the last era (the ‘‘siderikian’’) is dominated by the formation of anhydrous ferric oxides in a slow superficial weathering, without liquid water playing a major role across the planet.
Article
Full-text available
By the time eukaryotic life or photosynthesis evolved on Earth, the martian surface had become extremely inhospitable, but the subsurface of Mars could potentially have contained a vast microbial biosphere. Crustal fluids may have welled up from the subsurface to alter and cement surface sediments, potentially preserving clues to subsurface habitability. Here we present a conceptual model of subsurface habitability of Mars and evaluate evidence for groundwater upwelling in deep basins. Many ancient, deep basins lack evidence for groundwater activity. However, McLaughlin Crater, one of the deepest craters on Mars, contains evidence for Mg-Fe-bearing clays and carbonates that probably formed in an alkaline, groundwater-fed lacustrine setting. This environment strongly contrasts with the acidic, water-limited environments implied by the presence of sulphate deposits that have previously been suggested to form owing to groundwater upwelling. Deposits formed as a result of groundwater upwelling on Mars, such as those in McLaughlin Crater, could preserve critical evidence of a deep biosphere on Mars. We suggest that groundwater upwelling on Mars may have occurred sporadically on local scales, rather than at regional or global scales.
Article
Oxidation is observed in Ca-pyroxene subjected to a range of shock pressures (21–59 GPa). Changes in the pyroxene redox ratio as measured by the changes in %Fe3+ ranged from 2–6 times the starting composition. Mössbauer and reflectance spectroscopy record the changing Fe3+ concentration as a preferential oxidation of Fe2+ in the M2 crystallographic site. The oxidation is also accompanied by mechanical changes in the pyroxene crystals including fracturing, linear defects, and twinning. As oxygen fugacity is often calculated using mineral redox ratios and thought to represent the prevailing fO2 during crystallization, it is imperative to recognize that the fO2 values measured in impact-derived materials may represent that of the impact and not the magma source region.
Article
Accurate clay mineral identification is key to understanding past aqueous activity on Mars, but martian phyllosilicates are old (>3.5 Ga) and have been heavily bombarded by meteoroid impacts. Meteoroid impacts can alter clay mineral structures and spectral signatures, making accurate remote sensing identifications challenging. This paper uses nuclear magnetic resonance (NMR) spectroscopy to examine the short-range structural deformation induced in clay mineral samples of known composition by artificial impacts and calcination. Structural changes are then related to changes in the visible-near infrared (VNIR) and mid-infrared (MIR) spectra of these clay mineral samples. The susceptibility of phyllosilicates to structural deformation after experimental impacts varies by structure. Experimental results showed that trioctahedral, Mg(II)-rich saponite was structurally resilient up to peak pressures of 39.8 GPa and its unchanged post-impact spectra reflected this. Experimental data on kaolinite showed that this Al(III)-rich, dioctahedral phyllosilicate was susceptible to structural alteration at peak pressures ≥ 25.1 GPa. This result is similar to previously reported experimental results on the Fe(III)-rich dioctahedral smectite nontronite, suggesting that dioctahedral phyllosilicates may be more susceptible to shock-induced structural deformation than trioctahedral phyllosilicates. The octahedral vacancies present in dioctahedral phyllosilicates may drive this increased susceptibility to deformation relative to trioctahedral phyllosilicates with fully occupied octahedral sheets. Thermal alteration accompanies shock in meteoroid impacts, but shock differs from thermal alteration. NMR spectroscopy showed that structural deformation in thermally altered phyllosilicates differs from that found in shocked phyllosilicates. Similar to shock, dioctahedral phyllosilicates are also more susceptible to thermal alteration. This differential susceptibility to impact-alteration may help explain generic smectite identifications from heavily bombarded terrains on Mars.
Article
The dwarf planet Ceres is known to host phyllosilicate minerals at its surface, but their distribution and origin have not previously been determined. We used the spectrometer onboard the Dawn spacecraft to map their spatial distribution on the basis of diagnostic absorption features in the visible and near-infrared spectral range (0.25 to 5.0 micrometers). We found that magnesium- and ammonium-bearing minerals are ubiquitous across the surface. Variations in the strength of the absorption features are spatially correlated and indicate considerable variability in the relative abundance of the phyllosilicates, although their composition is fairly uniform. These data, along with the distinctive spectral properties of Ceres relative to other asteroids and carbonaceous meteorites, indicate that the phyllosilicates were formed endogenously by a globally widespread and extensive alteration process.
Article
INTRODUCTION The surface of the dwarf planet Ceres is known to host phyllosilicate minerals, but their distribution and origin have not previously been determined. Phyllosilicates are hydrated silicates, and their presence on the surface of Ceres is intriguing given that their structure evolves through an aqueous alteration process. In addition, some phyllosilicates are known to bear NH 4 , which places a constraint on the pH and redox conditions during the evolution of Ceres. We studied the distribution of phyllosilicates across the planet’s surface to better understand the evolutionary pathway of Ceres. RATIONALE Using the data acquired by the mapping spectrometer (VIR) onboard the Dawn spacecraft, we mapped the spatial distribution of different minerals on Ceres on the basis of their diagnostic absorption features in visible and infrared spectra. We studied the phyllosilicates through their OH-stretch fundamental absorption at about 2.7 µm and through the NH 4 absorption at about 3.1 µm. From our composition maps, we infer the origin of the materials identified. RESULTS We found that Mg- and NH 4 -bearing phyllosilicates are ubiquitous across the surface of Ceres and that their chemical composition is fairly uniform. The widespread presence of these two types of minerals is a strong indication of a global and extensive aqueous alteration—i.e., the presence of water at some point in Ceres’ geological history. Although the detected phyllosilicates are compositionally homogeneous, we found variations in the intensity of their absorption features in the 3-µm region of the reflectance spectrum. Such variations are likely due to spatial variability in relative mineral abundance (see the figure). CONCLUSION The large-scale regional variations evident in the figure suggest lateral heterogeneity in surficial phyllosilicate abundance on scales of several hundreds of kilometers. Terrains associated with the Kerwan crater (higher concentration of phyllosilicates) appear smooth, whereas the Yalode crater (lower concentration of phyllosilicates) is characterized by both smooth and rugged terrains. These distinct morphologies and phyllosilicate concentrations observed in two craters that are similar in size may reflect different compositions and/or rheological properties. On top of this large-scale lateral heterogeneity, small-scale variations associated with individual craters could result from different proportions of mixed materials in a stratified upper crustal layer that has been exposed by impacts. Variations associated with fresh craters, such as the 34-km-diameter Haulani, indicate the presence of crustal variations over a vertical scale of a few kilometers, whereas much larger craters, such as the 126-km-diameter Dantu, suggest that such stratification may extend for at least several tens of kilometers. Abundance maps Qualitative maps of the abundances of ( top ) phyllosilicates and ( bottom ) NH 4 , based on the depth of their absorption features. The two maps have a similar global pattern, although they differ in some localized regions such as Urvara. The scale bar is valid at the equator.
Article
Clay minerals on Mars have commonly been interpreted as the remnants of pervasive water-rock interaction during the Noachian period (>3.7 Ga). This history has been partly inferred by observations of clays in central peaks of impact craters, which often are presumed uplifted from depth. However, combined mineralogical and morphological analyses of individual craters have shown that some central peak clays may represent post-impact, possibly authigenic processes. Here we present a global survey of 633 central peaks to assess their hydrous minerals and the prevalence of uplifted, detrital, and authigenic clays. Central peak regions are examined using high-resolution Compact Reconnaissance Imaging Spectrometer for Mars and High Resolution Imaging Science Experiment data to identify hydrous minerals and place their detections in a stratigraphic and geologic context. We find that many occurrences of Fe/Mg clays and hydrated silica are associated with potential impact melt deposits. Over 35% of central peak clays are not associated with uplifted rocks; thus, caution must be used when inferring deeper crustal compositions from surface mineralogy of central peaks. Uplifted clay-bearing rocks suggest the Martian crust hosts clays to depths of at least 7 km. We also observe evidence for increasing chloritization with depth, implying the presence of fluids in the upper portions of the crust. Our observations are consistent with widespread Noachian/Early Hesperian clay formation, but a number of central peak clays are also suggestive of clay formation during the Amazonian. These results broadly support current paradigms of Mars' aqueous history while adding insight to global crustal and diagenetic processes associated with clay mineral formation and stability.
Article
Many phyllosilicate deposits remotely detected on Mars occur within bombarded terrains. Shock metamorphism from meteor impacts alters mineral structures, producing changed mineral spectra. Thus, impacts have likely affected the spectra of remotely sensed martian phyllosilicates. We present spectral analysis results for a natural nontronite sample (NAu-1) before and after laboratory-generated impacts over five peak pressures between 10 – 40 GPa. We conducted a suite of spectroscopic analyses to characterize the sample's impact-induced structural and spectral changes. Nontronite becomes increasingly disordered with increasing peak impact pressure. Every infrared spectroscopic technique used showed evidence of structural changes at shock pressures above ~25 GPa. Reflectance spectroscopy in the visible near-infrared (VNIR) region is primarily sensitive to the vibrations of metal-OH and interlayer H2O groups in the nontronite octahedral sheet. Mid-infrared (MIR) spectroscopic techniques are sensitive to the vibrations of silicon and oxygen in the nontronite tetrahedral sheet. Because the tetrahedral and octahedral sheets of nontronite deform differently, impact-driven structural deformation may contribute to differences in phyllosilicate detection between remote sensing techniques sensitive to different parts of the nontronite structure. Observed spectroscopic changes also indicated that the sample's octahedral and tetrahedral sheets were structurally deformed, but not completely dehydroxylated. This finding is an important distinction from previous studies of thermally altered phyllosilicates in which dehydroxylation follows dehydration in a step-wise progression preceding structural deformation. Impact-alteration may thus complicate mineral-specific identifications based on the location of OH-group bands in remotely detected spectra. This is a key implication for martian remote sensing arising from our results.