41st Lunar and Planetary Science Conference (2010)
2275.pdf
ORBITAL SPECTRAL MAPPING OF SURFACE COMPOSITIONS IN THE ANTARCTIC DRY
VALLEYS: REGIONAL DISTRIBUTIONS OF SECONDARY MINERAL-PHASES AS CLIMATE
INDICATORS AND IMPLICATIONS FOR MARS. M. B. Wyatt1, J. W. Head1, D. R. Marchant2, R. P. Harvey3, P. R. Christensen4, M. R. Salvatore1, and U. N. Horodyskyj1, 1Dept. of Geological Sciences, Brown University, Providence, RI 02912, 2Dept. of Earth Sciences, Boston University, Boston, MA 02215 3Dept. of Geological
Sciences, Case Western Reserve University, Cleveland, OH 44106, 4School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287.
Introduction: Physical weathering dominates over
chemical weathering in the current environment of the
Antarctic Dry Valleys (ADV) due to extremes of very
low moisture availability and very low temperatures.
Although chemical weathering is limited, the effects of
aqueous alteration at the surface-atmosphere interface
are evident in the production of a variety of secondary
mineral-phases. Phyllosilicates [1, 2], carbonates [3],
sulfate salts [4], amorphous silica [4], zeolites [5] and
iron staining [6] are all found on stable, old surface
materials. Characterizing compositions in the top
hundred microns of ADV rocks and soils is thus fundamentally important towards understanding the alteration effects from past and present climate regimes.
In the current martian environment, physical weathering also dominates over chemical weathering and a
diversity of secondary mineral-phases similar to those
found in the ADV have been identified using data
from near infrared (NIR) and thermal infrared (TIR)
orbiting spectrometers (OMEGA-CRISM and TESTHEMIS) [e.g. 7-10]. The aqueously derived mineralphases on Mars are thought to reflect an ancient, warmer and wetter environment compared to current martian climate conditions [e.g. 11]. A major outstanding
question that remains, however, is how warm and how
wet ancient Mars must have been for the observed
diversity of secondary alteration mineral-phases to
form. The ADV are an ideal natural laboratory for
such an investigation.
We are currently addressing this key question
through a multidisciplinary investigation that combines
ADV field work during the 2009-2010 summer season
with NIR and TIR laboratory spectroscopy and orbital
remote sensing. In this abstract, we provide context
for our ongoing research, present preliminary field
work results, and outline future studies that will begin
upon returning from Antarctica.
ADV Climate Background: The ADV are generally described as a hyper-arid, cold-polar desert [12].
New climate and geomorphic data show that the region
can be subdivided into three narrow zones distinguished on the basis of varying elevation, temperature,
and precipitation [13]. The microclimate zones include: 1) a seasonally dynamic coastal thaw zone
(CTZ), 2) a transitional inland mixed zone (IMZ), and
3) a stable upland frozen zone (SUZ). Within micro-
climate zones, subtle variations in temperature and
soil-moisture are sufficient to produce variations in
surface topography. Changes in relative humidity and
soil-moisture content, both of which are strongly influenced by atmospheric temperature and wind
speed/direction [14], regulate salt weathering, frost
action, and soil development [15]. These processes in
turn control rates of downslope movement, fan development, gullying, polygon morphology/evolution, and
rock weathering. Each microclimate zone in the ADV
thus features a unique assemblage of landforms [13].
ADV Compositional Investigations:
Several
previous studies have also examined secondary mineral‐phases in the ADV at local‐scales and associated
compositional variations with changes in temperature,
water chemistry, pH, water/rock ratio, and dissolution
rates of primary minerals [e.g. 15 and references therein]. Correlations between secondary mineral‐phases
and climate variables over regional‐scales, however,
remain poorly constrained. This gap in scale and
knowledge is largely due to the difficulty in accurately
characterizing fine‐grained, poorly‐crystalline secondary mineral‐phases on exposed surfaces during field
mapping. Nevertheless, it is important to understand
the distribution of secondary mineral‐phases across the
ADV because regional‐scale trends in surface compositions provide the best insight into regional‐scale
changes in climate conditions.
The major focus of our ADV work is to thus quantitatively evaluate the linkage between different regional microclimate environments and surface compositions. This is being pursued in three integrated studies: (1) Establishment of key NIR and TIR spectral
indices for “ground-truth” identification of ADV surface compositions. (2) Mapping distributions of primary lithologies and secondary mineral-phases over the
entire ADV region using multispectral Advanced
Spaceborne Thermal Emission and Reflection Radiometer (ASTER) TIR data and hyperspectral Hyperion
NIR data. (3) Determining if regional distributions of
secondary mineral‐phases are linked to current climate
variables as measured by Long Term Ecological Research Automatic Weather Network (LAWN) stations
or instead provide insight to past climate conditions.
(1) Ground Truth Field Spectroscopy. In a companion LPSC abstract by M. R. Salvatore, we present
41st Lunar and Planetary Science Conference (2010)
Wright
Upper
Glacier
N
2 km
OL
YM
S
PU
GE
RD
GA
AS
N
RA
Mc
Ke
lve
y
NG
RA
Dais
E
Lake Vanda
Wright Valley
B
0.92
0.90
0.96
Emissivity
Avg Scene
Dolerite
Emissivity
0.94
0.96
0.94
1
2
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
A
Avg Scene
Granodiorite
0.92
0.96
Avg Scene
Quartz/
Conglom
0.92
0.90
0.94
0.90
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
Emissivity
Emissivity
0.96
Va
lley
Bull Pas
s
Labyrinth
0.94
3
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
Avg Scene
Gneiss
0.92
0.90
4
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
Figure 1: (A) ASTER VIS and atm. corrected TIR emissivity
image showing compositional diversity of ADV lithologies.
Dashed lines are IMZ 2009-2010 field location. (B) Average
scene spectra taken from points 1-4 compared to lab measured rock spectra resampled to ASTER spectral resolution.
Emissivity
0.97
0.96
Weathered
Fresh
0.95
Β
0.94
0.93
0.96
Emissivity
initial results of ongoing spectroscopic field measurements from the SUZ type locale of Beacon Valley.
NIR spectra of the Ferrar Dolerite, which are compositionally analogous to basaltic martian meteorites [16],
reveal variations in the type and extent of aqueous
alteration minerals-phases (phyllosilicates) produced
in one of the coldest (mean annual temperature of 22°C [13]), driest (mean annual relative humidity of
43% [13]), and thus Mars-like environments on Earth.
These results illustrate the diversity of spectral features
associated with a single lithology and will be used to
constrain the diversity seen in orbital spectral datasets.
(2) Orbital Mapping of Surface Compositions.
ASTER and Hyperion data are analyzed to uniquely
identify and map primary and secondary surface compositions at high-spatial resolutions (90 and 30 m/pixel
respectively). Figures 1 and 2 show examples of ongoing spectroscopic mapping in the ADV and the effectiveness of using ASTER TIR data to map sediment
pathways and mixing of surface materials in the IMZ.
(3) Linking Climate and Compositions. Upcoming
work will focus on measuring surface exposure ages to
develop a spectral maturity index for different primary
lithologies.
The objective of this combined
approach is to develop an understanding of how
2275.pdf
0.94
0.92
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
Scene
Ferrar
Dolerite
0.90
0.88
C
8.5 9.0 9.5 10.0 10.5 11.0
Wavelength (μm)
Α
Figure 2: (A) High-resolution ASTER VIS-TIR map of Upper Wright Valley Dais. (B) Lab spectra of fresh and weathered Ferrar dolerite with spectral variation due to secondary silica phases. (C) ASTER spectra of Ferrar dolerite
(white boxes in A). Spectral variations likely caused by variable secondary coatings and/or mixing of lithologies.
surface exposure ages, secondary compositions, and
climate are linked and expressed in the upper 100 μm
of a surface. We will integrate environmental LAWN
data to determine if surface compositions reflect
current climate variables or instead provide insight into
past climate conditions and alteration processes.
Implications for Mars: The ADV microclimate
zones serve as ideal locations for developing an understanding of the link between surface compositions and
climate variables in a Mars-like, hyper-arid, cold-polar
desert. NIR and TIR field and orbital data of the ADV
are thus valuable for comparison to NIR and TIR data
from OMEGA-CRISM and TES-THEMIS. Constraining the diversity of secondary alteration mineralphases in the ADV will directly influence interpretations of martian surface compositions and the search
for evidence of climate variations over geologic time.
References: [1] Claridge G.G.C. (1965) N .Z. J. Geol
Geo, 186-220. [2] Robert C. and Kennett J.P. (1997) Geology, 25, 587-590. [3] Glazovskaya M.A. (1958) Geol. Geog.
Nauki 1: 63-76. [4] Giorgetti G. and Baroni C. (2007) Eur. J.
Min., 19, 381-389. [5] Gibson E.K. et al (1983) Geophys.
Res. 88, suppl. A912-A918. [6] Glabsy G.P. et al. (1981) N.
Z. J. Geol Geo, 389-397. [7] Bibring J.P. et al. (2005)
Science, 307, 1576-1581. [8] Mustard J.F. et al. (2008) Nature, 454, 305-309. [9] Michalski J.R. et al. (2005) Icarus,
174, 161-177. [10] Osterloo M. M. et al. (2008) Science,
319, 1651-1654. [11] Bibring J.P. et al. (2006) Science, 312,
400-404. [12] Denton G. H. (1993) Geogr. Ann. A., 82, 167211. [13] Marchant D. R. and Head J. W. (2007) Icarus,
192, 187-222. [14] Keys J.R. (1980) Well. Geol. Dept. NZ.
[15] Campbell G.G.C. and Claridge I.B. (1987) Ant: Soils,
Weath. Proc, and Env, 368 pp. [16] Harvey R. P. (2001)
Wkshp. Mars Hlnds. & Mojave Dsrt. Anal., Abstract #4012.