Hyperspectral Mapping of an Ancient Hydrothermal System

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Hyperspectral Mapping of an Ancient Hydrothermal
System

• Adrian Brown

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If all else fails, immortality can always be
assured by spectacular error. John Kenneth
Galbraith
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Presentation Overview

• Earlier descriptions of North Pole Dome
• Hyperspectral mapping
• Fieldwork and Geochemical analysis
• SWIR mineralogical analysis
• Computer Modeling
• Hydrothermal Systems on Mars
• Summary of 2003 milestones

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Previously at the North Pole Dome

• Hickman initial granite greenstone mapping, 1977
• Walter, Buick Dunlop stromatolites, 1980
• Buick, Groves Dunlop An early habitat of
  life, 1981
• Lowe description of SPC, 1983
• Barley introduced hydrothermal activity, 1984
• Collins and Van Kranendonk diapiric vertical
  tectonics, 1994
• What could I possibly add?

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Hyperspectral Mapping

• 600 m2 of coverage
• 400-2400nm (Visible-Near InfraRed)
• 126 bands (avg 20 microns per band)
• Primary targets - sericite, chlorite alteration

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Geochemical Analysis

• XRF analyses of 21 samples analysed so far
• Apex and Mt Ada Basalts

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FloydWinchester

• Most samples plot in basalt/andesite range

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Magmatic affinity
Tholeiitic
Transitional
Calc-alkaline

• Most samples plot in tholeiitic range (except
  rhyolites)

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Rock classification
Komatiite
ChloritisedBasalts
Basalts
Fe-rich vein
Rhyolite
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Immobile Elements
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Pearce Cann (1973)

• Supports mostly mid ocean ridge/volcanic arc
  basalt, though some in within plate basalt range

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Petrological Thin Sections

• 22 Petrological Thin Sections examined
• Revealed high degrees of replacement
• Evidence for replacement of plag by epidote,
  olivine by serpentine, pyroxene
• Gives clues on least altered sample
• EMP Analysis on 4 samples
• Chemical composition of minerals to relate to
  detection of varying Mg-Fe-Al-OH
• sericite
• chlorite
• epidote

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Oxygen Isoptope Analysis

• stand by!

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SWIR Ground Measurements with PIMA

• SWIR instruments like PIMA cover 1300-2500nm
• Hand held, point spectra possible
• Over 250 rock spectra collected so far

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Computer Modeling

• Finite Element Model (FEM) Code HYDROTHERM
  used to model fluid-rock interaction at high
  pressures and temperatures
• Limits of 0-10,000 bars, 0-1200 degrees C
  (includes boiling, not freezing)
• Initial simulations
• Pluton 5km deep, 4km cube
• Uniform Porosity 0.1, Permeability 10-11 cm2
• Pluton held at 950 deg. C for 15,000 years then
  allowed to cool

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Overall model
Zones of sulphur, silica, oxide deposition
Least altered zones away from reaction zones
Zones of alkali transport show fluid metasomatism
Sub-vertical sericite zones record fluid paths
Sub-parallel chlorite zones record
paleo-surface(s)
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Flood basalts of Mars

• Viking shows flood basalt plains
• Phobos shows two pyroxenes in flood basalts
• Researchers suggest komatiites and ultramafic
  basalts
• MGS results show two basalt compositions
• Pathfinder returns elemental compositions

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Summary of 2003 milestones

• Fieldwork collected 119 basalt and felsic
  volcanic samples at NPD
• 22 XRF and ICP-MS analyses
• 6 thin sections
• 22 Oxygen isotope analyses
• 41 EMP analyses
• Immobile Element Alteration Maps from fieldwork
• 250 SWIR spectra collected
• 3D map of NPD from 9 second DEM and movie
• 3 alteration mineral maps of NPD area from
  hyperspectral imagery
• Two hydrothermal events identified and modeled
  in software and testable characteristics
  hypothesized
• 7 public presentations, including international
  and interstate
• Estimated budget 34,000
• Endnote database of 1850 references
• Website for project established, 1,500 photos of
  field sites on display
• 1 paper (almost) ready for submission

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Future Work

• Further computer modeling of hydrothermal
  activity
• Further fieldwork to increase area covered by
  immobile element alteration maps
• Use of gamma ray spectroscopy for comparison
  with element alteration maps

2004

• Generation of computerised Mars hydrothermal
  systems and identification of relevant features
  for hyperspectral mapping
• Use of REE analysis to further constrain eruptive
  environment

2005
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Acknowledgements

• Prof. Malcolm Walter, ACA
• Dr. Tom Cudahy, CSIRO
• Dr. Martin Van Kranendonk, GSWA
• Dr. Kath Grey, GSWA
• Prof. R. Flood, HOD ELS MQ
• Dr. Norm Pearson, Mr. Peter Wieland and Ms.
  Carol Lawson _at_ GEMOC
• Mr. Luke Milan
• Dr. Anita Andrew

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References
Farmer, J. D. and Des Marais, D. J. (1999)
Exploring for a record of ancient Martian life.
Journal of Geophysical Research-Planets, 104
(E11), 26977-26995. Hoffman, H. J., Grey, K.,
Hickman, A. H. and Thorpe, R. I. (1999) Origin of
3.45 Ga coniform stromatolites in Warrawoona
Group, Western Australia. GSA Bulletin, 111 (8),
1256-1262. Macleod, G., McKeown, C., Hall, A. J.
and Russell, M. J. (1994) Hydrothermal and
Oceanic Ph Conditions of Possible Relevance to
the Origin of Life. Origins of Life and Evolution
of the Biosphere, 24 (1), 19-41. Pirajno, F.,
(1992) Hydrothermal mineral deposits principles
and fundamental concepts for the exploration
geologist, Springer-Verlag, Berlin. Thompson, A.
J. B., Hauff, P. L. and Robitaille, A. J. (1999)
Alteration mapping in exploration application of
short-wave infrared (SWIR) spectroscopy. SEG
Newsletter, 39, 16-27. Walter, M. R. and Des
Marais, D. J. (1993) Preservation of Biological
Information in Thermal-Spring Deposits -
Developing a Strategy for the Search for Fossil
Life on Mars. Icarus, 101 (1), 129-143. Floyd and
Winchester! Cocks, T. Jenssen, R., Stewart A.,
Wilson, I., Shields, T., 1998. The Hymap
airborne hyperspectral sensor the system,
calibration and performance. Presented at 1st
EARSEL Workshop on Imaging Spectroscopy, Zurich,
October 1998. Griffith, L.L., and Shock, E.L.,
1997. Hydrothermal hydration of martian crust
Illustration via geochemical model calculations.
Journal of Geophysical Research 102, p. 9135-9143.
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Website
http//aca.mq.edu.au/abrown.htm