remote detection of b i o s i g n a t u r e s a d r i a n b r o w n
TRANSCRIPT
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Remote Detection ofB i o S i g n a t u r e s
A d r i a n B r o w n
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Who am I – why am I here?
• First Year PhD student at Australian Centre for Astrobiology, Macquarie University
• Supervisors Prof Malcolm Walter (Director of ACA), Dr. Thomas Cudahy (CSIRO)
• Background of Engineering and Software Engineering, now traveling on the Astrobiology wheel along the ‘Geology’ spoke
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Overview
• Introduction• Definitions – My Dictionary• Three Year Plan• Mineral Mapping of the North Pole Dome
– Backgrounder: Development of the North Pole Dome– Backgrounder: Hyperspectral mapping and HyMap– What do I hope to achieve?
• Spatial Geochemical Modeling of a Hydrothermal Vein– Backgrounder: Hydrothermal alteration– What do I hope to achieve?
• Martian Simulation– What do I hope to achieve?
• Conclusion – questions?
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Definitions
• Remote sensing – detection of physical characteristics of solid surfaces at distances over 2km
• Hyperspectral – high spectral resolution data sets (ie. HyMap 126 spectral bands) as opposed to multispectral (LANDSAT 7 bands) data sets.
• Hydrothermal zone – water at elevated temperatures in disequilibrium with the rock through which it travels
• Stromatolites – microlaminated sedimentary structure ?created by the secretions of cyanobacteria in algal mats or benthic bacteria around hydrothermal vents
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Three Year Plan
• Research covers remote sensing and interpretation of mineral maps, geochemical modeling and Martian geology
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Year 1 – Mineral Mapping of the North Pole Dome(or, let’s find a weird Earth analogue)
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North Pole Dome
• Setting – eastern Pilbara, north Western Australia• Situated north of Hamersley Ranges (BIFs)• Warrawoona Group - early Archaean (3.2-3.5 Gya)• ‘North Pole’ Dome ironically named
North Pole Dome
Shark Bay
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North Pole Dome
• Doming due to periodic mantle events (Van Kranendonk 2000)
• Very contentious – my main sources are Van Kranendonk 2000, Nijman, 1998, Buick et al 1995, Barley 1993.
• Hydrothermal and volcanic activity spans less than 85 million years, doming started during same time interval.
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Development of North Pole Dome
• Exposed over 6km2 at core of North Pole Dome• Synvolcanic laccolith – medium to coarse grained
biotite monzogranite• Dated at 3459 Ma, same age as the volcanic
Panorama Formation
North Pole North Pole MonzograniteMonzogranite
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Development of North Pole Dome
• Massive thoelitic basalt with pillow basalt occurences
• Lower contact is intrusive - North Pole monzogranite
• Setting is sub-aqueous• Cherts absent except where
transected by boxwork of chert-barite dykes, however these are post-depostional
Mount Ada BasaltMount Ada Basalt
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Development of North Pole Dome
• Contains the worlds oldest stromatolites and microfossils• Buick interpreted the environment as coastal (Barley 1993)• Nijman hypothesized hydrothermal origin, deep marine
environment (Van Kranendonk 2000)• Perhaps a combination of the two is possible? (note small
smokers on Buick photo)
Dresser FormationDresser Formation
Nijman/Van KranendonkNijman/Van KranendonkBuickBuick
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Development of the North Pole Dome
• 3466 Mya• Dacitic tuff, agglomerate and lava flows• Only thin thickness (100m) but an important
horizon marker around the Dome
Duffer FormationDuffer Formation
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Development of the North Pole Dome
• Basalt and Felsic volcaniclastics respectively• ‘Panorama volcano’ located just NW of NPD• 3458 Mya for Panorama
Apex Basalt and Apex Basalt and Panorama FormationPanorama Formation
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Development of the North Pole Dome
• Silicifed carbonate forms chert veins, in some parts incompletely altered
• Stromatolitic horizons up to 8m thick, including ‘Trendall locality’
• Formed during a hiatus in volcanism but with continuing hydrothermal activity
• Conformably overlain by the sub-aqueously deposited Euro Basalt, dated at 3434 Mya.
Strelley Pool ChertStrelley Pool Chert
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Why the North Pole Dome?
• Why choose North Pole? – We have stromatolites and microfossils– Little to no metamorphism due to never being deeply
buried– We have an excellent dataset with low vegetation
• Is it actually like Mars?– Similar age but different weathering processes– Sulfate deposits on Mars and NPD, but barite?– Low vegetation but not *no* vegetation– Dust not as prevalent– Vertical tectonics?– Weathering beneath a oxygen and water laden
atmosphere
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Hyperspectral Mapping
• Basic Principles of Passive Remote Sensing
RockYour House A tree
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Hyperspectral Mapping
• Absorption bands caused by photons being absorbed at specific wavelengths
• Large number of frequencies covered means we can discriminate between individual minerals
• We can discriminate using band ratios (basic) or continuum removal (more complex) or principal components analysis inspired methods (more complex again)
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Vibrational Processes for H2O
• 3 – asymmetric stretch (fundamental 2.903 m)
• 1 – symmetric stretch (fundamental 3.106 m)
• 2 – H-O-H bend stretch (fundamental 6.08 m)
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What is this SWIR thing?
• SWIR = Short Wave Infra Red (2.0-2.4 micrometers)• No water absorption lines• In IR, photon interactions are due to vibrational
processes
• Strong hydroxl overtone (2 ) OH stretch absorption line
• Modified according to the ion the OH molecule is attached to Mg or Al
• Makes it possible to determine alteration minerals on the ground
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Hyperspectral Complications• Spatial and spectral crossover (calibration)• Atmospheric correction• Sun’s energy output described by Planck’s
function• Unmixing– when two or more minerals occupy a
pixel• These are all surmountable to some degree!
pixel width (5m)
Mineral B
Mineral A
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What do we hope to achieve?
• Produce mineral maps showing occurrences of OH altered minerals around the Dome
• Spatially relate occurrences of stromatolites and microfossiliferous horizons
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How are stromatolites and microfossils related to minerals?
• Stromatolites may occur in shallow water around hydrothermal vents (though not cyanobacteria)
• Microfossils may occur in kerogenous hydrothermal veins of black and white chert
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Year 2 – Modeling the Hydrothermal Vein
(or – how on Earth did that get there?)
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Hydrothermal Alteration
• Mineralogy of hydrothermally altered rocks depends on prevailing physical conditions at time of alteration– Chemistry of fluid phase
• pH
• Salinity
• Fugacities of oxygen and sulfur
– Composition of original host rocks– Temperature of host rocks and fluids
• Ideally alteration varies vertically and horizontally , most intense closest to source
• Often controlled by veins, fractures and faults
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Relevant Previous Research
• Lovell and Guilbert researched alteration zoning of Cu porphyries in Nevada
• Helgeson modeled geochemistry of alteration minerals
• Griffith and Shock and EQ3/6 researched geochemical alteration pathways in Martian meteorites
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What can we hope to achieve?
• Can we state something about the conditions under which the system formed, eg. Was a brine (perhaps seawater) involved?
• Can we get an idea of the temperature and pressure conditions in various parts of the Dome? Vapour phase? Acid-sulfate vs. Neutral chloride?
• Can we work out where the barite came from? (hard)
• Is the spatial resolution of our data set good enough to discriminate alteration zones (typically 50m wide) ?
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Year 3 – Martian Simulation
(or, what on Earth will Mars look like?)
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Relevant Research
• Newsom, Gulick, Griffith and Shock, Harrison and Grimm have studied Martian hydrothermal systems, including impact related melt sheets
• Viking IR, Phobos ISM, but large pixel size• TES, THEMIS operate in mid IR• OMEGA - 500m pixel size (2004) and CRISM - 13m
pixel size (2008)
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What can we hope to achieve?
• Can we translate dust seen in TES/THEMIS to the VNIR/SWIR?
• Use characteristics of North Pole Dome to simulate a hydrothermal system on Mars– But which characteristics are reasonable? Size of intrusion,
country rock, temperature, what about barite?
• Following simulation, we can predict what we might see with CRISM on MRO
• Can we map hydrothermal systems and alteration zones with CRISM and then point out the hotspots for stromatolites or microfossiliferrous horizons?
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Stargazing (thrown in for free)
• Ore deposits on Mars – for the future colonist – look for lineaments and alteration zones
• Ore deposits on asteroids or planetary satellites?
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Conclusion
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References• Barley, M.E., 1993. Volcanic, sedimentary and tectonostratigraphic environments of the
~3.46 Ga Warrawoona Megasequence: a review. Precambrian Research 60 p. 47-67.• Buick, R., Thornett, J.R., McNaughton, N.J., Smith, J.B., Barley, M.E. and Savage, M.,
1995. Record of emergent continental crust ~3.5 billion years ago in the Pilbara Craton of Australia, Nature, 375, p. 574-577.
• 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.
• Gulick V.C., 1998. Magmatic intrusions and a hydrothermal origin for fluvial valleys on Mars. Journal of Geophysical Research 103, no. E8, p. 19365-19387.
• Harrison K.P. and Grimm, R.E., 1999. A conservative approach to Hydrothermal Systems on Mars, LPSC XXX Proceedings, p. 1941.
• Lowell and Gilbert, 1970. Lateral and Vertical Alteration-Mineralization Zoning in Porphyry Ore Deposits, Economic Geology 65, p. 373-408
• Newsom, H.E., 1980. Hydrothermal alteration of impact crater melt sheets with implications for Mars, Icarus, 44, p. 207-216
• Nijman, W., de Bruijne, K.C.H. and Valkering, M.E., 1998. Growth fault control of Early Archaean cherts, barite mounds and chert barite veins, North Pole Dome, eastern Pilbara, Western Australia. Precambrian Research 88, p. 25-52.
• Van Kranendonk, M.J., 2000. Geology of the North Shaw 1:100 000 Sheet Western Australia Geological Survey, 1:100 000 Geological Series Explanatory Notes, 86p. Department of Minerals and Energy, Western Australia.
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Picture/Movie Acknowledgements
• MER website, MER website, http://athena.cornell.edu/the_mission/rov_video.html
• Introduction to Hyperspectral Analysis by Peg Shippert, Introduction to Hyperspectral Analysis by Peg Shippert, www.rsi.com
• Black Smoker Webquest, Black Smoker Webquest, http://www3.district125.k12.il.us/faculty/bfisher/blacksmokerlinks.html
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Questions
(or, what was all that about?)
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