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

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

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

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?

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

Three Year Plan

• Research covers remote sensing and interpretation of mineral maps, geochemical modeling and Martian geology

Year 1 – Mineral Mapping of the North Pole Dome(or, let’s find a weird Earth analogue)

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

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.

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

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

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

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

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

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

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

Hyperspectral Mapping

• Basic Principles of Passive Remote Sensing

RockYour House A tree

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)

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)

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

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

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

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

Year 2 – Modeling the Hydrothermal Vein

(or – how on Earth did that get there?)

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

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

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) ?

Year 3 – Martian Simulation

(or, what on Earth will Mars look like?)

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)

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?

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?

Conclusion

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.

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

Questions

(or, what was all that about?)