Australian Centre for Astrobiology

Hyperspectral and Field mapping of an Archean Serpentinized Komatiite unit in Western Australia Applications for CRISM Adrian Brown Malcolm Walter Thomas Cudahy Australian Centre for Astrobiology

Presentation Overview Airborne Hyperspectral VisNIR MappingAirborne Hyperspectral VisNIR Mapping Ground truthing through field workGround truthing through field work Why? How? 3.5 Ga rocks 3.5 Ga rocks Ancient Microfossils Ancient Microfossils Signs of water: Signs of water: - Stromatolites - Pillow basalts - Serpentine

Hyperspectral mapping project HyMap instrument flown at 2km AGL 126 bands from nm 600 sq. km, 14 swathes, ea. approx. 2km wide 5m horizontal pixel size Data were calibrated for instrument response, and then atmosphere was removed using HyCorr (ATREM). Before analysis, continuum was removed using IDL continuum removal

Serpentine? Hydrously metamorphosed peridotites contain serpentine, these may be found near mid ocean ridges, or subduction zones, where olivine rich rocks react with sea water to form serpentineHydrously metamorphosed peridotites contain serpentine, these may be found near mid ocean ridges, or subduction zones, where olivine rich rocks react with sea water to form serpentine Archaean greenstone belts – occurs as altered komatiite flowsArchaean greenstone belts – occurs as altered komatiite flows –Usually associated with overlying High Mg ‘komatiite basalts’

Serpentinisation reaction 2Mg 2 SiO 4 + 3H 2 O ↔ Mg 3 Si 2 O 5 (OH) 4 + Mg(OH) 2 2Mg 2 SiO 4 + 3H 2 O ↔ Mg 3 Si 2 O 5 (OH) 4 + Mg(OH) 2 forsterite water serpentine brucite forsterite water serpentine brucite Magnetite (Fe 3 O 4 ) can form to take excess iron in olivine – no Fe in serpentine, however chlorite does take FeMagnetite (Fe 3 O 4 ) can form to take excess iron in olivine – no Fe in serpentine, however chlorite does take Fe In some cases, further reaction of serpentine forms talc and carbonate:In some cases, further reaction of serpentine forms talc and carbonate: 2Mg 3 Si 2 O 5 (OH) 4 + 3CO 2 → Mg 3 Si 4 O 10 (OH) 2 +3MgCO 3 +3H 2 O 2Mg 3 Si 2 O 5 (OH) 4 + 3CO 2 → Mg 3 Si 4 O 10 (OH) 2 +3MgCO 3 +3H 2 O serpentine carbon dioxide talc magnesite serpentine carbon dioxide talc magnesite

Komatiite? Ultramafic lava flowUltramafic lava flow Rich in high Mg olivineRich in high Mg olivine Olivine alters to serpentineOlivine alters to serpentine Only occurs in Archaean terrainsOnly occurs in Archaean terrains High temperatures - associated with mantle plumesHigh temperatures - associated with mantle plumes

Characteristics of komatiite flow in Pilbara Probably formed when komatiite erupted into Archaean seawater and was subsequently buried and heated by subsequent flowsProbably formed when komatiite erupted into Archaean seawater and was subsequently buried and heated by subsequent flows Lateral extent - ~20km x 30mLateral extent - ~20km x 30m Possible pillow flowsPossible pillow flows Ultrabasic lavaUltrabasic lava High MgO (>18 wt.%)High MgO (>18 wt.%) Chloritised basalts overly the komatiite flow and provide a more easily detected targetChloritised basalts overly the komatiite flow and provide a more easily detected target 2mm

VNIR Spectra of serpentine

Rule Based Detection of serpentine with hyperspectral data Serpentine (note micron region) Chlorite Shallow depth of ~2.4 feature could be due to lack of Fe

Detection of serpentine with hyperspectral data Chlorite in red Serpentine in black (picks out 2 komatiite layers) N is up, 2.5km across

Photomontage Hyperspectral [126-band] Image cube Principal Component Analysis [PCA] Hierarchical Cluster Analysis [HCA] PCA|HCA Classes Spectra Artificial Neural Network [ANN] pc3 pc1 pc2 WNW 5 m Dendrogram For more information: M. Storrie-Lomardi, or see us at poster location 583, Thursday PM Classification Feature Extraction Bayesian Estimates

Applications for CRISM Multispectral survey of CRISM uses 59 bands with coarse resolutionMultispectral survey of CRISM uses 59 bands with coarse resolution Band coverage should naturally be as intense as possible in SWIR, but particularly in to detect serpentineBand coverage should naturally be as intense as possible in SWIR, but particularly in to detect serpentine OH fundamentals at microns will be instructiveOH fundamentals at microns will be instructive Strategy – find the chlorite first, then the serpentine on high resolution runsStrategy – find the chlorite first, then the serpentine on high resolution runs