3 ansir australian national seismic imaging … · 3 gswa, kalgoorlie ansir australian national ......

Seismic: A key tool in Seismic: A key tool in understanding crustal architecture understanding crustal architecture

and mineral systemsand mineral systems

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B.R. Goleby1, R.S. Blewett1, B.L.N. Kennett2, L.E.A. Jones1, R.J. Korsch1, B.J. Drummond1, T. Fomin1, A.M. Reading2,

K.F. Cassidy1, D.C. Champion1, P. Henson1, P.B.Groenewald3, M. Nicoll1 and T. Brennan1

‘‘Reduced Discovery Risk through Improved Targeting’Reduced Discovery Risk through Improved Targeting’

1 Geoscience Australia, pmd*CRC2 Research School of Earth Sciences (ANU)

3 GSWA, KalgoorlieANSIR AUSTRALIAN

NATIONALSEISMIC IMAGINGRESOURCE

pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery

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ANSIR AUSTRALIANNATIONALSEISMIC IMAGINGRESOURCE

Why collect seismic in a Why collect seismic in a mineral province?mineral province?

• provides geometrical and depth constraints (architecture)

• provides velocity info and hence density information (infer lithology)

• Seismic has always shown up the unexpected

• Seismic provides a quantum leap in knowledge

Mineral Systems, a 5 Questions approach:Architecture, geodynamic inferences, fluid pathways, drivers, focus and deposition


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Talk OutlineTalk Outline

• Lithosphere velocityBroadband stations (distant earthquakes P-wave, S-wave & surface wave)

• Crustal velocityReceiver function (inversion of earthquake data)


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Talk OutlineTalk Outline

• Wide-angle refraction (long offset seismic energy from vibs)

• Deep seismic reflection (record near-vertical incident seismic waves)


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Broadband DataBroadband Data

• Broadband stations P-wave, S-wave and surface wave velocity from distant earthquakes

• Deep velocity structure beneath the Australian Continent

• Investigate characteristics of Australian Lithosphere.


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Shear wave velocity at 75 km (upper mantle).

B.L.N. KennettRed/Brown slower than the world averageBlue faster than the world average.

BROADBAND DATA

WESTWESTfastfast

depleteddepletedrefractoryrefractory

coldcoldless denseless dense

drydrystrongstrong

buoyantbuoyant

EASTEASTslowslow

undepletedundepletedfertilefertiledensedensewarmwarmwetwet

weakweakless buoyantless buoyant


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Shear wave velocity modelShear wave velocity model

Blue S-wave velocities slower than the world average, Pink S-wave velocities faster than the world average.

350 km

Leonora01AGSNY1


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3D surfaces of S3D surfaces of S--wave velocitieswave velocities


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4.8 km/s S-wave isosurface



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3D visualisation3D visualisation--Broad BandBroad Band

350 km

EEGPSCM

• Steps in 4.8 km/s isosurface• Intriguing geometry of the fast velocity body


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Broad Band data summaryBroad Band data summary•• Yilgarn mantle lithosphere: fast, Yilgarn mantle lithosphere: fast,

depleted, refractory, cold, light, dry, depleted, refractory, cold, light, dry, strong, buoyantstrong, buoyant

•• Heterogenous lithosphere and stratified Heterogenous lithosphere and stratified –– what would a fossil mantle plume do what would a fossil mantle plume do to this layering?to this layering?

500 km


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Broad Band data summaryBroad Band data summary•• Step changes in highStep changes in high--velocity layer velocity layer

correspond? with terrane boundaries?correspond? with terrane boundaries?•• EastEast--dipping fossil slab dipping fossil slab –– too shallow, too shallow,

wrong way?wrong way?

Gutscher et al. (2000)


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Receiver Function DataReceiver Function Data

• Good Yilgarn-wide coverage

• Broadband transect of Yilgarn

• Non-linear inversion for crustal velocity

• Characterising provinciality

WTWT

WVWV


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ANSIR AUSTRALIANNATIONALSEISMIC IMAGINGRESOURCE Reading, Kennett & Dentith, 2003

WV

WT

World average crustal velocity profile

Calculated crustal velocity profile


W

NE


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• Moho: shallow east dip– consistent with reflection

moho and eastward tilt of Yilgarn?

• Characteristic velocity functions across terranes– cf Kalgoorlie upper crustal

(10 km) low velocity anomaly

Southern Cross Kalgoorlie

10 km

Velocity increase

World average crustal velocity profile

Calculated crustal velocity profile


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• Drop in velocity means less density

• Low-Ca granite (Champion and Sheraton, 1997) ‘underplate’ or transfer to base of upper crust from mid crustal anatexis?

Southern Cross Kalgoorlie Laverton

10km

Velocity increaseWorld average

Calculated


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• Laverton velocity function similar to Southern Cross?

• The Kalgoorlie terrane as a ‘rift’

Southern Cross Kalgoorlie Laverton


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WideWide--Angle Refraction Data Angle Refraction Data

• Pioneering work• Refraction recording

using portable short-period instruments. Passive technique

• Vibrator source to record refracted seismic energy to offsets over 50 km

• Velocity structure of crust

• Infer some lithological information


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Wide Angle Refraction Data Wide Angle Refraction Data

0 200

Dep

th, k

m

0

76-6.2km/s

6.2-6.4km/s

5.0-5.8km/s

6.4-6.6km/s

6-6.2km/s

Leonora Laverton

Velocity model for top 7 km.

Upper crustal velocity model from first arrivalsCoincident with deep seismic reflection traverse

3D viewof wide-angle

velocity functions

14 km


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Seismic Reflection DataSeismic Reflection Data

• Deep seismic reflection explosives & vibs (1991-2001)

• Resulting sections provide information on crustal architecture

• Some velocity and lithological information

• Quantum leap in 3D understanding and geodynamics

NY1NY1

EGF1EGF1


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213x45km

WESeismic Reflection DataSeismic Reflection Data

91EGF01


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Leonora Laverton Lake-YeoYamarna

16 s

EW

• crustal thickness change across the NE Yilgarn• subdivision of crust into three broad layers• prominent east dip• three east-dipping crustal-penetrating shear zones


384 km in length , 48 km in depth01AGSNY1

http://www.ga.gov.au/pdf/RR0110.pdf


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Leonora Laverton Lake-YeoYamarna

384 km in length , 48 km in depth 01AGSNY1

EW

http://www.ga.gov.au/pdf/RR0110.pdf

• Major gold deposits associated with major structures• East-dipping crustal shear zones coincident with

known mineral fields• Fault zone reflectivity due to alteration

Leonora Mineral Field

Laverton Mineral Field

Possible New Mineral Field

Au bearing fluids?Au bearing fluids?



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• Excellent tool for architecture (underpins mineral systems analysis)

• Invaluable for 3D model building as potential field data (mag and gravity) below greenstone base (< 7 km) is useless

• Speculate about fluid flow and focussing from derived geometries and texture


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MineMine--scale seismic datascale seismic data

• Mine-scale seismic reflection profiling (2001 and 2004)

• Information on mine-scale architecture

• Good fit to drill hole and mine scale geology

• Leading to drill targets

NY1NY1

EGF1EGF1


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MineMine--scale seismic datascale seismic data

Sons of Gwalia (Leonora)


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ConclusionsConclusions

• Exciting and novel results• Successfully imaging

crustal structure = architecture

• Crust and uppermost mantle lithology variations and velocity distribution

• Providing inputs for the geodynamic and metallogenic history of Yilgarn terranes


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Future Yilgarn WorkFuture Yilgarn Work

• pmd*CRC Y-New project 2005-2008 (see poster)

• Magneto-telluric study across existing seismic reflection profiles (EGF01)

• Refine and integrate the characterisation of Receiver Functions with 3D models

• Explore questions raised by these intriguing techniques (geodynamics and mineral systems)


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Thanks for listening

3 ansir australian national seismic imaging … · 3 gswa, kalgoorlie ansir australian national ......

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