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‘‘Reduced Discovery Risk through Improved TargetingReduced Discovery Risk through Improved Targeting’’
pmd CRCLithosphericGeodynamics: a seismicview of the Yilgarn Craton
The Y2 project (2001-2004)The Y2 project (2001-2004)
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
OutlineOutline
Seismic (general sense) signature of:
• subduction and slabs
• mantle plumes
• delamination and possiblegeneration of Low-Ca granites
• Provinciality/terranes
• Conclusions
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Subduction and tomographySubduction and tomography
• Yilgarn subduction atvarious times(geochemistry)
• Both east- and west-dipping slabs
• Can we see the‘signature’ ofsubduction?
• Slabs characterised byfast S-wave velocities
Tomography of slabs under Japan (Fukao et al. 2001)
velocity
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
YouanmiYouanmi
KalgoorlieKalgoorlieN
?
?
Felsicvolcanism
2760-2730 MaYoung east?
Felsicvolcanism?
2740-2730 MaZircon
inheritance
SE-dipping subduction zones?SE-dipping subduction zones?
Cassidy & Champion (2004)
Postulated SE-dipping slab ca 2.76-2.73 Ga
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Mafic/calc-alkaline
High-Ca
High-HFSE
Fault
Co
nti
nen
tal
cru
st
Oce
anic
cru
st
Slab
EAST
Mantle upwelling produceskomatiites
Together?
Kalgoorlie Terrane Kurnalpi Terrane
Ca 2.705 Ga
Morris & Witt (1997)
Models for West-dipping subductionat ~2.7 Ga
Champion & Cassidy (2001)
W-dipping subduction zones?W-dipping subduction zones?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)
• no evidence for the W-dipping 2.7 Ga slab?
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)
• no evidence for the W-dipping 2.7 Ga slab?
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
• The age of the high-velocity layer is unknown
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
EEGPY (SC)M
120km
350 km
W
500 km
• SE-dipping (low-angle) fast layer (4.8 km/s)• possibly a fossil slab (cf. Narryer at 2.75Ga)
• no evidence for the W-dipping 2.7 Ga slab?
Ida F Yamarna F
Stratified lithosphere as a slab?Stratified lithosphere as a slab?
We can not rule slabs in or out on this evidence
• The age of the high-velocity layer is unknown
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Gutscher et al. (2000)
EEGPY (SC)M
120km
350 km
W
500 km
500 km
Ida F Yamarna F
Chilean analogue for flat subductionChilean analogue for flat subduction
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Gutscher et al. (2000)
EEGPY (SC)M
120km
350 km
W
500 km
500 km
Ida F Yamarna F
Chilean analogue for flat subductionChilean analogue for flat subduction
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Bijwaard et al. (2004)
Mantle plumes and tomographyMantle plumes and tomography
Iceland plume tomography
Modern mantleplumes are:
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Bijwaard et al. (2004)
Mantle plumes and tomographyMantle plumes and tomography
• large (several100’s to 1000’skms in diameter)
Iceland plume tomography
Modern mantleplumes are:
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Bijwaard et al. (2004)
Mantle plumes and tomographyMantle plumes and tomography
• large (several100’s to 1000’skms in diameter)
• Originate from thevery deep earth
Iceland plume tomography
Modern mantleplumes are:
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Bijwaard et al. (2004)
Mantle plumes and tomographyMantle plumes and tomography
• large (several100’s to 1000’skms in diameter)
• Originate from thevery deep earth
• Have low P- and S-wave velocities
Iceland plume tomography
Modern mantleplumes are:
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Plume Morris & Witt (1997)
Mafic/calc-alkaline
High-Ca
High-HFSE
Fault
Co
ntin
enta
lcr
ust
Oce
anic
cru
st
Slab
EAST
Mantle upwelling produceskomatiites
Together?
Kalgoorlie Terrane Kurnalpi Terrane
Ca 2.705 Ga
Champion & Cassidy (2001)
Plumes havebeenhypothesisedfor komatiites(eg Morris & Witt, 1997;
Champion etc),
and manygranites (egCampbell & Hill, 1988 andlater papers)
Yilgarn mantle plumes?Yilgarn mantle plumes?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
• If a high-level plume: it would disrupt this stratification(assuming stratification is old)
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
• If a high-level plume: it would disrupt this stratification(assuming stratification is old)
• Or, horizontal reworking was dominant after the plume
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
• If a high-level plume: it would disrupt this stratification(assuming stratification is old)
• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
• If a high-level plume: it would disrupt this stratification(assuming stratification is old)
• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane• If a deep plume we wouldn’t see it in this section
120 km
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
350 km
EEGPY (SC)M
500 km
• If a high-level plume: it would disrupt this stratification(assuming stratification is old)
• Or, horizontal reworking was dominant after the plume• Or, disruption is out of this plane• If a deep plume we wouldn’t see it in this section
120 km
We can not rule plumes in or out on this evidence
Ida F Yamarna F
Impingement of a mantle plume?Impingement of a mantle plume?W
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
• Major types(Low-Ca, High-Ca)
• Crustal melts
• Intrudeexternalgranites (atbase ofgreenstone)
• Late <2655 MaLow-Ca granite greenstone
Champion & Sheraton (1997)
Yilgarn delamination?Yilgarn delamination?
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
AMIRA P624; Blewett et al., 2004
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
AMIRA P624; Blewett et al., 2004
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)
AMIRA P624; Blewett et al., 2004
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)
AMIRA P624; Blewett et al., 2004
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)• Synchronous with Au ages?
AMIRA P624; Blewett et al., 2004
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)• Synchronous with Au ages?
AMIRA P624; Blewett et al., 2004
DelaminationDelaminationDelaminationDelamination
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)• Synchronous with Au ages?
AMIRA P624; Blewett et al., 2004
DelaminationDelaminationDelaminationDelamination
Heat?Heat?
Delamination:
Ida F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
500 km
• delivers heat across entire Yilgarn (Low-Ca arecraton-wide)
• Initiated at ~2670 Ma (first D2a event in east)• Low-Ca granites ~2655 Ma (E) to 2640 (W)• Synchronous with Au ages?
AMIRA P624; Blewett et al., 2004
DelaminationDelaminationDelaminationDelamination
Heat?Heat?
Delamination:
meltIda F Yamarna F
Fast layer as delaminated Fast layer as delaminated ‘‘restiterestite’’??
Restite layer??
350 km
120 km
EEGPY (SC)MW
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
• Intrude externalgranites (base ofgreenstone)
• Relatively lowdensity,relatively slow(seismically)
Terranes of the Yilgarn Craton:the Low-Ca granites
Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:the Low-Ca granitesthe Low-Ca granites
Low-Ca granite greenstone
Ida
Fau
lt
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
• Intrude externalgranites (base ofgreenstone)
• Relatively lowdensity,relatively slow(seismically)
Terranes of the Yilgarn Craton:the Low-Ca granites
Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:the Low-Ca granitesthe Low-Ca granites
Low-Ca granite greenstone
Ida
Fau
ltNext 2 slides
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Youanmi Kalgoorlie
S-wave velocity increase
dept
h
E• Kalgoorlie has
low-velocitylayer at ~10 km= less density
• Not simplyreflectingoverlyinggreenstones
Moho
Terranes of the Yilgarn Craton:upper crust from receiver functions
Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:upper crust from receiver functionsupper crust from receiver functions
Kurnalpi
10 km
Australian average velocity profile
Calculated crustal velocity profile
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Youanmi Kalgoorlie
S-wave velocity increase
dept
h
E
World average crustal velocity profile
Calculated crustal velocity profile
Moho
Terranes of the Yilgarn Craton:upper crust from receiver functions
Terranes of the Yilgarn Craton:Terranes of the Yilgarn Craton:upper crust from receiver functionsupper crust from receiver functions
• Thick Low-Cagranite‘underplate’under Kal fromcrustal anatexis(link to Au)
• Thick Low-Casignature of Kalendowment??
Kurnalpi
Crustal melts
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Jon Hronsky(WMC)
Lots of arm waving isLots of arm waving isinteresting, but how does it helpinteresting, but how does it help
us?us?Better
understanding ofthe minerals system
process –geodynamics is anintegral component
and driver of themass and energy
flux
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
ConclusionsConclusions
• ‘Signatures’ of the mass and energy fluxat the largest scale are visible in variousseismic methods (tomography, receiverfunctions)
• We don’t always understand the‘signatures’
• a complex mantle lithosphere and crust,especially the temporal component
• Geodynamic implications for slabs,plumes and delamination; tectonicdevelopment in general
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Predictive Mineral DiscoveryPredictive Mineral Discovery
• Yilgarn is data-rich and we need abetter methodology (paradigm?) tounderstand the ‘signatures’
• The way forward is clearly a holisticsystems approach across alllithospheric scales and dimensions
• Need to integrate in 3D with time
• Erect multiple hypotheses and applysuitable tests
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Challenge for us allChallenge for us all
• Challenge is being predictive with thisnew understanding and knowledge
• The system may be recognised eventhough the precise genetic links withmineralisation are unclear (Hronsky,2004),
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Challenge for us allChallenge for us all
• Challenge is being predictive with thisnew understanding and knowledge
• The system may be recognised eventhough the precise genetic links withmineralisation are unclear (Hronsky,2004),
but we are working hard on itbut we are working hard on it(pmd*(pmd*CRC Y-New project)CRC Y-New project)
pppredictiveredictiveredictive mmmineralineralineral dddiscoveryiscoveryiscovery
Thanks for listening