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Delamerian Orogeny John Foden
(plus acknowledgements to Anthony Reid, Pete Be<s, Chris Clark, Alan Collins, Frank Robinson, David Tassone
and others) 1. Geology and Geophysics, School of Physical Sciences, Department of Earth
Science, University of Adelaide, Adelaide, SA 5005, Australia
Collins, 2002; Cawood et al. 2009 Aitchison and Buckman, 2012
DisPncPve West Pacific –Style Orogenesis Opposing Models
Though in fact the truth may include elements of both models
Li and Evans (2011)
The “Palaeo-‐Pacific” east Gondwanan Passive Margin
Palaeo Pacific
Delamerian Orogen: The Mid-‐ to Cambrian Orogenic Inversion of the Late Neoproterozoic to Early Cambrian passive margin of the Australian secPon of the Pacific Margin of Gondwana
Tasmania
Delamerian Foreland Fold-‐Thrust Belt, N. Kangaroo Island
Lower Ordovician Owen Conglomerate
Delamerian Unconformity
Burnie FormaPon (Late Neoproterozoic)
The Delamerian in Tasmania
Tasmania.. “Tyennan” = Delamerian
The “Delamerian” = the Ross Orogen in the TransantarcRc Mountains
~550 Ma
The post “Delamerian” Unconformity in Cape Town, South Africa.. Saldania/ Cape Orogen
Ordovician Siliciclastics
Malmesbury Shale
Cape Granite (S-type, 550 Ma)
The “Delamerian” in South Africa from 555Ma
Pampeanas(555Ma-515 Ma)
Saldania (Cape)(555Ma-510 Ma)
The Gondwanan Pacific Margin: TerraAustralis Orogen (Cawood, 2005)
Ross (540Ma-490 Ma)
Delamerian(515Ma- 490
Grenville & Pan-African Foldbelts
PalaeozoicAdditions 555-‐515Ma
Progressive decrease in age S to N: = assembly of east and west Gondwana fragments
Progressive On-set of Subduction on Gondwanan Pacific Margin ?
Australia
Australia
West Gondwana
West Gondwana
Tasmania?
Tasmania?Pacific
Pacific
Passive Margins
Mawson Craton/ Ant.
Ross Orogen
Leeuwin Orogen 522 Ma 525 Ma
565 Ma
585 Ma Passive margin Ri`
King Island Ri` Tholeiites and Picrites
Mt Arrowsmith 585 Ma ri` basalts
f. f ?
Sinistral Transcurrent MoPon of Australian wrt AntarcPca (Mawson Craton) ??
Neoproterozoic RiXed Margin
The Earliest Stages of Delamerian in South
Australia : The IniPaPon of SubducPon
PAD32 Quartz Diorite
LD3
Cambrian Basement Thinly Covered by Young Sediments Below Murray
Basin
Quartz Diorite
517 Ma
513 Ma
LD3 deformed quartz diorite 517.9± 2 Ma
KTH12 foliated Boninite ~517 Ma?
Boninites
• The magmas that are most unequivocally of subducPon origin
• Very high MgO parent magmas • Quite SiO2-‐rich (for “basalts”) • Very depleted LREE,HFSE,LIL.. eg v. low TiO2 , Nb etc
• Product of hot, shallow melPng of depleted mantle at the INCEPTION of SUBDUCTION
Murray Basin Boninite Lava (Drill holes near Keith)
Harzburgite- Orthopyroxenite Layering towards the base of the Heazelwood complex.. Boninitic Ophiolite complex in NW Tasmania
Boninite and the initiation of subduction
• (Modern) Boninite magmatism is typically associated with high T, shallow, mantle upwelling in the forearc of oceanic arcs and often ascribed to subduction initiation
• If boninite complexes are in the margin of continents, then they are often (logically) considered to be thrust into place during arc collision and associated with subduction reversal… see Tony Crawford and Ron Berry’s model for the Tasmanian boninitic ophiolite
Issue of boninite origin. Allocthonous or Autochthonous? boninite
allocthonous boninite
Ultra-depleted mantle.. origin?
515 Ma
1350 oC
BS
B
Boninite
Deformation
BS -‐ Boninite source mantle
South Aust. Victoria
OR… Perhaps emplaced directly in the conRnental margin generated by subducRon iniRaRon beneath thinned passive margins ?
515 ± 5Ma SubducRon IniRaRon and Boninite MagmaRsm ..
Pre-‐Delamerian Ri`
Harvey’s Return, W. Kangaroo Island Deformed and metamorphosed Kanmantoo Sediment
The Compressional Stage of the Delamerian Orogen
502.42 ± 4.37 Ma
350
380
410
440
470
500
530
560
590
620
650
0 10 20 30 40 50 60 70 80 90 100
Age
(Ma)
Cumulative 39Ar Released (%)
MSWD = 0.34, probability = 0.997
504.65 ± 5.50 Ma
250 300 350 400 450 500 550 600 650 700 750 800 850 900
0 10 20 30 40 50 60 70 80 90 100
Age
(Ma)
Cumulative 39Ar Released (%)
MSWD = 0.15, probability = 0.99
Delamerian Compression 515-‐490 Ma Ar-‐Ar daPng of muscovite forming axial-‐planar fabrics to North (craton-‐ward) –verging, recumbent folding of Kanmantoo group metased. (lowest amphibolite facies).
Harvey’s Return, Western Kangaroo Island
Lower amphibolite metamorphism and folding These age may have some element of cooling (ie the event may be a li<le older)
Tasmania
IniPal Cambrian Arc (SA) 517-‐~510
E. Cambrian Sinistral Shear Australia wrt Mawson Craton/ AntarcPca
Mt Wright – Bancannia Arc 510-‐508 Ma
Stavely –”Minga” Arc 504 Ma
Mt Read Arc (505-‐495 Ma)
Stavely Volcanic Arc Felsic Volcanics Age ~503Ma
Fore-‐Arc boninite (DDH Keith K-‐12)
Eastwards Arc retreat due to slab Roll-‐Back
So if we think we have subducPon and arcs, do we have magmaPc rocks with arc-‐like chemistry?
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
Modern Calc-‐alkaline suite (Rindjani Volcano, Lombok Indonesia)
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
Stavely Arc
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
Mt Wright Arc (NSW)
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
Mt Read Arc , Tasmania
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
South Australia (Murray Basin Basement)
0.00
1.00
2.00
3.00
4.00
5.00
40.00 50.00 60.00 70.00 80.00
The SubducPon Phase (515Ma -‐ ~495 Ma)
Wt% SiO2
Wt% TiO2
South Australia, Late Tectonic (post ~ 504 Ma?)
So the late to post compressional magmas in the Murray Basin and Adelaide Hills
don’t look very arc-‐like.
RhyoliPc Ash flow tuff
PADD28: Undeformed andesite 478 ± 5 Ma
• Cambrian magma4c sequences in the Murray Basin record
1. pre-‐subducPon ri`ing : anorogenic alkalic
basalts (> 517 Ma) 2. Late Early Cambrian to upper Middle
Cambrian subducPon-‐related magmaPsm (517 -‐ ~ 505 ma)
3. Post Delamerian mafic and felsic (A-‐type granite) magmaPsm ( <490 Ma)
0
100
200
300
400
500
0 1 2 3 4 5
Zr ppm)
TiO2 Wt%
Global Back arc data set
0
100
200
300
400
500
0 1 2 3 4 5
Zr ppm)
TiO2 Wt%
MORB
Global Back arc data set
0
100
200
300
400
500
0 1 2 3 4 5
Zr ppm)
TiO2 Wt%
MORB
Rindjani (Calc Alk)
0
100
200
300
400
500
0 1 2 3 4 5
MORB
Zr ppm)
TiO2 Wt%
Mt Stavely, Mt Read, Mt Wright
0
100
200
300
400
500
0 1 2 3 4 5
More arc-‐like (earlier?) South Australian
0
100
200
300
400
500
0 1 2 3 4 5
More alkalic/ later(?) South Australian
It looks like much of the (later?) Murray Basin suite is more ri`-‐ / back arc like than axial arc-‐like
Tasmania
IniPal Cambrian Arc (SA) 517-‐~510
E. Cambrian Sinistral Shear Australia wrt Mawson Craton/ AntarcPca
Mt Wright – Bancannia Arc 510-‐508 Ma
Stavely –”Minga” Arc 504 Ma
Mt Read Arc (505-‐495 Ma)
Fore-‐Arc boninite (DDH Keith K-‐12)
Eastwards Arc retreat due to slab Roll-‐Back
Extensional TerminaPon of the Delamerian from 490 Ma
Slab roll back and outboard stepping to be re –established under the Macquarie Arc
“Padthaway Ridge” Post Tectonic A-‐type Granites (and Post-‐tectonic Mafic Magmas) Hot, dry, F-‐rich with relaPvely mantle-‐like isotopic signatures.
PAD 28
Padthaway Ridge A-‐type Granites : Late Cambrian – Early Ordovician: Post Delamerian Slab Tear/ Roll Back/ Out-‐Stepping ..~485-‐475 Ma
+/-‐
South Coast of Kangaroo Island
Evidence for transiRon to extension at ~490 Ma
238U/ 206Pb Age (Ma)
206 P
b/ 2
38U
207Pb/ 235U
238U/ 206Pb Age (Ma)
206 P
b/ 2
38U
207Pb/ 235U
206 P
b/ 2
38U
207Pb/ 235U
238U/ 206Pb Age (Ma)
238U/ 206Pb Age (Ma)
206 P
b/ 2
38U
207Pb/ 235U
206 P
b/ 2
38U
207Pb/ 235U
238U/ 206Pb Age (Ma) 238U/ 206Pb
Age (Ma)
206 P
b/ 2
38U
207Pb/ 235U
South Coast KI Migmatites: Age of Deformation and Melting
Leucosomes crystallised at ~490 ± 4.0 Ma on the south coast
• structural relationships? • timing of convergence? • crystallisation of melt? • age comparisons… • tectonic interpretation…
498.9±3.4 Ma MSWD=0.93
494.7±4.5 Ma MSWD=1.7
490.4±4.9 Ma MSWD=1.4
496.1±4.5 Ma MSWD=1.1
492.8±3.5 Ma MSWD=1.16
488.5±3.1 Ma MSWD=0.43
The Transition to ENE -WSW extension at around 490Ma
• tectonic interpretation…
tectonic interpretation…
@ 516-‐500 Ma
@ 493 Ma
σ1
σ1 σ3
σ2 σ3
σ2
σ3
σ 1
σ 1
σ2 ≈σ3
σ1 σ1
σ2
σ2 σ 1/σ2
σ 1/σ2
σ2 /σ1
σ2 /σ1
σ1 σ1
@ 491 Ma σ2
σ2
σ3
σ1
σ1
σ2 ≈σ3
σ2 ≈σ3
σ2 ≈σ3
S-type granite generation Kangaroo Island : Partial Melting of E. Cambrian Kanmantoo Grp Sediment
490 Ma extensional collapse of the Delamerian Orogen -‐> Core complex exposure on South Coast of Kangaroo Island
A-‐type magmaRsm due to asthenospheric influx due to…Slab Break-‐off and roll-‐back at 490-‐485 Ma ?
Asthenospheric up-‐welling
N
The Delamerian: the transiPon from passive to acPve subducPon margin
• Cryogenian to Early Cambrian Ri`s with developing mantle deplePon (lithospheric) and mafic underplaPng (now present as eclogite in the upper lithospheric mantle) • Mid Cambrian iniPaPon of subducPon (with boninite) and marginal deformaPon • TransiPon to arc tholeiite and calc-‐alkaline magmaPsm • EvoluPon of back-‐arc extension from the end of the middle Cambrian (back-‐arc basalts in S. Australia and W. NSW) • Catastrophic rollback/ slab tearing at ~490Ma yielding asthenosphere influx and A-‐type magmas
Passive Margin Extension:Neoproterozoic - Early Cambrian Sedimentation
East Gondwana
800- 515 Ma
Buoyant Highly Depleted MantleMantle Flow?
Plate Motion?
A
515 Ma
1350 oC
BS
B
Boninite
Deformation
BS -‐ Boninite source mantle
515 ± 5Ma SubducRon IniRaRon and Boninite MagmaRsm ..
South Aust. Victoria
~30 Ma
C
TS
Deformation
TS -‐ Arc tholeiite source mantle
515 -‐500 Ma SubducRon MagmaRsm and Delamerian Shortening
South Aust. Victoria Gawler Craton
Slab Roll-‐back
Back Arc Extensional Basin
~505-‐ 490 Ma Back Arc Extension , Slab Roll-‐Back
Stavely Arc
Victoria South Aust.
Slab steps back outboard – Macquarie Arc
490-‐470 Ma Post Tectonic Extension, UpliX, ExhumaRon Erosion
Victoria South Aust.
A-‐type Granite MagmaRsm
DelaminaPon
Slab Tear/ Break-‐off
Collins, 2002; Cawood et al. 2009 Aitchison and Buckman, 2012
DisPncPve West Pacific –Style Orogenesis
Conclusion: At least the Delamerian is an “Accordian” style orogenic
event :
• Extension • Compression • Extension
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