2015 Broken Hill Resources Investment Symposium - University of Adelaide - John Foden
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"Delamerian Orogeny". Professor John Foden, University of Adelaide. Technical presentation at 2015 Broken Hill Resources Investment symposium.
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2015 Broken Hill Resources Investment Symposium - University of Adelaide - John Foden
- 2. 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
- 3. 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
- 4. Li and Evans (2011) The “Palaeo-‐Pacific” east Gondwanan Passive Margin Palaeo Pacific
- 5. 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
- 6. Delamerian Foreland Fold-‐ Thrust Belt, N. Kangaroo Island
- 7. Lower Ordovician Owen Conglomerate Delamerian Unconformity Burnie FormaPon (Late Neoproterozoic) The Delamerian in Tasmania
- 8. Tasmania.. “Tyennan” = Delamerian
- 9. The “Delamerian” = the Ross Orogen in the TransantarcRc Mountains ~550 Ma
- 10. 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
- 11. Pampeanas (555Ma-515 Ma) Saldania (Cape) (555Ma-510 Ma) The Gondwanan Pacific Margin: Terra Australis Orogen (Cawood, 2005) Ross (540Ma- 490 Ma) Delamerian (515Ma- 490 Grenville & Pan- African Foldbelts Palaeozoic Additions 555-‐515Ma Progressive decrease in age S to N: = assembly of east and west Gondwana fragments
- 12. 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
- 13. 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
- 14. The Earliest Stages of Delamerian in South Australia : The IniPaPon of SubducPon
- 15. PAD32 Quartz Diorite LD3 Cambrian Basement Thinly Covered by Young Sediments Below Murray Basin Quartz Diorite 517 Ma 513 Ma
- 16. LD3 deformed quartz diorite 517.9± 2 Ma KTH12 foliated Boninite ~517 Ma?
- 17. 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
- 18. Murray Basin Boninite Lava (Drill holes near Keith)
- 19. Harzburgite- Orthopyroxenite Layering towards the base of the Heazelwood complex.. Boninitic Ophiolite complex in NW Tasmania
- 20. 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
- 21. Issue of boninite origin. Allocthonous or Autochthonous? boninite allocthonous boninite Ultra-depleted mantle.. origin?
- 22. 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`
- 23. Harvey’s Return, W. Kangaroo Island Deformed and metamorphosed Kanmantoo Sediment The Compressional Stage of the Delamerian Orogen
- 24. 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)
- 25. 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
- 26. So if we think we have subducPon and arcs, do we have magmaPc rocks with arc-‐like chemistry?
- 27. 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)
- 28. 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
- 29. 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)
- 30. 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
- 31. 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)
- 32. 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.
- 33. RhyoliPc Ash flow tuff PADD28: Undeformed andesite 478 ± 5 Ma
- 34. • 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)
- 35. 0 100 200 300 400 500 0 1 2 3 4 5 Zr ppm) TiO2 Wt% Global Back arc data set
- 36. 0 100 200 300 400 500 0 1 2 3 4 5 Zr ppm) TiO2 Wt% MORB Global Back arc data set
- 37. 0 100 200 300 400 500 0 1 2 3 4 5 Zr ppm) TiO2 Wt% MORB Rindjani (Calc Alk)
- 38. 0 100 200 300 400 500 0 1 2 3 4 5 MORB Zr ppm) TiO2 Wt% Mt Stavely, Mt Read, Mt Wright
- 39. 0 100 200 300 400 500 0 1 2 3 4 5 More arc-‐like (earlier?) South Australian
- 40. 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
- 41. 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
- 42. Extensional TerminaPon of the Delamerian from 490 Ma Slab roll back and outboard stepping to be re –established under the Macquarie Arc
- 43. “Padthaway Ridge” Post Tectonic A-‐type Granites (and Post-‐tectonic Mafic Magmas) Hot, dry, F-‐rich with relaPvely mantle-‐like isotopic signatures.
- 44. PAD 28
- 45. Padthaway Ridge A-‐type Granites : Late Cambrian – Early Ordovician: Post Delamerian Slab Tear/ Roll Back/ Out-‐Stepping ..~485-‐475 Ma +/-‐
- 48. South Coast of Kangaroo Island Evidence for transiRon to extension at ~490 Ma
- 49. 238U/ 206Pb Age (Ma) 206Pb/238U 207Pb/ 235U 238U/ 206Pb Age (Ma) 206Pb/238U 207Pb/ 235U 206Pb/238U 207Pb/ 235U 238U/ 206Pb Age (Ma) 238U/ 206Pb Age (Ma) 206Pb/238U 207Pb/ 235U 206Pb/238U 207Pb/ 235U 238U/ 206Pb Age (Ma) 238U/ 206Pb Age (Ma) 206Pb/238U 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
- 50. 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 σ2σ 1/σ2 σ 1/σ2 σ2 /σ1σ2 /σ1 σ1σ1 @ 491 Ma σ2 σ2 σ3 σ1 σ1 σ2 ≈σ3 σ2 ≈σ3 σ2 ≈σ3
- 51. 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
- 52. A-‐type magmaRsm due to asthenospheric influx due to…Slab Break-‐off and roll-‐back at 490-‐485 Ma ? Asthenospheric up-‐welling N
- 53. 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
- 54. Passive Margin Extension: Neoproterozoic - Early Cambrian Sedimentation East Gondwana 800- 515 Ma Buoyant Highly Depleted MantleMantle Flow? Plate Motion? A
- 55. 515 Ma 1350 oC BS B Boninite Deformation BS -‐ Boninite source mantle 515 ± 5Ma SubducRon IniRaRon and Boninite MagmaRsm .. South Aust. Victoria
- 56. ~30 Ma C TS Deformation TS -‐ Arc tholeiite source mantle 515 -‐500 Ma SubducRon MagmaRsm and Delamerian Shortening South Aust. Victoria Gawler Craton
- 57. Slab Roll-‐ back Back Arc Extensional Basin ~505-‐ 490 Ma Back Arc Extension , Slab Roll-‐Back Stavely Arc Victoria South Aust.
- 58. 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
- 59. Collins, 2002; Cawood et al. 2009 Aitchison and Buckman, 2012 DisPncPve West Pacific –Style Orogenesis
- 60. Conclusion: At least the Delamerian is an “Accordian” style orogenic event : • Extension • Compression • Extension