Dalamerian Lachlan transition - Department of Primary ......S. Soengkono, Journal of Volcanology and...
Transcript of Dalamerian Lachlan transition - Department of Primary ......S. Soengkono, Journal of Volcanology and...
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Transition between the Delamerian and Lachlan Orogens
A ramble through the Koonenberry Belt, Stawell Zone, Dimboola Arc, Thomson Orogen, and the Macquarie Arc
Bob MusgraveWith much assistance from
John Greenfield and Phil Gilmore
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Let’s look at where we are…
“Tasman line”
Koonenberry Belt
TMIGeoscience Australia
Tilt-filter on TMIGeological Survey of NSW
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Koonenberry Belt: Geological outline
250 km
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Elements of the Mt Wright (Koonenberry) Arc
• Arc• Back-arc• Fore-arc/accretionary prism• Continental backstop (including
Neoproterozoic rift volcanics)
Mt Wright Volcanics+ Bancannia Trough
Tilt-filter + TMI, with gravity
“worms”
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Potential field modelling
Bouguer gravityTotal Magnetic Intensity
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Deep structure: reflection seismics and potential field modelling
TMI
1VD
Bouguer grav
Low-pass grav
TMI
1VD of TMI
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Modelling 3D structure
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Koonenberry 3D model
Mt Wright Arc
Mt Arrowsmith – deep bodies
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• Linear structure of Koonenberry Belt looks simple enough – but note:
• Broad magnetic anomalies in Bancannia Trough – Mt Wright Volcanic Arc under Devonian basin
• Re-entrant bend at Grasmere Knee Zone – and nearby deep magnetic sources
• Bend at the Cobham Kink Zone – and “mystery” deep reversed remanence source
• And note how the gravity “ignores” both bends in the linear belt
– Suggests the bend is restricted to shallower structure
Structures from potential fields
Curnamona
Koonenberry Belt
Bancannia Trough
Grasmere Knee Zone
Cobham Kink Zone Mystery
source
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Restoring the Bancannia rift20°
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New Zealand CVZ and Bancannia
Parson & Wright, 1996
2.3 A/m
S. Soengkono, Journal of Volcanology and Geothermal Research 68 (1995) 193-207
Thanks to Supri Soengkono and Glass Earth (NZ) Inc
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Grasmere Knee Zone: subducted seamount in accretionary margin?
0 20
km
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Seamount subduction
Dominguez et al., 1998, 2000
Kodaira et al., 2000
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Thomson accretionary margin: Benambran overprint on Delamerian wedge
Seamount deformation in the Thomson Orogen?
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Thomson Orogen arc-arc collision?
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Stawell
Bendigo
StavelyGlenelg
Hay- Booligal
Bootheragandra
Fault
Thomson
Delamerian accretionary margin - connection to the Stawell Zone
Scheibner & Basden, 1998
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Delamerian and Benambran
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Ponto GroupMarine- pelagic mudstone—siltstoneFelsic tuff (Mt Wright Arc equivalent)Mte-Qtz exhalativebasalt lava, tuff (tholeiite, MORB)
~511 Ma
(Evans 1993)
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Grasmere (Ponto Gp) – Besshi-style VMSLate
qtz-carb-chalveins in FW
HWNon-mag
Massive sulphide ore
Brecciated & MS ore
FWMag
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Orogenic Au - Warratta Inlier
Victorian Goldfields(Ramsay, 1998)
Australian Earth Sciences Convention, Perth, July 2008Warratta Inlier (Greenfield, 2008)
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Mt Wright – Menidee – Dimboola Arc?
Dimboola Arc:Cambrian calc-alkaline volcs, supra- subduction zone ophiolite (oceanic arc)
Volcanic basement of Stawell Zone: Cambrian tholeiites, Besshi-style VMS, Benambran gold
Mt Wright (Koonenberry) Arc:Cambrian calc-alk volcs in rifted arc setting on continental margin.
Ponto Group: Cambrian tholeiites, Besshi-style VMS
Warrata inlier: Benambran orogenic gold
Bendigo Zone: Benambran orogenic gold