Mount Isa Seismic Workshop, June 2008
Seismic reflection profiling as a tool to better understand the
geodynamic and metallogenic evolution of the Mount Isa Inlier
George Gibson (plus GA, GSQ & pmd*CRC team)
Acknowledgements: Peter Southgate, Narelle Neumann, Dave Huston (GA); Dave Mason (GSQ) & Russell Korsch (pmd*CRC)
Australian Government
Geoscience Australia
Mount Isa Seismic Workshop, June 2008
Specific Scientific Objectives:
• Acquire series of E-W and N-S transects to image crustal architecture of Western and Eastern Successions and adjacent undercover areas
• Integrate seismic with potential field and geological datasets to constrain 3D and 4D models for the Mount Isa Inlier
• Determine depth, geometry & distribution of pre-1800 Ma basement
• Capture deep-tapping faults & low-angle detachments• Determine extent & geometry of basin inversion• Determine structural & crustal setting of
mineralisation– Zn-Pb-Ag– Au, Cu (IOCG)
Mount Isa Seismic Workshop, June 2008
Getting down to business: capturing basin & crustal architecture in seismic reflection images
What gets imaged:• Moho• Non-vertical faults & shear
zones (incl. detachments)• Basement topography• Unconformity-bounded
supersequences• Basin margins & sedimentary
stacking patterns (pre-, syn- & post-rift sequences)
• Basin inversion structures (thrusts, reactivated normal faults)
From McClay 2007
From McClay 2007
Mount Isa Seismic Workshop, June 2008
Seismic maps sequence not lithostratigraphic boundaries
(Bradshaw & Scott, 1999)
Mount Isa Seismic Workshop, June 2008
Seismic maps sequence not lithostratigraphic boundaries: Upper vs. Lower Gunpowder Formation
Gun Supersequence Prize SupersequenceSequence Boundary ~20my missing
Mount Isa Seismic Workshop, June 2008
Gunpowder
Mount Oxide
Seismic maps unconformity bounded sedimentary packages:
-
Base Gun Supersequence
in mapped
Gunpowder Creek Formation -
Sharp lithological change
-
Abrupt facies change
Mount Isa Seismic Workshop, June 2008
For successful interpretation of seismic data & mineralising system need to know:
• Geodynamic evolution• Temporal Framework
– Isotopic dating– Sequence Stratigraphy (correlatable
surfaces)– syn-sedimentary (Pb-Zn?) vs syn-inversion
age (Cu) for mineralisation– Tectonothermal & magmatic history
Mount Isa Seismic Workshop, June 2008
Western Succession supersequences
&
mineralisation events
Guide
Myally
Big
Quilalar
Prize
Gun
Loretta
Term
River
Lawn
WideDoom
Leic
hhar
dtC
alve
rtIs
a
Three Superbasins:•Isa Superbasin (~1670-1575 Ma) •Calvert Superbasin (~1740-1690 Ma) •Leichhardt Superbasin (~1790-1750 Ma)
•Alternatively, Gun Supersequence is part of Calvert Superbasin
•Pb-Zn & U mineralisation associated with supersequence boundaries
ZincDeposits
UraniumDeposits
Mount Isa Seismic Workshop, June 2008
Geodynamic framework: passive margin setting or failed rift?Geological elements:
• Western & eastern successions
Stacked superbasins
• Isa (1650-1595 Ma)
• Calvert (1730-1650 Ma)
• Leichhardt (1800- 1750 Ma)
Isa Superbasin
Calvert & Leichhardt
Rift Geometrypreserved
Inversionstructuresdominant
Mount Isa Seismic Workshop, June 2008
Transgression/Sag Phase
Renewed extension
Isa superbasin –sag or foreland
basin ?
Syn-rift(Fluviatile-lacustrine)felsictholeiitic bimodal
Syn-rift(Fluviatile-shallow marine)
bimodal
Basin InversionIsa D2
(1585 Ma)
Isa D1 (1640- 1600 Ma)
Calvert Superbasin
(1730-1670 Ma)
Leichhardt Superbasin
(1800-1750 Ma)
Gun Supersequence (1670-1645 Ma?)
1800
1750
1650
1700
1575
1600
Ma Isa Superbasins
& Stacking
Mount Isa Seismic Workshop, June 2008
Sybella
Granite
Leichhardt
CalvertPost-rift sediments
Syn-rift sediments
Syn-rift sediments
Syn-rift volcanics
Syn-rift volcanics
(ECV)
(Fiery Ck)
N
10 km
Myally
Subgroup 3D
Isopach
Map0km
1km
1.5km
Leichhardt River Fault
Trough
Twenty-nine Mile FZ
Leichhardt Superbasin
-
syn-rift sediments (Myally)
Mount Isa Seismic Workshop, June 2008
NW-SE oriented growth faults
Fluviatile –shallow marine sedimentary facies (west)
Deep marine (east & NE)
Calvert Superbasin: Surprise Creek Formation (1690 Ma)
3xVertical Exaggeration
Gunpowder
Mt Isa
Mt Watson
0 Km
5.5 km
σ3
σ3
Soldiers Cap Group : Eastern Succession (1685 Ma)
N
Mount Isa Seismic Workshop, June 2008
Superbasin
formation accompanied by:Superbasin
formation accompanied by:
Leichhardt Superbasin:
•Bimodal magmatism (including continental flood basalts)
•Half-graben formation
•Mid-crustal detachment faulting (Eastern Succession)
Calvert Superbasin:
•Bimodal magmatism (including oceanic tholeiites)
•Magmatic inflation & doming
•Uplift & erosion
•Extensional unroofing of mid- crustal rocks & 1670 Ma granite
Upper Plate
Lower Plate
Wonga
GraniteDetachment
Post-rift = sag
Holcombe et al., 1991
NE SW
(1780-1740 Ma)
Mount Isa Seismic Workshop, June 2008
Crustal
Thinning
Fluviatile-
Lacustrine
Fluviatile –Shallow Marine
Deep Water–
Open Marine
IntracontinentalRift
DevelopingPassive Margin;
Off-shelf
Mount Isa Seismic Workshop, June 2008
Syn-rift Depositional Environment through timeSyn-rift Depositional Environment through time
Dyke
Mount Isa Seismic Workshop, June 2008
•Younger basins better preserved on Lawn Hill Platform (Lines M1-M2)
•Leichhardt basin geometry (M3)
•Calvert & Isa basin geometries (M2)
•D1 inversion (M1 & M2)
•D2 inversion (M2 & M3)3
M1
M2
M3
Seismic as a test of previously inferred crustal geometries
Regional tilt
Calvert-Isa
Leic
hhar
dt
D1
D2
Mount Isa Seismic Workshop, June 2008
1
2
Little Ra. FZTermite Ra. FZ
RiversleighFZ
NE-trending faults best imaged in M1
Mount Isa Seismic Workshop, June 2008
30km
BMR1
M6
M5
M4BMR2
Seismic Lines 4-6:
•Rift geometry preserved in west
•Basement exposed in central zone (LK)
•Rift basins inverted in east
•Mid-crustal detachments
sw NEAtlas MountainsINVERSION FEATURES:
•Harpoon structures
•Segmented asymmetric hangingwall
anticlines
LK