Magnetotelluric imaging of intracontinental deformation zones: example of the Musgraves Province in Central Australia

S. Thiel1,2, B. Goleby3, G. Heinson2

1Geological Survey of South Australia, Adelaide, Australia

2The University of Adelaide, Adelaide, Australia

3OPM Consulting

Musgrave Province

• Area of intraplate deformation

• At the triple junction between WAC,

NAC, SAC

• Interesting for mineralization

associated with Giles Complex, e.g.

Ni potential of Nebo Babel

• Central Australia largely dominated

by EW trending structure due to NS

compression, decoupled from

western or eastern Australia

• 1.6 Ma ages throughout, subsequent

deformation events younging to the

west.

Gawler Craton

Coompana

Province

Musgrave Province

Mundrabilla

Shear zone

Moho and LAB depth

Kennett et al., 2013, AusREMSalmon et al., 2013

Geophysical signatures of the 1070 Ma Warakurna LIP

• Alghamdi et al., 2018

• Higher crustal density associated with

mafic underplate of Warakurna Large

Igneous Province linking to the Giles

Complex

Wade et al., 2008

Musgrave Geology

Gravity Map

Age Event Orientations / Observations

~ 1680 – 1550 Ma Volcanic Arc formation - sedimentation, volcanism

and granite intrusions (Birksgate Complex)

?Volcanic Arc – N-S orientated

~ 1340 – 1270 Ma Wirku Metamorphics Deposition of sediments

~ 1300 Ma Wankanki Supersuite - Mount West Orogeny c.

1345 to 1293 Ma.

Orientation Unknown?

~ 1220 – 1120 Ma Musgravian Orogeny - granite intrusions,

deformation and high grade metamorphism

E-W major shear zones - east-west ”grain” (e.g. Hinckley-Scarface,

Mann-Ferdinand, Davenport and Woodroffe Shear Zones). MO

structures typically NW-SE close folding

~ 1085 – 1040 Ma Layered ultramafic–mafic–anorthosite intrusions

(Giles Complex), dolerite, granite and volcanics and

rift sediments - rift architecture

Part of the Warakurna Large Igneous Province, affecting much of

central and western Australia.

broadly N-S to NE-SW shortening, NW-SE extension

~ 1000 Ma Regional olivine dolerite (Kullal) dyke intrusion

~ 825 – 760 Ma Regional dolerite (Amata) dyke swarms

~ 850 – ~ 540 Ma Sedimentation around margins (Centralian

Superbasins)

Deposition of sediments

~ 570 – 530 Ma Petermann Orogeny - crustal shortening including

thrust faulting and thrust nappes

Reactivation of several crustal scale east-west trending shears under

horizontal compression of the lithosphere - high strain zones along

existing shear zones

~ 530 Ma Final thrust exhumation of the Musgrave Block from

beneath the Centralian Superbasins

N-S Shortening

~ 380 Ma Alice Springs Orogeny - significant alteration and

faulting. uplift of the Arunta Block from beneath the

Centralian Superbasin

N-S Compression

From: http://minerals.statedevelopment.sa.gov.au/geoscience/geology/musgrave_province

The Musgrave Province MT Survey – SA AusLAMP

• Access to 25 long period (approx. 1 – 104 s)

ANSIR MT Systems recorders housed at Adelaide

University, each unit comprising

• Earth Data Logger,

• Bartington Fluxgate Magnetometers,

• Pb-Pb Electrodes

• Solar Panel and Battery

Model fits

SA AusLAMP Musgraves MT Data

Modeling parameters• A total of 96 stations spaced roughly 50 km inverted using

Z and T to final rms of 2.10

• 23 periods (8 s – 16,000 s) for Z, with error floors of 3%

and 10% for the off-diagonal and diagonal elements,

respectively

• 21 periods (8 s – 7000 s) for T, 0.03 error floor

• Size of the model is 2517 x 2805 x 2131 km with 115 x 163

x 81 cells in x,y,z-direction

• Horizontal cell size is 6 km x 6 km around stations with 15

padding cells each side

• Vertical cell thickness is 50 m beneath the surface,

increasing by a factor of 1.11

• 100 Ωm starting half-space, bathymetry (0.3 Ωm sea

resistivity) and ocean sediments

Upper crustal model slices.

Nebo Babel

Mid-lower crust model slices. East west trend.

Nebo Babel

Mid-lower crust model slices. East west trend.

Follows the gravity signature, Moho offset?

Mantle model slices. East west trend turning to NNE trend.

65 km depth 100 km depth

Moho uplift

Conclusions

• Western N-S conductivity trends reflect a Mesoproterozoic N-S boundary edge

along which volcanic arc was formed and which was reactived at various times

• E-W conductivity grain within the model reflects initial Musgravian Orogeny

deformation that was also reactivated at later times

• Good similarity of the E-W resistivity distribution in the crust with the regional

gravity highs.

• Evidence that the mantle is retaining earlier lithospheric structures and therefore has

been attached to the crust since the Mesoproterozoic.

Acknowledgements

• Funding through AuScope Ltd. And Geological Survey of South Australia

• AuScope technical officer Goran Boren for keeping the instruments alive

• AusLAMP SA acquisition crew: Philippa Mawby, Geoff Axford and Dr Bruce Goleby

• Traditional Owners and landholders for land access

• National Computational Infrastructure for running 3D inversions using ModEM (Kelbert et al., 2014, Egbert and Kelbert, 2012)

• Images produced with GMT, MTPy and 3Dgrid

GSSA Upcoming Events

4th December 2018 - Gawler Craton Airborne

Survey (GCAS) Workshop

5th December 2018 - National MT Workshop and

AusLAMP SA Release Day

6th December 2018 – Discovery Day

7th December 2018 - South Australian Exploration

and Mining Conference (SAEMC)

Contacts

Stephan Thiel, Program coordinator – Lithospheric Architecure

E: stephan.thiel@sa.gov.au

Department for Energy and Mining

11 Waymouth StreetAdelaide, South Australia 5000

GPO Box 320Adelaide, South Australia 5001

E: demreception@sa.gov.au

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