Authors / CoAuthors
Drummond, B.J. | Goleby, B.R.
Abstract
Gold deposits in the Archaean Eastern Goldfields Province in Western Australia were deposited in greenstone supracrustal rocks by fluids migrating up crustal scale fault zones. Regional ENE-WSW D2 shortening of the supracrustals was delaminated from lower crustal shortening at a regional sub-horizontal detachment surface below the base of the greenstones. Major gold deposits lie close to D3 strike slip faults that extend through the detachment surface and into the middle to lower crust. The detachment originally formed at a depth corresponding to the brittle/ductile transition. In orogenic systems the brittle/ductile transition correlates with a low permeability pressure seal separating hydrostatic fluid pressure gradients in the upper crust from suprahydrostatic fluid pressure gradients in the lower crust. Fluid pressures near the base of the low permeability pressure-seal can intermittently exceed lithostatic pressures, leading to tensile strength failure and fluid filled extension fractures. In orogens, the extension fractures will be sub-horizontal, have poor vertical connectivity and become fluids reservoirs. This would create an ideal depth to nucleate a regional detachment surface in a deforming crust. Seismic bright spots at ~6s TWT in Tibet and the western United States are probable examples. If the low permeability pressure seal is subsequently broken by a through going fault, the fluids will be drained into the upper crust. Large, deeply penetrating faults are therefore ideal for focussing fluid flow into the upper crust.
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nonGeographicDataset
eCat Id
61043
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Cnr Jerrabomberra Ave and Hindmarsh Dr GPO Box 378
Canberra
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Keywords
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- External PublicationAbstract
- ( Theme )
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- seismics
- ( Theme )
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- mineral exploration
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- AU-WA
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
Publication Date
2004-01-01T00:00:00
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geoscientificInformation
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[-32.0, -30.0, 120.0, 122.3]
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