Evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a Proterozoic continental rift sequence at Broken Hill, Australia

Low-pressure (P) high-temperature (T) metamorphism previously attributed to crustal thickening accompanying nappe emplacement in the Paleoproterozoic Willyama Supergroup at Broken Hill is reinterpreted as a response to crustal extension (D1) and bimodal magmatism commencing circa 1700 Ma. D1 deformation occurred under amphibolite-granulite facies conditions, producing layer-parallel fabrics (S1) and metapelitic mineral assemblages in which andalusite dominated over sillimanite. Crustal extension ceased soon after 1640 Ma to be followed by crustal thickening, higher-pressure metamorphism, and northeast vergent recumbent folding (D2) attendant on inversion of the original D1 extensional structures. D2 recumbent folding has previously gone unrecognized but probably peaked around 1600 Ma before further amphibolite facies metamorphism between 1600 and 1590 Ma accompanying upright folding and northwest directed thrust faulting (D3). In the light of this revised tectonothermal history, geodynamic models erected to explain elevated thermal gradients and low-P-high-T granulite facies metamorphism in tectonically thickened crust may not be as relevant to Broken Hill as once thought. Above average crustal temperatures and low-P-high-T metamorphism in the Willyama Supergroup more likely occurred in response to voluminous magmatic intrusion accompanying crustal thinning, mantle upwelling and emplacement and unroofing of midcrustal rocks along a major detachment surface. A second major structural and/or stratigraphic break in the Willyama Supergroup is indicated by the absence of D1 fabrics from the uppermost part of the sequence.

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Date (Publication)
2004-01-01T00:00:00
Citation identifier
Geoscience Australia Persistent Identifier/https://pid.geoscience.gov.au/dataset/ga/71093

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Digital Object Identifier/http://dx.doi.org/10.1029/2003TC001552

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Gibson, G.M.

 1
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Peljo, M.

 2
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Chamberlain, T.

 3
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MNHD
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Commonwealth of Australia (Geoscience Australia)
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Commonwealth of Australia (Geoscience Australia)

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Australian and New Zealand Standard Research Classification (ANZSRC)

  • Earth Sciences

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2018-11-01T00:00:00
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English
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Australian Government Security ClassificationSystem

Edition date
2018-11-01T00:00:00
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https://www.protectivesecurity.gov.au/Pages/default.aspx

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Unclassified

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urn:uuid/a05f7892-f9b5-7506-e044-00144fdd4fa6

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English
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UTF8
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Commonwealth of Australia (Geoscience Australia)

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nonGeographicDataset

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Geoscience Australia - short identifier for metadata record with

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eCatId/71093

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https://ecat.ga.gov.au/geonetwork/srv/eng/catalog.search#/metadata/a05f7892-f9b5-7506-e044-00144fdd4fa6

Date info (Revision)
2018-04-22T08:44:53
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2010-09-30T00:00:00

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AU/NZS ISO 19115-1:2014

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ISO 19115-1:2014

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ISO 19115-3

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Geoscience Australia Community Metadata Profile of ISO 19115-1:2014

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Version 2.0, September 2018

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https://pid.geoscience.gov.au/dataset/ga/122551

 
 

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