Abstract

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.
Google map showing geographic bounding box with values North bound -28.0 East bound 144.0 West bound 138.0 South bound -32.0
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Product Type/Sub Type

dataset - External Publication - Scientific Journal Paper

Constraints

license
Creative Commons Attribution 3.0 Australia Licence

IP Owner

Commonwealth of Australia (Geoscience Australia)

Author(s)

Date (publication)

2004

Product Type

dataset

Topic Category

geoscientificInformation

Keywords

External Publication
Scientific Journal Paper
Earth Sciences

Resource Language

English

Resource Character Set

utf8

Resource Security Classification

unclassified

Geographic Extent

North bound
-28.0
East bound
144.0
West bound
138.0
South bound
-32.0

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Unknown

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onLine

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distributor
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address

Metadata File Identifier

a05f7892-f9b5-7506-e044-00144fdd4fa6

Metadata Standard Name

ANZLIC Metadata Profile: An Australian/New Zealand Profile of AS/NZS ISO 19115:2005, Geographic information - Metadata

Metadata Standard Version

1.1

Metadata Date Stamp

2010-09-30

METADATA SECURITY CLASSIFICATION

unclassified

Metadata Contact

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pointOfContact
Organisation Name
Geoscience Australia
City
Canberra
Administrative Area
ACT
Postal Code
2601
Country
Australia
Email Address
Related Links
For information on acquiring this product,
please contact the Geoscience Australia Sales Centre via:

fax:
+61 2 6249 9960; or
phone:
1800 800 173 (within Australia);
 
+61 2 6249 9966 (outside Australia).

Please note that support hours are 9 am to 5 pm weekdays