From Geoscience Australia
JSON format icon JSON RDF format icon RDF ISO19115-3 XML

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

Created 17/10/2025

Updated 17/10/2025

JSON format icon JSON RDF format icon RDF ISO19115-3 XML

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.

Files and APIs

Tags

Additional Info

Field Value
Title Evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a Proterozoic continental rift sequence at Broken Hill, Australia
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/233a00d1-728e-4ae3-95dd-c08613ba8999
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 22/04/2018
Geospatial Coverage
Map data © OpenStreetMap contributors
{
  "coordinates": [
    [
      [
        138.0,
        -32.0
      ],
      [
        144.0,
        -32.0
      ],
      [
        144.0,
        -28.0
      ],
      [
        138.0,
        -28.0
      ],
      [
        138.0,
        -32.0
      ]
    ]
  ],
  "type": "Polygon"
}
Data Portal Geoscience Australia

Data Source

This dataset was originally found on Geoscience Australia "Evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a Proterozoic continental rift sequence at Broken Hill, Australia". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/evidence-and-timing-of-crustal-extension-versus-shortening-in-the-early-tectonothermal-evolutio