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The Oenpelli Dolerite - a Precambrian continental tholeiitic suite from the Northern Territory, Australia

Created 17/10/2025

Updated 17/10/2025

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The Oenpelli Dolerite comprises at least four major sheet-like intrusions up to 250 m thick of continental tholeiitic composition, which have a lateral extent of about 20 000 km^2. The intrusions were emplaced at about 1720 m.y. into Lower Proterozoic metasediments of the Pine Creek Geosyncline, and postdate an 1880 m.y. regional metamorphic event. The intrusions consist of symmetrically differentiated layers of olivine dolerite, minor felsic differentiates, and rare crosscutting gabbroic pegmatites. Within the thicker sheets minor rhythmic layering is found in olivine dolerite. The Oenpelli Dolerite contains normative orthopyroxene and the major and trace element chemistry closely parallels the trends of major continental mafic tholeiitic suites. Projection of the chemical data into the anhydrous CMAS system shows that the rocks crystallised in the pressure range 1 atmosphere to 5 kb. The close match between the observed equilibrium and the 1 atmosphere phase diagrams for dry tholeiitic magmas suggests that the last equilibration of these magmas was at very low pressure. It is concluded that the tholeiitic Oenpelli Dolerite rocks have evolved by polybaric olivine fractionation during slow, or intermittent, uprise from higher magnesia magma generated by partial melting within the upper mantle; plagioclase is an additional liquidus phase at shallow-crustal levels.

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Field Value
Title The Oenpelli Dolerite - a Precambrian continental tholeiitic suite from the Northern Territory, Australia
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/a6aecc5a-21c1-4860-84ee-84cd44b63d53
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 20/04/2018
Geospatial Coverage
Map data © OpenStreetMap contributors
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      [
        132.25,
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      ],
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    ]
  ],
  "type": "Polygon"
}
Data Portal Geoscience Australia

Data Source

This dataset was originally found on Geoscience Australia "The Oenpelli Dolerite - a Precambrian continental tholeiitic suite from the Northern Territory, Australia". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/the-oenpelli-dolerite-a-precambrian-continental-tholeiitic-suite-from-the-northern-territory-au