Abstract
The cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia. Such reconstructions of Nuna fundamentally rely on palaeomagnetic and geological evidence. In the geological record, eclogite-facies rocks are irrefutable indicators of subduction and collisional orogenesis, yet occurrences of eclogites in the ancient Earth (> 1.5 Ga) are rare. Models for Palaeoproterozoic amalgamation between Australia, East Antarctica, and Laurentia are based in part on an interpretation that eclogite-facies metamorphism and, therefore, collisional orogenesis, occurred in the Nimrod Complex of the central Transantarctic Mountains at c. 1.7 Ga. However, new zircon petrochronological data from relict eclogite preserved in the Nimrod Complex indicate that high-pressure metamorphism did not occur in the Palaeoproterozoic, but instead occurred during early Palaeozoic Ross orogenesis along the active convergent margin of East Gondwana. Relict c. 1.7 Ga zircons from the eclogites have trace-element characteristics reflecting the original igneous precursor, thereby casting doubt on evidence for a Palaeoproterozoic convergent plate boundary along the current eastern margin of the Mawson Continent. Therefore, rather than a Palaeoproterozoic (c. 1.7 Ga) history involving subduction-related continental collision, a pattern of crustal shortening, magmatism, and high thermal gradient metamorphism connected cratons in Australia, East Antarctica, and western Laurentia at that time, leading eventually to amalgamation of Nuna at c. 1.6 Ga.
Highlights
The cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia
Eclogites are crucial markers of subduction-style orogenic p rocesses[19] and the c. 1720 Ma eclogites from the Miller Range have been used as a cornerstone in the interpretation that the current eastern margin of the Mawson Continent was a Palaeoproterozoic convergent plate boundary adjacent to western Laurentia (Fig. 1)
The Palaeoproterozoic record from the Nimrod Complex is in accord with other evidence of c. 1.7 Ga low-pressure, high-temperature metamorphism and magmatism extending from the North Australian Craton to the South Australian Craton, East Antarctica, and western Laurentia[24,25,26,27,28]
Summary
The cratonic elements of proto-Australia, East Antarctica, and Laurentia constitute the nucleus of the Palaeo-Mesoproterozoic supercontinent Nuna, with the eastern margin of the Mawson Continent (South Australia and East Antarctica) positioned adjacent to the western margin of Laurentia. Models for Palaeoproterozoic amalgamation between Australia, East Antarctica, and Laurentia are based in part on an interpretation that eclogite-facies metamorphism and, collisional orogenesis, occurred in the Nimrod Complex of the central Transantarctic Mountains at c. A key geological constraint underpinning Nuna reconstructions is the documentation of contemporaneous 1730–1720 Ma orogenic events in South Australia’s Gawler Craton and in the central Transantarctic Mountains of East Antarctica, which appear to link the Palaeoproterozoic Kimban Orogeny in South Australia and the Nimrod Orogeny in East A ntarctica[10,11,13,14,15] This led to the suggestion of a continuous 1730–1690 Ma collision-subduction margin connecting these two regions and defining the eastern active margin of the Mawson. Our findings highlight the importance of using trace-element compositions in zircon to distinguish eclogite-facies from igneous protolith signatures in order to evaluate the global Palaeoproterozoic record of high-pressure metamorphism and to determine the timing of amalgamation between crustal elements within supercontinent reconstructions
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