GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 11-6
Presentation Time: 9:30 AM

A NUNA LAURENTIA-AUSTRALIA LINK: VIEWS FROM DOWN UNDER


BAROVICH, Karin1, WADE, Claire1, MORRISSEY, Laura2, HAND, Martin1, PAYNE, Justin2 and REID, Anthony3, (1)Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia, (2)Department of Natural and Built Environments, University of South Australia, Adelaide SA, 5001, Australia, (3)Geological Survey of South Australia, Adelaide, SA 5000, Australia

Proterozoic links between Laurentia and Australia have been speculated on for over 30 years. Connections have been based on every combination of paleomagnetic, geochemical, geochronological, lithological, geophysical and sedimentary provenance evidence. This work has been part of the larger efforts on understanding the configuration and timing of the assembly of the Proterozoic supercontinent Columbian (or Nuna). We have recently investigated two Mesoproterozoic events in southern Australia: 1) A previously unrecognized ca 1.45 Ga magmatic and metamorphic event and; 2) Mafic intrusive rocks associated with the southern Australian ca. 1590 Ma Silicic Large Igneous Province (SLIP). The ca 1.45 Ga magmatism and high geothermal gradient metamorphism in southern Australia shares similarities to some aspects of the widespread southern Laurentian A-type magmatism, sedimentation and metamorphism. This correlation would pull Australia further south along Laurentia than its position in proto-SWEAT configurations. Mafic intrusives related to the ca. 1590 Ma southern Australian SLIP, covering 2500 km2 in the subsurface, are generally characterised by enrichment in high field strength elements (HFSE) and light rare earth element (LREE), negative Nb-Ta-Ti anomalies, and variable Nd isotopic compositions. Th/Nb ratios for the suite are mostly high and the vast majority of ╬ÁNd(t) values are slightly negative. The mantle source for the magma is interpreted to be dominantly sub-continental lithospheric mantle (SCLM) with varying magma compositions interpreted to represent a heterogeneous and enriched SCLM. Previous work has suggested a plume centre for this SLIP that can also explain ca. 1590 Ma Western Laurentian dike swarms. This configuration is more akin to the proto-SWEAT configurations that place southern Australia adjacent to northern Laurentia. These two studies support previous suggestions of southerly translation of Australia from a proto-SWEAT position from after about 1.6 Ga to 1.5 Ga.