Tectonic evolution and crustal growth processes revealed by detrital zircon petrochronology: Insights from dispersed Paleozoic-Mesozoic sedimentary basins of Zealandia

Campbell, Matthew J 1, Rosenbaum, Gideon 1, Allen, Charlotte M. 2, Spandler, Carl 3

1School of Earth and Environmental Sciences, The University of Queensland, Brisbane, QLD, Australia,  2Institute for Future Environments, Queensland University of Technology, Brisbane, QLD, Australia, 3Geosciences, James Cook University, Townsville, QLD, Australia.

Paleozoic-Mesozoic supra-subduction units, which originally formed along the paleo-Pacific margin of east Gondwana, are now preserved in eastern Australia, Antarctica and Zealandia. Previous works have characterized the temporal and geochemical history of magmatism within this broad accretionary orogenic system but the Zealandia continent remains a problematic piece of the Gondwana puzzle due to (1) 94% of the continent being submerged beneath the southwest Pacific Ocean and (2) a number of major phases of deformation that culminated in the oceanward dispersal of continental fragments of Zealandia. Here we reconstruct the Paleozoic and Mesozoic evolution of the active continental margin of Zealandia (eastern Gondwana), using a combination of detrital zircon geochronology, trace-element geochemistry, and Hf isotope data from several Paleozoic-Mesozoic terranes in New Zealand and New Caledonia. We find that zircon grains dated 360–160 Ma from New Zealand are characterized by εHfi (+15 to +2) and trace-element compositions typical of predominantly juvenile magmatic sources. In contrast, the εHfi (+15 to –5) and trace-element compositions of detrital zircon grains dated 245-140 Ma from New Caledonia reflect a mix of juvenile and evolved crustal sources. Secular trends in trace-element and Hf isotope compositions of zircon grains suggest that magmatism and continental crustal growth in Zealandia during the Devonian–Cretaceous were controlled by switches from trench advance to trench retreat. Orogenesis and crustal growth were controlled by a long-lived westward-dipping subduction system, which during the Permian–Triassic, was intermittently affected by distinct phases of arc accretion (e.g., of the Brook Street intra-oceanic arc) and orogenesis (e.g., driven by trench advance). These phases of orogenesis coincided with the Gondwanide Orogen (265–230 Ma), which might have been controlled by a plate-scale reorganization event following the final assembly of Pangea supercontinent.


Biography

Recent PhD graduate in geology from the University of Queensland. My PhD was focused on the Paleozoic to Mesozoic tectonic history and crustal architecture of the southwest Pacific region (Zealandia).

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