Continental Crustal Growth Processes Revealed by Detrital Zircon Petrochronology: Insights From Zealandia

Establishing spatial, temporal, and geochemical relationships between magmatism and the broader tectonics of accretionary orogens is important for understanding continental crustal growth processes. 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. 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 intraoceanic 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.