Finding Argoland: Reconstructing a microcontinental archipelago from the SE Asian accretionary orogen

Abstract

Based on the marine magnetic anomalies identified in the Argo Abyssal Plain offshore northwestern Australia, the conceptual continent of Argoland must have rifted off in the Late Jurassic (∼155 Ma) and drifted northward towards SE Asia. Intriguingly, in SE Asia there are no intact relics of a major continent such as India, but instead the region displays an intensely deformed, long-lived accretionary orogen that formed during more than 100 million years of oceanic and continental subduction. Within this orogen, there are continental fragments that may represent parts of Argoland. After accretion of these fragments, the orogen was further deformed. We compiled the orogenic architecture and the history of post-accretionary deformation of SE Asia, as well as the architecture and history of the NW Australian passive margin. We identified the Gondwana-derived blocks and mega-units of SW Borneo, Greater Paternoster, East Java, West Burma, and Mount Victoria Land as fragments that collectively may represent fragments of Argoland. These fragments are found between sutures with relics of Late Triassic to Middle Jurassic oceanic basins that all pre-date the break-up of Argoland. We systematically restore deformation within SE Asia in the upper plate system above the modern Sunda trench, use this to estimate where Gondwana-derived continental fragments accreted at the Sundaland (Eurasian) margin in the Cretaceous (∼110–85 Ma), and subsequently reconstruct their tectonic transport back to the Australian-Greater Indian margin. Our reconstruction shows that Argoland originated at the northern Australian margin between the Bird's Head in the east and Wallaby-Zenith Fracture Zone in the west, south of which it bordered Greater India. We show that the lithospheric fragment that broke off northwest Australia in the Late Jurassic consisted of multiple continental fragments and intervening Triassic to Middle Jurassic oceanic basins, which we here call Argopelago. Argoland broke up into Argopelago during the Late Triassic rifting of Lhasa from the northern margin of Gondwana, and consisted of multiple continental fragments that were surrounded by oceanic basins, similar to Zealandia offshore modern east Australia, and the reconstructed history of Greater Adria in the Mediterranean.