Tectonics, geology and origins of Te Riu‐a‐Māui / Zealandia

ABSTRACT Te Riu‐a‐Māui / Zealandia is a 95% submerged, five million square km southern hemisphere continent that includes the islands of New Zealand and New Caledonia. For the last 45 million years (Ma) Zealandia has been cut by the Pacific‐Australian plate boundary which today changes character from a west‐dipping subduction zone in the north to highly oblique, east‐dipping subduction zone in the south. Zealandia consists of Cambrian to Late Cretaceous (∼540–105 Ma) variably tectonised crystalline basement terranes and batholiths draped by Late Cretaceous to Holocene (∼105–0 Ma) Zealandia Megasequence stratified sedimentary and volcanic cover. The basement rocks formed by episodic subduction‐accretion processes along the south polar edge of the Gondwana supercontinent. At about 105 Ma long‐lived subduction was replaced by a regime of extensional tectonics and magmatism. From ∼80–60 Ma Zealandia progressively unzipped from Gondwana and, from ∼55 Ma, became a separate continent. Zealandia Megasequence sedimentary rocks form a classic transgressive‐regressive sequence with maximum marine inundation in the Oligocene (∼35–25 Ma). Zealandia Megasequence volcanic rocks formed in Gondwana rift intraplate, hotspot track intraplate, diffuse intraplate, and subduction‐related settings. Zealandia's tectonics, geology and origins provide context for understanding its natural hazards and resources.