Evolution and interaction of migrating cross‐arc volcanism and backarc rifting: An example from the Southern Havre Trough (35°20′–37°S)

The active southern Havre Trough (35°20′ – 37°S) backarc basin is interpreted to form from the evolution and interaction of migrating cross‐arc magmatism, and the progressive development of longitudinal rift grabens. The proposed migration of the proto‐Kermadec arc front from the Colville arc at ∼5 Ma to the active Kermadec arc margin is recorded by the construction of arc edifices trailed across the intervening, and contemporaneously rifting, backarc complex. Migration trails are identified for at least four arc volcano sources. The Rumble V arc migration trail is the most prominent, forming a continuous, high‐standing, magmatic arc ridge. These postulated arc trails segment the backarc region and initially limit rift development to the intervening proto‐arc crust blocks. Early rifting between the arc volcanoes forms fully developed rift grabens which, with progressive basin widening, propagate longitudinally across the trails of migrating constructional arc magmatism. A model of the balance between rates of constructional arc magma production M R and destructive back‐arc (rifting) extension V E is proposed. When V E is high, M R is insufficient to keep abreast of destructional rifting, resulting in small, isolated arc massifs quickly dismembered by rifting. Conversely, when V E is low, M R is sufficiently greater than rifting to produce a continuous, high‐standing cross‐arc ridge which segments longitudinal rift development. Migrating arc magmatism will be best observed, and preserved, in rifting backarc basins when M R is >600 km 3 m.y. −1 100 km −1 of plate boundary and V E is <25 mm a −1 .