Morphostructure and magnetic fabric of the northwestern North Fiji Basin

Four successive spreading phases are distinguished in the northwestern part of the North Fiji Basin. After an initial NE‐SW opening, a N‐S spreading phase took place, up to the northwesternmost tip of the basin, along the South Pandora, Tikopia and 9°30 Ridges. The N‐S spreading phase in the northern North Fiji Basin was followed by an E‐W opening phase along the central North Fiji Basin axis. A triple junction was probably active during an intermediate stage between the two phases. E‐W spreading underwent a reorganisation that induced the functioning of the 16°40′S triple junction and the development of the E‐W trending Hazel Holme Extensional Zone from the active central spreading axis to the southern tip of the New Hebrides Back‐Arc Troughs. Active extension also occurs along the E‐W Santa Cruz Trough which crosscuts the arc platform at the northern end of the N‐S trending Back‐Arc Troughs. The existence of the Back‐Arc Troughs is mainly due to the construction of the 400 km‐long volcanic Duff Ridge which trapped a piece of the old North Fiji Basin oceanic crust.