Havre Trough

The trough extends northward from New Zealand's offshore Taupō Volcanic Zone commencing at Zealandia's continental shelf margin and continuing as a tectonic feature, as the Lau Basin which currently contains active seafloor spreading centers.

[2] The eastern basins in the trough are shallower, and associated with evidence of active extension including little sedimentary cover, high heat flow, shallow seismicity, poorly defined magnetic zones and lavas with a more pronounced island arc basalt signature as one moves west to east towards the active volcanism of the Kermadec Ridge.

[11] This is consistent with the ambient mantle wedge under the Havre Trough being Pacific during its current rifting stage of backarc development.

[12] The oldest dredged samples are as expected over 100 million years old, but most are far younger and there is compositional variation.

[11] The slightly more northern back arc Gill volcano which is towards the western area of the trough north of the Rumbles V Ridge has ages between 880,000 and 1.19 million years ago,[11] while the Rapuhia Ridge, which extends southwest from the Rapuhia volcano in the centre of the Havre Trough, so can be regarded as part of the rifting line has much younger ages of between 50,000 and 110,000 years ago.

[11] Four hundred and fifty miles to the north of the Gill volcano, in the western Harve Trough a basaltic volcanic sample was dated at 1.1 ± 0.4 Ma.

[3] It is now thought seafloor spreading at the Havre Trough started about 5.5 to 5.0 million years ago in response to the rollback of the subducting Pacific Plate and terminated abruptly about 3.0 to 2.5 million years ago[7] In the western Havre Trough the evidence for historic seafloor spreading is believed to have resulted from the initial phase of extension after the break-up of the original proto-Colville-Kermadec arc[2] (Vitiaz Arc).

[9] This means the rate of spreading and thus recent tectonics will not be resolved without drill sampling and other studies.