Kermadec rocks reveal tectonic youth

In the paper ‘Ar-Ar age constraints on the timing of Havre Trough opening and magmatism’ published in the New Zealand Journal of Geology and Geophysics, researchers have been using Ar-Ar dating on rocks from the Havre Trough. Ar-Ar is an accurate form of dating established by testing Argon found in rock samples. The results from the data suggest that the Kermadec Arc and associated Havre Trough subduction system are, geologically-speaking, very young.

The present-day Kermadec Arc is formed due to the convergence of the Pacific and Australian Plates.  This convergence is occurring at a rate of 11cm per year – which may be one of the fastest rates on Earth.  The result is a system of arcs and troughs that make the Kermadec Arc so distinctive. The Kermadec Ridge goes from northeast of the Bay of Plenty towards Tonga and features approximately 50 volcanoes, most of which are submarine. 

The area around the Kermadec Arc is important from a global perspective due to its amazing biodiversity and geology. It is recognised as a globally important marine area due to the plethora of marine life that call it home — including whales, sharks, turtles and the unique animals that live around the hydrothermal vents.

The Kermadec area also plays an important historical role in linking Polynesian travellers to Aotearoa New Zealand.

The Havre Trough, which lies next to the Kermadec Arc, is the area where the crust of Earth is stretching apart. The trough is opening, and is therefore moving the entire Kermadec Ridge, with its volcanoes, eastwards.

Determining the age of the opening of the Havre Trough and the birthdate of the Kermadec Arc has been challenging, due to the difficulty of getting results from young, glassy, and vesicular submarine volcanic rocks with low potassium content. The tectonic complexity and limited seafloor sampling of the region has also played a part.

In this study, 19 volcanic rocks of variable composition were taken from the Kermadec Arc and Havre Trough. Samples were taken from along the entire width of the southern Havre Trough, from volcanoes to deep basins.

The Ar-Ar dating combined with other radioisotopic ages from other literature suggests that the opening of the Havre Trough initiated approximately < 2 million years ago, or perhaps as recently as approximately 1 million years ago.  The findings of this research are important for understanding the tectonic evolution of the area. This research also shows how Ar-Ar age can be obtained and used in challenging samples such as those from Havre Trough.

The journal article paper ‘Ar-Ar age constraints on the timing of Havre Trough opening and magmatism’ published in the New Zealand Journal of Geology and Geophysics is by researchers Richard Wysoczanski (NIWA), Graham Leonard, Christian Timm (both GNS) , Ian Wright (University of Canterbury), John Gamble, Monica Handler, and Alex Zohrab (all from Victoria University of Wellington) and researchers James Gill, Andre Calvert, William McIntosh, Brian Jicha and Elizabeth Drewes-Todd all from the USA. The article is available to read in full at Taylor and Francis Online.