AGE AND GEOCHEMISTRY OF THE NORTH CAPE INTRUSIONS, NORTHLAND, NEW ZEALAND

The Northland Allochthon is part of an ophiolite sequence emplaced during the Oligocene onto the Northland area of the North Island of New Zealand. Both micro and macro fossils in the upper sedimentary sequences give an age of Late Cretaceous to Early Paleocene. The igneous suites (Tangihua Complex) within the allochthon have a suprasubduction zone signature and have been altered from zeolite up to greenschist facies.

The lowermost cumulate sections of the ophiolite sequence are only found at North Cape, New Zealand’s most northeastern point. These mafic intrusions do not display the high degree of alteration consistent with the Tangihua rocks at other locations. This has caused some debate to whether they are indeed part of the allochthon or the earliest occurrence of the Northland Volcanic Arc, a Miocene series of volcanism.

This project seeks to analyze the intrusive rocks of North Cape. The geochemistry of these rocks will be compared with the known geochemistry of the Tangihua complex, the Northland Volcanic Arc, and Miocene arc rocks in order to establish any chemical or tectonic region relation. Laser ablation inductively coupled mass spectrometry (LA-ICP-MS) will be used for zircon geochronology as well as the trace element mineral chemistry of plagioclases and pyroxenes.

With these analyses the timing and geochemical conditions of these intrusion can be identified and potentially elucidate our understanding of the complex tectonic history of the Southwest Pacific.