K-Ar ages of early Miocene arc-type volcanoes in northern New Zealand

Understanding the temporal and spatial development of the early Miocene Nor thland Volcanic Arc is critical to interpreting the patterns of volcanic ac tivity in northern New Zealand through the late Cenozoic. The northwesterly trending are is considered to have developed above a southwest-dipping sub duction system. The distribution of its constituent eruptive centres is des cribed in terms of an eastern belt that extends along the eastern side of N orthland and a complementary broad western belt which includes subaerial an d submarine volcanic edi ices. Critical examination of all 216 K-Ar ages av ailable, including 180 previously unpublished ages, and their assessment ag ainst tectonic, lithostratigraphic, seismic stratigraphic, and biostratigra phic constraints, leads us to deduce a detailed chronology of periods of ac tivity for the various early (and middle) Miocene are-type volcanic complex es and centres of northern New Zealand: Waipoua Shield Volcano Complex (19- 18 Ma, Altonian); Kaipara Volcanic Complex (23-16 Ma, Waitakian-Altonian); Manukau Volcanic Complex (c. 23-15.5 Ma, Waitakian-Clifdenian); North Cape Volcanic Centre (23-18 Ma, Waitakian-Altonian); Whangaroa Volcanic Complex (22.5-17.5 Ma, Waitakian-Altonian); Taurikura Volcanic Complex (22-15.5 Ma, Otaian-Clifdenian); Parahaki Dacites (22.5-18 Ma, Waitakian-Altonian); Kua otunu Volcanic Complex (18.5-11 Ma, Altonian-Waiauan). In general, volcanic activity does not show geographic migration with time, and the western (25 -15.5 Ma) and eastern (23-11 Ma) belts appear to have developed concurrentl y.