Paleomagnetism, K-Ar dating and tectonic interpretation of Upper Cretaceous and Cenozoic volcanic rocks of the Chatham Islands, New Zealand

Publisher Website
Google Scholar
Abstract
New K-Ar age determinations on basaltic volcanic sequences in the Chatham Islands, 900 km east of South Island, New Zealand, combined with additional field and paleontologic studies, have led to a stratigraphic revision and the recognition of three distinct volcanic episodes—Late Cretaceous (70–85 m.y.), Eocene-early Oligocene (35–53 m.y.), and late Miocene-Pliocene (2–6m.y.). Paleontology, palynology, and K-Ar dating place the earliest alkali basalt-trachyte volcanism of the Kahuitara Tuff and Southern Volcanics in the early Senonian, at the time of separation of the Chatham Rise-Campbell Plateau block from West Antarctica. The Southern Volcanics were formerly considered to be Eocene and the Kahuitara Tuff was included in the Waihere Bay Group (Albian). The Waihere Bay Group (s.s.) of Albian-Cenomanian age comprises mainly estuarine to deltaic sediments, derived from the Chatham Rise and/or West Antarctica, prior to continental separation. The Eocene and Pliocene volcanics comprise limburgitic plugs, flows, and marine tuffs which correlate with changes in spreading rates on the Pacific-Antarctic ridge system. The K-Ar ages provide control points for the Miocene-Pliocene boundary (5 ± 0.2 m.y.) and Mata-Raukumara Series boundary (78 ± 2 m.y.) in the New Zealand region. Paleomagnetic measurements indicate Pliocene and Eocene paleopole posItions similar to the present, but the Late Cretaceous pole position differs by 19° ± 4° suggesting a relative northward drift of the Chatham Rise-Campbell Plateau block from West Antarctica, with little change in declination, in good agreement with sea floor spreading data. Assuming that the geomagnetic pole has remained within Antarctica for the past 90 m.y., as implied by paleomagnetic studies on Antarctic and East Australian rock sequences, the paleomagnetic results do not permit a significant independent clockwise rotation of the Chatham Rise relative to the New Zealand mainland as postulated in some geotectonic models.