Volcanic history of Macauley Island, Kermadec Ridge, New Zealand

Abstract

Macauley Island (3 km2) is the tiny emergent part of the large submarine Macauley volcano (c. 380 km2 at the 900 m isobath) on the Kermadec Ridge. It is composed mainly of arc tholeiite basalts, with a single interbedded dacite tephra. The oldest rocks seen are subaerial aa flows (North Cliff Lavas), overlain by basaltic tephra deposits (Boulder Beach Formation). Continued eruption of thin basalt flows (Annexation Lavas) built a large shield volcano, at least 150 m above sea level, with a crater in the vicinity of what is now Mt Haszard. A large eruption of dacite tephra (Sandy Bay Tephra) caused collapse of the flanks of the submarine volcano, to form a caldera immediately northwest of the present island. Renewed basaltic volcanism produced scoria cones, flows, and tephra (Haszard Formation), and the final stage of this eruptive phase was associated with the collapse of the northwest edge of the island into the caldera. The freshness of the exposed rocks on Macauley Island indicates a late Quaternary (possibly Holocene) age for the whole succession, and this is supported by a radiocarbon date of 6310 ﾱ 90 yr B.P. on the Sandy Bay Tephra.