New Zealand Journal of Geology and Geophysics abstracts

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Volcanic history of Macauley Island, Kermadec Ridge, New Zealand

E. F. LLOYD

formerly DSIR Geology & Geophysics
Rotorua, New Zealand

SIMON NATHAN

Institute of Geological & Nuclear Sciences
P.O. Box 30368
Lower Hutt, New Zealand

I. E. M. SMITH

Department of Geology
University of Auckland
Private Bag 92019
Auckland, New Zealand

R. B. STEWART

Department of Soil Science
Massey University
Private Bag 11222
Palmerston North, 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 +/- 90 yr B.P. on the Sandy Bay Tephra.

Keywords  volcano; arc tholeiite; basalt; dacite; pumice; caldera; tephra; crater; phreatomagmatic; radiocarbon; Macauley I.

New Zealand Journal of Geology and Geophysics, 1996, Vol. 39: 295-308

0028-8306/96/3902-0295 $2.50/0 (c) The Royal Society of New Zealand 1996

PDF file of entire paper: medium quality (6908K); (scanned from paper original: notes about this process)

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