EARLY TO MIDDLE PLEISTOCENE TEPHROCHRONOLOGY OF NORTH-ISLAND, NEW-ZEALAND - IMPLICATIONS FOR VOLCANISM, TECTONISM, AND PALEOENVIRONMENTS

Citation
Par. Shane et al., EARLY TO MIDDLE PLEISTOCENE TEPHROCHRONOLOGY OF NORTH-ISLAND, NEW-ZEALAND - IMPLICATIONS FOR VOLCANISM, TECTONISM, AND PALEOENVIRONMENTS, Geological Society of America bulletin, 108(8), 1996, pp. 915-925
Citations number
44
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
108
Issue
8
Year of publication
1996
Pages
915 - 925
Database
ISI
SICI code
0016-7606(1996)108:8<915:ETMPTO>2.0.ZU;2-7
Abstract
Thick volcaniclastic sequences of early to middle Pleistocene age in s outhern North Island, New Zealand, contain rhyolitic tephra beds that record the early history of the Taupo volcanic zone (TVZ). At least 54 different tephra beds are recorded, and their chronology is defined b y glass fission-track ages and paleomagnetism, The tephra beds span th e interval ca, 2.0-0.6 Ma and provide an event frequency of 1/19 ky., significantly higher than the frequency of sheet-forming ignimbrites p reserved in the TVZ at this time (approximate to 1/100 k.y.). The dist al tephra beds thus provide a record of volcanism not revealed in the proximal volcanic region and suggest a major period of explosive activ ity at ca, 1.79-1.60 Ma. Several important marker horizons are identif ied: Pakihikura tephra (1.63 Ma), Mangatewaiiti tephra (1.24 Ma), Pota ka tephra (1.00 Ma), Kidnappers B tephra (1.00 Ma), and Kaukatea tephr a (0.88 Ma). These tephra beds allow direct correlation between (1) ma rine and nonmarine facies and (2) the fore-are and back-are regions of New Zealand. The tephra beds provide a framework for a paleoenvironme ntal reconstruction of the southern North Island, Volcaniclastic trans port routes from the TVZ to basins in the south and southeast, and thr ough the site of present mountain ranges, supplied material to a terre strial lowland fore-are area in the interval 1.64-0.7 Ma. Uplift and d eformation since 0.7 Ma have disrupted paleodrainage routes, diverting them to the north and southwest.