Deep‐ocean record of major late Cenozoic rhyolitic eruptions from New Zealand

Abstract

A 12 m.y. record of large rhyolitic eruptions from the Coromandel (CVZ) and Taupo (TVZ) Volcanic Zones of New Zealand is contained in cores retrieved by Leg 181 of the Ocean Drilling Program. Site 1124, located 670 km from the TVZ, has a maximum of 134 macroscopic tephra layers with a total thickness of 13.18 m. These units, along with between 7 and 63 tephras from 3 other sites, were dated by a combination of magnetostratigraphy, biostratigraphy, isothermal plateau fission track determinations, and geochemical correlation with onshore tephra deposits. Additional time control for the last 3 m.y. came from an orbitally tuned, benthic, oxygen isotope profile for Site 1123.Results extend the incomplete terrestrial record of volcanism by placing the first major rhyolitic eruption in the CVZ at c. 12 Ma, c. 1.6-1 m.y. earlier than previously known. Tephras became thicker and more frequent from the late Miocene into the Quaternary-a trend that probably reflected (1) more frequent and intense volcanism and (2) reduced distances between sources and depositional sites on the evolving Australian/Pacific plate system. The passage from CVZ to Quaternary TVZ occurred without a major hiatus in activity, suggesting the transition was gradational. The ensuing TVZ volcanism was more continuous than known previously from the onshore geology. Ash dispersal was primarily eastward, highlighting the dominance of westerly winds since the middle Miocene. Nevertheless, variations in dispersal patterns suggest periodic changes in wind direction/speed and/or ejection of ash beyond the Roaring Forties.

Fire and slice: palaeogeography for biogeography at New Zealand's North Island/South Island juncture

“…Prior to about 2 Ma the TVZ had not formed (Wilson et al 1995b;Carter et al 2003Carter et al , 2004) and the extensive modern plains of the Bay of Plenty area, which are partly the product of crustal rifting and voluminous volcaniclastic deposition, probably did not exist. Marine macrofossils indicate that the Ohope area, near the eastern edge of the modern TVZ, was at shallow marine depths during the Early Quaternary (Beu & Maxwell 1990).…”

A Quaternary uplift record for the Auckland region, North Island, New Zealand, based on marine and fluvial terraces

“…) dated to~1 Ma (Shane et al, 1996b) (Table 3). The Potaka tephra is one of the farthest traveled ignimbrites known and it has covered much of the North Island (Wilson et al, 1995;Carter et al, 2004). It was deposited as a pyroclastic density current (primary emplacement), identified at a number of Auckland localities (Alloway and Newnham, 1995) and informally named the Waiuku tephra .…”

Stratigraphy, age and correlation of middle Pleistocene silicic tephras in the Auckland region, New Zealand: A prolific distal record of Taupo Volcanic Zone volcanism

“…Waiuku tephra can be subdivided into two distinctive units enabling unequivocal field correlation: a lower prominent stratified unit (dominantly pyroclastic surge with lesser fall Hall et al 2001;Carter et al 2003Carter et al , 2004; Auckland region (this study); Waikato (Horrocks 2000;Lowe et al 2001); TVZ ; Wanganui Basin Naish et al 1995;Pillans et al 1996); and North Island east coast (Shane et al 1995a(Shane et al ,b, 1996B. V. Alloway unpubl.…”

“…Glass-ITPFT ages have also been recently determined on six stratigraphically important tephra layers from ODP181 core 1124C (Carter et al 2003(Carter et al , 2004. This technique was first applied in New Zealand on three widespread and stratigraphically important rhyolitic horizons from Wanganui Basin .…”

“…In the Auckland area, no associated tephra-fall deposit is recognised, a feature consistent with the lack of any such fall deposit directly below Ongatiti Ignimbrite in the King Country (Wilson 1986). However, a fall deposit of Ongatiti tephra has been recognised in ODP core 1124 located offshore eastern North Island (Carter et al 2004).…”