Clay mineralogy of tephras and associated paleosols and soils, and hydrothermal deposits, North Island [New Zealand]

Abstract

Tour themes and itinerary The tour centres on the occurrence and genesis of clay minerals, especially allophane, halloysite, and ferrihydrite, associated with both Quaternary rhyolitic airfall tephra (volcanic ash) deposits and volcanogenic alluvium, and on mineralisation and thermal activity in hydrothermal fields. After a brief overview of the basaltic volcanoes of Auckland City, our route essentially traverses the Central Volcanic Region by way of a large loop with overnight stops at Rotorua (2 nights), Tokaanu, and Auckland (Fig. 0.1). We have around five stops planned for each day (including lunch), three of these being scientific stops except on Day 4 when we have only one scientific stop because of the need to travel greater distances. Our route takes us progressively towards the locus of the most recently active volcanic centres of the Central Volcanic Region, and so the surficial tephra deposits and buried paleosols become successively younger and generally less weathered: tephras at the Mangawara section (Day 1) span c. 1 Ma; at Tapapa (Day 2), c. 140 ka; at Te Ngae (Day 2), c. 20 ka; and at De Bretts, c. 10 ka, and Wairakei, c. 2 ka (Day 3). Interspersed with these tephra-paleosol sections are stops to examine an allophane-halloysite soil drainage (leaching) sequence on volcanogenic alluvium (Day 1), hydrothermal activity and mineral deposits at Whakarewarewa (Day 2) and Waiotapu (Day 3), and pure ferrihydrite seepage deposits in Hamilton (Day 4). Following introductory and detailed background review material, the tour guide has been arranged on a day-by-day basis and includes an outline of the route and stops, and several pages describing the stratigraphy, mineralogy, chemistry, and pedology of the deposits or features at each of the main stops. We will attempt to point out and describe geological and other features as appropriate during travel periods. Other activities Examples of New Zealand's distinctive fauna and flora, including kiwis and tuataras, will be seen at close quarters at Rainbow Springs (Day 2), where we will also enjoy an agricultural farm show. In Rotorua we will partake in a Maori hangi (steam-cooked feast) and concert including traditional dance forms (hakas) and songs (Day 2). In Tokaanu, hot pools will be available to relax in near the slopes of Mt Tongariro (Day 3). At Waitomo, we will visit the Waitomo Cave and in Hamilton spend a short time at the Waikato Museum of Art and History (Day 4). Finally, the tour will conclude with a farewell dinner in Auckland.