Mafic Plinian volcanism and ignimbrite emplacement at Tofua volcano,Tonga |
| |
Authors: | J T Caulfield S J Cronin S P Turner L B Cooper |
| |
Institution: | (1) GEMOC National Key Centre, Dept. of Earth and Planetary Sciences, Macquarie University, 2109 Sydney, NSW, Australia;(2) Institute of Natural Resources, Massey University, Palmerston North, New Zealand;(3) Institute of Geochemistry and Petrology, ETH, Zurich, CH, 8092, Switzerland |
| |
Abstract: | Tofua Island is the largest emergent mafic volcano within the Tofua arc, Tonga, southwest Pacific. The volcano is dominated
by a distinctive caldera averaging 4 km in diameter, containing a freshwater lake in the south and east. The latest paroxysmal
(VEI 5–6) explosive volcanism includes two phases of activity, each emplacing a high-grade ignimbrite. The products are basaltic
andesites with between 52 wt.% and 57 wt.% SiO2. The first and largest eruption caused the inward collapse of a stratovolcano and produced the ‘Tofua’ ignimbrite and a sub-circular
caldera located slightly northwest of the island’s centre. This ignimbrite was deposited in a radial fashion over the entire
island, with associated Plinian fall deposits up to 0.5 m thick on islands >40 km away. Common sub-rounded and frequently
cauliform scoria bombs throughout the ignimbrite attest to a small degree of marginal magma–water interaction. The common
intense welding of the coarse-grained eruptive products, however, suggests that the majority of the erupted magma was hot,
water-undersaturated and supplied at high rates with moderately low fragmentation efficiency and low levels of interaction
with external water. We propose that the development of a water-saturated dacite body at shallow (<6 km) depth resulted in
failure of the chamber roof to cause sudden evacuation of material, producing a Plinian eruption column. Following a brief
period of quiescence, large-scale faulting in the southeast of the island produced a second explosive phase believed to result
from recharge of a chemically distinct magma depleted in incompatible elements. This similar, but smaller eruption, emplaced
the ‘Hokula’ Ignimbrite sheet in the northeast of the island. A maximum total volume of 8 km3 of juvenile material was erupted by these events. The main eruption column is estimated to have reached a height of ∼12 km,
and to have produced a major atmospheric injection of gas, and tephra recorded in the widespread series of fall deposits found
on coral islands 40–80 km to the east (in the direction of regional upper-tropospheric winds). Radiocarbon dating of charcoal
below the Tofua ignimbrite and organic material below the related fall units imply this eruption sequence occurred post 1,000 years
BP. We estimate an eruption magnitude of 2.24 × 1013 kg, sulphur release of 12 Tg and tentatively assign this eruption to the AD 1030 volcanic sulphate spike recorded in Antarctic
ice sheet records. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|