About 9,800 yr ago a major pulse of andesitic volcanism lasting about 100 yr began in the Tongariro volcanic center at the southern end of the Taupo volcanic zone in North Island, New Zealand. Immediately following the onset of this intense period of andesitic volcanism, two voluminous rhyolitic eruptions from the Taupo volcanic center, located a few kilometres northeast of the Tongariro volcanic center, occurred after a period of quiescence of about 10,000 yr.
The andesite volcanism marks a change in composition of titanomagnetite, which shows lower vanadium, chromium, cobalt, and nickel contents when compared with older andesites. Titanomagnetites analyzed from fresh rhyolite lapilli erupted from the Taupo volcanic center show a similar change in vanadium, nickel, and cobalt contents. Their composition falls into two distinct chemical groupings, which correspond to an older (about 9,800 to 8,850 yr) and younger (about 6,300 to 1,820 yr) rhyolitic Taupo magma previously distinguished on the basis of major-element glass chemistry and iron-titanium oxide equilibration temperatures.
It is suggested that the timing of eruption of the andesite at about 9800 B.P. is related to that of the older Taupo rhyolitic magma, or that both were initiated by the same external trigger. Subsequent large-scale rhyolitic eruptions of the younger Taupo magma, however, showed no obvious temporal relationship to the later intermittent andesite activity.