Page 40 - Caldera Volcanism Analysis, Modelling and Response

Residence Times of Silicic Magmas Associated with Calderas 15

Figure 4 TaupoVolcanic Zone. (a) Erupted volume versus residence time. Dots are maxima
and squares the minima values (or single estimates), and lines are shown connecting the two.
The dashed lines show the uncertainties on the estimated volumes for the largeWhakamaru
and Ongatiti ignimbrites. Inset is a magni¢cation of the zone shown in the box. Abbreviations
for the units: On, Ongatiti,W,Whakamaru, Ro, Rotoiti, Ea, Earth quake £at,Ti,Tihoi, Ok,
Okaia, Po, Poihipi, Or, Oruanui, Ub, Unit B, Ud, Unit D, Ue, Unit E, Ug, Unit G, Us, Unit S.
(b) Erupted volume versus magma production rate ( ¼ erupted volume/residence time). Large
eruptions tend to have higher magma production rates.This could be explained by recycling
of old zircons in smaller eruptions, a real di¡erence in magma £uxes, or by the pre-caldera
deposits being issued from same reservoir as the caldera collapse magma (see discussion
Section 4). Data sources are inTable 3.

In detail, the age data are rather convoluted, with typically multiple age
peaks within a single deposit, the peaks defined by SIMS results are not always as
those defined by TIMS. The youngest ages of many deposits overlap with eruption
(e.g., the Oruanui eruption), although the youngest crystals can be also ca. 15 ky