Page 52 - Caldera Volcanism Analysis, Modelling and Response

Residence Times of Silicic Magmas Associated with Calderas 27

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Figure 8 LongValley system. (a) Eruption ages obtained by K--Ar, Ar/ Ar and Cvs.
calculated residence times for all ages obtained by other radioactive clocks (if K--Ar and
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Ar/ Ar ages were both available only the most recently published Ar/ Ar data have been
used; seeTable 6 for all data).The very long (ca.1Ma) residence times of Van den Bogaard and
Schirnick (1995) are not shown.The residence times de¢ned by the Rb--Sr feldspar ages are
typically longer than U--Th--Pb system, although for some post-caldera units they overlap.
Abbreviations used: felds, feldspar, Zrc, zircon, U--Th dis, U--Th series disequilibria, other,
multi-minerals (including zircon or not) and glass isochrons. Units: dOC, Glass Mountain old
dome C, dOL, Glass Mountain old dome L, dOD, Glass Mountain old dome, dYG, Glass
Mountain young dome G, dYA, Glass Mountain young dome A, BT, BishopTu¡,WMC,West
Moat Coulee, dDM, Deer Mountain dome, dMK, Mammoth Knolls domes, dY, Inyo dome.
(b) Eruption ages vs. calculated magma production rates which imply higher in£ux of magma
for the BishopTu¡ compared to smaller pre- and post-caldera eruptions (see discussion
Section 4). Data sources are given inTable 6.