Honours Thesis Abstract
U-TH DISEQUILIBRIA AT WHITE ISLAND, NEW ZEALAND:
TIMESCALES OF MAGMATIC PROCESSES AND IMPLICATIONS
FOR REGIONAL MANTLE HETEROGENEITY
Zarah Heyworth
Monash University, Victoria
2005 Cryptodome - AIG Honours Bursary Winner
White Island is an active arc volcano in the Taupo Volcanic Zone, New Zealand and
provides an excellent environment to assess the timescales and mechanisms of
magmatic processes. Repeated interaction between plagioclase-rich cumulate mush and
newly injected, high-Mg magma appears to be a common pre-eruptive process at White
Island and systematic changes in magma composition are inferred to be related to
variations in magma recharge. U-Th disequilibria at White Island indicates that fluid
flux to the mantle wedge occurred less than 28 ka and that a rapid melt transport
mechanism, such as channelled flow or hydraulic fracturing, is required to reconcile
these timescales. Based on an inverse correlation between mantle source fertility and UTh disequilibria along the Tonga-Kermadec-Taupo margin, it is suggested that mantle
source fertility can exert a strong control on the extent of U-excess. Two-component
mixing models indicate that the amount of crustal contamination is less than 1.2% in
White Island lavas and that only 0.2% of sediment addition is required to produce the
inferred mantle source fertility beneath White Island.