HR: 0830h
AN: V31C-0943    [PDF]
TI: High Field Strength Element Evolution of Telica and Izalco Volcanoes, Central America
AU: * Milidakis, K I
EM: kmili@eden.rutgers.edu
AF: Rutgers, The State University of New Jersey, 610 Taylor Rd., Piscataway, NJ 08854
AU: Carr, M J
EM: carr@admin.rutgers.edu
AF: Rutgers, The State University of New Jersey, 610 Taylor Rd., Piscataway, NJ 08854
AU: Feigenson, M D
EM: feigy@rci.rutgers.edu
AF: Rutgers, The State University of New Jersey, 610 Taylor Rd., Piscataway, NJ 08854
AB: Telica and Izalco are well sampled Central American volcanoes in Nicaragua and El Salvador, respectively. Telica is a complex volcano with a history of at least several tens of thousands of years. Izalco is a parasitic cone that first erupted on the flank of Santa Ana volcano in 1770. These two volcanoes provide stratigraphic sections on long and short times scales. Furthermore, Telica has one of the highest slab signals in Central America, whereas Izalco has a smaller slab signal. These two volcanoes were selected for detailed measurement of Nb, Ta and other HFS elements. Nb (and Ta) depletions relative to other similarly incompatible elements are a prevalent characteristic of island arc basalts. Nb (and Ta) may be depleted because of a residual Ti-bearing phase, such as rutile or Ti-amphibole, which preferentially retain these elements. All the Izalco samples and the majority of the Telica samples display significant Nb (and Ta) depletions. There are a few high-TiO2 samples ($>$1wt% TiO2) at Telica that do not have a negative Nb anomaly. At Telica, Nb/Ta decreases and Zr/Hf increases with age (youngest to oldest). Zr/Nb decreases then increases with age. Ratios that are proxies for total slab signal, such as Ba/La and U/Th, fluctuate with age in the same manner as Zr/Nb. U/La, which is used to track the hemipelagic sediment signal, increases with age whereas Ba/Th, which tracks the carbonate sediment signal, decreases then increases. Zr/Hf positively correlates with U/La (hemipelagic signal). Neither Nb/Ta nor Zr/Hf correlates with La/Yb hence the variations in these ratios are not the result of different degrees of melt. A variation in the HFSE might not be expected in Izalco, which is very young, however Nb/Ta does vary, whereas Ba/La, U/Th, Ba/Th, U/La do not. Nb/Ta is also not correlated with La/Yb; therefore, degree of melt is not responsible for the range in Nb/Ta values. However, the degree of melt is lower in the older Izalco samples, shown in La/Yb and Zr/Hf. The lack of a Nb anomaly in some Telica samples implies that these originated from a source with no residual rutile or Ti-amphibole to retain these elements. Overall, the HFS element abundances do not significantly vary compared to the rest of Central America.
DE: 8400 VOLCANOLOGY
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting