HR: 0800h
AN: V31C-1441    [Abstracts]
TI: Contrasting Isotope Systematics in Canarian Rift Zones: La Palma and Tenerife
AU: * Hamilton, A
EM: superam@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington 351310, Seattle, WA 98195 United States
AU: Nelson, B K
EM: bnelson@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington 351310, Seattle, WA 98195 United States
AU: Carrecedo, J C
EM: jcarracedo@ipna.csic.es
AF: Estacion Volcanologica de Canarias, IPNA-CSIC, La Laguna, TF 38206 Spain
AB: The Canary Islands are dominated by basaltic volcanism, like Hawaii, but in contrast show a greater range of differentiation and isotopic heterogeneity and differences in magma chamber and rift zone structures. Our study focuses on the NW rift zone which extends from the Pico-Teide volcanic complex on the island of Tenerife. Basaltic to phonolitic volcanism along the rift spans approximately 20,000 years. Major element data show a large range of differentiation with MgO concentrations ranging from 0.85 to 8.26%. Samples are strongly enriched in highly incompatible elements, La averages 320x chondrites, (La/Yb)$_{N}$ averages 21.1, and no Eu anomaly was observed. High-precision Pb isotope data from nearly all samples collected along the $\sim$15km length of the NW rift show a very restricted range. Most samples range in $^{206}$Pb/$^{204}$Pb from $\sim$19.732 to 19.775 with rare samples as low as 19.675, and $^{207}$Pb/$^{204}$Pb from $\sim$15.594 to 15.621, a range only slightly greater than analytical error ($\pm$180 ppm 2$\sigma$). This small range contrasts with that observed for other Canarian volcanoes over a similar time span. For example, over a period of 20,000 years Bejenado volcano on La Palma has $^{206}$Pb/$^{204}$Pb values that range from $\sim$19.415 to 19.965 and $^{207}$Pb/$^{204}$Pb values that range from $\sim$15.425 to 15.645. Our NW rift zone data are consistent with Simonsen et al. (2000) who report a somewhat wider range of $^{206}$Pb/$^{204}$Pb values (19.653 to 19.785, with two outliers at $\sim$19.32) for "younger basalts" of Tenerife. The range for the entire island is 19.323 to 20.085. The limited isotopic range observed on the NW rift and associated with the Pico-Teide volcanic complex contrasts strongly with isotopically heterogeneous volcanoes on La Palma (Bejenado and Taburiente). We have interpreted this heterogeneity to reflect multiple small, isolated magma chambers or conduits that preserve original isotope heterogeneities in the mantle. The homogeneity observed on Tenerife may indicate a subsurface magmatic configuration that is distinct from the western Canarian volcanoes. The relatively large Teide magma system may have a homogenizing effect, even on magmas erupting along the rift zone. Alternatively, a single homogeneous mantle source may have provided all the erupted magmas on Tenerife over the past 20,000 years compared to multiple heterogeneous sources in the western islands. Simonsen, S.L., Neumann, E.R., Seim, K. (2000) {\it J. Vol. and Geochem. Res.}, {\bf 103}, 299-312.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting