HR: 0800h
AN: V31C-1447    [Abstracts]
TI: Evaluating the role of crustal interaction with mantle-derived magmas: Sr-Nd-O isotope geochemistry of a Quaternary, caldera-forming, phonolitic eruptive sequence; the Diego Hernandez Formation, Tenerife, Canary Islands (Spain)
AU: * Hickes, H J
EM: vulcan@mail.wsu.edu
AF: Washington State University, Dept of Geology Webster 1228 Washington State University , Pullman, WA 99164-2812 United States
AU: Larson, P B
EM: plarson@wsu.edu
AF: Washington State University, Dept of Geology Webster 1228 Washington State University , Pullman, WA 99164-2812 United States
AU: Wolff, J A
EM: jawolff@wsu.edu
AF: Washington State University, Dept of Geology Webster 1228 Washington State University , Pullman, WA 99164-2812 United States
AU: Vervoort, J D
EM: vervoort@wsu.edu
AF: Washington State University, Dept of Geology Webster 1228 Washington State University , Pullman, WA 99164-2812 United States
AB: The Sr-Nd-Pb isotope composition of Miocene-Pliocene basalts from the Canary Islands has been well documented (e.g., Simonsen et al., 2000), and the data define a restricted range of compositions resulting from a mixture of two or more mantle sources. Trace-element and O-isotope variations among younger basalts and more highly differentiated eruptive products from these islands require the involvement of either hydrothermally altered MORB crust or the volcanic edifice during their ascent and petrogenesis (e.g., Wolff et al., 2000). Here we present new Sr-Nd-O data from all of the major pyroclastic deposits of the Diego Hernandez Formation (DHF), a Quaternary, caldera-forming sequence that includes the entire spectrum of magma types found on the island. Sr ($^{87}$Sr/$^{86}$Sr$_{i}$ = 0.70302 - 0.70311) and Nd ($^{143}$Nd/$^{144}$Nd = 0.51288 - 0.51290) ratios of DHF pumices fall within the range of Canary Islands basalts, over-lapping the low $^{87}$Sr/$^{86}$Sr end of the array. These data are also consistent with the Tenerife basalt isotope data of Simonson et al. (2000). Sr and Nd isotope variations among the phonolitic pyroclastic deposits have a more restricted range than those of the less differentiated and older basalts on the island. Initial isotopic data from syenite xenoliths, representative of at least two plutons within the volcanic edifice, suggests that they have Nd isotope compositions overlapping the highest $^{143}$Nd/$^{144}$Nd ratios of DHF phonolites but have a more radiogenic Sr isotopic composition. Mean \delta$^{18}O$ values produced by laser fluorination of feldspar phenocrysts from DHF pumices range from 5.63 to 6.33 \permil VSMOW. The lower \delta$^{18}O$_{FSP}$ values are within the range of MORB oxygen isotope values, but the higher \delta$^{18}O$_{FSP}$ values are lower than expected for some of the more differentiated units. \delta$^{18}O$_{FSP}$ values also display a negative correlation with $^{87}$Sr/$^{86}$Sr ratios. [1]Simonsen et al., 2000; JVGR, vol. 103, p. 299;[2]Wolff et al., 2000; JVGR, vol. 103, p. 343;[3]Hickes et al., 2003, Eos Trans. AGU, 84(46), V12A-0565
DE: 8400 VOLCANOLOGY
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting