HR: 1340h
AN: V13B-1485    [Abstracts]
TI: El Jorullo Revisited: Petrology, Geochemistry & Volcanology
AU: * Rubin, K H
EM: krubin@hawaii.edu
AF: SOEST, University of Hawai`i, Honolulu, HI 96822 United States
AU: Jurado-Chichay, Z
EM: zinzuni@hawaii.edu
AF: SOEST, University of Hawai`i, Honolulu, HI 96822 United States
AU: Pyle, D
EM: pyled@hawaii.edu
AF: SOEST, University of Hawai`i, Honolulu, HI 96822 United States
AU: Mor\'{a}n-Zenteno, D
EM: dantez@servidor.unam.mx
AF: Insituto de Geologia, UNAM, Mexico City, DF 04510 Mexico
AU: Rowland, S
EM: scott@higp.hawaii.edu
AF: SOEST, University of Hawai`i, Honolulu, HI 96822 United States
AB: El Jorullo (western Trans Mexican Volcanic Belt) was produced by a monogenetic eruption between 1759 and 1774. It and Paricutin are the only two historic cones of the nearly 1000 volcanoes in the Michoacan-Guanajuato volcanic field. In a seminal study, Luhr & Carmichael (CMP 90, 1985) demonstrated that El Jorullo lavas erupted from a few cones along a 4km long NE-SW trending fissure and in a compositional sequence from mafic calc-alkaline basalts to basaltic andesites (SiO$_{2}$, Al$_{2}$O$_{3}$, MgO = 53, 16.8, 8.6 and 55.4, 19, 4, wt % respectively). They divided the lavas into 3 flow units and concluded on primarily mineralogic and major element grounds that the compositional evolution was due to crystal fractionation at lower crustal/upper mantle depths. They ruled out a significant role for crustal assimilation. Our recent field observations include a new interpretation of the flow field (8 flow units) and a greater proportion of late stage lavas. New petrologic, petrographic and radiogenic isotope (Sr, Nd, Pb) data have been collected. Major/trace element trends are similar to Luhr & Carmichael (1985), although the new sampling and flow unit subdivision reveals a smoother compositional evolution in time, akin to Paricutin. The earliest flow units (1-3) erupted relatively uniform mafic compositions comprising about half of the flow field volume; middle sequence lavas (units 4, 5) are slightly more evolved, account for 12% of the flow field volume and commonly contain partially melted/disaggregated crustal xenoliths (granodiorite and tonalite); latest, most evolved lavas (units 6-8) show greater compositional shifts both internally and relative to earlier units, and account for 35% of the erupted lava volume. The lavas are sparsely phyric and xenocrysts (plag, rare sphene and quartz) occur mainly in later state lavas. Variations in Sr and Pb isotope and trace element ratios throughout the sequence require up to 15% crustal assimilation and $\sim$25% crystal fractionation (AFC) relative to the mafic parent. The large volume fraction of the more contaminated late stage magma and the extent of the compositional shifts suggest that assimilation is a primary control on erupted magma compositions, much like at Paricutin (e.g., McBirney et al. CMP 95, 1987).
DE: 8434 Magma migration
DE: 3640 Igneous petrology
DE: 3670 Minor and trace element composition
DE: 1020 Composition of the crust
DE: 1040 Isotopic composition/chemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting