HR: 0830h
AN: V51H-0377    [PDF]
TI: Geochemistry and Stable Isotopes of Tacana Volcano-Hydrothermal System, Mexico-Guatemala
AU: * Rouwet, D /
EM: dmitrirouwet@hotmail.com
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, 90146 Italy
AU: * Rouwet, D /
EM: dmitrirouwet@hotmail.com
AF: Insituto de Geofisica, UNAM, Ciudad Universitaria, Circuito Exterior, s/n, Mexico DF, 04510 Mexico
AU: Inguaggiato, S
EM: inguagg@pa.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo La Malfa 153, Palermo, 90146 Italy
AU: Taran, Y /
EM: taran@tonatiuh.igeofcu.unam.mx
AF: Insituto de Geofisica, UNAM, Ciudad Universitaria, Circuito Exterior, s/n, Mexico DF, 04510 Mexico
AU: Varley, N /
EM: eruption@softhome.com
AF: Universidad de Colima, Observatorio Volcan de Colima, Colima, 45181 Mexico
AB: Tacana volcano (4100 m.s.n.m.), situated on the border between Chiapas (Mexico) and Guatemala is considered an active volcano. In May 1986, after a minor phreatic explosion, a fumarole field was formed at an altitude between 3200 and 3600 m.a.s.l. Around the volcano, at altitudes between 1500 and 2000 m.a.s.l., exist several thermal springs, with temperatures up to 63 degrees C. Incomplete chemical composition of the Agua Caliente thermal waters in the period 1986-1993 were presented by Medina (1986), De la Cruz-Reyna et al. (1989) and Armienta and De la Cruz-Reyna (1995), a chemical analysis of fumarole gases were published by Martini et al. (1986). This study presents the first series of isotope data of water and gases: hydrogen, oxygen, carbon and helium. Data on gas and water chemistry of several thermal spring waters and gases are presented in more detail than ever. Hydrogen and oxygen isotopes of Tacana thermal spring waters show that meteoric water is the main contribution for the thermal waters. Cation geothermometry of the spring waters confirm these meteoric contribution, as all waters are immature in a dynamic system of water-rock interaction with a constant infiltration of fresh meteoric waters (precipitation of 6000 mm per year). The relatively high bicarbonate (up to 1100 ppm) and sulphate (up to 1200 ppm) concentrations in the thermal waters suggest an important degassing up to 2500 m below the volcano summit, which indicates the presence of a extended and complex volcano-hydrothermal system. Helium isotopes of free and dissolved gases confirm the existence of a magmatic contribution, so as for fumarole gases (6.6 R/R$_a$) as for gases sampled at the thermal springs (5.7-6.2 R/R$_a$ for free gases and between 0.50 and 5.55 R/R$_a$ for dissolved gases). These values are typical for gases liberated at volcanoes in clasic volcanic arcs. The lower values for the dissolved He is probably due to an interaction with the granitic basement, which can be found at hights upto 2000 m.a.s.l. Carbon isotopes of CO$_2$ from fumarole gases confirm the magmatic contribution for the Tacana volcano-hydrothermal system (-3.56 per mil vs PDB), as well as the total dissolved carbon with $\delta^1$$^3$C values between -1.40 and -3 per mil vs PDB. The bicarbonate and sulphate concentrations in the thermal spring waters correspond with those measured in the Agua Caliente spring up to December 1993, more than seven years after the phreatic explosion, which might suggest there weren't any drastic changes in the volcanic activity for the last ten years. These first data on isotopes and complete chemistry of thermal springs -many of them sampled for the first time- give a general characterization of the fluids, while next series of data might give a description of the changes in the Tacana volcano-hydrothermal system and related volcanic activity.
DE: 1749 Volcanology, geochemistry, and petrology
DE: 8424 Hydrothermal systems (8135)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting