HR: 0800h
AN: V41D-0801 [Abstracts]
TI: Magnetotelluric Survey Reveals Surficial Conductor Under the Jalisco Block, Possibly Linked to Magmatism in the Area
AU: * Alvarez, R
EM: rab@leibniz.iimas.unam.mx
AF: Instituto de Investigaciones en Matemáticas Aplicadas y en Sistemas, Universidad
Nacional Aut\'{o}noma de México, Ciudad Universitaria
Circuito Interior S/N, México, DF 04510, Mexico
AU: Arzate, J
EM: arzatej@geociencias.unam.mx
AF: Centro de Geociencias, Campus Juriquilla, Universidad Nacional Aut\'{o}noma de
México, Juriquilla, Querétaro, QRO 76230, Mexico
AU: Corbo, F
EM: fcorbo@geociencias.unam.mx
AF: Centro de Geociencias, Campus Juriquilla, Universidad Nacional Aut\'{o}noma de
México, Juriquilla, Querétaro, QRO 76230, Mexico
AB:
The composition of the volcanic rocks in the Jalisco Block (JB), particularly those from the Colima rift and Los
Volcanes and Mascota regions, are quite similar and show an anomalous enrichment in incompatible elements
(e.g., K). Luhr et al. (1989) proposed that the alkaline and calc-alkaline lavas from those areas originated in a
common source, which consisted of mantle overlying the subducting Rivera and Cocos plates. Such a source
was described as heterogeneously and variably enriched in the incompatible elements. However, besides the
surface location of the eruptive centers, no evidence is available for the depth and extent such a mixed
mantle/slab-derived source. We conducted two magnetotelluric transects in SW-NE and NW-SE directions that
sample a portion of the region where magmatism is present, in the vicinity of the San Sebastián-Mascota area,
whose lengths are 200 and 135 km respectively, with stations spaced 20 km on the average. The SW-NE transect
extends from the SW coast of the JB through a region 90 km in length, devoid of magmatism, crossing the
boundary between the coastal region and the uplifted domain of the JB, and continuing inland. Resistivity
inversion of the MT response along this line reveals the conductive character of the down going slab to depths of
60 km. There is a good correlation between the resistivity and the seismological trace of the slab. Beyond the
location of the deepest portion of the slab, a sudden change in resistivity pattern is obtained, where a surficial (8-
20 km depth) conductive anomaly is detected. This "perched'' conductor corresponds to the location of
volcanism in the Mascota-Los Volcanes area. The NW-SE transect also shows the presence of this conductor,
which extends 90 km along the SE portion of the line, from San Sebastián to Los Volcanes, and depths from 8
to 20 km. We submit that this conductor corresponds to the enriched magmatic source proposed by Luhr et al.
(1989), feeding the Quaternary volcanism of the region. Additional transects will be carried throughout the JB in
order to more fully define the characteristics of this conductor.
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8415 Intra-plate processes (1033, 3615)
DE: 8434 Magma migration and fragmentation
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting