HR: 17:10h
AN: V24A-04 INVITED [Abstracts]
TI: From Subduction to Continental Breakup: Neogene and Quaternary Magmatic Evolution of Baja California Peninsula and the Adjacent Gulf of California, Mexico
AU: * Calmus, T
EM: tcalmus@servidor.unam.mx
AF: Estación Regional del Noroeste, Instituto de Geología, Universidad Nacional Autónoma de
México, Blvd. Luis Donaldo Colosio y Madrid, S/N, Hermosillo, Son 83000, Mexico
AU: Maury, R
EM: Rene.Maury@univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, Place Nicolas Copernic, Plouzané, F-29280, France
AU: Pallares, C
EM: cpallares@sdt.univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, Place Nicolas Copernic, Plouzané, F-29280, France
AU: Aguillón-Robles, A
EM: aaguillonr@uaslp.mx
AF: Instituto de Geología, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava no.5,
Zona Universitaria, San Luis Potosí, SLP 78250, Mexico
AU: Benoit, M
EM: mbenoit@univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, Place Nicolas Copernic, Plouzané, F-29280, France
AU: Bellon, H
EM: bellon@univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, 6, Av. Le Gorgeu, Brest, F-29238, France
AU: Royer, J
EM: Jean-Yves.Royer @ univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, Place Nicolas Copernic, Plouzané, F-29280, France
AU: Cotten, J
EM: cotten@univ-brest.fr
AF: UMR 6538, Domaines Océaniques, Institut Universitaire Européen de la Mer, Université de
Bretagne Occidentale, 6, Av. Le Gorgeu, Brest, F-29238, France
AU: Bourgois, J
EM: bourgois@ccr.jussieu.fr
AF: CNRS-Géosciences Azur, Case 124, Université de Paris 6, 4 Place Jussieu, Paris, 75252,
France
AB:
After the subduction stopped at ca. 12.5 Ma off Baja California Peninsula, calc-alkaline volcanic activity vanished
progressively, and the Comondú volcanic arc was replaced by a post-subduction diversified volcanism which
derived from at least five distinct magmatic sources located beneath the Baja California Peninsula and the Gulf of
California. New field data, 40K-40Ar datings and geochemical and petrological studies of some volcanic fields
and isolated volcanic centers, including San Esteban island, allow us to define the following volcanic suites from
Late Miocene to Quaternary: 1) magnesian andesites, or "bajaites", 2) adakites, 3) tholeiitic basalts, 4) niobium-
rich basalts (NEB), 5) calc-alkaline andesites, and 6) alkali basalts, in order of decreasing volumetric abundance.
In the northern part of the Peninsula until the latitude of 29°N, where the oceanic ridge subduction has
been documented, volcanism is mainly represented by magnesian andesites and alkali basalts. To the south,
alkali basalts have not been reported, but, from Vizcaino peninsula to La Purísima volcanic field, we observe a
close association of Late Miocene magnesian andesites, adakites, niobium-rich basalts and tholeiitic basalts.
These rocks together indicate the presence of an asthenospheric window, related to the slab tear which
developed within the downgoing oceanic plate. Tholeiites are considered as a product of partial melting of the
lower plate asthenosphere, whereas adakites likely derive from partial melting of the edges of the slab window,
and NEB and magnesian andesites from the melting of the supraslab mantle following its interaction with
adakitic liquids. We propose that, after the oceanic accretion ceased off southern Baja California between 12 and
8 Ma, the slab tearing was due to the combination of the capture of the unsubducted remnant of the Magdalena
plate by the Pacific plate and of the progressive sinking of the deep subducted oceanic plate. The slab tearing
was probably initiated at the southernmost edge of the already existing southern Californian asthenospheric
window. During the Pliocene and the Quaternary, the thermal anomaly related with the asthenospheric window
and the crustal thinning linked with the opening of the Gulf of California led to MORB formation at spreading
centres of the Gulf and to partial melting of slab remnants to generate adakites, for example in Isla San Esteban.
This thermal event may have also triggered the partial melting of previously metasomatized supraslab mantle to
produce medium-K to high-K calc-alkaline magmas along the Main Gulf Escarpment and in the Gulf of California.
UR: http:www.geologia-son.unam.mx/
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 8104 Continental margins: convergent
DE: 8185 Volcanic arcs
DE: 9350 North America
DE: 9604 Cenozoic
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly