HR: 14:15h
AN: V23C-02 [Abstracts]
TI: Evolution of the Late Cretaceous-Paleogene Cordilleran arc magmatism in NW Mexico: a review from updated geochronological studies.
AU: * Valencia-Moreno, M
EM: valencia@geologia.unam.mx
AF: Estacion Regional del Noroeste, Instituto de Geologia, Universidad Nacional
Autonoma de Mexico, Luis Donaldo Colosio y Madrid S/N, Col. Los Arcos, Hermosillo, Son 83240, Mexico
AU: Iriondo, A
EM: iriondo@geociencias.unam.mx
AF: Centro de Geociencias, Universidad Nacional Autonoma de Mexico, Campus Juriquilla,
Apdo. Postal 1-742, Centro, Queretaro, Qro. 76001, Juriquilla, Qro 76230, Mexico
AU: Perez-Segura, E
EM: efrenpese@yahoo.com
AF: Departamento de Geologia, Universidad de Sonora, Blvd. Luis Encinas y Rosales
S/N, Col. Centro, Hermosillo, Son 83000, Mexico
AU: Noguez-Alcantara, B
EM: Benito_Noguez@penoles.com.mx
AF: Servicios Industriales Penoles S.A. de C.V., Leona Vicario 259 Poniente, Barrio
Cuaxustenco, Metepec, Mex 52140, Mexico
AB:
During most of the Mesozoic and Cenozoic, the locus of subduction related arc magmatism in northwestern
Mexico was relatively mobile, probably due to changes in the mechanical conditions of the Farallon-North America
plate convergence. The older Mesozoic events recognized in this region occurred in the Late Triassic and
Jurassic, but the associated rocks are poorly preserved. However, a belt of Late Cretaceous through Paleogene
magmatic rocks is well exposed along Baja California, Sonora and Sinaloa. Since the late 70's, it was noted that
during the Early Cretaceous the igneous activity along this belt remained relatively static in the westernmost part,
but migrated eastward in the Late Cretaceous, penetrating more than 1000 km into the continent. The arc
magmatism reached western Sonora at about 90 Ma, and then it started to move faster inland, presumably due to
flattening of the subducted oceanic slab. Recent U-Pb zircon data revealed unexpected old ages (89-95 Ma) near
the eastern edge of Sonora, which are difficult to explain on the basis of the classic tectonic interpretations. A
model based on two synchronic sites for magma emplacement may explain the age overlapping observed along
the belt; however, a profound re-evaluation a proper geodynamic scenario to support this model is required. Even
if restoration of the large Neogene crustal extension is made, particularly for central and northern Sonora, the
relatively flat-subduction regime commonly accepted for the Laramide event appears unable to explain the
anomalously broad expression of the magmatic belt in northwestern Mexico. An alternative model based on two
synchronic sites of magma emplacement, as suggested by the new age data, may better explain the large
volume of igneous rocks produced during this time in Sonora and most of Chihuahua. This mechanism may
differ southwards in Sinaloa, where the magmatic belt becomes considerably narrower. Moreover, the possible
existence of two spatially distinct sites for magma generation may help understand the post-Laramide volcanism,
commonly interpreted as a result of a fast return of a single magmatic arc to the trench, due to a progressive
steepening of the subducted oceanic slab.
UR: http:www.geologia-son.unam.mx
DE: 1037 Magma genesis and partial melting (3619)
DE: 1040 Radiogenic isotope geochemistry
DE: 1115 Radioisotope geochronology
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly