Paleomagnetic and rock-magnetic survey of eocene dike swarms from the Tecalitlan area (Western Mexico): Tectonic implications |
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| Authors: | Jose Rosas-Elguera Bertha Aguilar Reyes Avto Goguitchaichvili Macario Rocha Margarita López Martínez Miriam M Tostado-Plascencia Luis M Alva Valdivia Cecilia Caballero Miranda |
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| Institution: | 1.Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Ingeniería Sísmica - Sede Guadalajara, CUCEI,Universidad de Guadalajara,Guadalajara,Mexico;2.Laboratorio Interinstitucional de Magnetismo Natural, Instituto de Geofísica - Sede Michoacán,Universidad Nacional Autónoma de México,Morelia,Mexico;3.Servicio Geológico Mexicano,Pachuca,Mexico;4.Depto. de Geología,Centro de Investigación Científica y de Educación Superior de Ensenada,B.C. México,Mexico;5.Instituto de Geofísica,Universidad Nacional Autónoma de México, Ciudad Universitaria,México,Mexico |
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| Abstract: | For long time the western-central Mexico has been affected by oblique subduction caused by Farallon plate beneath North America.
As result, smaller plates (e.g. Cocos Plate), several fault systems outlining crustal blocks (e.g. Michoacán block) and magmatic
arcs (e.g. Paleocene-Early Oligocene magmatism and the Trans-Mexican Volcanic Belt) were developed. Still, no paleomagnetic
data are available for Oligocene and Miocene. The principal aim of this study is to evaluate whether the tectonic rotations
and relative motions of these blocks occurred before the Miocene. Here, we report a detailed rock-magnetic and paleomagnetic
results from Tecalitlan area, located in the Michoacán block. Sixteen sites (about 150 oriented samples) were collected including
one radiometrically dated diabase dike (35.0 ± 1.8 Ma). Rock-magnetic experiments permitted identification of magnetic carriers
and assessment of the paleomagnetic stability. Continuous susceptibility measurements vs temperature in most cases yield reasonably
reversible curves with Curie points close to that of magnetite. Reliable paleomagnetic directions were obtained for 12 sites.
Inclination I and declination D of the mean paleomagnetic direction obtained in this study are I = 33.1°, D = 345.0°, and
Fisherian statistical parameters are k = 25, α95 = 8.9°. The corresponding mean paleomagnetic pole position is Plat = 75.7°, Plong = 166.6°, K = 31, A95 = 8.0°. The mean inclination is in reasonably good agreement with the expected value, as derived from reference poles for
the stable North America. Magnetic declination is not significantly different from that expected which is in disagreement
with a counterclockwise tectonic rotation of about 20° previously reported for the studied area. Based on paleomagnetic results
obtained in this study compiled with those currently available from the Michoacán Block, we propose a simple model suggesting
that sometime in Eocene epoch the convergence vector of the Farallon plate relative to North America plate was normal to the
trench before reaching an actual oblique convergence. |
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