Paleomagnetic study of the Valle de Santiago volcanics, Michoacán-Guanajuato volcanic field, Mexico

The Valle de Santiago area of the Michoacán-Guanajuato volcanic field is characterized by a 7 km by 50 km NNW-SSE trending cluster of 20 maars, 13 in a smaller sub-area. This volcanic lineament may be associated with a pre-existing fault or zone of structural weakness, which is approximately normal...

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Bibliographic Details
Published inGeofísica internacional Vol. 38; no. 4; pp. 217 - 230
Main Authors Jaime Urrutia-Fucugauchi, Rosa María Uribe-Cifuentes
Format Journal Article
LanguageEnglish
Spanish
Published Universidad Nacional Autónoma de México, Instituto de Geofísica 01.12.1999
Subjects
Michoacan-Guanajuato volcanic field
Paleomagnetism
Plio-Quaternary
Tectonics
Valle de Santiago
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Summary:The Valle de Santiago area of the Michoacán-Guanajuato volcanic field is characterized by a 7 km by 50 km NNW-SSE trending cluster of 20 maars, 13 in a smaller sub-area. This volcanic lineament may be associated with a pre-existing fault or zone of structural weakness, which is approximately normal to the regional structure of the Trans-Mexican volcanic belt (TMVB). One hundred and twenty one samples were collected from 13 volcanic units of Pliocene andesites and Quaternary andesites and basalts, including the maars, cinder cones and composite volcanoes. The magnetic polarity except at one site is normal. The oldest K-Ar date associated with maar volcanism is 1.2 Ma. The magnetic polarity suggests that activity took place within the Brunhes Chron, implying ages younger than 0.78 Ma. The overall mean direction and paleomagnetic pole location from 10 sites are Dec = 353.7°, Inc = 39.2°, k = 42, α95 = 7.6°, and PLAT = 78.4° N and PLONG = 180.0° E. The Valle de Santiago lineament forms part of a larger system in the northern part of the TMVB that includes the Querétaro-Taxco fault zone (QTFZ). These NNW-SSE trending lineaments intersect the young E-W and ENE-WSW structural trends of the TMVB, represented in the area by the Chapala-Tula fault zone. Paleomagnetic studies in the eastern Chapala basin have documented counter-clockwise (CCW) rotations. Studies in the Acambay graben close to the intersection with the QTFZ yield variable amounts of clockwise (CW) and CCW rotations. The mean declination lies to the west -6.3° + 6.1° of the expected direction, within the statistical uncertainty. Results for the Valle de Santiago area suggest a possible small CCW rotation associated with the regional compressional stress field acting on the NNW-SSE Valle de Santiago lineament and the E-W Chapala-Tula fault system.
ISSN:0016-7169