%0 Journal Article
%A Ruiz Martínez, Vicente Carlos
%A Osete López, María Luisa
%A Vegas Martínez, Ramón
%A Núñez Aguilar, Juan Ignacio
%A Urrutia Fucugauchi, Jaime
%A Tarling, Donald H.
%T Palaeomagnetism of Late Miocene to Quaternary volcanicsfrom the eastern segment of the Trans-Mexican Volcanic Belt
%D 2000
%@ 0040-1951
%U https://hdl.handle.net/20.500.14352/57608
%X A systematic palaeomagnetic study in the eastern part of the Trans-Mexican Volcanic Belt includes 39 Miocene,Pliocene and Quaternary volcanic rocks in the southeastern Mexico Basin (Sierra Nevada and Sierra de Rı´o Frı´o),the Altiplano area, and the Palma Sola Massif. A total of 430 samples have been selectively demagnetized usingmostly alternating field demagnetizing methods, supplemented by thermal analyses. Most characteristic remanencesare carried by low-Ti titanomagnetites, with occasional titanohematites or slightly maghemitized low-Ti titanomagnetites,of similar direction. Seven sites were discarded because they presented intermediate directions, hydrothermalalteration or were remagnetized by lightning strikes. The mean directions of 32 sites, together with 24 sites fromSierra de las Cruces in the western Mexico basin, indicate rocks older than 2 Ma are rotated some 10° counterclockwisewith respect to Quaternary rocks, whereas there is no rotational difference between Miocene and Pliocene rocks.Statistical analyses between different regrouped populations confirm that the rotational pattern is due to the age ofthe volcanics rocks but not to their spatial distribution. The Quaternary mean direction from the three Mexico Basinranges is consistent with the geographical reference pole. In contrast, the Pliocene mean direction from volcanic rocksof the Altiplano area and the Sierra de Las Cruces is slightly rotated some 10° westwards with respect to the referencedirection from North America. No significant rotations have been observed in the eastern TMVB (from the westernMexico Basin to the border of the Altiplano), between late Miocene and late Pliocene times. It suggests that a verysmall, counterclockwise vertical-axis rotation may have been taken place in this segment of the TMVB between latePliocene and Quaternary times. Comparisons of these results with a summary of the available palaeomagnetic datain the area indicate that the previously reported Quaternary rotations are of questionable reliability, and that thelarge counterclockwise rotations, reported in Cretaceous to Miocene rocks, probably took place before the lateMiocene. These new palaeomagnetic data support the idea that the eastern TMVB since the late Miocene, has beena zone of extension with a little, left-lateral shear component.
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