Resumo

ROSAS-ELGUERA, José et al. The Carmichael Volcanic Succession of the Jalisco Block, Mexico: Magnetostratigraphy and tectonic implications. Bol. Soc. Geol. Mex [online]. 2022, vol.74, n.2, A061221.  Epub 05-Jun-2023. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2022v74n2a061221.

We report new paleomagnetic and rock magnetic data from 12 sites belonging to the Carmichael silicic ash-flow tuff volcanic succession. The base of this succession consists of volcanic breccias, lavas, and lithic tuffs of andesitic composition while the upper unit is composed of crystalline tuffs and welded tuffs both of rhyolitic composition, distributed in the northern central part of the Jalisco block. Their isotopic ages range between 61 and 83 Ma. The rock-magnetic experiments indicate to titanomagnetites with low titanium content as the main magnetic carrier, as well as the presence of titanomaghemites with minor magnetic contribution. Paleomagnetic directions were determined for eleven sites yielding eight normal and three reverse polarity magnetization. Considering all sites, the calculated average address is Dec = 344.7°, Inc = 43.2°, α95= 13.2, and N = 11, with a corresponding virtual geomagnetic pole of VGPlat, = 75.2°N, VGPlong= 186.6°E, A95= 11.7°. The paleomagnetic directions agree fits with expected ones and available mean paleodirections from nearby sites. Our results indicate the stability of the Jalisco block. The occurrence of rotational movements around a vertical axis is not sustained by paleomagnetic data. In addition, the transpressive tectonics previously reported for the northern continental boundary of the Jalisco block (which separates the Sierra Madre Occidental from the Trans-Mexican Volcanic Belt) is apparently not significant since it is not reflected in rotational movements of the Jalisco block.

Palavras-chave : Jalisco block; paleomagnetism; rock-magnetism; vertical-axis rotations; Carmichael volcanic succession.

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