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Le volcanisme hyperalcalin d'âge miocène moyen du nord-ouest du Mexique (Sonora). Minéralogie, Géochimie, cadre géodynamique

Abstract : A peculiar volcanic episode represented by peralkaline rhyolites and ignimbrites characterizes the continental break up that preceded the opening of the Gulf of California. Peralkaline rocks outcrop at the northwestern end of the Sonora State, east of the large Quaternary shield volcano of El Pinacate, and in the vicinity of the town of Hermosillo, in the central part of the State. Field studies, 40Ar/39Ar geochronology, mineral chemistry, geochemistry and isotopes (Sr, Nd, Pb) contribute to establishing the stratigraphy of the Tertiary volcanic successions and the petrogenesis of the peralkaline rhyolites. Variations in Sr isotopic ratios are evidence of contamination by the Precambrian crust. Modelling of the isotopic data support an origin for the peralkaline rhyolite by fractional crystallisation of transitional basalts in a shallow reservoir, with about 10 % contamination. Evidences of mixing also indicate that these liquids evolved in a periodically opened system. The distribution of the Middle Miocene peralkaline volcanism in Sonora is not fortuitous. The Pinacate area constitutes the southermost outcrops of a N-S belt of Miocene peralkaline rhyolites emplaced on the western margin of the North American craton. Outcrops of central Sonora are the counter part of similar sequences present in the Puertecitos area, in northern Baja California. These two groups are located on a major lithospheric discontinuity represented by the limit between the North American craton and the accreted exotic fragments of the Guerrero terranes. Volcanism seems to be related to asthenospheric upwelling (slab window ?) that induced lithospheric thinning and partial melting producing transitional basaltic magmas.
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https://tel.archives-ouvertes.fr/tel-00010346
Contributor : Jesus Roberto Vidal-Solano <>
Submitted on : Friday, September 30, 2005 - 5:49:54 PM
Last modification on : Wednesday, October 16, 2019 - 1:31:29 AM
Long-term archiving on: : Friday, April 2, 2010 - 10:51:05 PM

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  • HAL Id : tel-00010346, version 1

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Jesus Vidal-Solano. Le volcanisme hyperalcalin d'âge miocène moyen du nord-ouest du Mexique (Sonora). Minéralogie, Géochimie, cadre géodynamique. Géochimie. Université de droit, d'économie et des sciences - Aix-Marseille III, 2005. Français. ⟨NNT : 2005AIX3-0018⟩. ⟨tel-00010346⟩

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