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Isotope geochemistry and petrogenesis of peralkaline Middle Miocene ignimbrites from central Sonora: relationship with continental break-up and the birth of the Gulf of California

Vidal Solano, Jesús R. and Lapierre, Henriette and Stock, Joann M. and Demant, Alain and Paz Moreno, Francisco A. and Bosch, Delphine and Brunet, Pierre and Amortegui, Andrea (2008) Isotope geochemistry and petrogenesis of peralkaline Middle Miocene ignimbrites from central Sonora: relationship with continental break-up and the birth of the Gulf of California. Bulletin de la Société Géologique de France, 179 (5). pp. 453-464. ISSN 0037-9409. doi:10.2113/gssgfbull.179.5.453.

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Middle Miocene peralkaline ignimbrites constitute a specific geodynamic marker of the early stage of opening of the Gulf of California, preserved either in central Sonora or the Puertecitos area, in Baja California. Very uniform ages (12-12.5 Ma) obtained on these rocks show that this volcanic episode corresponds to a specific stage in the tectonic evolution of the proto-gulf area. Field observations and slightly different Sr and Nd isotopic signatures support eruptions from several small volume magma batches rather than from a large-volume caldera forming event. Isotopic ratios help to constrain the petrogenesis of the peralkaline liquids by fractional crystallization of transitional basalts in a shallow reservoir, with slight contamination by Precambrian upper crustal material. Less differentiated glomeroporphyritic icelandites erupted at about 11 Ma, mark an increase in the magma production rate and highlight an easier access to the surface, illustrating an advanced stage in the weakening of the continental crust. The tilting of the Middle Tertiary sequences results from a major change in the tectonic regime, from E-W extension giving rise to N-S grabens, to NNW-SSE strike-slip motion that can be related to the transfer of Baja California from North America to the Pacific plate. The location of peralkaline volcanism coincides with the southern edge of the Precambrian crust and the southernmost extension of the California slab window at 12.5 Ma.

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Stock, Joann M.0000-0003-4816-7865
Additional Information:© 2008 Société Géologique de France. Manuscript received 20 February 2007; accepted after revision 11 September 2007. This study is part of the Ph.D. thesis of the senior author at the Université Paul Cézanne (Aix-Marseille 3). This work was funded by CONACYT and SFERE (129313/168910) scholarship grant. Sampling and mapping were carried out from 1999 to 2005 with the financial support of the Departamento de Geología de la Universidad de Sonora. Thanks to M.O. Trensz (ICP-AES analyses, CEREGE) to J.-C. Girard (thin-section preparation) and C. Merlet (electron microprobe, ISTEEM Montpellier). ENS Lyon supported Pb isotope facilities. This work also benefited from a 6 months post-doctoral fellowship at Seismo Lab in Caltech, supported by the US National Science Foundation grant EAR-0336961. Reviews by Christian Picard and Marc Tardy help to improve the manuscript. [H.L.] - Décédée en Janvier 2006.
Group:Seismological Laboratory
Funding AgencyGrant Number
Consejo Nacional de Ciencia y Tecnología (CONACYT) (Mexico)UNSPECIFIED
Société Française d'Exportation des Ressources Éducatives (SFERÉ)129313/168910
Universidad de SonoraUNSPECIFIED
National Science FoundationEAR-0336961
Subject Keywords:Peralkaline ignimbrites; Middle Miocene; Isotope geochemistry; Gulf of California
Issue or Number:5
Record Number:CaltechAUTHORS:VIDbsgf08
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12557
Deposited By: Archive Administrator
Deposited On:13 Dec 2008 02:36
Last Modified:08 Nov 2021 22:29

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