Paper No. 16-1
Presentation Time: 8:30 AM-5:30 PM
LA PURISIMA VOLCANIC FIELD, BAJA CALIFORNIA SUR, MEXICO: MAGMATIC EVOLUTION FROM MIOCENE TO QUATERNARY
AGUILLÓN-ROBLES, Alfredo1, BELLON, Hervé2, CALMUS, Thierry3, MAURY, René C.4, BOURGOIS, Jacques5, and COTTEN, Joseph2, (1) Instituto de Geología, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava no. 5, San Luis Potosí, 78240, Mexico, aaguillonr@uaslp.mx, (2) UMR 6538, Domaines Océaniques, IUEM, Université de Bretagne Occidentale, 6, Av. Le Gorgeu, Brest, 29285, France, (3) Instituto de Geología, ERNO, Universidad Nacional Autónoma de México, Hermosillo, 83000, Mexico, (4) UMR 6538, Domaines Océaniques, IUEM, Université de Bretagne Occidentale, Place Nicolas Copernic, Plouzané, 29280, France, (5) IRD and CNRS Unité Mixte de Recherche "Géosciences Azur" 6526, Petroproducción-Centro de Investigaciones Geológicas, km 6.5 vía a la costa, Guayaquil, 09-03-30096, Ecuador

La Purísima Volcanic Field (PVF) displays a wide geochemical and petrologic variability for Middle Miocene to Quaternary volcanic rocks. It is limited to the east by the Main Gulf Escarpment and to the west by the Pacific shoreline. Baja California has been the locus of many events of volcanism including the emplacement of typical calc-alkaline lavas, magnesian andesites (adakite affinity), tholeiitic basalts and adakites. In that area, the calc-alkaline serie of the Comondú volcanic arc ranges in age from 16.4 ± 0.9 Ma to 11.0 ± 0.3 Ma. In the northwestern part, large mesas of tholeiitic basalts overlie tilted Tertiary sediments. They correspond to the southernmost tip of Esperanza Basalt. The low-K tholeiitic lavas are are silica-oversaturated. Their concentrations in most incompatible elements are low, and the corresponding multielement patterns normalized to primitive mantle present very flat shapes. Their whole-rock isotopic ages range between 10.6 ± 0.8 Ma to 9.33 ± 0.32 Ma obtained respectively from the well-crystallized cores of pillow lavas and their glassy margins. The Late Miocene to Quaternary volcanism belongs to the magnesian andesitic series. Their main geochemical characteristics are SiO2 contents ranging from 51.5 to 55.5 wt%, high values of MgO and K2O, together with high contents of incompatible elements such as Ba and Sr. In addition, these lavas are LREE-enriched and HREE-depleted. The oldest magnesian andesites are dated between 9.7 and 8.8 Ma. The second magnesian andesitic event, is dated at 5.48 Ma. A large magnesian andesitic mesa was emplaced at ca. 2.72 Ma. Younger mesas as well as rather small flows associated with spatter and strombolian cones were emplaced inside a N-NW trending elongated graben until very recent times, suggesting that Quaternary volcanic activity was discontinuous. The magnesian andesitic volcanism of La Purísima area is contemporaneous with adakitic volcanism, which occurred also in Baja California Sur well after the supposed end of the subduction of the Farallon plate. The geochemical characteristics of these magmas are still typical of subduction-modified sources and suggest partial melting of hot slab related to the formation of an asthenospheric window.

Cordilleran Section - 99th Annual (April 1–3, 2003)
General Information for this Meeting
Session No. 16--Booth# 1
Tectonics, Structure, and Geophysics of the Gulf of California–Salton Trough Region (Posters)
Hotel NH Krystal: La Capilla
8:30 AM-5:30 PM, Wednesday, April 2, 2003
 

© Copyright 2003 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.