HR: 17:30h
AN: V24A-05    [Abstracts]
TI: Mafic Volcanism Along the Sinaloa Coast, Mexico, and its Relation to the Opening of the Gulf of California
AU: * Orozco Esquivel, T
EM: torozco@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Ferrari, L
EM: luca@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, Queretaro, Qro 76230, Mexico
AU: Lopez Martinez, M
EM: marlopez@cicese.mx
AF: Departamento de Geologia, CICESE, Km. 107 Carretera Tijuana-Ensenada, Ensenada, BC 22800, Mexico
AB: We report on new localities with mafic volcanism along the Sinaloa coast, which record changes in the magma generation processes along the eastern margin of the Gulf of California. South of Culiacán, Sinaloa, isolated outcrops of basaltic lavas built a ca. 60 km long belt aligned to the SE. The similarity in the mineralogy and composition of the lavas suggest that these outcrops could have been part of a single flow. Lavas contain abundant plagioclase (up to 3 mm), and olivine (up to 1.5 mm) phenocrysts, and scarce clinopyroxene, in a relatively coarse matrix. In multiement diagrams, the lavas show the negative Nb and Ta, and positive Pb and Sr anomalies characteristic of subduction related rocks. The age determination of these rocks is in process, nevertheless, rocks with similar compositions are known from ~11 Ma mafic dikes that outcrop in southern Sinaloa. The Pericos volcanic field, located about 25 km to the NW of Culiacán is composed by lava flows, shield volcanoes, and cinder cones of basaltic composition that cover an area of aprox. 20 x 32 km, and have a well preserved morphology suggestive of a Pliocene-Quaternary age. Lavas are porphyritic and contain olivine, plagioclase and clinopyroxene in a microcrystalline matrix. Some lava flows contain abundant megacrysts of green clinopyroxene (up to 8 cm), olivine (up to 1 cm), and/or plagioclase (up to 1 cm), or aggregates of olivine and clinopyroxene. Trace element abundances are remarkably uniform among all analyzed samples and are characteristic of intraplate magmas. Rocks with very similar composition, mineralogy, and also containing megacrysts, have been reported in the Pliocene Punta Piaxtla and Mesa Cacaxtla, located 200 km to the SSE at the Sinaloa coast. Those similarities indicate that mafic intraplate volcanism related to the opening of the Gulf of California is more broadly represented in the area than previously considered.
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1065 Major and trace element geochemistry
DE: 8105 Continental margins: divergent (1212, 8124)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly