ARTICLE IN PRESS
Journal of Volcanology and Geothermal Research xxx (2009) xxx–xxx
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Journal of Volcanology and Geothermal Research
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A quaternary monogenetic volcanic ﬁeld in the Xalapa region, eastern Trans-Mexicanvolcanic belt: Geology, distribution and morphology of the volcanic vents
S.R. Rodríguez a,b,⁎, W. Morales-Barrera b, P. Layer c, E. González-Mercado d
Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, Av. Universidad 3000, Coyoacán 04510, D.F., Mexico Centro de Ciencias de la Tierra, Universidad Veracruzana, Francisco J. Moreno 207, Col.Zapata, 91090, Xalapa, Veracruz, Mexico Geophysical Institute, University of Alaska, Fairbanks, 903 Koyukuk Drive, Fairbanks AK, 99775, USA d PEMEX, Exploración, Urano 420, Módulo E. Ylang Ylang, Boca del Río, 94299, Veracruz, Mexico
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The most abundant volcanic manifestations along the east–west trending Trans-Mexican Volcanic Belt (TMVB) are thescoria cones. These have been grouped by other authors in extended monogenetic volcanic ﬁelds such as Michoacán-Guanajuato, Chichinautzin, Apan and Los Tuxtlas. Here we present geological and morphological data of a relatively unknown group of monogenetic volcanoes located on the east ﬂank of the Cofre de Perote volcano (CP), around the city of Xalapa in the state of Veracruz, Mexico. Within anarea of about 2400 km2, the “Xalapa Monogenetic Volcanic Field” (XMVF) contains over 50 late Quaternary volcanoes. Most of them are scoria cones, but small shield volcanoes and tuff rings also occur. The lava ﬂows produced by these volcanoes are constrained by an abrupt topography and cover a great percentage of the surface on the eastern and northeastern ﬂanks of CP, between 3000 and 500 m a.s.l.The representative rocks of the different volcanic centers include olivine basalt, basaltic andesite with phenocrysts of plagioclase, pyroxene and minor olivine, and andesite with phenocrysts of plagioclase and pyroxene. SiO2 and Al2O3 contents of the rocks vary between 45 and 62 wt% and 15 to 18 wt%, respectively. Most of the basaltic rocks have MgO contents between 4.2 and 9 wt%, Ni and Crconcentrations between 23 and 180 and 10 to 380 ppm, respectively, with a typical calc-alkaline behavior. Trace elements suggest two types of magmas; the most abundant are characterized by an enrichment of LILE and LREE with negative anomalies of Nb and Ti, which denote a calc-alkaline afﬁnity. Others are LILE depleted and show high concentrations of MgO, Cr, and Ni, which is typical of primarycalc-alkaline magmas. The mean scoria cone morphological values are: cone height (Hco) = 90.8 m, cone diameter (Wco) = 686.38 m, crater diameter (Wcr) = 208.49 m and 0.12 km3 for the cone volume. We dated twelve different scoria cones using the 40Ar/39Ar method; for the other cones we used morphologic indicators such as the ratio of the scoria cone height to basal diameter (Hco/Wco) and maximum slopeangle. Additionally, vegetation type, and cone and lava ﬂow morphologies were also considered in order to determine rough relative ages. In general, the ages fall into three groups, those older than 2.0 Ma, those between 0.25–0.40 Ma and those less than approximately 0.1 Ma. ©2009 Elsevier B.V. All rights reserved.
Article history: Received 16 December 2008 Accepted 10 August 2009 Availableonline xxxx Keywords: monogenetic volcanic ﬁeld basaltic volcanoes Trans-Mexican Volcanic Belt scoria cones
1. Introduction The Trans-Mexican Volcanic Belt (TMVB) is a major volcanic province that crosses the country in an east–west direction (Mooser, 1972; Demant, 1978). It is a continental volcanic arc produced by the subduction of the Cocos and Rivera oceanic plates, under the North America...