A quaternary monogenetic volcanic field in the Xalapa region, eastern Trans-Mexican volcanic 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 a Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, Av. Universidad 3000, Coyoacán 04510, D.F., Mexico b Centro de Ciencias de la Tierra, Universidad Veracruzana, Francisco J. Moreno 207, Col. Zapata, 91090, Xalapa, Veracruz, Mexico c 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 abstract article info Article history: Received 16 December 2008 Accepted 10 August 2009 Available online 22 August 2009 Keywords: monogenetic volcanic field basaltic volcanoes Trans-Mexican Volcanic Belt scoria cones The most abundant volcanic manifestations along the east–west trending Trans-Mexican Volcanic Belt (TMVB) are the scoria 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 an area of about 2400 km 2 , 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. SiO 2 and Al 2 O 3 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 Cr concentrations 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 primary calc-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 km 3 for the cone volume. We dated twelve different scoria cones using the 40 Ar/ 39 Ar 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 slope angle. 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. 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 continental plate. This subduction process occurs along the Middle America Trench (MAT) and is responsible for the past and present volcanic and seismic activities in a huge area for central Mexico (Fig. 1). Other hypothesis explains the TMVB origin arguing the existence of a mega-shear (Mooser, 1972), a mantle plume (Márquez et al., 1999a), or rifting (Sheth et al., 2000; Verma, 2003). The TMVB and its related tectonic elements have been studied from different points of view, trying to explain its origin, age, geometry and activity, among other topics (i.e. Nixon, 1982; Nixon et al., 1987; Pardo and Suárez, 1993; Ferrari et al., 1994; Pardo and Suárez, 1995; Bandy et al., 1995; Kostoglodov and Bandy, 1995; Ferrari et al., 1999; Gómez-Tuena and Carrasco-Núñez, 2000). One of the most conspicuous characteristics of the TMVB is the partially oblique relation with respect to the MAT. The superficial manifestations of this particular geometry form a well defined pattern of volcanic vents that include stratovolcanoes such as Fuego and Nevado de Colima, Tancítaro, Jocotitlán, Nevado de Toluca, Iztaccíhuatl, Popocatépetl, Malinche, Cofre de Perote, La Gloria, Las Cumbres and Citlaltépetl, major calderas like La Primavera, Los Azufres, Amealco and Journal of Volcanology and Geothermal Research 197 (2010) 149–166 ⁎ Corresponding author. Departamento de Geología Regional, Instituto de Geología, Universidad Nacional Autónoma de México, Av. Universidad 3000, Coyoacán 04510, D.F., Mexico. E-mail address: srre@unam.mx (S.R. Rodríguez). 0377-0273/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2009.08.003 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores