Journal of Volcanology and Geothermal Research 324 (2016) 15–27
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Journal of Volcanology and Geothermal Research 324 (2016) 15–27 Contents lists available at ScienceDirect Journal of Volcanology and Geothermal Research journal homepage: www.elsevier.com/locate/jvolgeores Internal architecture of the Tuxtla volcanic field, Veracruz, Mexico, inferred from gravity and magnetic data Juan Manuel Espindola a,⁎, Hector Lopez-Loera b,ManuelMenaa, Araceli Zamora-Camacho c a Instituto de Geofísica, Universidad Nacional Autónoma de México, Ciudad Universitaria, Ciudad de México, C.P. 04510, Mexico b División de Geociencias Aplicadas, Instituto Potosino de Investigación Científica y Tecnológica, Camino a la Presa San José 2055, Col. Lomas 4a sección, San Luis Potosí, C.P. 78216 S.L.P., Mexico c Centro de Sismología y Vulcanología de Occidente, Centro Universitario de la Costa. Universidad de Guadalajara, Av. Universidad 203, Delegación Ixtapa, Puerto Vallarta, C.P.48280, Jalisco, Mexico article info abstract Article history: The Tuxtla Volcanic Field (TVF) is a basaltic volcanic field emerging from the plains of the western margin of the Received 26 October 2015 Gulf of Mexico in the Mexican State of Veracruz. Separated by hundreds of kilometers from the Trans-Mexican Received in revised form 11 May 2016 Volcanic Belt to the NW and the Chiapanecan Volcanic Arc to the SE, it stands detached not only in location Accepted 12 May 2016 but also in the composition of its rocks, which are predominantly alkaline. These characteristics make its origin Available online 14 May 2016 somewhat puzzling. Furthermore, one of the large volcanoes of the field, San Martin Tuxtla, underwent an erup- tive period in historical times (CE 1793). Such volcanic activity conveys particular importance to the study of the Keywords: Tuxtla volcanic field TVF from the perspective of volcanology and hazard assessment. Despite the above circumstances, few investiga- Basaltic volcanic fields tions about its internal structure have been reported. In this work, we present analyses of gravity and aeromag- Magmatic processes netic data obtained from different sources. We present the complete Bouguer anomaly of the area and its Potential signals in volcanic areas separation into regional and residual components. The aeromagnetic data were processed to yield the reduction Volcanoes of Mexico to the pole, the analytic signal, and the upward continuation to complete the interpretation of the gravity anal- yses. Three-dimensional density models of the regional and residual anomalies were obtained by inversion of the gravity signal adding the response of rectangular prisms at the nodes of a regular grid. We obtained a body with a somewhat flattened top at 16 km below sea level from the inversion of the regional. Three separate slender bodies with tops 6 km deep were obtained from the inversion of the residual. The gravity and magnetic anoma- lies, as well as the inferred source bodies that produce those geophysical anomalies, lie between the Sontecomapan and Catemaco faults, which are proposed as flower structures associated with an inferred deep- seated fault termed the Veracruz Fault. These fault systems along with magma intrusion at the lower crust are necessary features to understand the origin and structure of the TVF. © 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 1. Introduction question for many investigators of the Mexican geology (e.g. Pichler and Weyl, 1976; Robin, 1976; Thorpe, 1977; Cantagrel and The Tuxtla Volcanic Field (TVF), also known as Los Tuxtlas Volca- Robin, 1979; Nelson et al., 1995; Verma, 2006). However, until now nic Field or Los Tuxtlas Massif, is an isolated basaltic field emerging there is no general agreement on this question (e.g. Nelson et al., from the lowlands of the western margin of the Gulf of Mexico. It 1995; Verma, 2006). The TVF has received less attention than other lies in the Veracruz Basin, in the Mexican State of Veracruz (Fig. 1) volcanic areas of Mexico despite being the site of a volcanic eruption 230 km to the SSE of the easternmost tip of the Trans-Mexican Volca- in historical times (San Martin Tuxtla volcano, 1773). Nevertheless, nic Belt (TMVB), and about the same distance from El Chichon volca- because the western margin of the Gulf of Mexico has been widely no to the SE, in the Chiapanecan Volcanic Arc. Due to its separation studied, mostly from the perspective of oil and gas exploration, sev- from these volcanic chains, as well as to the alkaline composition of eral geophysical surveys have included the TVF. In particular, the its rocks, the origin of this volcanic field has been an intriguing area is marked by conspicuous gravity and geomagnetic anomalies circumscribed to the field. Although these signals had not been ana- lyzed in a volcanological context, they offer insight into the structure fi ⁎ Corresponding author. of this volcanic eld. We carried out such analysis aiming to infer the E-mail address: [email protected] (J.M. Espindola). internal fabric of this volcanic field. http://dx.doi.org/10.1016/j.jvolgeores.2016.05.006 0377-0273/© 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 16 J.M. Espindola et al. / Journal of Volcanology and Geothermal Research 324 (2016) 15–27 Fig. 1. Location of the Tuxtla Volcanic Field (inset). Generalized Geologic and structural map of Los Tuxtlas Volcanic Field. Continuous lines: faults; dashed lines: inferred faults. CATF: Catemaco Fault. SONF: Sontecomapan Fault. Geology after Nelson and Gonzalez-Caver (1992); faults after Andreani et al. (2008). 2. Geology and tectonic setting region, if present, is much deeper than 150 km as judging from the extrapolation of seismic foci. Analyses of receiver functions yield no The TVF lies in the middle of the Veracruz Basin; a Tertiary NNW evidence of the subducted plate interface (Espíndola, 2009; Melgar trending basin extending from the eastern tip of the Transmexican and Perez-Campos, 2010), although recently Kim et al. (2011) also Volcanic Belt to the Salina del Istmo Basin (Padilla y Sánchez, 2007). It based on receiver functions, interpreted some phases as transformed lies approximately 230 km from the tip of the Trans-Mexican volcanic at the interphase with a relic slab some 50 km below the TVF. They belt (TMVB) and El Chichon volcano to the SE and 350 km from the propose that it was the result subduction of oceanic lithosphere, before closest point on the Pacific trench. The subducting slab beneath this the collision of the Yucatán Block with Mexico, about 12 Ma ago. Fig. 2. Cross section across the Veracruz Basin (about 100 km NW from the TVF) based on seismic reflection data. The horizontal axis is the distance in kilometers; the vertical axis is two- way travel time in seconds. CATF: Catemaco Fault. SONF: Sontecomapan Fault. Modified after Andreani et al. (2008). J.M. Espindola et al. / Journal of Volcanology and Geothermal Research 324 (2016) 15–27 17 Table 1 Melgar and Perez-Campos (2010) found similar depth to the Moho Equipment, procedures, and treatment of the geomagnetic data provided by the Servicio underneath the TVF pointing out to the existence of significant azimuth- Geológico Mexicano. al variations in the depth estimations. Zamora-Camacho et al. (2010) Equipment and instruments also used receiver functions to estimate crustal structure underneath Plane Islander BN2-B21; BN2-B27 three stations deployed around San Martin Tuxtla volcano. They in- Fight magnetometer Scintrex CS-3; Geometrics ferred an interface at a depth of about 28 km for rays arriving from G-822 A Cesium Opt. Pump the NW, and about 34 km for rays arriving from the east and south, Sensitivity 0.001 nT they proposed this interface as the Moho. They also deduced another Data acquisition system PICODAS P-101 Base Station magnetometer GEM systems GSM-19, Overhauser velocity contrast at depths between 10 (for rays from the NW) and Sensitivity 0.01 nT 14 km continental basement and sediments deposited from early Radar altimetry TERRA TRI40-TRA3000 Miocene. Navigation system GPS ASHTEC + GLONASS Flight parameters 2.1. The Veracruz Basin Direction of lines of flight North–south Distance between flight lines 1000 m The Veracruz Basin developed over the eroded structures of the Distance between control lines 10,000 m Zongolica fold-thrust belt and extended to the east towards the Gulf of Flight altitude 300 m Navigation Electronic (GPS) Mexico (Sawyer et al., 1991; Prost and Aranda-Garcia, 2001). The TVF offshore is located at the margin of the Campeche Salt shelf and south Data processing of the Laguna Madre-Tuxpan (LMT) shelf, an extensive geologic prov- Correction for plane movement Magnetic compensation Reductions Diurnal variation. Subtraction of the IGRF 2000 ince that spans the western Gulf of Mexico (Padilla y Sánchez, 2007; Leveling Control lines, microleveling Le Roy et al., 2007). Le Roy et al. (2007) carried out a structural analysis Projection Transverse universal mercator of the area based on seismic profiles, digital elevation models, and satel- Grid UTM every 5000 m lite imagery. The study is focused mostly on the LMT shelf, but it offers Spheroid Clarke 1866 Datum NAD 27 information about the regional tectonic and geologic characteristics of Contour interval 25 nT the Veracruz Basin. As stated by these authors the basin evolved during Center of chart geomagnetic Year of Flight: 2004 the Mesozoic and Cenozoic. In the early Mesozoic, the Mexican margin Field data Altitude: 0.80 km was divided by rifting into a series of basement blocks separated by a Intensity: 41,152 nT thinned continental crust (Le Roy et al., 2007). During the Jurassic and Cretaceous post-rift subsidence favored the deposition over the base- ment blocks of platformal carbonates, concurrently basinal carbonates Fig.