Location of the Two Magma Chambers of Tequila Volcano by Gravity Analysis

Location of the Two Magma Chambers of Tequila Volcano by Gravity Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Location of the Two Magma Chambers of Tequila Volcano by Gravity Analysis Román Alvarez, Miguel Camacho-Ascanio This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9430674/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Tequila volcano is located on the northeastern margin of the Jalisco Block, along the Tepic-Zacoalco rift in western Mexico, and its latest activity has been dated at approximately 90 ka. In this study, we use the GGMplus gravity data set to perform 3D gravity inversions to depths of up to 8 km to explore the possible location of the two magma storage regions previously proposed for Tequila volcano. During the inversion process, models with 1000 and 250 m resolution were evaluated to investigate possible magmatic ascent pathways beneath the main volcanic edifice and adjacent lava flows. The 1000 m resolution model reveals a shallow low-density region at about + 1500 masl beneath Tequila volcano, as well as a deeper anomaly located about 8 km southwest of the summit, at approximately − 6000 mbsl; these features are interpreted as being consistent with the shallow and deeper magma chambers previously suggested for the volcanic system. The inversion results also suggest a structurally controlled zone that may have facilitated magma ascent, including a narrow connection near − 3300 mbsl between both low-density regions. The 250 m resolution model further resolves a bifurcation of the shallow low-density region beneath the summit depression, a geometry that may help explain the origin of the summit’s caldera-like morphology and its relation to the central spine. One possible interpretation is that the spine partially obstructed an earlier ascent pathway, promoting a change in the position of eruptive discharge and the development of a lateral conduit; the inferred traces of these possible pathways are illustrated here. The study area also includes the segment of the Santiago River closest to Tequila volcano, which trends NW; in this sector, the inversion identifies shallow low-density materials that may be related to sediment accumulation, as well as a narrow vertical feature extending to ~ 4100 m depth, tentatively interpreted as a fault zone. Tequila volcano La Primavera caldera Jalisco Block 3D gravity inversions GGMplus gravity data Caldera depression Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 1. Introduction Tequila volcano is located within the Tepic-Zacoalco rift in central-western Mexico; the rift is a tectonic, extensional region containing several volcanic structures, Tequila volcano among them, whose youngest activity occurred at ~ 90 ka erupting through the flanks of the main cone (Vázquez-Duarte et al., 2011 ). In Fig. 1 a group of volcanic edifices are displayed, aligned with Tequila volcano (TQ). Ferrari et al. ( 2003 ) identify this alignment with the north limit of the Jalisco Block. The distance between TQ and its nearest volcanic neighbor, La Primavera domes, is ~ 30 km; it is worth noticing the closeness of the times of the latest activity of both volcanic centers: Tequila volcano developed its latest activity at 90 ka, whilst in La Primavera it occurred at 95 ka (Mahood, 1980 , 1981a , b ), and their locations along the north limit of the Jalisco Block. Tequila volcano reaches an altitude of 2,840 m, rising from a plateau of 1000 m and is composed of ~ 25 km 3 of pyroxene andesite (Harris, 1986 ; Wopat, 1990 ). When the volcano’s activity ceased, abundant eruptions emerged on its flanks (Wallace and Carmichael, 1994 ). TQ shows a peculiar summit, since it shows a depression resembling a caldera, which is common in other volcanoes of the region (e.g., Luhr and Prestegaard, 1988 ; Stoopes and Sheridan, 1992 ), or induced by powerful explosions (Luhr, 1978 ; Nelson, 1980 ). However, previous reports found that features associated with those phenomena are not present at TQ (Demant, 1979 ; Wallace and Carmichael, 1994 ) concluding that the summit depression probably originates in erosional processes. The latter authors mention that the most prominent feature of TQ is a 300 m spine occupying a summit depression that is breached on the eastern side. Here we will look at this problem, analyzing density cross-sections across the summit. The latest activity in TQ occurred ~ 90 ka through the flanks of the volcano; Vázquez-Duarte et al. ( 2011 ) conclude that TQ is an unusual stratovolcano that seems to evolve in pulses of petrologically unrelated magmas. According to Mahood ( 1980 , 1981a , b ) La Primavera caldera was formed at ~ 95 ka inducing a collapse of ~ 11 km diameter, closely coinciding with TQ latest activity. A connection between the two occurrences is not far-fetched given the proximity in time and space of these two events. For TQ, a chamber at 2–3 km depth is inferred from phenocryst assemblages. After a lapse of ~ 110 kyrs, eruptions followed on the NW and SE flanks of TQ, probably originating in a second magma chamber at ~ 6 km depth (Lewis-Kenedi et al., 2005 ). Cerro Tomasillo (~ 60 ka) is a small andesitic volcano SE of Tequila Volcano. A DEM of the Tequila Volcanic Region appears in Fig. 2 , where topographic contours help identify some of its surface characteristics. Of particular interest is the NW-SE alignment of the summit of the main structure (TQ), Cerro Tomasillo (CT), and five volcanic cones (VC) that extend along 14 km in the SE direction. Regions designated Younger Flows (YF) and Younger Andesitic Flows (YAF) west of the summit of TQ are described by Lewis-Kenedi et al. ( 2005 ); they suggest that a prominent NW-SE lineament of TQ and andesite flank lavas is an indication that they overlie a major passageway for the ascent of magmas from the lower to the middle crust. As will be seen, we find here the exact location of this passageway. The two chambers under TQ were probably the site of mingling between ascending magma batches. 2. Methods 2.1 Data acquisition High-resolution gravity data for the La Primavera–Tequila volcanic area were obtained from the satellite-derived GGMplus model (Hirt et al., 2013 ). This dataset provides near-global coverage within the latitudinal band between 60°N and 60°S, although some offshore regions remain less well constrained because of limitations in the underlying source data. The Bouguer anomaly (BA) used in this study was calculated following standard gravity reduction procedures commonly applied to satellite-derived gravity data and consistent with recent regional studies in Mexico (e.g., Camacho & Alvarez, 2020 , 2021 ; Alvarez & Camacho, 2023a , b , 2024, 2025a,b; Camacho-Ascanio & Alvarez, 2024 ; Guevara-Betancourt et al., 2023 ). To maximize comparability with previous work, data processing followed the standard reduction workflow recommended by the U.S. Geological Survey (Hildenbrand et al., 2002 ). This procedure applies the conventional gravity corrections, including free-air, Bouguer slab, terrain, and atmospheric terms, to enhance density-related crustal signals and make the data suitable for structural interpretation and derivative analysis. In general form, the Bouguer anomaly can be expressed as: $$\:BA=g-\gamma\:+\delta\:gFA-\delta\:gB-\delta\:gTC-\delta\:gAT\:$$ where g is the gravity value from the adopted product, 𝛾 is the normal gravity reference, 𝛿𝑔𝐹𝐴 is the free-air correction, 𝛿𝑔B is the Bouguer correction, 𝛿𝑔𝑇𝐶 is the terrain correction, and 𝛿𝑔𝐴𝑇 is the atmospheric correction. The detailed procedure—including specific formulations, adopted parameters, and implementation—has been fully described in previous studies using satellite-derived gravity data (e.g., Camacho & Alvarez, 2020 ; Camacho-Ascanio & Alvarez, 2024 ; Alvarez & Camacho, 2024; Alvarez & Camacho-Ascanio, 2025a ). In practice, the processing began with the Gravity Observed (GObs) product from GGMplus, from which the BA was calculated according to the USGS gravimetric reduction standard (Hildenbrand et al., 2002 ). Elevation values required for the reductions were extracted from the GEBCO global topographic model, with a spatial resolution of 15 arc-sec (approximately 450 m) (GEBCO Compilation Group, 2021). ETOPO 2022 was used as a complementary topographic reference where needed (NOAA National Centers for Environmental Information, 2022 ). Terrain corrections were computed in Oasis Montag using the implementation based on the method of Kane ( 1962 ), with the extension proposed by Nagy ( 1966 ). To emphasize the shallow-to-intermediate density contrasts associated with the volcanic structures, the gravity field was further processed using a Gaussian filter to separate the residual component. This residual BA dataset was then used as the basis for the structural interpretation presented below (Fig. 3 ). In volcanic regions, negative gravity anomalies commonly reflect low-density zones related to volcanic edifices, magma reservoirs, and associated plumbing systems (e.g., Alvarez and Yutsis, 2015 ; Guevara-Betancourt et al., 2023 ; Alvarez and Camacho, 2023b ; Suryanata et al., 2024 ; Alvarez & Camacho-Ascanio, 2025b ). 2.2 The Regional Bouguer Anomaly Regional gravity anomalies describe the behavior of gravity in extended regions; in the present case it describes the regional behavior of gravity in a region comprising La Primavera volcanic field and the Tequila volcano area. Residual gravity values in the map display a range of 37 mGal; a high gradient is observed on the cone of Tequila volcano, evolving into a NW-SE elongation across it. . 2.3 3D Gravimetric Inversion Following the calculation of the Bouguer anomaly (BA), a 3D gravity inversion was performed to obtain volumetric density-contrast models and thereby constrain the subsurface structure associated with the main tectonic features of the region. The inversion was carried out in Oasis Montag (Seequent, version 2025.2) using the workflow described by Macleod and Ellis ( 2013 ), based on the theoretical framework of Ellis et al. ( 2012 ). This approach discretizes the subsurface using a Cartesian cut-cell (CCC) representation and estimates the 3D distribution of density contrast by minimizing the misfit between observed and forward-calculated gravity data through an iterative reweighting inversion (IRI) procedure (Ingram et al., 2003 ). In the present implementation, iterations were continued until the data misfit was reduced to within 5% of the standard deviation of the observed BA values. This threshold was adopted as a practical convergence criterion to achieve an adequate balance between data fit and model stability under regularization. The inversion input consisted of gridded BA data (mGal), which were transformed into density-contrast models (g/cm³) through the 3D inversion process. Two inversions were computed using cell sizes of 1000 m and 250 m, respectively, in order to evaluate the density structure at different spatial resolutions. The maximum depth of each model was selected according to the adopted discretization, yielding model depths of approximately 9 km for the 1000 m grid and 5 km for the 250 m grid. Thus, the depth extent and lateral dimensions of the recovered density structure were controlled by the selected computational domain and model resolution. The resulting density distributions were subsequently analyzed and interpreted in terms of their possible relationship with subsurface geological materials and structural features. Figure 4 presents the inversion result obtained with the 1000 m resolution model, which extends to approximately − 6 km below sea level, equivalent to a total depth of about 9 km from the average surface elevation. In the 250 m resolution cross-sections, the corresponding DEM-derived topographic profile was included to facilitate comparison between density variations and surface morphology. Model performance was assessed by comparing observed and predicted gravity responses, including residual anomaly maps, and by confirming that the final solution satisfied the convergence criterion defined above. 3. Density cross-sections Two resolutions are used in these analyses: 1000 and 250 m. The finer-resolution model provides greater detail in the recovered density structure, although at the expense of a shallower depth extent. The locations of the density cross-sections are defined by Lines 1–4 in Fig. 3 , which traverse the black and green rectangles, respectively. 3.1 1000-m resolution Two orthogonal, density cross-sections through the summit of Tequila volcano are shown in Fig. 4 . In both, and directly under the summit of TQ, a low-density region shows a minimum at an elevation of + 500 m, as shown by the contours; we frequently associate this type of minimum with the location of magmatic deposits, which in the present case coincides with the depth of the shallow magma chamber proposed by Lewis-Kenedi et al., ( 2005 ). The N-S cross-section shows a high-density region at the summit; this type of response is obtained when domes are extruded close to the summit, although in the present case it appears to be associated with the spine reported by Wallace & Carmichael, ( 1994 ). We shall further comment on this when discussing the 250-m resolution profiles. In the N-end a low-density region is associated with Santiago River; the topographic profile corresponds to the presence of a canyon, or graben-like depression, with its associated shallow, low-density region, which may be ascribed to sedimentary materials. Figure 5 a corresponds to L3 in Fig. 3 , oriented in the SW-NE direction; the high-density region observed at the top of TQ in Fig. 4 b is not intersected in this orientation. In this projection, the width of the low-density region associated with TQ is ~ 5 km and is flanked by high-density regions, which appear to be divided by the fault plane of the prominent NW-SE lineament reported by Lewis-Kenedi et al.. ( 2005 ). The location of Santiago River is also intersected as a low-density region of shallow depth. Figure 5 b shows the NW-SE density cross-section through the summit of TQ. This orientation reveals that feeding of the TQ magma chamber at 500 masl occurs laterally, rather than vertically, as shown by the red arrows bifurcating at 5000 mbsl. This is the only cross-section showing a widespread distribution of low-density materials, drastically contrasting with the extent of the low-density region intersected in the SW-NE density cross-section (Fig. 5 a), implying that it coincides with a fault plane that reliefs magma ascent, confirming the account of Lewis-Kenedi et al. ( 2005 ). It also intersects the position of Cerro Tomasillo, a small andesite volcano SE of TQ and the regions to the NW and SE, the flows called the Younger Flanks; all appear to be fed by a source deeper than 6 km bsl. Continuing to the SE, the volcanic region ends in a high-density region; at the end of the line is La Primavera caldera, where lower density regions replace portions of the high-density region. At this resolution, regarding the magmatic chambers proposed by Lewis-Kenedi et al., ( 2005 ), we can establish the existence of a surficial magma deposit centered at an elevation of + 500 m, or 1.5 km depth, corresponding to the magma chamber suggested by them between 2–3 km depth. We find a feeding channel displaced ⁓8 km SE of the summit of TQ at a depth of -3300 mbsl that connects to a deeper magma source. Since the NW-SE density cross-section (Fig. 5 b) is the only one showing considerable dispersion of low-density materials, we conclude that this is probably a fault plane that enables magma ascent, particularly since the main edifice (TQ) is not directly above the main feeding channel but displaced ⁓8 km to the NW. A similar lateral feeding was registered for Popocatépetl volcano in the Sierra Nevada (Alvarez and Camacho-Ascanio, 2025b ). To elucidate the connection between the shallow and the deep magma chambers we obtained horizontal density sections at various depths (Fig. 6 ), where a dashed circle marks the surface location of Tequila volcano. At sea level (0 m) the low-density anomaly appears elongated in the NW-SE direction with its thickest portion to the SE. This anomaly is flanked by high-density regions to the NE and the SW, creating a sort of low-density channel; this arrangement persists down to -5900 m. The encircled, low-density anomaly persists to -3300 m, disappearing at -4500 m, being substituted by a larger, deeper anomaly to the SE that reaches the S limit of the sections, and begins to appear at -2100 m. At -3300 m, within the circle remains a thin, low-density passage that we interpret as the fault that connects the main magma chamber with the one located at + 500 m (Figure B/5). At -5900 m the NW-SE lowest-density region is clearly defined, which we interpret as the magma chamber at 6 km depth proposed by Lewis-Kenedi et al. ( 2005 ). 3.2 250-m resolution In this projection mid-density regions become high-density regions as they approach the surface on the volcano’s flanks. They appear to belong to abandoned flow trajectories that fed flank eruptions. 4. Discussion Regarding the depth and location of the deeper magma chamber we will consider Figs. 5 and 6 . The NW-SE cross-section in Fig. 5 b shows that the low-density anomaly feeding TQ and the surrounding volcanic formations reaches the bottom of the cross-section (6 km bsl) indicating its downward continuation. The horizontal section at -4500 m in Fig. 6 shows the top of the deeper magma chamber as a faint blue, whereas at -5900 m darker blue is established in half the area of the anomaly; the darker blue corresponds to the region where the density is lower, or where magmatic products are concentrating. We conclude that the center of the deeper magma chamber is located between 6200 and 6500 mbsl. From this location magmatic materials are sporadically ejected upwards through the feeding channel. A peculiar bifurcation of the low-density region systematically appears close to the summit in the 250-m resolution cross-sections (Figs. 7 – 10 ), which originates in the upper magma chamber located at + 1500 m. The mechanism we prefer to induce this bifurcation is the blockage of the initial chimney, most likely by the injection of the spine, potentially followed by an explosion that partially destroyed the summit, creating a new discharge trajectory. The spine appears in the cross-sections of Figs. 8 – 10 , as a small high-density region. We have reported similar chimney blockages and subsequent explosions at Nevado de Toluca (Alvarez & Camacho, 2023b ) and Popocatépetl volcanoes (Alvarez & Camacho-Ascanio, 2025b ) The latest activity in TQ occurred ~ 90 ka through the flanks of the volcano, probably originating in the second magma chamber at ~ 6 km depth, as inferred by Lewis-Kenedi et al., ( 2005 ). In Fig. 10 there are discharge trajectories ending at the flanks of TQ, which we interpret as the conduits of the flanks’ lava flows that have now solidified, presenting larger densities. The path of Santiago River is intersected in Figs. 4 – 5 associated with a topographic depression and a shallow, low-density region that we attribute to sediment accumulation. In Fig. 6 it displays a thin, semi-circular trajectory that persists from sea level to -2100 m, indicating a crustal incision of over 4 km from the surface. This is the section of SR closest to Tequila volcano and its trajectory appears to be influenced by the dominating NW-SE orientation of volcanic structures in this region. 5. Conclusions Applying gravimetric treatments to Tequila volcano and its surroundings, we confirmed the existence of the two magma chambers proposed by Lewis-Kenedi et al., ( 2005 ); we found that only the shallow chamber is directly under the volcanic cone, with the deeper one displaced 8 km to the SE. The connection has been established between the two magma chambers feeding Tequila volcano and the surrounding areas designated as the Younger Flanks, between elevations of -6 km and + 500 m, both connecting through a narrow passage located at -3300 m elevation. The caldera-type summit is explained based on the bifurcation of the low-density region close to the volcano’s summit, as the result of a blockade of a former chimney by an intrusive body, called the spine, inducing an explosion, and deviating the exhaust to its new trajectory. Declarations Conflicts of Interest The authors declare no conflicts of interest regarding the publication of this paper. Author Contribution RA wrote the main manuscript text, contributed to the definition of the project and to the organization of the manuscript.MC contributed with data acquisition and processing, writing portions of the manuscript, and content discussions. Acknowledgement The Instituto de Investigación en Matemáticas Aplicadas y Sistemas (IIMAS) and Instituto de Geofísica, both from Universidad Nacional Autónoma de México (UNAM) supported this research; no external funds supported it. Data Availability All data supporting the findings of this study are available within the paper or by request from the authors. References Alvarez R, Yutsis V (2015) Southward migration of magmatic activity in the Colima Volcanic Complex Mexico: An ongoing process. Int J Geosci, 6, 1077–1099. http://dx.doi.org/10.4236/ijg.2015.69085 Alvarez R, Camacho M (2023a) Plumbing System of Hunga Tonga Hunga Ha’apai Volcano. J Earth Sci 34:706–716. https://doi.org/10.1007/s12583-022-1792-0 Alvarez R, Camacho M (2023b) Applying High-Resolution Gravity Analysis to Volcanic Plumbing Systems: The Case of Nevado De Toluca Volcano, Mexico. Trans Eng Comput Sci 11(4):184–207. https://doi.org/10.14738/tecs.114.15392 Alvarez R, Camacho M, Rivera-Calderón E (2024) The Internal Structure of Paricutin And Tancítaro Volcanos, Mexico, From Rock Density Distributions. Trans Eng Comput Sci 12(2):50–69. https://doi.org/10.14738/tecs.122.16645 Alvarez R, Camacho-Ascanio M (2025a) Plausible Northern Extension of Los Humeros Caldera Geothermal Field and Correlation of Density and Electrical Resistivity within the Collapsed Structure. Engineering 17:659–679. 10.4236/eng.2025.1712037 Alvarez R, Camacho-Ascanio M (2025b) Gravimetric Definition of the Magmatic Chambers of the Popocatépetl-Iztaccíhuatl Volcanic Complex, Mexico. Earth Sci Eng. 10.57237/j.earth.2025.01.001 Camacho M, Alvarez R (2020) Gravimetric analysis of the rifts and volcanic fields of the Jalisco block. Mexico Tectonophysics 791(July):228577. https://doi.org/10.1016/j.tecto.2020.228577 Camacho M, Alvarez R (2021) Geophysical Modeling with Satellite Gravity Data: Eigen-6C4 vs. GGM Plus Engineering 13:690–706. 10.4236/eng.2021.1312050 Camacho-Ascanio M, Alvarez R (2024) Delineation of the boundaries of San Blas basin, Mexico, merging gravity, magnetic, and seismic data. J S Am Earth Sci 136:104818. https://doi.org/10.1016/j.jsames.2024.104818 Demant A (1979) Vulcanología y petrografía del sector occidental del Eje Neovolcánico. UNAM, Inst Geol Revista 3:39–57 Ellis RG, de Wet B, Macleod IN (2012) Inversion of magnetic data from remanent and induced sources. ASEG Extended Abstracts 2012 (1), 1–4. https://doi.org/726727 72810.1071/ASEG2012ab117 Ferrari L, Petrone CM, Francalanci L, Tagami T, Eguchi M, Conticelli S, Manetti P, Venegas-Salgado S (2003) Geology of the San Pedro–Ceboruco Graben, western Trans-Mexican Volcanic Belt. Rev. Mex. C. Geol. , v. 20, núm. 3, 2003, pp. 165–181 Guevara-Betancourt R, Yutsis V, Varley N, Almaguer J, Alvarez R, Calderón-Moctezuma A, Sieck P (2023) Insights into the plumbing system of Colima Volcanic Complex from geophysical evidence. J Volcanol Geoth Res 433:107711. https://doi.org/10.1016/j.jvolgeores.2022.107711 GEBCO Bathymetric Compilation Group (2021) The GEBCO_2021 Grid: A continuous terrain model of the global oceans and land. Br Oceanogr Data Centre. https://doi.org/10.5285/c6612cbe-50b3-0cff-e053-6c86abc09f8 Harris JM (1986) Silicic volcanics of Volcan Tequila, Jalisco, Mexico. MSc thesis, University of California, Berkeley, CA Hildenbrand TG, Briesacher A, Flanagan G, Hinze WJ, Hittelman AM, Keller GR, Kucks RP, Plouff D, Roest W, Seeley J, Stith DA, Webring M (2002) Rationale and operational plan to upgrade the U.S. gravity database. U.S. Geological Survey Open-File Report 2002 – 463, 12 p. https://doi.org/10.3133/ofr02463 Hirt C, Claessens S, Fecher T, Kuhn M, Pail R, Rexer M (2013) New Ultrahigh-Resolution Picture of Earth’s Gravity Field. Geophys Res Lett 40:4279–4283. https://doi.org/10.1002/grl.50838 Ingram DM, Causon DM, Mingham CG (2003) Developments in Cartesian cut cell methods. Math Comput Simul 61(3–6):561–572. https://doi.org/10.1016/S0378-4754(02)00107-6 Kane MF (1962) A comprehensive system of terrain corrections using a digital computer. Geophysics 27(4):455–462. https://doi.org/10.1190/1.1439044 Lewis-Kenedi CB, Lange RA, Hall CM et al (2005) The eruptive history of the Tequila volcanic field, western Mexico: Ages, volumes, and relative proportions of lava types. Bull Volcanol 67:391–414. https://doi.org/10.1007/s00445-004-0377-3 Luhr JF (1978) Factors controlling the evolution of the prehistoric, pyroclastic eruption of Volcan San Juan. Geol Soc Am Abstr Prog 10:114 Luhr JF, Prestegaard KL (1988) Caldera formation at Volcan Colima, Mexico, by a large Holocene volcanic debris avalanche. J Volcanol Geotherm Res 35:335–348 MacLeod IN, Ellis RG (2013) Magnetic Vector Inversion, a simple approach to the challenge of varying direction of rock magnetization. In: Proceedings of the 23rd International Geophysical Conference and Exhibition (ASEG), 11–14 August 2013, Melbourne, Australia. Geosoft Inc. (technical paper) Mahood GA (1980) Geological evolution of a Pleistocene rhyolitic center: Sierra La Primavera, Jalisco, México. J Volcanol Geoth Res 8(2–4):199–230 Mahood GA (1981a) A summary of the geology and petrology of the Sierra La Primavera, Jalisco, Mexico. J Geophys Research: Solid Earth 86(B11):10137–10152. https://doi.org/10.1029/JB086iB11p10137 Mahood GA (1981b) Chemical evolution of a Pleistocene rhyolitic center: Sierra La Primavera, Jalisco, Mexico. Contrib Miner Petrol 77:129–149 Nagy D (1966) The gravitational attraction of a right rectangular prism. Geophysics 31(2):362–371. https://doi.org/10.1190/1.1439779 Nelson SA (1980) Geology and petrology of Volcan Ceboruco. Nayarit Mexico Geol Soc Am Bull 91:2290–2431 NOAA National Centers for Environmental Information (2022) ETOPO 2022 15 Arc-Second Global Relief Model. https://doi.org/10.25921/fd45-gt74 Ryan WBF, Carbotte SM, Coplan JO, O’Hara S, Melkonian A, Arko R, Weissel RA, Ferrini V, Goodwillie A, Nitsche F, Bonczkowski J, Zemsky R (2009) Global multi-resolution topography synthesis. Geochem Geophys Geosyst 10:Q03014. https://doi.org/10.1029/2008GC002332 Stoopes GR, Sheridan MF (1992) Giant debris avalanches fi'om the Colima Volcanic Complex, Mexico: implications for long- runout landslides (> 100 km) and hazard assessment. Geology 20:299–302 Suryanata PB, Bijaksana S, Dahrin D, Nugraha AD, Harlianti U, Putra PRA et al (2024) Subsurface structure of Bali Island inferred from magnetic and gravity modeling: new insights into volcanic activity and migration of volcanic centers. Int J Earth Sci 113:523–538. https://doi.org/10.1007/s00531-024-02398-7 Vázquez-Duarte A, Gómez-Tuena A, Díaz-Bravo B (2011) Igneous Petrogenesis of Tequila Volcano, Western Mexico, American Geophysical Union , Fall Meeting 2011, Abstract ID V43C-2590, Pub. Date: December 2011 Wallace PJ, Carmichael ISE (1994) Petrology of Volcan Tequila, Jalisco, Mexico: disequilibrium phenocryst assemblages and evolution of the subvolcanic magma system. Contrib Mineral Petr 117:345–361 Wopat MA (1990) Quaternary alkaline volcanism and tectonics in the Mexican volcanic belt near Tequila, Jalisco, southwestern Mexico. PhD dissertation, University of California, Berkeley, CA Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviewers agreed at journal 12 May, 2026 Reviewers agreed at journal 06 May, 2026 Reviewers invited by journal 01 May, 2026 Editor assigned by journal 22 Apr, 2026 Submission checks completed at journal 22 Apr, 2026 First submitted to journal 15 Apr, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9430674","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":635175340,"identity":"219e8817-e298-4c2b-b88e-8b6407eb55dd","order_by":0,"name":"Román Alvarez","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2UlEQVRIiWNgGAWjYFAC5gYwxc8OogsYGCQIa2GEaJHsOcDAcMCAFC0GNxKI1GLefrBN4meOXR7DzcfHpD8Y2MhJNjA/fHQDjxaZM4ltkr3bkosZZ6elSRwwSDOWZmAzNs7Bo0WCIbHZgHcbc2KzdI4ZUMvhxHkMPGzSeLXwP2w2/LutHmjXGWK1SCQ2PubddjixR4IHomU2YS0PGx/LbjueOIMnLdniDNAvks2E/MKffODg223VifuPHz54o6LCRk7iePPDx/i0YAHMpCkfBaNgFIyCUYAFAACnsknOcwcBLAAAAABJRU5ErkJggg==","orcid":"","institution":"National Autonomous University of Mexico","correspondingAuthor":true,"prefix":"","firstName":"Román","middleName":"","lastName":"Alvarez","suffix":""},{"id":635175341,"identity":"626f20a7-dcc9-4ae8-984b-b92814ec20f1","order_by":1,"name":"Miguel Camacho-Ascanio","email":"","orcid":"","institution":"National Autonomous University of Mexico","correspondingAuthor":false,"prefix":"","firstName":"Miguel","middleName":"","lastName":"Camacho-Ascanio","suffix":""}],"badges":[],"createdAt":"2026-04-15 19:38:49","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9430674/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9430674/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108974325,"identity":"b1af4726-e0b7-42f2-8ca4-9108331599be","added_by":"auto","created_at":"2026-05-11 10:50:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1031864,"visible":true,"origin":"","legend":"\u003cp\u003eLocation map of Tequila volcano (TQ) showing the alignment of five volcanic structures. SJ, San Juan. TE, Tepeltitic. CE, Ceboruco. LP, La Primavera. GC, Gulf of California. The alignment defines the inferred northern boundary of the Jalisco Block (Ferrari et al., 2003). Digital Elevation Model from GeomapApp (Ryan et al., 2009).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/6f5255062c82fd484c31b8e3.png"},{"id":109202734,"identity":"cccd27b9-a896-4a02-9219-ab9f89819fae","added_by":"auto","created_at":"2026-05-13 14:16:13","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":803932,"visible":true,"origin":"","legend":"\u003cp\u003eDigital Elevation Model (DEM) of Tequila volcano and immediate surroundings; 25m contours enhance topographic features. Cerro Tomasillo (CT) is located SE of the summit, continuing with an alignment of volcanic cones (VC) traversing the Younger Flanks (YF) (Lewis-Kenedi et al., 2005). YAF, Younger Andesitic Flanks.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/47d5764889e04bcfe4cfaad9.png"},{"id":108974324,"identity":"4664da27-256c-433b-beba-53e6c264b17b","added_by":"auto","created_at":"2026-05-11 10:50:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1642888,"visible":true,"origin":"","legend":"\u003cp\u003eResidual Bouguer Anomaly map of the north portion of the Jalisco Block; the NW corner exhibits a sharp, low-gravity anomaly associated with Tequila volcano. A black and a green rectangle show the regions in which 3D gravity inversions are performed. The SE corner of the black rectangle is located close to the central portion of La Primavera volcanic field. Lines 1-4 intersect each other at the location of Tequila volcano and indicate the extent and orientation of the density cross-sections that will be obtained after performing the corresponding gravity inversions. TQ, Tequila. CC, Cerro Cuauhtépetl. LP, La Primavera. GDL, Guadalajara. CHA, Chapala. ZA, Zacoalco de Torres. Contours are topographic.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/679d139526b3b521d86c3d6b.png"},{"id":109202592,"identity":"f84d9eb5-e908-42dc-b6d6-5320411a110f","added_by":"auto","created_at":"2026-05-13 14:07:48","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":822298,"visible":true,"origin":"","legend":"\u003cp\u003eDensity cross-sections at 1000-m resolution through the summit of Tequila volcano reaching 6 km bsl. \u0026nbsp;a) E-W cross-section, L1 in Figure 3. b) N-S cross-section, L2 in Figure 3. TQ, Tequila volcano. SR, Santiago River. The color scale represents density values +2.67 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/66c45e47a6c231d607861578.png"},{"id":109067226,"identity":"e0da7196-54db-41cc-8f5f-12d5fbc8356d","added_by":"auto","created_at":"2026-05-12 09:29:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":850349,"visible":true,"origin":"","legend":"\u003cp\u003eDensity cross-sections through the summit of Tequila volcano; both reach 6 km bsl. a) SW-NE cross-section, L3 in Figure 3. b) NW-SE cross-section, L4 in Figure 3; red dashed lines indicate potential magmatic-flow trajectories. The question mark refers to the location of the feeding trajectory of CT, which probably occurs perpendicular to this plane. TQ, Tequila volcano. SR, Santiago River. CT, Cerro Tomasillo. YF, Younger Flank. The color scales represent density values +2.67 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/9144c4bc25c9fdaf2c35a884.png"},{"id":109202552,"identity":"b3d8cfdf-f098-4aaf-ba94-2e835529bb89","added_by":"auto","created_at":"2026-05-13 14:06:19","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":327231,"visible":true,"origin":"","legend":"\u003cp\u003eSequence of horizontal sections of the inverted volume corresponding to the black rectangle in Figure 3, at six depths below sea level (0 m) showing how the low-density region (blue) under TQ varies with depth (red circle), disappearing at 4500 m bsl, the location of the feeding channel, where only remains the low-density region associated with the deeper magma chamber at 6500-m depth. On the N portion of the sea-level section, the trace of Santiago River is clearly discerned as a concave, thin low-density region, whose finer trace begins to disappear at -2100 m. The density scale is the same as that in Figure 5.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/3d7134e0e48961b0fb2dc4a8.png"},{"id":109067381,"identity":"41114e3d-abe1-4a37-9b93-6289dad0dc0f","added_by":"auto","created_at":"2026-05-12 09:40:00","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":422027,"visible":true,"origin":"","legend":"\u003cp\u003eE-W density cross-section corresponding to L1 inside the green rectangle in Figure 3 with a resolution of 250 m and a 12 km extent. The two red, vertical lines enhance the correlation between the low-density region and the breached summit of TQ. The red, dashed line bifurcates near the summit, as indicated by the contours in the low-density region. The color scales represent density values +2.67 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/879a66f46bd3e1e582c8b28c.png"},{"id":109202459,"identity":"ed3f5b32-9ece-4bbd-8377-94fb1f654bff","added_by":"auto","created_at":"2026-05-13 14:04:25","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":467362,"visible":true,"origin":"","legend":"\u003cp\u003eN-S density cross-section corresponding to L2 inside the green rectangle in Figure 3 with a resolution of 250 m. In the upper section appears the corresponding topographic profile with the same horizontal scale as the cross-section. The red dashed line traverses the lowest density region, representing a likely feeding trajectory. The lowest density region reaches the summit where it bifurcates owing to a high-density region that we recognize as the 300 m spine (SP) described by Wallace \u0026amp; Carmichael, (1994), corresponding to the high-density region at the summit. The color scales represent density values +2.67 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/f2c55ba7660e6069111788d6.png"},{"id":108974329,"identity":"5d79820e-b3be-4479-b166-9eeb7c4a6457","added_by":"auto","created_at":"2026-05-11 10:50:33","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":578612,"visible":true,"origin":"","legend":"\u003cp\u003eSW-NE density cross-section corresponding to L3 inside the green rectangle in Figure 3 with a resolution of 250 m. In the upper section appears the corresponding topographic profile with the same horizontal scale as the cross-section. The central, red dashed line traverses the lowest density region, representing a likely feeding trajectory to the summit of TQ. The two red, vertical lines enhance the correlation between the low-density region and the breached summit of TQ. Similarly to the observation made in Figure 8, the lowest density region reaches the summit also bifurcates owing to the high-density region that we identify with the 300 m spine (SP). The gray dashed lines represent possible, abandoned trajectories of volcanic materials that reached the flanks of TQ, inducing the flank flows. The color scales represent density values +2.67 g/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/26ac18434f2032beb0204cea.png"},{"id":108974326,"identity":"f13a4699-7f59-40a8-b659-0e48bee04b08","added_by":"auto","created_at":"2026-05-11 10:50:33","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":623198,"visible":true,"origin":"","legend":"\u003cp\u003eNW-SE density cross-section corresponding to L4 inside the green rectangle in Figure 3 with a resolution of 250 m. The spine (SP), represented by a small high-density region, is located at the center of the bifurcation. Vertical red lines mark the limits of the summit and the associated low-density region. Bifurcation of the flux trajectory close to the summit is highlighted by the central, dashed line. The flanks’ flux trajectories also end up in the surface, coinciding with the Younger Andesite Flows (YAF) and Cerro Tomasillo (CT), confirming these were the paths feeding those volcanic structures, which have now solidified becoming high-density regions.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/8ed8ecb5be0d34a2e03499f0.png"},{"id":109295931,"identity":"57b93d54-c27c-42ac-bed4-971c374b3721","added_by":"auto","created_at":"2026-05-15 08:40:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8785082,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9430674/v1/c23747b7-cd77-4863-9ce4-8eda1f0d6fed.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"\u003cp\u003eLocation of the Two Magma Chambers of Tequila Volcano by Gravity Analysis\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eTequila volcano is located within the Tepic-Zacoalco rift in central-western Mexico; the rift is a tectonic, extensional region containing several volcanic structures, Tequila volcano among them, whose youngest activity occurred at ~\u0026thinsp;90 ka erupting through the flanks of the main cone (V\u0026aacute;zquez-Duarte et al., \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea group of volcanic edifices are displayed, aligned with Tequila volcano (TQ). Ferrari et al. (\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2003\u003c/span\u003e) identify this alignment with the north limit of the Jalisco Block. The distance between TQ and its nearest volcanic neighbor, La Primavera domes, is ~\u0026thinsp;30 km; it is worth noticing the closeness of the times of the latest activity of both volcanic centers: Tequila volcano developed its latest activity at 90 ka, whilst in La Primavera it occurred at 95 ka (Mahood, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1980\u003c/span\u003e,\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1981a\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003eb\u003c/span\u003e), and their locations along the north limit of the Jalisco Block.\u003c/p\u003e \u003cp\u003eTequila volcano reaches an altitude of 2,840 m, rising from a plateau of 1000 m and is composed of ~\u0026thinsp;25 km\u003csup\u003e3\u003c/sup\u003e of pyroxene andesite (Harris, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Wopat, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). When the volcano\u0026rsquo;s activity ceased, abundant eruptions emerged on its flanks (Wallace and Carmichael, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). TQ shows a peculiar summit, since it shows a depression resembling a caldera, which is common in other volcanoes of the region (e.g., Luhr and Prestegaard, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; Stoopes and Sheridan, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e1992\u003c/span\u003e), or induced by powerful explosions (Luhr, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Nelson, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1980\u003c/span\u003e). However, previous reports found that features associated with those phenomena are not present at TQ (Demant, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e1979\u003c/span\u003e; Wallace and Carmichael, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1994\u003c/span\u003e) concluding that the summit depression probably originates in erosional processes. The latter authors mention that the most prominent feature of TQ is a 300 m spine occupying a summit depression that is breached on the eastern side. Here we will look at this problem, analyzing density cross-sections across the summit.\u003c/p\u003e \u003cp\u003eThe latest activity in TQ occurred\u0026thinsp;~\u0026thinsp;90 ka through the flanks of the volcano; V\u0026aacute;zquez-Duarte et al. (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2011\u003c/span\u003e) conclude that TQ is an unusual stratovolcano that seems to evolve in pulses of petrologically unrelated magmas. According to Mahood (\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1980\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1981a\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003eb\u003c/span\u003e) La Primavera caldera was formed at ~\u0026thinsp;95 ka inducing a collapse of ~\u0026thinsp;11 km diameter, closely coinciding with TQ latest activity. A connection between the two occurrences is not far-fetched given the proximity in time and space of these two events.\u003c/p\u003e \u003cp\u003eFor TQ, a chamber at 2\u0026ndash;3 km depth is inferred from phenocryst assemblages. After a lapse of ~\u0026thinsp;110 kyrs, eruptions followed on the NW and SE flanks of TQ, probably originating in a second magma chamber at ~\u0026thinsp;6 km depth (Lewis-Kenedi et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Cerro Tomasillo (~\u0026thinsp;60 ka) is a small andesitic volcano SE of Tequila Volcano.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA DEM of the Tequila Volcanic Region appears in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, where topographic contours help identify some of its surface characteristics. Of particular interest is the NW-SE alignment of the summit of the main structure (TQ), Cerro Tomasillo (CT), and five volcanic cones (VC) that extend along 14 km in the SE direction. Regions designated Younger Flows (YF) and Younger Andesitic Flows (YAF) west of the summit of TQ are described by Lewis-Kenedi et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e); they suggest that a prominent NW-SE lineament of TQ and andesite flank lavas is an indication that they overlie a major passageway for the ascent of magmas from the lower to the middle crust. As will be seen, we find here the exact location of this passageway. The two chambers under TQ were probably the site of mingling between ascending magma batches.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2. Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Data acquisition\u003c/h2\u003e \u003cp\u003eHigh-resolution gravity data for the La Primavera\u0026ndash;Tequila volcanic area were obtained from the satellite-derived GGMplus model (Hirt et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). This dataset provides near-global coverage within the latitudinal band between 60\u0026deg;N and 60\u0026deg;S, although some offshore regions remain less well constrained because of limitations in the underlying source data.\u003c/p\u003e \u003cp\u003eThe Bouguer anomaly (BA) used in this study was calculated following standard gravity reduction procedures commonly applied to satellite-derived gravity data and consistent with recent regional studies in Mexico (e.g., Camacho \u0026amp; Alvarez, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Alvarez \u0026amp; Camacho, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2023a\u003c/span\u003e,\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003eb\u003c/span\u003e, 2024, 2025a,b; Camacho-Ascanio \u0026amp; Alvarez, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Guevara-Betancourt et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). To maximize comparability with previous work, data processing followed the standard reduction workflow recommended by the U.S. Geological Survey (Hildenbrand et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). This procedure applies the conventional gravity corrections, including free-air, Bouguer slab, terrain, and atmospheric terms, to enhance density-related crustal signals and make the data suitable for structural interpretation and derivative analysis.\u003c/p\u003e \u003cp\u003eIn general form, the Bouguer anomaly can be expressed as:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:BA=g-\\gamma\\:+\\delta\\:gFA-\\delta\\:gB-\\delta\\:gTC-\\delta\\:gAT\\:$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere g is the gravity value from the adopted product, \u0026#120574; is the normal gravity reference, \u0026#120575;\u0026#119892;\u0026#119865;\u0026#119860; is the free-air correction, \u0026#120575;\u0026#119892;B is the Bouguer correction, \u0026#120575;\u0026#119892;\u0026#119879;\u0026#119862; is the terrain correction, and \u0026#120575;\u0026#119892;\u0026#119860;\u0026#119879; is the atmospheric correction. The detailed procedure\u0026mdash;including specific formulations, adopted parameters, and implementation\u0026mdash;has been fully described in previous studies using satellite-derived gravity data (e.g., Camacho \u0026amp; Alvarez, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Camacho-Ascanio \u0026amp; Alvarez, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Alvarez \u0026amp; Camacho, 2024; Alvarez \u0026amp; Camacho-Ascanio, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2025a\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn practice, the processing began with the Gravity Observed (GObs) product from GGMplus, from which the BA was calculated according to the USGS gravimetric reduction standard (Hildenbrand et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). Elevation values required for the reductions were extracted from the GEBCO global topographic model, with a spatial resolution of 15 arc-sec (approximately 450 m) (GEBCO Compilation Group, 2021). ETOPO 2022 was used as a complementary topographic reference where needed (NOAA National Centers for Environmental Information, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Terrain corrections were computed in Oasis Montag using the implementation based on the method of Kane (\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1962\u003c/span\u003e), with the extension proposed by Nagy (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1966\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTo emphasize the shallow-to-intermediate density contrasts associated with the volcanic structures, the gravity field was further processed using a Gaussian filter to separate the residual component. This residual BA dataset was then used as the basis for the structural interpretation presented below (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). In volcanic regions, negative gravity anomalies commonly reflect low-density zones related to volcanic edifices, magma reservoirs, and associated plumbing systems (e.g., Alvarez and Yutsis, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Guevara-Betancourt et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Alvarez and Camacho, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e; Suryanata et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Alvarez \u0026amp; Camacho-Ascanio, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025b\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 The Regional Bouguer Anomaly\u003c/h2\u003e \u003cp\u003eRegional gravity anomalies describe the behavior of gravity in extended regions; in the present case it describes the regional behavior of gravity in a region comprising La Primavera volcanic field and the Tequila volcano area. Residual gravity values in the map display a range of 37 mGal; a high gradient is observed on the cone of Tequila volcano, evolving into a NW-SE elongation across it.\u003c/p\u003e \u003cp\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 3D Gravimetric Inversion\u003c/h2\u003e \u003cp\u003eFollowing the calculation of the Bouguer anomaly (BA), a 3D gravity inversion was performed to obtain volumetric density-contrast models and thereby constrain the subsurface structure associated with the main tectonic features of the region. The inversion was carried out in Oasis Montag (Seequent, version 2025.2) using the workflow described by Macleod and Ellis (\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2013\u003c/span\u003e), based on the theoretical framework of Ellis et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). This approach discretizes the subsurface using a Cartesian cut-cell (CCC) representation and estimates the 3D distribution of density contrast by minimizing the misfit between observed and forward-calculated gravity data through an iterative reweighting inversion (IRI) procedure (Ingram et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). In the present implementation, iterations were continued until the data misfit was reduced to within 5% of the standard deviation of the observed BA values. This threshold was adopted as a practical convergence criterion to achieve an adequate balance between data fit and model stability under regularization.\u003c/p\u003e \u003cp\u003eThe inversion input consisted of gridded BA data (mGal), which were transformed into density-contrast models (g/cm\u0026sup3;) through the 3D inversion process. Two inversions were computed using cell sizes of 1000 m and 250 m, respectively, in order to evaluate the density structure at different spatial resolutions. The maximum depth of each model was selected according to the adopted discretization, yielding model depths of approximately 9 km for the 1000 m grid and 5 km for the 250 m grid. Thus, the depth extent and lateral dimensions of the recovered density structure were controlled by the selected computational domain and model resolution.\u003c/p\u003e \u003cp\u003eThe resulting density distributions were subsequently analyzed and interpreted in terms of their possible relationship with subsurface geological materials and structural features. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e presents the inversion result obtained with the 1000 m resolution model, which extends to approximately\u0026thinsp;\u0026minus;\u0026thinsp;6 km below sea level, equivalent to a total depth of about 9 km from the average surface elevation. In the 250 m resolution cross-sections, the corresponding DEM-derived topographic profile was included to facilitate comparison between density variations and surface morphology.\u003c/p\u003e \u003cp\u003eModel performance was assessed by comparing observed and predicted gravity responses, including residual anomaly maps, and by confirming that the final solution satisfied the convergence criterion defined above.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Density cross-sections","content":"\u003cp\u003eTwo resolutions are used in these analyses: 1000 and 250 m. The finer-resolution model provides greater detail in the recovered density structure, although at the expense of a shallower depth extent. The locations of the density cross-sections are defined by Lines 1\u0026ndash;4 in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, which traverse the black and green rectangles, respectively.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 1000-m resolution\u003c/h2\u003e \u003cp\u003eTwo orthogonal, density cross-sections through the summit of Tequila volcano are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. In both, and directly under the summit of TQ, a low-density region shows a minimum at an elevation of +\u0026thinsp;500 m, as shown by the contours; we frequently associate this type of minimum with the location of magmatic deposits, which in the present case coincides with the depth of the shallow magma chamber proposed by Lewis-Kenedi et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The N-S cross-section shows a high-density region at the summit; this type of response is obtained when domes are extruded close to the summit, although in the present case it appears to be associated with the spine reported by Wallace \u0026amp; Carmichael, (\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e1994\u003c/span\u003e). We shall further comment on this when discussing the 250-m resolution profiles.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the N-end a low-density region is associated with Santiago River; the topographic profile corresponds to the presence of a canyon, or graben-like depression, with its associated shallow, low-density region, which may be ascribed to sedimentary materials.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea corresponds to L3 in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, oriented in the SW-NE direction; the high-density region observed at the top of TQ in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb is not intersected in this orientation. In this projection, the width of the low-density region associated with TQ is ~\u0026thinsp;5 km and is flanked by high-density regions, which appear to be divided by the fault plane of the prominent NW-SE lineament reported by Lewis-Kenedi et al.. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). The location of Santiago River is also intersected as a low-density region of shallow depth. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows the NW-SE density cross-section through the summit of TQ. This orientation reveals that feeding of the TQ magma chamber at 500 masl occurs laterally, rather than vertically, as shown by the red arrows bifurcating at 5000 mbsl. This is the only cross-section showing a widespread distribution of low-density materials, drastically contrasting with the extent of the low-density region intersected in the SW-NE density cross-section (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), implying that it coincides with a fault plane that reliefs magma ascent, confirming the account of Lewis-Kenedi et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). It also intersects the position of Cerro Tomasillo, a small andesite volcano SE of TQ and the regions to the NW and SE, the flows called the Younger Flanks; all appear to be fed by a source deeper than 6 km bsl. Continuing to the SE, the volcanic region ends in a high-density region; at the end of the line is La Primavera caldera, where lower density regions replace portions of the high-density region.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt this resolution, regarding the magmatic chambers proposed by Lewis-Kenedi et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e), we can establish the existence of a surficial magma deposit centered at an elevation of +\u0026thinsp;500 m, or 1.5 km depth, corresponding to the magma chamber suggested by them between 2\u0026ndash;3 km depth. We find a feeding channel displaced ⁓8 km SE of the summit of TQ at a depth of -3300 mbsl that connects to a deeper magma source. Since the NW-SE density cross-section (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) is the only one showing considerable dispersion of low-density materials, we conclude that this is probably a fault plane that enables magma ascent, particularly since the main edifice (TQ) is not directly above the main feeding channel but displaced ⁓8 km to the NW. A similar lateral feeding was registered for Popocat\u0026eacute;petl volcano in the Sierra Nevada (Alvarez and Camacho-Ascanio, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025b\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo elucidate the connection between the shallow and the deep magma chambers we obtained horizontal density sections at various depths (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e), where a dashed circle marks the surface location of Tequila volcano. At sea level (0 m) the low-density anomaly appears elongated in the NW-SE direction with its thickest portion to the SE. This anomaly is flanked by high-density regions to the NE and the SW, creating a sort of low-density channel; this arrangement persists down to -5900 m. The encircled, low-density anomaly persists to -3300 m, disappearing at -4500 m, being substituted by a larger, deeper anomaly to the SE that reaches the S limit of the sections, and begins to appear at -2100 m. At -3300 m, within the circle remains a thin, low-density passage that we interpret as the fault that connects the main magma chamber with the one located at +\u0026thinsp;500 m (Figure B/5). At -5900 m the NW-SE lowest-density region is clearly defined, which we interpret as the magma chamber at 6 km depth proposed by Lewis-Kenedi et al. (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 250-m resolution\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn this projection mid-density regions become high-density regions as they approach the surface on the volcano\u0026rsquo;s flanks. They appear to belong to abandoned flow trajectories that fed flank eruptions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eRegarding the depth and location of the deeper magma chamber we will consider Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. The NW-SE cross-section in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb shows that the low-density anomaly feeding TQ and the surrounding volcanic formations reaches the bottom of the cross-section (6 km bsl) indicating its downward continuation. The horizontal section at -4500 m in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the top of the deeper magma chamber as a faint blue, whereas at -5900 m darker blue is established in half the area of the anomaly; the darker blue corresponds to the region where the density is lower, or where magmatic products are concentrating. We conclude that the center of the deeper magma chamber is located between 6200 and 6500 mbsl. From this location magmatic materials are sporadically ejected upwards through the feeding channel.\u003c/p\u003e \u003cp\u003eA peculiar bifurcation of the low-density region systematically appears close to the summit in the 250-m resolution cross-sections (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e), which originates in the upper magma chamber located at +\u0026thinsp;1500 m. The mechanism we prefer to induce this bifurcation is the blockage of the initial chimney, most likely by the injection of the spine, potentially followed by an explosion that partially destroyed the summit, creating a new discharge trajectory. The spine appears in the cross-sections of Figs.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, as a small high-density region. We have reported similar chimney blockages and subsequent explosions at Nevado de Toluca (Alvarez \u0026amp; Camacho, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2023b\u003c/span\u003e) and Popocat\u0026eacute;petl volcanoes (Alvarez \u0026amp; Camacho-Ascanio, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2025b\u003c/span\u003e)\u003c/p\u003e \u003cp\u003eThe latest activity in TQ occurred\u0026thinsp;~\u0026thinsp;90 ka through the flanks of the volcano, probably originating in the second magma chamber at ~\u0026thinsp;6 km depth, as inferred by Lewis-Kenedi et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). In Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e there are discharge trajectories ending at the flanks of TQ, which we interpret as the conduits of the flanks\u0026rsquo; lava flows that have now solidified, presenting larger densities.\u003c/p\u003e \u003cp\u003eThe path of Santiago River is intersected in Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e associated with a topographic depression and a shallow, low-density region that we attribute to sediment accumulation. In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e it displays a thin, semi-circular trajectory that persists from sea level to -2100 m, indicating a crustal incision of over 4 km from the surface. This is the section of SR closest to Tequila volcano and its trajectory appears to be influenced by the dominating NW-SE orientation of volcanic structures in this region.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eApplying gravimetric treatments to Tequila volcano and its surroundings, we confirmed the existence of the two magma chambers proposed by Lewis-Kenedi et al., (\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2005\u003c/span\u003e); we found that only the shallow chamber is directly under the volcanic cone, with the deeper one displaced 8 km to the SE.\u003c/p\u003e \u003cp\u003eThe connection has been established between the two magma chambers feeding Tequila volcano and the surrounding areas designated as the Younger Flanks, between elevations of -6 km and +\u0026thinsp;500 m, both connecting through a narrow passage located at -3300 m elevation.\u003c/p\u003e \u003cp\u003eThe caldera-type summit is explained based on the bifurcation of the low-density region close to the volcano\u0026rsquo;s summit, as the result of a blockade of a former chimney by an intrusive body, called the spine, inducing an explosion, and deviating the exhaust to its new trajectory.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eConflicts of Interest\u003c/h2\u003e \u003cp\u003eThe authors declare no conflicts of interest regarding the publication of this paper.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eRA wrote the main manuscript text, contributed to the definition of the project and to the organization of the manuscript.MC contributed with data acquisition and processing, writing portions of the manuscript, and content discussions.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe Instituto de Investigaci\u0026oacute;n en Matem\u0026aacute;ticas Aplicadas y Sistemas (IIMAS) and Instituto de Geof\u0026iacute;sica, both from Universidad Nacional Aut\u0026oacute;noma de M\u0026eacute;xico (UNAM) supported this research; no external funds supported it.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eAll data supporting the findings of this study are available within the paper or by request from the authors.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAlvarez R, Yutsis V (2015) Southward migration of magmatic activity\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ein the Colima Volcanic Complex Mexico: An ongoing process. Int J Geosci, 6, 1077\u0026ndash;1099. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://dx.doi.org/10.4236/ijg.2015.69085\u003c/span\u003e\u003cspan address=\"10.4236/ijg.2015.69085\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlvarez R, Camacho M (2023a) Plumbing System of Hunga Tonga Hunga Ha\u0026rsquo;apai Volcano. J Earth Sci 34:706\u0026ndash;716. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12583-022-1792-0\u003c/span\u003e\u003cspan address=\"10.1007/s12583-022-1792-0\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlvarez R, Camacho M (2023b) Applying High-Resolution Gravity Analysis to Volcanic Plumbing Systems: The Case of Nevado De Toluca Volcano, Mexico. Trans Eng Comput Sci 11(4):184\u0026ndash;207. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.14738/tecs.114.15392\u003c/span\u003e\u003cspan address=\"10.14738/tecs.114.15392\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlvarez R, Camacho M, Rivera-Calder\u0026oacute;n E (2024) The Internal Structure of Paricutin And Tanc\u0026iacute;taro Volcanos, Mexico, From Rock Density Distributions. Trans Eng Comput Sci 12(2):50\u0026ndash;69. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.14738/tecs.122.16645\u003c/span\u003e\u003cspan address=\"10.14738/tecs.122.16645\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlvarez R, Camacho-Ascanio M (2025a) Plausible Northern Extension of Los Humeros Caldera Geothermal Field and Correlation of Density and Electrical Resistivity within the Collapsed Structure. Engineering 17:659\u0026ndash;679. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4236/eng.2025.1712037\u003c/span\u003e\u003cspan address=\"10.4236/eng.2025.1712037\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAlvarez R, Camacho-Ascanio M (2025b) Gravimetric Definition of the Magmatic Chambers of the Popocat\u0026eacute;petl-Iztacc\u0026iacute;huatl Volcanic Complex, Mexico. Earth Sci Eng. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.57237/j.earth.2025.01.001\u003c/span\u003e\u003cspan address=\"10.57237/j.earth.2025.01.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCamacho M, Alvarez R (2020) Gravimetric analysis of the rifts and volcanic fields of the Jalisco block. Mexico Tectonophysics 791(July):228577. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.tecto.2020.228577\u003c/span\u003e\u003cspan address=\"10.1016/j.tecto.2020.228577\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCamacho M, Alvarez R (2021) Geophysical Modeling with Satellite Gravity Data: Eigen-6C4 vs. GGM Plus Engineering 13:690\u0026ndash;706. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.4236/eng.2021.1312050\u003c/span\u003e\u003cspan address=\"10.4236/eng.2021.1312050\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCamacho-Ascanio M, Alvarez R (2024) Delineation of the boundaries of San Blas basin, Mexico, merging gravity, magnetic, and seismic data. J S Am Earth Sci 136:104818. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jsames.2024.104818\u003c/span\u003e\u003cspan address=\"10.1016/j.jsames.2024.104818\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDemant A (1979) Vulcanolog\u0026iacute;a y petrograf\u0026iacute;a del sector occidental del Eje Neovolc\u0026aacute;nico. UNAM, \u003cem\u003eInst Geol Revista\u003c/em\u003e 3:39\u0026ndash;57\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEllis RG, de Wet B, Macleod IN (2012) Inversion of magnetic data from remanent and induced sources. ASEG Extended Abstracts 2012 (1), 1\u0026ndash;4. https://doi.org/726727 72810.1071/ASEG2012ab117\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFerrari L, Petrone CM, Francalanci L, Tagami T, Eguchi M, Conticelli S, Manetti P, Venegas-Salgado S (2003) Geology of the San Pedro\u0026ndash;Ceboruco Graben, western Trans-Mexican Volcanic Belt. \u003cem\u003eRev. Mex. C. Geol.\u003c/em\u003e, v. 20, n\u0026uacute;m. 3, 2003, pp. 165\u0026ndash;181\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuevara-Betancourt R, Yutsis V, Varley N, Almaguer J, Alvarez R, Calder\u0026oacute;n-Moctezuma A, Sieck P (2023) Insights into the plumbing system of Colima Volcanic Complex from geophysical evidence. J Volcanol Geoth Res 433:107711. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jvolgeores.2022.107711\u003c/span\u003e\u003cspan address=\"10.1016/j.jvolgeores.2022.107711\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGEBCO Bathymetric Compilation Group (2021) The GEBCO_2021 Grid: A continuous terrain model of the global oceans and land. Br Oceanogr Data Centre. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.5285/c6612cbe-50b3-0cff-e053-6c86abc09f8\u003c/span\u003e\u003cspan address=\"10.5285/c6612cbe-50b3-0cff-e053-6c86abc09f8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHarris JM (1986) Silicic volcanics of Volcan Tequila, Jalisco, Mexico. MSc thesis, University of California, Berkeley, CA\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHildenbrand TG, Briesacher A, Flanagan G, Hinze WJ, Hittelman AM, Keller GR, Kucks RP, Plouff D, Roest W, Seeley J, Stith DA, Webring M (2002) Rationale and operational plan to upgrade the U.S. gravity database. U.S. Geological Survey Open-File Report 2002\u0026thinsp;\u0026ndash;\u0026thinsp;463, 12 p. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3133/ofr02463\u003c/span\u003e\u003cspan address=\"10.3133/ofr02463\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHirt C, Claessens S, Fecher T, Kuhn M, Pail R, Rexer M (2013) New Ultrahigh-Resolution Picture of Earth\u0026rsquo;s Gravity Field. Geophys Res Lett 40:4279\u0026ndash;4283. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1002/grl.50838\u003c/span\u003e\u003cspan address=\"10.1002/grl.50838\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIngram DM, Causon DM, Mingham CG (2003) Developments in Cartesian cut cell methods. Math Comput Simul 61(3\u0026ndash;6):561\u0026ndash;572. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0378-4754(02)00107-6\u003c/span\u003e\u003cspan address=\"10.1016/S0378-4754(02)00107-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKane MF (1962) A comprehensive system of terrain corrections using a digital computer. Geophysics 27(4):455\u0026ndash;462. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1190/1.1439044\u003c/span\u003e\u003cspan address=\"10.1190/1.1439044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLewis-Kenedi CB, Lange RA, Hall CM et al (2005) The eruptive history of the Tequila volcanic field, western Mexico: Ages, volumes, and relative proportions of lava types. Bull Volcanol 67:391\u0026ndash;414. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00445-004-0377-3\u003c/span\u003e\u003cspan address=\"10.1007/s00445-004-0377-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuhr JF (1978) Factors controlling the evolution of the prehistoric, pyroclastic eruption of Volcan San Juan. Geol Soc Am Abstr Prog 10:114\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLuhr JF, Prestegaard KL (1988) Caldera formation at Volcan Colima, Mexico, by a large Holocene volcanic debris avalanche. J Volcanol Geotherm Res 35:335\u0026ndash;348\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMacLeod IN, Ellis RG (2013) Magnetic Vector Inversion, a simple approach to the challenge of varying direction of rock magnetization. In: Proceedings of the 23rd International Geophysical Conference and Exhibition (ASEG), 11\u0026ndash;14 August 2013, Melbourne, Australia. Geosoft Inc. (technical paper)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahood GA (1980) Geological evolution of a Pleistocene rhyolitic center: Sierra La Primavera, Jalisco, M\u0026eacute;xico. J Volcanol Geoth Res 8(2\u0026ndash;4):199\u0026ndash;230\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahood GA (1981a) A summary of the geology and petrology of the Sierra La Primavera, Jalisco, Mexico. J Geophys Research: Solid Earth 86(B11):10137\u0026ndash;10152. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1029/JB086iB11p10137\u003c/span\u003e\u003cspan address=\"10.1029/JB086iB11p10137\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMahood GA (1981b) Chemical evolution of a Pleistocene rhyolitic center: Sierra La Primavera, Jalisco, Mexico. Contrib Miner Petrol 77:129\u0026ndash;149\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNagy D (1966) The gravitational attraction of a right rectangular prism. Geophysics 31(2):362\u0026ndash;371. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1190/1.1439779\u003c/span\u003e\u003cspan address=\"10.1190/1.1439779\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNelson SA (1980) Geology and petrology of Volcan Ceboruco. Nayarit Mexico Geol Soc Am Bull 91:2290\u0026ndash;2431\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNOAA National Centers for Environmental Information (2022) ETOPO 2022 15 Arc-Second Global Relief Model. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.25921/fd45-gt74\u003c/span\u003e\u003cspan address=\"10.25921/fd45-gt74\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRyan WBF, Carbotte SM, Coplan JO, O\u0026rsquo;Hara S, Melkonian A, Arko R, Weissel RA, Ferrini V, Goodwillie A, Nitsche F, Bonczkowski J, Zemsky R (2009) Global multi-resolution topography synthesis. Geochem Geophys Geosyst 10:Q03014. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1029/2008GC002332\u003c/span\u003e\u003cspan address=\"10.1029/2008GC002332\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStoopes GR, Sheridan MF (1992) Giant debris avalanches fi'om the Colima Volcanic Complex, Mexico: implications for long- runout landslides (\u0026gt;\u0026thinsp;100 km) and hazard assessment. Geology 20:299\u0026ndash;302\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuryanata PB, Bijaksana S, Dahrin D, Nugraha AD, Harlianti U, Putra PRA et al (2024) Subsurface structure of Bali Island inferred from magnetic and gravity modeling: new insights into volcanic activity and migration of volcanic centers. Int J Earth Sci 113:523\u0026ndash;538. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00531-024-02398-7\u003c/span\u003e\u003cspan address=\"10.1007/s00531-024-02398-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eV\u0026aacute;zquez-Duarte A, G\u0026oacute;mez-Tuena A, D\u0026iacute;az-Bravo B (2011) Igneous Petrogenesis of Tequila Volcano, Western Mexico, \u003cem\u003eAmerican Geophysical Union\u003c/em\u003e, Fall Meeting 2011, Abstract ID V43C-2590, Pub. Date: December 2011\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWallace PJ, Carmichael ISE (1994) Petrology of Volcan Tequila, Jalisco, Mexico: disequilibrium phenocryst assemblages and evolution of the subvolcanic magma system. Contrib Mineral Petr 117:345\u0026ndash;361\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWopat MA (1990) Quaternary alkaline volcanism and tectonics in the Mexican volcanic belt near Tequila, Jalisco, southwestern Mexico. PhD dissertation, University of California, Berkeley, CA\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bulletin-of-volcanology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"buvo","sideBox":"Learn more about [Bulletin of Volcanology](http://link.springer.com/journal/445)","snPcode":"445","submissionUrl":"https://www.editorialmanager.com/buvo/default2.aspx","title":"Bulletin of Volcanology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Tequila volcano, La Primavera caldera, Jalisco Block, 3D gravity inversions, GGMplus gravity data, Caldera depression","lastPublishedDoi":"10.21203/rs.3.rs-9430674/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9430674/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTequila volcano is located on the northeastern margin of the Jalisco Block, along the Tepic-Zacoalco rift in western Mexico, and its latest activity has been dated at approximately 90 ka. In this study, we use the GGMplus gravity data set to perform 3D gravity inversions to depths of up to 8 km to explore the possible location of the two magma storage regions previously proposed for Tequila volcano. During the inversion process, models with 1000 and 250 m resolution were evaluated to investigate possible magmatic ascent pathways beneath the main volcanic edifice and adjacent lava flows. The 1000 m resolution model reveals a shallow low-density region at about\u0026thinsp;+\u0026thinsp;1500 masl beneath Tequila volcano, as well as a deeper anomaly located about 8 km southwest of the summit, at approximately\u0026thinsp;\u0026minus;\u0026thinsp;6000 mbsl; these features are interpreted as being consistent with the shallow and deeper magma chambers previously suggested for the volcanic system. The inversion results also suggest a structurally controlled zone that may have facilitated magma ascent, including a narrow connection near \u0026minus;\u0026thinsp;3300 mbsl between both low-density regions. The 250 m resolution model further resolves a bifurcation of the shallow low-density region beneath the summit depression, a geometry that may help explain the origin of the summit\u0026rsquo;s caldera-like morphology and its relation to the central spine. One possible interpretation is that the spine partially obstructed an earlier ascent pathway, promoting a change in the position of eruptive discharge and the development of a lateral conduit; the inferred traces of these possible pathways are illustrated here. The study area also includes the segment of the Santiago River closest to Tequila volcano, which trends NW; in this sector, the inversion identifies shallow low-density materials that may be related to sediment accumulation, as well as a narrow vertical feature extending to ~\u0026thinsp;4100 m depth, tentatively interpreted as a fault zone.\u003c/p\u003e","manuscriptTitle":"Location of the Two Magma Chambers of Tequila Volcano by Gravity Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-11 10:50:01","doi":"10.21203/rs.3.rs-9430674/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"113814367760986722136888875997017485444","date":"2026-05-12T09:13:00+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"22143074459535328557472243847561030780","date":"2026-05-06T04:25:26+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-05-01T11:25:45+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-22T22:55:30+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-22T22:54:36+00:00","index":"","fulltext":""},{"type":"submitted","content":"Bulletin of Volcanology","date":"2026-04-15T19:30:44+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bulletin-of-volcanology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"buvo","sideBox":"Learn more about [Bulletin of Volcanology](http://link.springer.com/journal/445)","snPcode":"445","submissionUrl":"https://www.editorialmanager.com/buvo/default2.aspx","title":"Bulletin of Volcanology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"a67a18c3-2505-4229-ba6e-01a635b8d3d8","owner":[],"postedDate":"May 11th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"113814367760986722136888875997017485444","date":"2026-05-12T09:13:00+00:00","index":15,"fulltext":""},{"type":"reviewerAgreed","content":"22143074459535328557472243847561030780","date":"2026-05-06T04:25:26+00:00","index":13,"fulltext":""},{"type":"reviewersInvited","content":"5","date":"2026-05-01T11:25:45+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-11T10:50:02+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-11 10:50:01","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9430674","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9430674","identity":"rs-9430674","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}