Abstract

The Camargo Volcanic Field (CVF), located in the southeastern portion of the Mexican state of Chihuahua, is part of the Basin & Range province. With a surface of nearly 3000 km² and composed of approximately 300 cinder cones, it is considered the largest alkaline mafic volcanic field in northern Mexico. Radiometric analyses have yielded absolute ages ranging from 4 to 0.09 Ma. Cinder cones are landforms that do not show significant variations in composition or shape, leading to constant erosion. Specifically, the relationship between their slope and age has been analyzed in numerous studies, showing that slopes decrease with age; this can then be used as an indicator of the relative age of the cones. This study applies an equation from Miller (2006), which correlates radiometric ages with slope angles from other arid-region cinder cones. Using this method, an exponential trend equation was published in previous work, based on data from cones dated using absolute dating methods and measured using remote sensing imagery. This work presents a geomorphometric study in which slopes and the distribution of 51 cinder cones were measured and analyzed. Digital elevation models, topographic maps, Google Earth, and drone images were processed to measure the cinder cones. Results showed slopes ranging from 3˚ to 13˚, with ages ranging from 226,671 to 99,408 years. The oldest cones are located within the SW portion of CVF, while the youngest cones are found in its north and NE portions. The data obtained were consistent with previous studies; however, it is important to note that the parameters used vary with image resolution. It was concluded that drone images are more accurate for geomorphometric age calculations because they have higher spatial resolution, yielding more precise measurements. Geomorphometric dating is suggested as a preliminary tool in volcanic field studies, but it is always advised to apply radiometric dating to determine the volcanic history of an area.

Keywords

Camargo Volcanic Field, Cinder Cones, Geomorphometric Dating, Image Processing, Volcanic Geomorphology

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1. Introduction

Determining the age of rocks and/or minerals provides crucial insights into Earth’s history, helping to reconstruct the sequence of geological, geochemical, and tectonic events. Over time, the most widely applied dating techniques are the relative and the radiometric methods, each providing reliable rock ages [1] [2].

Relative dating establishes the chronological order of geological events based on stratigraphic principles and the continuity of the geological record, using stratigraphic relationships and fossil correlations, but does not assign numerical ages [3]. Radiometric dating determines absolute ages in years based on isotopic decay, allowing high precision in dating igneous and metamorphic rocks [2]. Among the radiometric methods, the most used are uranium-lead (U-Pb), potassium-argon (K-Ar), and rubidium-strontium (Rb-Sr) [2] [4]. The advances in analytical instruments have enhanced the accuracy of dating.

There is a third method, used only for certain cases, known as the geomorphometric dating method, which involves quantitative/physical analysis of geological structures or landform morphology, providing temporal information where isotopic or stratigraphic data are limited [5]. These methods develop an integrating approach to reconstructing the geochronology of Earth’s crust.

The geomorphometric dating method leverages climatic conditions and geological formations. For example, dating cinder cones is only useful in arid climates and in formations younger than 1 Ma [6].

Geomorphometric dating studies primarily include volcanic fields located in arid zones, among which are the El Potrillo Volcanic Field in New Mexico, USA [7], the Camargo Volcanic Field in Chihuahua, Mexico [8]-[10], and the Lunar Crater Volcanic Field in Nye County, Nevada, USA [11], among others. A brief overview of each is presented in Table 1.

In the Camargo Volcanic Field (CVF), the acquisition of isotopic ages is constrained by several factors that justify the use of geomorphometric dating as a complementary tool. Since most of this vast surface is privately owned, access to the sampling sites is limited and can even be dangerous. Additionally, the high cost of radiometric analysis has resulted in a sparse and uneven chronological dataset for the CVF; only one work in the 2000s published absolute ages [12]. These constraints hinder the development of a consistent and detailed geochronological record of eruptions within the CVF. Thus, geomorphometric dating provides a feasible, quick, and low-cost alternative, enabling the estimation of relative or approximate ages when absolute dating is insufficient and the development of a temporal framework for the CVF volcanic evolution.

Table 1. Previous work on cinder cone analyses.

This research compares previously published radiometric ages [12] with geomorphometric ages for the best-preserved cinder cones of the Camargo Volcanic Field (CVF) in Chihuahua, Mexico.

2. Geologic Setting

The study area is in the south-central portion of the state of Chihuahua, in the municipality of Camargo, 57 km east of Camargo city, on the border with the Mexican state of Coahuila, between UTM coordinates 533000E, 3042000N and 598000E, 3097000N (see Figure 1).

The region known as the Camargo Volcanic Field (CVF) is composed of flows distributed as large alkaline basalt plateaus containing olivine, clinopyroxene, and kaersutite xenocrysts, as well as lower crustal xenoliths that come from near the Mohorovicic discontinuity boundary (peridotites, granulites, paragneisses, and othogneisses [10] [12] [13].

The formation of the CVF is thought to be strongly related to a still-active normal fault trending NW-SE, with evidence that faulting and volcanism may have been contemporaneous [12] [14]. The CVF lies along the trace of the buried San Marcos regional fault [12], which formed during the Jurassic and was reactivated in multiple deformation pulses.

Based on its age, the field’s formation is attributed to the last reactivation, caused by extensional activity in the Basin and Range Province [15]. The most important structural feature of the CVF is a graben located in the center of the field, which divides it into three volcano-tectonic domains: 1) La Loba in the SW portion of the field; 2) El Venado in the central part, and 3) Las Maravillas in the NE portion of the CVF. Each domain is distinguished from the others by the age of its volcanic activity, the density of cones, and the density of faults [12].

The 51 cinder cones measured were selected for their best-preserved form, and are distributed throughout the three domains, with the majority located within the Las Maravillas domain [12] (see Figure 1). The cinder cones selected were chosen based on their conserved circular form. The rest of the cones have horseshoe shapes or irregular base forms that do not allow for measuring the true base and/or crater diameters, which negatively impact age calculations, since these measurements are important for determining the slope angle.

Figure 1. Location and geologic map of the Camargo Volcanic Field (CVF), which shows the 51 cinder cones measured for this research. Adapted from [12] by [9].

3. Methodology

The method used to measure slopes in cinder cones is based on techniques that analyze volcanic structures using satellite imagery, digital elevation models, Google Earth, and drone imagery. The information processing was performed using Global Mapper 14.

Cinder cones are landforms that do not show significant variations in their composition and shape [16]. This characteristic allows for the establishment of constants in the effects of erosion on them. However, it is important to highlight the role of extrinsic factors that affect or intervene in the erosion process of cones that have a direct influence on the slope angle [16]-[21].

• Climatic conditions: The degradation of any type of relief is mostly due to water and wind erosion. In temperate or tropical areas with high annual rainfall, water saturation on slopes often triggers landslides or mass wasting, which act as catalysts for the cones’ degradation. The opposite is true in arid zones, where the main erosive agent is wind, and vegetation is absent [16].

• Cone morphology: Erosion is more severe in geological structures or landforms with marked relief, while it will be less intense in those structures with bare relief. Young cinder cones will be more affected by erosion than older, semi- or well-degraded cones. As a result, over a given period, the effect of erosion is more evident in young volcanic structures than in semi-eroded ones [16]-[18]. Likewise, cuts in the volcanic structure caused by subsequent lava flows can accelerate erosion.

The choice of slope-angle analysis technique is influenced by the specific environments of the study areas, including location and climatic conditions, as well as the age and characteristics of each cone. Within CVF, a high percentage of volcanic cones are unsuitable for analysis because they are highly eroded, with most exhibiting a horseshoe-shaped crater rim [10]. Based on these criteria, only 51 of the 300 cinder cones [12] have a well-defined shape and were measured.

3.1. Morphometric Measurements

The cinder cones’ measurements include the base diameter/radius and the cone’s maximum elevation. The Global Mapper 14 software was used to determine these dimensions. The processed images included mostly the Mexican elevation continuum, 1:50,000-scale topographic maps (both provided by the Mexican National Institute of Statistics and Geography, INEGI), and, for two specific cones in the northern part of CVF, Google Earth and drone images (Figure 2).

The software allows us to obtain, in addition to a terrain’s 3D image, a topographic profile from a user-drawn line (Figure 3(a)) and the measurements needed to calculate the slope angle. Data acquisition was carried out as follows:

• Base diameter/radius: for each cone, six lines were drawn in different directions to cover most of the circumference of the volcanic structure, and then the average of the 6 lines’ lengths corresponds to the base diameter. The base radius measurement is half of the diameter.

• Cones’ maximum elevation (me): for each of the six lines drawn, the software provided a detailed profile section, obtaining from it the maximum (me) and basal elevation (be) of each line. The me and be of each cone were calculated

Figure 2. Images used for morphometric measurements: (a) digital elevation models (DEMs) and topographic maps, (b) Google Earth images, and (c) drone images [8].

Figure 3. (a) Topographic profile obtained in Global Mapper 14; (b) Measurements in cinder cones for using trigonometry to calculate slope angle [9].

as the average of the six initial heights of the profile. The difference (me-be) represents the maximum height (h) of the cone.

• Slope angle: using the base radius and maximum elevations, the slope angle was calculated using the trigonometric function in Equation (1) (see Figure 3(b)).

$\theta ={\tan }^{-1}\left(h/\text{average of radii}\right)$ (1)

3.2. Geomorphometric Dating Calculations

Considering previous studies that relate slope angles to the radiometric ages of cinder cones [6] [7] [11], an exponential plot with its corresponding equation was established (Figure 4). This equation was proposed by Joseph Miller (2006). In it, he relates data from young cinder cones radiometrically dated, all located in arid zones, to the volcanoes of CVF. The volcanoes considered for this plot were the Paricutin, with an assigned age of 0, since it formed in 1943 [22]; Black Mountain volcanic center from the El Potrillo volcanic field in New Mexico, USA, with an age of 125 ± 11 ka [23]; and Capulin volcano in New Mexico, USA, 56 ± 8 ka [24]; all dated with the ⁴⁰Ar/³⁹Ar radiometric technique. This equation was chosen because the author used cinder cones from similar arid climatic conditions to those in CVF; Black Mountain volcano is about 565 km to the NW of CVF and is part of the same tectonic event, also Chihuahua and New Mexico are within the Chihuahuan desert. The resulting plot shows an exponential trend line with a specific function (Equations (2), (3)), indicating that the degree of erosion reflected in the cones’ slope angles increases with time elapsed since the volcanic activity ceased.

$y= 35{\text{e}}^{-5x}\left(\text{where }R=1\right)$ (2)

$y= 3.179{\text{e}}^{-1E-5x}\left(\text{where }{R}^2=0.9999\right)$ (3)

Figure 4. Exponential plot showing the correlation between slope angle and absolute dating. The trend equation was used to calculate the geomorphometric age of the cinder cones. Note the values used for the Black Mountain, Capulín, and Paricutín.

To provide an approximation of Quaternary cinder cone ages, the variable X must be solved, which represents the age in Equation (3), where Y is the slope angle. The ages were calculated for each cone in Microsoft Excel.

4. Results

The cinder cones’ geomorphometric analyses from CVF show slope angles ranging from 3˚ to 13˚ and calculated ages ranging from 226,671 to 99,408 years (Table 2).

Table 2. Geomorphometric measurements and age calculations for the CVF cinder cones.

*All distances are in meters.

Since the cone age is related to the slope angle, the volcanoes analyzed can be clustered in three groups: 1) the oldest ones (3.6˚ - 6.9˚) with ages ranging from 226,671 to 162,153 years; 2) the intermediate age cones (7˚ - 9.98˚), with ages from 161,003 to 125,536 years; and 3) the youngest ones (10.6˚ - 12.96˚), with ages from 115,805 to 99,408 years (see Figure 5).

When analyzing the slope angles versus their corresponding geomorphometric ages, the data did not form a continuous gradient (Figure 4). This division into three age classes is supported by the natural clustering observed in the histogram of slope-angle frequency relationships (Figure 5). Having fewer or more than three classes would introduce artificial subdivisions not supported by the data distribution and would reduce the robustness of each group by producing clusters with very small sample sizes.

Figure 5. Histogram of cinder cone slope angle frequency in CVF. Colors indicate the three age groups: blue is the oldest, yellow is the intermediate, and red is the youngest.

To validate the slope angles calculated from remote sensing measurements, one of the cinder cones (CC51) was measured in situ. For this cone, the calculated slope angle was 8˚, and on the field, using a Brunton compass, the angle was 8.7˚. Since this small difference (0.7˚) may be due to several factors, such as the scale of measurement, instrument precision, etc., it is necessary to calculate the slope angle using survey instrumentation to obtain more precise data.

For the northernmost cinder cones of CVF, remote sensing analyses included Google Earth and drone images. The results are presented in Table 3. Just two cones were analyzed using drone imagery because access to this area is restricted and the land is privately owned. However, these two cones, being next to the road, allowed them to be measured without risking the drone or the handlers.

The digital elevation models (DEMs) and Google Earth images yield similar results, whereas the drone images, in both cones, indicate an age approximately 40,000 years younger.

Radiometric dating of 5 sites within the CVF (12) shows that the oldest lavas outcrop in the SW part of the volcanic field and become younger toward the NE (see Figure 1).

Table 3. Geomorphometric measurements and age calculations for 2 of the northernmost cinder cones in CVF, using 3 different types of images.

*All distances are in meters.

5. Conclusions

Of the approximately 300 cinder cones in CVF, only 51 could be measured using remote sensing techniques, including DEMs, Google Earth, and drone images. Only a sixth part of the cones have a preserved shape that allowed them to be measured.

The geomorphometric ages were calculated using an exponential trend that correlates radiometric ages with slope angles for 3 known cinder cones from arid zones. The trend expressed an equation that permitted the calculation of the age of a cinder cone under those climatic conditions. The ages of the 51 cinder cones range from 226,671 to 99,408 years, based on DEMs and Google Earth images. The cinder cones were arranged into 3 groups: the oldest to the SW part of the volcanic field, the intermediate-age in the central part of the field, and the younger ones in the north-northeastern portion of the CVF. It coincides with the evolution of CVF, explained by previous work [12]. Therefore, the three-class classification represents the most coherent and geologically meaningful partition of the dataset, capturing the main phases of cone degradation and providing a consistent framework for comparative analysis.

The drone images of two of the northern cones, close to the site and radiometrically dated to 0.09 Ma, yield an age of 97,952 years, while the other images yield ages of 146,000 to 164,000 years. Since the drone captured images with a spatial resolution of 9.47 cm, it can be inferred that errors are lower and calculations are more accurate; however, future work should focus on acquiring additional high-resolution drone data to validate this finding across the entire volcanic field.

Geomorphometric dating can provide an initial idea of a cinder cone’s age in arid zones, but it is not a definitive age. It is recommended as a tool for obtaining preliminary dates within a young basaltic volcanic field, but absolute/radiometric dating remains the better option for reconstructing the volcanic activity history of the area.

Acknowledgements

The authors gratefully acknowledge the contributions of all project members: our students (Martha Gallegos, Esmeralda Chavez, Ricardo Contreras & Irlanda Ramos) and drone specialists (Aracely Lopez & Fabricio Madrigal) for all their effort and for rigorous data acquisition, analytical support, and constructive discussions throughout the development of this long-term project. Their commitment to methodological precision and continuous feedback significantly strengthened the quality and scope of the study submitted here.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References