During the past 15 yr, volcanological studies in Mexico have been mostly focused on the pyroclastic stratigraphy and petrologic evolution of the volcanoes, with very little attention paid to detailed mapping of volcanic areas. In this study, we present a geologic map of the Colima volcanic complex, which covers ~3780 km 2 . The Colima volcanic complex is made of El Cántaro, Nevado de Colima, Paleofuego, and Colima volcanoes, totaling 422 km 3 in volume. The activity of the Colima volcanic complex started at El Cántaro with the emission of lava flows and domes ca. 1.7 Ma. About 0.53 Ma, 15 km southward, the formation of Nevado began with the emission of lava flows. Nevado produced at least four collapses that generated debris avalanches, debris flows, and pyroclastic-flow deposits. During late Pleistocene (>>38,500 yr B.P.), the formation of Paleofuego began 5 km further south with the emission of lava flows. Paleofuego collapsed at least five times, producing debris avalanches and pyroclastic-flow deposits. The last collapse of Paleofuego, at 2505 yr B.P., produced a 5-km-wide caldera, inside of which grew Colima volcano. Colima is the most active volcano in Mexico, with 45 eruptions during the past 426 yr, representing a potential hazard for the surrounding population of ~0.9 million people. From the geological mapping, it is clear that volcanic activity and collapses of the Colima volcanic complex have been controlled by the active Tamazula fault, which generated the NE-SW Alceseca-Atenquique graben.

Most of the largest volcanoes in México are located at the frontal part of the Trans-Mexican Volcanic Belt and in other isolated areas. This chapter considers some of these volcanoes: Colima, Nevado de Toluca, Popocatépetl, Pico de Orizaba (Citlaltépetl), and Tacaná. El Chichón volcano is also considered within this group because of its catastrophic eruption in 1982. The volcanic edifice of these volcanoes, or part of it, was constructed during the late Pleistocene or even during the Holocene: Colima 2500 yr ago, Pico de Orizaba (16,000 yr), Popocatépetl (23,000 yr), Tacaná (∼26,000 yr), and Nevado de Toluca (>45,000). The modern cones of Colima, Popocatépetl, Pico de Orizaba, and Tacaná are built inside or beside the remains of older caldera structures left by the collapse of ancestral cones. Colima, Popocatépetl, and Pico de Orizaba represent the youngest volcanoes of nearly N-S volcanic chains. Despite the repetitive history of cone collapse of these volcanoes, only Pico de Orizaba has been subjected to hydrothermal alteration and slope stability studies crucial to understand future potential events of this nature. The magmas that feed these volcanoes have a general chemical composition that varies from andesitic (Colima and Tacaná), andesitic-dacitic (Nevado de Toluca, Popocatépetl, and Pico de Orizaba) to trachyandesitic (Chichón). These magmas are the result of several magmatic processes that include partial melting of the mantle, crustal assimilation, magma mixing, and fractional crystallization. So far, we know very little about the deep processes that occurred between the upper mantle source and the lower crust. However, new data have been acquired on shallower processes between the upper crust and the surface. There is clear evidence that most of these magmas stagnated at shallow magma reservoirs prior to eruption; these depths vary from 3 to 4 km at Colima volcano, 4.5–6 km at Nevado de Toluca, and ∼6–8 km at Chichón volcano. Over the past 15 years, there has been a surge of studies dealing with the volcanic stratigraphy and eruptive history of these volcanoes. Up to the present, no efforts have achieved integration of the geological, geophysical, chemical, and petro logical information to produce conceptual models of these volcanoes. Therefore, we still have to assume the size and location of the magma chambers, magma ascent paths, and time intervals prior to an eruption. Today, only Colima and Popocatépetl have permanent monitoring networks, while Pico de Orizaba, Tacaná, and Chichón have a few seismic stations. Of these, Popocatépetl, Colima, and Pico de Orizaba have volcanic hazard maps that provide the basic information needed by the civil defense authorities to establish information programs for the population as well as evacuation plans in case of a future eruption.

Colima volcano is situated at the western edge of the Mexican volcanic belt within the Colima rift zone. This contribution presents new geochemical and Sr-Nd-Pb-O isotope data for Colima volcano rocks and plutonic xenoliths found in prehistorical lava flows. Colima volcano magmas display strong subduction signatures (positive peaks of Ba, K, Pb, and Sr, and negative anomalies of Nb and Ti) and were generated in a depleted mantle source and emplaced at crustal levels (garnet-free zone), where they experienced fractional crystallization of plagioclase and pyroxene. Gabbroic and granitoid xenoliths found in prehistorical lava flows show evidence for partial melting and are considered to be representative of the basement beneath Colima volcano. At upper-crustal levels, Colima volcano magmas were contaminated by granitoids, like those of the nearby Cretaceous Manzanillo and Jilotlán Batholiths. Sr-Nd isotope ratios of these intrusives are nearly identical to those of Colima volcano lavas. For that reason assimilation of the granitic crust is not detectable in diagrams of these isotopic systems but can be clearly seen in a ϵ Nd versus δ 18 O plot. In comparison to other large Mexican volcanic belt stratovolcanoes, Colima volcano lavas display the least evolved geochemical and isotopic signatures of this arc.