Two magmatic chambers beneath Iztaccíhuatl volcano revealed by 3D gravity modeling

Introduction: A recent gravimetric analysis of Iztaccíhuatl (IZ) volcano reported the existence of two magma chambers feeding the volcano; the present study extends the analysis, doubling the resolution of the inverted 3D gravity model from 500 to 250 m. Materials and methods: We use the high-resolution Global Gravity Model plus. By performing a 3D inversion of the gravity data, we obtain a volume density model. The Sierra Nevada region includes a gravity low, approximately 40 mGal below the surrounding values, where IZ volcano is located. At the new resolution, we identify two magmatic regions under this volcano, labeled the North Branch (NB) and the South Branch (SB). Results: An evolution model that starts with the emplacement of an original magma chamber, east of, and coeval with, the Llano Grande caldera (0.9 Ma), gave rise to an edifice with an altitude of 6200–6400 m, named Ancestral Iztaccíhuatl, that collapsed at 631 ka. When interpreting the density cross-sections, we infer that the collapse blocked the original magma ascent path, inducing its bifurcation into the NB and SB. Conclusions: The SB was displaced southwest of the original conduit, giving rise to the present Summit Series, while the NB was displaced to the north. The activity of the SB initiated the Younger Volcanic Series, which ended between 600 and 500 ka. We find evidence that La Cabeza (the head) is an edifice older than the Summit Series. Recent volcanic activity of Cerro Teyótl (80 ka), located northeast of La Cabeza, appears to be a reactivation of the NB.