GEOLOGY AND VOLCANIC STRATIGRAPHY OF SIERRA DE MIL CUMBRES

The Sierra de Mil Cumbres (SMC) is a Miocene volcanic range located at the northeastern part of the State of Michoacan, near the city of Morelia. It is a NE-SW oriented structural high that covers an area of 870 km², ~18 km wide and 60 km long; which includes a great variety of volcanic structures, such as calderas, lava domes, lava flows and cinder cones. The SMC represents a morphological piece of evidence of the formation of central Mexico, because it occurs at the interception of Miocene-Recent Trans-Mexican Volcanic Belt (TMVB) and the Eocene-Oligocene Sierra Madre Occidental (SMO). Although, the rocks of the SMC have a closer affinity to the SMO, it is a younger structure (Miocene) located at the south-central part of the TMVB. This particular spatial distribution allowed the interbedding of volcanic products from both SMO and TMVB, but SMC somehow managed to avoid the emplacement of new structures on top of it, representing a regional volcanic hiatus.

The SMC consists of four large and complex volcanic structures (from SW to NE): two calderas (Atécuaro and La Escalera), and two volcanic complexes (Indaparapeo and Garnica); each of them has its own geologic evolution, mainly consisting of andesitic to dacitic calc-alkaline lavas and large volume rhyolitic ignimbrites.

In this study we compile new and previous data of the area. We contribute with a new geological map of SMC, the volcanic stratigraphy, geochemistry, petrology and geochronological (⁴⁰Ar/³⁹Ar) data.