Geologic Framework[edit]
Prior to the formation of the Trans-Mexican Volcanic Belt, an older, but related volcanic belt, the Sierra Madre Occidental occupied the area. Resuming in the Eocene, post-Laramide deformation, subduction related volcanism formed the Sierra Madre Occidental silic volcanic arc at a paleo-subduction zone off the coast of Baja California, before the peninsula rifted away.[5][9][10] From the Late Eocene to the Middle Miocene, counterclockwise rotation of the volcanic arc transitioned the once active Sierra Madre Occidental to a now active Trans-Mexican Volcanic Belt.[5][9] By the Middle Miocene, the transition from the silicic to more mafic compositions was complete, and can be considered the beginning of the Trans-Mexican Volcanic Belt.[5] Due to the orthogonal orientation of the Trans-Mexican Volcanic Belt in relation to the trend of Mexican tectonic provinces, its Pre-Cretaceous basement is highly heterogeneous.[1] The Trans-Mexican Volcanic Belt east of 101°W rests uponPrecambrian terranes, assembled into the Oaxaquia microcontinent and on the Paleozoic Mixteco terrane. West of 101°W, the Trans-Mexican Volcanic Belt resides on top of the Guerro composite terrane - a make up of Jurassic to Cretaceous marine marginal arcs, which are built onTriassic - Early Jurassic siliclastic turbidites. Assemblage of these basement rocks results with a thickness of 50–55 km east of 101°W and 35–40 km west of 101°W.[1][8]
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