Volcanic stratigraphy of the Amealco Caldera and vicinity, central Mexican volcanic belt.

Abstract

The Amealco caldera is one of five major caldera complexes within the Mexican Volcanic Belt. Stratigraphy indicates five major volcanic units related with the volcanic of the Amealco caldera: 1 the Amealco Tuff, a widespread pyroclastic sequence that was erupted from the Amealco caldera at about 4.7 Ma and which represents 77 km super 3 of magma; 2 Brick pumice, a more localized post-Amealco Tuff pyroclastic sequence representing 2.4 km super 3 of magma; 3 Amealco Andesite and Campana Dacite, lava domes that were emplaced along a ring fracture at 4.3 Ma and actually form the topographic expression of the caldera, the former representing 3.5 km super 3 of trachyandesitic magma and the later 0.8 km super 3 of trachydacite magma; 4 La Cruz Rhyolite, which consists of five lava domes within the caldera that were emplaced at 3.9 Ma, with a total magma volume of 2.4 km super 3 ; and 5 Santa Rosa Andesite, which includes five trachyandesitic domes that were emplaced at 3.7 Ma, representing a magma volume of 4.3 km super 3 . Peripheral activity occurred at several vents: the trachydacitic Palomas volcano at 4.0 Ma Palomas Dacite; the basaltic-andesitic Hormigas volcano and rhyolitic lava domes Coronita Rhyolite, both at 3.7 Ma; a 2.5 Ma hornblende andesite dome Garabato Andesite; and finally, a 2.2 Ma andesitic scoria cone El Comal Andesite. In addition to the peripheral volcanism, Amealco Tuff is overlain by the 2.9 Ma El Rincon Rhyolite, a lava dome complex 12 km to the north of the caldera, and by a widespread 3.5-Ma felsic ignimbrite, here named the Huichapan Tuff, which is exposed 20 km to the east of the caldera and previously had been misidentified as Amealco Tuff. Amealco Tuff overlies 5.7 Ma basalts and 4.7 Ma felsic ignimbrites.

25 samples from this reference