Western Guatemala
Latitude: 15.13 N
Longitude: 92.10 W

Location of Tacaná and other volcanoes along the Guatemalan volcanic front.

The volcanic front of Guatemala begins at the triple junction of the North America, Cocos, and Caribbean plates, with the Cocos plate underthrusting the Caribbean plate along the Middle America trench. The front is a belt of large frequently active stratovolcanoes, which Stoiber and Carr divided into segments on the basis of volcanic lineaments and seismicity. Tacaná and Tajumulco are the highest volcanoes in all of Central America and are on a separate segment of the front, which has been historically inactive.

Guatemala is cut by several transcurrent faults. The northernmost of those is the Cuilco-Chixoy-Polochic system, a left-lateral fault zone which extends into southern Mexico. It represents the present boundary between the Caribbean and Americas plates, and has been active for the past 10 m.y.

Quaternary volcanoes north and west of the Polochic fault differ from those in the Guatemalan front. They occur in a NW trending belt and consist of small volume sphene bearing domes with intermediate silica content of the Chiapas volcanic belt. The volcanic centers of this belt (including Nicolas Ruiz, Tzomtehuitz and El Chichón) apparently result from oblique subduction of the Cocos plate under the Americas plate. (Capaul, 1987)

Burkhart and Self (1985) divided the volcanic front into four morphotectonic zones based on block rotation about the transcurrent faults. Tacaná lies on their Zone I, on basement rock, and is some 30 km south of the Polochic fault. In their model, Zone I is locked into place and unaffected by extensional tectonics.

Guatemala is an uplifted block of continental crust of at least Paleozoic age. The continental crust of Guatemala is characterized by metamorphic rocks, anatexites, and plutonites of granitic ocmposition, overlain by upper Paleozoic to Tertiary sediments. The Tertiary of Guatemala is characterized by violently explosive volcanism of cal-alkaline affinity, very similar to the Quaternary volcanism. The Quaternary vents lie mostly to the south of the Tertiary rocks.

Sibinal, Guatemala, seen from the W at the foot of the slope of the Sierra de Sibinal. The cone of Tajumulco and eroded volcanic topography can be seen in the distance. Photo by Bill Rose, 1986.

(Mercado and Rose, 1992)