Cerro Guacha ignimbrite centre

The La Pacana Complex/Cerro Guacha

The La Pacana Complex (LPC),is the largest of the caldera complexes in the APVC. It covers an area of ~17,000 km2 in N. Chile, SW Bolivia and NW Argentina, and consists of three major ignimbrite centres, which overlap temporally, spatially and structurally. Hot springs are found throughout the complex.

To the north of the La Pacana caldera, is Cerro Guacha (5,599 m; 22º40'S; 67º27'W) , the resurgent centre of the Cerro Guacha caldera, first indentifed by Francis and Baker (1978). Two overlapping uplifted blocks with apical graben oriented obliquely to one another form the central complex. These are inferred to represent two generations of resurgence; the westerly NW-SE apical graben being the younger event. Several dacite domes have been erupted to the north of the central uplifts in to the caldera moat, which is at an elevation of 4500 m, measures ~ 20 by 15 km and is bounded by an arcuate scarp ~15 km to the east. This scarp has considerable relief (~500m) and at least three major ignimbrite units can be identified in it. One of these is the 4.1 Ma Puripcar ignimbrite, which can be correlated from Cerro Guacha as far as N. Chile (de Silva & Francis, 1989), while the other units are the Atana ignimbrite (from the La Pacana caldera) and a younger unit related to Cerro Tortoral. A second large scarp,~ 50 km from the central uplift, also has about 300-500m of relief and defines the eastern structural margin of the Guacha caldera. This is contiguous with faults which bound the eastern part of the La Pacana caldera.