La Pacana Caldera
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.
Of the three centres, the most important is the eponymous La Pacana caldera, a 70 by 35 km caldera depression (average elevation 4,000 m) with a complex topographic outline. The caldera was first described by Gardeweg & Ramirez (1987), who concluded that it formed ~4 Ma ago by eruption of ~2,500 km3 of the Atana ignimbrite. The outflow ignimbrite can be correlated over several thousands of square kilometers of N. Chile, SW Bolivia and NW Argentina (Francis and Baker, 1978; de Silva & Francis, 1989; Lindsay et al., 2001). An ignimbrite sequence previously identifed at the Atana ignimbrite has now been named the lower and upper Tara ignimbrite, erupting at 5.6 Ma and 3.8 Ma, respectively (Lindsay et al., 2001). Another major ignimbrite, the rhyolitic Toconao ignimbrite, erupted between 4 and 5 Ma ago from La Pacana (Lindsay et al., 2001). A large thickness of ignimbrite accumulated in the caldera depression during the eruption which was followed by the resurgence of the caldera floor to form the Cerros de La Pacana (4,905 m), an elongate resurgent block ~50 x 12 km characterised by antiformally-dipping, densely welded ignimbrite and an apical graben complex. Post-caldera volcanism continued until 2 Ma (Lindsay et al., 2001).
de Silva, S.L., & Francis, P.W., 1989. Correlation of large ignimbrites - two case studies from the Central Andes of N. Chile. J. Volcanol. Geotherm. Res. v37, no.2, p.133-149.
Francis, P.W., & Baker, M.C.W., 1978. Sources of two large-volume ignimbrites in the Central Andes: Some Landsat evidence. J. Volcanol. Geotherm. Res. v.4, p81-87.
Gardeweg, P.M., & Ramirez, C.F., 1987. The La Pacana Caldera and the Atana ignimbrite: a major ash-flow and resurgent caldera complex in the Andes of northern Chile. Bull. Volcanol. v.49, p.547-566.
Lindsay, J. M., de Silva, S., Trumbull, R., Emmermann, R., Wemmer, K., 2001. La Pacana caldera, N. Chile: a re-evaluation of the stratigraphy and volcanology of one of the world's largest resurgent calderas. Journal of Volcanology and Geothermal Research, 106(1-2): 145-173.