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AAPG Bulletin, V.
Subandean thrust and fold belt of northwestern Argentina: Geometry and timing of the Andean evolution
1Conicet, Argentina, Cornell University; email: [email protected]
2XR Consultants, Argentina; email: [email protected]
3Cornell University; email: [email protected]
4Brevard College; email: [email protected]
Leandro E. Echavarria received his Licenciado en Geologia degree (1992) and his Ph.D. (1997) from La Plata University (Argentina). He joined XR Consultants and worked as a field and structural geologist in the Subandes from 1998 to 2000. He spent two years as a visiting scientist at Cornell University working on the Subandes stratigraphy and structural geology. Now, he is a postdoctoral research associate at Colorado School of Mines.
Roberto M. Hernndez earned his Licenciado en Geologia degree from La Plata University (1980) and then specialized in petroleum geology at Buenos Aires University (1981). He worked for 12 years for YPF where he was chief of surface geology for the northwestern Argentina section. Since 1993, he has been an XR Consultants geologist in charge of the stratigraphic and structural studies in Bolivia and Argentina. At present, he is the manager of XR Exploracionistas Regionales y Servicios.
Richard Allmendinger received his Ph.D. in structural geology from Stanford University in 1979. He joined the faculty at Cornell University in 1984, where he is now a full professor. He has worked in Andean geology since 1981 and also includes among his interests numerical modeling of fault related fold, analysis of fault populations, and neotectonics.
Jim Reynolds holds A.B. and M.A. degrees and Ph.D. from Dartmouth College, United States. He has worked on the magnetostratigraphy of Argentine Neogene foreland basins since 1984 as a graduate student (1984–1987), a Fulbright Scholar (1989), researcher (1987–present), and consultant (1994–present). He is currently a geology professor at Brevard College in Brevard, North Carolina, United States.
We wish to thank the geologists of the Yacimientos Petroliferos Fiscales Commission 6 who started with the field data recompilation and analysis of the area, with special thanks to A. Di Salvo, A. Schulz, L. Constantini, and D. Starck. Tecpetrol and the UTE Aguarage provided the seismic information; we also thank Lic. Mario Alarcon for his help with the seismic lines. The manuscript was greatly benefited from valuable comments and suggestions by Teresa Jordan and AAPG Bulletin reviewers J. Verges, N. Hanks, and D. Wiltschko.
The Subandean ranges of northwestern Argentina are an active thin-skinned fold and thrust belt. The main detachment level in Silurian shales dips 2–3W, and all the major east-verging faults detach from it. Important intermediate detachment levels in the Devonian shales generate lift-off structures and the decoupling of the lower and upper structural levels. The Subandean thrust belt has a minimum shortening of about 60 km (36%) at about 2240 latitude. The deformation started at about 8.5–9 Ma with the uplift of the El Pescado range and the formation of an important back thrust at the Cinco Picachos range. Fault generation gets young to the east; the Pintascayo range uplift started at 7.6 Ma, while the Baja Orn range uplift began at about 6.9 Ma. These two ranges continued growing simultaneously until at least 4.7 Ma. At San Antonio range, fault movement began at approximately 4.4 Ma, and the Aguarage uplift started at about 2.7 Ma. An important stage dominated by out-of-sequence movements spans from about 4.5 Ma to present. For both proposed models of shortening, the Quaternary rates of shortening between 8 and 11 mm/yr coincide well with global positioning system results from the area. The hydrocarbon generation and migration is contemporaneous with the deformation, enhancing the possibilities of hydrocarbon entrapment in the area.
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