Structure of the Patagonian-Fuegian Andes

The Cordillera Darwin, located in the Fuegian Andes, is an ~5000 sq. km massif of orthogneiss, paragneiss, and schist that defines the high-grade core of the Patagonian-Fuegian fold-thrust belt which formed during the Late-Cretaceous­–Paleogene Andean orogeny. Neogene to present transtensional tectonics associated with the separation of Antarctica from S. America and formation of the Scotia plate, combined with Quaternary glacial erosion, have exhumed the metamorphic core of the orogen and base of the retroarc fold-thrust belt. We study exposures of this paleo-brittle-ductile transition to investigate two processes that are common to convergent orogens around the world: 1) the influence of mechanical stratigraphy on the kinematic evolution of a retroarc fold-thrust belt; and 2) the interplay between ductile deformation of the middle and lower crust below a fold-thrust belt with brittle deformation of the overlying sedimentary basin. We combine field-based techniques including cross section construction, outcrop mapping and structural fabric analysis with laboratory techniques such as structural petrology, electron backscatter diffraction analysis, and thermochronology to determine the timing, kinematics, and deformation conditions of these processes. 

See our publications from the Patagonia project:

Betka, P.M., Mosher, S., Klepeis, K. 2022. Progressive development of a distributed ductile shear zone beneath the Patagonian retroarc fold-thrust belt, Chile. Lithosphere 2022 (1): 3820115.

Betka, P.M., Klepeis, K.A., Mosher, S. 2016.Fault kinematics of the Magallanes-Fagnano Fault System, southern Chile; an example of diffuse strain and sinistral transtension along a continental transform margin. Journal of Structural Geology. V. 85, pp 130-153.

Betka, P.M., Klepeis, K.A., Mosher, S. 2015. Along-strike variation in crustal shortening and kinematic evolution of the Magallanes fold-thrust belt, Chile 53°-55° S. Geol. Soc. Amer. Bulletin. v. 127, p. 1108-1134.  doi:10.1130/b31130.1

McAtamney, J., Klepeis, K., Mehrtens, C., Thomson, S., Betka, P., Rojas, L., Snyder, S.  2011. Along-strive variability of back-arc basin collapse and the initiation of sedimentation in the Magallanes foreland basin, southernmost Andes (53-54.4°S). Tectonics v. 30/5. TC002826.

Klepeis, K., Betka, P., Clarke, G., Fanning, M., H., Rojas, L., Mpodozis, C., & Thomson, S. 2010. Continental underthrusting and obduction during the Cretaceous closure of the Rocas Verdes rift basin, Cordillera Darwin, Patagonian Andes. Tectonics, V. 29, TC3024.

Maloney, K. T., Clarke, G. L., Klepeis, K. A., Fanning, C. M., & Wang, W. (2011). Crustal growth during back-arc closure: Cretaceous exhumation history of cordillera darwin, southern patagonia. Journal of Metamorphic Geology, 29(6), 649–672. http://doi.org/10.1111/j.1525-1314.2011.00934.x