Geodynamic processes in the Andes of Central Chile and Argentina: an introduction

Abstract

The Andes, the world's largest non-collisional orogen, is considered the paradigm for geodynamic processes associated with the subduction of an oceanic plate below a continental plate margin. In the framework of UNESCO-sponsored IGCP 586-Y project, this Special Publication includes state-of-the-art reviews and original articles from a range of Earth Science disciplines that investigate the complex interactions of tectonics and surface processes in the subductionrelated orogen of the Andes of central . This introduction provides the geological context of the transition from flat slab to normal subduction angles, where this volume is focused, along with a brief description of the individual contributions ranging from internal geodynamics and tectonics, Quaternary tectonics and related geohazards, to landscape evolution of this particular segment of the Andes.Convergent continental margins are one of the firstorder expressions of the movement of Earth's tectonic plates atop a convecting mantle. The topography of convergent margins is due to the interactions of rock uplift, climate and surface processes that are dominantly driven by upper crustal and internal lithospheric deformation as well as erosional processes (e.g. Molnar & Lyon-Caen 1988;Beaumont et al. 2004;Whipple & Meade 2006). The Andes of central Chile and Argentina (c. 32 -368S, Figs 1 & 2) straddle a potentially important transition in geodynamic boundary conditions imposed on the upper plate: a drastic change in the geometry of the subducting Nazca plate from 'flat' to normal subduction angles, from c. 5-108 to 308 (Cahill & Isacks 1992; Fig. 1). This segment of the Andes is therefore a particularly suitable setting to evaluate the interplay between constructive deep mechanisms, resulting in rock uplift and lateral expansion of the Andes, and the mechanisms of exhumation and erosion that shape the landscape in an active, convergent margin.The Central Andes are composed of different morphostructural units (from west to east; Figs 1 & 2): the Chilean Coastal Cordillera, the Principal Cordillera (spanning Chile and Argentina), the Frontal Cordillera, the Argentine Precordillera and the Pampean Ranges (Jordan et al. 1983). Although previous studies attempt to constrain the magnitudes of orogenic shortening for each morphostructural unit, limited amounts of geochronology complicate attempts to constrain more tightly the rates of shortening and topographic uplift. There are several outstanding questions regarding the interplay between deep and surface processes in the development of the Andean Orogen over different timescales, as follows. † What is the nature of the interaction between tectonic and surface processes in this sector of the Andes? In particular, are surface and tectonic processes part of a strongly coupled system? † What control does the geometry of the subducting slab exert over the timing and style of deformation in the South American plate? † How do deformation and denudation evolve in space and time? Are there differences between ...

Evidence for Self‐Similar Bedload Transport on Andean Alluvial Fans, Iglesia Basin, South Central Argentina

“…Journal of Geophysical Research: Earth Surface 1.97 × 10 8 m 3 /10 kyr and has the highest denudation rate, 0.07 mm/year, fan 1 exports 5.14 × 10 8 m 3 /10 kyr and has a denudation rate of 0.06 mm/year and the northern most fan, 3, has the lowest export, 1.48 × 10 8 m 3 /10 kyr and the lowest denudation rate, 0.04 mm/year. This relatively low rate of erosion is analogous to millennial catchment averaged erosion rates derived from cosmogenic-nuclide and thermochronometric studies, which typically report values between 0.04 and 0.1 mm/year (Sepulveda et al, 2015). This gives confidence that the catchment characteristics derived (Table 1) provide reasonable estimates of sediment export to within an order of magnitude.…”

Encoded Landscapes: A Link between Inka Wall Orientations and Andean Geomorphology

“…The Andes highland territory, a geological marvel spanning seven countries from Venezuela to Chile, offered more than just a backdrop to the Inka civilization. This mountain range, with its sedimentary, igneous, and metamorphic rocks, is a window into Earth's diverse geological history [10]. The Andes' fractal nature, a result of repetitive structures within the Earth's crust, offers a fascinating perspective on the potential inspirations behind Inka architectural designs [11,12].…”

Gold Deposits in Chile

“…Between 27º S and 33º S, the same Paleocene-Eocene magmatic event is recognised, followed by discrete Late Oligocene-Early Miocene, Mid-Miocene, and Late Miocene magmatic episodes. In this segment of the Andes magmatism ceased in the Late Miocene, when the subduction angle shallowed beneath this region, which today constitutes the nonvolcanic, "flat slab" segment of the Chilean Andes (Kay et al, 1987;Sepúlveda et al, 2015;Ramos and Folguera, 2016).…”