Detrital Thermochronology Reveals Major Middle Miocene Exhumation of the Eastern Flank ofthe Andes That Predates the PampeanFlat Slab (33°–33.5°S)

Abstract

The Cordón del Plata and Cordón del Portillo (32.6°-33.8°S) are the portions of the Frontal Cordillera that straddle the transition zone between the Pampean flat-slab subduction segment to the north and the normal subduction segment to the south. A complete understanding of how the Frontal Cordillera developed is necessary in order to evaluate different tectonic models for the Andes along with their relation to subduction dynamics and contractional upper-crustal deformation. Detrital apatite fission track thermochronology of modern river sediments that drain the eastern and western slopes of the Cordón del Plata and the northern Cordón del Portillo provides constraints on regional exhumation histories. AFT data from each catchment typically contain multiple age peaks, but all have a prominent 15.3-17 Ma age peak. One catchment, the Las Tunas River has a unimodal distribution at 17.0 ± 1.1 Ma, with a confined track length distribution indicative of rapid cooling at that time. These results, combined with provenance analysis in the adjacent Cacheuta Basin, indicate significant early to middle Miocene (~16 Ma) exhumation in the Cordón del Plata and the northern sector of the Cordón del Portillo. Exhumation related to rock uplift occurred prior to the~11 Ma onset of a flat slab geometry at these latitudes, but immediately after the main east vergent contractional event in the adjacent Principal Cordillera. Such Frontal Cordillera exhumation fits in an eastward, youngest to the foreland sequence of deformation of the different morphostructural Andean units at~33°-34°S, arguing against the recently proposed west vergent orogenic system at these latitudes.

Topographic response to Neogene variations in slab geometry, climate and drainage reorganization in the Northern Andes of Colombia

“…However, other recent papers in the Andes with robust geo-and thermochronology data have argued that the timing and spatial patterns of deformation pre-date the onset of flat slab subduction in the southern Andes (Buelow et al, 2018;Lossada et al, 2020).…”

Architecture, Kinematics, and Tectonic Evolution of the Principal Cordillera of the Andes in Central Chile (∼33.5°S): Insights From Detrital Zircon U‐Pb Geochronology and Seismotectonics Implications

“…After 16 Ma, the uplift of the Paleozoic basement (Heredia et al., 2012) led to the development of the Frontal Cordillera (Giambiagi & Ramos, 2002; Giambiagi et al., 2003a; Lossada et al., 2020; Ramos et al., 2004); simultaneously, out‐of‐sequence faults deformed the Mesozoic and Cenozoic units of the Principal Cordillera (Farías et al., 2008; Fock et al., 2006; Giambiagi & Ramos, 2002; Giambiagi et al., 2003a, 2015; Godoy et al., 1999; Tapia et al., 2015). Between 9 and 4 Ma, volcano‐magmatic activity declined but some pulses moved westwards, forming the El Teniente and Río Blanco‐Los Bronces porphyry copper deposits (Deckart et al., 2005; Maksaev et al., 2004).…”

“…Among these, the Pampean flat‐slab subduction zone (27°S‐33°S) is one of the most remarkable features in this orogen (Cahill & Isacks, 1992; Gutscher et al., 2000). It is characterized by a series of tectonic domains, with an accretionary wedge in the Coastal Cordillera, Quaternary deposits in the Central Valley, a hybrid thrust belt in the Principal Cordillera, a rigid block uplift in the Frontal Cordillera, basement uplift in the Precordillera and the Sierras Pampeanas, and a series of Neogene‐Quaternary broken foreland basins (Alvarado et al., 2009; Giambiagi et al., 2015; Lossada et al., 2020; Martínez et al., 2016; Ramos et al., 2002, 2004; Rodríguez et al., 2018; Suriano et al., 2017). A decrease of volcanic activity since the early and middle Miocene (Jones et al., 2016; Kay & Abbruzzi, 1996; Litvak et al., 2007; Ramos et al., 2002), and a complex history of shortening and exhumation (Barrionuevo et al., 2019; Lossada et al., 2017, 2020; Martos et al., 2020; Rodríguez et al., 2018; Suriano et al., 2017) is also one of the main features of this area.…”

Cenozoic exhumation history at the core of the Andes at 31.5°S revealed by apatite fission track thermochronology

“…The uplift/deformation sequence of the different morphostructural units during the Cenozoic has been interpreted to be a result of a foreland advance of deformation related to the increase in the mechanical coupling between the Nazca and South American plates during the flattening of the slab (Jordan et al, 1983;Ramos et al, 2002;Ramos and Folguera, 2009;Martinod et al, 2013), since the middle Miocene. However, recent work performed in other sectors of the Southern Central Andes point toward significant exhumation/uplift in the Frontal Cordillera (Lossada et al, 2017(Lossada et al, , 2020Riesner et al, 2019) and Precordillera (Levina et al, 2014;Suriano et al, 2017;Buelow et al, 2018) prior to the establishment of flat-slab conditions.…”