Near pure surface uplift of the Argentine Frontal Cordillera: insights from (U–Th)/He thermochronometry and geomorphic analysis

Abstract

Apatite (U-Th)/He thermochronology from palaeosurface-bounded vertical transects collected in deeply incised river valleys with .2 km of relief, as well as geomorphic analysis, are used to examine the timing of uplift of the Frontal Cordillera and its relation to the evolution of the proximal portions of the Andean foreland between 328 and 348S latitude. The results of apatite (U-Th)/He (AHe) analyses are complex. However, the data show positive age-elevation trends, with higher elevation samples yielding older AHe ages than samples at lower elevation. Slope breaks occur at c. 25 Ma in both profiles, separating very slow cooling and or residence within a partial retention zone (slope of c. 10 m/Myr) at the highest elevations from a slope of c. 60-100 m/ Myr cooling rate at lower elevations. The older AHe ages suggest either (1) minimal burial of the Frontal Cordillera and/or (2) significant pre -middle Miocene local relief. Geomorphic analysis of the adjacent, east-draining Río Mendoza and Río Tunuyán catchments reveals a glacial imprint to the landscape at elevations above 3000 m, including greater channel steepness and lower profile concavities developed during glacial erosion. Detailed analysis of headwall heights provides evidence of ongoing rock uplift along the entire eastern flank of the Frontal Cordillera and in the eastern flank of the Principal Cordillera south of the slab dip transition.

Revisiting the Crustal Structure and Kinematics of the Central Andes at 33.5°S: Implications for the Mechanics of Andean Mountain Building

“…Recently, zircons with affinities to the Paleo‐Proterozoic basement and Permo‐Triassic Choiyoi units of the Frontal Cordillera, early in the clastic series of this basin, have been interpreted to “correspond to recycled material within the Mesozoic units [of the Principal Cordillera] or else to a direct supply from a paleorelief at the current position of the Frontal Cordillera” (Porras et al, ). Recent thermochronological constraints on the exhumation of the Frontal Cordillera tend to support the second interpretation as they suggest that the uplift and exhumation of the Frontal Cordillera initiated early by ~25 Ma, and that it accelerated recently by ~10 Ma (Hoke et al, ). This early initiation of uplift has recently been corroborated by a new thermochronological data set (Riesner, ).…”

“…Finally, we upscale our reasoning and integrate geological, geophysical, and chronological constraints at the scale of the whole orogen at 33.5°S. In particular, we discuss the timing of the initiation of the tectonic uplift of the Frontal Cordillera basement culmination using recently published thermochronological data (Hoke et al, ) and additional constraints on the Andean eastern front (García et al, ; García & Casa, ; Giambiagi et al, ) to discriminate between the two existing conceptual models of Andean orogeny. These constraints allow us for discussing the mechanics of Andean mountain building and for proposing a crustal‐scale section of the Andes at this latitude.…”

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

“…Farías et al 2012), while other studies (Carretier et al , 2014 demonstrate that precipitation is negatively correlated with millennial-scale erosion rates. Hoke et al (2014b) present new apatite (UTh)/He thermochronology data and a geomorphic analysis of two large rivers from the Frontal Cordillera of Argentina that bear on the timing and origin of mountain uplift. Their data demonstrate that the Frontal Cordillera was never buried by a thick package of foreland basin sediments, as is commonly assumed; rather, there was always a positive or near-surface topographic feature since at least Miocene time.…”

Thermochronologic Evidence for Late Eocene Andean Mountain Building at 30°S

“…The Eocene compressive phase is widely recognized in the Puna/southern Altiplano, north of 28°S, where it represents the first stage of construction of the Andes (Coutand et al, ; del Papa et al, ; Elger, Oncken, & Glodny, ; Hong et al, ; Mpodozis et al, ; Oncken et al, ; Payrola et al, ). In contrast, in the Southern Central Andes, the Neogene is considered the main phase of crustal shortening and tectonic uplift (Giambiagi et al, , ; Hoke et al, ; Ramos, Cegarra, & Cristallini, ; Ramos, Cristallini, & Pérez, ), and direct evidence for Eocene deformation is scarce. Evidence of Paleogene deformation in the Andes south of the Altiplano/Puna has been more difficult to constrain due to sparse, poorly dated sedimentary record, and a limited number of thermochronology studies between 28° and 36°S.…”