More Like this

1. Assessing drivers of high exhumation magnitudes and young cooling ages in the eastern central Andes, southern Peru (13–18°S)

   https://doi.org/10.1016/j.epsl.2023.118281  

   Glover, Chloë O; McQuarrie, Nadine; Falkowski, Sarah; Ehlers, Todd A (October 2023, Earth and Planetary Science Letters)

   The potential structural controls on exhumation across the southern Peruvian Andes are not well understood, in part due to limited structural studies that co-locate with thermochronometric datasets. We integrate these two datasets and evaluate the relative contribution that fault geometry, magnitude, and shortening rate have on predicted cooling ages. Here we present a balanced cross-section constructed using new structural observations. This section, combined with existing thermochronometer data and a thermokinematic model, investigates the drivers of high exhumation and young canyon thermochronometric ages along the deeply incised Marcapata canyon in southern Peru. Together, these approaches constrain the timing and magnitude of exhumation in this portion of the southern Peruvian Andes and provide a mechanism for documenting how the internal architecture changes along strike. The balanced cross-section (oriented N30E) covers the Subandean Zone to the northeast, the Marcapata canyon on the eastern flank of the southern Peruvian Andes, and the Altiplano-Eastern Cordillera boundary to the southwest (13–18◦ S). Exhumation is constrained by four low-temperature thermochronometer systems, including apatite and zircon (U-Th)/He (AHe and ZHe, respectively) and fission-track (AFT and ZFT, respectively). The youngest AHe (∼1–3 Ma), AFT (∼3–7 Ma), ZHe (∼4–7 Ma), and ZFT (∼14–17 Ma) ages are located in the center and valley bottom of the Marcapata canyon. The thermokinematically modeled cross-section produces cooling ages determined by fault geometry and kinematics. Reset ZFT ages require burial of Ordovician rocks in excess of 5.5 km above the original 6.5 km depositional depth. We find that the ZFT and ZHe ages in the Eastern Cordillera are sensitive to the history and magnitude of burial, age and location of uplift, and canyon incision. Canyon incision is required to reproduce the youngest canyon thermochronometric ages while slow shortening rates from ∼10 Ma to Present are required to reproduce interfluve thermochronometric ages. Shortening is accommodated by basement faults that feed slip up through three different décollement levels before reaching the surface. The proposed stacked basement geometry sets the first-order cooling signal seen in modeled ages. We determined that the total shortening in this section from the Subandean Zone to the Altiplano is 147.5 km, similar to shortening estimates in an adjacent thermo-kinematically modeled section in the San Gabán canyon 50 km to the southeast. Both the ZHe and ZFT ages in the Marcapata section (4–5 and 14 Ma) are noticeably younger than cooling ages from the San Gabán section (16 and 29 Ma). The Marcapata section’s higher magnitude of exhumation is due to a repetition of basement thrusts that continues to elevate the Eastern Cordillera while active deformation occurs in the Subandean Zone. The youngest thermochronometric ages in all four systems are co-located with the overlapping basement thrust geometry. This basement geometry, kinematic sequence of deformation, and canyon incision co-conspire to produce the young cooling ages observed in the Eastern Cordillera. 

   more » « less
2. Timing and drivers of exhumation and sedimentation in the eastern Peruvian Andes: Insights from thermokinematic modelling

   https://doi.org/10.1016/j.epsl.2023.118355  

   Buford_Parks, Victoria M; McQuarrie, Nadine; Falkowski, Sarah; Perez, Nicholas D; Ehlers, Todd A (October 2023, Earth and Planetary Science Letters)

   This study assesses the impact of fold-thrust belt driven deformation on the topographic evolution, bedrock exhumation and basin formation in the southeastern Peruvian Andes. We do this through a flexural and thermokinematically modelled balanced cross-section. In addition, published thermochronology samples from low-elevation (river canyons) and high-elevation (interfluves) and Cenozoic sedimentary basin datasets along the balanced cross-section were used to evaluate the age, location, and geometry of fault-driven uplift, as well as potential relationships to the timing of ∼2 km of canyon incision. The integrated structural, thermochronologic, and basin data were used to test the sensitivity of model results to various shortening rates and durations, a range of thermophysical parameters, and different magnitudes and timing of canyon incision. Results indicate that young apatite (U-Th)/He (AHe) canyon samples from ∼2 km in elevation or lower are consistent with river incision occurring between ∼8–2 Ma and are independent of the timing of ramp-driven uplift and accompanying erosion. In contrast, replicating the young AHe canyon samples located at >2.7 km elevation requires ongoing ramp-driven uplift. Replicating older interfluve cooling ages concurrent with young canyon ages necessitates slow shortening rates (0.25–0.6 mm/y) from ∼10 Ma to Present, potentially reflecting a decrease in upper plate compression during slab steepening. The best-fit model that reproduces basin ages and depositional contacts requires a background shortening rate of 3–4 mm/y with a marked decrease in rates to ≤0.5 mm/y at ∼10 Ma. Canyon incision occurred during this period of slow shortening, potentially enhanced by Pliocene climate change. 

   more » « less
3. Regional Thermal History Trends From the Idaho‐Montana Fold‐Thrust Belt Using Multiple Low‐T Thermochronometers

   https://doi.org/10.1029/2024TC008557  

   Kaempfer, J_M; Guenthner, W_R; Pearson, D_M; Orme, D_A; Crawford, B.; Brennan, D_T (May 2025, Tectonics)

   Abstract Low‐temperature thermochronometric data can reveal the long‐term evolution of erosion, uplift, and thrusting in fold‐thrust belts. We present results from central Idaho and southwestern Montana, where the close spatial overlap of the Sevier fold‐thrust belt and Laramide style, basement‐involved foreland uplifts signify a complex region with an unresolved, long‐term tectono‐thermal history. Inverse QTQt thermal history modeling of new zircon (U‐Th)/He (ZHe,n = 106), and apatite (U‐Th)/He dates (AHe,n = 43) collected from hanging walls of major thrusts systems along a central Idaho to southwestern Montana transect, and apatite fission track results from 6 basement samples, reveal regional thermal and spatial trends related to Sevier and Laramide orogenesis. Inverse modeling of foreland basement uplift samples suggest Phanerozoic exhumation initiated as early as ∼80 Ma and continued through the early Paleogene. Inverse modeling of interior Idaho fold‐thrust belt ZHe samples documents Early Cretaceous cooling at ∼125 Ma in the Lost River Range (western transect), and a younger cooling episode in the Lemhi Arch region (mid‐transect) at ∼90–80 Ma through the late Paleogene. This cooling in the Lemhi Arch temporally overlaps with cooling in southwestern Montana's basement‐cored uplifts, which we interpret as roughly synchronous exhumation related to contractional tectonics and post‐orogenic collapse. These data and models, integrated with independent timing constraints from foreland basin strata and previously published thermochronometric results, suggests that middle Cretaceous deformation of southwestern Montana's basement‐cored uplifts was low magnitude and preceded tectonism along the classic Arizona‐Wyoming Laramide “corridor.” In contrast, Late Cretaceous and Paleogene thrust‐related exhumation was more significant and largely complete by the Eocene. The basement‐involved deformation was contemporaneous with and younger than along‐strike Sevier belt thrusting in central Idaho. 

   more » « less
4. Miocene Construction of the High Andes Recorded by Exhumation of the Frontal Cordillera, La Ramada Massif of Western Argentina (32°S)

   Howlett, C J; Ronemus, C B; Carrapa, B; DeCelles, P G (January 2025, Tectonics)

   Abstract The Frontal Cordillera is a first‐order geologic feature of the southern central Andes, hosting the highest hinterland topography above the modern Pampean flat‐slab segment. The timing of Frontal Cordillera exhumation is important for testing models of Andean tectonics, yet large latitudinal gaps exist between structural and thermochronological constraints for the region. We conducted a thermochronometric study using a 4.4 km age‐elevation transect along the northeast ridge of Cerro Mercedario, the highest peak in the La Ramada massif at ∼32°S. Zircon (U‐Th)/He dates indicate partial resetting, supporting a limited magnitude of exhumation in even the most extreme Andean topography. Single grain apatite (U‐Th‐Sm)/He dates range from 8.5 ± 0.9 to 35.8 ± 3.6 Ma, with median dates of ∼10.5 to ∼15.7 Ma with increasing elevation. Integrated with geologic mapping and thermal history modeling, these data suggest Early to Middle Miocene exhumation along the Santa Cruz and Espinacito faults concomitant with uplift of the La Ramada massif. New apatite helium data from the Cordillera del Tigre segment of the Frontal Cordillera are partially reset and preferred modeling interpretations suggest exhumation ca. 11–9 Ma, coeval with shortening in the eastward adjacent Precordillera. These data add to accumulating regional evidence for out‐of‐sequence deformation during the Miocene, consistent with internal (hinterland) growth of a subcritical orogenic wedge contemporaneous with surface uplift and crustal thickening in the south‐central Andes. 

   more » « less
5. Miocene Construction of the High Andes Recorded by Exhumation of the Frontal Cordillera, La Ramada Massif of Western Argentina (32°S)

   https://doi.org/10.1029/2024TC008433  

   Howlett, C_J; Ronemus, C_B; Carrapa, B.; DeCelles, P_G (January 2025, Tectonics)

   Abstract The Frontal Cordillera is a first‐order geologic feature of the southern central Andes, hosting the highest hinterland topography above the modern Pampean flat‐slab segment. The timing of Frontal Cordillera exhumation is important for testing models of Andean tectonics, yet large latitudinal gaps exist between structural and thermochronological constraints for the region. We conducted a thermochronometric study using a 4.4 km age‐elevation transect along the northeast ridge of Cerro Mercedario, the highest peak in the La Ramada massif at ∼32°S. Zircon (U‐Th)/He dates indicate partial resetting, supporting a limited magnitude of exhumation in even the most extreme Andean topography. Single grain apatite (U‐Th‐Sm)/He dates range from 8.5 ± 0.9 to 35.8 ± 3.6 Ma, with median dates of ∼10.5 to ∼15.7 Ma with increasing elevation. Integrated with geologic mapping and thermal history modeling, these data suggest Early to Middle Miocene exhumation along the Santa Cruz and Espinacito faults concomitant with uplift of the La Ramada massif. New apatite helium data from the Cordillera del Tigre segment of the Frontal Cordillera are partially reset and preferred modeling interpretations suggest exhumation ca. 11–9 Ma, coeval with shortening in the eastward adjacent Precordillera. These data add to accumulating regional evidence for out‐of‐sequence deformation during the Miocene, consistent with internal (hinterland) growth of a subcritical orogenic wedge contemporaneous with surface uplift and crustal thickening in the south‐central Andes. 

   more » « less