We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous l... more We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous levels from the Bermejo and Vinchina basins – both foreland depocentres of the Central Andes of Argentina – that define a low-temperature regime for the crust akin to a slab shallowing and flattening process. The contents of illite in illite/smectite interstratified (I/S) show a progressive illitization into the deeper parts of both basins.
The Argentine broken foreland has been the subject of continuous research to determine the uplift... more The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of NeS reverse faults that disrupted a WeE Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477À470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the KeAr dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 C). KeAr ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (~360e220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ~360 Ma and a last clay minerals forming event at ~220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (~360À311 Ma for 2À1 mm grain size fraction, ~326À286 Ma for 1e0.2 mm and ~291À219 Ma of <0.2 mm), we modeled discrete deformation events at ~417 Ma (ending of the Famatinian cycle), ~317e326 Ma (end of Gond-wanic orogeny), and ~194e279 Ma (Early Permian-Jurassic deformation). According to our data, the Neogene reactivation would not have affected the KeAr system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.
Quantifying denudation rates along orogenic systems is crucial to understand how tectonics and cl... more Quantifying denudation rates along orogenic systems is crucial to understand how tectonics and climate interact with each other to create topography. Long-term mean denudation rates estimated from geologic data in the Ambato range (Sierras Pampeanas) is 0.34 mm/yr. When compared with short-term denudation rates from other studies northward and southward along the Argentine South Central Andes foreland, our results are similar to those found in regions with higher mean annual precipitation. Here we utilize concentrations of 10 Be cosmogenic radionuclide (CRN) in river sediments from catchments along the eastern slope of the Ambato range to understand the relationship among short-term (10 2 e10 4 yrs) catchment-wide denudation rates and long-term denudation rates estimated from geologic data. CRN denudation rates range between ~0.038 and ~0.12 mm/yr. The relationship between geo-morphometric parameters (local relief, slope, hypsometric integral, and catchment mean channel steepness index, K sn) and CRN denudation rates shows linear behavior. The best correlation concerned K sn indicating a strong connection in the Ambato range between tectonics and denudation. When analyzed together with denudation rates from other studies northward and southward along the South Central Andes foreland, our results are similar to those found in more arid regions and suggest that bedrock strength variations should be contemplated in a regional analysis as well as climate.
We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous l... more We present mineralogic, isotopic and thermochronologic analyses on psammopelitic and tuffaceous levels from the Bermejo and Vinchina basins – both foreland depocentres of the Central Andes of Argentina – that define a low-temperature regime for the crust akin to a slab shallowing and flattening process. The contents of illite in illite/smectite interstratified (I/S) show a progressive illitization into the deeper parts of both basins.
The Argentine broken foreland has been the subject of continuous research to determine the uplift... more The Argentine broken foreland has been the subject of continuous research to determine the uplift and exhumation history of the region. High-elevation mountains are the result of NeS reverse faults that disrupted a WeE Miocene Andean foreland basin. In the Sierra de Ambato (northern Argentine broken foreland) the reverse faults offset Neogene sedimentary rocks (Aconquija Fm., ~9 Ma) and affect the basement comprising Paleozoic metamorphic rocks that have been dated at ~477À470 Ma. In order to establish a chronology of these faults affecting the previous continuous basin we date the formation age of clay minerals associated with fault gouge using the KeAr dating technique. Clay mineral formation is a fundamental process in the evolution of faults under the brittle regime (<<300 C). KeAr ages (9 fractions from 3 samples collected along a transect in the Sierra de Ambato) vary from Late Devonian to Late Triassic (~360e220 Ma). This age distribution can be explained by a long lasting brittle deformation history with a minimum age of ~360 Ma and a last clay minerals forming event at ~220 Ma. Moreover, given the progression of apparent ages decreasing from coarse to fine size fractions (~360À311 Ma for 2À1 mm grain size fraction, ~326À286 Ma for 1e0.2 mm and ~291À219 Ma of <0.2 mm), we modeled discrete deformation events at ~417 Ma (ending of the Famatinian cycle), ~317e326 Ma (end of Gond-wanic orogeny), and ~194e279 Ma (Early Permian-Jurassic deformation). According to our data, the Neogene reactivation would not have affected the KeAr system neither generated a significant clay minerals crystallization in the fault gouge, although an exhumation of more than 2 Km is recorded in this period from stratigraphic data.
Quantifying denudation rates along orogenic systems is crucial to understand how tectonics and cl... more Quantifying denudation rates along orogenic systems is crucial to understand how tectonics and climate interact with each other to create topography. Long-term mean denudation rates estimated from geologic data in the Ambato range (Sierras Pampeanas) is 0.34 mm/yr. When compared with short-term denudation rates from other studies northward and southward along the Argentine South Central Andes foreland, our results are similar to those found in regions with higher mean annual precipitation. Here we utilize concentrations of 10 Be cosmogenic radionuclide (CRN) in river sediments from catchments along the eastern slope of the Ambato range to understand the relationship among short-term (10 2 e10 4 yrs) catchment-wide denudation rates and long-term denudation rates estimated from geologic data. CRN denudation rates range between ~0.038 and ~0.12 mm/yr. The relationship between geo-morphometric parameters (local relief, slope, hypsometric integral, and catchment mean channel steepness index, K sn) and CRN denudation rates shows linear behavior. The best correlation concerned K sn indicating a strong connection in the Ambato range between tectonics and denudation. When analyzed together with denudation rates from other studies northward and southward along the South Central Andes foreland, our results are similar to those found in more arid regions and suggest that bedrock strength variations should be contemplated in a regional analysis as well as climate.
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