Central Andes Of Argentina Research Articles

Basking and retreat site selection of Phymaturus palluma, a rock-dwelling lizard in the Highlands of Aconcagua.

Basking and retreat sites constitute a key resource in the habitat of any ectotherm. Identifying the elements that are used and modelling the microhabitat selection of species is crucial for assessing the impact of anthropogenic disturbances at the population level and, therefore, focusing on conservation efforts. We investigated how structural attributes of the microhabitat and biotic factors influence the probability of basking and retreat sites use by Phymaturus palluma, a rock-dwelling and viviparous lizard endemic to the Central Andes of Argentina. We measured the characteristics of a series of rocks (basking sites) and shelters (retreat sites) in the study area and compared lizard resource use versus availability using resource selection analyses (RSFs). According to our best RSF model, P. palluma select high and large rocks as basking sites and prefer those near their retreat sites and far from the basking sites of their neighbours. In contrast, retreat site selection is related to the length, depth, slope, and width of the shelter. Microhabitat site selection of P. palluma is associated with behavioural improvements such as enhancing basking capacity, reducing both intraspecific competition with neighbours and predation risk.

Surface velocity fields of active rock glaciers and ice‐debris complexes in the Central Andes of Argentina

AbstractRock glaciers and transitional ice‐debris complexes predominate the Central Andean landform assemblage, yet regional studies on their state of activity and their kinematics remain sparse. Here we utilize the national glacier inventory of Argentina to quantify surface velocity fields of 244 rock glaciers and 51 ice‐debris complexes, located in the Cordón del Plata range, Argentina. Applying a feature‐tracking approach to repeated RapidEye satellite imagery acquired between 2010 and 2017/18, we find mean displacement rates between 0.37 and 2.61 m year−1 for 149 landforms, while for the remaining 146 features, surface movement remains below our level of detection. We compare our satellite‐derived velocity fields with ground‐truth data from two local field sites and find closely matching results in magnitude and spatial distribution. With average displacement of one‐third of the active rock glaciers and ice‐debris complexes exceeding 1 m year−1, the region hosts an exceptional number of fast‐flowing periglacial landforms, compared to other mountain belts. Using a random forest model, we test the predictive power of 25 morphometric and topoclimatic candidate predictors for modelling the state of activity of rock glaciers and ice‐debris complexes on two different scales. For entire landforms and individual landform segments, constructed along displacement centrelines, we can predict the state of activity with overall accuracies of 70.08% (mean AUROC = 0.785) and 74.86% (mean AUROC = 0.753), respectively. While topoclimatic parameters such as solar radiation and elevation are most important for entire landforms, geometric parameters become more important at the scale of landform segments. Despite tentative correlations between local slope and surface kinematics, our results point to factors integrating slope and distance to the source to govern local deformation. We conclude that feature tracking in optical imagery is feasible for regional studies in remote regions and provides valuable insight into the current state of the Andean cryosphere. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Ice Mass Loss in the Central Andes of Argentina Between 2000 and 2018 Derived From a New Glacier Inventory and Satellite Stereo-Imagery

Based on the recently released National Glacier Inventory (NGI), we analyzed the characteristics and the mass balance rates of ice masses in the Argentinean Central Andes (ca. 30°–37° S). The NGI provides unprecedented information on area, number and distribution of different ice masses, including debris-covered glaciers and rock glaciers. In the Central Andes, a number of 8,076 ice masses were identified covering a total area of 1767 km2. For the period 2000–2018, a general lowering of the ice surface was observed with a region-wide mass balance rate of −0.18 ± 0.19 m w.e. yr−1. Clear differences depending on the debris coverage of the different ice masses were identified, with mass balance rates ranging from −0.36 ± 0.19 m w.e. yr−1 for partly debris-covered glaciers to −0.02 ± 0.19 m w.e. yr−1 for rock glaciers. Considering different sub-periods, the region-wide mass balance rate was slightly positive (+0.12 ± 0.23 m w. e. yr−1) from 2000 to 2009 and negative (−0.21 ± 0.30 m w.e. yr−1) from 2009 to 2018. A comparison with the Randolph Glacier Inventory (RGI version 6.0) indicates that the NGI provides more detailed information regarding different type of ice masses whereas region-wide mass balance rates show limited sensitivity to the choice of the inventory. The inclusion of rock glaciers and “debris-covered ice with rock glacier” in the NGI causes mass balance rates to be slightly less negative than when using the RGI. Since the Central Andes are experiencing an unprecedented decade-long drought, our study provides crucial information to estimate current and future hydrological contribution of the different type of ice masses to river discharge in the arid subtropical Andes.

SNOW ALBEDO REDUCTION IN CENTRAL ANDES BY ATMOSPHERIC AEROSOLS: CASE STUDY ON THE TUNUYÁN BASIN (ARGENTINA)

Abstract. Changes in snow albedo (SA) on several basins of the central Andes of Argentina are associated with the possible deposition of light-absorbing particles (LAP) in the austral spring. To demonstrate this possibility, we correlate SA with daily data of snow cover (SC), aerosol optical depth (AOD) and land surface temperature (LST) available from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on board NASA Terra satellite during 2000–2016, and other derived parameters such as days after albedo (DAS) and snow precipitation (SP) from the Tropical Rainfall Measuring Mission (TRMM). We used satellite pixels with 100% snow cover to obtain monthly average value of SA, LST, AOD, DAS and SP performing multiple regression analysis. Further, we analysed biomass burning emissions in northern Argentina using MODIS products MCD64 collection C6 as possible source for snow pollution. Aerosol deposition and trajectories were analysed using WRF-Chem atmospheric numerical prediction model, with inventories of regional anthropogenic emissions of own elaboration (lat. 0.025° × long. 0.025°) and the estimation of open burning emissions from the FINN global inventory (Fire INventory from NCAR).

Avian remains from the Toro Negro Formation (Neogene), Central Andes of Argentina

We describe new avian remains from the lower levels of the Toro Negro Formation (~7-6 Ma, U–Pb), exposed in Quebrada de la Troya between Vinchina and Jagüé towns in La Rioja Province, Argentina. The Toro Negro Formation is composed of a thick continental sequence (~2.4 km) of sandstones, conglomerates and mudstones deposited in both fluvial and lacustrine systems at the base of the unit. The avifauna of Toro Negro is low in diversity, and the majority of the remains are fragmentary and isolated. However, it is interesting in that it includes carnivorous birds such as a new species of a large eagle (Vinchinavis paka gen. et sp. nov.), scavengers (condors) and large herbivores (rheas). On the whole, the occurrences documented within the Toro Negro Formation confirm the presence of taxa with strong temperate warm preferences that typically inhabits open areas with arboreal patches within an arid-semiarid zone. The palaeoenvironmental characteristics of the fauna are confirmed as fully compatible with the evidence previously obtained through sedimentology and facies analysis.

Neogene Retroarc Foreland Basin Evolution, Sediment Provenance, and Magmatism in Response to Flat Slab Subduction, Western Argentina

AbstractUnderstanding the effects of flat slab subduction on mountain building, arc magmatism, and basin evolution is fundamental to convergent‐margin tectonics, with implications for potential feedbacks among geodynamic, magmatic, and surface processes. New stratigraphic and geochronological constraints on Cenozoic sedimentation and magmatism in the southern Central Andes of Argentina (31°S) reveal shifts in volcanism, foreland/hinterland basin development, sediment accumulation, and provenance as the retroarc region was structurally partitioned during slab flattening. Detrital zircon U‐Pb age distributions from the western (Calingasta basin), central (Talacasto and Albarracín basins), and eastern (Bermejo foreland basin) segments of the retroarc basin system preserve syndepositional volcanism and orogenic unroofing of multiple tectonic provinces. Initial shortening‐related exhumation of the Principal Cordillera at 24–17 Ma was recorded by the accumulation of distal eolian deposits bearing Oligocene–Eocene zircons from the Andean magmatic arc. The Calingasta basin chronicled volcanism and basement shortening in the Frontal Cordillera at ~17–11 Ma, as marked by an upward coarsening succession of fluvial to alluvial fan deposits with a sustained zircon U‐Pb age component that matches pervasive Permian‐Triassic bedrock in the hinterland. An ~450 km eastward inboard sweep of volcanism at 11 Ma coincided with the inception of flat slab subduction, and subsequent thin‐skinned shortening in the Precordillera fold‐thrust belt that exhumed wedge‐top deposits and induced cratonward (eastward) advance of flexural subsidence into the Bermejo foreland basin. This foreland basin was structurally partitioned as basement uplifts of the Sierras Pampeanas transformed a fluvial megafan sediment routing network into smaller isolated alluvial fan systems fed by adjacent basement blocks.

Spatial distribution of active and inactive rock glaciers and protalus ramparts in a sector of the Central Andes of Argentina

Rock glaciers and protalus ramparts are two of the main morphological features of the Central Andes in the Province of San Juan, Argentina. This sector of the Andes has one of the highest densities of occurrence of rock glaciers in the world. In this region, which has semiarid climatic characteristics, the presence of these landforms is important due to their solid state water reserves and as water resource regulators. Their occurrence is vital in several basins where, due to the lack of glaciers, debris-covered glaciers and perennial snow patches, rock glaciers are the only solid-state water reserves. However, the topo-climatic factors controlling the development and evolution of rock glaciers and protalus ramparts are not well known, which prevents an integrated management of the basins. This contribution, first, analyzes the spatial distribution of active and inactive rock glaciers and of protalus ramparts with respect to different topographic variables in the upper section of the Santa Cruz River basin. In total, 375 landforms have been inventoried, out of which 83 are active rock glaciers, 81 are inactive and 211 are protalus ramparts, covering an area of 13.09 km2 (3.03 % of the total area). The active periglacial environment belt occurs between 4000 and 4200 m a.s.l. and slopes with a southwesterly aspect have a greater development of active rock glaciers. Secondly, the evolution of such landforms is addressed. While the development of protalus ramparts does not seem to be mainly controlled by the topographic variables analyzed, the evolution of protalus ramparts in rock glaciers would be mainly controlled by elevation and aspect. Besides, there are local topo-climatic factors that contribute to the development of such landforms.

Molecular data reveal hidden diversity in the central Andean speciesWeberbauera spathulifolia(Thelypodieae: Brassicaceae)

AbstractWeberbauera (Brassicaceae, tribe Thelypodieae) comprises 18 species distributed along the central Andes of Argentina, Bolivia, Chile and Peru. Of these species, W. spathulifolia has the largest geographical range in the genus, extending c. 3000 km along the Andean highlands from La Rioja Province in Argentina to Ancash Department in Peru. This species also shows the greatest morphological variation in the genus. However, whether this geographical and morphological variation represents one or more lineages remains unclear. In this study, we analyse W. spathulifolia across its entire distribution range using molecular, morphological and ecological data. Because there is no phylogenetic analysis for the genus, we generated a comprehensive molecular sampling using nuclear (ITS) and plastid (trnL-F and trnH-psbA) sequences for other Weberbauera spp. and representatives of South American Thelypodieae. Results support the presence of two different lineages within W. spathulifolia, one in the northern part of the species range and the other distributed across its southern and central range. In addition to the morphological differences and the allopatric distribution, these lineages also differ in their climatic niches. Therefore, we propose here to retain the northern lineage under W. spathulifolia and to treat the southern-central lineage under W. orophila, comb. nov. Phylogenetic placement of Weberbauera spp. among the South American Thelypodieae is also analysed and discussed. Results of this study contribute to understanding the biodiversity and evolution of the Andean Brassicaceae.

Debris flow susceptibility mapping using frequency ratio and seed cells, in a portion of a mountain international route, Dry Central Andes of Argentina

Debris flow and floods represent one of the main natural hazards that impact transport infrastructure, causing serious damage, economic losses and hinder regional economic development. These processes are eventually associated with massive traffic cuts and direct damage to road structures. To enable the prevention of such consequences, this paper employs statistical modeling techniques, various instability factors and geomorphological mapping to generate debris flow susceptibility maps in a portion of an important route on the Dry Andes of San Juan in the Agua Negra River basin, Argentina. A debris flows inventory map was prepared using satellite images and field checks. The debris flows inventory was randomly divided into a model dataset 80% (47 debris flows) and remaining 20% (12 debris flows) data was used for validation purpose. The instability factors chosen that influence debris flows occurrence were: elevation, slope angle, slope aspect, solar radiation, topographic wetness index, stream power index, topographic position index, Melton ruggedness number, terrain ruggedness index, sediment transport capacity index, plan curvature, profile curvature, lithology, distance to road and proximity to stream. Using these factors, six different models of debris flow susceptibility were calculated by Frequency ratio (Fr). Lithology (igneous complex) was found to be important debris flows-related factor in the study area. The precision of the results was evaluated by receiver operating characteristic (ROC) analysis. According to the area under the curve (AUC) the models of all flow track and natural breaks and all flow track and geometrical interval were 0.83 and 0.84, respectively, showing a practically identical predictive capacity.

Morphotectonic analysis of two axial tributary basins of the San Juan river controlled by the Precordillera fold and thrust belt, Central Andes of Argentina

Analysis of several morphotectonic tools (longitudinal river profiles, knickpoints, swath profiles, and geomorphic indices) together with geomorphological, lithological, and structural data provided objective and quantifiable elements to improve the knowledge of the Quaternary tectonic activity in a region. In this study, we analyzed and compared two large intermountain basins located in the Precordillera of the Central Andes of Argentina. Local distortions in longitudinal river profiles and river patterns may reflect resistant lithology, an increase in shear stress, or differential surface uplift. Both basins have similar shapes, although one mirrors the other producing a large-scale broom-shaped drainage pattern. The values of the Asymmetry Factor and Transverse Topographic Symmetry Factor show opposite signs and almost identical values, suggesting that both basins have mirror symmetry independently of order and scale. The asymmetry in both basins would be a result of the progressive migration of the Andean orogenic front towards the east. Knickpoints were mainly associated with resistant rocks, faults with the scarp facing upstream, or both. In the reaches where the rivers flow across areas with presumed higher rates of uplift, we observed a reduction in the width of the active channel belt by lateral confinement and river pattern changes. The results presented in this paper constitute one of the first attempts to apply geomorphic indices to large drainage basins in the Precordillera fold-and-thrust belt.

Geophysical analysis in a Quaternary compressive environment controlling the emplacement of travertine, eastern piedmont of Argentine Precordillera

This work carries out the analysis, through a geophysical (gravity) method, of an area in the eastern Piedmont of Eastern Precordillera, Central Andes of Argentina. Geological evidence shows several neotectonic reverse fault scarps affecting Quaternary alluvial deposits located to the East of the Sierra de Villicum. Topographic features observed in the understudy region suggest an important Holocene historical seismic activity, one of them the 15th January 1944 San Juan earthquake (Mw 7.0), the worst natural disaster in Argentina. Several N–S springs and carbonate deposits (travertine) are found aligned along the traces of these active faults, disappearing abruptly to the north and south, possibly due to a tectonic control. Travertine deposits are located along fault traces and have been traditionally considered to be contemporaneous with active faults. The existence of travertine bodies deposited by springs, and their low preservation potential, has for the understudy region a neotectonic significance. The eastern Piedmont of the Sierra de Villicum is characterized by the ~N–S La Laja west-vergent east-dipping reverse fault and several subparallel faults (e.g., Cantera and Museo faults) that uplift Neogene sedimentary rocks over Quaternary (Late Pleistocene-Holocene) alluvial deposits. Gravity data derived from the global Earth gravity model WGM 1.0 were used in the regional geophysical analysis. The analysis aims to delimit geological structures, which characterized the interest area. Three detailed gravimetric profiles were measured to analyze local anomalies related to the main structures. The gravimetric and geological analysis confirms the existence of north-south faults parallel to La Laja fault related to travertine deposits. On the other hand, a set of southeast-northwest structures that limit and control the travertine bodies both northward and southward are recognized. Employing the gravity method associated with structural analysis, the spatial continuity of these neotectonic structures was defined in those sectors where field evidence is not so clear or blind structures are present. Our study confirms the existence of probable cross strike structures trending NW. We suggest they would represent preexisting crustal fabrics reactivated during the Andean orogeny in the Precordillera province, segmenting this orogen-parallel fold and belt system. One of the main hypotheses is that these fault systems related to basement-involved strike-slip faults perform as control structures in fluid migration during the travertine bodies' emplacement. Thus, our work points to the relevance of travertine location in the analysis of the seismotectonic configuration of a region.

Regional relative tectonic activity of structures in the Pampean flat slab segment of Argentina from 30 to 32°S

The Pampean flat slab segment of the Central Andes in Argentina is a broad, active deformation zone subject to both plate boundary-related and intraplate deformation. To the west, plate boundary-related deformation is dominated by thin-skinned fold-and-thrusts of the Precordillera, while to the east, intraplate deformation involves thick-skinned reverse faults of the Sierras Pampeanas. GPS data and absolute dating of displaced geomorphic features suggest that most of the active permanent deformation occurs between these two regions at the Andean orogenic front and that there is a west-to-east trend of decreasing shortening rates. However, GPS stations and sites with geomorphic slip rate measurements are currently too sparse and cover too short a time period to make reliable inferences about the longer-term distribution and relative rates of deformation. Mountain range-scale geomorphic indices, on the other hand, reflect tectonic activity since at least the Pleistocene. In this study, we measured geomorphic indices (hypsometric integral and curves, basin elongation ratio, basin volume-to-area-ratio, valley floor width-to-height ratio, mountain front sinuosity, and normalized steepness indices of rivers) from 10 different N-S striking, range-bounding faults that span both the Precordillera and Sierras Pampeanas regions from west to east. We use these data to assess the regional relative tectonic activity of major Quaternary deformation features in the Pampean segment of the Central Andes. Even when variations in climate and geology are considered, mean values for each geomorphic index suggests uplift rates for the 10 mountain-range bounding faults display local trends that are closely associated with the structural style and tectonic evolution of these structures. Although vertical uplift rates vary little, horizontal shortening rates are higher for the Precordillera fold-and-thrusts in the west than the thick-skinned reverse faults of the Sierras Pampeanas in the east, due to shallower fault dips for Precordilleran structures. The similarity with decadal slip rate gradients from GPS studies could possibly indicate that the stress-field has been constant since at least the Pleistocene, but further slip rate studies over broader time intervals in the late Quaternary are necessary to confirm this. Variations observed in relative uplift rates along each fault point to sites that warrant further detailed study of slip rates and evaluation of associated seismic hazards.

Rockslides and rock avalanches in the Central Andes of Argentina and their possible association with permafrost degradation

AbstractThe identification of hazardous slopes with degrading permafrost is a key task in the mountain periglacial environment. If rockslides have previously been preconditioned by rock wall permafrost, similar events may be triggered from present unstable rock walls. An inventory of rockslides and rock avalanches in the austral part of the Santa Cruz river basin (31°40′–31°50′S, 70°30′–70°10’W), San Juan, Argentina, was made. The study area comprises a surface of approximately 432 km2 (50% above 3,500 m asl); 15 rockslides, 12 complex rockslides evolving to rock avalanches and 19 rock avalanches were identified. The deposits were analyzed with remote sensory imagery and during fieldwork in order to study processes under permafrost degradation caused by global warming. Rock sampling procedures and laboratory rock‐resistivity testing were also carried out. We characterized the detachment scars and deposits for two rockslides. Two different mechanisms were identified. In one rockslide, shallow active layer detachment was favored by shear‐displacement along pre‐existing joints, as a result of short‐term periods of climate warming. In the other, long‐term permafrost degradation favored a deeper failure process. The studied landslide processes could not be explained by permafrost degradation alone. Faults, the geometric arrangement of their structural elements and seismic activity may contribute to trigger these phenomena. It is expected that the magnitude and frequency of rockslide hazards will increase during the 21st century.

The Neuquén group: The reconstruction of a Late Cretaceous foreland basin in the southern Central Andes (35–37°S)

In the southern Central Andes of Argentina, between 34° and 41°S, the Neuquén Group records Upper Cretaceous nonmarine deposits that provide direct evidence of synorogenic sedimentation associated with the development of an early foreland basin. The configuration of this basin and its relation to the Malargüe fold and thrust belt are analyzed in this article using sedimentological analyses, U-Pb dating of detrital zircons and seismic and surface structural data. The remnant wedge-top depozone preserved in the Argentinian Andean slope exposes sedimentological information that indicates that braided fluvial systems, which may have formed part of broader fluvial fans, transported and deposited the sediments from an extensive relief area located in the present western Andean slope to the Chilean Coastal Range zones. The eastern border of this depositional system was defined by a basement uplift, interpreted either as a forebulge or an incipient broken foreland system, from where gravel-sandy braided river systems fed the foredeep depozone transporting and depositing sediments from the exposed cratonic area in the east. Consequently, an initial underfilled foreland basin was configured. The evolution of this early basin and the areas of sediment supply were controlled by the eastern expansion of the Malargüe fold and thrust belt, through the development of thick-skinned anticlines, which progressively fragmented the wedge-top zone. The evidence collected suggests that the Late Cretaceous uplift was a major tectonic event that exposed the entire Mesozoic column of the Neuquén basin up to the Permian-Triassic basement, which implies more than 2,500 m of denudation at that time. U-Pb determinations yielded a maximum depositional age of ca. 91 ± 2 Ma (Late Turonian), which suggests either non-deposition or cannibalization of a sedimentary interval of ca. 10 My at 36°S, when compared to the age of the basal sections of the Neuquén Group at other latitudes.

Pennellia yalaensis (Brassicaceae: Halimolobeae), a New Species from the Andes of Northern Argentina

Abstract—Pennellia yalaensis, a new species of Brassicaceae from Jujuy Province in Argentina, is described and illustrated, and its phylogenetic relationships with nearest relatives are discussed. This novelty is morphologically related to P. boliviensis and P. brachycarpa, which also grow in the Central Andes of Argentina. However, P. yalaensis clearly differs from both species by the plant height, inflorescence type, and petal length. In addition, trichomes of the basal leaves distinguish the new species from P. boliviensis, and fruit length and number of ovules/seed from P. brachycarpa. Phylogenetic analyses, based on DNA sequences of nuclear ITS and plastid trnL-F regions, confirmed these affinities.

A reevaluation of the Andean Genus Petroravenia (Brassicaceae: Thelypodieae) based on morphological and molecular data

AbstractPetroravenia was until recently considered as a genus of three species (P. eseptata, P. friesii, and P. werdermannii) distributed along the Central Andes of Argentina, Bolivia, Chile, and Peru. This genus was included in the tribe Thelypodieae and was morphologically characterized by being tiny rhizomatous perennial herbs with rosulate leaves, dendritic trichomes, capsular silicles, and incumbent cotyledons. However, the phylogeny of Petroravenia, and its tribal placement, was never analyzed using molecular data. The lack of such studies, as well as the paucity of herbarium collections, suggesting that Petroravenia species are vulnerable and/or endangered, prompted us to address the molecular phylogeny of this genus. For this purpose, we generated comprehensive molecular phylogenies using nuclear (ITS) and plastid (trnL‐F and trnH‐psbA) data, and conducted morphological comparisons between these species and their closest related taxa. Results from the phylogenetic analyses showed that Petroravenia represents a polyphyletic group, with P. eseptata included in tribe Halimolobeae, and P. friesii and P. werdermannii placed within tribe Eudemeae and related to the genus Alshehbazia. Based on the results obtained from morphological and molecular data, we decided herein to retain the original circumscription of Petroravenia as monospecific within the tribe Halimolobeae and to transfer P. friesii and P. werdermannii to the genus Alshehbazia within the tribe Eudemeae. Systematic implications of these results are also discussed.

Brief communication: Collapse of 4 Mm<sup>3</sup> of ice from a cirque glacier in the Central Andes of Argentina

Abstract. Among glacier instabilities, collapses of large parts of low-angle glaciers are a striking, exceptional phenomenon. So far, merely the 2002 collapse of Kolka Glacier in the Caucasus Mountains and the 2016 twin detachments of the Aru glaciers in western Tibet have been well documented. Here we report on the previously unnoticed collapse of an unnamed cirque glacier in the Central Andes of Argentina in March 2007. Although of much smaller ice volume, this 4.2±0.6×106 m3 collapse in the Andes is similar to the Caucasus and Tibet ones in that the resulting ice avalanche travelled a total distance of ∼2 km over a surprisingly low angle of reach (∼5∘).

Mesozoic to Cenozoic retroarc basin evolution during changes in tectonic regime, southern Central Andes (31–33°S): Insights from zircon U-Pb geochronology

The southern Central Andes of Argentina and Chile (27–40°S) are the product of deformation, arc magmatism, and basin evolution above a long-lived subduction system. With sufficient timing and provenance constraints, Andean stratigraphic and structural records enable delineation of Mesozoic-Cenozoic variations in subsidence and tectonic regime. For the La Ramada Basin in the High Andes at ∼31–33°S, new assessments of provenance and depositional age provided by detrital zircon U-Pb geochronology help resolve deformational patterns and subsidence mechanisms over the past ∼200 Myr. Marine and nonmarine clastic deposits recorded the unroofing of basin margins and sediment contributions from the Andean magmatic arc during Late Triassic to Early Cretaceous extension, thermal subsidence, and possible slab rollback. Subsequent sediment delivery from the Coastal Cordillera corresponded with initial flexural accommodation in the La Ramada Basin during Andean shortening of late Early Cretaceous to Late Cretaceous age. The architecture of the foreland basin was influenced by the distribution of precursor extensional depocenters, suggesting that inherited basin geometries provided important controls on later flexural subsidence and basin evolution. Following latest Cretaceous to early Paleogene tectonic quiescence and a depositional hiatus, newly dated deposits in the western La Ramada Basin provide evidence for a late Paleogene episode of intra-arc and proximal retroarc extension (development of the Abanico Basin, principally in Chile, at ∼28–44°S). Inversion of this late Paleogene extensional basin system during Neogene compression indicates the southern Central Andes were produced by at least two punctuated episodes of shortening and uplift of Late Cretaceous and Neogene age.

New evidence of glacier surges in the Central Andes of Argentina and Chile

In contrast to the large surge-type glacier clusters widely known for several mountain ranges around the world, the presence of surging glaciers in the Andes has been historically seen as marginal. The improved availability of satellite imagery during the last years facilitates investigating of glaciers in more detail even in remote areas. The purpose of the study was therefore to revisit existing information about surge-type glaciers for the Central Andes of Argentina and Chile (32° 40′–34° 20′ S), to identify and characterize possible further surge-type glaciers, providing new insights into the mass balance and evolution of the velocity of selected glaciers during the surge phase. Based on the analysis of 1962–2015 satellite imagery, historical aerial images, differencing of digital elevation models and a literature survey, we identified 21 surge-type glaciers in the study area. Eleven surge events and six possible surge-type glaciers were identified and described for the first time. The estimation of annual elevation changes of these glaciers for the 2000–2011 period, which encompasses the latest surge events in the region, showed heterogeneous behavior with strongly negative to positive surface elevation change patterns (−1.1 to +1.0 m yr−1). Additionally, we calculated maximum surface velocities of 3±1.9 m d−1and 3.1±1.1 m d−1for two of the glaciers during the latest identifiable surge events of 1985–1987 and 2003–2007. Within this glacier cluster, highly variable advance rates (0.01–1 km yr−1) and dissimilar surface velocities at the surge peak (3–35 m d−1) were observed. In comparison with other clusters worldwide, surge-type glaciers in the Central Andes are on average smaller and show minor absolute advances. Generally low velocities and the heterogeneous duration of the surge cycles are common between them and glaciers in the Karakorum, a region with similar climatic characteristics and many known surge-type glaciers. As a definitive assertion concerning the underlying surge mechanism of surges in the Central Andes could not be drawn based on the remote sensing data, this opens more detailed research avenues for surge-type glaciers in the region.

Validation of CHIRPS precipitation dataset along the Central Andes of Argentina

A validation covering a 30-year period (1987–2016) of the relatively new CHIRPS precipitation dataset was performed over the Central Andes of Argentina (CAA), a semi-arid region with complex topography and sparse ground observations. Precipitation data from 57 rain gauges and several well-known continuous and categorical validation statistics were assessed to evaluate the performance of CHIRPS estimations. The study area was divided into two zones based on the timing of the rainy season maximum, in order to determine regional differences in the characterization of precipitation patterns. The results of this study indicate that CHIRPS data reproduce adequately several characteristics of precipitation along the study area, as the seasonal and interannual variability and the spatial patterns of precipitation. CHIRPS dataset is able to capture the rainy season characteristics over the CAA, considering the Mediterranean climate features over the Andes ranges and the monsoonal regime in the lowlands. CHIRPS achieves better results for the stations located in the region with summer precipitation maximum, mostly located over Cuyo region (correlation = 0.86, bias = 11%, mean absolute error = 15.3 mm). Despite the strong correlation of 0.82 over Northern Patagonia region, CHIRPS showed a significant overestimation of the seasonal precipitation totals during the cold semester (April to September, bias = 65.8%, mean absolute error = 34.7 mm). These systematic errors can be attributed to the poor performance of CHIRPS in reproducing the precipitation features over the zones above 1000 m.a.s.l. One of the reasons behind the observed differences can be attributed to the limited number of anchor stations used in the CHIRPS calculation procedure, which highlights this study as an independent validation given the amount of meteorological stations used.