The late Miocene eolian record at the eastern margin of the Puna Plateau, NW Argentina: Evidence of upper-tropospheric paleocirculation

The Puna–Altiplano Plateau of the Central Andes is the second-highest plateau in the world (after Tibet), with a mean elevation of 4000 m.a.s.l. and an arid to hyperarid climate. Uplift of the Puna–Altiplano Plateau has affected lower-level atmospheric circulation, acting as a barrier to humid easterly winds from the Amazon basin and favoring an across-strike precipitation gradient resulting in a humid climate towards the east of the plateau and an arid to hyperarid climate in the orogen's interior. In the modern climate, the Bolivian High anticyclone regulates upper troposphere circulation, but little is known about the high-altitude tropospheric circulation of the past. This work focuses on the eolian record of the San Antonio de los Cobres basin along the eastern border of the Puna Plateau, NW Argentina, with the aim of analyzing its origin and thus elucidating the late Miocene winds. The eolian deposits are constrained by 7.8 Ma (K/Ar and U/Pb) and 6.4 Ma (U/Pb) ignimbrites at the nearly basal and upper contacts, respectively. Based on stratigraphic, sedimentological, and provenance analysis of the eolian units, we have identified three main facies associations (FAs): FA1) cross-stratified sandstones with large- to small-scale tabular, planar cross-bedding and with trough cross-stratification; FA2) sandstones with planar to low-angle stratification associated with thinly laminated ripple sandstone strata; FA3) medium- to coarse-grained massive sandstones associated with pebbly to bouldery, matrix-supported conglomerates and clast-supported conglomerates. The lateral and vertical facies assemblages indicate a dune field confined to topographic depressions dominated by transverse dunes with straight and sinuous crestlines that laterally grade into sandsheets associated with ephemeral streams. Paleoflows, lithotypes, and grain-size determinations indicate a persistent north-northwest provenance and wind velocities of 24–38 km/h (with maximum velocities of 55–75 km/h). The results of our analysis coupled with data from previous studies indicates that, for at least the last ca. 8 Myr, the winds have been blowing constantly from the north-northwest with an intensity similar to the present. This implies that the paleo-atmospheric circulation had a similar pattern to the present-day one. Therefore, we conclude that the upper-troposphere circulation in the Puna Plateau of NW Argentina was already regulated by the Bolivian High anticyclone during the Miocene, generating constant north-northwesterly winds.

Lithium and Sr isotopic composition of salar deposits in the Central Andes across space and time: the Salar de Pozuelos, Argentina

The Central Andes of South America host the largest known lithium resources in a confined area, but the primary lithium sources of the salar deposits and the mobilisation process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate near-surface chemical weathering in a cold and dry climate as the dominant mobilisation process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favoured source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by chemical weathering with only minor hydrothermal mobilisation of Li.

Assessing ground deformation in the Central Andes (NW Argentina) with Interferometric Synthetic Aperture Radar analyses: First results of SAOCOM data and Sentinel-1 data

<p>The region of the Argentine Central Andes located between 21° S and 25° S is characterized by multiple morphotectonic provinces that strongly control structural and geomorphologic surface deformation. This work focuses on the Puna Plateau and the Eastern Cordillera. The Puna is part of the orogenic Central Andean Plateau and is hydrologically dissected into internally drained catchments with mostly hyper-arid climatic conditions. The Puna’s eastern edge is bordered by the fold-and-thrust belt of the Eastern Cordillera with peaks up to ~6000 m. Both areas are repeatedly affected by earthquakes with surface deformation but seldom surface ruptures.</p><p>This research focuses on the first assessment of the L-band SAOCOM 1A data for estimating surface deformation rates. The SAOCOM 1A satellite, launched in 2018, integrates the SAOCOM mission managed by the Argentinean Space Agency (Comisión Nacional de Actividades Espaciales, CONAE). These interferometric analyses are combined with results from C-band Sentinel-1 data. Examples are shown from the surface deformation associated with the magnitude 6.3 earthquake on 30 November 2020, with an epicenter located around 70 km W of San Antonio de los Cobres village in the Southeastern portion of the Puna Plateau (~24.332° S, ~67.005° W; United States Geological Survey). Additional examples are shown for slow-moving landslide velocity estimation in the Calchaquíes range (Eastern Cordillera). Our research highlights the capabilities of the new SAOCOM satellite mission for estimating surface deformation and exploits the strength of L-band SAR in vegetated terrain.</p>