Lithospheric density structure of the Southern Central Andes and their forelands constrained by 3D gravity modelling

2020 ◽  
Author(s):  
Constanza Rodriguez Piceda ◽  
Magdalena Scheck-Wenderoth ◽  
Maria Laura Gómez Dacal ◽  
Judith Bott ◽  
Claudia Prezzi ◽  
...  
Keyword(s):  
Central Andes ◽  
Crustal Thickening ◽  
Velocity Variation ◽  
Mountain Range ◽  
South American ◽  
The South ◽  
Complex Deformation ◽  
Nazca Plate ◽  
Southern Central ◽  
The Relationship

<p>The Andean orogeny is a ~7000 km long N-S trending mountain range developed along the South American western margin. The formation of this mountain range is driven by the subduction of the oceanic Nazca plate beneath the continental South American plate, being the only known present-day case of subduction-type orogeny. In this tectonic setting, the intrinsic physical properties of the overriding plate govern the formation of zones of crustal strength and weakness and control the localization and the style of deformation. Furthermore, the dynamics of the subducting oceanic lithosphere is strongly conditioned by the properties of the continental counterpart. The southern segment of the Central Andes (29°S-39°S) is a suitable scenario to investigate the relationship between the two plates for several reasons. It is characterized by a complex deformation pattern with variations in horizontal shortening, crustal thickening and mean topographic elevation. In addition, the subduction angle changes at 33°S-35°S latitude from flat in the North to normal in the South. To gain insight into this geodynamic system, a detailed characterization of the lithosphere is needed. Therefore, we constructed a 3D model of the entire segment of the Southern Central Andes that is consistent with the available geological, seismic and gravity data in order to assess the geometry and density variation within the lithosphere. The derived configuration shows a spatial correlation between density domains and known tectonic features. It is also consistent with other independent observations such as S wave velocity variation and surface deformation. The generated structural model allows us to reach the first conclusions about the relationship between the characteristics of the overriding plate and the crustal deformation and dynamics of the subduction system. It is also useful to constrain thermomechanical experiments and therefore contributes to discussions about the crustal thermal and rheological fields within the region.</p>

scholarly journals Lithospheric density structure of the southern Central Andes constrained by 3D data-integrative gravity modelling

2020 ◽  
Author(s):  
Constanza Rodriguez Piceda ◽  
Magdalena Scheck Wenderoth ◽  
Maria Laura Gomez Dacal ◽  
Judith Bott ◽  
Claudia Beatriz Prezzi ◽  
...  
Keyword(s):  
Density Distribution ◽  
Gravity Data ◽  
Spatial Relationship ◽  
Central Andes ◽  
Crustal Thickening ◽  
South American ◽  
Short Term ◽  
Nazca Plate ◽  
Southern Central

AbstractThe southern Central Andes (SCA) (between 27° S and 40° S) is bordered to the west by the convergent margin between the continental South American Plate and the oceanic Nazca Plate. The subduction angle along this margin is variable, as is the deformation of the upper plate. Between 33° S and 35° S, the subduction angle of the Nazca plate increases from sub-horizontal (< 5°) in the north to relatively steep (~ 30°) in the south. The SCA contain inherited lithological and structural heterogeneities within the crust that have been reactivated and overprinted since the onset of subduction and associated Cenozoic deformation within the Andean orogen. The distribution of the deformation within the SCA has often been attributed to the variations in the subduction angle and the reactivation of these inherited heterogeneities. However, the possible influence that the thickness and composition of the continental crust have had on both short-term and long-term deformation of the SCA is yet to be thoroughly investigated. For our investigations, we have derived density distributions and thicknesses for various layers that make up the lithosphere and evaluated their relationships with tectonic events that occurred over the history of the Andean orogeny and, in particular, investigated the short- and long-term nature of the present-day deformation processes. We established a 3D model of lithosphere beneath the orogen and its foreland (29° S–39° S) that is consistent with currently available geological and geophysical data, including the gravity data. The modelled crustal configuration and density distribution reveal spatial relationships with different tectonic domains: the crystalline crust in the orogen (the magmatic arc and the main orogenic wedge) is thicker (~ 55 km) and less dense (~ 2900 kg/m3) than in the forearc (~ 35 km, ~ 2975 kg/m3) and foreland (~ 30 km, ~ 3000 kg/m3). Crustal thickening in the orogen probably occurred as a result of stacking of low-density domains, while density and thickness variations beneath the forearc and foreland most likely reflect differences in the tectonic evolution of each area following crustal accretion. No clear spatial relationship exists between the density distribution within the lithosphere and previously proposed boundaries of crustal terranes accreted during the early Paleozoic. Areas with ongoing deformation show a spatial correlation with those areas that have the highest topographic gradients and where there are abrupt changes in the average crustal-density contrast. This suggests that the short-term deformation within the interior of the Andean orogen and its foreland is fundamentally influenced by the crustal composition and the relative thickness of different crustal layers. A thicker, denser, and potentially stronger lithosphere beneath the northern part of the SCA foreland is interpreted to have favoured a strong coupling between the Nazca and South American plates, facilitating the development of a sub-horizontal slab.

Early exhumation of the Frontal Cordillera (southern Central Andes at ~33.5°S) and implications for Andean mountain-building

2020 ◽  
Author(s):  
Robin Lacassin ◽  
Magali Riesner ◽  
Martine Simoes ◽  
Tania Habel ◽  
Audrey Margirier ◽  
...  
Keyword(s):  
Central Andes ◽  
Crustal Thickening ◽  
Mountain Range ◽  
Mountain Building ◽  
Ongoing Debate ◽  
First Order ◽  
The Andes ◽  
Minimum Age ◽  
Southern Central ◽  
Basement Structures

&lt;p&gt;The Andes are the modern active example of a Cordilleran-type orogen, with mountain-building&amp;#8232; and crustal thickening within the upper plate of a subduction zone. Despite numerous studies of&amp;#8232; this emblematic mountain range, several primary traits of this orogeny remain unresolved or poorly documented. The timing of uplift and deformation of the Frontal Cordillera basement culmination of&amp;#8232; the Southern Central Andes is such an example, even though this structural unit appears as a first-order topographic and geological feature. Constraining this timing and in particular the onset of uplift is a key point in the ongoing debate about the initial vergence of the crustal-scale thrusts at the start of the Cenozoic Andean orogeny. To solve for this, new apatite and zircon (U-Th)/He ages from granitoids of the Frontal Cordillera at ~33.5&amp;#176;S are provided here. These data, interpreted as an age-elevation thermochronological profile, imply continuous exhumation initiating well before ~12&amp;#8211;14 Ma, and at most by ~22 Ma when considering the youngest zircon grain from the lowermost sample (Riesner et al. 2019). The inverse modeling of the thermochronological data using QTQt software confirms these conclusions and point to a continuous cooling rate since onset of cooling. The minimum age of exhumation onset is then refined to ~20 Ma by combining these results with data on sedimentary provenance from the nearby basins. Such continuous exhumation since ~20 Ma needs to have been sustained by tectonic uplift on an underlying crustal-scale thrust ramp. Such early exhumation and associated uplift of the Frontal Cordillera question the classically proposed east-vergent models of the Andes at this latitude. Additionally, this study provides further support to recent views on Andean mountain-building proposing that the Andes-Altiplano orogenic system grew firstly over west-vergent basement structures before shifting to dominantly east-vergent thrusts.&amp;#160;&lt;br&gt;Riesner M. et al. 2019, Scientific Reports, DOI: 10.1038/s41598-019-44320-1&lt;/p&gt;

Atmospheric monitoring with a new GNSS network in the south-central Andes

2021 ◽  
Author(s):  
Nikolaos Antonoglou ◽  
Kyriakos Balidakis ◽  
Bodo Bookhagen ◽  
Galina Dick ◽  
Florian Zus ◽  
...  
Keyword(s):  
Research Training ◽  
Training Group ◽  
Satellite System ◽  
Central Andes ◽  
Temporal Variations ◽  
Mountain Range ◽  
Spatial Correlations ◽  
The South ◽  
Climate Conditions ◽  
South Central

&lt;p&gt;The Central Andes are characterized by a steep climatic and environmental gradient with large spatial and temporal variations of associated hydrological parameters. There are two main atmospheric processes that influence climate conditions in our study area in northwestern Argentina: the South American Monsoon System that transports moisture via the low-level jet and the orographic barrier of the Eastern Cordillera that forces focused rainfall at the windward facing slopes.&lt;br&gt;As part of the International Research Training Group-StRATEGy project, our research aims at monitoring integrated water vapour (IWV) in the south-central Andes, in order to track moisture propagation. In accordance with the needs of the research, we processed data from two new Global Navigation Satellite System (GNSS) ground stations that were installed in spring 2019 along with - already calculated - solutions that were derived from an existing network. We used 10 year-long time-series from 31 stations spanning an altitude range from 198 to 5141m asl and stretching from the mountain front to the interior of the mountain range. This enhanced network helped us to examine spatial correlations, as well as differences in behaviour of the IWV across the climatic gradient. Moreover, we retrieved the gradients of the IWV at single positions, in order to study seasonal correlations between wind and gradient direction.&lt;/p&gt;

scholarly journals Measuring the seismic risk along the Nazca-Southamerican subduction front: Shannon entropy and mutability

2019 ◽  
Author(s):  
Eugenio E. Vogel ◽  
Felipe G. Brevis ◽  
Denisse Pastén ◽  
Víctor Muñoz ◽  
Rodrigo A. Miranda ◽  
...  
Keyword(s):  
Shannon Entropy ◽  
Seismic Risk ◽  
Background Activity ◽  
Large Earthquake ◽  
South American ◽  
The South ◽  
Nazca Plate ◽  
South American Plate ◽  
Major Earthquake ◽  
Similarities And Differences

Abstract. Four geographical zones are defined along the trench that is formed due to the subduction of the Nazca Plate underneath the South American plate; they are denoted A, B, C and D from North to South; zones A, B and D have had a major earthquake after 2010 (8.0), while zone C has not, thus offering a contrast for comparison. For each zone a sequence of intervals between consecutive seisms with magnitudes ≥ 3.0 is formed and then characterized by Shannon entropy and mutability. These methods show correlation after a major earthquake in what is known as the aftershock regime but they show independence otherwise. Exponential adjustments for these parameters reveal that mutability offers a wider range for the parameters characterizing the recovery to the values of the parameters defining the background activity for each zone before a large earthquake. It is found that the background activity is particularly high for zone A, still recovering for Zone B, reaching values similar to those of Zone A in the case of Zone C (without recent major earthquake) and oscillating around moderate values for Zone D. It is discussed how this can be an indication for more risk of an important future seism in the cases of Zones A and C. The similarities and differences between Shannon entropy and mutability are discussed and explained.

scholarly journals Multi‐Centennial‐Scale Variations of South American Summer Monsoon Intensity in the Southern Central Andes (24–27°S) During the Late Holocene

2020 ◽  
Vol 47 (4) ◽  
Author(s):  
Sebastian T. Kock ◽  
Karsten Schittek ◽  
Bertil Mächtle ◽  
Antonio Maldonado ◽  
Heinz Vos ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Late Holocene ◽  
Central Andes ◽  
South American ◽  
Monsoon Intensity ◽  
Southern Central

First record and a new species of Megarthrus Curtis (Coleoptera, Staphylinidae, Proteininae) from the Colombian Central Andes

Zootaxa ◽  
2011 ◽  
Vol 2916 (1) ◽  
pp. 62
Author(s):  
MARGARITA M. LÓPEZ-GARCÍA ◽  
DIANA M. Méndez-Rojas ◽  
JOSÉ LUÍS NAVARRETE-HEREDIA
Keyword(s):  
New Species ◽  
South America ◽  
Central America ◽  
First Record ◽  
Central Andes ◽  
South American ◽  
The South ◽  
The World ◽  
Northern South America ◽  
A New Species

The genus Megarthrus Curtis 1829 with about 139 species described around the world, is the largest of the subfamily Proteininae (Coleoptera: Staphylinidae) (Cuccodoro 2011). Megarthrus is distributed worldwide (Cuccodoro 1999) but it is apparently more diverse in the Holartic region (Navarrete-Heredia et al. 2002). However, the South American fauna is underestimated because many of the collected specimens are not yet described (Cuccodoro 2011). Newton et al. (2005) cited the genus as probable in Colombia because some species are known from Central America and northern South America, but until now, no species has been published from Colombia. Therefore, M. andinus sp. nov. represents the first record of the genus and subfamily for this country.

Proterozoic–Paleozoic development of the basement of the Central Andes (18–26°S) — a mobile belt of the South American craton

2000 ◽  
Vol 13 (8) ◽  
pp. 697-715 ◽  
Author(s):  
F. Lucassen ◽  
R. Becchio ◽  
H.G. Wilke ◽  
G. Franz ◽  
M.F. Thirlwall ◽  
...  
Keyword(s):  
Central Andes ◽  
Mobile Belt ◽  
South American ◽  
The South
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