What drives orogeny in the Andes?

Geology ◽  
2005 ◽  
Vol 33 (8) ◽  
pp. 617-620 ◽  
Author(s):  
S.V. Sobolev ◽  
A.Y. Babeyko
Keyword(s):  
Friction Coefficient ◽  
Crustal Structure ◽  
South American ◽  
The South ◽  
Nazca Plate ◽  
South American Plate ◽  
The Andes ◽  
Continental Lower Crust ◽  
Sediment Cover

Abstract The Andes, the world's second highest orogenic belt, were generated by the Cenozoic tectonic shortening of the South American plate margin overriding the subducting Nazca plate. We use a coupled thermomechanical numerical modeling technique to identify factors controlling the intensity of the tectonic shortening. From the modeling, we infer that the most important factor was accelerated westward drift of the South American plate; changes in the subduction rate were less important. Other important factors are crustal structure of the overriding plate and shear coupling at the plates' interface. The model with a thick (40–45 km at 30 Ma) South American crust and relatively high friction coefficient (0.05) at the Nazca–South American interface generates >300 km of tectonic shortening during 30–35 m.y. and replicates the crustal structure and evolution of the high central Andes. The model with an initially thinner (<40 km) continental crust and lower friction coefficient (<0.015) results in <40 km of South American plate shortening, replicating the situation in the southern Andes. Our modeling also demonstrates the important role of the processes leading to mechanical weakening of the overriding plate during tectonic shortening, such as lithospheric delamination, triggered by the gabbro-eclogite transformation in the thickened continental lower crust, and mechanical failure of the sediment cover at the shield margin.

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.

The nature of the North-South change of the magnitude of tectonic shortening in Central Andes at Altiplano-Puna latitudes: a thermomechanical modeling approach.

2020 ◽  
Author(s):  
Michaël Pons ◽  
Stephan Sobolev
Keyword(s):  
Cross Sections ◽  
Pure Shear ◽  
Foreland Basin ◽  
Central Andes ◽  
South American ◽  
Nazca Plate ◽  
South American Plate ◽  
The Andes ◽  
Subduction System ◽  
Roll Back

&lt;p&gt;&lt;span&gt;The Andean orogeny is a subduction-type orogeny, the oceanic Nazca Plate sinks under the continental South American Plate. While the subduction has been active since ~180 Ma, the shortening of the Andes initiated at ~50 Ma or less.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;In a oceanic-continental subduction system, the absolute velocity of the overriding-plate (OP) largely controls the style of subduction (stable, advancing, retreating), the geometry of the slab (dipping angle, curvature) and the style of deformation (shortening or spreading) within the OP. In the case of the Central Peru-Chile subduction, the South American plate is advancing westwards whereas the Nazca plate is anchored into the transition zone (~660 km). As a consequence, the trench is forced to retreat and the Nazca plate to roll-back. The dip of the slab decreases meanwhile the Andes experienced a maximum shortening of ~300 km at ~19-21&amp;#176;S latitudes.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;Previous study have shown that the strain localizes within areas of low strength and low gravitational potential of energy. In central Andes, weakening mechanisms of the OP such as lithospheric delamination have intensified the magnitude of tectonic shortening and contributed to formation of the Altiplano-Puna plateau. The deformation between the plateau and the foreland occurs in the form of pure shear or simple shear and is expressed in terms of different tectonic styles in the foreland basin, thick-skinned (e.g the Puna) and thin-skinned (e.g the Altiplano), respectively. Nevertheless, the influence of the strength variations of the OP on the subduction dynamics in the case of the central Andes has been &lt;/span&gt;&lt;span&gt;poorly&lt;/span&gt;&lt;span&gt; explored so far. Our hypothesis is that lateral variations of OP strength result in variable rates of trench roll-back. To test it, we have built 2D high-resolution E-W cross sections along the Altiplano and Puna latitudes (12-27&amp;#176;S) including the subduction of the Nazca plate. For that purpose, we used the FEM geodynamic code ASPECT. Our model includes visco-plastic rheology in addition to gabbro-eclogite phase transition. These preliminary results contribute to the discussion on the nature of the magnitude of shortening in a subduction system. They are also a first step to derive a 3D model of the entire region and to consider additional surface processes such as erosion, transportation and sedimentation. &lt;/span&gt;&lt;/p&gt;

scholarly journals GNSS Constraints to Active Tectonic Deformations of the South American Continental Margin in Ecuador

Sensors ◽  
2021 ◽  
Vol 21 (12) ◽  
pp. 4003
Author(s):  
José Tamay ◽  
Jesús Galindo-Zaldivar ◽  
John Soto ◽  
Antonio J. Gil
Keyword(s):  
Subduction Zone ◽  
Main Tool ◽  
South American ◽  
The South ◽  
Nazca Plate ◽  
South American Plate ◽  
The North ◽  
The Pacific ◽  
Active Tectonic ◽  
Plate Subduction

GNSS observations constitute the main tool to reveal Earth’s crustal deformations in order to improve the identification of geological hazards. The Ecuadorian Andes were formed by Nazca Plate subduction below the Pacific margin of the South American Plate. Active tectonic-related deformation continues to present, and it is constrained by 135 GPS stations of the RENAGE and REGME deployed by the IGM in Ecuador (1995.4–2011.0). They show a regional ENE displacement, increasing towards the N, of the deformed North Andean Sliver in respect to the South American Plate and Inca Sliver relatively stable areas. The heterogeneous displacements towards the NNE of the North Andean Sliver are interpreted as consequences of the coupling of the Carnegie Ridge in the subduction zone. The Dolores–Guayaquil megashear constitutes its southeastern boundary and includes the dextral to normal transfer Pallatanga fault, that develops the Guayaquil Gulf. This fault extends northeastward along the central part of the Cordillera Real, in relay with the reverse dextral Cosanga–Chingual fault and finally followed by the reverse dextral Sub-Andean fault zone. While the Ecuadorian margin and Andes is affected by ENE–WSW shortening, the easternmost Manabí Basin located in between the Cordillera Costanera and the Cordillera Occidental of the Andes, underwent moderate ENE–WSW extension and constitutes an active fore-arc basin of the Nazca plate subduction. The integration of the GPS and seismic data evidences that highest rates of deformation and the highest tectonic hazards in Ecuador are linked: to the subduction zone located in the coastal area; to the Pallatanga transfer fault; and to the Eastern Andes Sub-Andean faults.

scholarly journals A quantitative evaluation of the role of the Argentinean Col and the Low Pressure Tongue East of the Andes for frontogenesis in the South American subtropics

2009 ◽  
Vol 22 ◽  
pp. 67-72 ◽  
Author(s):  
H. M. J. Barbosa ◽  
J. M. Arraut
Keyword(s):  
Potential Temperature ◽  
Austral Summer ◽  
Low Pressure ◽  
Spatial Average ◽  
South American ◽  
The South ◽  
Time Step ◽  
The Andes ◽  
Hourly Data

Abstract. Previous studies have found the South American subtropics to exhibit high climatological frontogenesis in equivalent potential temperature during the austral summer. An important contribution to this pattern is given by frontogenesis over the Argentinean Col (AC), which separates the Northwestern Argentinean Low (NAL) from transient troughs to the south of it. The NAL and the Low Pressure Tongue east of the Andes (LPT) promote efficient transport of Amazonian humidity to the subtropics during the incursion of transient disturbances over the continent. The convergence of this strong warm and humid flow with mid-latitude air brought into the subtropics by the disturbance occurs preferentially in the neighborhood of the AC. The main difficulty in quantifying the contribution of the NAL, AC and LPT structure to frontogenesis in the South American subtropics is the automatic detection of the AC and LPT. In this paper an algorithm developed to this end is briefly presented and applied to obtain statistics on the role of these structures in frontogenesis. Six-hourly data from ECMWF ERA-40 Reanalysis over 21 austral summer periods (December–March) is used. Occurrences of the AC are highly concentrated between 34–39° S and 66–69° W, being present in this region in 42% of the time instants analyzed. The spatial average of the positive values of the frontogenesis over this region was calculated for each time step as a measure of intensity and histograms were built for the cases when the AC was and was not found inside this region. Mean, median and mode are larger for the distribution of cases with the presence of the AC. In addition, we present the frequency of occurrence of the AC as a function of the frontogenesis, showing that it grows with the intensity of the frontogenesis, rising above the 0.955 quantile. We have not found any correlation between the AC frequency and the frontolysis intensity.

Study for the Determination of Seismic Hazard for the Ocensa Oil Pipeline

2015 ◽  
Author(s):  
Julian Javier Corrales ◽  
Hugo Alberto García ◽  
Mauricio Gallego Silva ◽  
Elkin Gerardo Avila
Keyword(s):  
Seismic Hazard ◽  
Oil Fields ◽  
Mountain Range ◽  
South American ◽  
Nazca Plate ◽  
South American Plate ◽  
Oil Pipeline ◽  
The Andes ◽  
The Caribbean

The Andes mountain range crosses South America from South to North, is created by the subduction of the Nazca plate beneath the South American plate, this situation generates a high seismic and volcanic activity which have been decisive in shaping the relief of the continent. The OCENSA pipeline crosses the Andes Mountains on its way to transport crude from the oil fields of the eastern plains to the port of Coveñas on the Caribbean Sea. Therefore for the integrity department of Ocensa the assessment of seismic hazard is among one of its priorities. In this paper the results of the study in Ocensa for determination of seismic hazard for the pipeline and its major facilities are presented.

scholarly journals On the Pleistocene Snow-Line Depression in the Arid Regions of the South American Andes

1971 ◽  
Vol 10 (59) ◽  
pp. 255-267
Author(s):  
Stefan L. Hastenrath
Keyword(s):  
Arid Regions ◽  
South American ◽  
The South ◽  
Temperate Latitude ◽  
The Andes ◽  
Western Cordillera ◽  
Snow Line ◽  
The Pacific ◽  
The Arid Regions ◽  
June July

AbstractField observations during a journey through the arid regions of the South American Andes in June-July 1969 are evaluated in conjunction with available air photographs and reports from adjacent regions of the High Andes. Results indicate an increase of the Pleistocene snow-line depression in the western Cordillera from about 700 m at lat. 12° S. to more than 1 500 m at lat. 30° S. The Pleistocene snow-line depression decreases from the Pacific to the Atlantic side of the Andes, but particularly strongly so on the poleward fringe of the arid region. From this geomorphic evidence it is suggested that the atmospheric circulation during the glacial period was characterized by an Equatorward displacement of the boundary between tropical easterlies and temperate-latitude westerlies.

Tsunami and Seismic Damage Caused by the Earthquake Off Iquique, Chile, in April, 2014

2016 ◽  
Vol 10 (02) ◽  
pp. 1640003 ◽  
Author(s):  
Takashi Tomita ◽  
Kentaro Kumagai ◽  
Cyril Mokrani ◽  
Rodrigo Cienfuegos ◽  
Hisashi Matsui
Keyword(s):  
Seismic Damage ◽  
South American ◽  
Nazca Plate ◽  
South American Plate ◽  
Straight Line ◽  
Earthquake Resistant ◽  
Straight Line Distance ◽  
Run Up ◽  
Tsunami Run Up ◽  
The City

On Tuesday, April 1, 2014, at 8:46 p.m. local time in Chile, a subduction earthquake of Mw 8.2 occurred about 100[Formula: see text]km northwest of the city of Iquique, where the Nazca plate subducts beneath the South American plate. This earthquake triggered a tsunami, which hit coastal areas in northern Chile. A joint Japan–Chile team conducted a post-tsunami field survey to measure the height of the tsunami traces and to investigate the damage caused by the earthquake and tsunami. Based on measurements of the tsunami traces, it is estimated that a tsunami 3–4[Formula: see text]m in height hit the coast from Arica, which is near the border between Chile and Peru, to Patache, south of Iquique, a straight-line distance of approximately 260[Formula: see text]km. The tsunami caused only minor inundations near shorelines, and caused no damage to buildings because living spaces were higher than the tsunami run-up height. Seismic damage was more extensive than that caused by the tsunami, especially in Iquique, and included the destruction of houses, buildings, and other infrastructure. It also ignited fires. In the Port of Iquique, a wharf, before earthquake-resistant improvements were implemented, was destroyed by the strong ground motions that resulted from the earthquake.

Microsatellites and 16S sequences corroborate phenotypic evidence of trans-Andean variation in the parasitoidMicroctonus hyperodae(Hymenoptera: Braconidae)

2005 ◽  
Vol 95 (4) ◽  
pp. 289-298 ◽  
Author(s):  
L.M. Winder ◽  
C.B. Phillips ◽  
C. Lenney-Williams ◽  
R.P. Cane ◽  
K. Paterson ◽  
...  
Keyword(s):  
Andes Mountains ◽  
South American ◽  
The South ◽  
The Andes ◽  
16S Gene ◽  
Pasture Grasses ◽  
Geographical Populations ◽  
Listronotus Bonariensis ◽  
Microctonus Hyperodae ◽  
Chilean Populations

AbstractEight South American geographical populations of the parasitoidMicroctonus hyperodaeLoan were collected in South America (Argentina, Brazil, Chile and Uruguay) and released in New Zealand for biological control of the weevilListronotus bonariensis(Kuschel), a pest of pasture grasses and cereals. DNA sequencing (16S, COI, 28S, ITS1, β-tubulin), RAPD, AFLP, microsatellite, SSCP and RFLP analyses were used to seek markers for discriminating between the South American populations. All of the South American populations were more homogeneous than expected. However, variation in microsatellites and 16S gene sequences corroborated morphological, allozyme and other phenotypic evidence of trans-Andes variation between the populations. The Chilean populations were the most genetically variable, while the variation present on the eastern side of the Andes mountains was a subset of that observed in Chile.

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