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

<p>The Andes are the modern active example of a Cordilleran-type orogen, with mountain-building
 and crustal thickening within the upper plate of a subduction zone. Despite numerous studies of
 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
 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°S are provided here. These data, interpreted as an age-elevation thermochronological profile, imply continuous exhumation initiating well before ~12–14 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. <br>Riesner M. et al. 2019, Scientific Reports, DOI: 10.1038/s41598-019-44320-1</p>

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>

Cordilleran-type orogens and plateaus: new views from a quantitative re-evaluation of mountain-building in the western Central Andes.

2020 ◽  
Author(s):  
Martine Simoes ◽  
Magali Riesner ◽  
Tania Habel ◽  
Robin Lacassin ◽  
Daniel Carrizo ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Crustal Thickening ◽  
Thrust Belt ◽  
Mountain Building ◽  
First Order ◽  
Relative Contribution ◽  
The Andes ◽  
Western Flank ◽  
Fold And Thrust Belt ◽  
Back Arc

<p>The processes driving Andean mountain-building and crustal thickening have been largely questioned since the ~1970's but have remained relatively unclear. However, the discovery of an active fold-and-thrust belt along its western flank at the latitude of Santiago (Chili, ~33.5 °S) has launched a recent vigorous debate on the relative contribution of these structures to Andean mountain-building. Based on an original approach for structural mapping, we have quantitatively investigated the structure of this fold-and-thrust belt, as well as that of the other structural units of the range at this latitude. By combining these data to published structural geometries of the eastern mountain flank, together with constraints on the timing of faulting and exhumation, we were able to revise the overall structure of the range and to quantify the kinematics of Andean orogenic growth at ~33°S-33.5°S. We find that crustal shortening has first primarily been sustained along the western mountain flank by west-vergent structures, synthetic to the subduction zone, with the subsequent increasing contribution of out-of-sequence thrusting, followed by late east-vergent thrusting along the eastern mountain flank. This pattern seems not to be specific to the Andes at this latitude, as similar observations can be made to the first-order by ~20°S, ie ~1300 km further north. There, the kinematics of the fold-and-thrust belt forming the western flank of the Andes cannot be as precisely documented because most structures are hidden beneath the later Cenozoic Atacama gravels. However, first-order quantitative results indicate similar kinematics, where Andean mountain building initiated on west-vergent structures synthetic to the subduction zone and where the later significant cumulated take-over by east-vergent structures towards the South American continent has led to the building of the Altiplano-Puna Plateau.</p><p>We propose that such kinematics - ie deformation initially on west-vergent structures along the western mountain flank, with significant later back-arc antithetic deformation - are first-order characteristics of Andean mountain-building, and result from the limited mechanical flexure of the underthrusting forearc, eventually locally modulated by climate-driven erosion.</p>

scholarly journals Southward expanding plate coupling due to variation in sediment subduction as a cause of Andean growth

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jiashun Hu ◽  
Lijun Liu ◽  
Michael Gurnis
Keyword(s):  
Sediment Transport ◽  
Three Dimensional ◽  
Mountain Building ◽  
Crustal Shortening ◽  
First Order ◽  
The Andes ◽  
Tectonic Processes ◽  
History Of ◽  
Plate Coupling ◽  
Trench Sediments

AbstractGrowth of the Andes has been attributed to Cenozoic subduction. Although climatic and tectonic processes have been proposed to be first-order mechanisms, their interaction and respective contributions remain largely unclear. Here, we apply three-dimensional, fully-dynamic subduction models to investigate the effect of trench-axial sediment transport and subduction on Andean growth, a mechanism that involves both climatic and tectonic processes. We find that the thickness of trench-fill sediments, a proxy of plate coupling (with less sediments causing stronger coupling), exerts an important influence on the pattern of crustal shortening along the Andes. The southward migrating Juan Fernandez Ridge acts as a barrier to the northward flowing trench sediments, thus expanding the zone of plate coupling southward through time. Consequently, the predicted history of Andean shortening is consistent with observations. Southward expanding crustal shortening matches the kinematic history of inferred compression. These results demonstrate the importance of climate-tectonic interaction on mountain building.

scholarly journals Multiple Phases of Mountain Building on the Northern Tibetan Margin

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Fei Wang ◽  
Wenbei Shi ◽  
Weibin Zhang ◽  
Liekun Yang ◽  
Yinzhi Wang
Keyword(s):  
Evolutionary History ◽  
Mountain Range ◽  
Far Field ◽  
Mountain Building ◽  
First Order ◽  
Field Effects ◽  
Denudation Rates ◽  
History Of ◽  
Granitic Intrusions ◽  
Multiple Domain

Abstract The history of mountain building along the northern Tibetan margin since its initiation remains unclear. The exhumation evolutionary history of the Kunlun Belt, the first-order mountain range of northern Tibet, is resolved by using 40Ar/39Ar thermochronological analyses of Paleozoic and Mesozoic granitic intrusions. Four rapid exhumation events are identified from analyses employing multiple domain diffusion theories in the Carboniferous (~355-295 Ma), Triassic (~245-205 Ma), Cretaceous (~120-95 Ma), and Eocene (~40-35 Ma). The cooling rates and the therefrom deduced denudation rates are estimated for these stages. The events are interpreted to reflect the closure of the Prototethys Ocean in the early Paleozoic, closure of the Paleotethys ocean in the late Paleozoic, far-field effects from the closure of the Mesotethys Ocean, and far-field effects from the Paleogene convergence of India and Eurasia, respectively. These events collectively built up the present northern Tibetan margin.

Deformation of the western flank of the Andes at ~20–22°S: a contribution to the quantification of crustal shortening

2021 ◽  
Author(s):  
Tania Habel ◽  
Robin Lacassin ◽  
Martine Simoes ◽  
Daniel Carrizo ◽  
German Aguilar ◽  
...  
Keyword(s):  
Crustal Thickening ◽  
Thrust Belt ◽  
Mountain Building ◽  
Common View ◽  
Western Margin ◽  
The Andes ◽  
Kinematic Evolution ◽  
Western Flank ◽  
Fold And Thrust Belt ◽  
High Resolution Satellite Images

<p>The Andes are the case example of an active Cordilleran-type orogen. It is generally admitted that, in the Bolivian Orocline (Central Andes at ~20°S), mountain-building started ~50–60 Myr ago, close to the subduction margin, and then propagated eastward. Though suggested by some early geological cross-sections, the structures sustaining the uplift of the western flank of the Altiplano have often been dismissed, and the most common view theorizes that the Andes grow only by east-vergent deformation along its eastern margin. However, recent studies emphasize the significant contribution of the West Andean front to mountain-building and crustal thickening, in particular at the latitude of Santiago de Chile (~33.5°S), and question the contribution of similar structures elsewhere along the Andes.  Here, we focus on the western margin of the Altiplano at 20–22°S, in the Atacama desert of northern Chile. We present our results on the structure and kinematic evolution on two sites where the structures are well exposed. We combine mapping from high-resolution satellite images with field observations and numerical trishear forward modeling to provide quantitative constraints on the kinematic evolution of the western front of the Andes. Our results confirm two main structures: (1) a major west-vergent thrust placing Andean Paleozoic basement over Mesozoic strata, and (2) a west-vergent fold-and-thrust-belt deforming primarily Mesozoic units. Once restored, we estimate that both structures accommodate together at least ~6–9 km of shortening across the sole ~7–17 km-wide outcropping fold-and-thrust-belt. Further west, structures of this fold-and-thrust-belt are unconformably buried under much less deformed Cenozoic units, as revealed from seismic profiles. By comparing the scale of these buried structures to those investigated previously, we propose that the whole fold-and-thrust-belt has most probably absorbed at least ~15–20 km of shortening. The timing of the recorded main deformation can be bracketed sometime between ~68 and ~29 Ma – and possibly between ~68 and ~44 Ma – from dated deformed geological layers, with a subsequent significant slowing-down of shortening rates. This is in good agreement with preliminary modeling of apatite and zircon (U-Th)/He dates suggesting that basement exhumation by thrusting started by ~70–60 Ma, slowed down by ~50–40 Ma, and tended to cease by ~30–20 Ma. Minor shortening affecting the mid-late Cenozoic deposits indicates that deformation continued after ~29 Ma along the western Andean fold-and-thrust-belt, but remained limited compared to the more intense deformation that occured during the Paleogene. Altogether, the data presented here will provide a quantitative evaluation of the contribution of the western margin of the Altiplano plateau to mountain-building at this latitude, in particular at its earliest stages.</p>

Mountain building and species radiations in the Andes: a reconstruction of surface uplift and species diversification since the Late Cretaceous from a compilation of paleo-elevation estimates, thermochronology, and phylogenetic data.

2020 ◽  
Author(s):  
Lydian Boschman ◽  
Mauricio Bermúdez ◽  
Fabien Condamine
Keyword(s):  
Low Temperature ◽  
Mountain Range ◽  
The South ◽  
Mountain Building ◽  
Species Diversification ◽  
Origin And Evolution ◽  
Continental Scale ◽  
Surface Uplift ◽  
The Andes ◽  
History Of

<p>The Andes are the longest continental mountain range on Earth, stretching from tropical Colombia and Venezuela in the north to temperate to sub-polar Patagonia in the south along the western margin of the South American continent. Biological diversity is extraordinarily high, especially in the northern tropical Andes, which are considered to be the richest biodiversity hotspot in the world. The Andes are relatively young; a large part of the modern topography is the result of surface uplift that occurred during and since the Miocene. However, large differences exist in the timing of shortening, exhumation, and surface uplift between the northern, central, and southern Andes, as well as between the various parallel Cordilleras. Mountain building directly links to climate dynamics, the development of drainage patterns, and the evolution of biomes and biodiversity. Therefore, determining the timing of surface uplift for each of the different Andean regions is of crucial importance for our understanding of continental-scale moisture transport and atmospheric circulation, the origin and evolution of the Amazon River and Rainforest, and ultimately, the origin and evolution of species in South America.</p><p>Determining surface elevations through geological time is not straightforward because the geological record does not contain a direct measure of topography. Commonly used methods to indirectly estimate paleo-elevation include low temperature thermochronology, palynology/paleobotany, the identification and dating of paleosurfaces, and analyzing the stratigraphic record of foreland basins that quantitatively record the topographic and erosional history of an adjacent mountain range. Additionally, paleo-elevation can be estimated more directly by stable isotope paleo-altimetry: atmospheric δ<sup>18</sup>O and δD vary with elevation as precipitation from ascending air parcels along an orographic barrier removes the heavy isotopes. The δ<sup>18</sup>O and δD values in authigenic/pedogenic materials (paleosols or lakes), biogenic archives (e.g. fossil teeth), volcanic glass, or organic biomarkers (e.g. leaf-wax n-alkanes preserved in soils or sediments) may thus record paleo-elevation.</p><p>In this study, we present a compilation of (direct and indirect) estimates of paleo-elevation of the Andes. We generate a reconstruction of surface uplift, per latitudinal sector of the Andes and per Cordillera or range, containing elevation values per 1x1 degree cell and per Myr. We discuss the areas and/or times where this reconstruction is uncertain as a result of either a lack of data, or a discrepancy between different data sets. Next, we present a compilation of low temperature thermochronology data, and compare the paleo-elevation history of the Andes with its exhumation history. We analyze spatial and temporal variations in erosion rates during Andean mountain building. Last, we use the paleo-elevation reconstruction to analyze the role of Andean mountain building in the rates of species diversification for hummingbirds (clade of Brilliants and Coquettes), iguanians (Liolaemus), tree frogs (two families), and flowering plants (centropogonids and orchids). We use a model‐testing approach that compares various diversification scenarios including a series of biologically realistic models to estimate speciation and extinction rates using a phylogeny, while assessing the relationship between diversification and environmental variables.</p>

Neogene magmatic expansion and mountain building processes in the southern Central Andes, 36–37°S, Argentina

2012 ◽  
Vol 53 ◽  
pp. 81-94 ◽  
Author(s):  
Mauro G. Spagnuolo ◽  
Vanesa D. Litvak ◽  
Andres Folguera ◽  
Germán Bottesi ◽  
Victor A. Ramos
Keyword(s):  
Central Andes ◽  
Mountain Building ◽  
Southern Central

Neogene paleoelevation of intermontane basins in a narrow, compressional mountain range, southern Central Andes of Argentina

2014 ◽  
Vol 406 ◽  
pp. 153-164 ◽  
Author(s):  
Gregory D. Hoke ◽  
Laura B. Giambiagi ◽  
Carmala N. Garzione ◽  
J. Brian Mahoney ◽  
Manfred R. Strecker
Keyword(s):  
Central Andes ◽  
Mountain Range ◽  
Southern Central ◽  
Intermontane Basins

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.

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