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.

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>

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>

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>

Sea Urchins and Circuses: The Modernist Natural Histories of Jean Painlevé and Alexander Calder

2018 ◽  
Vol 13 (2) ◽  
pp. 187-211
Author(s):  
Patricia E. Chu
Keyword(s):  
New Media ◽  
Sea Urchins ◽  
Life Sciences ◽  
Three Dimensional ◽  
Machine Age ◽  
Avant Garde ◽  
History Of ◽  
And Performance ◽  
The One ◽  
Natural Historian

The Paris avant-garde milieu from which both Cirque Calder/Calder's Circus and Painlevé’s early films emerged was a cultural intersection of art and the twentieth-century life sciences. In turning to the style of current scientific journals, the Paris surrealists can be understood as engaging the (life) sciences not simply as a provider of normative categories of materiality to be dismissed, but as a companion in apprehending the “reality” of a world beneath the surface just as real as the one visible to the naked eye. I will focus in this essay on two modernist practices in new media in the context of the history of the life sciences: Jean Painlevé’s (1902–1989) science films and Alexander Calder's (1898–1976) work in three-dimensional moving art and performance—the Circus. In analyzing Painlevé’s work, I discuss it as exemplary of a moment when life sciences and avant-garde technical methods and philosophies created each other rather than being classified as separate categories of epistemological work. In moving from Painlevé’s films to Alexander Calder's Circus, Painlevé’s cinematography remains at the forefront; I use his film of one of Calder's performances of the Circus, a collaboration the men had taken two decades to complete. Painlevé’s depiction allows us to see the elements of Calder's work that mark it as akin to Painlevé’s own interest in a modern experimental organicism as central to the so-called machine-age. Calder's work can be understood as similarly developing an avant-garde practice along the line between the bestiary of the natural historian and the bestiary of the modern life scientist.

Computed Tomography and Magnetic Resonance Imaging-aided Diagnosis of Primary Essential Cutis Verticis Gyrata: A Case Report with 5-year Follow-up and Review of the Literature

2019 ◽  
Vol 15 (9) ◽  
pp. 906-910
Author(s):  
Hongzhang Zhu ◽  
Shi-Ting Feng ◽  
Xingqi Zhang ◽  
Zunfu Ke ◽  
Ruixi Zeng ◽  
...  
Keyword(s):  
Magnetic Resonance Imaging ◽  
Magnetic Resonance ◽  
Three Dimensional ◽  
Stable Condition ◽  
Resonance Imaging ◽  
Mri Findings ◽  
Cutis Verticis Gyrata ◽  
Essential Form ◽  
History Of ◽  
Magnetic Resonance Imaging Mri

Background: Cutis Verticis Gyrata (CVG) is a rare skin disease caused by overgrowth of the scalp, presenting as cerebriform folds and wrinkles. CVG can be classified into two forms: primary (essential and non-essential) and secondary. The primary non-essential form is often associated with neurological and ophthalmological abnormalities, while the primary essential form occurs without associated comorbidities. Discussion: We report on a rare case of primary essential CVG with a 4-year history of normal-colored scalp skin mass in the parietal-occipital region without symptom in a 34-year-old male patient, retrospectively summarizing his pathological and Computer Tomography (CT) and magnetic resonance imaging (MRI) findings. The major clinical observations on the CT and MR sectional images include a thickened dermis and excessive growth of the scalp, forming the characteristic scalp folds. With the help of CT and MRI Three-dimensional (3D) reconstruction techniques, the characteristic skin changes could be displayed intuitively, providing more evidence for a diagnosis of CVG. At the 5-year followup, there were no obvious changes in the lesion. Conclusion: Based on our observations, we propose that not all patients with primary essential CVG need surgical intervention, and continuous clinical observation should be an appropriate therapy for those in stable condition.

scholarly journals Sirenomelia: two case reports

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Asiyeh Shojaee ◽  
Firooze Ronnasian ◽  
Mahdiyeh Behnam ◽  
Mansoor Salehi
Keyword(s):  
Case Reports ◽  
Three Dimensional ◽  
First Trimester ◽  
Mendelian Inheritance ◽  
Lower Limbs ◽  
Congenital Deformity ◽  
White Family ◽  
Her Family ◽  
Caudal Regression ◽  
History Of

AbstractBackgroundSirenomelia, also called mermaid syndrome, is a rare lethal multi-system congenital deformity with an incidence of one in 60,000–70,000 pregnancies. Sirenomelia is mainly characterized by the fusion of lower limbs and is widely associated with severe urogenital and gastrointestinal malformations. The presence of a single umbilical artery derived from the vitelline artery is the main anatomical feature distinguishing sirenomelia from caudal regression syndrome. First-trimester diagnosis of this disorder and induced abortion may be the safest medical option. In this report, two cases of sirenomelia that occurred in an white family will be discussed.Case presentationWe report two white cases of sirenomelia occurring in a 31-year-old multigravid pregnant woman. In the first pregnancy (18 weeks of gestation) abortion was performed, but in the third pregnancy (32 weeks) the stillborn baby was delivered by spontaneous vaginal birth. In the second and fourth pregnancies, however, she gave birth to normal babies. Three-dimensional ultrasound imaging showed fusion of the lower limbs. Neither she nor any member of her family had a history of diabetes. In terms of other risk factors, she had no history of exposure to teratogenic agents during her pregnancy. Also, her marriage was non-consanguineous.ConclusionThis report suggests the existence of a genetic background in this mother with a Mendelian inheritance pattern of 50% second-generation incidence in her offspring.

scholarly journals Superconformal boundaries in 4 − ϵ dimensions

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Aleix Gimenez-Grau ◽  
Pedro Liendo ◽  
Philine van Vliet
Keyword(s):  
Three Dimensional ◽  
Spacetime Dimension ◽  
Perfect Agreement ◽  
Bootstrap Analysis ◽  
First Order ◽  
Free Theory ◽  
First Order Correction ◽  
Free Parameters ◽  
Superconformal Theories ◽  
Zumino Model

Abstract Boundaries in three-dimensional $$ \mathcal{N} $$ N = 2 superconformal theories may preserve one half of the original bulk supersymmetry. There are two possibilities which are characterized by the chirality of the leftover supercharges. Depending on the choice, the remaining 2d boundary algebra exhibits $$ \mathcal{N} $$ N = (0, 2) or $$ \mathcal{N} $$ N = (1) supersymmetry. In this work we focus on correlation functions of chiral fields for both types of supersymmetric boundaries. We study a host of correlators using superspace techniques and calculate superconformal blocks for two- and three-point functions. For $$ \mathcal{N} $$ N = (1) supersymmetry, some of our results can be analytically continued in the spacetime dimension while keeping the codimension fixed. This opens the door for a bootstrap analysis of the ϵ-expansion in supersymmetric BCFTs. Armed with our analytically-continued superblocks, we prove that in the free theory limit two-point functions of chiral (and antichiral) fields are unique. The first order correction, which already describes interactions, is universal up to two free parameters. As a check of our analysis, we study the Wess-Zumino model with a super-symmetric boundary using Feynman diagrams, and find perfect agreement between the perturbative and bootstrap results.

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