Shortening and structural architecture of the Andean fold-thrust belt of southern Bolivia (21°S): Implications for kinematic development and crustal thickening of the central Andes

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&#176;S-39&#176;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&#176;S-35&#176;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.

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The crustal structure in the transition from the on land fold-and-thrust belt to the offshore accretionary prism in the Taiwan arc-continent collision

10.5194/egusphere-egu2020-2846 ◽

2020 ◽

Author(s):

Joaquina Alvarez-Marrón ◽

Dennis Brown ◽

Juan Alcalde ◽

Ignacio Marzán ◽

Hao Kuo-Chen

Keyword(s):

Continental Margin ◽

Seismic Tomography ◽

Accretionary Prism ◽

Crustal Thickening ◽

Accretionary Wedge ◽

Thrust Belt ◽

Deformation Front ◽

Coast Line ◽

Transition Area ◽

Fold And Thrust Belt

The region of Taiwan is undergoing active, oblique arc-continent colision between the Luzon Arc on the Philippine Sea Plate and the continental margin of Eurasia. The Fold-and-Thrust Belt (FTB) in Taiwan passes southwards into a submarine accretionary wedge at the Manila subduction zone. The aim of this contribution is to examine how an on land FTB changes into a marine accretionary prism in the context of an oblique arc-continent collision. The Miocene pre-orogenic sediments of the continental margin are widespread in the FTB ca. 23&#176; latitude while the offshore wedge is built up dominantly by Pliocene to recent syn-orogenic sediments. In the transition area from the marine accretionary wedge ca. 21&#176; latitude to the on land FTB, the thrust wedge is climbing up the slope of the Eurasian continental margin. The deformation front is at sea floor depth of ca. 4 km in the south to less than 1 km as it reaches the coast line. Here we use the island surface geology, marine reflection seismic profiles, and seismic tomography models to construct contour maps of the basal thrust and the depth to the Moho across a transition area from near 23&#176; to near 21&#176; latitude. In this zone, the deformation front draws a convex curvature as the wedge widens from ca. 50 in the north and south, to more than 130 km near 22&#176; latitude. The basal thrust surface shows a scoop shape as its dip changes from southeast near the coast line to east southward. The basal thrust reaches over 7 km deep beneath the rear of the FTB before ramping into de basement and merging into the Chaochou fault at 10 km depth. Offshore, it shows a gentler dip from 7 km to c. 10 km depth before getting steeper towards the east below the Hengchung Ridge. The basal cuts laterally along-strike through the margin&#8217;s sedimentary cover to incorporate thicker Miocene pre-orogenic sediments onto its hanging wall as it passes from the offshore wedge to the on land FTB.In the offshore area, the Moho (we use a Vp proxy of 7.5 km/s extracted from the seismic tomography) shallows southeastward, from near 25 km depth below the shelf slope break to less than 17 km depth below the offshore wedge near 21.5&#176; latitude before it starts to deep east towards beneath the Taiwan coast. The Moho dips northeast from near 25 km depth below the coast near Kaohsiung, to near 40 depth below the rear of the FTB at 23.5&#176;, latitude. This complex morphology of the Moho may be related to the changes in crustal thickness and the obliquity of the collision. Because of this, crustal thickening is less pronounced beneath southern Taiwan where the thinner part of the margin is colliding with the arc.This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency from the Ministry of Science Innovation and Universities of Spain.

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Cenozoic sedimentation and exhumation of the foreland basin system preserved in the Precordillera thrust belt (31-32°S), southern central Andes, Argentina

Tectonics ◽

10.1002/2013tc003424 ◽

2014 ◽

Vol 33 (9) ◽

pp. 1659-1680 ◽

Cited By ~ 41

Author(s):

Mariya Levina ◽

Brian K. Horton ◽

Facundo Fuentes ◽

Daniel F. Stockli

Keyword(s):

Foreland Basin ◽

Central Andes ◽

Thrust Belt ◽

Southern Central ◽

Basin System

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