Comment on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile” by Rolando Armijo et al.

Astini, Ricardo A.; Dávila, Federico M.

doi:10.1029/2009tc002647

Cited by 12 publications

(17 citation statements)

References 41 publications

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“…Astini and Dávila () criticized the bivergent model first proposed by Armijo et al () and further discussed in detail here, mainly because of the lack of a prominent foreland basin to the west, in the fore‐arc region, in comparison to a well‐developed basin east of the Andes. We first note that latitudinal variations on the eastern side of the Andes are important.…”

Section: Conclusion: Kinematics and Mechanics Of Andean Mountain Builmentioning

confidence: 91%

Revisiting the Crustal Structure and Kinematics of the Central Andes at 33.5°S: Implications for the Mechanics of Andean Mountain Building

et al. 2018

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The Andean belt is the only present‐day active case example of a subduction‐type orogeny. However, an existing controversy opposes classical views of Andean growth as an east verging retro wedge, against a recently proposed bivergent model involving a primary west vergent crustal‐scale thrust synthetic to the subduction. We examine these diverging views by quantitatively reevaluating the orogen structural geometry and kinematics at the latitude of 33.5°S. We first provide a 3‐D geological map and build an updated section of the east vergent Aconcagua fold‐and‐thrust belt (Aconcagua FTB), which appears as a critical structural unit in this controversy. We combine these data with geological constraints on nearby structures to derive a complete and larger‐scale section of the Principal Cordillera (PC) within the fore‐arc region. We restore our section and integrate published chronological constraints to build an evolutionary model showing the evolving shortening of this fore‐arc part of the Andes. The proposed kinematics implies uplift of the Frontal Cordillera basement since ~20–25 Ma, supported by westward thrusting over a crustal ramp that transfers shortening further west across the PC. The Aconcagua FTB is evidenced as a secondary east verging roof thrust atop the large‐scale basement antiform culmination of the Frontal Cordillera. We estimate a shortening of ~27–42 km across the PC, of which only ~30% is absorbed by the Aconcagua FTB. Finally, we combine these findings with published geological data on the structure of the eastern back‐arc Andean mountain front and build a crustal‐scale cross section of the entire Andes at 33.5°S. We estimate a total orogenic shortening of ~31–55 km, mainly absorbed by crustal west vergent structures synthetic to the subduction. Our results provide quantitative key geological inferences to revisit this subduction‐type orogeny and compare it to collisional alpine‐type orogenic belts.

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Section: Conclusion: Kinematics and Mechanics Of Andean Mountain Builmentioning

confidence: 91%

Revisiting the Crustal Structure and Kinematics of the Central Andes at 33.5°S: Implications for the Mechanics of Andean Mountain Building

et al. 2018

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“…Existing geophysical data further north and south of our crustal-scale cross section (Gilbert et al, 2006), as well as at the latitude of our section (Gans et al, 2011), are compatible with a crustal root beneath the west vergent basement culmination of the Frontal Cordillera, with a Moho depth of~45-50 km. Astini and Dávila (2010) criticized the bivergent model first proposed by Armijo et al (2010a) and further discussed in detail here, mainly because of the lack of a prominent foreland basin to the west, in the forearc region, in comparison to a well-developed basin east of the Andes. We first note that latitudinal variations on the eastern side of the Andes are important.…”

Section: Conclusion: Kinematics and Mechanics Of Andean Mountain Building At 335°smentioning

confidence: 96%

Revisiting the crustal structure and kinematics of the Central Andes at 33.5°S : implications for the mechanics of Andean mountain-building

Riesner¹,

Lacassin²,

Simões³

et al. 2018

Preprint

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The Andean belt is the only present-day active case example of a subduction-type orogeny. However, an existing controversy opposes classical views of Andean growth as an east-verging retro-wedge, against a recently proposed bi-vergent model involving a primary west-vergent crustal-scale thrust synthetic to the subduction. We examine these diverging views by quantitatively re-evaluating the orogen structural geometry and kinematics at the latitude of 33.5°S. We first provide a 3D-geological map and build an updated section of the east-vergent Aconcagua fold-and-thrust belt (Aconcagua-FTB), which appears as a critical structural unit in this controversy. We combine these data with geological constraints on nearby structures to derive a complete and larger scale section of the Principal Cordillera within the forearc region. We restore our section and integrate published chronological constraints to build an evolutionary model showing the evolving shortening of this forearc part of the Andes. The proposed kinematics implies uplift of the Frontal Cordillera basement since ~20-25 Ma, supported by westward thrusting over a crustal ramp that transfers shortening further west across the Principal Cordillera. The Aconcagua-FTB is evidenced as a secondary east-verging roof thrust atop the large-scale basement antiform culmination of the Frontal Cordillera. We estimate a shortening of ~27-42 km across the Principal Cordillera, of which only ~30% is absorbed by the Aconcagua-FTB. Finally, we combine these findings with published geological data on the structure of the eastern back-arc Andean mountain front, and build a crustal-scale cross-section of the entire Andes at 33.5° S. We estimate a total orogenic shortening of ~31-55km, mainly absorbed by crustal west-vergent structures synthetic to the subduction. Our results provide quantitative key geological inferences to revisit this subduction-type orogeny and compare it to collisional alpine-type orogenic belts.

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“…We have proposed earlier a new tectonic model for the evolution of the Andes mountain belt as a bivergent orogen. Here, to reply to a comment by Astini and Dávila [2010], we discuss briefly the protracted diachronic evolution (over tens of million years) by propagating deformation at the large‐scale (over 10 2 –10 3 km), its influence on basin formation in the back‐arc region (retroarc foreland basin), and the mechanical implications of the bivergence in the tectonics of the fore‐arc region, particularly the possible effects of the underthrusting of the coastal crustal‐scale rigid block (the Marginal Block) beneath the West Andean Thrust.…”

Section: Introductionmentioning

confidence: 92%

“…The comment by Astini and Dávila [2010] criticizes our new model presented by Armijo et al [2010] suggesting that the Andes is a fundamentally bivergent (or doubly vergent) orogen and defends the conventional model of Andean orogeny, which we think obsolete, involving crustal shortening only by development of retroarc thrusts in the back‐arc region (e.g., as discussed, among many others, by Isacks [1988]). Our model is based on the structural study of the San Ramón Fault system and the Principal Cordillera at the front of the western flank of the Andes, which is used to characterize the crustal‐scale West Andean Thrust (WAT), a major fold‐thrust system in the fore‐arc region, synthetic to the subduction zone.…”

Section: Introductionmentioning

confidence: 95%

Reply to the comment by R. A. Astini and F. M. Dávila on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile”

et al. 2010

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Comment on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile” by Rolando Armijo et al.

Cited by 12 publications

References 41 publications

Revisiting the Crustal Structure and Kinematics of the Central Andes at 33.5°S: Implications for the Mechanics of Andean Mountain Building

Revisiting the Crustal Structure and Kinematics of the Central Andes at 33.5°S: Implications for the Mechanics of Andean Mountain Building

Revisiting the crustal structure and kinematics of the Central Andes at 33.5°S : implications for the mechanics of Andean mountain-building

Reply to the comment by R. A. Astini and F. M. Dávila on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile”

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