Buoyancy versus shear forces in building orogenic wedges
<p>The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces du...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-08-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/12/1749/2021/se-12-1749-2021.pdf |
| _version_ | 1818722639347187712 |
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| author | L. G. Candioti T. Duretz E. Moulas S. M. Schmalholz |
| author_facet | L. G. Candioti T. Duretz E. Moulas S. M. Schmalholz |
| author_sort | L. G. Candioti |
| collection | DOAJ |
| description | <p>The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive.
Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks.
We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 <span class="inline-formula">Myr</span>) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision.
Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins.
Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision.</p>
<p>We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material.
Densities are determined by linearized equations of state or by petrological-phase equilibria calculations.
The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>F</mi><mi mathvariant="normal">B</mi></msub><mo>/</mo><msub><mi>F</mi><mi mathvariant="normal">D</mi></msub><mo>=</mo><msub><mi mathvariant="normal">Ar</mi><mi mathvariant="normal">F</mi></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="347e304bceb2153fb690fc294a68fe8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-12-1749-2021-ie00001.svg" width="60pt" height="14pt" src="se-12-1749-2021-ie00001.png"/></svg:svg></span></span>, which controls the mode of orogenic wedge formation: <span class="inline-formula">Ar<sub>F</sub>≈0.5</span> causes thrust-sheet-dominated wedges, <span class="inline-formula">Ar<sub>F</sub>≈0.75</span> causes minor wedge formation due to relamination of subducted crust below the upper plate, and <span class="inline-formula">Ar<sub>F</sub>≈1</span> causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (<span class="inline-formula">>80</span> <span class="inline-formula">km</span>).
Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres.</p>
<p>We suggest that during the formation of the Pyrenees <span class="inline-formula">Ar<sub>F</sub><i>⪅</i>0.5</span> due to the absence of high-grade metamorphic rocks, whereas for the Alps <span class="inline-formula">Ar<sub>F</sub>≈1</span> during exhumation of high-grade rocks and <span class="inline-formula">Ar<sub>F</sub><i>⪅</i>0.5</span> during the post-collisional stage.
In the models, <span class="inline-formula"><i>F</i><sub>D</sub></span> increases during wedge growth and subduction and eventually reaches magnitudes (<span class="inline-formula">≈18</span> <span class="inline-formula">TN m<sup>−1</sup></span>) which are required to initiate subduction.
Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 <span class="inline-formula">Ma</span> and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate.</p> |
| first_indexed | 2024-12-17T20:57:49Z |
| format | Article |
| id | doaj.art-1bf13773f7504dceb3854da7a207ad5b |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-17T20:57:49Z |
| publishDate | 2021-08-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-1bf13773f7504dceb3854da7a207ad5b2022-12-21T21:32:49ZengCopernicus PublicationsSolid Earth1869-95101869-95292021-08-01121749177510.5194/se-12-1749-2021Buoyancy versus shear forces in building orogenic wedgesL. G. Candioti0T. Duretz1E. Moulas2S. M. Schmalholz3Institut des sciences de la Terre, Bâtiment Géopolis, Quartier UNIL-Mouline, Université de Lausanne, 1015 Lausanne (VD), SwitzerlandUniv Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, FranceInstitute of Geosciences & Mainz Institute of Multiscale Modeling (M³ODEL), Johannes-Gutenberg University, 55128 Mainz, GermanyInstitut des sciences de la Terre, Bâtiment Géopolis, Quartier UNIL-Mouline, Université de Lausanne, 1015 Lausanne (VD), Switzerland<p>The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 <span class="inline-formula">Myr</span>) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision.</p> <p>We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi>F</mi><mi mathvariant="normal">B</mi></msub><mo>/</mo><msub><mi>F</mi><mi mathvariant="normal">D</mi></msub><mo>=</mo><msub><mi mathvariant="normal">Ar</mi><mi mathvariant="normal">F</mi></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="60pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="347e304bceb2153fb690fc294a68fe8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="se-12-1749-2021-ie00001.svg" width="60pt" height="14pt" src="se-12-1749-2021-ie00001.png"/></svg:svg></span></span>, which controls the mode of orogenic wedge formation: <span class="inline-formula">Ar<sub>F</sub>≈0.5</span> causes thrust-sheet-dominated wedges, <span class="inline-formula">Ar<sub>F</sub>≈0.75</span> causes minor wedge formation due to relamination of subducted crust below the upper plate, and <span class="inline-formula">Ar<sub>F</sub>≈1</span> causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (<span class="inline-formula">>80</span> <span class="inline-formula">km</span>). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres.</p> <p>We suggest that during the formation of the Pyrenees <span class="inline-formula">Ar<sub>F</sub><i>⪅</i>0.5</span> due to the absence of high-grade metamorphic rocks, whereas for the Alps <span class="inline-formula">Ar<sub>F</sub>≈1</span> during exhumation of high-grade rocks and <span class="inline-formula">Ar<sub>F</sub><i>⪅</i>0.5</span> during the post-collisional stage. In the models, <span class="inline-formula"><i>F</i><sub>D</sub></span> increases during wedge growth and subduction and eventually reaches magnitudes (<span class="inline-formula">≈18</span> <span class="inline-formula">TN m<sup>−1</sup></span>) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 <span class="inline-formula">Ma</span> and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate.</p>https://se.copernicus.org/articles/12/1749/2021/se-12-1749-2021.pdf |
| spellingShingle | L. G. Candioti T. Duretz E. Moulas S. M. Schmalholz Buoyancy versus shear forces in building orogenic wedges Solid Earth |
| title | Buoyancy versus shear forces in building orogenic wedges |
| title_full | Buoyancy versus shear forces in building orogenic wedges |
| title_fullStr | Buoyancy versus shear forces in building orogenic wedges |
| title_full_unstemmed | Buoyancy versus shear forces in building orogenic wedges |
| title_short | Buoyancy versus shear forces in building orogenic wedges |
| title_sort | buoyancy versus shear forces in building orogenic wedges |
| url | https://se.copernicus.org/articles/12/1749/2021/se-12-1749-2021.pdf |
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