Rheology of the lithosphere beneath the central and western Tien Shan
The distribution of crustal velocity over a 800 by 400 km region of the Tien Shan shows strain rates with principal contractional axes aligned perpendicular to the mountain chain and with negligible velocity gradients in the along-strike direction. This configuration allows us to describe the dynami...
| Main Authors: | , |
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| Format: | Journal article |
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Wiley
2015
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| _version_ | 1797060235199774720 |
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| author | England, P Molnar, P |
| author_facet | England, P Molnar, P |
| author_sort | England, P |
| collection | OXFORD |
| description | The distribution of crustal velocity over a 800 by 400 km region of the Tien Shan shows strain rates with principal contractional axes aligned perpendicular to the mountain chain and with negligible velocity gradients in the along-strike direction. This configuration allows us to describe the dynamics by a force balance along profiles perpendicular to the chain. The velocities on each of these profiles fit, with root-mean-square misfits of ∼1 mm/yr, a constant rate of contractional strain. Gravitational potential energy per unit area varies along these profiles by at least 3 and maybe 5 TN m−1; the insensitivity of contractional strain rates to those variations implies a lower bound of ∼1022 Pa s on the effective viscosity of the lithosphere. Seismic tomography shows variations in P and S wave speeds that imply large lateral temperature variations in crust and upper mantle of the region. If the ductile portion of the lithosphere were deforming by the mechanisms of high-temperature creep, such temperature variations would be accompanied by variations in strength of 1 or 2 orders of magnitude. The observed velocity profiles allow variations in lithospheric strength by no more than a factor of 2 to 4, implying that the strength-controlling portion of the lithosphere cannot be strongly sensitive to temperature. Lithospheric strength profiles that incorporate flow laws for low-temperature plasticity of olivine reproduce both the effective viscosity and the insensitivity to lateral temperature variation that are observed in the Tien Shan. Plastic deformation of dry, pyroxene-rich lower crust may also contribute to such a temperature-insensitive strength profile. |
| first_indexed | 2024-03-06T20:14:29Z |
| format | Journal article |
| id | oxford-uuid:2bae34be-0cc2-455c-b153-e7ccc6efd95b |
| institution | University of Oxford |
| last_indexed | 2024-03-06T20:14:29Z |
| publishDate | 2015 |
| publisher | Wiley |
| record_format | dspace |
| spelling | oxford-uuid:2bae34be-0cc2-455c-b153-e7ccc6efd95b2022-03-26T12:32:22ZRheology of the lithosphere beneath the central and western Tien ShanJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:2bae34be-0cc2-455c-b153-e7ccc6efd95bSymplectic Elements at OxfordWiley2015England, PMolnar, PThe distribution of crustal velocity over a 800 by 400 km region of the Tien Shan shows strain rates with principal contractional axes aligned perpendicular to the mountain chain and with negligible velocity gradients in the along-strike direction. This configuration allows us to describe the dynamics by a force balance along profiles perpendicular to the chain. The velocities on each of these profiles fit, with root-mean-square misfits of ∼1 mm/yr, a constant rate of contractional strain. Gravitational potential energy per unit area varies along these profiles by at least 3 and maybe 5 TN m−1; the insensitivity of contractional strain rates to those variations implies a lower bound of ∼1022 Pa s on the effective viscosity of the lithosphere. Seismic tomography shows variations in P and S wave speeds that imply large lateral temperature variations in crust and upper mantle of the region. If the ductile portion of the lithosphere were deforming by the mechanisms of high-temperature creep, such temperature variations would be accompanied by variations in strength of 1 or 2 orders of magnitude. The observed velocity profiles allow variations in lithospheric strength by no more than a factor of 2 to 4, implying that the strength-controlling portion of the lithosphere cannot be strongly sensitive to temperature. Lithospheric strength profiles that incorporate flow laws for low-temperature plasticity of olivine reproduce both the effective viscosity and the insensitivity to lateral temperature variation that are observed in the Tien Shan. Plastic deformation of dry, pyroxene-rich lower crust may also contribute to such a temperature-insensitive strength profile. |
| spellingShingle | England, P Molnar, P Rheology of the lithosphere beneath the central and western Tien Shan |
| title | Rheology of the lithosphere beneath the central and western Tien Shan |
| title_full | Rheology of the lithosphere beneath the central and western Tien Shan |
| title_fullStr | Rheology of the lithosphere beneath the central and western Tien Shan |
| title_full_unstemmed | Rheology of the lithosphere beneath the central and western Tien Shan |
| title_short | Rheology of the lithosphere beneath the central and western Tien Shan |
| title_sort | rheology of the lithosphere beneath the central and western tien shan |
| work_keys_str_mv | AT englandp rheologyofthelithospherebeneaththecentralandwesterntienshan AT molnarp rheologyofthelithospherebeneaththecentralandwesterntienshan |