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Tectonic overpressure in weak crustal‐scale shear zones and implications for the exhumation of high‐pressure rocks
Author(s) -
Schmalholz Stefan M.,
Podladchikov Yuri Y.
Publication year - 2013
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/grl.50417
Subject(s) - overpressure , geology , shear zone , shear (geology) , shear stress , lithosphere , simple shear , tectonics , overburden pressure , petrology , seismology , geotechnical engineering , mechanics , physics , thermodynamics
Abstract A two‐dimensional numerical simulation of lithospheric shortening shows the formation of a stable crustal‐scale shear zone due to viscous heating. The shear zone thickness is controlled by thermomechanical coupling that is resolved numerically inside the shear zone. Away from the shear zone, lithospheric deformation is dominated by pure shear, and tectonic overpressure (i.e., pressure larger than the lithostatic pressure) is proportional to the deviatoric stress. Inside the shear zone, deformation is dominated by simple shear, and the deviatoric stress decreases due to thermal weakening of the viscosity. To maintain a constant horizontal total stress across the weak shear zone (i.e., horizontal force balance), the pressure in the shear zone increases to compensate the decrease of the deviatoric stress. Tectonic overpressure in the weak shear zone can be significantly larger than the deviatoric stress at the same location. Implications for the geodynamic history of tectonic nappes including high‐pressure/ultrahigh‐pressure rocks are discussed.