Intraplate lithosphere deformation and the strength of the lithosphere

Abstract

Summary The intraplate deformation of continental lithosphere in response to applied stress has been investigated using a mathematical model which incorporates the elastic, ductile and brittle response of lithosphere material. Ductile deformation is assumed to be controlled in the crust by dislocation creep in quartz, and in the mantle by dislocation creep and plasticity in olivine. Brittle failure is predicted using modified Griffith theory. A fundamental feature of the model is the redistribution of stress within the lithosphere following stress release by both ductile and brittle deformation. This redistribution produces high levels of stress in the middle or lower crust immediately above the elastic‐ductile or brittle‐ductile transition. Lithosphere deformation is shown to be critically dependent on the temperature structure of which surface heat flow is a convenient indicator. For higher geothermal gradients, the release of stress in the lower lithosphere by ductile deformation is more rapid and complete and results in large stress levels in the upper lithosphere. For sufficiently large applied stresses or steep geothermal gradients, the stress levels in the upper and middle crust will cause complete fracture of the upper lithosphere. Whole lithosphere failure (WLF) then results, by continued brittle and ductile deformation, causing geologically significant strains. The critical value of applied stress required to give WLF has been calculated for both tensional and compressional deformation as a function of surface heat flow. The predicted lithosphere bulk strength is then compared with expected levels of intraplate stress arising from plate boundary forces and isostatically compensated loads, which are thought to give net stress levels in the continental lithosphere in the range +0.25 to ‐0.25 kB. Using these expected maximum stress levels, the model predicts significant extensional deformation in regions of moderate heat flow with q > c. 60mW m‐2 (e.g. Central Europe) as well as for areas of high heat flow like the Basin‐ and‐Range Province. Significant compressional deformation is predicted for areas of high heat flow with q > c. 75 mWm‐2 but only for restricted conditions of stress combination. These results are in good agreement with the observed rather widespread incidence of extensional intraplate deformation and the restricted occurrence of compressional deformation which may be confined to areas of unusually high heat flow or weak crust. The model may also be used to calculate the depth of the brittle‐ductile transition which is shown to become shallower with increase in heat flow, in good agreement with seismic evidence.

Thermal and mechanical structure of the central Iberian Peninsula lithosphere

“…Here, total lithospheric strength exceeds 2.5Â10 12 N m À1 , except for wet rocks in tension. For a lithosphere 100 km thick, this value is equivalent to a vertically averaged horizontal stress of the order of 25 MPa, assumed to be the upper threshold for deformation of the lithosphere (Kusznir and Park, 1984). From calculated total lithospheric strength values, it can be inferred that for wet rocks in tension and compression, the Tajo Basin and Central System are liable to fail; decreasing to 1.5Â10 12 N m À1 for wet rocks in tension.…”

Crustal-scale pop-up structure in cratonic lithosphere: DOBRE deep seismic reflection study of the Donbas fold belt, Ukraine

“…earlier. However, bulk rheological models of the lithosphere generally predict thermal weakening as a precondition of whole lithospheric failure, given conventionally adopted rheological parameters and intraplate forces (e.g., Kusznir and Park, 1984). The association of a mega-pop-up structure with this inverted intracratonic basin, however, implies brittle deformation of relatively cold crust.…”

Interpretación De Los Sismos Pequeños Y Moderados Bajo El Volcán Irazú

“…La influencia de un cuerpo magmático adelgaza la litósfera, la cual se vuelve más caliente y por lo tanto más débil (Kusznir y Park, 1984). A medida que progresa el afinamiento de la litósfera y de la corteza por ascenso del magma, la zona de transición frágil-dúctil se torna somera (Kusznir y Park, 1987;Reston y Pérez-Gussinyé, 2007).…”