The jelly sandwich model describes the continental lithosphere's strength profile with a strong upper crust and mantle
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Peer-reviewed literature describes the jelly sandwich model of the continental lithosphere as comprising a strong upper crust and a strong mantle lithosphere.
Abstract Geodynamical models investigate the rheological and physical properties of the lithosphere that peels back (delaminates) from the upper–middle crust. Meanwhile, model predictions are used to relate to a set of observations in the geological context to the test the validity of delamination. Here, we review numerical and analogue models of delamination from these perspectives and provide a number of first-order topics which future modeling studies may address. Models suggest that the presence of the weak lower crust that resides between the strong mantle lithosphere (at least 100 times more viscous/stronger) and the strong upper crust is necessary to develop delamination. Lower crustal weakening may be induced by melt infiltration, shear heating or it naturally occurs through the jelly sandwich type strength profile of the continental lithosphere. The negative buoyancy of the lithosphere required to facilitate the delamination is induced by the pre-existing ocean subduction and/or the lower crustal eclogitization. Surface expression of the peeling back lithosphere has a distinct transient and migratory imprint on the crust, resulting in rapid surface uplift/subsidence, magmatism, heating and shortening/extension. New generation of geodynamical experiments can explain how different types of melting (e.g hydrated, dry melting) occurs with delamination. Reformation of the lithosphere after removal, three dimensional aspects, and the termination of the process are key investigation areas for future research. The robust model predictions, as with other geodynamic modeling studies should be reconciled with observations.
Mechanics of the continental lithosphere require the presence of a high-strength uppermost mantle that defines the “jelly sandwich” model for lithosphere strength layering. However, in deforming regions, growing numbers of geological and geophysical data predict a sub-Moho mantle strength lower than the crustal strength, or a “creme brulee” model. To reconcile these two opposite views of lithosphere strength layering, we account for a new olivine rheology, which could promote some weakening during dynamic grain size reduction that enhances grain boundary sliding. We performed a one-dimensional numerical model of a deforming rock in order to quantify strain localization due to this weakening rheology. Strain localization occurs at temperatures lower than 800 °C and reaches a maximum at 610 °C, increasing the strain rate from 10 −15 to >10 −13 s −1 . These results imply the existence of a sub-Moho ductile localizing mantle on a lithosphere scale, which occurs at Moho temperatures lower than 800 °C. Also, the localizing degree of this ductile mantle increases with decreasing Moho temperatures down to 550 °C. Such a ductile localizing mantle could therefore promote large strain localization during lithosphere deformation, like the brittle mantle that is commonly assumed in the “jelly sandwich” model. Furthermore, the long-term deformation (≥10 6 yr) of the ductile localizing mantle could change the lithosphere strength layering from “jelly sandwich” to “creme brulee” in response to the grain boundary sliding–induced weakening in mantle shear zones.
Stress and strain distributions in the Yakutsk-Vilyui large igneous province (LIP) are numerically simulated under geotectonic extension. A two-dimensional model of the geological structure of a part of the Yakutsk-Vilyui LIP is developed using the geophysical data from the profile “Craton-1980”. However, these geophysical data can only be a source of the geometrical model and elastic properties of Earth’s layers. To describe non-elastic strains during the geological process, the Drucker-Prager-Nikolaevsky model of plasticity is adopted. For elastoplastic analysis of the geotectonic process, the “Jelly Sandwich” shear strength model for the continental lithosphere is used, which is based on the variation of the strength properties with depth. Zones of shear stress concentration and plastic strain localization are observed as a result of the extension in the Lindenskaya basin and Khapchagaiskaya reclamation complying with oil and gas deposit locations in the Yakutia region. Stress components have non-linear distributions determined by the dependence of strength properties on the depth and structural inhomogeneity of continental lithosphere. The pressure distribution obtained in the simulation can partially complement the geological information employed when analyzing the possibility of phase transitions in the rocks in different locations of the studied region.
Computer modeling constrained by positional data collected in the aftermath of the 2008 Wenchuan earthquake indicates the lower crust is less viscous than the upper mantle below it.
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