HR: 11:20h
AN: U42A-05    [Abstracts]
TI: Integrating Full Three-dimensional Mantle Circulation Models with Lithospheric Deformation Models
AU: * Holt, W
EM: william.holt@sunysb.edu
AF: Department of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11794, United States
AU: Ghosh, A
EM: aghosh@mantle.geo.sunysb.edu
AF: Department of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11794, United States
AU: Wen, L
EM: lianxing.wen@sunysb.edu
AF: Department of Geosciences, SUNY at Stony Brook, Stony Brook, NY 11794, United States
AU: Haines, J
EM: ajh50@cam.ac.uk
AF: Department of Earth Sciences, Cambridge University, Cambridge, CB2-3eQ, United Kingdom
AU: Flesch, L
EM: lmflesch@purdue.edu
AF: Department of Earth and Atmospheric Sciences, Purdue University, 550 Stadium Mall Drive, West Lafayette, IN 47907, United States
AB: Our study provides insight into the lithosphere-mantle coupling problem through joint modeling of lithosphere dynamics and three dimensional mantle circulation. We use the global lithospheric stress field as well as plate motions in order to infer the nature of coupling between the lithosphere and the mantle. There are two types of stresses acting on the Earth's lithosphere, (1) internal buoyancy forces arising from lateral density variations within the lithosphere and (2) basal tractions associated with mantle convection that gets coupled to the base of the lithosphere. The relative contribution of these stresses vary laterally depending on the viscosity of the asthenosphere. Lateral viscosity variation arises through various factors, such as, presence of continental keels below Archaean shields, temperature differences in the oceans due to cooling of old oceanic lithosphere, as well as presence of weak, deforming plate boundary zones. We incorporate laterally variable viscosities within the asthenosphere in our mantle convection model and compute the global lithospheric stress field response to the traction distribution. The lithosphere response is computed using a thin-shell method with lateral viscosity variations, internal density buoyancy variations, and applied basal traction distributions computed from mantle circulation models. The modeled total deviatoric stress field is scored with deformation indicators from the Global Strain Rate Map (GSRM), which is constrained using over 5000 GPS velocity vectors. We also compare the predicted plate motions generated by the convection model with observed plate velocities. Based on such a combination of matching plate velocities and deformation indicators we are able to eliminate certain models and the joint criteria enable us to significantly narrow down the range of possible models that fit the observations. We also employ an inverse method and directly solve for the distribution of basal tractions that yields a best-fit lithospheric response that is scored with the GSRM. We define the deviatoric stresses associated with the global distribution of basal tractions using a spherical harmonic expansion out to degree and order 9, and solve for the coefficients of this series in a least-squares inversion. The best-fit solution suggests roughly equal contributions of lithospheric stress associated with GPE differences and basal tractions associated with mantle circulation. Moreover, the best-fit model shows traction distributions that are similar to our best-fit mantle convection model. In both the inverse and forward models, zones of mantle downwelling, most likely associated with the history of subduction, play a prominent role for North and South America, and central Asia.
DE: 7218 Lithosphere (1236)
DE: 8110 Continental tectonics: general (0905)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8160 Rheology: general (1236, 8032)
SC: Union [U]
MN: 2007 Joint Assembly