The structure, stability, and potential instability of ancient continental 的结构，稳定性，和古大陆的潜在不稳定性.ppt

Geologic Time Past Present Future Craton Yield Stress (Mpa) Mantle Stress (Mpa) Reference (dry) Weakened (rehydrated) Mantle Stress Can Increase Over Time Due To Increasing Mantle Viscosity Greater Potential for INSTABILITY in Geologic Present Vs. Ancient Past High Craton Viscosity Leads to Stability in Thick Root Limit. INSTABILITY: Rehydrate to Lower Viscosity High Yield Stress Relative to Ocean Peripheral Continental Lithosphere Leads to Stability INSTABILITY: Lower Yield Stress (water) or No Peripheral Buffer * GLOBAL TOPOGRAPHY CONTINENTAL OCEANIC LITHOSPHERE Age Topography Heat Flow mid ocean ridge mantle CONTINENTAL OCEANIC LITHOSPHERE tectothermal age of plate (ta) mantle heat loss (q ) mantle flow ? t MOR thermal ??????Thermal boundary layer of mantle convection t T T s o t=0 t=0 _ + z T T s o time z Region of T gradient is a Thermal Boundary Layer ? m mantle heat loss (q ) mantle flow MOR thermal ??????Thermal boundary layer of mantle convection t mechanical : Layer of long term strength m ? ? c chemical/mechanical : Dehydrated Layer (dry=hi viscsoity) m ? (cold=hi viscosity) ? t tectothermal age of plate (ta) Oceanic Thermal Lithosphere defines convection pattern - it is the cold, overturning boundary layer. Continental Chemical Lithosphere does not participate in convective mantle overturn (inherently buoyant). Continent Oceanic Chemical Lithosphere subducts - overturning portions of the Earth see a constant temperature boundary condition. Provides a more complex thermal coupling condition for covecting mantle below. “subducting” lithosphere viscosity = 10 Pa s 25 warm mantle viscosity = 10 Pa s 21 hot cold convecting mantle failed region extension failed region compression cratonic root lower crust upper crust bulk mantle local geotherm Cooper et al. 2004 Cooper et al