lithosphere

lithospheric strength profile

rep of how rock strength varies w/ depth in lithosphere

general trend seen in lithospheric strength w/ depth

rocks transition from brittle behavior near surface to ductile behavior at depth

‘jelly sandwich’ model

continental lithosphere strong upper crust, weak lower crust, strong upper mantle

why is upper crust strong in continental lithosphere

cold & deforms by brittle fracturing & faulting

why is lower continental crust weak

higher temps allow ductile deformation in minerals

why is lithospheric mantle

high confining pressure increases strength despite high temps

how does oceanic lithosphere differ from continental in strength profile

simpler, more uniform, lacks pronounced weak lower crust

aging oceanic lithospheric

cools, thickens, strengthens

what type of rocks dominate oceanic crust

mafic rocks like basalt & gabbro

at what depth does brittle-ductile transition typically occur in continental crust

~ 10-20 km, varies w/ geothermal gradient

how does pressure influence deformation

increasing suppresses fracturing & promotes ductile flow

what is confining pressure

pressure applied = in all directions, prevents rocks from fracturing

what processes do fluids enhance in rocks

pressure solution & metamorphic reactions

how does strain rate affect deformation

high strain rate - brittle behavior, low strain rate - ductile

why do rocks become more ductile at low strain rates

minerals have more time to deform & flow

how does rock composition influence deformation

silica rich felsic are weaker, mafic rocks stronger

what deformation mechanisms occur in ductile conditions

crystal plasticity & diffusion creep