2Next Journal Article Reading: For Monday Oct 13: Watts & Burov (2003)Lithospheric strength and its relationshipto the elastic and seismogenic layerthicknesses. Earth Planet. Sci. Lett.213(1-2)(Xiaofei will prep discussion materials)
3Laboratory studies & mineral physics suggest two dominant “flavors” of non-recoverable strain:(1) Linear viscoelastic creep: “Diffusion”where viscosityHere:R = gas constantT = temperature Ea = activation energyP = pressure Va = activation volumed = grain diameter D0 = frequency factorm = 2 in crystal interiors (rock mat’l prop’s)3 on crystal boundaries
4Laboratory studies & mineral physics suggest two dominant “flavors” of non-recoverable strain:(2) Nonlinear Viscoelastic:“Dislocation creep”where effective viscosityHere:R = gas constantT = temperatureP = pressure Ea = activation energyb = dislocation density Va = activation volumen ~ D0 = frequency factor = shear modulus (rock mat’l prop’s)Edge dislocationScrew dislocation
5Laboratory studies of rock strain use roughly the same equations as those derived from first principles in mineralphysics, but collapse them to observable constant paramsdepends on:• Lithology(pyroxene > olivine > feldspar > quartz)• Water fugacity fH2O• Temperature T(and to a lesser extent)• Strain rate • Grain size d• Pressure P.Ideally, we would like to use geophysics todetermine each in situ! But it’s not so simple.
7Moho temperature TMoho from Pn phase: Pn velocity variationMoho temperature fromPn & mineral physicsBuehler & Shearer, JGR 2010Schutt et al., Geology in prep
8Wait… What? Temp under ND > NV-UT? Moho temperature fromPn & mineral physics(Partly, but not entirely,because the Moho isdeeper in the stable partof the continent…)Schutt et al., Geology in prep
9Dry Wet These temperatures are sufficiently high to ensure lower crustal flow forall likely crustallithologies,wet or dry…Viscosity isvery sensitivealso to lithology& water!PyroxeneFeldsparQuartz10191022