2 Next 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)
3 Laboratory 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
4 Laboratory 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
5 Laboratory 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.
7 Moho temperature TMoho from Pn phase: Pn velocity variationMoho temperature fromPn & mineral physicsBuehler & Shearer, JGR 2010Schutt et al., Geology in prep
8 Wait… 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
9 Dry Wet These temperatures are sufficiently high to ensure lower crustal flow forall likely crustallithologies,wet or dry…Viscosity isvery sensitivealso to lithology& water!PyroxeneFeldsparQuartz10191022