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Physical properties

This lecture covers topics such as densities of solids and liquids, Vp, Vs, and Poisson ratio, as well as heat production and geotherms. Learn how to calculate phase chemistry and explore the relationship between heat productivity and heat flux. Use various tools and parameters to determine the physical properties of rocks and compare them to seismic data. Consider crustal architecture using constraints like isostasy and gravity.

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Physical properties

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  1. Physical properties Geos 408/508 Lec 11

  2. What matters • Densities of solids and liquids • Vp, Vs, Poisson ratio • Heat production and geotherms

  3. How to get the norms • Use MELTS supp calc to go from phase chemistry in oxides to rel props of fo/fa dy/hed etc; • Point count modes • Make sure stuff adds up to 100

  4. Use the Lee parametrization for garnet peridotites (STP)

  5. Densities • For solid densities, use Hacker and Abers • For liquid, either IgPet (under extra params) or MELTS

  6. Heat flow, heat production • Flux (flow) - measured on the ground or in borehole • Production - measured in rocks

  7. Use Brady excel file for production • Need the depth of sample - barometry etc • Need K, U and Th concentrations • The sum of their production equals the heat production

  8. Heat productivity vs. heat flux relationship The crust is highly concentrated in radioactive elements such as Uranium. As Uranium decays it makes heat which is termed the heat productivity in micro-Watts per unit volume units. By measuring the surface rock heat productivity, a linear relation between heat productivity and heat flux is often found. This mean the upper crustal rocks heat production controls the heat flux. The y-intercept value is the reduced heat flow (qr ) which is from the mantle.

  9. Temperature re-equilibration Adding sediments quickly to the top of the crust, causes a thermal disequilibrium that will be brought to thermal equilibrium over Ma time-scales. Thrusting 20 km of the upper crust over the surrounding surface quickly, creates a disequilibrium that takes greater than 50 Ma to reach thermal equilibrium.

  10. Finally • Calculate all your phys pros at T and P; • Compare against seismic data; • Double check possible crustal architecture arrangements using the following constraints: isostasy gravity

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