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Earth Structure

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obvious from space that Earth has two fundamentally different physiographic features: oceans (71%) and continents (29%) global topography from: http://www.personal.umich.edu/~vdpluijm/gs205.html crust

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Earths Plates

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MORB Genesis

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Submarine Pillow Basalt Formation

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Volumes of Igneous Rocks on Earth

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Convergent Margin Magma Genesis

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Forms of Energy Energy: commonly defined as the capacity to do work (i.e. by system on its surroundings); comes in many forms Work: defined as the product of a force (F) times times a displacement acting over a distance (d) in the direction parallel to the force work = Force x distance Example: Pressure-Volume work in volcanic systems. Pressure = Force/Area; Volume=Area x distance; PV =( F/A)(A*d) = F*d = w

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Forms of Energy Kinetic energy: associated with the motion of a body; a body with mass (m) moving with velocity (v) has kinetic energy E (k) = 1/2 mass * velocity 2 Potential energy: energy of position; is considered potential in the sense that it can be converted or transformed into kinetic energy. Can be equated with the amount of work required to move a body from one position to another within a potential field (e.g. Earths gravitational field). E (p) = mass * g * Z where g = acceleration of gravity at the surface (9.8 m/s 2 ) and Z is the elevation measured from some reference datum

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Forms of Energy (cont.) Chemical energy: energy bound up within chemical bonds; can be released through chemical reactions Thermal energy: related to the kinetic energy of the atomic particles within a body (solid, liquid, or gas). Motion of particles increases with higher temperature. Heat is transferred thermal energy that results because of a difference in temperature between bodies. Heat flows from higher T to lower T and will always result in the temperatures becoming equal at equilibrium.

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Heat Flow on Earth An increment of heat, q, transferred into a body produces a Proportional incremental rise in temperature, T, given by q = Cp * T where Cp is called the molar heat capacity of J/mol-degree at constant pressure; similar to specific heat, which is based on mass (J/g-degree). 1 calorie = 4.184 J and is equivalent to the energy necessary to raise 1 gram of of water 1 degree centigrade. Specific heat of water is 1 cal/gC, where rocks are ~0.3 cal/gC.

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Heat Transfer Mechanisms Radiation: involves emission of EM energy from the surface of hot body into the transparent cooler surroundings. Not important in cool rocks, but increasingly important at Ts >1200C Advection: involves flow of a liquid through openings in a rock whose T is different from the fluid (mass flux). Important near Earths surface due to fractured nature of crust. Conduction: transfer of kinetic energy by atomic vibration. Cannot occur in a vacuum. For a given volume, heat is conducted away faster if the enclosing surface area is larger. Convection: movement of material having contrasting Ts from one place to another. T differences give rise to density differences. In a gravitational field, higher density (generally colder) materials sink.

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Magmatic Examples of Heat Transfer Thermal Gradient T between adjacent hotter and cooler masses Heat Flux = rate at which heat is conducted over time from a unit surface area Heat Flux = Thermal Conductivity * T Thermal Conductivity = K; rocks have very low values and thus deep heat has been retained!

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Convection Examples

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Rayleigh-Bernard Convection

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Convection in the Mantle

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convection in the mantle models observed heat flow warmer: near ridges colder: over cratons from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270 from: http://www-personal.umich.edu/~vdpluijm/gs205.html

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From: "Dynamic models of Tectonic Plates and Convection" (1994) by S. Zhong and M. Gurnis

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note continuity of blue slab to depths on order of 670 km blue is high velocity (fast) interpreted as slab from: http://www.pmel.noaa.gov/vents/coax/coax.html examples from western Pacific

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example from western US all from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270

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Earths Geothermal Gradient Approximate Pressure (GPa=10 kbar) Average Heat Flux is 0.09 watt/meter 2 Geothermal gradient = / z C/km in orogenic belts; Cannot remain constant w/depth At 200 km would be 4000C ~7C/km in trenches Viscosity, which measures resistance to flow, of mantle rocks is 10 18 times tar at 24C !

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Earths Energy Budget Solar radiation: 50,000 times greater than all other energy sources; primarily affects the atmosphere and oceans, but can cause changes in the solid earth through momentum transfer from the outer fluid envelope to the interior Radioactive decay: 238 U, 235 U, 232 Th, 40 K, and 87 Rb all have t 1/2 that >10 9 years and thus continue to produce significant heat in the interior; this may equal 50 to 100% of the total heat production for the Earth. Extinct short-lived radioactive elements such as 26 Al were important during the very early Earth. Tidal Heating: Earth-Sun-Moon interaction; much smaller than radioactive decay Primordial Heat: Also known as accretionary heat; conversion of kinetic energy of accumulating planetismals to heat. Core Formation: Initial heating from short-lived radioisotopes and accretionary heat caused widespread interior melting (Magma Ocean) and additional heat was released when Fe sank toward the center and formed the core

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Rates of Heat Production and Half-lives

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Heat Production through Earth History

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Gravity, Pressure, and the Geobaric Gradient Geobaric gradient defined similarly to geothermal gradient: P/ z; in the interior this is related to the overburden of the overlying rocks and is referred to as lithostatic pressure gradient. SI unit of pressure is the pascal, Pa and 1 bar (~1 atmosphere) = 10 5 Pa Pressure = Force / Area and Force = mass * acceleration P = F/A = (m*g)/A and (density) = mass/volume

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Earth Interior Pressures P = Vg/A = gz, if we integrate from the surface to some depth z and take positive downward we get P/ z = g Rock densities range from 2.7 (crust) to 3.3 g/cm 3 (mantle) 270 bar/km for the crust and 330 bar/km for the mantle At the base of the crust, say at 30 km depth, the lithostatic pressure would be 8100 bars = 8.1 kbar = 0.81 GPa

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Changing States of Geologic Systems System: a part of the universe set aside for study or discussion Surroundings: the remainder of the universe State: particular conditions defining the energy state of the system

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Definitions of Equilibrium