Earth Structure. obvious from space that Earth has two fundamentally different physiographic...
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Earth Structure
Earth Structure. obvious from space that Earth has two fundamentally different physiographic features: oceans (71%) and continents (29%) global topography
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
Slide 3
Earths Plates
Slide 4
MORB Genesis
Slide 5
Submarine Pillow Basalt Formation
Slide 6
Volumes of Igneous Rocks on Earth
Slide 7
Convergent Margin Magma Genesis
Slide 8
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
Slide 9
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
Slide 10
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.
Slide 11
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.
Slide 12
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.
Slide 13
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!
Slide 14
Convection Examples
Slide 15
Slide 16
Rayleigh-Bernard Convection
Slide 17
Convection in the Mantle
Slide 18
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
Slide 19
From: "Dynamic models of Tectonic Plates and Convection" (1994)
by S. Zhong and M. Gurnis
Slide 20
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
Slide 21
example from western US all from:
http://www.geo.lsa.umich.edu/~crlb/COURSES/270
Slide 22
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
!
Slide 23
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
Slide 24
Rates of Heat Production and Half-lives
Slide 25
Heat Production through Earth History
Slide 26
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
Slide 27
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
Slide 28
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