Transcript Earth Structure and Plate Tectonics

OCEAN/ESS 410
Class 1. Earth Structure and
Plate Tectonics
William Wilcock
Lecture/Lab Learning Goals
• Know and be able to sketch the basic structure of the
Earth (crust, lower/upper mantle, core).
• Be able to describe the process of planetary
differentiation
• Be able to define plate tectonic theory and the three
types of plate boundary
• Understand the linkages between plate tectonics and
mantle convection
• Be able to identify tectonic features on a global scale
map of topography/bathymetry (with or without
seismicity) – LAB 1
• Compare topography on Earth with other planets and
interpret differences in tectonics – LAB 2
Plate Tectonics
island arc
trench
fracture
zone
trench
MOR
earthquakes
ocean crust
melt
sediments, igneous
crust & mantle
magma
adiabatically rising
mantle material
continental crust
earthquakes
Mantle
Mantle
melt
Internal
Structure
of the
Earth.
The Earth is a
differentiated
Planet
Differentiation
Planetary
Differentiation - early in Earth’s history
Perhaps the most important process a planet goes through
The Earth as a Heat Engine
Heat generated by
1. Radioactivity (U, Th, K isotopes)
2. Solidification of Inner Core
Heat Lost from the Earth by
1. Mantle Convection
Heat Convection - Heating From Below
}
Conduction
Important
}
Conduction
Important
Downwelling Plume
Upwelling Plume
It is a very
efficient means
to transport
heat
Thermal Boundary Layer
Convection Important
Convection (or
advection)
refers to the
transport of
heat by motion
in a liquid or a
gas
Thermal Boundary Layer
A simplistic model of mantle
convection and plate tectonics
You will commonly
see mantle
convection depicted
in a simple manner,
similar to this figure.
This depiction is
reasonable at
subduction zones but
wrong at mid-ocean
ridges.
(figure from Earth by F. Press and R. Siever, 3rd. edition, 1982)
Heat Convection - Internal Heating
Thermal Boundary Layer
Broad Region of
Diffuse Upwelling
Downwelling Plume
Convection in the
Earth’s mantle is
driven primarily (8090%) by internal
heating from the
decay of long lived
radioactive isotopes
of potassium,
uranium and thorium
and not heat loss
from the core (1020%).
The pattern of
convection for
internal heating is
different from bottom
heating.
Many Aspects Mantle Convection in the
Earth are Still Incompletely Understood
volcanic island chain
trench
ocean crust
mid-ocean ridge
island arc
cont.
crust
from Kellogg et al., 1999
Global Bathymetry
Sandwell and Smith
Plate Tectonic Theory
The Earth’s surface is made up of a number of a small
number of rigid plates that move relative to one
another. Deformation near the Earth’s surface is
concentrated along the boundaries. Plates boundaries
may be sites of
•Divergence - oceanic spreading centers and rifts
•Convergence - subduction zones and regions of
continental collision
•Motions that are orthogonal to the plate boundary transform faults.
Tectonic Plates