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 melt island arc trench fracture zone MOR earthquakes trench ocean crust continental crust earthquakes magma Mantle Mantle melt sediments, igneous crust & mantle adiabatically rising mantle material

Internal Structure of the Earth.

The Earth is a differentiated Planet

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 Convection (or advection) refers to the transport of heat by motion in a liquid or a gas Thermal Boundary Layer } Conduction Important It is a very efficient means to transport heat Thermal Boundary Layer } Conduction Important

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, 3 rd . edition, 1982)

Heat Convection - Internal Heating Thermal Boundary Layer Convection in the Earth ’ s mantle is driven primarily (80 90%) by internal heating from the decay of long lived radioactive isotopes of potassium, uranium and thorium and not heat loss from the core (10 20%).

The pattern of convection for internal heating is different from bottom heating. Broad Region of Diffuse Upwelling

cont.

crust Many Aspects Mantle Convection in the Earth are Still Incompletely Understood volcanic island chain ocean crust mid-ocean ridge trench island arc 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