Class 1. Earth Structure and Plate Tectonics William Wilcock 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 3 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

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

Internal Structure of the Earth. The Earth is a differentiated Planet

Planetary Differentiation - early in Earth’s history

The Earth as a Heat Engine Heat generated by Radioactivity (U, Th, K isotopes) Solidification of Inner Core Heat Lost from the Earth by Mantle Convection

Heat Convection - Heating From Below } Conduction Important Convection (or advection) refers to the transport of heat by motion in a liquid or a gas It is a very efficient means to transport heat Thermal Boundary Layer Upwelling Plume Downwelling Plume Convection Important 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 not very accurate at mid-ocean ridges. (figure from Earth by F. Press and R. Siever, 3rd. 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 Downwelling Plume

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