Class 1. Earth Structure and Plate Tectonics William Wilcock OCEAN/ESS 410

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

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

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 1.Radioactivity (U, Th, K isotopes) 2.Solidification of Inner Core Heat Lost from the Earth by 1.Mantle Convection

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 } Conduction Important Conduction Important } Convection Important Heat Convection - Heating From Below Thermal Boundary Layer Upwelling Plume Downwelling Plume

A simplistic model of mantle convection and plate tectonics (figure from Earth by F. Press and R. Siever, 3 rd. edition, 1982) 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.

Heat Convection - Internal Heating 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. Thermal Boundary Layer Downwelling Plume Broad Region of Diffuse Upwelling

volcanic island chain mid-ocean ridge trench island arc cont. crust ocean crust from Kellogg et al., 1999 Many Aspects Mantle Convection in the Earth are Still Incompletely Understood

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