OCEANESS 410 Class 1 Earth Structure and Plate

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 melt

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

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, 3 rd. 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