Plate boundary interactions separating coming together sliding past one another Plate boundary interactions

Plates slide past each other – side by side, or up and down Creates faults and earthquakes rift valley ridge ridge transform boundaries

San Andreas - a strike-slip fault 1906 earthquake Animation index San Andreas - a strike-slip fault

30mya A zone of faults, rather than a single ‘edge’

Heading NW past Santa Cruz North through the Carrizzo Plain (central coast) Heading NW past Santa Cruz Mussel Rock Heading to Sea Gulf of CA

Sea floor spreading center: what boundaries are present? divergent transform divergent Sea floor spreading center: what boundaries are present?

Ex: Mid-Atlantic ocean ridge

What boundaries are present? Convergent subduction convergent divergent What boundaries are present?

Related topic: HOT SPOTS Time 1 Time 2 As plate moves, volcano disconnects from plume, new volcano forms plate magma source A volcanic "hotspot" is an area in the mantle from which heat rises as a thermal plume from deep in the Earth. High heat and lower pressure at the base of the lithosphere (tectonic plate) facilitates melting of the rock. This melt, called magma, rises through cracks and erupts to form volcanoes. As the tectonic plate moves over the stationary hot spot, the volcanoes are rafted away and new ones form in their place. This results in chains of volcanoes, such as the Hawaiian Islands. Related topic: HOT SPOTS

Hawaiian islands Idaho Wyoming Nevada HOT SPOTS Hot spot index

Related topic: SEA FLOOR SPREADING RECALL: Outer core is molten, contains metals, which circulate, creating Earth’s magnetosphere Thus, like a magnet, Earth has two poles N is normal (current) polarity S is reversed polarity the core is made up of iron and nickel which are both magnetic, however at 5000°c it's not quite like a bar magnet that we're used to in the science lab. The outer core is molten and the convection currents are thought to act like a giant dynamo which produces electricity and induces the Earth's magnetic field. What is interesting is that the poles keep flipping every couple of million years, so north does indeed become south. These rocks contain minerals that are magnetic. One such mineral is called magnetite. If magnetite is heated over 500°c (called its Curie temperature) it loses its magnetism. So the magma pouring out at the ridge will not be magnetic until it cools to form new Basalt. The key point is that when magnetite is cooled it once again becomes magnetic (a phenomena called remanent magnetism). Detailed study of the sea floor with magnometers (devices which measure magnetism) gave some amazing results. The zebra like pattern below is what a segment of ocean crust actually looks like (in magnetism terms that is). The pattern was centered along, and symmetrical to, the mid-ocean ridge. :- Related topic: SEA FLOOR SPREADING

Iron-rich minerals – i. e Iron-rich minerals – i.e. magnetite - in rocks are magnetized by Earth’s magnetosphere In magma temperatures > 500C, magnetite loses its magnetism. As the magma cools, the magnetite aligns with the Earths current field, forming a permanent record of the polarity of the Earth at that point in time the core is made up of iron and nickel which are both magnetic, however at 5000°c it's not quite like a bar magnet that we're used to in the science lab. The outer core is molten and the convection currents are thought to act like a giant dynamo which produces electricity and induces the Earth's magnetic field. What is interesting is that the poles keep flipping every couple of million years, so north does indeed become south. These rocks contain minerals that are magnetic. One such mineral is called magnetite. If magnetite is heated over 500°c (called its Curie temperature) it loses its magnetism. So the magma pouring out at the ridge will not be magnetic until it cools to form new Basalt. The key point is that when magnetite is cooled it once again becomes magnetic (a phenomena called remanent magnetism). Detailed study of the sea floor with magnometers (devices which measure magnetism) gave some amazing results. The zebra like pattern below is what a segment of ocean crust actually looks like (in magnetism terms that is). The pattern was centered along, and symmetrical to, the mid-ocean ridge. :- SEA FLOOR SPREADING

SEA FLOOR SPREADING Oldest deposits Oldest deposits Today graph of intensity and polarity SEA FLOOR SPREADING symmetric about a rift zone

The sea floor is a record of earths history for the last 180my Provides evidence for… oldest youngest oldest • sea floor spreading N S N S • relative ages of sea floor deposits • magnetic reversal N! • moving landmasses N? N? SO WHAT?