PLATE TECTONICS PLATE BOUNDARIES LAYERS OF THE EARTH

PLATE TECTONICS: PLATE BOUNDARIES

LAYERS OF THE EARTH 1. Crust (brown/tan) 2. Mantle (light & dark orange) 3. Core (yellow & white)

LAYERS OF THE EARTH Lithosphere { Crust and upper mantle make up the LITHOSPHERE § rigid plates (OCEANIC & CONTINENTAL plates) Beneath the lithosphere is the ASTHENOSPHERE § plastic” mantle (flows, moves the plates) § higher temperature & pressure § low temperature & pressure

PLATE TECTONICS the surface of the Earth is made of rigid plates § Size and position of plates can change over time § PLATE BOUNDARIES Edges of plates, where two plates “float” side-by-side, is where geologic activity takes place § Plates movement is from convection currents deep in the mantle

EARTH’S MAJOR PLATES: Pacific, N. American, S. American, African, Eurasian, Indian, Antarctic

CONVECTION CURRENTS MOVE THE PLATES

CONVECTION CURRENTS MOVE THE PLATES This continual movement (called convection currents) causes the crust to move in plate tectonics.

CONVECTION CURRENTS MOVE THE PLATES § Material in the mantle is heated by the radioactive core § it floats to the surface next to the crust § as it cools, it moves back down towards the core 7 c Movement of matter among reservoirs is driven by Earth’s internal and external sources of energy

PLATE BOUNDARIES n Divergent boundaries plates move apart n Convergent boundaries plates move together n Transform boundaries plates slide past

DIVERGENT BOUNDARIES Make new crust When two plates move apart and magma surfaces forming NEW crust (usually oceanic) • continental rift zones (landmass splits into two or more segments) • mid-ocean ridges (sea-floor is elevated)

DIVERGENT BOUNDARIES Make new crust Rift valley continent-continent

DIVERGENT BOUNDARIES Make new crust: Sea Floor Spreading n Youngest rocks form at ridge n Older rocks are further from ridge n Oldest rocks are located at subduction zones

DIVERGENT BOUNDARIES Make new crust: Sea Floor Spreading Every ~20, 000 years the polarity of the Earth changes. This is change is reflected in the rocks, whose polarity is fixed once the magma is cooled. § As magma rises and cools, iron and magnesium minerals align themselves to the Earth’s magnetic field § “Magnetic Stripes” are formed § The Earth’s magnetic field reverses polarity § Magnetic stripes are mirrored on each side of the mid-ocean ridge

CONVERGENT BOUNDARIES plates colliding § Destroys old crust and forms new mountains § Three types of convergent boundaries

CONVERGENT BOUNDARIES plates colliding Continent-continent convergence: Folded mountains Ex Himalayas Eurasian/Indian plates

CONVERGENT BOUNDARIES plates colliding: Subduction Zones n Subduction Zones: where ocean plates slide under another plate n Creates magma which moves upward, pushing up the land above it. n Magma/lava solidifies into intrusive/extrusive igneous rock n Heat from the magma can change the rock around it. Rock that recrystallizes without melting becomes metamorphic rock. . Denser oceanic plates always subduct beneath less dense continental plates

CONVERGENT BOUNDARIES plates colliding Ocean-continent convergence: Trench & Coastal Volcanoes Andes Mountains Nazca & S. American plates

CONVERGENT BOUNDARIES plates colliding Ocean-ocean convergence: Trench & Island arc

TRANSFORM BOUNDARIES When two plates slide past each other § no tearing or crushing - no damage occurs to the lithosphere § Faults –San Andreas Fault § Cause most earthquake damage

Summary of Plate Movements Convection currents