Lab 2: Plate Tectonics and the Origin of Magma

 

Introduction:

            Tectonism: large-scale movements and deformation of Earth’s crust and lithosphere

            Lab 1 – understand vertical differences between OC and CC from isostasy

            Horizontal motions of crust are important in determining topography

           

            Plate boundaries: the boundaries that occur between stable sheets or plates of lithosphere

 

            Plate tectonics: new idea in the 1960’s

 

2A: Is Earth’s size increasing, decreasing or staying about the same?

            Is earth’s volume changing? To answer, must investigate earths forces and distributions

 

            Compression – compaction of rock into less space

            Tension / Extension – pulls a rock apart to increase its length

            Shear – smearing of a rock and may result in sliding of blocks past one another

 

2B: What drives plate tectonics?

            According to the Plate Tectonics model, the lithosphere is broken into 12 major plates

            At each plate boundary, plates are forming and spreading, sliding past each other, or

converging

            Convection: circular flow in mantle

            Slab push: magma erupting along plate boundaries push plates apart

            Slab pull: subducting plates pull dense plates back into the mantle

 

            Lava lamp: convection

                        Why is “lava” going from bottom to top and back again

 

2C: The origin of magma

            Magma: melted rock

            Temperature (T)

                  Melting point: the specific temperature at which crystals of a given mineral will melt

                  All minerals have different melting points – partial melting of rocks

                  Geothermal gradient – 25^o C per 1 km

            Pressure (P)

                  Force per unit Area

                  Confining pressure – pressure from surroundings

                        1 atm normally, in water increases every 10 m (34 ft)

                  Pressure confines the atoms and molecules, prevents them from flowing apart

                  Decompression melting – T constant, changing confining pressure

            P-T Diagrams

                  (Draw diagram on board, just OC and CC gradients)

                  Used to relate depth, pressure, temperature and melting

                  Peridotite (mantle rock): liquidus line, solidus line, partial melting and complete

melting zones, decompression melting or increased temperature

2D: Measuring and evaluating plate tectonics

            Hot spots: centers of volcanic activity in a stationary location

                 Plate migrate over these, and can be used to determine rates of plate motion

                 Examples: Hawaii and Yellowstone

            Fault motion: measure displacement of rock types

                 Hazards associated with this displacement