Plate Tectonics

Polar wandering

Rocks record apparent movement of the magnetic pole.

Oceanic crust

Primarily mafic igneous rocks (basalts) with a thin layer of sediments derived from continents and from dead marine organisms.

Continental crust

Composed of igneous, metamorphic, and sedimentary rocks, mostly felsic (granites).

Continental Drift

Hypothesis proposed by Alfred Wegener in 1915.

Geometric evidence

Continents align better using continental shelves than modern coastlines.

Fossil evidence

Similar land-dwelling animals and plant distributions across continents.

Paleoclimate evidence

Ice sheets found in tropical areas and coal swamps in temperate regions.

Geological evidence

Similar rock types, structures, and mountain belts across continents.

Rock magnetism

Concept involving normal vs. reversed polarity, polar wandering, and seafloor stripes.

Polar wandering

rocks record apparent movement of the magnetic pole, indicates either that the continents have moved or magnetic north pole has moved over time

Stress

Force applied per unit area.

Strain

Change in shape and/or volume due to applied stress.

Compressional stress

Shortens rock bodies.

Tensional stress

Lengthens rock bodies.

Shear stress

Causes horizontal displacements along faults.

Brittle deformation

Rocks break in response to stress, forming faults.

Ductile deformation

Rocks bend and distort without breaking, forming folds.

Factors that influence the strength of a rock and how it will deform

Due to temperature, confining pressure, strain rate, and rock minerals

Lithosphere

Crust and upper part of the mantle, rigid plates.

Asthenosphere

Weak solid part of the mantle below the lithosphere, allows plate movement.

Oceanic crust

Denser and thinner than continental crust.

Divergent Plate Boundary

Found at mid-ocean ridges, creates new oceanic crust. Associated with tensional stresses, plates move apart.

Convergent Plate Boundary

Associated with compressive stresses, plates collide, one plate is pulled into the mantel and recycled. Oceanic-continental boundaries lead to subduction zones. ex. andes, cascades

Oceanic-oceanic convergence

Older plate subducts, creating volcanic island arcs (e.g., Aleutian Islands).

Continental-continental convergence

Mountain building occurs (e.g., Himalayas).

Transform Fault Boundaries

Associated with shear stresses. Plates slide past each other, no lithosphere created or destroyed (e.g., San Andreas fault).

Seafloor spreading

Occurs at divergent plate boundaries, creating new oceanic crust.

Subduction zones

Found at convergent plate boundaries, associated with oceanic trenches and volcanic activity.

Mid-ocean ridges

Found at divergent plate boundaries.

Age of ocean crust

Youngest at mid-ocean ridges, older further away.

Hot spot

Area with hotter magma beneath the Earth's surface. ex. Hawaiian Islands