Module 6: Earth's Properties, Geologic Processes & Plate Tectonics

crust

earth’s outermost solid layer

mantle

thick layer of silicate rock between the crust and core

core

earth’s central region, composed mainly of iron and nickel

continental crust

thicker, less dense crust, generally felsic in composition

oceanic crust

thinner, denser crust, generally mafic in composition

lithosphere

rigid outer layer consisting of teh crust and uppermost mantle

asthenosphere

weak, slowly flowing region of the upper mantle beneath the lithosphere

outer core

liquid metallic layer surrounding the inner core

inner core

solid central part of earth’s core

mantle convection

slow movement of mantle material driven by temperature and density differences

geothermal gradient

rate at which earth’s temperature increases with depth

seismic waves

energy waves travelling through earth, commonly generated by earthquakes

P-waves

compressional seismic waves that travel through solids AND liquids

S-waves

shear seismic waves that travel through solids, but NOT liquids

earth’s magnetic field

magnetic field generated mainly by motion of conducting liquid metal in the outer core

isostasy

gravitational balance of earth’s lithosphere over the underlying mantle

buoyancy

upward force exerted by a fluid on an immersed object

density

mass per unit volume

subsidence

downward movement or sinking of earth’s crust

uplift

upward movement of earth’s crust

isostatic rebound

uplift caused by removal of weight from the crust

plate tectonics

movement and interaction of rigid lithospheric plates over the asthenosphere

tectonic plate

large, rigid section of earth’s lithosphere

continential drift

hypothesis that continents move relative to one another over geologic time

pangaea

ancient supercontinent containing most of earth’s landmasses

seafloor spreading

formation of new oceanic crust at mid-ocean ridges

divergent boundary

boundary where two tectonic plates move apart

convergent boundary

boundary where two tectonic plates move toward each other

transform boundary

boundary where two tectonic plates slide horizontally past each other

subduction

sinking of one tectonic plate beneath another into the mantle

mid-ocean ridge

underwater mountain chain where new oceanic crust forms

continental rift

region where continental crust stretches and separates

ocean trench

deep depression commonly formed where oceanic lithosphere subducts

volcanic island arc

chain of volcanic islands formed above an ocean-ocean subduction zone

continental volcanic arc

chain of volcanoes on a continent above a subduction zone

orogeny

process of mountain building, commonly associated with plate convergence

orogen

mountain belt formed by tectonic processes

hotspot

localized region of volcanism associated with an underlying magma source

mantle plume

upwelling of unusually hot mantle material

wilson cycle

cycle of continental rifting, ocean opening, subduction, and continental collision

triple junction

location where 3 plate boundaries meet

stress

force per unit area acting on rock

strain

deformation produces in response to stress

compression

stress that squeezes rocks together

tension

stress that pulls rocks apart

shear

stress that causes rocks to slide past each other

brittle deformation

rock deformation involving fracturing or faulting

ductile deformation

rock deformation involving bending or flowing without breaking

fault

fracture along which rock movement has occurred

joint

fracture in rock without significant displacement

fold

bend in originally planar rock layers

normal fault

fault where the hanging wall moves downward relative to the footwall

reverse fault

fault where the hanging wall moves upward relative to the footwall

strike-slip fault

fault with predominantly horizontal displacement

graben

down-dropped crustal block bounded by faults

anticline

fold that arches upward, with older rocks generally in its core

syncline

fold that bends downward, with younger rocks generally in its core