• Crust (lithosphere): 22 miles of SOLID rock (thinner on ocean floor)• Mantle: 2,220 miles of SEMI-SOLID rock (thick, molten magma)
• Outer core: 1,400 miles of LIQUID iron and nickel• Inner core: SOLID iron-nickel alloy (750 miles across, 3,200 mi. deep)
Pangaea• a theoretical, single super-continent• developed by Alfred Wegener• widely accepted since the 1960s• assumes the presence of 12 or so rigid tectonic "plates"• assumes rate of continental drift has always
Evidence for Pangaea• continents seem to fit together like pieces of a jigsaw puzzle• similar rock types and landforms found on different continents• similar plant and animal fossils that date to the same age found on separate modern-day continents
Tectonic Plate Theory • Earths crust divided into 14 major "plates" – continents are embedded in these sections of crustSeismic Activity • Plates "float" above Earths semi-solid mantle • Evidence supplied by: – worldwide seismology • earthquakes • volcanic eruptions – magnetic stratigraphy – deep sea exploration – satellite imagery
Earthquakes: Rapid sliding of earths crust along fault lines as pressure is released Google Earth Volcanism: themovement of magma onto Earths surface
Tectonic Plate Boundaries
Why Do Tectonic Plates Move?• Convection currents in the mantle below move plates – hot = less dense (rises up) – cool = denser atomic structure (sinks down)• Plates move at a rate of about 1 - 6 cm per year
What Occurs at Plate Boundaries?• Mountain building & trench formation• Volcanism• Earthquakes• Metamorphism & destruction of crust• Crust formation at ocean floor rifts
Tectonic Earthquakes• The edges of a fault (walls of rock) are stuck together.• As each tectonic plate slowly moves, pressure builds up at fault lines.• When the force of the moving plates overcomes the friction of the jagged edges of the fault, it rapidly gives way (slips), releasing the pressure as compression waves.
Fault Lines• A fault is a large crack in the Earths crust where one section of crust moves against another, releasing pressure built-up by moving tectonic plates. • Normal – the hanging wall (the block of rock positioned above the plane) pushes down across the footwall, (the block of rock below the plane) • Reverse – hanging wall pushes up, footwall pushes down (thrust fault) • Strike-slip – walls of rock move in opposite horizontal directions
Normal Reverse (thrust) fault fault
Earthquakes under the Ocean• Tsunamis (tidal waves) result when a large section of the sea floor suddenly moves and therefore displaces a massive amount of water.
Tectonic Plate Movement• Transform: plates slide alongside each other• Divergent: plates move away from each other• Convergent: plates move toward one another
Divergent Boundaries• Plates are rifted apart, creating large expanses of oceanic crust• Crust is created in rift zones as rising magma is cooled by seawater• Volcanism• Normal faulted cliffs
Convergent Boundaries• One plate is pushed down under another plate• Crust is destroyed as its pushed down into the mantle (called subduction zones) – Ocean-continent & Ocean-ocean arc – Continental collision• Metamorphism• Volcanism• Sedimentary wedges• Reverse faulted mountains
Metamorphism• An experiment using wax layers shows how rock layers tend to bend and fold before they break.
Transform Boundaries• Plates slide past one another with no loss or creation of crust.• Not as common as convergent and divergent boundaries. • Shearing metamorphism • Occasional igneous intrusions • Strike-slip earthquakes
San Andreas Fault
Uplift and Erosion • The movement of Earth’s tectonic plates can cause a lifting up of previously buried rock layers.• Uplift simply moves the strata, allowing for erosion to expose formerly buried layers.• Without uplift (& volcanism), the earths surface might eventually become completely smooth and flat and entirely covered with water.
In Conclusion…• The rock cycle demonstrates the relationships among the three major rock groups• It is powered by the interior heat of the Earth• As well as earth’s gravitational forces and…• The energy from the sun• It involves processes on the Earth’s surface as well as the Earth’s interior• It connects the “hydrologic cycle” with the “tectonic cycle”.
Week 18 Lab Rock Identification
Identifying Minerals• Color: extremely variable, complex causes• Hardness: strength of atomic bonds• Density: mass and spacing of atoms• Luster: how electrons interact with light• Crystal Form: useful, but not for beginners• Cleavage: weak atomic planes• Other properties distinctive at times
The Crystal Classes
Crystal Form and Cleavage• How minerals break apart gives a clue to what type of crystal shapes are present in the rock.
Identification by Geologic Setting• Some minerals occur in all geologic settings – quartz, feldspar, pyrite• Mostly sedimentary: – calcite, dolomite• Primarily igneous: – olivine• Metamorphic settings – garnet, kyanite
Other Methods of IdentificationSpecial Properties• Taste, Magnetism, Etc.Experience and Reading• “The best geologist is the one who’s seen the most rocks.”Professional Methods• Chemical Analysis• X-Ray Studies