Continental DriftContinental DriftAlfred Wegener (1912)Alfred Wegener (1912) First serious proponentFirst serious proponent

Alfred manning the weather station, Greenland - 1913

Fit of the Continents Fit of the Continents A more modern view than Wegener’s uses 1000 or 2000 m A more modern view than Wegener’s uses 1000 or 2000 m isobath as estimate of edge of continental crustisobath as estimate of edge of continental crust

Fit of Structural Elements Fit of Structural Elements

Pennsylvanian (300 Ma) GlaciationPennsylvanian (300 Ma) Glaciation

Glacial striations in bedrock, South Australia

Pennsylvanian (300 Ma) GlaciationPennsylvanian (300 Ma) Glaciation

Using present continental locations

Arrows indicate ice movement directions

Pennsylvanian (300 Ma) GlaciationPennsylvanian (300 Ma) Glaciation

Using pre-drift continental locations

Arrows indicate ice movement directions

Fossil EvidenceFossil EvidenceGlossopteris: an ancient seed fern(200 Ma)

Distribution of Glossopteris fossils

Fossil EvidenceFossil Evidence

Mesosaurus couldn’t swim in open ocean

Distribution of Mesosaurus fossils

PaleomagnetismPaleomagnetismThe Earth as a dipoleThe Earth as a dipole

Magnetic declination and inclination

PaleomagnetismPaleomagnetismMagnetization of volcanic rocks and sedimentsMagnetization of volcanic rocks and sediments

PaleomagnetismPaleomagnetism

““Polar Wandering” curvesPolar Wandering” curves

2) The Earth’s Interior2) The Earth’s Interior

Miles from ridge axis

Plate Tectonics: a breakthroughPlate Tectonics: a breakthroughBrian Mason (Scripps) led a group that studied a 2-D area spanning

the Mid-Atlantic Ridge in detail

An explanation of the An explanation of the curious magnetic anomaly curious magnetic anomaly patternpattern

The process at mid-ocean ridges

The process at mid-ocean ridges

Black SmokersBlack Smokers

SeismicitySeismicityEarthquakes occur due to motion along faultsEarthquakes occur due to motion along faults

Dip-slip FaultsDip-slip Faults

Normal FaultNormal Fault Reverse Fault (thrust) Reverse Fault (thrust)

View is cross-section

SeismicitySeismicity

Earthquakes occur due to motion along faultsEarthquakes occur due to motion along faults

Strike-slip FaultsStrike-slip Faults

Right-LateralRight-Lateral Left-Lateral Left-Lateral

Map View

Seismicity: global distribution of earthquakesSeismicity: global distribution of earthquakes

Earthquake foci in the vicinity Earthquake foci in the vicinity of the Japan trenchof the Japan trench

SeismicitySeismicityFirst motion studies

Bomb

SeismicitySeismicityFirst motion studies

Earthquake

SeismicitySeismicityFirst motion studies tell us that earthquakes:First motion studies tell us that earthquakes: At ridges At ridges normal faults (extension) normal faults (extension) At trenches At trenches thrust faults (compression) thrust faults (compression) At fracture zones At fracture zones strike-slip faults strike-slip faults

Seismicity: global distribution of earthquakesSeismicity: global distribution of earthquakes

The Deep-Sea Drilling The Deep-Sea Drilling ProgramProgram

Sediment ages directly on crustSediment ages directly on crust

Age of the ocean crustAge of the ocean crust

Hot Spots Hot Spots

Hot Spots Hot Spots

Hot Spots Hot Spots

The Modern PlatesThe Modern Plates

Three types of plate boundariesThree types of plate boundaries

Three types of plate boundariesThree types of plate boundaries

Divergent boundaryDivergent boundary

Divergent boundaryDivergent boundaryWhere on Earth is continental rifting occurring today?Where on Earth is continental rifting occurring today?

Transform boundaryTransform boundaryNote opposite sense of motion (first motion studies)Note opposite sense of motion (first motion studies)

San Andreas Transform

Transform boundaryTransform boundary

ConvergentConvergent boundary boundary

Three sub-typesThree sub-types Ocean-ContinentOcean-Continent Ocean-OceanOcean-Ocean Continent-ContinentContinent-ContinentCan you name an Can you name an

example of each? example of each?

Convergent boundaryConvergent boundary

Ocean-Continent: Ocean-Continent: Andes, CascadesAndes, Cascades

Ocean-Ocean: Ocean-Ocean: Aleutians, JapanAleutians, Japan

Continent-Continent: Continent-Continent: Himalaya, AlpsHimalaya, Alps

Convergent boundaryConvergent boundary Trench and subduction zoneTrench and subduction zone EarthquakesEarthquakes Linear chain of andesitic volcanoes (granites below)Linear chain of andesitic volcanoes (granites below) Creation of mountain ranges (also linear chains)Creation of mountain ranges (also linear chains)

Andean type - continental arcAndean type - continental arc Himalayan type - collisional (a terminal type)Himalayan type - collisional (a terminal type)

““Andean-type” Andean-type” orogenesisorogenesis

Continental crust Continental crust thickens by addition thickens by addition of magma from the of magma from the subduction zonesubduction zone

Compression due to Compression due to plate convergenceplate convergence

““Himalayan-type” Himalayan-type” orogenesisorogenesis

Begins as Andean-typeBegins as Andean-type

““Himalayan-type” Himalayan-type” orogenesisorogenesis

How do you locate the suture zone today?How do you locate the suture zone today?How can you determine the “polarity” of subduction?How can you determine the “polarity” of subduction?

Slivers of oceanic crust and upper mantle (ophiolites) become incorporated into the “mélange” in the accretionary wedge of deformed sediments

The “suture zone” is marked by the mélange and particularly by the occurrence of ultramafic rocks composing the mantle portion of the ocean lithosphere

Chain of ultramafic bodies in Vermont indicating a suture zone of the Ordovician Taconic Orogeny. The ultramafics mark a closed oceanic basin between North American rocks and an accreted island arc terrane. From Chidester, (1968) in Zen et al., Studies in Appalachian Geology, Northern and Maritime. Wiley Interscience.

AppalachiaAppalachian Historyn History

Can “accrete” Can “accrete” island arc island arc

terranes as well terranes as well as continentsas continents

Plate MotionsPlate Motions

Plate Tectonics in the Pacific NorthwestPlate Tectonics in the Pacific Northwest

The Wilson The Wilson CycleCycle

The Breakup of PangeaThe Breakup of Pangea

The History of an Ocean

Basin

Igneous ProcessesIgneous Processes

Decompression partial melting at divergent zonesDecompression partial melting at divergent zones

Igneous ProcessesIgneous Processes

Partial melts: low-T fraction is always more Si-Al-Na-K-Partial melts: low-T fraction is always more Si-Al-Na-K-rich and Fe-Mg-poor than source rock. rich and Fe-Mg-poor than source rock.

Leaves behind Mg-Fe-rich refractory residueLeaves behind Mg-Fe-rich refractory residue

Decompression partial melting at divergent zonesDecompression partial melting at divergent zones

Igneous ProcessesIgneous Processes

Hot spots and mantle plumesHot spots and mantle plumes Subduction zones: Subduction zones:

Conveyor of basalt to melt Conveyor of basalt to melt andesite andesite Water lowers melting point of mantle wedgeWater lowers melting point of mantle wedge

Igneous ProcessesIgneous Processes

Subduction zones: water lowers melting pointSubduction zones: water lowers melting point