Continental Drift Alfred Wegener (1912) First serious proponent First serious proponent Alfred manning the weather station, Greenland

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

Fit of Structural Elements

Pennsylvanian (300 Ma) Glaciation Glacial striations in bedrock, South Australia

Pennsylvanian (300 Ma) Glaciation Using present continental locations Arrows indicate ice movement directions

Pennsylvanian (300 Ma) Glaciation Using pre-drift continental locations Arrows indicate ice movement directions

Fossil Evidence Glossopteris: an ancient seed fern (200 Ma) Distribution of Glossopteris fossils

Fossil Evidence Mesosaurus couldn’t swim in open ocean Distribution of Mesosaurus fossils

Paleomagnetism The Earth as a dipole Magnetic declination and inclination

Paleomagnetism Magnetization of volcanic rocks and sediments

Paleomagnetism “Polar Wandering” curves

2) The Earth’s Interior

Miles from ridge axis Plate Tectonics: a breakthrough Brian Mason (Scripps) led a group that studied a 2-D area spanning the Mid-Atlantic Ridge in detail An explanation of the curious magnetic anomaly pattern

The process at mid-ocean ridges

Black Smokers

Seismicity Earthquakes occur due to motion along faults Dip-slip Faults Normal Fault Reverse Fault (thrust) Normal Fault Reverse Fault (thrust) View is cross-section

Seismicity Earthquakes occur due to motion along faults Strike-slip Faults Right-Lateral Left-Lateral Right-Lateral Left-Lateral Map View

Seismicity: global distribution of earthquakes

Earthquake foci in the vicinity of the Japan trench

Seismicity First motion studies Bomb

Seismicity First motion studies Earthquake

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

Seismicity: global distribution of earthquakes

The Deep-Sea Drilling Program

Sediment ages directly on crust

Age of the ocean crust

Hot Spots

The Modern Plates

Three types of plate boundaries

Divergent boundary

Where on Earth is continental rifting occurring today?

Transform boundary Note opposite sense of motion (first motion studies) San AndreasTransform

Transform boundary

Convergent boundary Three sub-types l Ocean-Continent l Ocean-Ocean l Continent-Continent Can you name an example of each?

Convergent boundary l Ocean-Continent: Andes, Cascades l Ocean-Ocean: Aleutians, Japan l Continent-Continent: Himalaya, Alps

Convergent boundary l Trench and subduction zone l Earthquakes l Linear chain of andesitic volcanoes (granites below) l Creation of mountain ranges (also linear chains) F Andean type - continental arc F Himalayan type - collisional (a terminal type)

“Andean-type” orogenesis Continental crust thickens by addition of magma from the subduction zone Compression due to plate convergence

“Himalayan-type” orogenesis Begins as Andean-type

“Himalayan-type” orogenesis How do you locate the suture zone today? 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.

Appalachia n History Can “accrete” island arc terranes as well as continents

Plate Motions

Plate Tectonics in the Pacific Northwest

The Wilson Cycle

The Breakup of Pangea

The History of an Ocean Basin

Igneous Processes l Decompression partial melting at divergent zones

Igneous Processes l Partial melts: low-T fraction is always more Si-Al-Na- K-rich and Fe-Mg-poor than source rock. l Leaves behind Mg-Fe-rich refractory residue l Decompression partial melting at divergent zones

Igneous Processes l Hot spots and mantle plumes l Subduction zones:  Conveyor of basalt to melt  andesite F Water lowers melting point of mantle wedge

Igneous Processes l Subduction zones: water lowers melting point