Module 11 Plate Tectonics

PLATE TECTONICS Continental drift (Alfred Wegener) The theory that the continents have moved in relation to one another Seafloor Spreading (Harry Hess) The theory telling that the floor of the ocean spread away one to another part Plate tectonics The theory of global dynamics in which the lithosphere is believed to be broken into individual plates that move in response to convection in the (upper) mantle. The margins of the plates are sites of considerable geologic activity.

Crust Mantle Core (CMC)-sphere

Crust Mantle Core (CMC)-sphere

Crust Mantle Core (CMC)-sphere Depth (km) rocks cold, rigid, brittle hot, plastic Δ = 3,3– 4,3 g/cm3 hot, high pressure, rigid, brittle ultrabasic igneous rocks (MgO, SiO2) Liquid 45000 C Fe, Ni solid

Plate Tectonic Theory Lithosphere is broken into individual pieces called plates Plates move over the asthenosphere as a result of underlying convection cells

What drives plate motions

What drives plate motions Models of plate-mantle convection Any model must be consistent with observed physical and chemical properties of the mantle Horizontal movement of plates causes mantle upwelling Models Layering at 660 km Explains why basalts erupted at mid-ocean ridges are different (more evolved, relatively shallow source) compared to those erupted at hot-spots (more primitive, deeper source). We know that subducting slabs descend beneath 660 km

What drives plate motions Whole-mantle convection Would mix the entire mantle in the space of a few hundred million years, removing heterogeneities

Antonio Snider-Pelligrini’ Map (1858) Continental Drift Antonio Snider-Pelligrini’ Map (1858)

Continental Drift Alfred Wegener’ Map (1915)

Wegener’s Concept of Continental Drift and Orogenesis Note: Most geologists and geophysicists rejected Wegener’s ideas because they violated what was known about the STRENGTH OF ROCKS. Also, centrifugal force (from Earth’s rotation) along with tidal forces were deemed to be TOO SMALL to move the continents!

Evidence on Continent Continents Fit Together Best fit at 100 m below sea level

Evidence on Continent Rocks and Structures Match Up

Evidence on Continent

Evidence on Continent Mountain Belts of the Same Age Caledonides Appalachians Caledonides Mauritanides

Evidence on Continent Direction of ice flow Glacial Features

Permian-Pennsylvanian Evidence on Continent Fossils Early Triassic Lystrosaurus Cynognathus Glossopteris Permian-Pennsylvanian Permian Mesosaurus

Evidence on Continent Paleoclimate of Pangea

Evidence on Seafloor Seafloor Morphology

Magnetic Stripe Formation at Ridge Crest Evidence on Seafloor Paleomagnetism and seafloor spreading Magnetic Stripe Formation at Ridge Crest Magnetic Time Scale

Evidence on Seafloor Paleomagnetism and seafloor spreading

Evidence on Seafloor Seafloor Age Map

Mantle Plume Hot Spot Tracks Evidence on Seafloor Mantle Plume Hot Spot Tracks

Reconstruction

Plate Movement due Time

Plate Movement due Time

Plate Tectonics Directions of Motion and Plate Velocities Determined by Mantle Plume Hot Spot Tracks and Age-Dating of Rocks

Plate Tectonics Directions of Motion and Plate Velocities Determined by GPS (Global Positioning System) Satellites Directions of Motion and Plate Velocities Determined by GPS (Global Positioning System) Satellites

Earth’s Tectonic Plates Plate Tectonics Earth’s Tectonic Plates North American North American Eurasian Arabian Juan de Fuca Caribbean Pacific Philippine Cocos African South American Nazca Indo Australian Pacific Antarctic Scotian Antarctic

What drives Plate Tectonics???

Plate Tectonics Internal Heat

Plates Boundaries

Results in the formation of Oceanic Crust Plate Tectonics Divergent Boundary Results in the formation of Oceanic Crust

Plate Tectonics Transform Boundary

Convergent Boundary: Subduction Plate Tectonics Convergent Boundary: Subduction Melting Produces More Felsic Magma Results in the formation & growth of Continental Crust and destruction of Oceanic Crust

Plate Tectonics Convergent Boundary: Collision Results in the growth of Continental Crust

Hot Spot

BASIC PLATE TECTONICS – Revised Earth’s lithosphere is broken into 12-24 rigid plates Plates move about 1-10 cm/yr on the plastic Asthenosphere “Geology happens” where the plates interact with one another along Divergent, Transform, Subduction and Collisional Boundaries

World Plate Tectonic BMG LEMPENG AMERIKA UTARA LEMPENG SAM. PASIFIK LEMPENG EURASIA LEMPENG FILIPINA LEMPENG CARIBIA LEMPENG COCOS LEMPENG AMERIKA SELATAN LEMPENG SAM INDAO-AUSTRALIA LEMPENG NAZCA LEMPENG ANTARTIKA LEMPENG SCOTIA

Tectonic Map of Indonesia Pasific 11 cm / tahun Eurasia 7 cm / tahun Indo-australia 9 cm / tahun

Volcanoes distribution in Indonesia

Seismicity Map of Indonesia

GROUP DISCUSSION