PLATE TECTONICS: A SCIENTIFIC REVOLUTION UNFOLDS

CHAPTER 7

FOCUS ON CONCEPTS What evidence was used to support the

continental drift hypothesis? What was one of the main objections to

the continental drift hypothesis? What is the theory of plate tectonics? In what major way does the plate

tectonics theory depart from the continental drift hypothesis?

FOCUS ON CONCEPTS What are the three types of plate

boundaries? Where does new lithosphere form? How do mountain systems such as the

Himalayas form? What type of plate motion occurs along

a transform fault boundary?

FOCUS ON CONCEPTS What evidence is used to support the

plate tectonics theory? What are the major driving forces for

plate tectonics? What models have been proposed to

explain the driving mechanism for plate motion?

7.1FROM CONTINENTAL DRIFT TO

PLATE TECTONICS

THE COLLISION OF INDIA AND ASIA PRODUCED THE HIMALAYAS

K7 IN PAKISTAN’S KARAKORAM (HIMALAYAS)

7.2CONTINENTAL DRIFT: AN IDEA

BEFORE ITS TIME

ALFRED WEGENER• Pangaea• Continental Drift Hypothesis

EDUARD SUESSGondwana

CONTINENTAL DRIFT HYPOTHESIS Began in early Mesozoic (~200 mya) Evidence

Continental jigsaw puzzle Fossil distribution Rock types & geologic features Ancient climates

CONTINENTAL JIGSAW PUZZLE

CONTINENTAL JIGSAW PUZZLE

EVIDENCE

FOSSIL DISTRIBUTION

FOSSIL DISTRIBUTION

BEARDMORE GLACIER

Location of the fossil site at the Oliver Bluffs on the Beardmore Glacier

ROCK TYPES & GEOLOGIC FEATURES There are rock formations (such as

mountain ranges) on different continents that match up beautifully when the continents are put back together.

ROCK TYPES & GEOLOGIC FEATURES

ANCIENT CLIMATES Paleoclimatic data Extreme global cooling? Wegener’s explanation

GLACIAL STRIATIONS

POST-DRIFT ICE SHEETS

PRE-DRIFT ICE SHEET

7.3THE GREAT DEBATE

OBJECTIONS TO THE CONTINENTAL DRIFT HYPOTHESIS

What mechanism allows movement? Not all evidence supported the

hypothesis.

Some thought the idea was intriguing or an answer to a previously unexplained phenomena.

OBJECTIONS TO THE CONTINENTAL DRIFT HYPOTHESIS

7.4PLATE TECTONICS

PLATE TECTONICS THEORY 1968; more encompassing than CDH Lithosphere broken into plates, slide

over asthenosphere

EARTH’S MAJOR TECTONIC PLATES

EARTH’S MAJOR TECTONIC PLATES LARGE – 94% of Earth’s S.A.

North American South American Pacific African Eurasian Australian-Indian Antarctic

EARTH’S MAJOR TECTONIC PLATES INTERMEDIATE – mostly oceanic

Caribbean Nazca Phillipine Arabian Cocos Scotia Juan de Fuca

PLATE BOUNDARIES Divergent (constructive) Convergent (destructive) Transform (conservative)

PLATE BOUNDARIES

PLATE BOUNDARIES

7.5DIVERGENT BOUNDARIES

DIVERGENT BOUNDARIES “spreading center” constructive plate margin

OCEANIC RIDGES Elevated are of seafloor characterized

by high heat flow, volcanism Rift valley @ center of ridge is proof

that tensional forces are pulling the ridge apart

OCEANIC RIDGES

OCEANIC RIDGES

SEAFLOOR SPREADING Average 5 cm/year New ocean crust is hot

Less dense Rises

SEAFLOOR SPREADING

CONTINENTAL RIFTING Opposing tectonic forces pull the lithosphere

apart

CONTINENTAL RIFTING Brittle rocks break into large slabs

EAST AFRICAN RIFT

EAST AFRICAN RIFT

Mt. Kilimanjaro

EAST AFRICAN RIFT

EAST AFRICAN RIFT

CONTINENTAL RIFT

CONTINENTAL RIFT

7.6CONVERGENT BOUNDARIES

CONVERGENT BOUNDARIES Planet isn’t getting bigger Subduction zones Deep ocean trenches

OCEANIC-CONTINENTAL CONVERGENCE

PERU-CHILE TRENCH

PERU-CHILE TRENCH

PERU-CHILE TRENCH

OCEANIC-CONTINENTAL CONVERGENCE Continental crust is less dense –

“floats” – which means that subducting oceanic crust is denser (and wetter)

OCEANIC-CONTINENTAL CONVERGENCE

CONTINENTAL VOLCANIC ARCS Mountain ranges produced by volcanic

activity associated with subduction of oceanic lithosphere

CONTINENTALVOLCANIC ARCS

CONTINENTAL VOLCANIC ARCS

Mount Rainier

CONTINENTAL VOLCANIC ARCSMount Shasta with Shastina, its highest satellite cone; one of four overlapping volcanic cones which together form

the most voluminous stratovolcano in

the Cascade Range. At 3,758 m, Shastina is taller

than Mount Adams and would rank as the third highest volcano in the Cascades behind Mount Rainier and

Shasta were it not nestled on the western flank of its higher

neighbor.

CONTINENTAL VOLCANIC ARCS

Mount St Helens, before and after 5/1/80

OCEANIC-OCEANIC CONVERGENCE One plate descends under another

OCEANIC-OCEANIC CONVERGENCE

OCEANIC-OCEANIC CONVERGENCE

Mariana Islands at map-right, east of the Philippine Sea, and just west of the Mariana Trench in the ocean floor.

OCEANIC-OCEANIC CONVERGENCETonga is a sovereign state and an archipelago comprising 176 islands scattered over 700,000 km2 in the southern Pacific Ocean.

Fifty-two of these islands are inhabited.

OCEANIC-OCEANIC CONVERGENCE Atlantic island arcs are less common The Lesser Antilles more or less

coincide with the outer edge of the Caribbean Plate. Many of the islands were formed as a result of the subduction of oceanic crust of the South American Plate under the Caribbean Plate in the Lesser Antilles subduction zone. 

PUERTO RICO TRENCH

Map of the North American - Caribbean tectonic plate boundary. Colors denote depth below sea level and elevation on land. Bold numbers are the years of moderately large (larger than about M7) historical earthquakes written next to their approximate location. Asterisk - Location of the January 12, 2010 earthquake. Barbed lines- boundary where one plate or block plunges under the other one. Heavy lines with half arrows - faults along which two blocks pass each other laterally.

PUERTO RICO TRENCH

PUERTO RICO TRENCH The Puerto Rico Trench, the largest and deepest trench in

the Atlantic, is located about 75 miles north of Puerto Rico in the at the boundary between the Caribbean and North American plates. It is 1,090 miles long and about 60 miles wide. At its deepest point, named the Milwaukee Deep, it is 27,493 feet , or about 5.2 miles.

The image on the previous slide is a perspective view of the sea floor of the Atlantic Ocean and the Caribbean Sea. The Lesser Antilles are on the lower left side of the view and Florida is on the upper right. The purple sea floor at the center of the view is the Puerto Rico trench, the deepest part of the Atlantic Ocean and the Caribbean Sea.

LESSER ANTILLES

AGE Crust under younger island arcs < 20

km Older arcs: crust is thicker & more

complex

CONTINENTAL-CONTINENTAL CONVERGENCE

Subduction of intervening seafloor Continents don’t subduct Intracontinental mountain ranges form

this way

CONTINENTAL-CONTINENTAL CONVERGENCE

CONTINENTAL-CONTINENTAL CONVERGENCE

CONTINENTAL-CONTINENTAL CONVERGENCE

CONTINENTAL-CONTINENTAL CONVERGENCE

7.7TRANSFORM FAULT BOUNDARIES

TRANSFORM FAULT BOUNDARIES 2 plates slide horizontally against one

another Conservative plate boundary since

crust is neither produced nor deformed J. Tuzo Wilson

FRACTURE ZONE

FRACTURE ZONE• not continuous

features• offset by

numerous transform faults

• transform faults are not divergent boundaries

• fracture zones are not plate boundaries

• crust on both sides of a fracture zone are part of the same plate and moving in the same direction

MENDOCINO FAULT

SAN ANDREAS FAULT

SAN ANDREAS FAULT Video: California's San Andreas

Fault could rupture, cause mega-quake - study says

SAN ANDREAS FAULT

Dragon's Back (Elkhorn Scarp) in the Carrizo Plain

SAN ANDREAS FAULT

SAF in gouge in Tejon Pass

SAN ANDREAS FAULT

shutter ridge with offset streamCurtis Palms, Riverside County

SAN ANDREAS FAULT Interactive Map of the San Andreas

Fault

7.8TESTING THE PLATE TECTONICS

MODEL

EVIDENCE: OCEAN DRILLING

Deep Sea Drilling Project - Glomar Challenger - 1968-1983

EVIDENCE: OCEAN DRILLING

Deep Sea Drilling Project - Glomar Challenger - 1968-1983

EVIDENCE: OCEAN DRILLING

OCEAN DRILLING PROGRAM

INTEGRATED OCEAN DRILLING PROGRAM (2007)

Chikyu

INTEGRATED OCEAN DRILLING PROGRAM (2007)

INTEGRATED OCEAN DRILLING PROGRAM (2007)

IODP Exp. 313 IODP Expedition 320 – Micropaleon

tology Episode THREE - IODP 342 Newfou

ndland

EVIDENCE: HOT SPOTS Hawaiian Islands/Emperor Seamount

EVIDENCE: HOT SPOTS Mantle plume

beneath Hawaii Hot spot Hot spot track

HAWAIIAN ISLANDS

HAWAIIAN ISLANDS

Kilauea

HAWAIIAN ISLANDS

MANTLE PLUMES Some originate at core-mantle

boundary 12 of 40 hot spots world-wide are near

spreading centers

MANTLE PLUMES

MANTLE PLUMES

The LVZ has been interpreted to indicate the presence of a significant degree of partial melting, and alternatively as a natural consequence of a thermal boundary layer and the effects of pressure and

temperature on the elastic wave velocity of mantle components in the solid state

MANTLE PLUMES

3D view of mantle plume under Iceland

MAGNETIC POLES

CURIE POINT

The development of the remnant magnetic signature of rocks as they cool below the Curie Point

CURIE POINT At temperatures above the Curie Point, permanent

magnetization of materials is not possible. Since the magnetic minerals take on the orientation of

the magnetic field present during cooling, we can determine the orientation of the magnetic field present at the time the rock containing the mineral cooled below the Curie Point, and thus, be able to determine the position of the magnetic pole at that time. 

This made possible the study of Paleomagnetism (the history of the Earth's magnetic field).

Magnetite is the most common magnetic mineral in the Earth's crust and has a Curie Temperature of 580oC

APPARENT POLAR WANDERING If magnetic poles remain stationary,

apparent movement is produced by continental drift

MAGNETIC REVERSALS AND SEAFLOOR SPREADING Earth’s magnetic field periodically

reverses polarity Normal polarity – rocks have the same

magnetism as the present field Reverse polarity – rocks exhibit

opposite magnetism

PALEOMAGNETISM IN LAVA FLOWS

7.9HOW IS PLATE MOTION

MEASURED?

HOW IS PLATE MOTION MEASURED? Paleomagnetism Hot spot tracks

MANTLE PLUMES & PLATE MOTIONS Length of hot spot track Time interval between formation of

oldest and youngest volcanic structures Hot spot tracks

MEASURING PLATE MOTION FROM SPACE Rotational plate movement Relative plate motion GPS

WORLDWIDE PLATE MOVEMENT

7.10WHAT DRIVES PLATE MOTIONS?

PLATE TECTONICS THEORY Describes plate movement but not the

cause of plate movement.

PLATE-MANTLE CONVECTION Heat loss from Earth’s core Decay of radioactive isotopes Cooling from top Horizontal plate movement Mantle convection

PLATE-MANTLE CONVECTION

FORCES THAT DRIVE PLATE MOTION Slab pull Ridge push Mantle drag Subduction zones

MODELS OF PLATE-MANTLE CONVECTION Different setting, different chemical

composition Layering at 600 km Whole mantle convection

MORAL OF THE STORYUnequal heat distribution

Some type of thermal convection

Plate motion

The End