what evidence was used to support the continental drift hypothesis? what was one of the main...
TRANSCRIPT
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 SUESS
Gondwana
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 CONVERGENCE
Tonga 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 STORY
Unequal heat distribution
Some type of thermal convection
Plate motion
The End