Olympic Mtns., WA

MountainsDescribe what you see…

1122

33 44

55

66

MountainsWhere are they located?

Half Dome, Yosemite Valley, CA

MountainsWhat are they made of?

http://www.tulane.edu/~sanelson/eens212/regionalmetamorph.htm

The Barrovian Facies Series occurs in the southern Appalachians, extending from Central Virginia to Alabama.  Interpretation of the relationship between deformation and metamorphism is complicated by the fact the region has experienced at least three mountain building events, and thrust faults cut the area.

Barrovian Facies Series of the Southern Appalachians

Vertical movement of the crust !

James D. DanaPermanence of oceans

Wrote “Geological results of the Earth’s contraction in consequence of cooling” - 1847

Oceans are permanent, continents are stable

(1813-1895)

Albert HeimAlpine terrain, fold nappes

Worked in the Alps, documented mountain-scale folds and large horizontal displacements; constructed terrain models of Swiss alps

Mountainside fold nappe in Norway

(1849-1937)

However…

• What is the heat source for metamorphism or melting?

• What produces the petrologic complexity among mountain ranges?

• How do we account for kilometers of horizontal displacement in mountain ranges like the alps?

Isostasy suggested that mountains formed by

vertical movement of the crust

James HallGeosynclinal theory

State Paleontologist of New York; proposed geosynclinal theory in 1857

(1811-1898)

GEOSYNCLINES• fixed linear troughs at margins of, or within, continents• deep water sediments and volcanic rocks in center,

(eugeosyncline: high deformation) • shallow water sedimentary rocks on flanks

(miogeosyncline: mild deformation) • deformation is symmetrical with thrusting away from center onto adjacent continental platforms to produce orogens

George Marshall KayGeosynclinal theory

Wrote “North American Geosynclines” - 1951(1904-1974)

What part of the southern Appalachians would be the miogeosyncline?

Geosynclinal theory

Geosynclinal theory

Geosynclinal theory

So now we have a mechanism for both horizontal and vertical displacements in mountains

But what about fossil correlations between continents?

Other geological evidence??

Eduard SuessGondwanaland

(1831-1914)

Documented the Glossopteris fern on present-day continents:

Gondwanaland connected by ancient land bridges

Glossopteris

But isostasy says that land bridges shouldn’t sink !

Antonio Snider-PellegriniContinental fit and “drift”

1858 - “Creation and its Mysteries Resolved”

Noah’s flood caused the continents to break up and drift apart

S. America and Africa break up and drift apart

Frank Bursey TaylorDrift of continents toward equator

1910 - “Bearing of the Tertiary mountain belt on the origin of the Earth’s plan”

Tidal forces induced movement of continents toward equator

Alfred Lothar WegenerPaleoclimatic evidence

Evidence for Permo-Carboniferous inland glaciation on several present-day continents

(1880-1930)

Alfred Lothar WegenerContinental Drift

1915 - “Die Entstehung der Kontinente und Ozeane”

1924 - “The Origin of Continents and Oceans”

(1880-1930)

“Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence…It is only by combing the information furnished by all the earth sciences that we can hope to…find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw.”

Emile ArgandGondwanaland reconstruction

1916 - “Sur l'arc des Alpes occidentales”

1922 - “La Tectonique de l'Asia”

(1879-1940)

Wegener’s paleogeography

Iron/Magnesum-rich rocks Silica/Aluminum-rich rocks

Alexander Du ToitSouth America - Africa geologic connections

1927 “A Geological Comparison of South America with South Africa”

1937 “Our Wandering Continents”

(1878-1948)

The same fossils and the same rock units in Africa and South America

Reginald A. DalyGravity sliding

1926 - “Our Mobile Earth”

(1871-1957)

Arthur HolmesConvection in a molten substrate

1945 - “Principles of Physical Geology”

(1890-1965)

• Causal mechanism for drift?• Tidal forces?• Rotation-induced movement towards the equator?• Gravity sliding?• Molten substrate?

Complications for Continental Drift

• And what about isostasy??• How can more felsic continent crust move through

denser, more mafic oceanic crust?• Why isn’t there any evidence for this movement on

the ocean floor?

The Accumulation of Anomalies

The Submarine Cable Project

Samuel Morse invented the telegraph in the 1830’s, but it would only work on land.

Messages to/from Europe still required ships, but in 1858, a transoceanic cable was laid

But they found that the ocean floor was not as deep as expected in the middle.

The Challenger Expedition of 1872

HMS Challenger was the first dedicated oceanographic expedition

Soundings not only determined ocean depth, but returned samples from the ocean floor

Depths varied widely, sediments varied, fossils varied, contrary to current thought

So What?

- Conventional theory stated that the ocean floor was simply submerged land;

- The shallowing in the mid-ocean seemed to support this, but only marine fossils were found in the mid-ocean;

- Areas of incredible depth were not accounted for by this theory.

Sonar• During WWI, German U-boats nearly destroyed

the British merchant fleet. As a result, the British sought a technological edge, using passive hydrophones to listen for U-boats;

• In the 1920’s the British feared a repeat in the future, forming the Anti-Submarine Detection Investigative Committee (ASDIC) to create an active system;

• A similar device was invented in the US, called SONAR (Sound Navigation and Ranging);

• Sound waves were sent out and timed for the return reflected waves.

Sonar• Harry Hess, naval

reserve officer, called up during WWII, used the SONAR on his ship to collect data on shape of the sea floor;

• Not only did the depth vary, but so did the thickness of the sediment layers on top of the sea floor

Gravity Surveys• As stated earlier, the force of gravity varied in

unexpected ways, being stronger or weaker in ways that could not be accounted for by current theory;

• Sensitive torsional balances could detect variations in mass, but were sensitive to vibrations;

• Pendulums were less sensitive to vibration, but more sensitivity was needed.

Gravity Surveys• A Dutch scientist, Felix Vening Meinesz

developed such a gravitometer, detecting differences in the period of co-planar pendulums;

• A difference in T meant a difference in g.• Traveling in the US submarine, S-21, he found

variations in gravity to be unexpected - less in areas of sedimentation and more in deep ocean basins.

Gravity Surveys

• A later cruise in the S-48 included a young geologist and naval reserve officer, Harry Hess;

• A Caribbean cruise found very strong negative anomalies in the deep ocean trenches.

George Airy, revisited

George Airy, revisited

If Fg > Fg , then the difference is a positive anomaly

If Fg < Fg , then the difference is a negative anomaly

Fg= Gm1m2

d2

Fg= GmEm2

d2Fg= G

mEm2

d2

An anomaly is the difference between the predicted and the observed measurement.

Difference between predicted and observed measurements come from:

• Higher or lower density rocks, i.e. basalts & gabbros vs. sediments and granites;

• Displacement of higher density material by lower density material, i.e. roots of mountains displacing mantle material, subduction zones;

• Large masses of rock, such as mountains or ultramafic concentrations.

http://www.csr.utexas.edu/grace/gravity/gravity_definition.html

Magnetic Variations• During WWII, the renewed U-boat threat

lead to improvements in SONAR, but also other detection methods;

• RADAR could detect surfaced subs, but deep-diving subs could escape even SONAR;

• The disruption of the local magnetic field was sought as a way of detecting submerged U-boats.

Magnetic Variations

Local field

Disrupted field lines

Magnetic Variations• The first such

detectors were towed behind a ship, but later were made more compact to fit in aircraft;

• More sensitive magnetometers began to detect reversals in the local magnetic field preserved in the sea floor rocks.

Magnetometer boom

Magnetic Variations• Vine and Matthews

found linear patterns of these variations, with mirror images of the patterns on opposite sides of ocean ridges;

• These same rocks were of similar age on opposite sides of the ridge;

• Patterns were also offset by apparent faults.

Magnetic Poles

• Sensitive magnetometers on land were also used to detect the position of the magnetic poles over time, looking for past shifts of the pole;

• But different continents had apparently different pole positions for the same point in geologic time;

Magnetic Poles

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

So What?

• Ocean floor topography more highly variable than expected;

• No submerged land bridges found;• Sediment thickness and type more variable than

expected;• Variations in gravity not accounted for by vertical

movement alone;• Crust was likely more rigid than previously throught;• Magnetic field signature in rocks varied in consistent

pattern;• Paleomagnetic poles did not line up for static continents;• Vertical movement could not account for such variations

alone.

Differences?• Paleomagnetic

measurements on land revealed differing polar wandering paths on different continents;

• Paleomagnetic variations and ages of seafloor material indicated new crust was formed with polarity the same as when it was created;

• Geometric solutions of plates as rigid bodies could be resolved to past positions;

• Seismic data indicated variations in structure of the subsurface

• Fossil evidence across oceans suggested prior interchange among land species;

• Similarities in stratigraphic layers across the ocean suggest prior close connection;

• Climate change indicators, including glacial patterns, could not be accounted for by warm or cool periods alone;

• Continental shelves exhibited closer fit than current coastlines.