Physical Geology: GEOL 107

GEOL 107: Physical Geology

Dr. Lijun Liu1AnnouncementsFirst CPR writing due Fri. Sep 11; assignment will show up in Compass on Fri. Sep 4.Carefully follow instructions in CompassWork has to be submitted to the CPR server at https://cpr.molsci.ucla.edu/cpr/cpr/login.asp You should have all received your username and password in email.Finish each step of the CPR assignment in timeChap 5 quiz due next WednesdayThis is a reading quiz based on the textbook.3Magnetic field intensity (absolute values)

(2x10-5, 6x10-5 T)

Global magnetic anomalymap(-2x10-7, 2x10-7 T)

~1% anomalyRefrig magnet

(5x10-3 T)

~100 times stronger than the total geomagnetic strengthReview last lecture

Continent moved over timeGeomagnetic fieldchangedorApparent polar wander

Relative plate motionorBoth the above The plate moved toward the _______ in the ________ Hemisphere. (Lets assume the geomagnetic field has never changed during the geological past.)

a. Equator; Southern b. Equator; Northernc. Pole; Southern d. Pole; Northern

YoungOldReview last lecture

Continent moved over timeGeomagnetic fieldchangedorGeomagnetic fieldchangedApparent polar wanderRelative plate motionGeomagnetic polarity reversalorBoth the aboveEarth-like magnetic field generation in a 3D simulation:

Dipolar dominant surface magnetic field

Periodic magnetic polarity reversals8

Courtesy of G. GlatzmaierEarth-like magnetic field generation in a 3D simulation:

Dipolar dominant surface magnetic field

Periodic magnetic polarity reversals9

Courtesy of G. GlatzmaierEarth-like magnetic field generation in a 3D simulation:

Dipolar dominant surface magnetic field

Periodic magnetic polarity reversals10

Courtesy of G. GlatzmaierEarth-like magnetic field generation in a 3D simulation:

Dipolar dominant surface magnetic field

Periodic magnetic polarity reversals11

Courtesy of G. GlatzmaierEarth-like magnetic field generation in a 3D simulation:

Dipolar dominant surface magnetic field

Periodic magnetic polarity reversals12

Courtesy of G. GlatzmaierWhat is the least likely for this rock record?PaleomagThe paleomagnetic anomaly pattern is irregular.

This record is symmetric with respect to part II.

A possible age order is part I > part II > part III.

Part II could be younger than both part I and part III.Part IIPart IIIPart IUp

Evidence I: Seafloor TopographyNotice the topographic symmetry across mid-ocean ridgesEvidence II: Paleomagnetic anomalies

What caused these?ambientMagnetometers towed by ships moving perpendicular to the mid-ocean ridges recorded alternating strong and weak magnetic fields.

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Polarity reversals would work!Magnetometers towed by ships moving perpendicular to the mid-ocean ridges recorded alternating strong and weak magnetic fields.

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Marine magnetic anomalies are symmetric across mid-ocean ridges

Polarity reversal is a global phenomenonSome notes:

Magnetic polarity reversal is a global phenomenon

Reversals happened many times during the geological past

Reversals are independent of surface tectonic motions --- so we can use them as a reference

Reversal chart is a time table, so we can find age of the seafloor from its magnetic pattern

UpHint:

How did this paleomagnetic record suggest for the growth of seafloor?From left to right.From right to left.From side to center.From center to side.

Deep sea drilling project

Lab measurements:PaleomagAge

Ages of polarity reversals are determined by radiometric dating of lava flowsAll measurements reveal the same reversal sequence Evidence III: Seafloor age distribution

TopographyPaleomagAgeyoungoldoldTopography + paleomag + ageMid-ocean ridgeSeafloor spreading!

Magnetic field directions are registered during the formation of ocean crust The Atlantic ocean opened up since 180 million years ago (Ma) and is still expanding

Seafloor spreading rate varies from ocean to ocean: the Pacific is the fastestSea Floor Spreading

Continents move with ocean plates - they dont plow through them!Most direct evidence for Plate Tectonics Calibrated Peer-Review writing #1