University:
Amherst College
Course:
GEOL 111 | Planet Earth: Introduction to Geology
Academic year:

2020
Views:

90

Pages:

25
Author:

pigamdomo81d

mid-ocean ridge Symmetrical magnetic field intensity mid-ocean ridge Magnetic highs are positive anomalies Magnetic lows are negative anomalies Magnetic anomalies make a striped pattern on the ocean floor. The stripes are parallel to midocean ridges and the stripe widths are symmetrical across the ridge mid-ocean ridge Ocean floor becomes a tape recorder- recording magnetic reversals AND sea-floor spreading Sea-floor magnetic anomalies create a VERY PRECISE absolute time scale the MAGNETIC REVERSAL TIME SCALE Good for as long as we have ocean floor ….approx. the past 200 Ma Based on anomaly shape, magnetic anomalies can be correlated across ocean basins From anomaly spacing, spreading rates can be determined Pacific basin Mid-Atlantic ridge 0 5 Ma 5 Ma 1 5 4 3a 3 2a 2 2 2a 3 ridge axis Spreading rate = 225 km/ 5 Ma = 45 km/Ma = 4.5 cm/yr 3a 4 5 South Atlantic magnetic anomalies Sea floor younger than anomaly 5 (< 10 Ma) Sea floor younger than anomaly 21 (< 50 Ma) Sea floor younger than anomaly 34 (< 90 Ma) South Atlantic magnetic anomalies Sea floor younger than anomaly 5 (< 10 Ma) Anomaly 5 (10 Ma) reconstruction Sea floor younger than anomaly 21 (< 50 Ma) Anomaly 21 (50 Ma) reconstruction Sea floor younger than anomaly 34 (< 90 Ma) Anomaly 34 (90 Ma) reconstruction Apparent magnetic pole position PaleomagneticInclination: distance from the magnetic pole. Steep inclination means short distance Declination: direction towards the pole Apparent polar wander: Apparent pole positions from rocks of different ages Plate reconstruction FROM apparent polar wander curves. For a viable reconstruction, APW curves MUST point towards a common pole

Mid-ocean Ridge

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