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

2011
Views:

226

Pages:

32
Author:

Elena Gentry

Oceanic lithosphere formed at MOR Lithosphere ages, cools, contracts and subsides away from MOR MOR ~ 4 km depth Abyssal plains ~6 km depth Young, hot, shallow, ocean floor: above CCD Old, cold, deep, ocean floor: below CCD Based on anomaly shape, magnetic anomalies can be correlated across ocean basins From anomaly spacing, spreading rates can be determined Pacific basin 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 Mid-Atlantic ridge 0 5 Ma 5 Ma 1 5 4 3a 3 2a 2 2 2a 3 3a 4 ridge axis Spreading rate = 225 km/ 5 Ma = 45 km/Ma = 4.5 cm/yr 5 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 MOR magma chamber -forms new oceanic crust -rocks of ophiolite suite make up oceanic crust Mid-Atlantic ridge, slow spreading center, transform faults Mid Atlantic ridge, axial graben –rough topography East Pacific rise, fast spreading center, triple junction Compare with EPR with MAR fast spreading center Indian Ocean, triple junction Indian Ocean Africa-Australia-Antarctica triple junction Rifting: formation of a new MOR Continental rifting: stretching of old continental lithosphere Drifting: formation of new oceanic lithosphere Rift initiation: East African rift Initiation at a triple junction Space Shuttle image: East African rift New spreading center: Red Sea

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