Lecture-5 - Lecture 5 More on Sea-floor Spreading Tuesday,...

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1 Lecture 5 More on Sea-floor Spreading T uesday , September 1 6 th , 200 8 A Mechanism for Sea-Floor Spreading ± New oceanic crust is created through volcanic activity at ridge crests. ± This material then moves away from the ridge crest as additional new material is constantly added.
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2 Magnetic Anomalies ± The crust retains the magnetic signature (normal or reversed) that was in effect at the time of its formation Reverse Reverse Normal Normal Another diagram just to make it clearer!
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3 A Review of Magnetic Evidence for Sea-floor Spreading
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4 Spreading Rates ± The linear magnetic anomalies provide an estimate of the age of the oceanic crust (like tree rings). ± Since we know how far an anomaly is from the spreading ridge axis we can estimate the spreading rate . ± Velocity = Distance/Time Calculating Spreading Rate Spreading Rate = Distance (cm)/Age (years) Spreading Rate = (40 x 10 5 )/(4 x 10 6 ) Spreading Rate = 1 cm/yr Typical spreading rates range from 1 – 10 cm/yr Distance of 7th normal stripe is about 40 km from the ridge crest. The age is about 4 million years.
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This note was uploaded on 08/09/2009 for the course GEOSCIENCE GEO-105 taught by Professor Rhodes during the Fall '08 term at UMass (Amherst).

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Lecture-5 - Lecture 5 More on Sea-floor Spreading Tuesday,...

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