PLATE MOTIONS AT MIDOCEAN RIDGES AND TRANSFORMS

(Press & Siever)

RATE OF RELATIVE PLATE MOTION – SPREADING RATE – IS FOUND FROM THE DISTANCE OF MAGNETIC ANOMALIES OF KNOWN AGE FROM THE RIDGE AXIS, BECAUSE THIS IS THE RATE AT WHICH THE PLATES MOVE APART AND NEW LITHOSPHERE IS CREATED

A 3 MYR OLD ANOMALY, 30 KM FROM THE RIDGE AXIS

SHOWS THAT THIS SIDE SPREAD AT

30/3 = 10 KM/MY = 10 MM/YR

SO THE FULL SPREADING RATE BETWEEN THE TWO-PLATES IS 20 MM/YR

DIRECTION OF RELATIVE PLATE MOTION IS FOUND FROM THE DIRECTION OF TRANSFORM FAULTS BECAUSE ALONG THESE PLATES SLIDE BY EACH OTHER

THUS TRANSFORMS ARE PARALLEL TO PLATE MOTION