Page 153 - Global Tectonics

OCEAN RIDGES 139

Magmatic segment center Transform fault Magmatic segment center

0
2
4
km
6 Moho
8 Lithosphere
10 Asthenosphere

Slow-spreading ridge

Segment center

1

km 3

5 Moho

Fast-spreading ridge

Volcanics/basalt Melt lens
Crystal mush zone
Dikes Lower crust (partially molten)
Gabbro Transition zone
(largely solid)
Ultramafic/peridotite

Fig. 6.15 Along axis sections illustrating the variation in crustal structure between segment centers and segment
ends on slow- and fast-spreading ridges, as envisioned by Cannat et al. (1995) and Sinton and Detrick (1992)

respectively (redrawn from Cannat et al., 1995, with permission from the Geological Society of America, and modified
from Sinton and Detrick, 1992, by permission of the American Geophysical Union. Copyright © 1992 American
Geophysical Union).

Tolstoy et al., 2001) and studies of ophiolites (Harper, geochemical differences imply that adjacent segments
1978). Ridge axis discontinuities consequently occur of ridge have distinct, different sources in the mantle.

where the magmatic pulses finally come to rest. The First to third order segmentation is caused by the vari-
variable bathymetry and associated geophysical and able depth associated with magma migration; fourth