Classification of Passive Margins
There are four different perspectives needed to classify passive margins:
- map-view formation geometry (rifted, sheared, and transtensional),
- nature of transitional crust (volcanic and non-volcanic),
- whether the transitional crust represents a continuous change from normal continental to normal oceanic crust or this includes isolated rifts and stranded continental blocks (simple and complex), and
- sedimentation (carbonate-dominated, clastic-dominated, or sediment starved).
The first describes the relationship between rift orientation and plate motion, the second describes the nature of transitional crust, and the third describes post-rift sedimentation. All three perspectives need to be considered in describing a passive margin. In fact, passive margins are extremely long, and vary along their length in rift geometry, nature of transitional crust, and sediment supply; it is more appropriate to subdivide individual passive margins into segments on this basis and apply the threefold classification to each segment.
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