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Figure F1. A. Basement age versus depth of basement penetration for scientific drill holes deeper than 50 m drilled into in situ ocean crust formed at the mid-ocean ridges. B. Depth of penetration of drill holes into in situ basement clustered by broad spreading rate subdivisions where slow < 40 mm/y < moderate < 80 mm/y < fast. Note the boundaries between the erupted lavas, dikelava transition zone, and the sheeted dike complex/upper gabbro boundary are placed at arbitrary depths based loosely on the Hole 504B stratigraphy. Predictions based on marine seismic reflection studies indicate that the combined thickness of the lava-dike sequences should decrease with spreading rate but are yet to be tested, and whether it is the dikes or lavas that are thinned is so far unknown. Black lines = DSDP drill holes, dark blue lines = ODP drill holes, red lines = Holes 1256C and 1256D drilled into basement during Leg 206.