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Figure F1. A. Basement age vs. 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 that boundaries between erupted lavas, the dike–lava transition zone, and the sheeted dike complex/upper gabbro boundary are placed at arbitrary depths based loosely on 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 and Expedition 309. For complete discussion see Wilson, Teagle, Acton, et al. (2003).

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