Do we really need to drill through the intact ocean crust?

Abstract

We must persevere to drill through the intact ocean crust to fully address fundamental questions towards completion of the plate tectonics theory. The primary questions include: what is the ocean crust made up of, how thick is it and what is the petrological nature of the crust-mantle boundary (i.e., Mohorovičić discontinuity or Moho)? These questions may sound naive because they are widely believed to be well-understood facts, but they are not. Correctly, our current knowledge remains incomplete, and some popular misperceptions come from interpretations based on convenient assumptions. One assumption is that the ocean crust inferred from seismic data is of magmatic origin. Testing this assumption is a principal motivation of Project Mohole (1957–1966), attempting to drill intact ocean crust across the Moho into the mantle. Project Mohole failed because of its high cost, engineering challenges and insufficient tries, but the technologies developed made subsequent ocean drilling successful. However, answers to the original questions remain unsatisfactory. For example, seismic crust interpreted to be of magmatic origin is shown to have globally uniform thickness of 6.0 ± 1.0 km, but crust with such thickness at many slow-spreading ridge segments is dominated by serpentinized mantle peridotites exposed on seafloors. Therefore, the popular view on ocean ridge magmatism must be re-examined, which needs intact ocean crust drilling into the mantle. Drilling at geologically simple sites in the fast-spreading Pacific seafloor is most promising.

Keywords

Ocean crust formation / Ocean crust makeup and thickness varication / Hess-type ocean crust / Nature of the oceanic Moho / Scientific ocean drilling

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