Workshop Reports Workshop report: Exploring deep oceanic crust off Hawai'i

For more than half a century, exploring a complete sequence of the oceanic crust from the seafloor through the Mohorovicic discontinuity (Moho) and into the uppermost mantle has been one of the most challenging missions of scientific ocean drilling. Such a scientific and technological achievement would provide humankind with profound insights into the largest realm of our planet and expand our fundamental understanding of Earth's deep interior and its geodynamic behavior. The formation of new oceanic crust at mid-ocean ridges and its subsequent aging over millions of years, leading to subduction, arc volcanism, and recycling of some components into the mantle, comprise the dominant geological cycle of matter and energy on Earth. Although previous scientific ocean drilling has cored some drill holes into old (> 110 Ma) and young (< 20 Ma) ocean crust, our sampling remains relatively shallow (< 2 km into intact crust) and unrepresentative of average oceanic crust. To date, no hole penetrates more than 100m into intact average-aged oceanic crust that records the long-term history of seawater-basalt exchange (60 to 90 Myr). In addition, the nature, extent, and evolution of the deep subseafloor biosphere within oceanic crust remains poorly unknown. To address these fundamentally significant scientific issues, an international workshop Exploring Deep Oceanic Crust off Hawai'i brought together 106 scientists and engineers from 16 countries that represented the entire spectrum of disciplines, including petrologists, geophysicists, geochemists, microbiologists, geodynamic modelers, and drilling/logging engineers. The aim of the workshop was to develop a full International Ocean Discovery Program (IODP) proposal to drill a 2.5 km deep hole into oceanic crust on the North Arch off Hawai'i with the drilling research vessel Chikyu. This drill hole would provide samples down to cumulate gabbros of mature (similar to 80 Ma) oceanic crust formed at a half spreading rate of similar to 3.5 cm a(-1). A Moho reflection has been observed at similar to 5.5 km below the seafloor at this site, and the workshop concluded that the proposed 2.5 km deep scientific drilling on the North Arch off Hawai'i would provide an essential pilot hole to inform the design of future mantle drilling.

Automated summary

Study of the oceanic crust and deep mantle through scientific ocean drilling is a challenging mission that expands our understanding of the Earth's interior and geodynamic behavior. International workshops and drilling proposals aim to further explore oceanic geology and biosphere through deep scientific drilling.