FEC Recovery for Co-Chief Scientists Duties for Prof Damon A.H. Teagle and Petrologist Dr Michelle Harris; IODP Expedition 335 Superfast 4

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

The mid-ocean ridges form a chain of mountains in the oceans that circuit the Earth like seams on a baseball. These ridges are the constructive plate boundaries where new ocean crust is formed by plate tectonic spreading. This is the major process by which the Earth releases its internal heat, and ~60% of the Earth's surface was formed in the past 180 million years. Because magma is erupted onto and intruded into the ocean crust at ~1200 deg C, seawater that percolates into the crust becomes vigorously heated, commonly resulting in submarine geysers known as black smokers that disgorge >350 deg C, sulfide-rich fluids. There is a very close relationship between magma and hydrothermal "hot water" circulation.

Because the ocean ridges are beneath >2000 m of water many of the processes related to their formation remain poorly understood. Scientists using submersibles can observe only the most recently erupted lavas. Geophysicists can make measurements of the ocean crust using seismic velocities (the speed that waves travel through rocks), but their results must be calibrated against actual rocks to be understood. Sampling the sub-surface of the ocean crust requires deep drilling and the recovery of basement rock cores has been a major goal of scientific ocean drilling since the 1960s. Ancient oceanic rocks preserved on land, known as ophiolites, suggest that the ocean crust is made of three basic layers: erupted lavas, commonly with pillowed shapes, that overly vertical intrusions known as sheeted dikes, which overly, coarse-grained gabbroic rocks that are crystallized magma chambers. To date only two scientific drill holes have penetrated the completely through lavas into the dikes; ODP Holes 504B and 1256D. IODP Expeditions 309-312 returned to Hole 1256D in 2005 and deepened that hole to >1500 m, completely through the lavas, dikes, and into the dike-gabbro transition.

Hole 1256D in the eastern Pacific Ocean, was drilled into crust that formed at a very fast spreading rate (>200 mm/yr), because gabbros were correctly predicted to be at their shallowest there. Although only ~20% of the global ridge axis is spreading at fast spreading rates (>80 mm/yr full rate), 60% of the current ocean basins and ~30% of the Earth's surface was formed by fast spreading. Crust formed at fast spreading rates should be relatively uniform, therefore drilling at a single location can be reasonably extrapolated to describe a significant portion of the Earth's crust. This hole is now at a depth where we will be able to sample gabbros for the first time in intact ocean crust. These rocks make up two thirds of the oceanic basement formed in ancient magma chambers. However, the volume and geometry of such magma chambers are poorly known. Also poorly known is the influence of seawater percolating down through the crust on cooling the lower crust and removing heat generated during crystallization. Other fundamental parameters such as the geological meaning of Seismic Layer 3 and the Layer 2/3 boundary, as well as the contribution of the lower oceanic crust to seafloor magnetic anomalies remain poorly understood.

The cores and geophysical data recovered on IODP Expedition 335 from Hole 1256D will provide a unique resource for understanding the igneous construction of the ocean crust. By making careful descriptions linked with shipboard (and post-cruise) chemical analyses we will be able to calculate the size of magma chambers, the physical conditions of fluid-rock interactions, and calibrate remote regional seismic and magnetic geophysical measurements. This will lead a significantly improved knowledge of how the oceanic crust is constructed and ages away from the ocean ridges, and test long-standing, competing models magmatic accretion and hydrothermal cooling.

Planned Impact

1. Who will benefit from this research?
This project will make a significant scientific advancement towards understanding the magmatic construction of the oceanic crust and the role that hydrothermal alteration of the ocean crust plays in global chemical cycles.
This project will benefit the following specific users:
(a) Marine geologists
(b) Hydrothermal ore system geologists
(c) Earth System Scientists
(d) The large community of scientists working towards drilling to the Mantle
(e) School children and the wider public excited by the exploration of the Earth

2. How will they benefit from this research?
(a) The formation of new ocean crust at the mid-ocean ridges is the largest magmatic process on our planet and is the foundation step in the plate tectonic cycle. With successful coring and wireline measurements we will test long-standing, competing hypotheses of magma chamber size, shape and distribution.
(b) Hydrothermal Ore Geologists: This project will establish the extent and vigor of hydrothermal circulation in the deep crust. Better knowledge of these processes will inform mineral exploration and allow improved estimates of hydrothermal fluid fluxes.
(c) Earth System Scientists: Robust knowledge of the hydrothermal contribution to seawater chemistry is an essential component for understanding records of past seawater chemical and isotopic compositions that record the changing balance between major Earth system processes.
(d) Drilling a complete section of oceanic crust, through the MoHole and a significant distance in to the upper mantle is a Primary Challenge of the New Science Plan for the next phase of scientific ocean drilling ("Illuminating Earth" International Ocean Discovery Program Science plan for 2013-2023). Knowledge of drilling conditions gained from IODP Expedition 335 will be critical step for future planning of deep crustal drilling.

3. What will be done to ensure that they benefit?
A number of activities will be undertaken:
(a) We will engage with Geologists, Earth System Scientists, Ore System Geologists, Global Chemical Cycle Modelers through publications, conference attendance and hosting of workshops (at no cost to this proposal). The PI will ensure that this work features in invited talks at other institutions. The multidisciplinary nature of ocean drilling science naturally leads to contact with scientists from the wider earth system science community.
(b) The PI is closely engaged with the deep ocean lithosphere drilling community as a proponent of Mission Moho, and a common contributor at relevant workshops and sessions at international meetings. The recent Comment in Nature "Journey to the Mantle of the Earth" by Teagle and Ildefonse (Nature, 471:437-439; 24 March, 2011) has already generated huge scientific, media and public awareness of IODP Expedition 335 and future plans to drill to the mantle.
(c) We will engage with wider users of this work via the development of a "Deep Ocean Drilling" web presence on the Univ. Southampton website and keep this up to date with publicly accessible as well as specialist scientific information (at no cost to this proposal). All analytical data will be published in peer-reviewed journals but the meta-data for this data and publications will be made available on the "Deep Ocean Drilling" website.
(d) At the request of the Co-chiefs, the Consortium for Ocean Leadership (COL; Washington, DC) has recruited a scientific graphic artist, Ms Sarah McNaboe, who will sail on Expedition 335 and work closely with the Co-Chief Scientists. Ms McNoboe will prepare synthesis illustrations for this specific cruise and also for the wider ocean lithosphere / Mission MoHole / Mantle community to make more professional the graphic images available for scientific and outreach documents.
(e) Ms Wendy Gorton (Teacher at Sea, American International School, Chenai), and Ms Sarah Saunders (COL), will be sailing to ensure the widest possible public outreach.

Publications

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Harris M (2017) Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D in Earth and Planetary Science Letters

 
Description Teagle - lead proponent and Co-Chief Scientist on IODP Expedition 335 "Superfast Spreading Rate Crust IV". This cruise encountered numerous difficulties with hole instability and the lost of a hard formation drill bit, but we managed to remove debris, clean and secure the formations for future drilling
Exploitation Route IODP Proposal 522Full5 is still in the system and awaiting re-scheduling. The Superfast mission has been re-classified as a Multiphase Drilling Proposal.
Sectors Energy,Environment

URL http://publications.iodp.org/proceedings/335/335title.htm