Details of Award
NERC Reference : NE/G013942/1
Structural and magmatic evolution of the ocean crust from re-oriented IODP cores
Fellowship Award
- Fellow:
- Dr N Pressling, University of Southampton, Sch of Ocean and Earth Science
- Grant held at:
- University of Southampton, Sch of Ocean and Earth Science
- Science Area:
- Marine
- Earth
- Overall Classification:
- Earth
- ENRIs:
- Global Change
- Environmental Risks and Hazards
- Science Topics:
- Properties Of Earth Materials
- Tectonic Processes
- Technol. for Environ. Appl.
- Volcanic Processes
- Abstract:
- Studying the dynamic processes involving the creation of oceanic crust is problematic due to the inaccessibility of the seafloor. However, over the last 35 years, millions of pounds have been invested in large scientific ocean drilling vessels that are now capable of drilling hundreds of meters into the ocean floor to directly sample a cross section of the Earth's crust. By drilling in all the major oceans and seas, and analysing over 300km of hard rock and soft sediment, we have been able to make fundamental contributions to our understanding of the solid Earth cycle. However, the interpretation of any directional measurements made on recovered core samples is severely limited because the core is allowed to rotate inside the drill barrel during drilling. Example 1. Plate divergence at mid-ocean ridges generates 60% of the Earth's crust, but there are currently two competing models describing the large-scale faulting processes involved: one suggests that displacement occurs along flat low angle faults; the other suggests that the faults start steeper and then rotate to shallower angles over time. We can use the variation in the dip of the magnetic field direction (known as inclination) with depth, recorded by the rocks as they solidify, to track the amount of tectonic rotation experienced. However, because the core is free to spin inside the drill barrel, we do not know how the magnetic field direction changes relative to geographic north (known as declination). Therefore, we are forced to make assumptions about the direction and angle of the rotation axis, and there are an infinite number of solutions that can explain the data. Example 2. In slow-spreading crust, studies have shown that magma is transported laterally away from isolated magma chambers along the spreading axis, before moving upward to feed seafloor volcanoes. However, at fast-spreading ridges passive studies suggest that smaller magma lenses extend along the length of the ridge and little or no horizontal melt migration is needed to build the upper crust. Where magmatic intrusions cut through a drill core, the magmatic flow direction is recorded by aligned magnetic crystals. However, if we do not have information about the flow direction in terms of the geographic co-ordinate system, we cannot quantitatively comment on melt pathways. As part of this proposal I will be developing and computerising a technique that restores core pieces to their original orientation, thus recovering a wealth of lost directional information. The method uses data from a tool that is lowered into the empty borehole after the completion of drilling. The tool measures the variation in resistivity of the rocks making up the borehole wall and can pick out brittle features such as fractures, and magmatic and hydrothermal veins. The key is that the dip of these features is measured in the geographical reference frame because included on the same toolstring is a magnetometer that records the direction of magnetic north. It is then possible to match features seen on these borehole wall images to those measured on the core and calculate a re-orientation angle that brings the core back into its original position. Automating the re-orientation process will allow directional information to be recovered much more efficiently and robustly. Only with fully oriented data can I test hypotheses and constrain models describing the structural and magmatic evolution of ocean crust, like those proposed in the examples above.
- NERC Reference:
- NE/G013942/1
- Grant Stage:
- Completed
- Scheme:
- Postdoctoral Fellow (FEC)
- Grant Status:
- Closed
- Programme:
- Postdoctoral Fellowship
This fellowship award has a total value of £236,344
FDAB - Financial Details (Award breakdown by headings)
| DI - Other Costs | Indirect - Indirect Costs | DA - Estate Costs | DI - Staff | DI - T&S |
|---|---|---|---|---|
| £7,360 | £92,853 | £34,146 | £96,275 | £5,709 |
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