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Quantifying Hydrothermal Exchanges between Seawater and the Lower Oceanic Crust: Evidence from the Oman Drilling Project


Project Description

Project Rationale:

Thermal and chemical exchanges between the oceans and the oceanic crust during hydrothermal circulation at mid-ocean ridges exert major controls on the chemistry of seawater. These exchanges influence global chemical cycles as well as the size and location of ocean ridge magma chambers. Observing the lower oceanic crust has proved extremely challenging and to date there are no deep drillholes that sample the in situ lower oceanic crust formed at fast spreading rates. Consequently, geologists have refocused efforts on the ocean crust exposed in the Semail ophiolite, an ancient slab of the ~95 Ma Tethyan ocean floor now exposed in the Omani mountains. The Oman Drilling Project (OmanDP) has drilled a series of boreholes through the lower oceanic crust and uppermost mantle exposed in Oman. 3500 m of diamond drillcores with near 100% recovery have been described and instrumentally scanned in unprecedented detail. The boreholes have been geophysically logged using wireline tools including optical imagery. The cores recover background and alteration features including delicate fault-zones and hydrothermal breccias. The cores and these instrumental data suites provide a unique opportunity to characterize and quantify the extent of seawater exchange with the lower oceanic crust.

Methodology:

This project will integrate traditional petrologic and geochemical techniques to determine the conditions and impacts of hydrothermal alteration with new machine learning approaches applied to the huge (>42 Tb) database of optical, X-ray CT and infrared scans to quantify the extents of alteration and the abundances of features such as veins, alteration halos and fault-zones. Whole rock and mineral petrography and isotope geochemistry (e.g., stable and Sr isotopes) will be used to identify alteration fluid sources and their chemical evolution, and the extents of hydrothermal exchange at different temperatures. Machine learning interrogations of drill core instrumental scans and wireline logs will be used to identify, count and quantify different features by deploying AI techniques already developed for similar geological and seafloor environments. However, confidence in such algorithmic approaches will require careful integration with and calibration against geological observations.

Similar large scale instrumental data suites are now starting to be collected by the minerals exploration industry but often without the complementary petrographic and analytical observations. The OmanDP drill cores coupled with the comprehensive instrumental data offer a unique opportunity to develop and calibrate approaches to provide quantitative drill core information to improve resource evaluation.

Training:

The INSPIRE DTP provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted in the Graduate School of the National Oceanography Centre Southampton.

Specific training includes:
• Training in all geochemical techniques, including sample preparation, elemental analysis by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and isotope analyses via Thermal Ionization Mass Spectrometry (TIMS), Stable isotope MS, and Multi-collector-ICPMS.
• The refinement of machine learning algorithms to automatically quantify drillcore images (optical, X-ray CT, Infrared) and wireline data. The student will develop Convolutional Neural Networks (CNN) that learn from partially labelled input data (drillcore and borehole images) to automatically identify different rocktypes and alteration styles to generate quantitative estimates of hydrothermal exchange and flag suspect intervals for closer human inspection.

Funding Notes

You can apply for fully-funded studentships (stipend and fees) from INSPIRE if you:
Are a UK or EU national.
Have no restrictions on how long you can stay in the UK.
Have been 'ordinarily resident' in the UK for 3 years prior to the start of the project.

Please click View Website for more information on eligibility and how to apply

References

Zihlmann, B., Müller, S., Coggon, R.M., Koepke, J., Garbe-Schönberg, Teagle, D.A.H., (2018) Hydrothermal fault zones in the lower oceanic crust: An example from Wadi Gideah, Samail ophiolite, Oman. Lithos: 323:103-124. https://doi.org/10.1016/j.lithos.2018.09.008

Harris, M., Coggon, R.M., Wood, M., Smith-Duque, C.E., Henstock, T.J., Teagle, D.A.H., (2017) Hydrothermal cooling of the ocean crust: Insights from ODP Hole 1256D. Earth Planet. Sci. Letts. 462:110–121. doi: 10.1016/j.epsl.2017.01.010

Coggon, R.M., Teagle, D.A.H., Harris, M., Davidson, G.J., Alt, J.C., Brewer, T.S., (2016) Hydrothermal contributions to global biogeochemical cycles; Insights from the Macquarie Island ophiolite. Lithos 264:329-347. http://dx.doi.org/10.1016/j.lithos.2016.08.024

How good is research at University of Southampton in Earth Systems and Environmental Sciences?

FTE Category A staff submitted: 68.62

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