Application of imaging spectroscopy to investigate seafloor fluid/rock reactions

Lead Supervisor: Dr Michelle Harris

Location: University of Plymouth, School of Geography, Earth and Environmental Sciences

Duration:  6-8 weeks

Suitable undergraduate degrees: Earth Sciences, Chemistry (if interested in application of spectroscopy data) 

Project background

Seafloor hydrothermal systems are an integral component of mid-ocean ridges, they influence the formation and cooling of the oceanic crust, host unique ecosystems and modify the chemistry of the crust, oceans and ultimately the mantle via the subduction of altered ocean crust. Despite this importance, fundamental questions remain about the subsurface structure of these hydrothermal systems, including the distribution of pathways. Progress is also limited by the low recovery of drill core form the oceans, and limited by the number of thin sections that can be analysed. The Oman Drilling Project has addressed the first of these challenges by diamond coring (with100% core recovery) multiple stratigraphic levels within the Semail ophiolite in Oman. To address the second challenge, a novel dataset has been generated where all the cores have been imaged using a bespoke imaging spectrometer equipped with both visible-near infrared and shortwave infrared sensors. This approach exploits known absorption features within a mineral to allow the mineralogy to be determined at high (~250 micron) resolution (and is increasingly being used by mineral exploration companies). Subsequent processing of these datasets have generated high resolution mineral maps over many kilometres of drill core (Greenberger eta al 2021,https://doi.org/10.1029/2021JB021976), and provide an exceptional opportunity to investigate the type and distribution of fluid/rock reactions in the ocean crust. To exploit this dataset further, we need to translate mineral occurrence into an alteration type, which is defined by the mineralogy, textural relationships and spatial occurrence.  The ultimate aim is to be able to robustly quantify the proportion of each alteration type and integrate this with the geochemistry of each alteration type to quantify the chemical changes associated with seafloor hydrothermal systems.

In this project you will work with a subset of the Oman Drilling Project imaging spectroscopy dataset and accompanying individual samples to develop a library of characteristic alteration type maps and explore ways to use these to estimate the abundance of each alteration type. You will be trained in traditional optical petrography of secondary mineralogy and petrology using a range of suitable thin sections and individual samples to provide a thorough understanding of the minerals and their range of textural occurrences. You will be introduced to the imaging spectroscopy dataset, develop an understanding of the benefits and limitations of the dataset and use it to identify key alteration types. A range of data already exists for these cores, and you will become familiar with core logging procedures and how to analyse and manipulate a variety of descriptive and quantitative data.  There are also opportunities to learn how major and trace element geochemical data is generated. You will become part of an international team working on the hydrothermal alteration of the Oman ophiolite, and will participate in regular zoom meetings with collaborators at Caltech (who generated the imaging spectroscopy dataset) along with summer interns also working on this dataset at Caltech. We have an active group at UoP working on the Oman ophiolite and you will interact with researchers at all academic levels.