Overview

Project Highlights:

 

  • Development of a new technique for isotopic dating and tectonic-source fingerprinting of K-feldspar
  • Training in advanced geochemical techniques
  • Working at the cutting edge of the new field of LA- ICP-MS/MS geochronology development
  • Project co-development by the student and supervisors
  • Development of industrial applications with CASE partner

Potassium feldspar is one of the most common minerals in the continental crust, yet is undervalued for the information it can reveal about it’s source. Radioactive 40K decays to both Ar (11%) and Ca (89%) with a half-life of c.1.2 Ga (Fig 1).   This means that K-feldspar can be dated using two radioactive decay schemes: K-Ar (Ar/Ar) and K-Ca. K-Ar and Ar-Ar dating of K-feldspar is common, but it is both expensive and time-consuming.   For provenance studies, i.e. tracking sediment to source, igneous pluton to melting source, or economic resource to source, a rapid and cheap technique for both dating and chemical fingerprinting is desirable. K-Ca dating, long ignored because of the difficulties in separating and measuring 40Ca and 40K (because they have the same mass), is now made possible by modern analytical equipment like SIMS and LA-ICP-MS/MS that can distinguish between the two isotopes. Furthermore, because of its high concentrations of Pb, K-feldspar source can be “fingerprinted” using Pb isotopes (e.g. White et al, 2016; Tyrell et al 2007; Fig 1).  

Many different minerals are used to link sediment to its source (i.e. Fig 1): the resistant mineral zircon is the most common provenance indicator. However the more fragile K-feldspar has a different story to tell as it does not survive long during energetic sedimentary transport. K-feldspar is also highly unstable in tropical environments and acidic conditions. It is thus ideal for investigating first-cycle sedimentary provenance in cooler climate conditions.

This project will develop a new and promising technique for rapid, precise and accurate in-situ K-Ca dating of K-feldspar. The student will be trained to find the optimum instrument set-up, will develop new standards and, in combination with Pb isotope chemistry, will apply this tool to a variety of topical geological problems. Various applications include, but or not limited to: comparison of heavy and light detrital mineral ages and sources within long river drainage systems, provenance of glaciogenic sediments in tillites and/or in ice rafted debris recovered from deep sea drill cores, the unroofing of batholiths within an orogenic system from syn-orogenic sediments and the effect of microstructure and alteration on age. The final application for this new tool within this PhD can be chosen by the student in collaboration with the supervisory team.

 

Figure 1: Left: K-feldspar in hand specimen and thin section (XPL)).  Middle: Main isotopic age and source tracers in K-feldspar.  Right: The weathering processes and provenance of individual detrital grains that can be tracked using K-feldspar.

Methodology

This project will develop the potential of K-Ca dating using the ion microprobe at Edinburgh on which the supervisory team have been developing the technique. It will also develop the use of laser ablation ICP-MS/MS K-Ca dating at the Open University: this is an emerging alternative technique that has the potential to offer cheaper and more rapid analysis with less sample preparation, with industrial applications through the CASE partner Chemostrat. Pb isotopes will be measured by laser ablation MC-ICPMS at the University of Portsmouth, which has been one of the pioneers of this technique.

A variety of samples suitable for initial development work are immediately available in the Open University and Portsmouth collections. Once specific settings of interest have been identified, there will be opportunities for fieldwork to collect further samples as needed. In addition, mineral major and trace element chemistry data will be collected using the OU electron microprobe and LA-ICP-MS, respectively.

Training and Skills

Students will be awarded CENTA2 Training Credits (CTCs) for participation in CENTA2-provided and ‘free choice’ external training. One CTC equates to a 1⁄2 day session and students must accrue 100 CTCs across the three years of their PhD. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes and environmental challenges specific to CENTA2 research themes.

Specific training in analytical techniques and data reduction methods will be provided at the Open Portsmouth and Edinburgh Universities and via external courses. In addition to scientific skills, the student will be trained in a variety of transferrable skills including science communication, data management and project/budget management.

Timeline

Year 1: Petrographic analysis of available samples. Initial major and trace element analyses. Fieldwork to collect samples as required. Initial development of K-Ca dating methods, including setting up standards.

Year 2: Processing and selection of collected samples as necessary for further specific and in-depth analyses with the aim of completing the bulk of the analytical work during this year. Preparation of first manuscript for publication.

Year 3: Attendance at an international conference. Completion of data collection and synthesis. Preparation/revision of further paper manuscripts and thesis writing.

Partners and collaboration (including CASE)

Chemostrat, the CASE partner on this project, is a world-leading company providing chemostratigraphy and stratigraphic services around the globe. This project involves collaboration with Alex Finlay (alexfinlay@chemostrat.com) and will allow the student to experience working in a multi-disciplinary geo-services company and contribute to their ongoing success. Specifically, the student will help develop K-Ca dating of detrital K-feldspar as part of Chemostrat’s Sandtrak provenance product, including marketing and sales.

 

Further Details

Students should have experience with analytical geochemistry and a passion for detailed and precise labwork. Experience of geological fieldwork is desirable. The successful student will join a well-established team researching Dynamic Earth processes at the Open and Portsmouth Universities.

Please contact Clare Warren (clare.warren@open.ac.uk) or Craig Storey (craig.storey@port.ac.uk) for further information.

Applications must include: