Overview

Project Highlights:

  • First geochronological - geochemical transects across a little known, but major, continental arc, to establish composition-age progressions
  • Petrogenetic study of the first recognised volcanic adakites from Antarctica
  • Link geochemical variability among the arc rocks to plate reorganisations and magmatic flare-ups

The poorly understood Antarctic Peninsula continental volcanic arc was active between Late Jurassic and Early Miocene times. Although many expeditions have visited parts of the arc, and the northern end of the arc has been well-studied, there are vast tracts of the arc for which there are neither geochronological - stratigraphic constraints nor geochemical charcterisations . A recent review of the available data (Leat and Riley, in press) found four chemically distinct volcanic groups within the arc: calc-alkaline, high-Mg andesites, adakites and a peralkaline high-Zr group. Within the calc-alkaline group, compositions range from those generated from both depleted and enriched mantles, and variability in the importance of crustal contributions to the magmas is evident in previous studies of volcanic anf plutonic rocks of the arc. However, few constraints between the magma groups are known, including their timing within arc development and their relation to each other. The Leat and Riley (in press) study highlighted for the first time the perhaps unusual feature of numerous high-Mg adakites within the arc, but the significance of this is uncertain due to a lack of geochronological controls, and the chemical relationship between the adakites and dominant calc-alkaline group. The origin of high-Mg adakites globally is still uncertain but likely to result from melting of mantle that has consumed partial melts of subducting slabs. The study will test this hypothesis in a location where normal arc rocks (the calc-alkaline group) and adakites were erupted in close proximity. A migration of the arc toward the trench of 25-100 km is indicated to have occurred during the Cretaceous, but again, its timing is very poorly constrained due to lack of geochronological data. New isotopic ages will enable this to be confirmed, and tectonic explanations developed.

This project will take advantage of the exceptional collection of samples from the length of the arc held by the British Antarctic Survey collected over decades, with access to it through collaboration with BAS scientist Dr Riley. The link between UoL and BAS is enhanced by two honorary Leicester scientists Drs Leat and Smellie who have formerly been BAS-scientists and whom collected many of the legacy samples. The aim of the project is to establish how the high-Mg adakites fit into the development of the Antarctic Peninsula arc, what the controls on these rocks were, and what the interplay between the slab dynamics and the crustal controls was in the evolution this arc.

The project will suit a student interested in geochemistry and geochronology, taking apart a poorly explored region, and with a keen interest in petrogenesis and arc magmatism.

a) Columnar jointed Cretaceous arc volcanic rocks from Central Palmer Land

Methodology

The student will work with Drs Leat, Smellie and Riley to assess the legacy sample archive to put together a subset of samples for the research. This will involve characterisation of the samples, and compilation of their geographic localities and available data. With the selected samples, the student will (1) date the samples using the technique best suited for the rock (either U/Pb or Ar-Ar dating) and (2) geochemically characterise the samples using whole rock XRF, ICP-MS, and radiogenic isotopes (Sr-Nd-Pb-Hf). The student will receive full training in these techniques and be taught how to run the samples for themselves, where possible. The data will be used to assess fractional crystallisation processes, source characteristics of the rocks, and build up a picture of the evolution of the arc. Continuous along and across-arc variations have previously not been possible due to large areas not having any available data. This study will fill significant gaps in our understanding by producing data-rich transects that can be used to assess geochemical changes in sources with time and place within the arc. This will be the first study to examine the arc evolution, and the student will be expected to compare the arc development to other well-characterised arcs such as the South American arc. Although no fieldwork is required for the sample collection, fieldtrips will be arranged to suitable analogous examples of arc volcanism.

The student will join a well established research group in geochemistry and petrogenesis.

Training and Skills

In addition to the geochemical techniques described above, and geochemical modelling, there will be opportunities to present within lab groups and seminars at Leicester and to national and international meetings (e.g. Volcanic and Magmatic Studies Group and Goldschmidt). Training will be provided on science writing for international publications, and for research proposals.

Timeline

Year 1: Bring together the available information for the Antarctic Peninsula arc. Examine the rock collections for the arc and together with staff from BAS bring together a representative range of rock types from across and along the arc. Assess what geochemical techniques will be best employed to characterise the rocks. Using the rock crushing, XRF and ICPMS facilities at Leicester, begin characterising the samples. Give a presentation within the School.

Year 2: Select a sub-set of samples for geochronology and prepare samples for either U/Pb or Ar/Ar dating. Using the chemical data, determine the petrogenesis of the rocks by undertaking chemical modelling. Select a subset of samples for radiogenic isotope study. Give a presentation at a national meeting.

Year 3: Interpret the isotope, geochronological and wholerock data to draw together an evolutionary model of the development of the volcanic arc. Contrast this with the development of other continental arcs and assess the implications for regional dynamics. Give presentation at international meeting. Thesis writing.

Partners and collaboration (including CASE)

A strength of the project is that the student will benefit from working closely with experts who have worked in Antarctica for many years and been involved in the collection of many of the sample suits. Two of the scientists are expert geochemists and the other a highly experienced volcanologist. This project is made possible only by their involvement.

Further Details

Please contact Dr Tiffany Barry at the University of Leicester, on tlb2@le.ac.uk, for further details.