Overview

Project Highlights:

 

  • Explore the key factors controlling the distribution of economically important metals in the crust.
  • Use electron microprobe and state-of-the-art laser ablation (LA) ICP-MS imaging of igneous minerals to understand the processes taking place in magma chambers prior to volcanic eruptions.
  • Calculate the total loss of sulphur to the atmosphere during different styles of volcanic eruptions.

There is a global association between the occurrence of magmatic hydrothermal ore deposits and subduction zones. This association indicates that subduction zone magmas contain the necessary ‘ingredients’ required to fuel the formation of copper-sulfide-rich ore deposits. However, the distribution of ore deposits in the crust above subduction zones is sporadic. Recent studies have shown that the majority of magmas that erupt though the continental crust above subduction zones are typically depleted in economically important metals such as copper and gold1. It remains unclear which crustal and/or mantle processes predispose some subduction-zone magmatic systems to be associated with ore deposits compared to others. In addition to the sporadic formation of ore deposits, it also remains unclear why some subduction zone magmas release voluminous poisonous sulphur-rich gases during eruption, whereas others do not.

Popocatépetl volcano (5426 m) is one of the most dangerous and active volcanoes in Mexico. It is located only 70 km from Mexico City, with more than 30 million people living in a radius of 70 km from the crater. It is characterised by extremely high SO2 emission rates2, a wide range of eruption styles including highly explosive Plinian events, alternating with persistent activity characterised by lava dome growth and moderately explosive vulcanian activity3. One of the largest Plinian eruptions, the Pumice with Andesite Plinian Eruption (PwA)4, occurred 14,000 years ago. It is well known that magma mixing is one possible trigger of an eruption. Recent studies5 are questioning the existing paradigm that there is a direct relationship between frequency and magnitude of eruption and magma injection.

 

 

Figure 1: Popocatépetl volcano is one of the most dangerous and active in Mexico (photo by Petrone).

Methodology

The Natural History Museum holds a collection of over 200 specimens of the last 40 kyrs of activity of Popocatépetl volcano, Mexico. Recently-developed laser ablation (LA) ICP-MS protocols will be employed for in situ analysis of critical trace element concentrations in key minerals and mineral-hosted melt inclusions, including both spot and laser mapping techniques. Alongside electron probe micro-analysis (EPMA) for major and volatile element contents, this data will be used to reconstruct the behaviour of the economically important elements (e.g., S, Cu, Se, Ag and Au) during crustal processes (e.g., fractionation). Elemental diffusion between melt inclusions and hosting minerals will be used to investigate the timescales of mobility of the economically important elements. These constraints will be used to calculate the total loss of sulphur to the atmosphere during different styles of volcanic eruptions.

Training and Skills

The successful student will be trained in advanced petrological and geochemical analysis of igneous rocks. In situ analysis and laser mapping will be central to the project. Training in modelling techniques, including the behaviour of trace elements during melting of the mantle, fractionation and diffusion will be provided.

The School of Environment, Earth and Ecosystem Sciences has a thriving postgraduate community. Online teaching opportunities via the Open University Virtual Learning Environment are available, including on the new Massive Open Online Courses (MOOCs). Our current graduate students are very active in science outreach on digital platforms (e.g. http://www.fieldworkdiaries.com/) and at local primary schools. The student will also benefit from constant interaction with the Natural History Museum, which hosts cutting edge facilities and a world-leading collection of samples from Popocatépetl volcano.

Timeline

Year 1: Learning from the previous literature the potential controls on the behaviour of the economically important elements during magmatic processes. Sample preparation and initial data collection.

Year 2: Further data collection, modelling of igneous processes, initial synthesis of findings (paper or conference).

Year 3: Final data collection and synthesis of results. Preparation of publications and thesis chapters. Presentation of results at an international conference.

Partners and collaboration (including CASE)

The PhD project will be run in collaboration with a NERC funded consortium (From Arc Magmas to Ore Systems, FAMOS) of international researchers. The project aims to develop new exploration tools to help locate metal resources in volcanic arcs by understanding the fundamental processes involved in cycling magmas, fluids ad metals in these zones (http://www.nhm.ac.uk/our-science/our-work/sustainability/from-arc-magmas-to-ores.html).

Further Details

Students should have a strong background in geochemistry and enthusiasm for igneous petrology. Experience of geochemical modelling is desirable. The student will join a well-established team researching geochemical processes at the Open University.

Please contact Frances Jenner [frances.jenner@open.ac.uk] or Chiara Petrone, [C.Petrone@nhm.ac.uk] for further information.

Applications must include: