Fieldwork Grants - Reports

The Loch Maree Group: An archive of the Palaeoproterozoic carbon cycle

Gemma Kerr of the University of St Andrews was awarded a grant in 2011 to undertake detailed mapping and chemical analysis of the Loch Maree Group (LMG) in northwest Scotland. These two-billion year old rocks are Scotland's archive of the hallmark events that record oxygenation of the Earth's atmosphere and unprecedented fluctuations in the global carbon cycle. The aim of the project was to help refine geological relationships in the Loch Maree rocks and perform high-resolution carbon and oxygen isotope analysis. The project has resulted in better documentation of one of the oldest and largest known Carbon Isotope Excursions (CIE) and will enable more robust age determinations of the Loch Maree rocks and better place them in Earth history.

One month was spent mapping the Flowerdale and Cloiche marble belts and collecting 74 samples of multiple sections of each unit. The prepared marble samples were transported to the stable isotope facility at the Scottish Universities Environmental Research Centre (SUERC) for analysis. To help contribute to the geochronological efforts to constrain Paleoproterozoic CIEs, appropriate samples were collected for dating in the NERC Isotope Geoscience Laboratory (NIGL) in Keyworth (due to be completed in late January).

The results of the project have been highly satisfactory. The carbon and oxygen isotope analysis and XRF analysis confirm that there are distinct chemical signatures preserved in each of the marble belts. From this - and from mapping insights gained in the field - it can be inferred that each marble belt represents a distinct event in time. The Cloiche belt yielded delta 13C values as high as +13.5 parts per thousand, a signal similar to that recorded in the Lomagundi-Jatulian CIE rocks of the Fennoscandian shield. In contrast, the Flowerdale marbles yield delta 13C values around zero and therefore represent a return to the "norm". The XRF results may be used to infer possible depositional settings for the carbonates. Of particular note are the elevated levels of trace metals (copper, zinc, vanadium and barium) which suggest that the Flowerdale carbonates have formed in a deep marine environment associated with "white smokers" - hydrothermal vents on the ocean floor.

Due to the current levels of interest within the scientific community and the significance of the results, the data are being presented in lectures by Gemma Kerr and Tony Prave.

Figure 3: Cathodoluminescence image of a zircon taken from an intrusive gneiss body within the Loch Maree Group. Photo: NIGL.

Mapping the internal structure of faults in basalt in the North Atlantic Igneous Province (NAIP)
Rachael Ellen

Rachael Ellen from the University of Glasgow (now at University of Strathclyde, Glasgow) was awarded a grant in 2011 to study the internal structure of faults in basalt exposed in the Faroe Islands as part of her PhD project. With basalt sequences becoming increasingly important for hydrocarbon production and as potential host rock for CO2 and radioactive waste storage, it is crucial to understand what effect faults within these sequences have on fluid flow.

The Faroe Islands provided exceptional exposure of faults in basalt, allowing detailed mapping (1:3 scale) of each fault zone studied to highlight different components within the fault that can affect fluid flow migration. These components include fault rocks i.e. breccia (Fig.1), gouge, cataclasite, and slip surfaces, and sites of previous fluid flow pathways, i.e. mineral veins and zones of alteration (Fig.2). Fault displacement ranged from 18cm to 6m. The faults mapped in the Faroe Islands are being compared with fault maps collected from sites in Scotland and Iceland. Together these will provide the basis of a conceptual evolution model for faults in basalt. This evolution model, along with samples taken from each site for micro-structural analysis, will ultimately lead to a conceptual permeability evolution model for faults in basalt sequences, allowing the spatial variability of faults and fluid flow to be predicted and modeled.

Andrew Bell from the University of Edinburgh was awarded funds to study brittle deformation features on the Isle of Rum. Despite some recent advances, the origin of patterns of seismicity and ground deformation at active volcanoes is generally poorly understood. The Isle of Rum provides an opportunity to examine in the field the faults and fractures that would have been responsible for controlling deformation and generating volcano-tectonic earthquakes when the volcano was active.

Fieldwork focussed on a search for brittle deformation features in the central region of the layered ultramafic intrusion. Populations of significant (>100m in length) faults, with a range of strikes and dips, were identified within ultramafic breccias (Fig. 1). Mapping these features will constrain the relative timing of faulting with respect to specific magmatic events and allow quantification of the population statistics. In the Long Loch fault zone, there is clear evidence of alternation between brittle and ductile shear deformation within partially consolidated crystal mush, suggesting faulting contemporaneous with magmatism (Fig.2). The major fracture lineations in this zone that are visible on satellite images can also be traced in the field. On the basis of this visit, plans are being developed for further data analysis and modelling. Future field studies of the Rum volcano are likely.

Figure 1: Steeply dipping fault in ultramafic breccia on the slopes of Ruinsival, Rum

Figure 2: Interrelated brittle and ductile deformation processes in ultramafic breccia, Long Loch fault zone, Glen Fiachanis, Rum

William Hutchison – Report on field work at Volcán de Colima, Mexico. As an essential part of my Master’s Thesis, field work was undertaken at Volcán de Colima between the 21st of June and the 6th of September. Volcán de Colima- located in the Trans-Mexican Volcanic belt- is a typical subduction-originated calc-alkaline volcano. The recent history is one of distinctive episodes of effusive and explosive activity. In 2004 a substantial block-lava flow was extruded, reaching 2200m from the crater while in 2005/06 major explosive activity ensued, characterised by extensive ash clouds and pyroclastic flows.

The project aim was to constrain the dynamics of dome growth for the current lava dome. Growth began in 2007, and as of September 2010 it continues to grow in size although the effusion rate has noticeably decreased. The dome now partly fills the crater and the overhanging debris cascade down the south/southwestern flanks as rockfalls. Fieldwork was undertaken to collect infrared thermal data of the volcano. Images were collected from flights over the volcanic edifice and from overnight trips to the extinct Nevado de Colima, 6km to the North and where a permanent Protection Civil base is located.

The thermal data from the flights show heterogeneous temperature profiles. Features such as hotspots, ash rings and depressions on the dome surface can be readily identified. In addition time series can be generated to show max/mean temperature, heat flux and effusion rate to potentially reveal if there exists obvious systematic change during this effusive episode.
Thermal data from Nevado de Colima can be used to monitor fumaroles temperatures, this will be analysed to constrain if there exists any relationship between the internal plumbing systems of the dome and fumaroles. Infrared data may be of particular use in giving insight into volcanic activity and processes, making it an increasingly integral component of the continued monitoring effort.