Initiation of melting in large igneous provinces – a role for halogens?
Dr. Linda Kirstein, School of Geosciences, University of Edinburgh
([email protected]); Prof. Godfrey Fitton, School of Geosciences, University of
Edinburgh
Large igneous provinces (LIPs) include continental flood basalt provinces, oceanic plateau
and volcanic rifted margins. They are large volume, short duration events during which vast
quantities of mainly basaltic magma are erupted at the Earth’s surface. Their occurrence is
commonly associated with mass extinction events, although the nature of the relationship is
highly controversial. A number of different models exist to explain LIPs but the majority
agree that a thermal anomaly is required in order to produce the volumes of magma erupted
over geologically short periods of time (<5 Myr). The role of volatiles and of potentially more
fertile mantle sources is less well understood.
Associated with these large, basaltic lava eruptions remarkable quantities of SO2, CO2 and
halogens are released. In addition fluorite deposits are commonly associated with LIP
occurrences, for example the giant Amba Dongar deposit, Gugarat, India and the extensive
mineralisation associated with Permian-Carboniferous magmatism in northern Europe. What
affect these halogens have on the emplacement and chemical evolution of the system is not
clear.
High halogen concentrations in melts can result in deep degassing. Chlorine (Cl) and
fluorine (F) partition differently between fluid and melt, with Cl partitioning into aqueous
phases whilst F has a higher solubility in the melt phase. F will affect the concentrations of
elements that form complexes with it such as Nb, Ga and certain actinides.
In this project the early eruptive products of the rift-related Permo-Carboniferous magmatic
province in Norway (and elsewhere in Europe) will be sampled along with co-existing fluorite
deposits in order to evaluate the effect that F and Cl have on the chemistry of the magmas.
Halogen ratios (F/Cl) in the melt inclusions in the lavas will be determined along with whole
rock and mineral chemistry. The associated fluorite deposits will also be investigated and
fluid inclusions will be used to determine fluid composition and pressure-temperature
constraints. A comparison will be made with geochemical and geobarometry data collected
from alkaline magmatism associated with the Paraná LIP in order to evaluate the role of
fluids in the initiation and early evolution of the system.
Figure 1: Siberian LIP linked to end Permian mass extinction from Wignall, Nature, 2011
A comprehensive training programme will be provided comprising both specialist scientific
training and generic transferable and professional skills. This will include mineral chemistry,
whole rock geochemical analyses as well as melt and fluid inclusion analyses.
Applicants should have a natural science background ideally in the areas of Geology or
Earth and Environmental Sciences. A Masters in a relevant field would be an added
advantage.
Further reading or any references referred to in the proposal
Kirstein et al., 2001, Contributions to Mineralogy and Petrology 142:309-322; Elements vol 1,
December 2005 Large Igneous Provinces.
A project summary - (30 words max) which could be used for advertising
Large igneous provinces are some of the most dramatic igneous features on Earth, yet the
triggering mechanism that initiates these provinces is not well understood. This project will
explore the role of halogens in the evolution of these extraordinary systems.