HR: 0800h
AN: V31D-0688    [Abstracts]
TI: Experimental Determination of Trace Element Partition Coefficients Between Zircon, Garnet and Melt
AU: * Taylor, R J
EM: rich.taylor@ed.ac.uk
AF: University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh, Mid EH9 3JW, United Kingdom
AU: Harley, S L
EM: simon.harley@ed.ac.uk
AF: University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh, Mid EH9 3JW, United Kingdom
AU: Hinton, R W
EM: richard.hinton@ed.ac.uk
AF: University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh, Mid EH9 3JW, United Kingdom
AU: Elphick, S
EM: stephen.elphick@ed.ac.uk
AF: University of Edinburgh, Kings Buildings, West Mains Road, Edinburgh, Mid EH9 3JW, United Kingdom
AB: The problem of relating ages, as calculated by zircon U-Pb geochronology, to processes and hence geoological events is central to understanding mountain building and crustal evolution. Accurate P-T-t paths can only be produced if zircon growth can be linked to specific rock and mineral processes used to establish pressure and temperature values for metamorphic episodes. As a major metamorphic mineral in crustal events, garnet is widely used as a thermobarometric tool, and linking garnet growth to zircon formation could be used to refine the interpretation of U-Pb ages. Attempts to resolve this issue have focussed on REE partitioning between zircon and garnet, both of which strongly incorporate the HREE into their structure, and so it is possible there is a distinct REE partitioning signature which will highlight whether the two minerals have grown in equilibrium. There are two complementary methods to obtaining this information, empirical and experimental. Empirical methods of determining this signature using carefully selected rocks have proved troublesome, with a wide range of partitioning signatures found. This work has used experimental techniques to produce zircon-melt, garnet-melt and zircon-garnet-melt partition coefficients at a range of P-T conditions using synthetic materials. Zircon and garnet are grown in trace element equilibrium with a water-undersaturated granitic melt, which represents partial melts formed in the lower crust during anatexis. Temperature ranges from 850°C to 1000°C at a pressure of 5Kbar were produced using internally heated gas apparatus. Trace element concentrations were measured using SIMS analysis at the Ion Microprobe Facility at the University of Edinburgh. The experimental data produced will be applied to interpret chemical signatures in zircon in garnet-bearing metamorphic rocks, and will provide an objective basis for interpretation of the timing of growth or recrystallisation of zircon in many high-grade terrains.
DE: 3630 Experimental mineralogy and petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting