HR: 12:05h
AN: V12A-08    [Abstracts]
TI: What's in a Whole Rock Analysis? Integrating Crystal Size Distributions and Micro-Scale Isotopic Variations at Stromboli Volcano
AU: * Morgan, D
EM: daniel.morgan@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Science Laboratories South Road, Durham, DH1 3LE United Kingdom
AU: Chertkoff, D G
EM: d.g.chertkoff@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Science Laboratories South Road, Durham, DH1 3LE United Kingdom
AU: Jerram, D A
EM: d.a.jerram@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Science Laboratories South Road, Durham, DH1 3LE United Kingdom
AU: Davidson, J P
EM: j.p.davidson@durham.ac.uk
AF: Department of Earth Sciences, University of Durham, Science Laboratories South Road, Durham, DH1 3LE United Kingdom
AU: Francalanci, L
EM: lorella@unifi.it
AF: Dipartimento di Scienze della Terra, Università degli Studi di, Firenze, Firenze Italy
AB: Analysis of feldspar crystals by microsampling at high spatial resolution has allowed the construction of a detailed crystal isotopic stratigraphy for a lava from the lower Vancori sequence (26,000 years before present) of Stromboli volcano. The crystals record the magmatic evolution of the Stromboli system prior to the eruption of the sample. ⁸⁷Sr / ⁸⁶Sr isotope ratios at nucleation were elevated, with ⁸⁷Sr / ⁸⁶Sr of 0.70650 relative to ⁸⁷Sr / ⁸⁶Sr of 0.70617 in the groundmass glass, with gradual mixing between core and rim towards the glass values. Quantifying the crystal size distribution data then provides a time aspect for the isotopic evolution of the crystal population. Integrating these two types of analysis allows the investigation of changes in the chemical budget through time as the crystal population evolved, a powerful tool for investigating magmatic processes. The presence of isotopically distinct cores and rims shows significant retention of crystals occurring beneath Stromboli and the subsequent incorporation of these crystals into erupted materials. These isotopic core-rim relationships are found consistently between different crystals of the same population. That the variations are correlated across crystals shows that the system was both simple in structure and well-mixed in the Vancori period, and that crystal inheritance was likely between different magma batches at Stromboli. After establishing a timeline of variation in the isotopic data, the isotopic variation can be integrated through the CSD analysis to determine the mean isotopic ratio of the crystal population. This can then be compared with the groundmass glass values and, when mixed, reproduces the whole rock isotopic ratio. That the measured whole-rock ratio does indeed reflect the theoretical sum of its component parts confirms the relative simplicity of the feldspar population as well as the validity of assumptions inherent in the CSD analysis of a simple, linear growth rate.
UR: http://www.dur.ac.uk/erupt.geolsci/
DE: 3600 MINERALOGY AND PETROLOGY
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3618 Magma chamber processes (1036)
DE: 3625 Petrography, microstructures, and textures
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005