HR: 0800h
AN: U21B-0423    [Abstracts]
TI: Putting the Dynamics in Chemical Geodynamics
AU: * Spiegelman, M
EM: mspieg@ldeo.columbia.edu
AF: LDEO/Columbia, Rt 9W, Palisades, NY 10964,
AU: * Spiegelman, M
EM: mspieg@ldeo.columbia.edu
AF: APAM, Columbia, New York, 10027,
AU: Katz, R F
EM: rfk22@cam.ac.uk
AF: ITG, Univ. Cambridge, Cambridge, CB3 OEZ, United Kingdom
AU: Kelemen, P B
EM: peterk@ldeo.columbia.edu
AF: LDEO/Columbia, Rt 9W, Palisades, NY 10964,
AU: Fang, Y
EM: yf91@columbia.edu
AF: APAM, Columbia, New York, 10027,
AU: Collier, M
EM: collier@ldeo.columbia.edu
AF: LDEO/Columbia, Rt 9W, Palisades, NY 10964,
AU: Holtzman, B
EM: benh@ldeo.columbia.edu
AF: LDEO/Columbia, Rt 9W, Palisades, NY 10964,
AB: An outstanding goal for both geochemists and geophysicists is to understand how to use the wide range of proxy geochemical (and geophysical) data to make useful inferences about the current and past dynamics of the planet. To relate data to dynamics, however, requires models that include the fundamental processes that affect chemical variability: i.e. source heterogeneity, chemical fractionation (melting/reactions), chemical transport and mixing. In particular, most models of chemical evolution do not include explicit fluid or magma transport and questions remain as to how much observed chemical variability can be attributed to magma dynamics. We discuss recent developments and models that suggest that at least some of the observed variability arises from transport processes. Driven by field observations, experiments and computational models, there is an emerging picture of partially molten regions as highly localized, channelized plumbing systems. Computations suggest that melt localization can arise from both chemical/physical and purely mechanical instabilities and can provide non-trivial mixing pathways through the mantle. Questions remain as to how the different instabilities interact and which may be dominant in the mantle. Regardless, a highly localized melt transport system can lead to significant trace element (and U-series) variability and fractionation even for a homogeneous source. Recent work extends these results to consider the interaction of a channelized melt system with a heterogeneous source and suggests that small scale spatial variations in partitioning can lead to significant scatter in the ratios of highly incompatible elements (Fang, Spiegelman & Kelemen). Current work is extending these approaches to try to understand the variability of major elements and reaction in open systems (Collier, Kelemen & Spiegelman) Looking forward, the integration of magma dynamics and small-scale localization into global mantle dynamics presents a major scientific and computational challenge. A key addition to magma dynamics models will be the consistent coupling of fluid/solid mechanics with thermodynamics to resolve both melting and crystallization of magmas (e.g. see Katz U06, this meeting). These models will also require advanced methods for the efficient solution of highly multi-scale problems. The CIG Magma dynamics project is actively pursuing these computational objectives with the long-term goal of developing true dynamic geochemistry models whose output can be directly compared to observations.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 1213 Earth's interior: dynamics (1507, 7207, 7208, 8115, 8120)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Union [U]
MN: 2007 Fall Meeting