HR: 0800h
AN: U41A-0728    [Abstracts]
TI: A Comparison of Methods for Modeling Geochemical Variability in the Earth's Mantle
AU: * Kellogg, J B
EM: kellogg@ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive, East, Los Angeles, CA 90095
AU: Tackley, P J
EM: tackley@ess.ucla.edu
AF: University of California, Los Angeles, 595 Charles Young Drive, East, Los Angeles, CA 90095
AB: Numerial models of isotopic and chemical heterogeneity of the Earth's mantle fall into three categories, in decreasing order of computational demand. First, several authors have used chemical tracers within a full thermo-chemical convection calculation (e.g., Christensen and Hofmann, 1994, van Keken and Ballentine, 1999; Xie and Tackley, 2004). Second, Kellogg et al.\ (2002) proposed an extension of the traditional geochemical box model calculations in which numerous subreservoirs were tracked within the bulk depleted mantle reservoir. Third, All\`egre and Lewin (1995) described a framework in which the variance in chemical and isotopic ratios were treated as quantities intrinsic to the bulk reservoirs, complete with sources and sinks. Results from these three methods vary, particularly with respect to conclusions drawn about the meaning of the Pb-Pb pseudo-isochron. We revisit these methods in an attempt to arrive at a common understanding. By considering all three we better identify the strengths and weaknesses of each approach and allow each to inform the other. Finally, we present results from a new hybrid model that combines the complexity and regional-scale variability of the thermochemical convection models with the short length-scale sensitivity of the Kellogg et al.\ approach.
DE: 8125 Evolution of the Earth
DE: 3210 Modeling
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
SC: Union [U]
MN: 2004 AGU Fall Meeting