HR: 13:50h
AN: V23C-01 INVITED     [Abstracts]
TI: Timescales of Geological Processes: a Diffuse Spectrum
AU: * Chakraborty, S
EM: Sumit.Chakraborty@rub.de
AF: Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Bochum, NRW D-44780 Germany
AU: Costa, F
AF: Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Bochum, NRW D-44780 Germany
AU: Trepmann, C A
AF: Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Bochum, NRW D-44780 Germany
AU: Dueffels, K
AF: Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Bochum, NRW D-44780 Germany
AU: Dohmen, R
AF: Institut fuer Geologie, Mineralogie und Geophysik, Ruhr Universitaet Bochum, Bochum, NRW D-44780 Germany
AB: One of the most significant recent advances in the study of geological processes is the ability to identify and quantify a hierarchy of time scales ranging from days to millions of years. Modeling diffusion related processes provides one of the most versatile tools for studying the lower end of this temporal spectrum. We will demonstrate this versatility with two examples chosen from very different milieus. (1) Volcanic processes in the Chilean Andes: We use somewhat novel modeling techniques to show that magma mixing can cause igneous differentiation in a subduction zone setting over decadal time scales. This provides a link between processes occurring over thousands to millions of years (melt generation and transport) and pre-eruptive processes that occur over days to months. (2) Plutonism and mid-crustal metamorphic processes in the Alps. Here, dike emplacement was triggered over time scales of days, cooling in magma chambers occurred over hundreds of years while metamorphism in the mid crustal level lasted millions of years. The regional distribution of such rates allows us to infer differential uplift across a section of the Alps. Traditionally, diffusion modeling has been plagued by large uncertainties arising from a number of sources. Large extrapolations of diffusion coefficients measured at high temperatures, simplified numerical models and inadequate understanding of diffusion mechanisms are some of these. Technical and theoretical developments now allow us to circumvent many of these problems. For example, the ability to manipulate complex silicate compositions on the nanometer scale through the use of thin film technology (e.g. pulsed laser ablation) allows us to measure diffusion coefficients at conditions that were inaccessible only a few years ago. In addition, these experiments are faster and more accurate. Consequently, it is now possible to determine parameters such as enhancement of diffusion rates in defective crystals or due to reactive processes. Contributions of such diffusion studies to the understanding of deformation rates will also be discussed. Coupling of processes occurring on different time scales is crucial for the stability of geochemical and geological cycles. Knowing the rates of individual processes, analyzing the mechanism of coupling across temporal hierarchies should be a central goal of future research.
DE: 8000 STRUCTURAL GEOLOGY (New field, replaces single entry 8165)
DE: 5120 Plasticity, diffusion, and creep
DE: 5139 Transport properties
DE: 3660 Metamorphic petrology
DE: 1035 Geochronology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting