HR: 16:55h
AN: V42G-04    [PDF]
TI: Deciphering Metamorphic Processes Through 3D Visualization of Thermal and Textural Modeling
AU: * Dutrow, B
EM: dutrow@geol.lsu.edu
AF: Louisiana State Univ., Dept. Geology \& Geophysics, Baton Rouge, LA 70803 United States
AU: Foster, C
EM: tom-foster@uiowa.edu
AF: Univ. of Iowa, Dept. of Geosciences, Iowa City, IA 52242
AU: Gable, C W
EM: gable@lanl.gov
AF: Los Alamos Ntl. Lab., EES-6, Los Alamos, NM 87545 United States
AU: Travis, B
EM: bjtravis@lanl.gov
AF: Los Alamos Ntl. Lab, EES-2, Los Alamos, NM 87545 United States
AB: Mineral assemblages and textures associated with regional contact metamorphic events provide a natural laboratory for analyzing the effects of heat and fluid transport. Typically these include the maximum temperature, $T_{max}$, (or pressure) attained by the rocks. Early progression to $T_{max}$ is often obscured in the rock record, as is the retrograde path. Similarly, thermal modeling of these systems provides a controlled laboratory for deciphering important geologic processes and their magnitude over the aureole's entire metamorphic history. Numerous previous modeling studies focus on extracting snapshots in time (t) by plotting temperature (T) at some time $(t_i)$, often with velocity vectors at $(t_i)$ if fluid flow is included. However, contained in these four dimensional calculations is much more information that provides insights into the spatial and temporal aspects of a metamorphic event. Advanced visualization and analyses tools permit extraction and analyses of that diagnostics data. For example, one of the fundamental controls on crystal size distribution and porphyroblast growth in metamorphic rocks is the heating rate (dT/dt) experienced by the rocks. The rate at which the rocks traverse a reaction boundary (analogous to an isotherm) dictates the number of nuclei that form. Textural modeling based on thermal profiles demonstrates that rapid heating produces many small nuclei whereas lower dT/dt produce fewer, larger nuclei. Various thermal scenarios display contrasting dT/dt. If permeability is sufficient for fluid circulation to develop, rapid heating is followed by a continuous T decrease to a local minimum, with reheating as warm fluids infiltrate; in contrast to single heating and cooling scenario (conductive regime). Visualization techniques allow 3D spatial mapping of dT/dt throughout the metamorphic event to permit analyses of the distribution of fast vs. slow heating rates, and hence nucleation. By tracking the time spent in specific T intervals, the resultant porphyroblast size can be estimated.Our modeling studies suggest that mineral growth may take place during periods of cooling, within a specific T intervals that post-date $T_{max}$.In addition, by examining dT/dt at one spatial location through time, sequential periods of porphyroblast nucleation and growth can be observed and crystal size distribution predicted. Additional and non-traditional diagnostic output allows analyses and visualization of model behavior and provides new insights into processes controlling the development of metamorphic rocks.
DE: 3210 Modeling
DE: 3660 Metamorphic petrology
DE: 3665 Mineral occurrences and deposits
DE: 8045 Role of fluids
DE: 8135 Hydrothermal systems (8424)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting