HR: 16:35h
AN: V42G-03 INVITED     [PDF]
TI: Porphyroblast Microstructures and the Coupling of Deformation and Metamorphism
AU: * Johnson, S E
EM: johnsons@maine.edu
AF: University of Maine, Department of Earth Sciences, Orono, ME 04469 United States
AU: Koons, P O
EM: peter.koons@maine.edu
AF: University of Maine, Department of Earth Sciences, Orono, ME 04469 United States
AB: Evidence suggesting that metamorphic reactions can be driven by deformation is ubiquitous. The example we discuss here is the spatial and temporal correlation between deformation and porphyroblastic mineral growth. Many porphyroblasts show synkinematic microstructures, and in general the evidence favors growth relative early during the deformation. These microstructural observations have been with us for decades, but mechanical descriptions of the coupling are lacking. We explore the relations between deformation and porphyroblast growth by employing three-dimensional coupling among diffusion, reaction and deformation. Both linear and non-linear coupling can significantly reduce the characteristic times of these processes, leading to enhanced strain-rate partitioning and porphyroblast growth rates. Porphyroblast growth is inherently a non-equilibrium process, controlled by the rate and distribution of strain. Correlatively, strain and strain-rate distribution are inherently controlled by porphyroblast growth and other microstructural changes associated with metamorphism. Results of linked mechanical and microstructural modeling show coupling between deformation and porphyroblast growth, as well as associated microstructural changes that occur in the surrounding matrix. Feedbacks among the various processes involved can follow many paths leading to the finite state preserved in the field.
DE: 1206 Crustal movements--interplate (8155)
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 1744 Tectonophysics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting