HR: 1340h
AN: V53A-0621    [Abstracts]
TI: Applying computer modeling to constrain and support the recovery of kinetic information from igneous rocks.
AU: * Amenta, R V
EM: amentarv@jmu.edu
AF: Department of Geology and Environmental Science, James Madison University, Harrisonburg, va 22807
AB: Computer modeling of nucleation and crystal growth resulted in 3-dimensional, hypidiomorphic textures due to grain to grain impingements. Crystal size distributions (CSDs) recovered from 2-dimensional slices show differences depending on crystal shapes grown. For tetragonal shaped (biaxial) prisms and plates the recovered CSDs are linear with slopes that are close to the predicted slopes and the slopes of the actual CSDs. However, for orthorhombic (triaxial) plates the recovered CSD is slightly curvilinear even though the predicted and actual CSD is clearly linear. This is believed to be due to the slice effect that renders the intersection length of each crystal to vary in length between the intermediate axis and either the long or short axis, respectively. Nevertheless, it was found that a best fit linear approximation to the curvilinear CSD gives a slope that is close to the predicted linear slope. These results have application to mildly curvilinear CSDs of plagioclase crystals that occur in many igneous rocks such as a 16 feet thick, plagioclase-clinopyroxene, diabase dike in Shenandoah Valley, Virginia. Samples were taken from the center of the dike. The aspect ratio of the plagioclase in the dike is triaxial and the recovered CSD is mildly curvilinear. With the assumption of linearity based on the modeling and using available plagioclase growth rate data from Hawaiian igneous rocks the average crystal residence time in the dike is estimated to be about 10 years and the characteristic crystallization time for the plagioclase in the dike is in the order of a 100 years. Some of the largest pyroxenes partially surround the plagioclase which suggests that pyroxene growth continued after plagioclase growth ceased. This suggests that the crystallization time for the dike might have been longer than 100 years.
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting