Joint 118th Annual Cordilleran/72nd Annual Rocky Mountain Section Meeting - 2022

Paper No. 9-2
Presentation Time: 8:30 AM-6:00 PM


SCHROEDER, Hannah, MCFADDEN, Rory and HENTGES, Cora, Geology, Gustavus Adolphus College, 800 W College Ave, St. Peter, MN 56082

In this study, we are investigating the effect of preexisting layering on the formation and organization of leucosome networks in migmatitic orthogneiss and paragneiss from the Pioneer Mountains, Idaho. The Pioneer Mountains comprise a metamorphic core complex that underwent large magnitude extensional deformation and partial melting in the Eocene, exposing migmatitic orthogneiss and paragneiss in the footwall of the core complex. The migmatites are predominantly stromatic metatexites with foliation-parallel leucosomes. The transfer of melt through the crust in the leucosome networks of migmatites is an important process within crustal differentiation. The spacing and thickness of leucosomes within migmatites provides limited evidence for a power-law relationship, which suggests leucosome networks may be self-organized systems. To evaluate the power-law distribution, we quantified the thickness and spacing of leucosomes through 13 one-dimensional transects ranging from 0.8-2.0 meters in length. In addition, we examined the effect of preexisting layering through a comparison of the migmatitic orthogneisses and paragneisses. The percentage of leucosome for migmatitic orthogneiss traverses range from 33%-66%, whereas the migmatitic paragneiss traverses range from 18%-62% leucosome. The migmatitic orthogneiss also contain leucosomes with slightly larger maximum thickness. For most samples the cumulative thickness plots comprise a stairstep pattern with a range of step sizes consistent with a power-law distribution. On average, the cumulative frequency versus leucosome thickness plots of the migmatitic orthogneiss have greater scaling exponents. The thickness of leucosomes in the migmatitic paragneiss suggests preexisting layering may restrict leucosome thickness and the power law distributions indicate the leucosome network is potentially a self-organized system in the Pioneer Metamorphic Core Complex.