Zircons from quartzo-feldspathic gneiss within the Precambrian (>725 Ma) siliciclastics of the House Mountain Metamorphic Complex of southwestern Idaho were studied to determine its origin and evolution. Cathodoluminescence imaging of internal zoning due to growth and recrystallization of zircon, along with laser ablation inductively coupled plasma mass spectrometer (LA-ICPMS) analysis of these zircons, reveal a complex history of metamorphism at House Mountain. Primary igneous crystallization in the orthogneiss occurred near 130 Ma. Convoluted regions of the zircons have ages ranging from 130 to 85 Ma. These younger ages are hypothesized to be related to lead loss and new crystal growth during and after a series of metamorphic recrystallization and melt infiltration events. Uranium and rare earth element (REE) concentrations illustrate a trend of removal of incompatible trace elements from the zircon lattice during recrystallization. Changes in REE concentrations and pattern suggest late zircon growth in the presence of garnet. Further work is being done on garnets from the study rock to verify partitioning of heavy rare earth elements (HREE) between zircon and garnets. The igneous and metamorphic history extracted from this gneiss is supported by independent metamorphic zircon and titanite ages from adjacent siliciclastics rocks and amphibolite sills.
Andersen, Eli and Schmitz, Mark, "Reconstructing the Geologic History of the House Mountain Metamorphic Complex (Southern Idaho) Through Zircon Age and Geochemical Analysis" (2015). College of Arts and Sciences Presentations. Paper 44.