Title

Investigating Sequence Boundaries Between Middle Proterozoic Bonner, McNamara, and Garnet Range Units Through Detrital Zircon Geochronology

Presentation Type

Poster

Abstract

I am focusing on collecting geochronologic data from detrital zircon grains within three rock units within the lower Missoula Group of the Belt Supergroup located in Western Montana. These three rock units are of Middle-Proterozoic age (~1.4-1.5 billion years old) and include, from oldest to youngest the, Bonner Formation, McNamara Formation, and Garnet Range Formation. I collected one sample from each formation as exposed along Highway 200 near Potomac, Montana. In addition, a second sample of the McNamara and Garnet Range units was collected from the Flint Creek drainage in the Northern Flint Creek Range (Porters Corner area). Each sample was trimmed of weathering rind, crushed, and milled to ~250 microns. The resulting sediment was washed and separated based on grain density on a Gemini water table. The dense fraction was further separated based on magnetic susceptibility using a Franz magnetic separator. Lithium polytungstate (density 2.85 g/cm3 ) was used for the final isolation of zircon grains for radiometric data.

The zircon separates are currently being mounted in epoxy for analysis and will be analyzed by laser ablation inductively-coupled mass spectrometry (LA-ICP-MS) at Boise State University in early March. This analysis will yield a set of radiometric ages for each individual zircon grain, based on the uranium-lead radiometric series. Collectively, these data should provide the ability to document detrital contributions from source terranes of specific ages. Multiple sources with similar ages should be resolvable by analyzing differences in trace element abundance. Approximately 110 individual spots (laser shot and analysis of individual zircon target grain) will be used to document provenance ages as well as provide a better understanding of changes in tectonics and regional geology across the sequence boundaries. This data will also lead to a stronger provenance model for tectonic events during the deposition of these sedimentary rock units.

Category

Physical Sciences

This document is currently not available here.

Share

COinS
 
Apr 11th, 3:00 PM Apr 11th, 4:00 PM

Investigating Sequence Boundaries Between Middle Proterozoic Bonner, McNamara, and Garnet Range Units Through Detrital Zircon Geochronology

I am focusing on collecting geochronologic data from detrital zircon grains within three rock units within the lower Missoula Group of the Belt Supergroup located in Western Montana. These three rock units are of Middle-Proterozoic age (~1.4-1.5 billion years old) and include, from oldest to youngest the, Bonner Formation, McNamara Formation, and Garnet Range Formation. I collected one sample from each formation as exposed along Highway 200 near Potomac, Montana. In addition, a second sample of the McNamara and Garnet Range units was collected from the Flint Creek drainage in the Northern Flint Creek Range (Porters Corner area). Each sample was trimmed of weathering rind, crushed, and milled to ~250 microns. The resulting sediment was washed and separated based on grain density on a Gemini water table. The dense fraction was further separated based on magnetic susceptibility using a Franz magnetic separator. Lithium polytungstate (density 2.85 g/cm3 ) was used for the final isolation of zircon grains for radiometric data.

The zircon separates are currently being mounted in epoxy for analysis and will be analyzed by laser ablation inductively-coupled mass spectrometry (LA-ICP-MS) at Boise State University in early March. This analysis will yield a set of radiometric ages for each individual zircon grain, based on the uranium-lead radiometric series. Collectively, these data should provide the ability to document detrital contributions from source terranes of specific ages. Multiple sources with similar ages should be resolvable by analyzing differences in trace element abundance. Approximately 110 individual spots (laser shot and analysis of individual zircon target grain) will be used to document provenance ages as well as provide a better understanding of changes in tectonics and regional geology across the sequence boundaries. This data will also lead to a stronger provenance model for tectonic events during the deposition of these sedimentary rock units.