05/20/2022
By Erica Gavin

The Kennedy College of Science, Department of Environmental, Earth, and Atmospheric Sciences, invites you to attend a Master’s thesis defense by Klementina Mato on “Reconstructing a Mesoproterozoic Tectonic Puzzle by Revisiting the Provenance of the Belt Supergroup in Western U.S.”

Candidate Name: Klementina Mato
Defense Date: Friday, June 3, 2022
Time: Noon to 1 p.m.
Location: Olney 212, North Campus
Thesis/Dissertation Title: “Reconstructing a Mesoproterozoic Tectonic Puzzle by Revisiting the Provenance of the Belt Supergroup in Western U.S.”

Committee: 

  • Advisor Richard Gaschnig, Environmental, Earth, and Atmospheric Department, University of Massachusetts Lowell
  • Kate Swanger, Environmental, Earth, and Atmospheric Department, University of Massachusetts Lowell
  • Reed Lewis, Idaho Geological Survey, University of Idaho

Abstract

The provenance of the Belt Supergroup (Idaho and Montana) plays an important role in the reconstruction of the Nuna supercontinent, as the Belt received some of its detritus from another continental block. The identity of the western continent has been described in two competing models: the SWEAT model (linking East Antarctica to the western U.S and Australia to western Canada) and the AUSWUS model (linking Australia to the western U.S and East Antarctica to the south). To test these models, we determined the U-Pb ages and trace element compositions of detrital zircon and monazite from the Prichard Formation, Ravalli Group, and Lemhi Subbasin of the Belt.

Most detrital zircons from the Prichard Formation yield ages of ~1.60 Ga with a minor peak at ~1.70 Ga. The Ravalli Group yields zircon ages of ~1.65 Ga, including some components at 2.60-2.70 Ga. Quartzites from the Lemhi Subbasin yield zircon ages of ~1.70-1.75 Ga with a few grains dating at 2.20-2.50 Ga. Gd/Yb and U/Yb in zircon display a slightly decreasing trend with decreasing age for all three groups, an indication that the younger zircon population came from a less evolved source. Rare detrital monazites in the Prichard Formation have ages ranging from 1.56 to 1.72 Ga whereas detrital monazites in the Ravalli Group yield age peaks at 1.50, 1.60, and 1.70 Ga. Monazites from the Lemhi Subbasin displays one major peak at 1.67 Ga and a smaller peak at 1.77 Ga. The older zircon and monazite peaks from the Lemhi Subbasin could be derived from Yavapai/Mazatzal sources from SW US, whereas the younger ages from the Prichard Formation could be derived from Australian sources. Initial Hf isotope values of the Belt samples range from -10 to +14 for ages ranging from 1.40 to 1.80 Ga, whereas data from other literature shows epsilon Hf values ranging from -10 to +15 during the same timeline for the continents of Australia, East Antarctica, and parts of SW Laurentia. The array of values from all three continents portrays a mixture of significantly evolved Mesoproterozoic and Paleoproterozoic sources (particularly Australia and Southwest Laurentia), and coeval juvenile mantle input to the Belt from all three regions of Nuna.  These data together may allow for the more detailed pinpointing of specific off-continental sources for the Prichard and Ravalli and SW North American sources for the Lemhi Subbasin.