Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Ronald B. Chase
Dr. John D. Grace
Dr. W. Thomas Straw
Masters Thesis-Open Access
The magmas which formed the northeastern Idaho batholith were contaminated with, or derived from, old crustal material as evidenced, from previous studies, by high whole-rock 87Sr/86Sr ratios, relatively high 207Pb/206Pb ages, and Archean to Proterozoic upper intercept ages for batholithic zircons.
The old zircon component has been identified in this study by separating zircons into fractions based on size and morphology. Pb/U isotopic ratios are distributed on a chord with a lower concordia intercept intrusive age of 73.6+6 m.y. Zircons from a batholithic sample located one kilometer inward from the contact were separated according to mineral association. This method was not successful in segregating old inherited zircon from euhedral zircon. Upper-intercept ages from this project, when combined with those from other studies, range from 1700 m.y. and indicate the complexity and variety of the 'older continental crust' source terrain.
Dexter, "Uranium-Lead Zircon Ages and Crustal Contamination of the Northeastern Idaho Batholith" (1984). Master's Theses. 1506.