Year of Award
Master of Science (MS)
Other Degree Name/Area of Focus
Department or School/College
Department of Geology
University of Montana
Numerous calc-alkaline plutons are exposed along the southern and eastern flank of the Pioneer batholith in southwestern Montana. The plutons are emplaced to shallow depths into upper Paleozoic carbonates and Mesozoic elastics. Petrographic and chemical data, and their occurence in space and time, suggest a petrogenetic link with the nearby batholith.
Pyroxene-bearing quartz monzonite and microgranodiorite exposed at Argenta possibly represent an ancestral phase of the Pioneer batholith. The Argenta Stock shows evidence of both a 'wet' and 'dry' magmatic environment. Interception of a meteoric water source at a high level of emplacement by an initially dry magma is postulated to reconcile this occurence.
A large dacite sill southwest of the McCartney Mountain stock is possibly an offshoot of a 'tabular conduit' proposed by Chandler (1973) to connect the stock and batholith. Reconnoitering of a quartz latite porphyry sill at Trout Creek and a quartz diorite pluton at Melrose provides chemical and petrographic data.
The plutons are chemically compatible with the volumetrically minor 'Sodic Series' plutons recognized by Tilling (1973) in the Boulder batholith.
Eaton, Gary D., "PETROLOGY, PETROGRAPHY AND GEOCHEMISTRY OF SOME PLUTONS SATELLITE TO THE PIONEER BATHOLITH, SOUTHWESTERN MONTANA" (1983). Graduate Student Theses, Dissertations, & Professional Papers. 10954.
© Copyright 1983 Gary D. Eaton