Overlapping plutonism, volcanism, and tectonism in the BoulderBatholith region, western Montana
Robinson, G D; Klepper, M R; Obradovich, J D (1968) Overlapping plutonism, volcanism, and tectonism in the BoulderBatholith region, western Montana. Memoir - Geological Society of America, pp.557-576, 1968
| Authors | Robinson, G D; Klepper, M R; Obradovich, J D |
|---|---|
| Year | 1968 |
| Title | Overlapping plutonism, volcanism, and tectonism in the BoulderBatholith region, western Montana |
| Source | Memoir - Geological Society of America, pp.557-576, 1968 |
| ISSN | 0072-1069 |
| GeoRef | 1968-059052 |
| Keywords | absolute age; areal studies; Boulder batholith region; dates; dynamicevents; Elkhorn Mountain; Elkhorn Mountain volcanics; Helena area;igneous rocks; Montana; structural geology; tectonics; United States;volcanic rocks |
| Notes | 116 |
Abstract
Recent stratigraphic, structural, paleontologic, and radiometricevidence makes it possible to date dynamic events in the Boulderbatholith region closely. Time relations form an intertwined complexof volcanism-folding-thrusting-batholith emplacement. These eventsbegan and ended within a few million years of each other, during thelast 20 m.y. of the Cretaceous. Major folding, thrusting, andvolcanism started about the same time and a little earlier thanplutonism. In any given locality, volcanism ended before majorfolding; the climax of plutonism followed that of volcanism; thrustingpreceded and accompanied plutonism near the batholith, but followedplutonism farther away; thrusting ended a little later than folding.Gilluly's conclusion that orogeny producing Cretaceous thrusts ofMontana was ""essentially without plutonic associations' is nottenable.