Record Details
Plutonic rocks of the southern Seven Devils Mountains, Idaho
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Plutonic rocks of the southern Seven Devils Mountains, Idaho |
| Names |
White, Willis Harkness
(creator) Taubeneck, William H. (advisor) |
| Date Issued | 1968-05-02 (iso8601) |
| Note | Graduation date: 1968 |
| Abstract | Eleven small Mesozoic plutons crop out within a 76-squaremile area of the southern Seven Devils Mountains in west-central Idaho. The plutons are divided into a mafic suite, an older granitic suite, and a younger granitic suite on the basis of age, lithology, and degree of metamorphism. The six plutons of the mafic suite are Late Triassic-Middle Jurassic (?) in age. Maximum dimensions are slightly over 3 miles in length and about 4,000 feet in width. Rock types, which may vary within individual plutons, are quartz-bearing hornblende metagabbro, hornblende metanorite, metadiorite, and metamorphosed quartz diorite. Chemically, the rocks are dioritic. The elongation of plutons suggests that emplacement was guided by the northeasttrending zone of weakness exemplified by the mylonite of the Oxbow- Cuprum shear zone. Forceful emplacement is indicated by local deflection of mylonite around plutons. Amphibolitization of pyroxene implies an increase in water pressure during the late stages of crystallization. The mafic plutons were subjected to greenschist facies regional metamorphism. The three plutons of the older granitic suite are Late Jurassic (?) in age. Maximum dimensions are 2 1/2 miles long and 4, 200 feet wide. Rock types include quartz diorite and granodiorite; the Crystal Lake pluton shows a faint compositional zonation. The elongation of plutons indicates that emplacement was guided by the northeast trend of the country rocks, including the Oxbow-Cuprum shear zone. Forceful emplacement is shown by the deformation of mylonite around the Crystal Lake pluton. The three intrusions show slight effects of greenschist facies regional metamorphism. The two plutons of the younger granitic suite, Deep Creek and Echols Mountain stocks, are Late Jurassic-Early Cretaceous (?) in age. The Deep Creek stock, largest intrusive mass in the thesis area, covers 9 1/2 square miles and has a thermal aureole as much as 5,000 feet in width. Twelve tabular marble xenoliths, the largest about half a mile in length, were probably derived from the Martin Bridge limestone at depth. Platy flow structure, defined by the orientation of hornblende, biotite, and schliern, forms a concentric funnel-shaped closure in the main body of the stock and a glacierlike pattern in part of the eastern prong. The flow structure is thought to have originated, (1) by rotational alignment of platy minerals into parallelism with contacts early in the emplacement history of the stock, and (2) by orientation of platy minerals normal to the direction of greatest magmatic pressure during the later stages of intrusion. Marginal fissures, which form the only consistent joint pattern in the main body of the stock, indicate late stage adjustment of the consolidated shell to pressures from the interior. The main body of the quartz diorite pluton is compositionally zoned. Potassium feldspar and quartz increase inward; whereas color index decreases inward. Chemically, the stock exhibits a calc-alkaline trend of differentiation. The Echols Mountain stock, about four square miles in area, is similar in petrography to the Deep Creek stock. Flow structure outlines a dome, however, rather than a funnel. Neither the Deep Creek nor the Echols Mountain stock is metamorphosed. The eleven plutons of the map area represent three episodes of Mesozoic plutonism that in part straddle the time interval between emplacement of the Late Permian-Middle Triassic Canyon Mountain complex (Thayer and Brown, 1964) and the Middle Cretaceous-Early Tertiary Idaho batholith. |
| Genre | Thesis/Dissertation |
| Topic | Geology -- Idaho -- Seven Devils Mountains |
| Identifier | http://hdl.handle.net/1957/46429 |
