Record Details
Petrology of the southern Pine Forest Range, Humboldt County, Nevada
ScholarsArchive at Oregon State University
| Field | Value |
|---|---|
| Title | Petrology of the southern Pine Forest Range, Humboldt County, Nevada |
| Names |
Smith, James Gordon II
(creator) |
| Date Issued | 1966 (iso8601) |
| Note | Access restricted to the OSU Community |
| Abstract | The Pine Forest Range in northwest Nevada has the most western and northern exposures in the state of pre-Tertiary eugeosynclinal and iniogeosynclinal rocks. Pre-Tertiary rocks record effects of a widespread low grade regional metamorphism. This study was undertaken to examine the effects of contact metamorphism caused by granitic intrusions on these rnetavolcanic and metasedimentary rocks. The 30 units mapped range from Upper Paleozoic to Recent. The oldest rocks (Permian?) consist of 1,000+ feet of marble,siliceous and sandy ?fels, metapelite and stretched pebble conglomerate. The Happy Creek volcanic serles (10,000+ feet) is the most interesting unit. Its five informal units are characterized by varying proportions of volcanic and nonvolcanic debris: 1) 2,000+ feet of thin-bedded graywacke and hornfels with lesser amounts of volcanic sandstone and conglomerate, and minor epiclastic breccia; 2) 2,100-2,500 feet of poorly sorted epiclastic hornblende andesite volcanic breccia, conglomerate, sandstone, siltstone and thin discontinuous limestone beds; 3) the thin-bedded Dyke Canyon member (2,000-2,400 feet), which is domi.nantly nonvolcanic metachert, siliceous hornfels, slate, sandstone, and carbonaceous iron-bearing limestone; 4) 2,100± feet of interbedded massive tuff-breccias, tuffs, and hornblende andesite flows; 5) 400-1,000 feet of porphyritic pyroxene andesite and andesitic basalt flows with scarce tuff-breccia. Happy Creek rocks in the western part of the area correlate with the lower part of the section just described and are hornblende andesite volcanic clastic rocks. Happy Creek rocks formed from locally derived, reistively untransported volcanic material which settled as ash or was sluiced In by turbidity currents and underwater pyroclastic flows. During volcanic quiescence finer grained nonvolcanic material was deposited. An unconformity separates Paleozoic metavolcanics from Middle Triassic miogeosynclinal rocks. From oldest to youngest the units mapped are: 1) 300-500 feet of Interbedded carbonaceous limestone, graywacke, pebble conglomerate, and slate; 2) 450+ feet of white to gray, sandy to clean limestone; 3) 300± feet of intercalated black chert, phyllite, and sandy hornfels; 4) 1,000± feet of massive white to yellow-buff limestone which grades upward into sandy limestone and finally into 5) 1,000+ feet of dark phyllite. Plutonic units were intruded into older rocks during the Cretaceous. From oldest to youngest they are: 1) Cove Camp syenodiorite; 2) Corral Creek quartz monzonite; 3) fine-grained quartz monzonite; 4) Snow Creek trondhjernite; 5) alaskite and aphte; and 6) Pole Canyon granodiorite. Mapped units of Tertiary rocks are: 1) water laid and ash fall tuff; 2) high alkali platy andesite; 3) silicic welded tuff; and 4) porphyritic olivine basalt. Structures include Tertiary normal faults and a thrust fault developed during a pre-intrusive greenschist facies dynamothermal metamorphism. Granitic intrusions produced contact metamorphic aureoles. Pehitic rocks became porphyroblastic cordieriteandalusite phyllites and schists. Metavolcanics in the outer part of aureoles preserve relict plagioclase, augite, and hornblende, and textures. Metamorphic minerals Include albite, epidote (Fe⁺⁺⁺/(Fe⁺⁺⁺ + Al) < 0.2), actinolite, sphene-leucoxene, and quartz. About 2 mIles from intrusions the above minerals were replaced by plagioclase > An₇, epidote with Fe⁺⁺⁺ /(Fe⁺⁺⁺ + Al) > 0.2, actinolite, opaques, and stable green biotite. A few thousand feet from intrusions stable red biotite appeared; plagioclase became greater than An₂₅, while epidote disappeared. Equilibrium was not obtained In metavolcanics because of insufficient H₂O to convert arthydrous igneous minerals to hydrous metamorphic minerals. Correlation of metapelite equilibrium assemblages with synthetic hydrothermal systems indicates pressures during contact metamorphism were less than 4 kb and temperatures were 475-575°C. |
| Genre | Thesis |
| Topic | Petrology -- Nevada -- Pine Forest Range |
| Identifier | http://hdl.handle.net/1957/53812 |
