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| Abstract |
- The Oregon Mountain area contains an ophiolitic assemblage of rocks which can he divided into two major zones on the basis of lithology: (1) spilite and diabase, with minor chert, and (2) plagiogranite, hornblende gabbro, cumulate gabbro and cumulate ultramafic rocks. The two zones have a total estimated thickness of about 4.6 km. The lower contact of the cumulate zone is gradational into the Josephine Peridotite, an extensive body of alpine-type harzburgite. The uppermost spilites are depositionally overlain by the Galice Formation (Jurassic, Kimmeridgian). Rocks in the diabase-spilite zone have
undergone metamorphism similar to sea-floor burial metamorphism.
Metamorphic grade progresses from zeolite facies through chlorite,
epidote and actinolite zones of the greenschist facies to amphibolite facies. Prehnite-pumpellyite facies metamorphism has been superimposed on the lowest temperature assemblages, probably
owing to later burial by the Galice Formation. The plutonic zone
consists of a sequence of ultramafic and mafic cumulate rocks which culminates in a residue of granophyric plagiogranite. Hornbiende gabbro, in part cumulate and in part intrusive, occurs near the top of the sequence.
The Josephine Peridotite consists of olivine-rich harzburgite
and minor amounts of dunite, chromitite and pyroxenite, all with
tectonite textures. It is essentially indistinguishable from other
occurrences of alpine-type harzburgite.
The Galice Formation is predominantly slaty shale. Lithic
graywacke and pebbly conglomerate are volumetrically minor components. The graywacke contains abundant quartz, volcanic fragments with minor feldspar, mafic minerals and metamorphic fragments which indicate a mixed continental and volcanic arc provenance.
Rocks of the Oregon Mountain area chemically resemble other
well known and well studied ophiolites. Major element variations in the diabase-spilite zone are interpretable in terms of sea water interacton with mid-ocean ridge tholeiite. Increases in SiO₂, Na₂O, H₂O and FeO and decreases in CaO and MgO relative to mid-ocean ridge basalts were observed in most specimens. Less consistent changes occur in K₂O, Al₂O₃, TiO₂ and MnO.
Titanium and zirconium abundances suggest affinities to mid-ocean
ridge basalts, but there is some evidence of mobilization of
these elements.
Rare earth element distributions in rocks from the diabasespilite
zone appear to have been generally unchanged during metamorphism
although modification of Ce abundance has evidently occurred
in one specimen. The distribution patterns are typically flat
(La/Lu = 1 - 1.5) with low abundances (av. La = 15x chronditic abundance) indicating that basaltic rocks from the Oregon Mountain area have affinities with mid-ocean ridge basalts and arc tholeiites.
Theoretical models indicate that a 15 to 20 percent melt of mantle
source rock with a REE abundances about 2 to 3 times those of
chondrites is a reasonable mechanism to produce the observed REE
distributions.
The ophiolite exposed in the Oregon Mountain area apparently
formed as oceanic crust in a marginal basin environment during
Jurassic time prior to the Nevadan Orogeny. The marginal basin
probably lay between the Rogue-Galice island arc and the western
continental margin. Nevadan deformation telescoped the arc-marginal basin terrain and caused accretion of the Jurassic rocks onto the continental margin.
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| Digitization Specifications |
- Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 Grayscale + 265 b+w), using Capture Perfect 3.0.82, on a Canon DR-9080C. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR. Master file scanned at 600 dpi (8-bit grayscale) using SlmartLF 1.3.05 on a Paradigm ImagePRO GxT 42 HD (OEM version of ColortracSmartLF Bx 42). Image manipulated by SmartLF1.3.05.
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| Additional Information |
- description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2009-07-06T23:21:28Z (GMT) No. of bitstreams: 5
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- description.provenance : Made available in DSpace on 2009-07-06T23:37:14Z (GMT). No. of bitstreams: 5
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- description.provenance : Submitted by Sara Mintonye (smscanner@gmail.com) on 2009-07-06T20:35:14Z
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No. of bitstreams: 5
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- description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2009-07-06T23:04:16Z (GMT) No. of bitstreams: 5
Vail_Scott_Garret_1977.pdf: 5763556 bytes, checksum: b340effae34c2a61fa966bc536d4d1df (MD5)
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- description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2009-07-06T21:15:02Z (GMT) No. of bitstreams: 1
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- description.provenance : Rejected by Laura Wilson(laura.wilson@oregonstate.edu), reason: Sue's mistake this time! on 2009-07-06T23:16:19Z (GMT)
- description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2009-07-06T23:37:14Z (GMT) No. of bitstreams: 5
Vail_Scott_Garret_1977.pdf: 5767957 bytes, checksum: a05363b7e0e3bcf4367619ee3457df9c (MD5)
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- description.provenance : Rejected by Sue Kunda(sue.kunda@oregonstate.edu), reason: Abstract pages out of order; maps not attached on 2009-07-06T21:28:17Z (GMT)
- description.provenance : Submitted by Sara Mintonye (smscanner@gmail.com) on 2009-07-06T23:02:37Z
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