Donato, Mary M. (1992) A newly recognized ductile shear zone in the northern Klamath Mountains, Oregon; implications for Nevadan accretion. Bulletin 2028. US Geological Survey doi:10.3133/b2028
| Reference Type | Report (issue) | ||
|---|---|---|---|
| Title | A newly recognized ductile shear zone in the northern Klamath Mountains, Oregon; implications for Nevadan accretion | ||
| Report | Bulletin | ||
| Authors | Donato, Mary M. | Author | |
| Year | 1992 | ||
| Issue | < 2028 > | ||
| Publisher | US Geological Survey | ||
| URL | |||
| Download URL | https://pubs.usgs.gov/bul/2028/report.pdf | ||
| DOI | doi:10.3133/b2028Search in ResearchGate | ||
| Generate Citation Formats | |||
| Classification | Not set | LoC | Not set |
| Mindat Ref. ID | 607619 | Long-form Identifier | mindat:1:5:607619:5 |
| GUID | 0 | ||
| Full Reference | Donato, Mary M. (1992) A newly recognized ductile shear zone in the northern Klamath Mountains, Oregon; implications for Nevadan accretion. Bulletin 2028. US Geological Survey doi:10.3133/b2028 | ||
| Plain Text | Donato, Mary M. (1992) A newly recognized ductile shear zone in the northern Klamath Mountains, Oregon; implications for Nevadan accretion. Bulletin 2028. US Geological Survey doi:10.3133/b2028 | ||
| In | US Geological Survey - Bulletin | ||
| Abstract/Notes | An 800-to 1,500-m-thick ductile shear zone in the northernmost Klamath Mountains marks the contact between metasedimentary rocks of the May Creek Schist and structurally underlying amphibolite. The shear zone trends approximately east-west, dips southward, and has been traced about 13 km along strike. Petrographic criteria and quartz petrofabric analyses of semipelitic schists and quartzofeldspathic gneisses of the May Creek Schist in the hanging wall consistently demonstrate a top-to-the-northwest sense of shear, indicating northwestward thrusting (present-day geographic framework) of schist over amphibolite in the footwall. Syntectonic sillimanite in deformed May Creek Schist indicates that amphibolite-facies conditions prevailed during deformation. The tectonic transport direction is perpendicular to the northeast-trending structural grain of the northernmost Klamaths, and in particular to southeast-dipping thrusts related to accretion of jurassic volcanic rocks which lie to the west. The age of the ductile deformation is inferred to be approximately 145 Ma, based on 40Ar;39Ar cooling age determinations of metamorphic hornblende from amphibolite in the footwall. I suggest that the ductile shear zone is a manifestation of Nevadan (144-157 Ma) convergence, during which an incipient back-arc spreading center (the protolith of the amphibolite) and its sedimentary cover (now the May Creek Schist) were shortened by contractive faulting during accretion to North America. Available Nevadan stretching lineations and transport directions from various Klamath Mountain localities are disparate and underscore the apparent structural complexity of the Nevadan orogen. | ||
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