Isotopic Age of the Nevadan Orogeny and Older Plutonic and Metamorphic Events in the Klamath Mountains, California

Lanphere, Marvin A.; Irwin, William P.; Hotz, Preston Enslow

doi:10.1130/0016-7606(1968)79[1027:iaotno]2.0.co;2

Cited by 125 publications

(48 citation statements)

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“…K-Ar dates for actinolite (125 Ma by Coleman et al, 1983, andHelper, 1986), phengite (142 Ma by Coleman et al, 1983;144 Ma by Suppe and Armstrong, 1972;and 128 Ma by Helper, 1986),crossite (118 Ma by Coleman, pers. commun., and Helper, 1986;127 Ma by Helper, 1986), and whole-rock (159 Ma by Lanphere et al, 1968) suggest Late Jurassic to Early Cretaceous subduction-zone metamorphism.…”

Section: Jurassic To Early Cretaceous Blueschistsmentioning

confidence: 92%

Blueschists and Eclogites of the World and Their Exhumation

Maruyama

Liou

Terabayashi

1996

International Geology Review

578

364

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Section: Jurassic To Early Cretaceous Blueschistsmentioning

confidence: 92%

Blueschists and Eclogites of the World and Their Exhumation

Maruyama

Liou

Terabayashi

1996

International Geology Review

578

364

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“…This igneous activity in the Klamaths ceased at the beginning of Cretaceous time. The youngest such body is the apparently *136 Ma Shasta Bally pluton (Lanphere et al 1968;Lanphere and Jones 1978;Irwin and Wooden 1999). However, this date may represent the time of cooling and c Fig.…”

Section: Formation Of the Klamath Mountains Salientmentioning

confidence: 96%

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Ernst

2015

Chin. J. Geochem.

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“…There remains some uncertainty regarding the geochronology of events in the Trinity peridotite but the range of dates probably indicates a polygenetic history. Based on ages of plagiogranites that intrude the gabbros of the ophiolite and structural relations to these bodies, plastic deformation in the peridotite body is interpreted to have ceased by 450 -480 Ma (Lanphere et al, 1968;Quick, 1981a). A single two point Sm-Nd isochron indicates an age of 472 Ϯ 37 Ma for the plagioclase lherzolite at China Mountain (Jacobsen et al, 1984).…”

Section: Geologic Setting and Samplesmentioning

confidence: 99%

Observations of Li isotopic variations in the Trinity Ophiolite: Evidence for isotopic fractionation by diffusion during mantle melting

Lundstrom

Chaussidon

Hsui

et al. 2005

Geochimica et Cosmochimica Acta

166

124

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The Trinity peridotite (northern CA) contains numerous lithologic sequences consisting of dunite to harzburgite to spinel lherzolite to plagioclase lherzolite. Previous workers have documented geochemical gradients in these sequences consistent with melt-rock reaction processes occurring around dunites, interpreted to reflect conduits for melt ascent. We have undertaken a study of Li isotope compositions of clinopyroxene and some olivine within these sequences using ion probe techniques to test the hypothesis that the geochemical gradients are related to diffusive fluxing of alkali elements into or away from the melt conduit.Results show large variations in 7 Li/ 6 Li occurring in a consistent pattern across three transects from dunite to plagioclase lherzolite within the Trinity peridotite. Specifically, measurements of average ␦ 7 Li for single thin sections along the traverse reveal a low in ␦ 7 Li in the harzburgite adjacent to the dunite returning to higher values farther from the dunite with a typical offset of ϳ10 per mil in the low ␦ 7 Li trough. This pattern is consistent with a process whereby Li isotopes are fractionated during diffusion through a melt either from the dunite conduit to the surrounding peridotite, or from the surrounding peridotite into the dunite conduit. The patterns in 7 Li/ 6 Li occur over a length scale similar to the decrease in REE concentration in these same samples. Explaining both the trace element and Li isotopic gradients requires a combined process of alkali diffusion and melt extraction.We develop a numerical model and examine several scenarios of the combined diffusion-extraction process. Using experimentally constrained values for the change in Li diffusion coefficient with isotope mass, large changes in ␦ 7 Li as a function of distance can be created in year to decade timescales. The addition of the melt extraction term allows larger Li concentration gradients to be developed and thus produces larger isotopic fractionations than diffusion only models. The extraction aspect of the model can also account for the observed decrease in rare earth element concentrations across the transects.

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Isotopic Age of the Nevadan Orogeny and Older Plutonic and Metamorphic Events in the Klamath Mountains, California

Cited by 125 publications

References 0 publications

Blueschists and Eclogites of the World and Their Exhumation

Blueschists and Eclogites of the World and Their Exhumation

Review of Late Jurassic-early Miocene sedimentation and plate-tectonic evolution of northern California: illuminating example of an accretionary margin

Observations of Li isotopic variations in the Trinity Ophiolite: Evidence for isotopic fractionation by diffusion during mantle melting

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