Upper Jurassic mafic magmatic rocks of the eastern Klamath Mountains, northern California: remnant of a volcanic arc built on young continental crust
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Abstract
Diabasic and gabbroic dikes intruding the lower Paleozoic Trinity Ophiolite in the Lovers Leap section, Klamath Mountains, California, display strong calc-alkalic petrological and geochemical features (occurrence of primary amphiboles, zoned plagioclase phenocrysts and biotite, low TiO2, high incompatible trace-element contents, and light rare earth element enrichment). These dikes, of Late Jurassic age (149 ±6 Ma by K-Ar), are petrographically and geochemically similar to the contemporaneous calc-alkalic ultramafic-mafic magmatism well developed through the Klamath Mountains. They present negative Nb, Zr, and Ti anomalies typical of subduction-related magmatism and probably belong to a volcanic arc on an active continental margin. Their ϵSr (between -9.7 and -12.5) and ϵNd (between 5.6 and 6.3) values compare with some western U.S. Mesozoic granites. The Nd isotopic values, lower than those of mid-oceanic ridge basalts and intra-oceanic island arcs, suggest that these dikes, deriving from a depleted mantle source, have been slightly contaminated by continental material, probably subducted sediments. Values of ϵNd suggest, moreover, that no old continental crust underlies the Klamath Mountains.
Suggested Citation
Brouxel, M., Lapierre, H., and Zimmermann, J., 1989, Upper Jurassic mafic magmatic rocks of the eastern Klamath Mountains, northern California: remnant of a volcanic arc built on young continental crust: Geology, v. 17, no. 3, p. 273-276, https://doi.org/10.1130/0091-7613(1989)017<0273:UJMMRO>2.3.CO;2.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Upper Jurassic mafic magmatic rocks of the eastern Klamath Mountains, northern California: remnant of a volcanic arc built on young continental crust |
| Series title | Geology |
| DOI | 10.1130/0091-7613(1989)017<0273:UJMMRO>2.3.CO;2 |
| Volume | 17 |
| Issue | 3 |
| Year Published | 1989 |
| Language | English |
| Publisher | Geological Society of America |
| Description | 4 p. |
| First page | 273 |
| Last page | 276 |