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.
| 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 |
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