H. Lapierre J.-L. Zimmermann M. Brouxel 1989 <div id="15572826" class="article-section-wrapper js-article-section js-content-section " data-section-parent-id="0"><p>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 ϵ_Sr<span>&nbsp;</span>(between -9.7 and -12.5) and ϵ_Nd<span>&nbsp;</span>(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 ϵ_Nd<span>&nbsp;</span>suggest, moreover, that no old continental crust underlies the Klamath Mountains.</p></div> application/pdf 10.1130/0091-7613(1989)017<0273:UJMMRO>2.3.CO;2 en Geological Society of America Upper Jurassic mafic magmatic rocks of the eastern Klamath Mountains, northern California: remnant of a volcanic arc built on young continental crust article