Tectonic implications of isotopic variation among Jurassic and Early Cretaceous plutons, Klamath Mountains

摘要: Jurassic and Early Cretaceous plutons in the Klamath Mountains province of California Oregon were intruded both before after thrusting during Nevadan orogeny (ca. 155-148 Ma). Plutons range from calc-alkalic to calcic display a compositions that changes consistently with time. Among this group, Rb, K 2 O, initial 87 Sr/ 86 Sr (Sr i ; 0.7034 0.7047) decrease ϵ Nd (range 2.0 4.8) increases younger plutons. Within individual plutons, varies considerably, whereas is nearly constant. The isotopic data typically plot right mantle array. δ 18 O values these are greater than +8.0‰. Tonalitic trondhjemitic calcic, contain low Rb contents, have less These narrow SR (0.7033-0.7036) (4.7 7.4); pre-Nevadan requires assimilation metasedimentary rocks or mixing crustal melts at deep-crustal levels. component not exposed was presumably truncated thrusting. Post-Nevadan show little evidence crust but trace-element (low rare-earth-element concentrations) consistent an origin by partial melting young ophiolitic underthrust orogeny.