Tilted plutons in the Klamath Mountains of California and Oregon

Abstract

Geologic and petrologic evidence indicates that the Ashland pluton and the Wooley Creek batholith, two major plutons of the Klamath Mountain province, have been significantly tilted subsequent to emplacement. Late Cretaceous sandstone depositionally overlies the Ashland pluton and dips approximately 25° toward the ENE. Contact metamorphic assemblages in diverse wall rocks surrounding the Wooley Creek batholith suggest at least 30° of tilt toward the WSW. Subsequent erosion has exposed at least 12 km of structural relief in the Wooley Creek batholith. Tilting was accomplished, at least in part, by thrusting of the plutons and their host rocks over low‐density rocks of the western Jurassic belt, followed by regional doming of deeply buried rocks of the underthrust terrane (Condrey Mountain Schist). Diagrammatic reconstruction of the plutons to pretilt positions suggests inward chemical fractionation of the Ashland pluton but upward fractionation of the Wooley Creek batholith and comagmatic Slinkard pluton. The results of this study indicate that rootless plutons in accretionary margins can undergo significant tilting, facilitating petrologic interpretations. In addition, the study suggests that for Klamath plutons, the effects of tilting must be taken into account before meaningful paleomagnetic interpretations can be made.