PETROGRAPHIC AND GEOCHRONOLOGIC STUDY ACROSS A 10KM TRANSECT OF THE CANYON CREEK PLUTON, KLAMATH MOUNTAIN PROVINCE, NW CALIFORNIA

The Klamath Mountain Province (KMP) in northwestern CA is situated at the southern margin of the Cascadia subduction zone, exhibiting the highest relief and topography along the southern Cascadia forearc. The KMP consists of a series of accreted Paleozoic terranes intruded by Jurassic-Cretaceous calc-alkaline plutons, primarily associated with the Nevadan Orogeny. The Canyon Creek Pluton (CCP) is a hornblende-bearing biotite tonalite that covers roughly 90 sq-km, intruding into the Central Metamorphic Belt of the KMP during the early Cretaceous Pickett Peak accretionary episode, when the Western Klamath terrane overrode Franciscan rocks to the west. The CCP belongs to a tonalite-trondhjemite-granodiorite suite of plutons including the Sugar Pine, Craggy Peak, Caribou Mountain and Deadman Peak plutons, emplaced 136-140Ma (e.g., Allen and Barnes, 2006).

The CCP outcrops fairly well at low elevations and occurs as bare slab outcrops at high elevations, making it an ideal candidate for a detailed transect of samples from edge to center of the plutonic complex. In this study, we sample a vertical bedrock transect spanning >1.8km of relief, 10km of horizontal distance that traverses the radius of the CCP, including nine samples for petrographic analysis, and one zircon U-Pb geochronologic age.

The CCP marks the highest elevation of the Klamath Mountain Province and in the southern Cascadia forearc (Thompson Peak, 2,744m.a.s.l.). Timing and mechanism of rock exhumation and relief generation is enigmatic. Previous studies constrain detachment-driven exhumation generated by the east-west striking LaGrange Fault in the KMP to the middle Tertiary (Piotraschke et al., 2015), with three apatite (U-Th)/He cooling ages from the CCP, ranging from ~6-18Ma. This integrated study of field observation, petrographic analysis and age-dating approach places the Canyon Creek Pluton in a broader regional context by comparison to the nearby well-studied English Peak and Wooley Creek plutonic complexes, and develop a model for understanding Mesozoic through Cenozoic tectonism, crustal cooling and rock exhumation of the CCP.