QUATERNARY EXPRESSION OF NORTHERN GREAT VALLEY FAULTS AND FOLDS: ACCOMMODATING NORTH-SOUTH CONTRACTION BETWEEN THE SIERRAN MICROPLATE AND OREGON BLOCK

The Northern California Shear Zone accommodates North American intraplate right-lateral transpressional shear driven by the relative motions of the northwest translating Sierran microplate and clockwise rotation of the Oregon block. Within this zone, between the latitudes of 40^o and 42^o, 1 – 4 mm/yr of north-south geodetic contraction is observed and for the most part remains geologically unaccounted for. The northeast trending Inks Creek fold belt, north of Red Bluff, CA, marks an abrupt change in structural orientation within the northern Great Valley and Sierra boundary, and consists of anticline-syncline pairs that appear optimally oriented to accommodate northwest directed crustal shortening. The folds plunge to the southwest where they are incised and deflect the course of the Sacramento River into a sinuous path. We will present new geomorphic mapping and analysis of fluvial terraces from airborne lidar data and field observations made along the Sacramento River within the fold belt. Evidence of uplift is observe from drain patterns and topographic profiling of Quaternary strath terrace surfaces, which show broad progressive arching through the fold belt. It is anticipated that radiocarbon, terrestrial cosmogenic nuclides, and OSL dating of the deformed terrace surfaces hold the potential to quantify the lateral and vertical propagation rates of fold growth, as well as, constrain rates of regional contractional deformation.