PROGRESSIVE ARCWARD CONTRACTION OF A MESOZOIC-TERTIARY FORE-ARC BASIN, SOUTHWESTERN SACRAMENTO VALLEY, CALIFORNIA

The modern Sacramento Valley intermontane basin is the successor to a deformed Mesozoic-Tertiary fore-arc basin. Based on analysis of seismi c reflection profiles, drill hole data, and surface mapping, we propos e a model for progressive arcward contraction of the fore-arc basin in the Rumsey Hills region, southwestern Sacramento Valley, beginning in Cretaceous and continuing episodically through Cenozoic time. We pres ent our interpretation in the form of a kinematically restorable forwa rd model. The major tectonic and depositional events include (1) mid-C retaceous or older shortening of fore-arc basin strata along imbricate , west-dipping thrust faults; (2) erosion of the deformed fore-arc str ata; (3) onlap of Cenomanian and younger forearc strata onto deformed older strata and crystalline Sierran basement; (4) renewed shortening in latest Cretaceous to early Tertiary, accommodated by delamination o f Upper Cretaceous strata from the mid-Cretaceous angular unconformity , tectonic wedging, and west-directed backthrusting; (5) erosion of th e deformed Upper Cretaceous strata and deposition of the Eocene Capay Formation; (6) uplift and east-directed shortening from Eocene to late Neogene, with local erosion of the Capay Formation over the ancestral Rumsey Hills; (7) uplift of the northern Coast Ranges beginning ca. 3 .4 Ma, and deposition of the Pliocene-Pleistocene Tehama Formation in the western Sacramento Valley as a syntectonic molasse; and (8) fault- propagation folding of the Tehama Formation beginning ca. 0.5-1.0 Ma. With the exception of Quaternary shortening, progressive arcward contr action of the western basin margin occurred during east-dipping subduc tion and plate convergence beneath western California. The deformation of the ancestral Sacramento Valley fore-arc basin is analogous to arc ward contraction of the Tobago Trough in the Lesser Antilles arc-trenc h system, and suggests that tectonic wedging may be a relatively commo n process in the evolution of fore-arc regions. Late Quaternary shorte ning has occurred in a transpressional setting and suggests a continui ty in structural style despite a change in plate boundary kinematics f rom convergence to transpression during the past 3-5 m.y.