PALEOTECTONICS AND PALEOGEOGRAPHY OF SOUTHWESTERN CALIFORNIA 30-0 MA BASED ON FINITE-ELEMENT RECONSTRUCTION

Finite-element program Restore simulates paleokinematics by weighted least squares and integrates displacements, strains and rotations, producing paleogeologic maps, as well as maps of velocity, heave rate, strain rate and stress direction at 6my intervals. The input data derive from a thorough literature search from 49° to 20° N. Piercing-point pairs restored along the San Andreas-Gulf of California plate boundary include the Chocolate Mountains anticlinorium at 6 Ma, the Pinnacles/Neenach Volcanics at 22 Ma, and the Jolla Vieja and Poway conglomerates adjacent their Sonoran source at 48-42 Ma. First contact between the Pacific and North America plates at 28 Ma initiated the unstable Mendocino triple junction and slab windows, which were associated with extension in the Plush Ranch-Vasquez-Diligencia basins 25-18 Ma and highly extended terranes of the Mojave and Colorado River regions (23-12 Ma). Transrotation of the western Transverse Ranges was most rapid 18-12 Ma, as Catalina Schist was excised from beneath the Peninsular Ranges along the Oceanside detachment fault. Dextral slip along the northern San Andreas fault connected to the Canton-Verdugo-Eagle Rock fault northeast of the western Transverse Ranges during transrotation. Northern SAf slip was connected to the San Gabriel-Vasquez Creek-Chino Hills-Cristianitos fault system (12-6 Ma), inducing transtensional opening of the Puente-Modelo sub-basins. The transpressional phase of the Los Angeles basin developed 6-0 Ma, as northern SAf dextral slip migrated from the San Gabriel to the southern SAf, creating the big bend between the southern Sierra Nevada and the Salton trough. Paleogeologic maps created by Restore provide templates on which paleogeographic maps may be created based on sedimentologic, petrographic, geochemical, stratigraphic, paleontologic and structural data. These maps, in turn, provide tests of Restore reconstructions, which can be adjusted accordingly.