GEOLOGIC TIES ACROSS A RELOCATED TRACE OF THE LATE JURASSIC MOJAVE-SONORA MEGASHEAR

Mapping and complementary geochronologic studies by Nourse and colleagues (2005, 2022, 2024) in Sonora and the San Gabriel Mountains of California provide additional refinements on the trace of the postulated Mojave-Sonora megashear as shown by Anderson (2015, Plate 1, Restoration). If effects of Cenozoic extension and dextral shear are restored, then the principal megashear fault bounds the western margins of the San Gabriel and San Bernardino Mountains each of which contains rock units with isotopic signature compatible to the Mojave province basement. Juxtaposition of rocks of the Mazatzal province against exposures of the Yavapai-Mojave transition zone in northwest Sonora reaffirms a basic characteristic of the proposed fault zone (Silver and Anderson, 1974; Anderson and Silver, 2005). Multiple, previously recognized stratigraphic characteristics such as age, composition, setting, and fossil content among Neoproterozoic and Paleozoic sections (Stewart, 2005) in addition to cross-fault correlations of Mesozoic igneous and sedimentary rocks are compatible with displacement of as much as 800 km during Oxfordian time. Restoration of the Sonora Caborca block to a position adjacent to the Sierra Nevada not only juxtaposes distinctive features of Paleozoic and Triassic formations but also results in formation of: (1) a regional eastward-younging domain of Permo-Triassic plutons, if outcrops at Sierra Los Tanques are aligned with the central and eastern Sierran igneous rocks; (2) an elongate peninsula of Paleoproterozoic arc rocks, now exposed at Sierra Los Alacranes and Quitovac, that is conveniently situated to shed detritus northeastward into the Belt Basin. Correlations of sections on the Caborca block to Neoproterozoic, Early Paleozoic and Triassic sections of Inyo Mountains-Death Valley region also are compatible with some structures and unconformities that formed during regional, tectonic episodes such as Humboldt, ca. 306 to 295+/- Ma (e.g. Stevens et al., 2015). In Sonora, on the Caborca block, extensive stratigraphic sections in ranges such as those near Rancho Bamori, as well as Sierra del Alamo and Santa Teresa, provide opportunities for comparisons between Sonora and the California-Nevada region. We present these ideas in map view with a series of reconstruction diagrams to highlight details of the proposed cross fault geologic ties.