GLEN CANYON AND SAN RAFAEL TECTONOSEQUENCES: IMPLICATOINS FOR THE EARLY AND MIDDLE JURASSIC EVOLUTION OF THE PANTHALASSAN MARGIN OF SOUTHWESTERN LAURENTIA

Regional unconformities within the Triassic and Jurassic stratigraphy of the western United States define eight tectonosequences. From oldest to youngest they are the Moenkopi, Holbrook, Chinle, Dinosaur Canyon, Glen Canyon (GCt), San Rafael (SRt), and Brushy Basin (BBt). The basal GCt boundary crosscuts older tectonosequence boundaries defining piercing points. The piercing points document over 1,000 km of left-lateral displacement of western North America relative to the Caborca terrane of northwest Mexico along the Mojave-Sonora megashear. Displacement coincided with SRt deposition - < 163 Ma to ~ 150Ma. The megashear is interpreted to lie along the 0.076 Sr isopleth along the western edge of Death Valley-like cratonal rocks of the Snow Lake terrane. The eastern boundary, Schweickert and Lahren's Mojave-Snow Lake fault, is interpreted as an obduction decollement placing Paleozoic eugeoclinal rocks and Triassic volcanic-arc rocks on the cratonal assemblage. Initiation of obduction coincides with forebulge development in the Navajo Sandstone and rapid subsidence of the Twin Creek - Carmel seaway. These interpretations imply the megashear cut the tectonically stacked cratonal margin after GCt deposition. SRt deposition proceeded in left-lateral transtensional basins. BBt deposition coincides with post megashear subduction along the cratonal margin. Deposition of the GCT is interpreted to coincide with the J-1 to J-2 cusp segment of the North American apparent polar wander path; initiation of the megashear, with the J-2 cusp; and deposition of the SRt with early segment of the post J-2 cusp path.