Western North America
Corridor C-3 (Fig. 1) traverses the transition from oceanic crust to cratonal rocks of North America along a 1,500-km transect from offshore southern California to central New Mexico (Howell and others, 1985; Gibson and others, 1985). The western end of the transect is offshore in an oceanic seamount province of the Pacific plate. Eastward, it crosses the southern California borderland and emerges onshore in the batholith-dominated Peninsular Ranges. C-3 spans the Salton trough, a transform rift floored by nascent oceanic crust, and the Basin and Range structural province, formed by extension and disruption of cratonal rocks. The eastern end of C-3 is on the stable craton.
Neogene tectonism has severely disrupted the older structural grain between the oceanic lithosphere and the craton. Much of this young tectonism is attributed to interactions along the plate edges after the spreading ridge system separating the Pacific and Farallon plates inpinged upon the North American plate in late Oligocene time. Two triple junctions—one migrating northward, the other southward relative to the Pacific plate—formed as the spreading system moved eastward relative to the North American plate. The San Andreas fault system began to develop within a broad zone of right shear as the triple junctions moved apart. The main strand of the San Andreas is but one of many northwest-trending right-lateral faults in the system. The boundary between the Pacific and North American plates is best perceived as a broad zone of right shear rather than a specific fault trace.
The continental crust of the
Figures & Tables
This volume presents syntheses in twelve chapters of the tectonic evolution of continent-ocean transitions of North America (Canada-Mexico-U.S.A.) since the Precambrian. The syntheses are interpretations based on the 19 continent-ocean transects across North American margins published by GSA as part of its Decade of North American Geology (DNAG) series. The transitional region is the part of North America between the craton, little deformed in Phanerozoic time, and the modern ocean basins. The region developed heterogeneously within plate boundary zones that led to sequences of passive, collisional, and active margins that differ place to place. Nine chapters address individual segments of the transitional region, two consider active and passive margin tectonics topically, and one treats the evolution of Phanerozoic transitions of North America as a whole.