RELATIVE MAGNITUDES OF SEAFLOOR SPREADING AND CONTINENTAL RIFTING ACROSS THE GULF OF CALIFORNIA: AN EXAMPLE OF OROGEN–SCALE STRAIN COMPATIBILITY

Palinspastic reconstructions of nine serial crustal profiles drawn parallel to transform faults yield consistent magnitudes (450-500 km) of total tectonic transport across the Gulf of California despite marked variations in magnitudes of seafloor spreading. Magmatically robust spreading ridges with well developed magnetic anomalies like the East Pacific Rise, Alarcon and Guaymas have accommodated 210-340 km of separation. In contrast, magmatically starved spreading centers that form deep rhombochasmic basins like the Pescadero, Carmen and Farallon have accommodated only 80-130 km of separation. Nonetheless, differences in the magnitude of seafloor spreading are systematically compensated by differences in the magnitude of continental extension, which was calculated by reconstructing thinned continental crust to its pre-rifting thickness. Continental crustal thickness was calculated from topographic profiles assuming local airy isostatic compensation, and model parameters like crust-mantle density contrast and thickness of a reference crust were calculated by fitting independent gravity and crustal thickness data throughout the Gulf extensional province. The remarkable similarity and large magnitude of total tectonic separation 450-500 km across the Gulf, indicates that since 12.5 Ma, it opened in one kinematic phase with transport subparallel to modern transforms.