Continetal accretion and evolution of the southwest North American continental margin; new insight from detrital zircon U-Pb provenance data
Dr. Dave Kimbrough
Professor – San Diego State University
Wednesday September 2, 2020
Watch Dave’s talk here
The processes by which arc crust is amalgamated to convergent margins range from the comparatively simple case of the modern Andean ocean-continent margin to highly complex situations involving migrating oceanic island arcs. The latter is well illustrated by the Taiwanese example of the ongoing collision between the Luzon arc and mainland China where subduction polarities flip as collision proceeds. Analogous processes have been envisioned for the Jurassic convergent margin of North American. While island arcs are thought to have been sutured to continental convergent margins at different times and places throughout Earth’s history, it has proven sufficiently challenging to confirm or disprove specific instances of arc-continent collisions due to preservation issues that many applications of the arc-continent collision model remain controversial
The ~1500 km-long Baja California peninsula, underpinned by crystalline basement of the Cretaceous Peninsular Ranges batholith, is at the center of debate regarding the Mesozoic-Cenozoic growth history of continental crust along this segment of the southwest North American margin. For example, does the western half of the PRB (the ‘Alisitos arc’) – together with the widespread Guerrero terrane of adjacent mainland Mexico – represent a major oceanic arc terrane accreted to the margin in the middle Cretaceous along an intervening subduction zone, or alternatively is the PRB a coherent single subduction system that evolved across transitional oceanic-continental crust? Other questions relate to the controversial Baja-British Columbia hypothesis that calls for 4000 km of post-mid Cretaceous south to north displacement of major crustal blocks between Baja and B.C.
Detrital zircon U-Pb study has driven major advancements in provenance investigations of sedimentary basins and dispersal systems over the past 20 years. The many hundreds of DZ studies published in this interval document rapidly advancing successes in assessing provenance, paleogeography, and tectonics reconstructions. This talk discusses a big new detrital zircon data set from 1) prebatholithic rocks sampled throughout the 1400 km length of Peninsular California between the Santa Ana Mountains of southern California (34°N) to the Los Cabos block (23°N) including offshore islands, and 2) conglomerate clast and olistolith block data from the Vizcaino terrane in west-central Baja California that represents the most outboard tectonic element of Peninsular California. The new data indicate close proximity of ‘accreted’ tectonic elements of the margin to adjacent native Gondwana and Laurentian North American basement throughout its Mesozoic-Cenozoic history.