DEATH VALLEY, CALIFORNIA AS THE KEYSTONE TO THE LATE CENOZOIC MAGMATIC AND TECTONIC EVOLUTION OF THE PLATE MARGIN EXTENSIONAL SYSTEM OF SOUTHWESTERN NORTH AMERICA

The late Cenozoic tectonic evolution of southwestern North America is a well-studied example of continental margin extensional tectonics. Despite this intense study, there is no complete geodynamic model for the regional tectonic and magmatic evolution. The critical missing link occurs between the Miocene tectono-magmatic evolution of the Colorado River extensional corridor (CREC) in eastern California and western Arizona, to the Pliocene and younger activity of the Walker Lane belt along the Nevada-California border. This key missing segment coincides with the Death Valley extensional region (DVER).

We use new high-precision U-Pb zircon crystallization ages and interpretations from Chan et al. (2024; this session) of late Miocene plutonic rocks in the DVER combined with prior work on tectonic restorations and volcanic rocks in the DVER and regionally. New and compiled geochronologic results for the DVER show two distinct and spatially concentrated magmatic episodes with spatially and temporally associated large-magnitude extension.

The DVER fits into the regional tectono-magmatic evolution as the previously unrecognized middle segment of a northwestward migrating locus of magmatism and extension from the CREC to Owens Valley, California. The northwestward migration of WSW-ENE directed large-magnitude extension in the CREC with its associated locus of magmatism begins in Sonora, Mexico during Basin and Range extension at ~30 Ma, migrating northwestward to southern Nevada by ~13 Ma. Activity continues to the northwest of the CREC in the DVER with WSW-directed extension on the Kingston-Halloran detachment fault with a locus of magmatism from 13 to 11 Ma; magmatism continues with a regional change in tectonics at ~10 Ma to a dextral component. A pull-apart setting of northwest-directed extensional occurs in the DVER with associated magmatism until ~8 Ma when major extension and magmatism ceases in DVER. The locus of major extension and magmatism then shifts NW to Owens Valley with the associated Long Valley caldera and Mono Lake volcanic field. The CREC is interpreted as driven by asthenospheric flow at the edge of the slab window related to the northwestward migration of the Mendocino triple junction and growth of the San Andreas fault. The DVER data support a 30 m.y. continuous northwest-migrating process from the southern CREC to Owens Valley.