Structural controls on the spatial distribution, volume, and composition of rift-related volcanism in Owens Valley, California, USA

Bimodal volcanism is common across intracontinental rifts. However, tectonic controls on the composition of synextensional volcanism remain inadequately understood. In this study, we examined the spatial distributions of late Cenozoic faults and volcanic centers throughout the active Owens Valley rift basin (California, USA) in the western Basin and Range province of North America. Based on synthesized structural, topographic, geophysical, and geochemical observations, we suggest that the 3-D geometries of major faults in Owens Valley control the location, volume, residence time, and composition of synextensional volcanism. Specifically, northern and southern Owens Valley are wide, asymmetric grabens where master, listric normal faults have breakaways on one basin margin and extend beneath the opposing margin. Beneath opposing basin margins, master faults have thinned the lithosphere, creating space for decompression melting and enabling mantle melt to ascend into the crust in large volumes. Crustal dilatation and increased permeability allowed for some melt to stall and develop felsic compositions, whereas other mafic melt ascended with limited compositional change, resulting in bimodal volcanism. The asymmetric grabens in the north and south transition to a narrow, symmetric graben in central Owens Valley featuring high-angle, basin-bounding normal faults. There, normal and strike-slip faults serve as conduits for mafic melt to rapidly ascend with minimal wall rock contamination and compositional change. Our model linking rift-fault geometry to the location, volume, residence time, and composition of synextensional volcanism may apply to other intracontinental rifts with similar relationships.