Owens Valley — A Major Rift between the Sierra Nevada Batholith and Basin and Range Province, U.S.A.

Abstract

Owens Valley is a graben in eastern California that extends approximately 250 km northward from the Garlock fault to Mono Lake, The rift zone is 10 km wide with a vertical displacement of more than 5 km. The graben contains from 1.5 to 2.5 km of sediments, but the mountain fronts rise 2.75 km above the valley floor to an elevation above 4,000 m. This rift valley is thought to have formed within the last 3 million years. Seismicity and faulting are still active: the last major fault occurred in 1872 and showed a maximum displacement of 5.5 m.

Quaternary volcanic features associated with the rift include: 1) Long Valley, a 17 by 32 km rhyolitic caldera at the northern end of the rift, that formed 0.7 m.y. ago with the eruption of 600 km³ of Bishop Tuff, 2) Mono Craters rhyolitic ring structure north of Long Valley, 3) Big Pine basaltic field at the midsection of the rift, and 4) Coso volcanic field that may represent incipient collapse at the southern end of the rift.

This region is characterized by bimodal basalt-rhyolite volcanism. The magma for the Long Valley and Mono Craters silicic centers was probably derived from partial melting of a detached subducted plate. The basaltic fields have a mantle origin related to continental fragmentation and development of a thin crust above an anomalous asthenoshpere.