Miocene silicic volcanism in southwestern Idaho: geochronology, geochemistry, and evolution of the central Snake River Plain

Abstract

New 40 Ar-39 Ar geochronology, bulk rock geochemical data, and physical characteristics for representative stratigraphic sections of rhyolite ignimbrites and lavas from the west-central Snake River Plain (SRP) are combined to develop a coherent stratigraphic framework for Miocene silicic magmatism in this part of the Yellowstone 'hotspot track'. The magmatic record differs from that in areas to the west and east with regard to its unusually large extrusive volume, broad lateral scale, and extended duration. We infer that the magmatic systems developed in response to largescale and repeated injections of basaltic magma into the crust, resulting in significant reconstitution of large volumes of the crust, wide distribution of crustal melt zones, and complex feeder systems for individual eruptive events. Some eruptive episodes or 'events' appear to be contemporaneous with major normal faulting, and perhaps catastrophic crustal foundering, that may have triggered concurrent evacuations of separate silicic magma reservoirs. This behavior and cumulative time-composition relations are difficult to relate to simple caldera-style single-source feeder systems and imply complex temporal-spatial development of the silicic magma systems. Inferred volumes and timing of mafic magma inputs, as the driving energy source, require a significant component of lithospheric extension on NNWtrending Basin and Range style faults (i.e., roughly parallel to the SW-NE orientation of the eastern SRP). This is needed to accommodate basaltic inputs at crustal levels, and is likely to play a role in generation of those magmas. Anomalously high magma production in the SRP compared to that in adjacent areas (e.g., northern Basin and Range Province) may require additional sub-lithospheric processes.

Rheomorphic ignimbrites of the Rogerson Formation, central Snake River plain, USA: record of mid-Miocene rhyolitic explosive eruptions and associated crustal subsidence along the Yellowstone hotspot track

“…2) and comprises rhyolitic ignimbrites and thinner ashfall layers thought to be derived from eruptive sources concealed beneath basalts in the central Snake River Plain ). Prior to this study, it was subdivided into five members (Andrews and Branney 2005;Andrews et al 2008), with another 12 informal units ('BBU 1-12' of Bonnichsen et al 2008) reported on the adjacent Brown's Bench scarp (Fig. 1) of which two were correlated with units in the graben ).…”

“…2; 'BBU-2' of Bonnichsen et al 2008) is a crystal-poor (<2 %) intensely welded and rheomorphic rhyolitic ignimbrite, >20 m thick, exposed near the base of the Corral Creek section (Fig. 1).…”

A Study of Cathodoluminescence and Trace Element Compositional Zoning in Natural Quartz from Volcanic Rocks: Mapping Titanium Content in Quartz

“…Bonnichsen et al, 2008;Leeman & Lee, 2008!. These crystals formed in slowly cooling silica-rich magmas within crustal reservoirs.…”

Extensive soft-sediment deformation and peperite formation at the base of a rhyolite lava: Owyhee Mountains, SW Idaho, USA

“…1a). The thermal anomaly of the Yellowstone hotspot softened the lithosphere, triggering failure along planes with weak lithostatic strength and initiated rifting (Pierce and Morgan 1992;Wood and Clemens 2002;Bonnichsen et al 2004Bonnichsen et al , 2008. Rifting of the WSRP began at 12 Ma, correlating with the passage of the hotspot to the south and ceased at~7 Ma (Pierce and Morgan 1992;Wood and Clemens 2002;Bonnichsen et al 2004).…”

“…Associated with the initial rifting of the WSRP, between 11.7 and 11.0 Ma, localised rhyolite lavas, the BOwyhee Front volcanism^(the Jump Creek Rhyolite lava, the Reynolds Creek Rhyolite lava, the Cerro el Otoño Dome Field and the Wilson Creek Ignimbrite) were extruded from venting zones at the margins of the WSRP (Pierce and Morgan 1992;Perkins and Nash 2002;Bonnichsen et al 2004Bonnichsen et al , 2008Bonnichsen Walker and MacLeod (1991), Pierce and Morgan (1992), Cummings et al (2000) and Lewis et al (2012). Owyhee Mountains highlighted by box.…”