Miocene silicic volcanism in southwestern Idaho: geochronology,geochemistry, and evolution of the central Snake River Plain |
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| Authors: | Bill Bonnichsen William P Leeman Norio Honjo William C McIntosh Martha M Godchaux |
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| Institution: | (1) Idaho Geological Survey, Moscow, ID 83844, USA;(2) National Science Foundation, Arlington, VA 22203, USA;(3) Rice University, Houston, TX 77251, USA;(4) New Mexico Inst. of Mining and Technology, Socorro, NM 87801, USA;(5) Mount Holyoke College, 927 East 7th Street, Moscow, ID 83843, USA |
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| Abstract: | New 40Ar-39Ar 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 large-scale 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 NNW-trending 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.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. |
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| Keywords: | Caldera Crustal foundering Ignimbrite flare-up Lava flow Rhyolite Rifting Snake River Plain 40Ar-39Ar dating |
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