Mid-Tertiary ignimbrite flare-up

The Mid-Tertiary ignimbrite flare-up,[lower-alpha 1] was a dramatic period of volcanic eruptions in mid-Cenozoic time, approximately 25–40 million years ago, centered in the western United States.[2] These eruptions are seen today as deposits of ignimbrite, the pyroclastic material that was laid down from these effusions.

Mid-Tertiary ignimbrite flare-up
The Fish Canyon Tuff ignimbrite
Volcano	Multiple cumulative events
Date	25-40 million years ago
Location	Western United States
Impact	Deposited vast swatches of ignimbrite across the western United States

Overview

There are countless eruptions within the flare-up; the total volume includes 5x10⁵ km³ of ash flow tuff and 5x10⁶ km³ of intermediate and silicic lava.[3] This amount is on par for some of the largest non-explosive volcanic provinces (see World's largest eruptions). For reference, the 1980 eruption of Mt. St. Helens was about 1 km³. The largest eruption on the flare-up, and also the largest explosive eruption ever known, was the Fish Canyon tuff in southwest Colorado. Its volume alone is 5,000 km³. The three primary volcanic centers of the flare-up are the Central Nevada volcanic field of central Nevada, Indian Peak volcanic field of eastern Nevada/western Utah, and the San Juan volcanic field in Colorado.

Cause

The primary tectonic driving force behind this explosive volcanic activity is slab rollback.[4] During the Laramide orogeny, the subducting Farallon Plate subducted at a very shallow angle. When this stopped, the mantle wedge was opened up, and the result was the flare-up. The specifics of this opening, including possible windows or buckling of the plate, can explain specific volcanic trends within the flare-up.

See also

• List of large volume volcanic eruptions in the Basin and Range Province
• Slab gap hypothesis

Notes

1. This designation has as a part of it a term, 'Tertiary', that is now discouraged as a formal geochronological unit by the International Commission on Stratigraphy.[1]

References

1. Ogg, James G.; Gradstein, F. M; Gradstein, Felix M. (2004). A geologic time scale 2004. Cambridge, UK: Cambridge University Press. ISBN 0-521-78142-6.
2. Cannon, Eric. "The Mid-Tertiary ignimbrite flare-up". Archived from the original on 16 July 2012. Retrieved 14 August 2010.
3. Cannon, Eric. "1. Introduction: The Mid-Tertiary ignimbrite flare-up". Archived from the original on 13 February 2012. Retrieved 14 August 2010.
4. Cannon, Eric. "5. Tectonics: The Mid-Tertiary ignimbrite flare-up". Retrieved 14 August 2010.