Mid-Tertiary ignimbrite flare-up

Mid-Tertiary ignimbrite flare-up
The Fish Canyon Tuff ignimbrite
Volcano	Multiple cumulative events
Date	25-40 million years ago
Type	Hawaiian, Strombolian, and/or Vulcanian
Location	Western United States
VEI	1-3
Impact	Deposited vast swatches of ignimbrite across the western United States

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

Overview

There are countless eruptions within the flare-up; the total volume is 500,000 to 5,000,000^[2] cubic kilometers (km³). 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 roll back.^[3] 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

• Slab gap hypothesis

References

1. ^ Cannon, Eric. "The Mid-Tertiary ignimbrite flare-up". http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/ignimbrite_intro.html. Retrieved 14 August 2010. 
2. ^ Cannon, Eric. "1. Introduction: The Mid-Tertiary ignimbrite flare-up". http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_1/investigation_intro.html. Retrieved 14 August 2010. 
3. ^ Cannon, Eric. "5. Tectonics: The Mid-Tertiary ignimbrite flare-up". http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_1/tectonics_intro.html. Retrieved 14 August 2010. ^{[dead link]}