| Mid-Tertiary ignimbrite flare-up | |
| Date: | 25-40 million years ago |
| Volcano: | Multiple cumulative events |
| Location: | Western United States |
| Impact: | Deposited vast swatches of ignimbrite across the western United States |
The Mid-Tertiary ignimbrite flare-up, was a dramatic period of volcanic eruptions in mid-Cenozoic 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.
There were numerous eruptions within the flare-up. The total volume includes 5x105 km3 of ash flow tuff and 5x106 km3 of intermediate and silicic lava.[2] 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.
The primary tectonic driving force behind this explosive volcanic activity is slab rollback.[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 slab rollback,[4] slab windows,[5] or buckling of the plate,[6] can explain specific volcanic trends within the flare-up.