Mid-Tertiary ignimbrite flare-up
{{Short description|Period of volcanic eruptions in mid-Cenozoic time}}
{{Infobox eruption
| name = Mid-Tertiary ignimbrite flare-up
| photo = File:WheelerGACO.jpg
| photo-size =
| caption = Wheeler Geologic Area, rocks of the San Luis Caldera complex
| date = 25-40 million years ago
| volcano = Multiple cumulative events
| location = Western United States
| coordinates =
| map =
| location-map =
| map-size =
| map-caption =
| impact = Deposited vast swatches of ignimbrite across the western United States
}}
The Mid-Tertiary ignimbrite flare-up,{{efn|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.{{cite book|author1=Ogg, James G. |author2=Gradstein, F. M |author3=Gradstein, Felix M. |title=A geologic time scale 2004|publisher=Cambridge University Press|location=Cambridge, UK|year=2004|isbn=0-521-78142-6}}}} was a dramatic period of volcanic eruptions in mid-Cenozoic time, approximately 25–40 million years ago, centered in the western United States.{{cite web|last=Cannon|first=Eric|title=The Mid-Tertiary ignimbrite flare-up|url=http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/ignimbrite_intro.html|accessdate=14 August 2010|archive-url=https://web.archive.org/web/20120716192901/http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/ignimbrite_intro.html|archive-date=16 July 2012|url-status=dead}} These eruptions are seen today as deposits of ignimbrite, the pyroclastic material that was laid down from these eruptions.
Overview
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.{{cite web|last=Cannon|first=Eric|title=1. Introduction: The Mid-Tertiary ignimbrite flare-up|url=http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_1/investigation_intro.html|accessdate=14 August 2010|archive-url=https://web.archive.org/web/20120925015901/http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_1/investigation_intro.html|archive-date=25 September 2012|url-status=dead}} 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 one of the largest explosive eruptions 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.{{cite web|last=Cannon|first=Eric|title=5. Tectonics: The Mid-Tertiary ignimbrite flare-up|url=http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_5/tectonics_intro.html|accessdate=14 August 2010|archive-date=4 March 2016|archive-url=https://web.archive.org/web/20160304060910/http://www.colorado.edu/GeolSci/Resources/WUSTectonics/CzIgnimbrite/INVESTIGATION/SECTION_5/tectonics_intro.html|url-status=dead}} 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,{{cite journal |last1=Best |first1=Myron G. |last2=Christiansen |first2=Eric H. |last3=de Silva |first3=Shanaka |last4=Lipman |first4=Peter W. |title=Slab-rollback ignimbrite flareups in the southern Great Basin and other Cenozoic American arcs: A distinct style of arc volcanism |journal=Geosphere |date=August 2016 |volume=12 |issue=4 |pages=1097–1135 |doi=10.1130/GES01285.1|bibcode=2016Geosp..12.1097B |doi-access=free }} slab windows,{{cite journal |last1=Breitsprecher |first1=K. |last2=Thorkelson |first2=D.J. |last3=Groome |first3=W.G. |last4=Dostal |first4=J. |title=Geochemical confirmation of the Kula-Farallon slab window beneath the Pacific Northwest in Eocene time |journal=Geology |date=1 April 2003 |volume=31 |issue=4 |pages=351–354 |doi=10.1130/0091-7613(2003)031<0351:GCOTKF>2.0.CO;2|bibcode=2003Geo....31..351B }} or buckling of the plate,{{cite journal |last1=Humphreys |first1=Eugene D. |title=Post-Laramide removal of the Farallon slab, western United States |journal=Geology |date=1 November 1995 |volume=23 |issue=11 |pages=987–990 |doi=10.1130/0091-7613(1995)023<0987:PLROTF>2.3.CO;2|bibcode=1995Geo....23..987H }} can explain specific volcanic trends within the flare-up.
See also
Notes
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