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(super 40) Ar/ (super 39) Ar and paleomagnetic constraints on the age and areal extent of the Picabo volcanic field; implications for the Yellowstone Hotspot

Mark H. Anders, Victor J. DiVenere, Sidney R. Hemming and Joel Gombiner
(super 40) Ar/ (super 39) Ar and paleomagnetic constraints on the age and areal extent of the Picabo volcanic field; implications for the Yellowstone Hotspot
Geosphere (Boulder, CO) (May 2019) 15 (3): 716-735

Abstract

The Picabo volcanic field is one of the key silicic volcanic fields in the time-transgressive track of the Yellowstone hotspot. The Picabo volcanic field is also one of the most poorly defined volcanic fields along the track of the Yellowstone hotspot. Determining the age and areal extent of the Picabo volcanic field ignimbrites is one of the primary objectives of this study. In our effort to correlate ignimbrites within the Picabo volcanic field as well as identify those from the neighboring Twin Falls and Heise volcanic fields, we present new petrographic, (super 40) Ar/ (super 39) Ar, and paleomagnetic data. With these data, we correlated several ignimbrites within the Picabo volcanic field. In some cases, we correlate units previously thought to be in the Picabo volcanic field to older volcanic fields. This includes the Picabo Tuff, which we suggest originates from the Twin Falls volcanic field rather from its namesake volcanic field. The first and best documented major silicic eruption of the volcanic field, the Arbon Valley Tuff, is also the largest ignimbrite in the Picabo volcanic field. There is disagreement as to whether the Arbon Valley Tuff is the result of a single ignimbrite eruption or multiple eruptions. We previously have suggested that the Arbon Valley Tuff is the result of two eruptions, one at 10.41 + or - 0.01 Ma and the other at 10.22 + or - 0.01 Ma (Anders et al., 2014). Those combining radiometric dates into a single eruption age report ages of 10.2 Ma, 10.27 + or - 0.01 Ma, 10.34 + or - 0.03 Ma, and 10.44 + or - 0.27 Ma. We also suggest the final eruption of the Picabo volcanic field was the tuff of American Falls dated at 7.58 + or - 0.02 Ma. Estimates of the location of Picabo volcanic field have been used to mark a major change in the migration rate of the Yellowstone-Snake River Plain silicic volcanic system. Based on our new data, we found only minor changes of the boundaries of the Picabo volcanic field from previous studies. Using the age of the Arbon Valley Tuff (10.41 Ma), we calculated an extension-corrected migration rate of 2.27 + or - 0.2 cm/yr between the position of the Picabo volcanic field and that of the Yellowstone volcanic field over the past approximately 10 m.y. This estimate is close to the extension corrected 2.38 + or - 0.21 cm/yr value based on the migration of the hotspot deformation field. These rates are consistent with independent estimates of North American plate velocity over the past 10 m.y. and therefore consistent with a fixed reference frame for the Yellowstone hotspot. These results stand in contrast with several recent models for the evolution of the Yellowstone-Snake River Plain volcanic system. We also discovered a new ignimbrite from the Heise volcanic field, the 4.37 + or - 0.08 Ma tuff of Birch Creek Sinks, in core from the U.S. Geological Survey (USGS) borehole 2-2A, which now represents the youngest outflow ignimbrite of the Heise volcanic field. Although recently, several intracaldera ignimbrites younger than 4 Ma have been identified in the volcanic field, the age range of outflow ignimbrites from the Heise volcanic field is now extended from 6.66 Ma to at least 4.37 Ma.


EISSN: 1553-040X
Serial Title: Geosphere (Boulder, CO)
Serial Volume: 15
Serial Issue: 3
Title: (super 40) Ar/ (super 39) Ar and paleomagnetic constraints on the age and areal extent of the Picabo volcanic field; implications for the Yellowstone Hotspot
Affiliation: George Mason University, Department of Atmospheric, Oceanic and Earth Sciences, Fairfax, VA, United States
Pages: 716-735
Published: 20190508
Text Language: English
Publisher: Geological Society of America, Boulder, CO, United States
References: 94
Accession Number: 2019-046835
Categories: StratigraphyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N42°30'00" - N44°30'00", W114°00'00" - W112°00'00"
Secondary Affiliation: Long Island University, USA, United StatesLamont-Doherty Earth Observatory, USA, United StatesUniversity of Washington, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201924
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