Duration of sedimentation of Creede Formation from 40Ar/39Ar ages
GSA Special Papers
By: Marvin A. Lanphere
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Abstract
The Oligocene Creede Formation was deposited in the moat of the Creede caldera, which formed as a result of eruption of ythe Snowshoe Mountains Tuff. The Creede Formation in the two moat drill holes contains ash layers that are considered fallout tuffs derived from Fisher Dacite volcanoes that were erupting during accumulation of the Creede Formation. The duration of sedimentation of the Creede Formation could hnot be determinted directly by measuring the ages of the ash layers because 40Ar/39Ar ages of biotite from the asj layers do not stack in the correct stratigraphic order, indicating that the ash layers have been contaminated by biotite from older units. The duration of sedimentation is constrained by the ages of volcanic unites that stratigraphically bracket the Creede Formation. Pooling all ages for the underlyinh Snowshoe Mountain Tuff yields an age of 26.92 ± 0.07 Ma for the unit. The age of the stratigraphically highest lavas of Fisher Dacite, which overlie the Creede Formation, is 26.26 ± 0.04 Ma. The two limits give a maximum duration for sedimentation of the Creede Formation of 0.66 m.y. Using the ages of older Fisher Dacite lavas, on which some beds of the Creede Formation were deposited, a more realistic maximum duration of 0.34 m.y. for sedimentation of the Creede Formation can be determined.
Suggested Citation
Lanphere, M.A., 2000, Duration of sedimentation of Creede Formation from 40Ar/39Ar ages: GSA Special Papers, v. 346, p. 71-76, https://doi.org/10.1130/0-8137-2346-9.71.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Duration of sedimentation of Creede Formation from 40Ar/39Ar ages |
| Series title | GSA Special Papers |
| DOI | 10.1130/0-8137-2346-9.71 |
| Volume | 346 |
| Year Published | 2000 |
| Language | English |
| Publisher | Geological Society of America |
| Contributing office(s) | Earthquake Science Center |
| Description | 6 p. |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | GSA Special Papers |
| First page | 71 |
| Last page | 76 |
| Country | United States |
| State | Colorado |
| Other Geospatial | Oligocene Creede Formation;San Juan Mountains |