Title

Determining eruption ages and erosion rates of Quaternary basaltic volcanism from combined U-series disequilibria and cosmogenic exposure ages

Authors

Kenneth W.W. Sims, Woods Hole Oceanographic Institution
Robert P. Ackert Jr., Harvard University
Frank C. Ramos, Central Washington UniversityFollow
Robert A. Sohn, Woods Hole Oceanographic Institution
Michael T. Murrell, Los Alamos National Laboratory
Donald J. DePaolo, University of California - Berkeley

Document Type

Article

Department or Administrative Unit

Geological Sciences

Publication Date

5-1-2007

Abstract

We present ²³⁸U-²³⁰Th -²²⁶Ra disequilibria and cosmogenic ³He and ³⁶Cl data for the Bluewater flow of the Zuni-Bandera volcanic field in western New Mexico. The ²³⁸U-²³⁰Th disequilibria measured on separated groundmass phases yield an internal isochron age of 68 ka (+24/–20 ka; 2σ). This value cannot be directly compared with surface exposure ages unless erosion rates are known. The apparent (zero erosion) ages determined from both the ³He concentration (47.5 ± 5 ka; 2σ) and the ³⁶Cl concentration (41.2 ± 8.8 ka; 2σ) are significantly younger than the U-Th isochron age. When minimum estimates of surface erosion based on flow morphology are considered, the ³He concentrations indicate a minimum exposure age of 60 ka, in good agreement with the U-Th isochron age, with a minimum erosion rate of 1.7 mm/k.y. and an erosion rate as high as 5 mm/k.y. in other locations. Correcting for erosion has little effect on the model ³⁶Cl age and, as a result, the ³⁶Cl age is significantly younger than the U-Th isochron age and erosion-corrected ³He ages; this discordance is attributed to a lack of closed-system behavior in the ³⁶Cl system. These new ages have local significance for the geochronology of the Zuni-Bandera volcanic field; however, their larger significance is in their applicability to dating Quaternary basalts and quantifying erosion rates.

Comments

This article was originally published in Geology. The full-text article from the publisher can be found here.

Due to copyright restrictions, this article is not available for free download from ScholarWorks @ CWU.

Recommended Citation

Sims, K. W. W., Ackert, R. P., Ramos, F. C., Sohn, R. A., Murrell, M. T., & DePaolo, D. J. (2007). Determining eruption ages and erosion rates of Quaternary basaltic volcanism from combined U-series disequilibria and cosmogenic exposure ages. Geology, 35(5), 471. https://doi.org/10.1130/g23381a.1

Journal

Geology

Rights

© 2007 The Geological Society of America.