Fumarolic pipes in the Tshirege Member of the Bandelier Tuff on the Pajarito Plateau, Jemez Mountains, New Mexico

Florie A. Caporuscio, Jamie N. Gardner, Emily S. Schultz-Fellenz, Richard E. Kelley

Research output: Contribution to journalArticlepeer-review

8 Scopus citations

Abstract

The objective of this study is to demonstrate the relationships among devitrification, vapor phase alteration, localization of gas emanations into fumarolic pipes, and initial deformation of the ash flow sheet during cooling and lithification. Utilizing a unique and temporary exposure of the Tshirege Member of the Bandelier Tuff near Los Alamos, New Mexico, we identify several zones of distinctly preserved fossil fumarolic activity. The fumarolic zones vary in width from a few centimeters to more than a meter. Almost ubiquitously, these zones demonstrate fines-depletion, induration of the margins, upward-flaring geometries, and intense fracturing of overlying geologic units. The fumaroles were preferentially located on post welding, early formed cooling joints that vented to the surface after the vapor phase alteration stage. The pipes were regularly spaced at distances of approximately 4.5 m (N-S) to 7 m (E-W). In turn the pipes were covered by a surge deposit and overlying tuff which rapidly lithified. The overlying tuff was then brecciated during continued fumarolic pipe emissions. Geochemical evaluations confirm the presence of high-temperature mineral (scapolite) indicative of transport of hot volcanic gases through these zones. The pipe centers and walls are depleted in SiO 2, and enriched in Al 2O 3 and FeO. The overlying tuff breccia zones are enriched in Al 2O 3, FeO and MgO, and depleted in SiO 2, NaO, and K 2O. From comparison to other ignimbrite cooling histories, the fissures, fumaroles, and structures observed all likely formed in the first few decades after the deposition of the upper Tshirege subunits. This may have significant implications as to timing of initial cooling fractures and subsequent consolidation of gas emission pathways.

Original languageEnglish
Pages (from-to)1023-1037
Number of pages15
JournalBulletin of Volcanology
Volume74
Issue number5
DOIs
StatePublished - Jul 2012
Externally publishedYes

Keywords

  • Bandelier Tuff
  • Fumaroles
  • Pajarito Plateau
  • Scapolite

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