Moderate temperature zeolitic alteration in a cooling pyroclastic deposit
The locally zeolitized Topopah Spring Member of the Paintbrush Tuff, Yucca Mountain, Nevada, USA is part of a thick sequence of zeolitized pyroclastic units. Most of the zeolitized units are nonwelded tuffs that were altered during low temperature diagenesis, but the distribution and textural setting of zeolite (heulandite-clinoptilolite and smectite in the densely welded Topopah Spring tuff suggests that these hydrous minerals formed while the tuff was still cooling after pyroclastic emplacement and welding. The hydrous minerals are concentrated within a transition zone between devitrified tuff in the central part of the unit and underlying vitrophyre. Movement of liquid and convected heat along fractures from the devitrified tuff to the vitrophyre caused local devitrification and hydrous mineral crystallization. Oxygen isotope geothermometry of cogenetic quartz confirms the nondiagnetic moderate temperature origin of the hydrous minerals at temperatures of about 40 to 100{sup 0}C, assuming a meteoric water source. 14 refs., 3 figs., 1 tab.
- Research Organization:
- Los Alamos National Lab., NM (United States); Geological Survey, Menlo Park, CA (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 60096
- Report Number(s):
- DOE/NBM--7013294; LA-UR-86-3286; ON: DE87013294
- Country of Publication:
- United States
- Language:
- English
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