Stable-isotope compositions of fracture- and cavity-filling calcite from the unsaturated zone of three drill cores at Yucca Mountain Tertiary volcanic complex indicate that the water from which the minerals precipitated was probably meteoric in origin. A decrease in 18 O in the calcite with depth is interpreted as being due to the increase in temperature in drill holes corresponding to an estimated average geothermal gradient of 34° per kilometer. A few of the calcite samples and all of the opal samples yielded uranium-series ages older than 400 000 yr, although most of the calcite samples yielded ages between 26 000 and 310 000 yr. The stable-isotope and uranium-series dates from precipitated calcite and opal of this reconnaissance study suggest a complex history of fluid movement through the volcanic pile, and episodes of fracture filling predominantly from meteoric water during at least the past 400 000 yr. -Authors
CITATION STYLE
Szabo, B. J., & Kyser, T. K. (1990). Ages and stable-isotope compositions of secondary calcite and opal in drill cores from Tertiary volcanic rocks of the Yucca Mountain area, Nevada. Geological Society of America Bulletin, 102(12), 1714–1719. https://doi.org/10.1130/0016-7606(1990)102<1714:AASICO>2.3.CO;2
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