OTHER RESEARCH

Transition metal stable isotope ratios have recently been the focus of a lot of research, primarily due to advances in instrumentation. Work in our lab at Washington State University has developed protocols for measuring Cu isotope ratios in Cu-rich minerals, and has applied these measurements to investigating the range of Cu ratio variations in ore minerals. Some of the details of our work can be found in:

Larson, P.B., Maher, K., Ramos, F.C., Chang, Z., Gaspar, M., and Meinert, L.D., 2003, Copper isotope ratios in magmatic and hydrothermal ore forming environments, Chemical Geology, v. 201, pp. 337-350.

This and additional work were the topic of Dr. Kierran Maher’s Ph.D. research. Kierran completed his Ph.D. under my direction in 2005. Further research on Cu isotope ratios in continental hydrothermal deposits will focus on determining Cu ratios in hydrothermal source reservoirs and on measuring empirical and experimental Cu isotope fractionations. Graduate student opportunities are available for this research. Please contact me for more information (plarson@wsu.edu).

Cu isotope ratios in hydrothermal environments

I have conducted research on hydrothermal systems in the San Juan Mountains, Colorado, for nearly the past 30 years, and this area remains of great interest. My initial research there focused on applying stable isotope analyses to understanding water/rock reactions and to mapping the extent of hydrothermal systems associated with specific intrusive environments. Over the past 15 years, the research has expanded to include other measures of water/rock interaction that have been applied to estimating the duration of hydrothermal activity, and to integrating stable isotope and mineral reaction data into three dimensional models that evaluate the flow and reaction. Graduate student opportunities are available for continuing this research. Please contact me for more information (plarson@wsu.edu).

Hydrothermal systems in the San Juan Mountains, Colorado

Publications on my prior work in this area include:

Cole, D.R., Larson, P.B., Riciputi, L.R., and Mora,C.I., 2004, Oxygen isotope zoning profiles in hydrothermally altered feldspars: Estimating the duration of water-rock interaction, Geology, v. 32, pp. 29-32.

Campbell, A.R., and Larson, P.B., 1998, Introduction to Stable Isotope Applications in Hydrothermal Systems: In, Richards, J.P., and Larson, P.B., eds., Reviews in Economic Geology, Society of Economic Geologists, v. 10, pp. 173-193.

Larson, P.B., Cunningham, C.G., and Naeser, C.W., 1994, Large-scale alteration effects in the Rico paleothermal anomaly: Economic Geology, v. 89, p. 1769-1779.

Larson, P.B., Cunningham, C.G., and Naeser, C.W., 1994, Hydrothermal alteration and mass exchange in the hornblende latite porphyry, Rico, Colorado: Contributions to Mineralogy and Petrology, v. 116, p. 199-215.

Lea, D.W., Larson, P.B., Taylor, H.P., Jr., and Crawford, M.L., 1989, Oxygen isotope and fluid inclusion study of rocks from the Mineral Point area, Eureka graben, Colorado: Economic Geology, v. 84, p. 1656-1662.

Larson, P.B., 1987, Stable isotope and fluid inclusion investigations of epithermal vein and porphyry molybdenum mineralization in the Rico mining district, Colorado: Economic Geology, v. 82, p. 2141-2157.

Larson, P.B., and Taylor, H.P., Jr., 1987, Solfataric alteration in the San Juan Mountains, Colorado: Oxygen isotope variations in a boiling hydrothermal environment: Economic Geology, v. 82, p. 1019-1036.

Larson, P.B., 1986, Progressive mineral alteration and coupled 18O depletions in the Lake City hydrothermal system (23 Ma), Colorado: In Proceedings of the Workshop on Geochemical Modeling, Lawrence Livermore National Laboratory, California, CONF-8609134, pp. 66-71. (Not peer reviewed)

Larson, P.B., and Taylor, H.P., Jr., 1986, An oxygen isotope study of hydrothermal alteration in the Lake City caldera, San Juan Mountains, Colorado: Journal of Volcanology and Geothermal Research, v. 30, p. 47-82.

Larson, P.B., and Taylor, H.P., Jr., 1986, An oxygen study of water/rock interaction in the granite of Cataract Gulch, western San Juan Mountains, Colorado: Geological Society of America Bulletin, v. 97, p. 505-515.

Larson, P.B., and Taylor, H.P., Jr., 1986, 18O/16O ratios in ash-flow tuffs and lavas erupted from the central Nevada caldera complex and the central San Juan caldera complex, Colorado: Contributions to Mineralogy and Petrology, v. 92, p. 146-156.

Panorama of the eastern side of the Rico dome, southwest Colorado, with the town of Rico in the foreground. Much of my more recent work in the San Juan Mountains has focused on the hydrothermal system at Rico. See below for a list publications on this area.

Diamond drill core from deep within the Rico dome, showing stockwork molybdenite in the Uncompahgre quartzite (upper two) and Precambrian diabase (lower two).

Oxygen isotope ratios in altered Mesozoic sediments in the Rico dome. Note the gradual and systematic decrease in ratios from >11 per mil (fresh) to near 0 per mil in the center of the dome. The depletion is a function of hydrothermal water/rock interaction in the shallow parts of the system that produced the deeper stockwork Mo deposit. This work was completed with NSF funding by graduate student Tom Muezelaar.

Oxygen and hydrogen isotope ratios of vein and alteration minerals in the Rico hydrothermal system.

Studying long-term topographic evolution of mountain belts and plateaus is very important to fully understand Earth’s dynamic system in the lithosphere and climate change. For the past several years, we have conducted research on topographic evolution of Cascade Range and Blue Mountains using stable isotope paleoaltimetry. Our lab at Washington State University is capable of separation, purification, and identification of authigenic clay minerals, authigenic oxides, pedogenic carbonates and others from bulk rocks and sediments, and analyzing their isotopic compositions. Some of the details of our work can be found in:

Takeuchi, A., and Larson, P.B., 2005, Oxygen isotope evidence for the late Cenozoic development of an orographic rain shadow in eastern Washington, USA. Geology, v. 33, pp. 313-316.

This work is the Ph.D. research of graduate student Akinori Takeuchi. There are a number of other research projects available on this topic for graduate study. Topographic evolution of the Blue Mountains is poorly constrained. The topographic state of the early Cascade Range (~40 Ma) and the pre-Cascade evolution are poorly known. Also, stable isotope records on the windward side are missing. Please contact me for more information if you are interesting in working on these projects (plarson@wsu.edu).

Topographic evolution of Cascade Range & Blue Mountains

Generalized DEM map of the present-day Pacific Northwest of the U.S. and a regional map of mean annual precipitation (MAP). Regions with colder colors (blues), indicating higher MAP, exist on the windward side of the Cascade range. On the other hand, a large arid to semi-arid region is present on the leeward side. This is a classic example of how the presence of a mountain belt can affect regional climate.

The calculated oxygen isotope values of ancient precipitation over time on the leeward side of the southern Washington Cascades. The isotopic shift indicates that approximately 1.4–1.7 km of topographic uplift of the southern Washington Cascades took place in the past 16 Ma.

To the left, desert environment in central Oregon, near the Columbia River. Note the outcrop of Columbia River Basalt in the foreground, and Mount Hood on the horizon (look closely).

To the right, sunset at Mt. Jefferson, central Oregon Cascades.