My primary research focus is the movement of fluids in the earth's crust, with an emphasis on dating and tracing studies utilizing two cosmogenic isotope systems, 129I and 36Cl. We used these isotopic systems in studies of volcanic fluids associated with the subduction process in order to detect the origin and history of volatiles in arc volcanoes. The initial focus of this study was Central America, followed by subsequent investigations in New Zealand, Japan and the Andes. The second focus is the determination of the history of 129I deposition in marine sediments over the last 80 Ma and the relation to the presence of different types of organic material. An important application of this approach is the determination of origin and migration of iodine and methane in marine gas hydrates and their relation to climatic changes during the Tertiary. The isotopes we use for tracing/dating studies are also produced during nuclear activities and their release into the environment from nuclear explosions and reprocessing has made possible applications in environmental studies and in short-term geologic questions.
For the study of cosmogenic isotopes, iodine and/or chlorine concentrations are first measured in the samples, using either ICP-MS or IC determinations. Once the concentrations are known, targets for the determination of isotope ratios are produced either as AgI or AgCl. The actual measurements of isotope ratios are carried out in dedicated accelerator mass spectrometry laboratories such as PrimeLab at Purdue University.
- Primary research focus is the movement of fluids in the earth's crust, with an emphasis on dating and tracing studies.
- U. Fehn (2012). Tracing Crustal Fluids: Applications of Natural 129I and 36Cl. Ann. Rev. Earth Planet. Sci. 40, 45-67. doi: 10.1146/annurev-earth-042711-105528. Full Text
- H. Tomaru and U. Fehn (2012). Data report: distribution of iodine concentrations and 129I in interstitial fluid in the Nankai Trough accretionary prism collected during IODP Expeditions 315 and 316. In Kinoshita et al., Proc. IODP, 314/315/316: Washington, DC (Integrated Ocean Drilling Program Management International, Inc.). doi: 10.2204/iodp.proc.314315316.220.2012
- Z. Lu, H. Tomaru and U. Fehn (2011). Comparison of iodine dates from mud volcanoes and hydrate occurrences: Relevance for the movement of fluids and methane in active margins. Am. J. Sci., 311, 632-650.
- F. Scholz, C. Hensen, Z. Lu and U. Fehn (2010), Controls on the 129I/I ratio of deep-seated marine interstitial fluids: ‘old’ organic versus fissiogenic 129-iodine, Earth Planet. Sci. Lett., 294, 27-36.
- H. Tomaru, Z. Lu, U. Fehn and Y. Muramatsu (2009), Origin of hydrocarbons in the Green Tuff region of Japan: 129I results from oil field brines and hot springs in the Akita and Niigata Basins. Chem. Geol., 264, 221-231.
- Z. Lu, H. Tomaru and U.Fehn (2008), Iodine ages of pore waters at Hydrate Ridge (ODP Leg 204), Cascadia Margin: implications for sources of methane in gas hydrates, Earth Planet. Sci. Lett., 267, 654-665.
- M. Reich, C. Palacios, M.A. Parada, U. Fehn, E. M. Cameron, M.I. Leybourne and A. Zúñiga (2008). Atacamite formation by deep saline waters in copper deposits from the Atacama Desert, Chile: Evidence from fluid inclusions, groundwater geochemistry, TEM, and 36Cl data. Mineralium Deposita, 43, 663-675.
- Z. Lu, C. Hensen, U. Fehn and K. Wallmann (2008), Halogen and 129I systematics in gas hydrate fields, at the northern Cascadia Margin (IODP Expedition 311) - Insights from numerical modeling. Geochem. Geophys. Geosyst., 9, 10.1029/2008GC002156, 18p.
- U. Fehn, G.T. Snyder and Y. Muramatsu (2007). Iodine as a tracer of organic material: 129I results from gas hydrate systems and fore arc fluids. J. Geochem. Explor., 95, 66-80.
- U. Fehn, J.E. Moran, G.T. Snyder and Y. Muramatsu (2007). The initial 129I/I ratio and the presence of 'old' iodine in continental margins. Nuclear Instruments and Methods in Physics Research, B, 259. 496-502.
- U. Fehn, Z. Lu and H. Tomaru (2006). Data Report: 129I/I ratios and halogen concentrations in pore waters of the Hydrate Ridge and their relevance for the origin of gas hydrates: a progress report. Proc. ODP, Sci. Results 204, 1-25, MS 204SR-107.
- U. Fehn and G.T. Snyder (2005): Residence times and source ages of deep crustal fluids: Interpretation of 129I and 36Cl results from the KTB-VB drill site, Germany. Geofluids, 5, 42-51.
- U. Fehn and G.T. Snyder (2003): Origin of iodine and 129I in volcanic and geothermal fluids from the North Island of New Zealand: Implications for subduction zone processes. Econ. Geol., Spec. Publ.10, 159-170.
- G.T. Snyder and U. Fehn (2002): The origin of iodine in volcanic fluids: 129I results from the Central American Volcanic Arc. Geochim. Cosmochim. Acta, 66, 3827-3838.
- U. Rao, U. Fehn, Y. Muramatsu, H. McNeil, P. Sharma and D. Elmore (2002): Tracing the history of nuclear releases: Determination of 129I in tree rings. Environmental Science & Technology, 36, 1271-1275.
- U. Fehn, G. Snyder and P.K. Egeberg (2000): Dating of pore waters with 129I: Relevance for the origin of marine gas hydrates. Science, 289, 2332-2335.
Research Opportunities for Graduate Students
I have ended active preparation of samples in my laboratory and do not accept additional graduate students. Being involved in collaborations with colleagues at other institutions, I still organize applications of the methods developed here.