Sulfur isotope values (δ34S and Δ33S) of pyrite in sediment from steam-heated hydrothermal vents on the floor of Yellowstone Lake (WY) were measured using secondary ionization mass spectrometry (SIMS). The high resolution of the SIMS data place important constraints on sulfur cycling processes at/near the vent fluid-lake water interface. Pyrite with a distinct mantle-basalt (δ34S = 0‰) isotope composition (δ34S = +0.5 to +3.1‰) replaces pyrrhotite during incipient stages of alteration at moderately high temperature. Disseminated cubic pyrite (δ34S = +2.0 to +5.3‰) occurs in zones where more extensive oxidation is likely. Framboidal pyrite with δ34S values ranging from –5.2 to +4.1‰ and Δ33S up to +0.30‰ suggest formation from low-temperature microbial sulfate reduction in sediments near but not directly in the vent fluid up-flow zone. The co-occurrence of pyrite with S isotope values characteristic of distinct formation processes, coupled with notable intra-crystal S isotope variations, suggests the venting locus is dynamic in time and space.
Bibliographical noteFunding Information:
This work was funded by the National Key R&D Program of China ( 2016YFE0203000 ) and NSF grants EAR 1515377 and OCE 1434798 . The authors thank Dave Lovalvo, Todd Gregory, Bobby Mohr, and Josh Carlson from the Global Foundation for Ocean Exploration for their efforts in obtaining core materials utilized in this study. We thank Yang Li, Yu Liu, Guoqiang Tang for their help during the SIMS analyses. We also thank Dr. Rob Sohn and members of the HD-YLAKE research team for constructive advice. Part of this work was performed at the Institute for Rock Magnetism (IRM) at the University of Minnesota. The IRM is a U.S. National Multi-user Facility supported through the Instrumentation and Facilities program of the National Science Foundation, Earth Sciences Division, and by funding from the University of Minnesota. All work in Yellowstone National Park was completed under an authorized Yellowstone Research permit (YELL-2018-SCI-7018.
- Hydrothermal dynamics
- Sulfur isotopes
- Yellowstone Lake