Tubular Nontronite-Bearing Hydrothermal Deposits from a Galápagos Seamount

Monday, 30 January 2017
Marina/Gretel (Hobart Function and Conference Centre)
Megan Lubetkin1, Steven Carey2, Katherine A Kelley2, Genevieve Robert1, Winton C Cornell3, Nicole Raineault4, Jacob R Balcanoff2, Robert D. Ballard2,4 and Pelayo Salinas de León5, (1)Bates College, Geology, Lewiston, ME, United States, (2)Graduate School of Oceanography, University of Rhode Island, Narragansett, RI, United States, (3)University of Tulsa, Geosciences, Tulsa, OK, United States, (4)Ocean Exploration Trust, Narragansett, RI, United States, (5)Charles Darwin Foundation, Santa Cruz, Ecuador
Abstract:
An unusual tubular deposit of Fe-rich hydrothermal nontronite has been discovered by remotely operated vehicle (ROV) exploration on a young seamount of the Wolf-Darwin lineament in the Galápagos Islands. X-ray diffraction, ICP-MS, ICP-AES, and SEM-EDS analyses show that this deposit is chemically and mineralogically similar to other deep-sea hydrothermal nontronites indicating a likely formation temperature of about 30º to 50º C by diffuse hydrothermal activity. These deposits contain Fe-oxides and Fe-rich, Al-poor nontronite, with bulk composition of 38-51 wt.% SiO2 and 40-50 wt.% Fe2O3. The presence of filamentous and lepispherical structures in the samples suggests that mineral deposition was facilitated by chemosynthetic bacteria. Although hydrothermal nontronite has been sampled at a number of seafloor sites by coring and dredging, this is the first in situ documentation of its unusual sinuous, tubular structure, on the seafloor. Quantitative image-analysis of ROV imagery indicates that hydrothermal fluid pathways that developed through an underlying pillow lava sequence likely control the distinctive pattern.