Magnetic properties of marine sediment near the active Dead Dog Mound, Juan de Fuca Ridge, allow to refine hydrothermal alteration zones

• Published in: Physics and chemistry of the earth. Parts A/B/C 2003, Vol.28 (16), p.701-709
• Main Authors: Urbat, Michael, Brandau, Andreas
• Format: Article
• Language: English
• Subjects: Environmental magnetism; Hydrothermal fluids; Marine; ODP Site 1036; Sediment alteration
• ISSN: 1474-7065; 1873-5193
• DOI: 10.1016/S1474-7065(03)00124-4

We use environmental magnetic methodology to assess the effects of focused hydrothermal fluid discharge on Pleistocene marine sediment, that covers the Juan de Fuca Ridge in Middle Valley. Ocean Drilling Program Leg 169 Holes 1036A through C were drilled in the vicinity of one of the active mounds in the Dead Dog Vent Field (DDVF). Previous shipboard visual core description, geochemical, and smear slide analyses indicated that these three holes represent a transect from moderately to strongly hydrothermally altered sediment. The latter was best represented by the definition of lithological zones based on sediment-mineralogical criteria, for example, the first occurrence of anhydrite. The latter suggested that the 100–150 °C isotherm dips away from the active mound over a short lateral distance of about 100 m. The ubiquitous trace amount of the remanent magnetic minerals in marine sediment in Holes 1036 is highly sensitive to both temperature and fluid induced post-depositional alteration of the sediment and indicates that our environmental magnetic approach allows for a refined definition of the lithological alteration zones as well as the establishment of additional lateral hydrothermal fluid flow.