Chapter 9 Effects of Hydrothermal Fluids on the Heavy Mineral Assemblage of a Late Pleistocene Succession Deposited in an Oceanic Ridge Valley (Escanaba trough, Juan De Fuca Plate)

摘要: Abstract This short contribution deals with the behaviour and modification of heavy mineral assemblages in a 500 m-thick turbidite succession deposited rift valley 3300 m deep Escanaba Trough Juan de Fuca Plate. To our knowledge, there have been no previous studies on effects hydrothermal fluid circulation minerals such an active geochemical environment. The sediments were transported mainly from glacial lakes Columbia drainage basin by cataclysmic floods during last 60 ka. Climatic sediment transport conditions imply minor weathering source rocks, little sorting mechanical abrasion transit. Our results indicate that experienced severe chemical etching dissolution circulating pore fluids caused, at various depths, complete loss particular species, especially chemically highly unstable ortho- clinopyroxenes. These specific also generated new minerals, titanite, iron-rich magnesite, barite, pyrite. However, present is insufficient data to fully constrain kinetics as function pH, temperature, composition fluids, sediment-permeability. length time which affected movements constrained very young (Late Pleistocene, ∼60 ka) age sediments.