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Unraveling the sequence of serpentinization reactions: petrography, mineral chemistry, and petrophysics of serpentinites from MAR 15°N (ODP Leg 209, Site 1274)
Author(s) -
Bach Wolfgang,
Paulick Holger,
Garrido Carlos J.,
Ildefonse Benoit,
Meurer William P.,
Humphris Susan E.
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl025681
Subject(s) - brucite , olivine , geology , magnetite , petrography , geochemistry , mineral , ultramafic rock , petrophysics , hydrothermal circulation , mineralogy , petrology , chemistry , paleontology , magnesium , porosity , organic chemistry , geotechnical engineering
The results of detailed textural, mineral chemical, and petrophysical studies shed new light on the poorly constrained fluid‐rock reaction pathways during retrograde serpentinization at mid‐ocean ridges. Uniformly depleted harzburgites and dunites from the Mid‐Atlantic Ridge at 15°N show variable extents of static serpentinization. They reveal a simple sequence of reactions: serpentinization of olivine and development of a typical mesh texture with serpentine‐brucite mesh rims, followed by replacement of olivine mesh centers by serpentine and brucite. The serpentine mesh rims on relic olivine are devoid of magnetite. Conversely, domains in the rock that are completely serpentinized show abundant magnetite. We propose that low‐fluid‐flux serpentinization of olivine to serpentine and ferroan brucite is followed by later stages of serpentinization under more open‐system conditions and formation of magnetite by the breakdown of ferroan brucite. Modeling of this sequence of reactions can account for covariations in magnetic susceptibility and grain density of the rocks.