Open AccessOxide mineral formation during the serpentinization of a Cr‐spinel seam: Insights from rock magnetic experiments
Author(s) -
O'Driscoll Brian,
Petronis Michael S.
Publication year - 2009
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2008gc002274
Subject(s) - olivine , ultramafic rock , geology , magnetite , spinel , peridotite , geochemistry , chromite , mineral , chromitite , oxide , layered intrusion , mineralogy , mantle (geology) , materials science , mafic , metallurgy , ophiolite , tectonics , paleontology
Serpentinization of ultramafic rocks results in the growth of serpentine and magnetite, following hydration of magmatic olivine. Cr‐spinel seams in ultramafic intrusions that also contain olivine might produce magnetite during the serpentinization process. However, hysteresis and temperature dependence of susceptibility experiments on serpentinized chromitite (>80% Cr‐spinel) from the Dawros peridotite (western Ireland) reveal the presence of small quantities of a Fe‐Ti oxide phase, likely titanomaghemite. Reflected light petrography reveals that the oxides occur as 0.1 μ m to 20 μ m grains that are typically intergrown with serpentine. It is suggested that the formation of the minute quantities of low‐susceptibility‐high Curie point titanomaghemite occurred by low‐temperature alteration of the magnetite produced during serpentinization. The presence of such low quantities of the oxide phase may be either a function of the very high Mg content of the magmatic olivine or the decoupling of oxide growth from the process of serpentinization, where magnetite formed later than the reaction of olivine with the infiltrating fluids. Our data highlight the usefulness of rock magnetic techniques to the investigation of oxide mineral phases in serpentinized ultramafic rocks.