Open AccessAlteration at the ultramafic‐hosted Logatchev hydrothermal field: Constraints from trace element and Sr‐O isotope data
Author(s) -
Augustin N.,
Paulick H.,
Lackschewitz K. S.,
Eisenhauer A.,
GarbeSchönberg D.,
Kuhn T.,
Botz R.,
Schmidt M.
Publication year - 2012
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2011gc003903
Subject(s) - peridotite , geology , ultramafic rock , geochemistry , hydrothermal circulation , trace element , metasomatism , rare earth element , gabbro , mineral , layered intrusion , mantle (geology) , mineralogy , igneous rock , mafic , rare earth , chemistry , seismology , organic chemistry
Serpentinized peridotite and gabbronorite represent the host rocks to the active, ultramafic‐hosted Logatchev hydrothermal field at the Mid‐Atlantic Ridge. We use trace element, δ 18 O and 87 Sr/ 86 Sr data from bulk rock samples and mineral separates in order to constrain the controls on the geochemical budget within the Logatchev hydrothermal system. The trace element data of serpentinized peridotite show strong compositional variations indicating a range of processes. Some peridotites experienced geochemical modifications associated with melt‐rock interaction processes prior to serpentinization, which resulted in positive correlations of increasing high field strength element (HFSE) concentrations and light rare earth element (LREE) contents. Other serpentinites and lizardite mineral separates are enriched in LREE, lacking a correlation with HFSE due to interaction with high‐temperature, black‐smoker type fluids. The enrichment of serpentinites and lizardite separates in trace elements, as well as locally developed negative Ce‐anomalies, indicate that interaction with low‐T ambient seawater is another important process in the Logatchev hydrothermal system. Hence, mixing of high‐T hydrothermal fluids during serpentinization and/or re‐equilibration of O‐isotope signatures during subsequent low‐T alteration is required to explain the trace element and δ 18 O temperature constraints. Highly radiogenic 87 Sr/ 86 Sr signatures of serpentinite and lizardite separates provide additional evidence for interaction with seawater‐derived fluids. Sparse talc alteration at the Logatchev site are most likely caused by Si‐metasomatism of serpentinite associated with the emplacement of shallow gabbro intrusion(s) generating localized hydrothermal circulation. In summary the geochemistry of serpentinites from the Logatchev site document subsurface processes and the evolution of a seafloor ultramafic hydrothermal system.