Gillis, Kathryn M.; Banerjee, Neil R. (2000): Hydrothermal alteration patterns in supra-subduction zone ophiolites. Geological Society of America (GSA), Boulder, CO, United States, In: Dilek, Yildirim (editor), Moores, Eldridge M. (editor), Elthon, Don (editor), Nicolas, Adolphe (editor), Ophiolites and oceanic crust; new insights from field studies and the Ocean Drilling Program, 349, 283-297, georefid:2002-010618

The geologic and alteration characteristics of 11 supra-subduction zone (SSZ) ophiolites have been compiled in order to assess the variability of hydrothermal alteration patterns. All SSZ ophiolites show evidence for high-temperature hydrothermal discharge in the form of polymetallic sulfide deposits and/or metalliferous sedimentary rocks. Metamorphic zonations are commonly subparallel to the igneous stratigraphy, and metamorphic grade increases with depth, but varies laterally in response to local magmatic and tectonic activity. The degree of alteration is more pervasive in sheeted-dike complexes than in volcanic or plutonic sequences. The greatest variability in the style of alteration is in volcanic sequences, where alteration occurred at low-temperature to greenschist-facies conditions. The prevalence of high porosity and permeability within volcanic sequences in modern oceanic crust, which maintains low temperatures, indicates that special conditions are required to develop zeolite- or greenschist-facies zones away from sites of hydrothermal discharge. Recent study of sediment-covered ridges show that early burial of oceanic crust, at or near a spreading center, does not lead to the widespread development of high-temperature alteration zones in the uppermost volcanic rocks. Alteration patterns in the Izu-Bonin and Tonga forearcs show many similarities to SSZ ophiolites interpreted to have formed in a forearc, such as the presence of epidosites and the nature of alteration within plutonic sequences. However, modern forearc volcanic sequences only record low-temperature alteration. Much more detailed documentation of most ophiolites is required in order to fully understand the effects of geologic setting on the evolution of hydrothermal systems.
West: -129.0000 East: -127.0000 North: 48.2800 South: 40.5600
Expedition: 139
Expedition: 168
Expedition: 169
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