Wiens, J. A. (ed.), 2013. Oil in the Environment: Legacies and Lessons of the Exxon Valdez Oil Spill. Cambridge, NY: Cambridge
University Press. ISBN 9781107027176.
Wolfe, D. A., Hameedi, M. J., Galt, J. A., Watabayashi, G., Short, J.,
O’Claire, C., Rice, S., Michel, J., Payne, J. R., Braddock, J.,
Hanna, S., and Sale, D., 1994. The fate of the oil spilled from
the Exxon Valdez. Environmental Science & Technology,
28(3), 560A–568A, doi:10.1021/es00062a712.
Cross-references
Beach Processes
Coasts
Energy Resources
Geohazards: Coastal Disasters
Mangrove Coasts
OPHIOLITES
Adolphe Nicolas
Geosciences Montpellier, University of Montpellier 2,
Montpellier, France
Definition
Ophiolites represent fragments of oceanic lithosphere that
have been detached from their ocean of origin and
transported by plate tectonic processes onto a continent.
Historical development of the ophiolite concept
Ophiolite, the “snake stone” in Greek for its serpentine
component appears for the first time with Brongniard in
1813. At the turn of the same century, Italian alpine geologists had fully recognized its deep marine origin and its
main components: with, from sea bottom, radiolarian
cherts and basaltic pillow lavas, over and associated to
gabbros and serpentinites. The surge of plate tectonics in
the 1960s, that was a direct result of oceanic floor mapping, fostered studies on ophiolites. Ten years earlier, De
Roever (1957) and Brunn (1959) had equated with the
so-called alpine ophiolites to the Atlantic oceanic ridge,
and by that time, most European geologists knew that
ophiolites derived from oceanic spreading centers. Interestingly, marine geophysicists remained for a long time
reluctant to this connection. In the 1960s with only a few
exceptions, American colleagues were not convinced by
the comprehensive concept of “ophiolite.” They had correctly identified “peridotite-gabbro” complexes as the
basement of seafloor but were doubting any connection
to the upper crust of ophiolites. Outstanding among American dissidents was Harry Hess, a geologist who was promoted admiral in the US Navy during the Second World
War, launching the mapping of the oceans’ seafloor that
has been critical when he anticipated the seafloor spreading theory. During a famous field trip meeting in Oregon,
European and American communities adopted the
following manifesto on ophiolites, a modern concept that
we revisit here.
Ophiolites refers to a distinctive assemblage of mafic to ultramafic rocks. It should not be used as a rock name or
a lithologic unit in mapping. In a completely developed
ophiolite, the rock types occur in the following sequence,
starting from the bottom and working up:
– Ultramafic complex, consisting of variable proportions of
harzburgite, lherzolite, and dunite, usually with
a metamorphic and tectonic fabric (more or less
serpentinized)
– Gabbroic complex, ordinarily with cumulus textures,
commonly containing cumulus peridotites and pyroxenites and usually less deformed than the ultramafic
complex
– Mafic sheeted dike complex
– Mafic volcanic complex, commonly pillowed
– Associated rock types include (1) an overlying sedimentary section typically including ribbon cherts, thin shelled
interbeds, and minor limestones; (2) podiform bodies of
chromite, generally associated with dunites; and (3) sodic
felsic intrusive and extrusive rocks.
Faulted contacts between mappable units are common.
Whole sections may be missing. An ophiolite may be incomplete, dismembered, or metamorphosed. Although ophiolite
generally is interpreted to be oceanic crust and upper mantle,
the use of the term should be independent of its supposed
origin.
Importance of studies in ophiolites
Beyond the interest for mineral resources historically
extracted from ophiolites (copper, chrome, PGE,
dunites, . . .), two scientific aspects should be mentioned.
The structural, petrological, and geochemical features of
ophiolites that have been implied in collision belts can
be used to constrain their marine environment of origin,
for instance, a mid-ocean ridge (MOR), a suprasubduction zone (SSZ), or any other marine environment.
This concern appears in a vast number of studies on
ophiolites using geochemical data, considered as discriminant for the different environments of origin. Initiated by
Miyashiro in Cyprus (1973), this concept has been applied
to the Oman ophiolite the conclusion that it was generated
within a SSZ environment. Developed in the entry “Sea
floor spreading,” another aim in studying ophiolites deals
with seafloor accretion processes operating at oceanic
ridges where the 3D information obtained in ophiolites is
important, complementing and interacting with the geophysical observations: for instance, on shape and dynamics of mantle diapirs and overlying magma chambers at
fast-spreading ridges and on deep rooting of oceanic core
complexes and kinematics of their emplacement at slowspreading ridges.
Typology of ophiolites
The first attempt to classify ophiolites has been presented in
1985, independently by Ishiwatari and by Boudier and
Nicolas. Both started from the idea to classify ophiolites
on the degree of partial melting in the mantle of origin.
592
OPHIOLITES
University Press. ISBN 9781107027176.
Wolfe, D. A., Hameedi, M. J., Galt, J. A., Watabayashi, G., Short, J.,
O’Claire, C., Rice, S., Michel, J., Payne, J. R., Braddock, J.,
Hanna, S., and Sale, D., 1994. The fate of the oil spilled from
the Exxon Valdez. Environmental Science & Technology,
28(3), 560A–568A, doi:10.1021/es00062a712.
Cross-references
Beach Processes
Coasts
Energy Resources
Geohazards: Coastal Disasters
Mangrove Coasts
OPHIOLITES
Adolphe Nicolas
Geosciences Montpellier, University of Montpellier 2,
Montpellier, France
Definition
Ophiolites represent fragments of oceanic lithosphere that
have been detached from their ocean of origin and
transported by plate tectonic processes onto a continent.
Historical development of the ophiolite concept
Ophiolite, the “snake stone” in Greek for its serpentine
component appears for the first time with Brongniard in
1813. At the turn of the same century, Italian alpine geologists had fully recognized its deep marine origin and its
main components: with, from sea bottom, radiolarian
cherts and basaltic pillow lavas, over and associated to
gabbros and serpentinites. The surge of plate tectonics in
the 1960s, that was a direct result of oceanic floor mapping, fostered studies on ophiolites. Ten years earlier, De
Roever (1957) and Brunn (1959) had equated with the
so-called alpine ophiolites to the Atlantic oceanic ridge,
and by that time, most European geologists knew that
ophiolites derived from oceanic spreading centers. Interestingly, marine geophysicists remained for a long time
reluctant to this connection. In the 1960s with only a few
exceptions, American colleagues were not convinced by
the comprehensive concept of “ophiolite.” They had correctly identified “peridotite-gabbro” complexes as the
basement of seafloor but were doubting any connection
to the upper crust of ophiolites. Outstanding among American dissidents was Harry Hess, a geologist who was promoted admiral in the US Navy during the Second World
War, launching the mapping of the oceans’ seafloor that
has been critical when he anticipated the seafloor spreading theory. During a famous field trip meeting in Oregon,
European and American communities adopted the
following manifesto on ophiolites, a modern concept that
we revisit here.
Ophiolites refers to a distinctive assemblage of mafic to ultramafic rocks. It should not be used as a rock name or
a lithologic unit in mapping. In a completely developed
ophiolite, the rock types occur in the following sequence,
starting from the bottom and working up:
– Ultramafic complex, consisting of variable proportions of
harzburgite, lherzolite, and dunite, usually with
a metamorphic and tectonic fabric (more or less
serpentinized)
– Gabbroic complex, ordinarily with cumulus textures,
commonly containing cumulus peridotites and pyroxenites and usually less deformed than the ultramafic
complex
– Mafic sheeted dike complex
– Mafic volcanic complex, commonly pillowed
– Associated rock types include (1) an overlying sedimentary section typically including ribbon cherts, thin shelled
interbeds, and minor limestones; (2) podiform bodies of
chromite, generally associated with dunites; and (3) sodic
felsic intrusive and extrusive rocks.
Faulted contacts between mappable units are common.
Whole sections may be missing. An ophiolite may be incomplete, dismembered, or metamorphosed. Although ophiolite
generally is interpreted to be oceanic crust and upper mantle,
the use of the term should be independent of its supposed
origin.
Importance of studies in ophiolites
Beyond the interest for mineral resources historically
extracted from ophiolites (copper, chrome, PGE,
dunites, . . .), two scientific aspects should be mentioned.
The structural, petrological, and geochemical features of
ophiolites that have been implied in collision belts can
be used to constrain their marine environment of origin,
for instance, a mid-ocean ridge (MOR), a suprasubduction zone (SSZ), or any other marine environment.
This concern appears in a vast number of studies on
ophiolites using geochemical data, considered as discriminant for the different environments of origin. Initiated by
Miyashiro in Cyprus (1973), this concept has been applied
to the Oman ophiolite the conclusion that it was generated
within a SSZ environment. Developed in the entry “Sea
floor spreading,” another aim in studying ophiolites deals
with seafloor accretion processes operating at oceanic
ridges where the 3D information obtained in ophiolites is
important, complementing and interacting with the geophysical observations: for instance, on shape and dynamics of mantle diapirs and overlying magma chambers at
fast-spreading ridges and on deep rooting of oceanic core
complexes and kinematics of their emplacement at slowspreading ridges.
Typology of ophiolites
The first attempt to classify ophiolites has been presented in
1985, independently by Ishiwatari and by Boudier and
Nicolas. Both started from the idea to classify ophiolites
on the degree of partial melting in the mantle of origin.
592
OPHIOLITES