is a section of the Earth's oceanic crust
and the underlying upper
that has been uplifted or
emplaced to be exposed within continental crustal
is Greek for "snake", lite
means "stone" from the Greek
The term ophiolite was originally used by Alexandre Brongniart
for an assemblage
of green rocks (serpentine
) in the Alps
later modified its use to include serpentine, pillow lava
, and chert
("Steinmann's trinity"), again based on occurrences in the Alps.
The term was little used in other areas until the late 1950s to
early 1960s, with the recognition that this assemblage provided an
analog for oceanic crust and the process of seafloor spreading
. This recognition was
tied to two events: (1) the observation of magnetic anomaly stripes
on the seafloor, parallel to oceanic
ridge systems, interpreted by Frederick Vine and Drummond Matthews to represent the
formation of new crust at the oceanic ridge and its subsequent
spreading away from that ridge, and (2) the observation of a
sheeted dike complex within the
ophiolite (Cyprus) by Ian
Graham Gass and co-workers, which must have formed by 100%
intrusion of new magma, since no older wall rocks are preserved
within the complex.
Moores and Vine concluded that the
sheeted dike complex at Troodos could only form by a process
similar to the seafloor spreading proposed by Vine and Matthews.
Thus, it became widely accepted that ophiolites represent oceanic
crust that had been emplaced on land.
Their great significance relates to their occurrence within
mountain belts such as the Alps or the Himalayas, where they
document the existence of former ocean basins that have now been
consumed by subduction
. This insight was
one of the founding pillars of plate
, and ophiolites have always played a central role in
plate tectonic theory.
A simplified structure of an ophiolite
1. axial magma chamber
3. pillow basalts
4. sheeted basaltic dykes
5. layered gabbro
6. dunite/peridotite cumulates
Stratigraphy and definition
sequence observed in
ophiolites corresponds to the lithosphere
-forming processes at mid-oceanic ridges
- Sediments: Muds (black shale) and cherts
deposited since the crust formed.
- Extrusive sequence: Basaltic pillow lavas show magma/seawater contact.
- Sheeted dikes: Vertical, parallel dikes which fed the pillow lavas above.
- High level intrusives: Isotropic Gabbro,
indicative of fractionated magma chamber.
- Layered Gabbro, resulting from settling
out of minerals from a magma chamber.
- Cumulate peridotite: Dunite-rich layers
of minerals that settled out from a magma chamber.
- Tectonized peridotite: Harzburgite/lherzolite-rich mantle rock.
An international conference on ophiolites in 1972 redefined the
to include only the igneous rocks listed
above, excluding the sediments formed independently of the crust
they sit on. This definition has been challenged recently because
new studies of oceanic crust by the Integrated Ocean Drilling
and other research cruises have shown that in situ
ocean crust can be quite variable, and that in places volcanic
rocks sit directly on peridotite tectonite
, with no intervening gabbros
. Many ophiolites have similar variations in
their stratigraphy, some of which are primary and others of which
formed later (for example, during emplacement into a mountain
Scientists have only drilled about 1.5 km into the 6–7 km
thick oceanic crust, so their understanding of oceanic crust
largely comes from comparing ophiolite structure to seismic
soundings of in situ
oceanic crust. Oceanic crust has a
layered velocity structure that implies a layered rock series
similar that listed above. In detail there are problems, with many
ophiolites exhibiting thinner accumulations of igneous rock than
are inferred for oceanic crust. Another problem relating oceanic
crust and ophiolites is that the thick gabbro layer of ophiolites
calls for large magma chambers beneath mid-ocean ridges. Seismic
sounding of mid-ocean ridges has only revealed a few magma chambers
beneath ridges, and these are quite thin. A few deep drill holes
into oceanic crust have intercepted gabbro, but it is not layered
like ophiolite gabbro.
The circulation of hydrothermal
through young oceanic crust causes serpentinization
of the peridotites and alteration of
minerals in the gabbros and basalts to lower temperature
assemblages. For example, plagioclase, pyroxenes, and olivine in
the sheeted dikes and lavas will alter to Albite, chlorite
and serpentine, respectively. Often,
bodies such as iron
deposits are found above highly
rocks) that are
evidence of (the now relict) black
which continue to operate within the seafloor spreading
centers of ocean ridges today.
Thus there is reason to believe that ophiolites are indeed oceanic
mantle and crust; however, certain problems arise when looking
closer. Compositional differences regarding silica
) and titania
) contents, for example, place ophiolite basalts in
the domain of subduction zones (~55% silica, <1%
), whereas mid-ocean ridge basalts typically have
~50% silica and 1.5-2.5% TiO2
. These chemical
differences extend to a range of trace elements as well (that is,
chemical elements occurring amounts of 1000 ppm or less). In
particular, trace elements associated with subduction zone (island
arc) volcanics tend to be high in ophiolites, whereas trace
elements that are high in ocean ridge basalts but low in subduction
zone volcanics are also low in ophiolites.
The crystallization order of feldspar
in the gabbros is unexpectedly
reversed, and ophiolites also appear to have a multi-phase magmatic
complexity on par with subduction zones. Indeed, there is
increasing evidence that most ophiolites are generated when
subduction begins and thus represent fragments of fore-arc
lithosphere. This led to introduction of the term "supra-subduction
zone" (SSZ) ophiolite in the 1980s to acknowledge that some
ophiolites are more closely related to island arcs than ocean
ridges. Ironically, some of the classic ophiolite occurrences used
to relate ophiolites to seafloor spreading (Troodos in Cyprus,
Semail in Oman) were found to be "SSZ" ophiolites, formed by rapid
extension of fore-arc crust during subduction initiation.
A fore-arc setting for most ophiolites also solves the otherwise
perplexing problem of how oceanic lithosphere can be emplaced on
top of continental crust. It appears that continental crust, if
carried by the downgoing plate into a subduction zone, will jam it
up and cause subduction to cease, resulting in the rebound of the
continental crust with forearc lithosphere (ophiolite) on top of
it. Ophiolites with compositions comparable with hotspot
-type eruptive settings or normal mid-oceanic ridge basalt
are rare, and those examples are generally strongly dismembered in
subduction zone accretionary complexes.
Ophiolite groups and assemblages
Most ophiolites can be divided into one of two groups: Tethyan and
Cordilleran. Tethyan ophiolites are characteristic of those that
occur in the eastern Mediterranean sea area, e.g., Troodos in
Cyprus and Semail in Oman, which consist of relatively complete
rock series corresponding to the classic ophiolite assemblage and
which have been emplaced onto a passive continental margin
more or less intact
(Tethys is the name given to the ancient sea that once separated
Europe and Africa). Cordilleran ophiolites are characteristic of
those that occur in the mountain belts of western North America
(the "Cordillera" or backbone of the continent). These ophiolites
sit on subduction zone accretionary complexes (subduction
complexes) and have no association with a passive continental
margin. These include the Coast Range ophiolite of California, the
Josephine ophiolite of the Klamath Mountains (California, Oregon),
and ophiolites in the southern Andes of South America. Despite
their differences in mode of emplacement, both types of ophiolite
are exclusively SSZ in origin.
Ophiolite assemblages in the Alps and some other collisional
mountain belts are not formed during subduction, but rather
represent the thinned margin of the continent that forms during
rifting and continental drift. This incipient ocean crust remains
locked to the continental margin when the ocean basin closes,
emplacing the incipient ocean crust into the collision zone.
Interestingly, the age of ophiolite formation is often surprisingly
close to the age of their emplacement into the continental crust.
Ophiolites are found in all the major mountain belts of the world
whether collisional (e.g. Himalayas) or not (e.g. Andes). The
subduction-related chemistry of ophiolites and their association
with mountain belts suggests that their formation and emplacement
are related to oceanic closure and continental collision (final
stages of the Wilson Cycle
rather than oceanic opening and seafloor spreading as was first
Furthermore, the occurrence of ophiolites throughout Earth history
is not constant but rather they were formed and emplaced at
specific intervals. These intervals correspond closely to times of
super-continent break-up and dispersal—not because they form at the
ridges that separate the drifting continents, but because the large
ocean basin that must coexist with any super-continent must subduct
along new subduction zones as rifting progresses.
Examples of ophiolites include:
- Zambales Ophiolite in western Luzon, Philippines
Ophiolite in eastern Luzon, Philippines
Ophiolite in Oman and the
- Troodos Ophiolite in the Troodos
Mountains of Cyprus
- Kizildag Ophiolite, southern Turkey
Ophiolite in Finland
- Vourinos and Pindos Ophiolites
in Northern Greece
Cove, St. Anthony, Little Port, Advocate, Gander River, Pipestone
Pond, Great Bend and Annieopsquotch ophiolites in Newfoundland
of Islands Ophiolite in Gros Morne National Park, Newfoundland, named a UNESCO World Heritage Site in 1987 because of
its superbly exposed complete ophiolite stratigraphic
- Lizard complex
in Cornwall, United
- Josephine Ophiolite in Southern Oregon
Range, Smartville, and Klamath
Mountains of northern California
- Papuan ophiolite in Papua New
- Yakuno, Horokanai, and Poroshiri, three full
ophiolite sequences in Japan
- Ballantrae Ophiolite Complex,
Girvan-Ballantrae area, SW Ayrshire, Scotland
Mountain Ophiolite Belt, South Island, New Zealand
- Payson Ophiolite, Payson, Arizona
- Brogniart, A. (1813)
- Steinmann, G (1927)
- Vine F.J. and Matthews D.H. (1963)
- Gass, I.G. (1968)
- Moores E.M. and Vine, F.J. (1971)
- eg Shervais, J.W., (2001)
- Brogniart, A. (1813) "Essai de classifacation mineralogique des
roches melanges" Journal des Mines, v. XXXIV,
- Gass, I.G. (1968) "Is the Troodos massif of Cyprus a fragment
of Mesozoic ocean floor?" Nature, 220,
- Church, W.R. and Stevens, R.K. (1970) "Early Paleozoic
ophiolite complexes of the Newfoundland Appalachians as
mantle-oceanic crust sequences." Journal of Geophysical Research,
- Coleman, R.G. (1977) "Ophiolites: Ancient Oceanic Lithosphere?"
Springer Verlag, 229 pp.
- Encarnacion, J. (2004) "Multiple ophiolite generation preserved
in the northern Philippines and the growth of an island arc
complex" Tectonophysics, 392, 103-130.
- Moores E.M. and Vine, F.J. (1971) "The Troodos massif, Cyprus,
and other ophiolites as oceanic crust: Evaluation and implications"
Philosophical Transactions of the Royal Society of London,
- Moores, E.M. (2003) "A personal history of the ophiolite
concept" in Dilek and Newcomb, editors, Ophiolite Concept and
the Evolution of Geologic Thought. Geological Society of
America Special Publication 373, 17-29.
- Shervais, J.W., (2001) "Birth, Death, and Resurrection: The
Life Cycle of Suprasubduction Zone Ophiolites," Geochemistry,
Geophysics, Geosystems, v. 2, Paper number 2000GC000080.
- Steinmann, G (1927) "Die ophiolitshen zonen in den mediterranen
Kettengebirgen," translanted and reprinted by Bernoulli and
Friedman, in Dilek and Newcomb, editors, Ophiolite Concept and
the Evolution of Geologic Thought. Geological Society of
America Special Publication 373, 77-91.
- Vine F.J. and Matthews D.H. (1963) "Magnetic anomalies over
ocean ridges", Nature 199, 947-949.