Ophiolites are important to geologists since they occur within mountain belts like the Himalayas and Alps, and help in identifying former ocean basins and are the center of the plate tectonic theory. The formation of the ophiolites did not occur all at once, but rather in intervals. Ophiolites contain several layers of rocks.
Why are ophiolites important to geologists?
Ophiolites are important to geologists since they occur within mountain belts like the Himalayas and Alps, and help in identifying former ocean basins and are the center of the plate tectonic theory. The formation of the ophiolites did not occur all at once, but rather in intervals.
What is the chemistry of an ophiolite?
The chemistry of many ophiolite rocks does not quite match the chemistry of mid-ocean ridge rocks. They more closely resemble the lavas of island arcs. And dating studies showed that many ophiolites were pushed onto the continent only a few million years after they formed.
Why are ophiolites so similar to peridotite?
And when hot peridotite reacts with seawater, the product is the soft and slippery serpentinite that is so common in ophiolites. This detailed resemblance led geologists in the 1960s to a working hypothesis: ophiolites are tectonic fossils of the ancient deep seafloor.
How were ophiolites formed in mountains?
Many geologists believe that ophiolites formed at oceanic ridges were emplaced by tectonic forces at convergent plate boundaries and then became exposed in highly deformed orogenic (mountain) belts. In fact, the same sequences of rocks were first reported in the Alps and were considered…
What do ophiolites tell us about the earth?
Ophiolites are suites of temporally and spatially associated ultramafic, mafic, and felsic rocks that are interpreted to be remnants of ancient oceanic crust and upper mantle. Ophiolites show significant variations in their internal structure, geochemical fingerprints, and emplacement mechanisms.
Why do ophiolites form?
Many geologists believe that ophiolites formed at oceanic ridges were emplaced by tectonic forces at convergent plate boundaries and then became exposed in highly deformed orogenic (mountain) belts. In fact, the same sequences of rocks were first reported in the Alps and were considered…
What is ophiolite in geography?
An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.
What is an ophiolite rock?
Ophiolites or the ophiolite complex is the general name for the community of mafic and ultramafic intrusives (gabbro, peridotite, and pyroxenite), and extrusive igneous rocks (spilite–keratophyre–basalt) that originate from the oceanic crust and mantle, and greywacke sandstone, shales and siliceous sedimentary rocks— ...
What is an ophiolite quizlet?
An ophiolite is a section of oceanic crust and upper mantle (oceanic lithosphere) that has been transported along thrust faults and uplifted and emplaced on the margins of a continent or other land mass.
What is the composition of ophiolite?
Ophiolite is a stratified igneous rock complex composed of upper basalt member, middle gabbro member and lower peridotite member (Fig. 1). Some large complexes measure more than 10 km thick, 100 km wide and 500 km long. The term "ophiolite" means "snake stone" in Greek.
Where is ophiolite located in the Philippines?
Abstract. The Zambales Ophiolite Complex (ZOC) in the western portion of Luzon Island, Philippines represents a typical exposure of an emplaced crust-upper mantle section of an ancient lithosphere.
What are ophiolite suites?
[ ŏf′ē-ə-līt′, ō′fē- ] A sequence of rocks consisting of deep-sea marine sediments overlying (from top to bottom) pillow basalts, sheeted dikes, gabbro, dunite, and peridotite.
What is the best preserved and largest ophiolite?
Jormua ophioliteThe Jormua ophiolite is the best preserved one along a larger chain of ophiolites that occur within the Kainuu Schist Belt. The crustal rocks of the ophiolite include pillow lava, hyaloclastite, sheeted dykes, gabbro, plagiogranite and ultramafic cumulate rock.
What does ophiolite look like?
The name ophiolite means “snakestone” from “ophio” (snake) and “lithos” (stone) in Greek. The rock sequence is named for the brilliant green, snake-like serpentine minerals which form in altered ocean crust and mantle. Ophiolites are rare but nonetheless found throughout the world.
How does an ophiolite form at the subduction zone?
Supra-subduction zone (SSZ) ophiolites have the geochemical characteristics of island arcs but the structure of oceanic crust and are thought to have formed by sea-floor spreading directly above subducted oceanic lithosphere.
Why is it rare to see an entire ophiolite sequence in an accreted terrane?
It is rare to find ophiolites on land because oceanic crust is usually dragged down into the mantle at subduction zones.
What is ophiolite in the ocean?
Ophiolite literally means snakestone. In modern usage it refers to an intact section of oceanic lithosphere that has been thrust onto a continental margin. A typical section of oceanic lithosphere consists of ultramafic rock and serpentinite near its base, overlain by gabbro and basalt, with bedded chert or turbidite at the top. Turbidite is a fine-grained sediment (or sedimentary rock) that gradually changes from coarse- to fine-grained and that was deposited by turbidity currents. It is rare for a complete, intact section of oceanic lithosphere to be thrust (obducted) onto a continent. The only complete section in the Appalachians is the Bay of Islands Ophiolite, which is spectacularly exposed in Gros Morne National Park in the Long Range Mountains of western Newfoundland. Fairly complete sections in the Cordillera include the Trinity ophiolite in the Klamath Mountains and the Coast Range ophiolite in the Coast Range of California. The obduction of intact oceanic lithosphere onto a continental margin implies that a subduction zone once existed at that location, but it does not imply collision between two terranes. Obduction can occur during the subduction process, and following obduction the subduction process could continue. Complications arise if collision with another terrane occurs long after obduction as depicted in Figure 20.11. In this case, a geologist must differentiate between the obduction event and the later collision event. This can be an especially difficult task if rocks representing the two events are intermingled.
Where is the ophiolite sequence located?
Ophiolite sequences occupy a considerable part of eastern Sabah . The chromitite concentrations in the peridotite and serpentinized peridotite are too small for commercial mining (Bailey, 1963; Hutchison and Dhonau, 1971 ). The reason for the absence of large deposits from Sabah, as compared with the Zambales of nearby Philippines, is that only the upper layers of the Sabah ophiolite are exposed, and the chromitite layers are thin and podiform. They represent the lower ultrabasic cumulate part of the gabbro layer. By contrast the rich Zambales deposits occur well into the mantle sequence.
What is the name of the rock that is uplifted and exposed above sea level?
Ophiolite is thrust sheets of ancient oceanic crust and upper part of mantle rocks that have been uplifted and exposed above sea level and often emplaced on top of the continental lithosphere.
What is the granular texture of mantle peridotite?
Figure 4.12. The photomicrograph of mantle peridotite showing crushed to fine-grained matrix with a granular texture of olivine (Ol), orthopyroxene (Opx), and clinopyroxene (Cpx) and resembled harzburgite. Serpentinization has taken place mostly around uncrushed olivine grains. The ophiolite environment is for chromium and associated mineral deposits.
Who made the study of the Sabah chromite?
Hutchison (1972) made a systematic study of the Sabah chromite. It shows a range of Al/Cr substitution and the unit cell (a,Å) edge varies systematically thus:
Can geochemical studies be supported by structural information?
In such ophiolites, one might question the results of geochemical studies that cannot be supported by any structural information. By contrast, in an ophiolite whose internal structure has been preserved and decrypted, the solution of further problems depends largely on dedicated geochemical studies.
How do ophiolites differ from seafloor crust?
Ophiolites differ from intact seafloor crust in some important ways, most notably in that they aren't intact. Ophiolites are almost always broken apart, so the peridotite, gabbro, sheeted dikes and lava layers don't stack up nicely for the geologist. Instead, they are usually strewn along mountain ranges in isolated bodies. As a result, very few ophiolites have all the parts of the typical oceanic crust. Sheeted dikes are usually what is missing.
What type of crust is a Franciscan ophiolite?
Caribbean-type ophiolites represent the subduction of oceanic plateaus or Large Igneous Provinces. Franciscan-type ophiolites are accreted pieces of oceanic crust scraped off the subducted plate onto the upper plate, as in Japan today.
What is the name of the assemblage of serpentinite?
In 1821 Alexandre Brongniart named this assemblage ophiolite ("snake stone" in scientific Greek) after its distinctive exposures of serpentinite ("snake stone" in scientific Latin). Fractured, altered and faulted, with almost no fossil evidence to date them, ophiolites were a stubborn mystery until plate tectonics revealed their important role.
What is the product of hot peridotite?
And when hot peridotite reacts with seawater, the product is the soft and slippery serpentinite that is so common in ophiolites. This detailed resemblance led geologists in the 1960s to a working hypothesis: ophiolites are tectonic fossils of the ancient deep seafloor.
Which type of ophiolites formed during the interaction of two oceanic plates like today's Izu-?
Mediterranean-type ophiolites formed during the interaction of two oceanic plates like today's Izu-Bonin forearc.
Do ophiolites have all the crust?
As a result, very few ophiolites have all the parts of the typical oceanic crust. Sheeted dikes are usually what is missing. The pieces must be painstakingly correlated with each other using radiometric dates and rare exposures of the contacts between rock types.
Why are ophiolites important?
Ophiolites are important to geologists since they occur within mountain belts like the Himalayas and Alps, and help in identifying former ocean basins and are the center of the plate tectonic theory. The formation of the ophiolites did not occur all at once, but rather in intervals.
What is an ophiolite?
An ophiolite is a part of the Earth’s oceanic crust that is uplifted and exposed above sea level. Geologists first observed ophiolites in the European Alps. In 1821, Alexandre Brongniart used the name “ophiolite” to refer to an assemblage of green rocks that had serpentinite features on it. 150 years later, during the advent of plate tectonics, researchers adopted the name ophiolites to refer to the pieces of oceanic crusts attached to the continents. Ophiolites are important to geologists since they occur within mountain belts like the Himalayas and Alps, and help in identifying former ocean basins and are the center of the plate tectonic theory. The formation of the ophiolites did not occur all at once, but rather in intervals.
How thick is the ophiolite?
The entire sequence of ophiolite layers is about 15 km thick.
Where are the Cordilleran ophiolites found?
Examples of the Cordilleran ophiolites include the Josephine ophiolite found in the Klamath Mountains in Oregon and California, ...
Where did ophiolites originate?
One theory suggests they are formed as ocean lithosphere. Researchers proved this theory by studying a an ophiolite complex in the Bay of Islands, Newfoundland.
What are the materials that make peridotite?
The materials that make the peridotite found at the base of the ophiolites is harzburgite rock. The dikes and volcanic rocks that form the cap of ophiolites result from the eruptions that occur on the ocean floor.
What is an ophiolite?
The Penrose field conference on ophiolites in 1972 redefined the term ophiolite 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 Program 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 .
Why do ophiolites have fore arcs?
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 accretion sediments, 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 accretionary prism with fore-arc 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.
What are the two components of ophiolite formation?
However, two components of ophiolite formation are under debate: the origin of the sequence and the mechanism for ophiolite emplacement. Emplacement is the process of the sequence's uplift over lower density continental crust.
How is ophiolite subduction explained?
Ophiolite generation and subduction may also be explained, as suggested from evidence from the Coast Range ophiolite of California and Baja California, by a change in subduction location and polarity. Oceanic crust attached to a continental margin subducts beneath an island arc. Pre-ophiolitic ocean crust is generated by a back-arc basin. The collision of the continent and island arc initiates a new subduction zone at the back-arc basin, dipping in the opposite direction as the first. The created ophiolite becomes the tip of the new subduction's forearc and is uplifted (over the accretionary wedge) by detachment and compression. Verification of the two above hypotheses requires further research, as do the other hypotheses available in current literature on the subject.
Why did researchers conduct a seismic study on an ophiolite complex?
For this reason, researchers carried out a seismic study on an ophiolite complex ( Bay of Islands, Newfoundland) in order to establish a comparison. The study concluded that oceanic and ophiolitic velocity structures were identical, pointing to the origin of ophiolite complexes as oceanic crust.
What is the upper mantle of the Earth?
An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed above sea level and often emplaced onto continental crustal rocks.
Where did the term "ophiolite" come from?
The term ophiolite originated from publications of Alexandre Brongniart in 1813 and 1821. In the first, he used ophiolite for serpentinite rocks found in large-scale breccias called mélanges. In the second publication, he expanded the definition to encompass a variety of igneous rocks as well such as gabbro, diabase, ultramafic and volcanic rocks. Ophiolites thus became a name for a well-known association of rocks occurring in the Alps and Apennines of Italy. Following work in these two mountains systems, Gustav Steinmann defined what later became known as the "Steinmann Trinity": the mixture of serpentine, diabase - spilite and chert. The recognition of the Steinmann Trinity served years later to build up the theory around seafloor spreading and plate tectonics. A key observation by Steinmann was that ophiolites were associated to sedimentary rocks reflecting former deep sea environments. Steinmann himself interpreted ophiolites (the Trinity) using the geosyncline concept. He held that Alpine ophiolites were "submarine effusions issuing along thrust faults into the active flank of an asymmetrically shortening geosyncline". The apparent lack of ophiolites in the Peruvian Andes, Steinmann theorized, was either due to the Andes being preceded by a shallow geosyncline or representing just the margin of a geosyncline. Thus, Cordilleran-type and Alpine-type mountains were to be different in this regard. In Hans Stille 's models a type of geosyncline called eugeosynclines were characterized by producing an "initial magmatism" that in some cases corresponded to ophiolitic magmatism.
What is the study of ophiolites?
oceanic crust. In oceanic crust: Study of ophiolites. Great strides in understanding the oceanic crust were made by the study of ophiolites. These are slices of the ocean floor that have been thrust above sea level by the action of plate tectonics.
What is the name of the crust that is preserved on land?
In plate tectonics: Mountains by terrane accretion. …of ocean crust, known as ophiolites, are preserved on land. They provide a valuable natural laboratory for studying the composition and character of the oceanic crust and the mechanisms of their emplacement and preservation on land.
What is the process of obduction?
Since the late 1970s, the term ophiolite has been used to describe sections of oceanic crust and upper mantle, along with sedimentary rocks deposited on the sea floor, emplaced as thrust slices onto continental lithosphere . This process, called obduction, results from continent-continent collision following subduction of oceanic crust and the closure of oceans or back-arc basins. A typical ophiolite suite comprises (from base to top): 1 Harzburgite, dunite, peridotite, and pyroxenite (ultramafic igneous rocks composed of varying amounts of olivine and pyroxene) representing upper, oceanic mantle. They are commonly altered to the slippery, shiny green-black rock serpentinite. Serpentinite is named after its resemblance to the skin of a snake. Indeed, the word ophiolite is derived from the Greek words ophis, meaning snake, and lithos, meaning stone, because of the presence of serpentinites. 2 Iron-titanium and magnesium gabbros. Layered, cumulate-textured gabbros dominate the basal section of oceanic crust. Higher-level gabbros tend to be more massive and associated with plagiogranites. 3 Sheeted mafic dykes, feeders to overlying volcanics. 4 Pillow basalts, formed as lava flows on the sea floor. The characteristic pillow shapes result from rapid cooling when lava contacts seawater. 5 Radiolarian chert and limestone , graywacke and mud-stone or their metamorphic equivalents marble , quartzite and mica schist. Oceanic crust in ophiolites is produced at spreading centers, above zones of subduction in extensional or transtensional arcs (supra- subduction zone ophiolites), and along some leaky transform faults . Ophiolites that lack ultramafic, upper mantle rocks may represent obducted slices of seamounts or oceanic plateaus.
What is blue schist?
Blueschists are named after blue-colored glaucophane and other sodium-rich amphiboles formed in rocks of appropriate composition . Eclogite facies metamophism occurs when rocks are subducted to greater depth. In eclogites, pyroxene, olivine, and plagioclase recrystallize to sodium-rich pyroxene and garnet. During collision, blueschists plus or minus eclogites are thrust as a series of imbricate slices onto lower-grade, continental rocks. Ophiolites may be overprinted by greenschist facies metamorphic assemblages and exhumed during collapse of a thrust-thickened orogen.
What type of rock is ophiolite?
ophiolite (ophiolite complex) Sequence of rock types, consisting of deep-sea sediments lying above basaltic pillow lavas, dykes, gabbro, and ultramafic peridotite. Some are the remnants of main oceanic crust, others of crust formed in back-arc basins.
What is the name of the rock that is a snake?
They are commonly altered to the slippery, shiny green-black rock serpentinite. Serpentinite is named after its resemblance to the skin of a snake. Indeed, the word ophiolite is derived from the Greek words ophis, meaning snake, and lithos, meaning stone, because of the presence of serpentinites.
What are the two minerals that make up the oceanic crust?
Iron-titanium and magnesium gabbros. Layered, cumulate-textured gabbros dominate the basal section of oceanic crust. Higher-level gabbros tend to be more massive and associated with plagiogranites.
How are pillow basalts formed?
Pillow basalts, formed as lava flows on the sea floor. The characteristic pillow shapes result from rapid cooling when lava contacts seawater.
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What Is An Ophiolite?
Components of An Ophiolite
- Ophiolites contain several layers of rocks. These layers, from the base to the top, include tectonized and cumulate peridotites, layered and massive gabbro, dikes, basaltic lavas, and volcanic rocks. The entire sequence of ophiolite layers is about 15 km thick. The materials that make the peridotite found at the base of the ophiolites is harzburgite rock. The dikes and volcani…
Ophiolite Groups and Assemblages
- Two broad categories of ophiolites exist: Cordilleran and Tethyan. Cordilleran ophiolites form in the mountain belts of the Cordillera (which is the name given to western North America). Their locations include subduction zones and have no relation to the passive continental margins. Examples of the Cordilleran ophiolites include the Josephine ophiolite found in the Klamath Mou…
Origin of Ophiolites
- Several theories attempt to explain the origin of ophiolites. One theory suggests they are formed as ocean lithosphere. Researchers proved this theory by studying a an ophiolite complex in the Bay of Islands, Newfoundland. The study revealed that ophiolitic and oceanic velocity structures were indeed identical. Hence, this proved that ophiolites originated as ocean crusts. The secon…
Typical Ophiolites and Where to Find them?
- Examples of areas that have ophiolites include Oman, California, New Guinea, Cyprus, and Newfoundland. The Samail ophiolite in southeastern Oman has been studied the most by researchers. Furthermore, some popular ophiolites include: Macquarie Island and Tasmania (Australia); Yakuno, Poroshiri, and Horokanai (Japan); and the Zambales ophiolite complex (Phili…