An ophiolite is a section of Earth's oceanic crust and the underlying upper mantle that has been uplifted and exposed, and often emplaced onto continental crustal rocks.
58-776: The Highland Border Ophiolite (HBO) is a set of rocks that are ophiolitic in character found within the Highland Border Complex . They are exposed in a series of fault-bounded outcrops along the line of the Highland Boundary Fault that forms the southeastern boundary to the Grampian Highlands in Scotland. They represent fragments of a piece of oceanic crust or exhumed mantle that has been obducted onto continental crust . These rocks provide an important constraint on models of how
116-465: A data management system integrates core and laboratory data collected by all three implementing organizations and the two IODP legacy programs. A web-based search system will eventually aggregate post-expedition data and related publications. Requests for data and samples can be made online. A web-based Site Survey Data Bank enabled proponents to access and deposit the large amounts of data required to document potential drill sites for evaluation. This data
174-451: 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 fluids through young oceanic crust causes serpentinization , alteration of the peridotites and alteration of minerals in the gabbros and basalts to lower temperature assemblages. For example, plagioclase , pyroxenes , and olivine in
232-457: A layered velocity structure that implies a layered rock series similar to that listed above. But in detail there are problems, with many ophiolites exhibiting thinner accumulations of igneous rock than are inferred for oceanic crust. Another problem relating to oceanic crust and ophiolites is that the thick gabbro layer of ophiolites calls for large magma chambers beneath mid-ocean ridges. However, seismic sounding of mid-ocean ridges has revealed only
290-946: A passive continental margin. They 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 supra-subduction zone (SSZ) in origin. Based on mode of occurrences, the Neoproterozoic ophiolites appear to show characteristics of both mid-oceanic ridge basalt (MORB)-type and SSZ-type ophiolites and are classified from oldest to youngest into: (1) MORB intact ophiolites (MIO); (2) dismembered ophiolites (DO); and (3) arc-associated ophiolites (AAO) (El Bahariya, 2018). Collectively,
348-696: A problem arises concerning compositional differences of silica (SiO 2 ) and titania (TiO 2 ). Ophiolite basalt contents place them in the domain of subduction zones (~55% silica, <1% TiO 2 ), whereas mid-ocean ridge basalts typically have ~50% silica and 1.5–2.5% TiO 2 . These chemical differences extend to a range of trace elements as well (that is, chemical elements occurring in 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. Additionally,
406-422: A riser drilling system, a dynamic positioning system, and a high-density mud circulation system to prevent borehole collapse during drilling, among other assets. Chikyu can berth 150 people, cruise at 12 knots (22 km/h; 14 mph), and drill more than 7,000 m (23,000 feet) below the seafloor in water depths exceeding 2,000 m (6,600 feet). Chikyū was damaged during the tsunami of 11 March 2011, and
464-640: A snakeskin. (The suffix -lite is from the Greek lithos , meaning "stone".) Some ophiolites have a green color. The origin of these rocks, present in many mountainous massifs , remained uncertain until the advent of plate tectonic theory. Their great significance relates to their occurrence within mountain belts such as the Alps and the Himalayas , where they document the existence of former ocean basins that have now been consumed by subduction . This insight
522-659: A type of geosyncline called eugeosynclines were characterized by producing an "initial magmatism" that in some cases corresponded to ophiolitic magmatism. As plate tectonic theory prevailed in geology and geosyncline theory became outdated ophiolites were interpreted in the new framework. They were recognized as fragments of oceanic lithosphere , and dykes were viewed as the result of extensional tectonics at mid-ocean ridges . The plutonic rocks found in ophiolites were understood as remnants of former magma chambers. In 1973, Akiho Miyashiro revolutionized common conceptions of ophiolites and proposed an island arc origin for
580-791: A voluntary basis. Participation took many forms: submission of a drilling proposal; sailing on an expedition; participation in an advisory capacity; attendance at a planning workshop or topical symposium. The program's central management office, IODP Management International, coordinated an integrated work plan between and among all IODP organizational partners. An annual program plan was written each fiscal year and included objectives and tasks necessary for drilling vessel operation, from science coordination to publications, data management, and outreach. IODP distinguishes itself from its legacy programs by employing multiple drilling technologies/platforms and science/drilling operators to acquire sediment and rock samples and to install monitoring instrumentation beneath
638-686: Is consistent with the presence of ophicarbonates that are associated with serpentinization in such an environment. The parts of the Highland Border Complex that are not ophiolitic have been assigned to the Trossachs Group, interpreted to be the youngest part of the Dalradian Supergroup , although this interpretation has been questioned. The Trossachs Group as interpreted ranges in age from Lower Cambrian to Lower Ordovician , based on trilobite fossils found in
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#1732775515645696-590: Is uplifted onto continental margins despite the relatively low density of the latter. All emplacement procedures share the same steps nonetheless: subduction initiation, thrusting of the ophiolite over a continental margin or an overriding plate at a subduction zone, and contact with air. A hypothesis based on research conducted on the Bay of Islands complex in Newfoundland as well as the East Vardar complex in
754-570: The Deerpark Complex of western Ireland, which consists of fault-bounded lenses of serpentinite, juxtaposed with amphibolites and metasediments . It is faulted against the Clew Bay Complex , which has been correlated with the Highland Border Complex. Ophiolite The Greek word ὄφις, ophis ( snake ) is found in the name of ophiolites, because of the superficial texture of some of them. Serpentinite especially evokes
812-732: The Initial Science Plan (ISP) guided IODP investigation. Specific scientific themes were emphasized in the ISP : As described in the ISP, IODP sought to develop better understandings of: Tools critical to these goals included a riser-equipped drilling vessel, a riserless vessel, additional platforms suited to mission specific expeditions, enhanced downhole measurement devices, and long-term monitoring instrumentation. An engineering proposal submission process, initiated in April 2007, facilitated
870-697: The closure of the Tethys Ocean . Ophiolites in Archean and Paleoproterozoic domains are rare. 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 in the Middle East, such as Semail in Oman, which consist of relatively complete rock series corresponding to
928-441: The crystallization order of feldspar and pyroxene (clino- and orthopyroxene) in the gabbros is 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
986-607: 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
1044-433: The metal-ore deposits present in and near ophiolites and from oxygen and hydrogen isotopes suggests that the passage of seawater through hot basalt in the vicinity of ridges dissolved and carried elements that precipitated as sulfides when the heated seawater came into contact with cold seawater. The same phenomenon occurs near oceanic ridges in a formation known as hydrothermal vents . The final line of evidence supporting
1102-539: 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
1160-516: The 1980s to acknowledge that some ophiolites are more closely related to island arcs than ocean ridges. Consequently, some of the classic ophiolite occurrences thought of as being related 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
1218-478: The Apuseni Mountains of Romania suggest that an irregular continental margin colliding with an island arc complex causes ophiolite generation in a back-arc basin and obduction due to compression. The continental margin, promontories and reentrants along its length, is attached to the subducting oceanic crust, which dips away from it underneath the island arc complex. As subduction takes place,
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#17327755156451276-490: 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
1334-754: The IODP Science Advisory Structure. The Republic of Korea joined IODP as an Associate Member in June 2006 through the sponsorship of the Korea Institute of Geoscience and Mineral Resources (KIGAM). South Korea's memorandum of understanding with the lead agencies created the Interim Asian Consortium. Ministry of Earth Sciences (MoES), Government of India joined the IODP in 2008 as an Associate member. Since then,
1392-561: The IODP documented environmental change, Earth processes and effects, the biosphere, solid earth cycles, and geodynamics. The program began a new 10-year phase with the International Ocean Discovery Program , from the end of 2013. Scientific ocean drilling represented the longest running and most successful international collaboration among the Earth sciences. Scientific ocean drilling began in 1961 with
1450-914: The Leny Limestone and conodont fossils found in the Margie Limestone. There is evidence that the HBO was thrust on top of the Trossachs Group before the first phase of the Caledonian Orogeny (the Grampian phase ) affected either of these units later in the Ordovician. In this model, the HBO represents pieces of exhumed mantle from the non-volcanic margin of Laurentia, transported onto the Dalradian Supergroup with its sedimentary cover. The HBO has been correlated with
1508-662: The National Centre for Antarctic and Ocean Research (NCAOR), Goa has been designated by India to look after all IODP related activities in India (IODP-India). In this direction, an international workshop on IODP drilling in Indian Ocean was organized in Goa during 17–18 October 2011. The workshop was co-hosted by IODP Management International and ANZIC. Hundreds of international Earth and ocean scientists participated in IODP on
1566-536: The Science Advisory Structure (SAS), a group of technical review panels. Only those proposals judged as the greatest value based on scientific and technical merit were scheduled for implementation. SAS panels provided advice on drilling proposals to both proponents and IODP management. Drilling proposals were accepted twice a year, in April and October, and could be submitted to IODP electronically via their website. A ten-year program plan called
1624-537: The United Kingdom) and Canada that together comprise an IODP-funding agency. Working alongside Japan and the United States, ECORD provided the IODP scientific community with access to mission-specific platforms, which chosen to fulfill specific scientific objectives. These platforms have limited space on board for labs and scientists, and require an onshore science meeting to describe, process, and analyze
1682-526: The acquisition of existing or latent technology to be used in IODP operations. Drilling operations were conducted and managed by three IODP implementing organizations: Each drilling expedition was led by a pair of co-chief scientists, with a team of scientists supported by a staff scientist. Each implementing organization provided a combination of services: technical, operational, and financial management; logging; laboratory; core repository; data management; and publication. Although each implementing organization
1740-495: The buoyant continent and island arc complex converge, initially colliding with the promontories. However, oceanic crust is still at the surface between the promontories, not having been subducted beneath the island arc yet. The subducting oceanic crust is thought to split from the continental margin to aid subduction. In the event that the rate of trench retreat is greater than that of the island arc complex's progression, trench rollback will take place, and by consequence, extension of
1798-477: 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
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1856-473: The current geometry arose during the Caledonian Orogeny . The main lithologies found within the HBO are serpentinite , often in the form of ophicarbonate , with associated sedimentary rocks , including sandstone, limestone, chert and black mudstone (now black slate ). The serpentinite is interpreted to be derived from exhumed mantle peridotites , altered to serpentinite at the seafloor. This
1914-432: The current knowledge of the oceanic crust's composition. 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. The observations that follow support this conclusion. Rocks originating on
1972-526: The famous Troodos Ophiolite in Cyprus , arguing that numerous lavas and dykes in the ophiolite had calc-alkaline chemistries . Examples of ophiolites that have been influential in the study of these rocks bodies are: Integrated Ocean Drilling Program The Integrated Ocean Drilling Program ( IODP ) was an international marine research program, running from 2003 to 2013. The program used heavy drilling equipment mounted aboard ships to monitor and sample sub-seafloor environments. With this research,
2030-489: The first phase of IODP. The vessel then underwent a rebuild, allowing for increased laboratory space; improved drilling, coring, and sampling capacity; and enhanced health, safety, and environmental protection systems on board. Japan began building a state-of-the-art scientific drilling vessel for research in 2001 with the intent of reaching Earth's mantle and drilling into an active seismogenic zone. The resulting drilling vessel, Chikyū (Japanese for "Planet Earth") features
2088-663: The first sample of oceanic crust recovered aboard the CUSS 1 , a modified U.S. Navy barge. American author John Steinbeck , also an amateur oceanographer, documented Project Mohole for LIFE Magazine . The Deep Sea Drilling Project (DSDP), established in June 1966, operated Glomar Challenger in drilling and coring operations in the Atlantic, Pacific, and Indian Oceans, as well as in the Mediterranean and Red Seas. Glomar Challenger' s coring operations enabled DSDP to provide
2146-497: 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
2204-591: The investigated ophiolites of the Central Eastern Desert (CED) fall into both MORB/back-arc basin basalt (BABB) ophiolites and SSZ ophiolites. They are spatially and temporally unrelated, and thus, it seems likely that the two types are not petrogenetically related. Ophiolites occur in different geological settings, and they represent change of the tectonic setting of the ophiolites from MORB to SSZ with time. The term ophiolite originated from publications of Alexandre Brongniart in 1813 and 1821. In
2262-567: The next intellectual step in verifying the hypothesis of plate tectonics associated with seafloor spreading, by dating basal sediments on transects away from the Mid-Atlantic Ridge . In June 1970, Glomar Challenger' s DSDP engineers devised a way to replace worn drill bits and then re-enter boreholes for deeper drilling while in the Atlantic Ocean off the coast of New York, in 3,000 m (10,000 feet) of water. This required
2320-443: The ophiolite is emplaced onto the continental margin. Based on Sr and Nd isotope analyses, ophiolites have a similar composition to mid-ocean-ridge basalts, but typically have slightly elevated large ion lithophile elements and a Nb depletion. These chemical signatures support the ophiolites having formed in a back-arc basin of a subduction zone. Ophiolite generation and subduction may also be explained, as suggested from evidence from
2378-462: The origin of ophiolites as seafloor is the region of formation of the sediments over the pillow lavas: they were deposited in water over 2 km deep, far removed from land-sourced sediments. Despite the above observations, there are inconsistencies in the theory of ophiolites as oceanic crust, which suggests that newly generated ocean crust follows the full Wilson cycle before emplacement as an ophiolite. This requires ophiolites to be much older than
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2436-425: The orogenies on which they lie, and therefore old and cold. However, radiometric and stratigraphic dating has found ophiolites to have undergone emplacement when young and hot: most are less than 50 million years old. Ophiolites therefore cannot have followed the full Wilson cycle and are considered atypical ocean crust. There is yet no consensus on the mechanics of emplacement, the process by which oceanic crust
2494-671: 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. Ophiolites are common in orogenic belts of Mesozoic age, like those formed by
2552-455: The overriding plate will occur to allow the island arc complex to match the trench retreat's speed. The extension, a back-arc basin, generates oceanic crust: ophiolites. Finally, when the oceanic lithosphere is entirely subducted, the island arc complex's extensional regime becomes compressional. The hot, positively buoyant ocean crust from the extension will not subduct, instead obducting onto the island arc as an ophiolite. As compression persists,
2610-521: The rise in global sea levels since the last ice age, and a liftboat for sampling the New Jersey Shallow Shelf (2009). Mission-specific expeditions required substantial flexibility. Publications, data management, online tools, and databases are in development to support information- and resource-sharing, so as to expand the ranks of scientists who engage in ocean drilling investigations. IODP publications are freely available online and
2668-460: The seafloor show chemical composition comparable to unaltered ophiolite layers, from primary composition elements such as silicon and titanium to trace elements. Seafloor and ophiolitic rocks share a low occurrence of silica-rich minerals; those present have a high sodium and low potassium content. The temperature gradients of the metamorphosis of ophiolitic pillow lavas and dykes are similar to those found beneath ocean ridges today. Evidence from
2726-422: The seafloor. Samples and data collected during IODP drilling expeditions are available to scientists and teachers on an open-access basis, once members of the expedition parties have completed their initial studies. Drilling proposals originated with science proponents, often researchers in geology, geophysics, microbiology, paleontology, or seismology. Once submitted to IODP, the proposal was carefully evaluated by
2784-579: The sediment samples collected immediately following a drilling expedition. In April 2004, the People's Republic of China joined IODP as an Associate Member through sponsorship of China's Ministry of Science and Technology (MOST). China's participation in IODP has given the Chinese marine science community a new impetus and increased their opportunity for deep-sea research. Chinese scientists participated in research expeditions and represent China's interests in
2842-551: The sheeted dikes and lavas will alter to albite , chlorite , and serpentine , respectively. Often, ore bodies such as iron -rich sulfide deposits are found above highly altered epidosites ( epidote - quartz rocks) that are evidence of relict black smokers , 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. Beyond issues of layer thicknesses mentioned above,
2900-628: The term "ophiolite" to include all of the layers listed above, including the sediment layer formed independently of the rest of the ophiolite. 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 in thickness and composition, and that in places sheeted dikes sit directly on peridotite tectonite , with no intervening gabbros . Ophiolites have been identified in most of
2958-532: 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. Scientists have drilled only about 1.5 km into the 6- to 7-kilometer-thick oceanic crust, so scientific understanding of oceanic crust comes largely from comparing ophiolite structure to seismic soundings of in situ oceanic crust. Oceanic crust generally has
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#17327755156453016-1035: The use of sonar scanning equipment and a large-scale re-entry cone. Process-oriented Earth studies continued from 1985 until 2003 aboard JOIDES Resolution , which replaced Glomar Challenger in January 1985 as DSDP morphed into the Ocean Drilling Program (ODP). JOIDES Resolution is named for the 200-year-old HMS Resolution which explored the Pacific Ocean and Antarctica under the command of Captain James Cook . The Ocean Drilling Program contributed significantly to increased scientific understanding of Earth history, climate change , plate tectonics , natural resources, and geohazards. ODP discoveries included validation of: National consortia and government funding agencies supported IODP science and drilling platform operations. Participation in IODP
3074-410: The world's orogenic belts . 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. Several studies support the conclusion that ophiolites formed as oceanic lithosphere . Seismic velocity structure studies have provided most of
3132-449: Was one of the founding pillars of plate tectonics , and ophiolites have always played a central role in plate tectonic theory and the interpretation of ancient mountain belts. The stratigraphic -like sequence observed in ophiolites corresponds to the lithosphere -forming processes at mid-oceanic ridges . From top to bottom, the layers in the sequence are: A Geological Society of America Penrose Conference on ophiolites in 1972 defined
3190-530: Was out-of-service for several months. Chikyū returned to ocean drilling in April 2012. ECORD commissioned ships on an expedition-by-expedition basis, depending on specific scientific requirements and environment. ECORD contracted the use of three icebreakers for the Arctic Coring Expedition (2004), drilling vessels diving for use in shallow Tahitian (2005) and Australian waters (2010), where scientists sampled fossil coral reefs to investigate
3248-553: Was proportional to investment in the program. The European Consortium for Ocean Research Drilling (ECORD) was established in December 2003 with 13 European countries to represent the European contribution in IODP. The consortium grew into a collaborative group of 17 European nations (Austria, Belgium, Denmark, Finland, France, Germany, Iceland, Ireland, Italy, The Netherlands, Norway, Poland, Portugal, Spain, Sweden, Switzerland and
3306-555: Was responsible for its own platform operations and performance, its science operations was funded by the lead agencies. The operators conducted the following expeditions during the IODP: IODP employed two dedicated drilling vessels, each sponsored by a lead agency and managed by their respective implementing organization: The U.S.-sponsored drilling vessel was operated throughout the Ocean Drilling Program and
3364-460: Was reviewed to assure IODP expeditions could meet their objectives and comply with safety and environmental requirements. Three IODP core repositories located in Bremen, Germany (IODP Bremen Core Repository) , College Station, Texas (IODP Gulf Coast Repository) , and Kochi, Japan, archive cores based on geographical origin. Scientists may visit any one of the facilities for onsite research or request
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