Georges Ceuleneer

French National Centre for Scientific Research | CNRS

The footprints of mafic melts travelling from the depths to the surface are abundant in the mantle section of ophiolites. They constitute an important source of information about the melt migration mechanisms and related petrological processes in the shallowest part of the mantle beneath former oceanic spreading centres. In the field, these so-call...

Nodular chromite ore deposits are found in ophiolites and crop out in structures interpreted as former dykes, most of them transposed parallel to the plastic foliation of the host peridotite. Many studies have been conducted in order to decipher the origin and evolution of nodular chromite but the outstanding lack of consensus paves the way for an...

It is common knowledge that the Moho is the boundary between the crust and the Earth's mantle. Here we show along several seismic profiles through the Pacific Plate that a correlation exists between the strength of Moho reflections, crustal thickness, and water depth. Where the Moho can be detected clearly, the overlying oceanic crust is systematic...

Infiltration triggered by selective dissolution of pyroxenes is a major mode of melt migration in the mantle. A common view, supported by experiments and numerical models, is that the geometry of the melt plumbing system is governed by the stress field induced by solid-state flow of the host peridotite. Yet, salient melt migration structures frozen...

Hadean zircons, from the Jack Hills (Western Australia) and other localities, are currently the only window into the earliest terrestrial felsic crust, the formation of which remains enigmatic. Based upon new experimental results, generation of such early crust has been hypothesized to involve the partial melting of hydrated peridotite interacting...

The Bahla massif exposes the lower crustal section of the Oman ophiolite located close to the thrust front of the Semail nappe. It is affected by intense faulting previously attributed to tectonic events that dismembered a classical ophiolitic sequence during or after the obduction. Here we show that most of this complexity is primary, inherited fr...

Visible-shortwave infrared (VSWIR) imaging spectrometers map composition remotely with spatial context, typically at many meters-scale from orbital and airborne data. Here, we evaluate VSWIR imaging spectroscopy capabilities at centimeters to sub-millimeter scale at the Samail Ophiolite, Oman, where mafic and ultramafic lithologies and their altera...

Occurrences of diopsidites, rocks made predominantly of gem-like diopside whose composition precludes a purely igneous origin, allow tracking the pathway of high-temperature fluids and fluid-saturated melts in the oceanic lithosphere in vicinity of the mantle-crust transition zone (the Moho) and the adjacent mantle in an oceanic setting. We have ex...

Current theories suggest that the first continental crust on Earth, and possibly on other terrestrial planets, may have been produced early in their history by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients for this crustal formation remain elusive. To fill this gap, we conducted time-series exp...

Current theories suggest that the first continental crust on Earth, and possibly on other terrestrial planets, may have been produced early in their history by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients for this crustal formation remain elusive. To fill this gap, we conducted time-series exp...

An isotopically diverse suite of felsic dikes, sills, and plugs (εNd(t) = −7.8 to +7.8) intrude the uppermost mantle and lower crust in the Samail ophiolite in Oman and the United Arab Emirates (UAE). These features have been interpreted to represent amphibolite and metasediment melts from an underthrust sheet of oceanic lithosphere. As such, the i...

Abundant silica-undersaturated potassic lavas are found in the centre of the Turkish-Iranian plateau (NW Iran) as flows, pillows and dykes. They display abundant zoned clinopyroxene macrocrysts and xenoliths of igneous cumulates. We determined four types of zoned crystals (Type-I,-II,-III and-IV) on the basis of their composition and zoning pattern...

Abundant silica-undersaturated potassic lavas are found in the centre of the Turkish-Iranian plateau (NW Iran) as flows, pillows and dykes. They display abundant zoned clinopyroxene macrocrysts and xenoliths of igneous cumulates. We determined four types of zoned crystals (Type-I, -II, -III and -IV) on the basis of their composition and zoning patt...

The mantle-crust boundary beneath oceanic spreading centres is a major chemical and thermal interface on Earth. Observations in ophiolites reveal that it is underlined by a dunitic transition zone (DTZ) that can reach a few hundred meters in thickness and hosting abundant chromitite ore bodies. The dunites have been deciphered as essentially mantle...

In the Trinity ophiolite, California, USA, several mafic-ultramafic plutons intruded a peridotitic host 435 to 405 m.y. ago in a tectonic setting interpreted as an arc-related spreading centre. One of these intrusions, in the Bear Creek area, exposes basal ultramafic cumulates with igneous layering comprising an alternation of uncommonly thin (down...

We analyzed high-quality seismic reflection profiles across the ocean-continent transition in the Enderby Basin between the Kerguelen Plateau and the Antarctic margin. There, we observe numerous high-amplitude dipping reflections in the lower oceanic crust which was accreted at a magmatic spreading center as testified by the almost uniform 6.4-7 km...

A small peridotite massif (~5 km x ~ 0.6 km) crops out on the Northern flank of the Jabal Nakhl close to the Taww oasis in the Northern Oman mountains. It rests directly on the autochthonous and is over-thrusted by the Hawasina nappes, which contrasts with the structural position of the Semail ophiolite. The lack of pervasive high-temperature mylon...

The transition between the mantle section and the oceanic crust in the Maqsad area (Oman ophiolite) is mainly made of variably impregnated dunites lo- cally associated with chromitite ore bodies. There, the dunitic transition zone (DTZ) developed above a mantle diapir that fed with MORB the former oceanic spreading centre. However, orthopyroxene an...

The transition between the upwelling and partially molten peridotitic mantle and the accreting gabbroic lower crust beneath oceanic spreading centres is supposed to be a major interface in terms of chemical and thermal exchanges between the inner part of the Earth and external envelopes. In most ophiolites worldwide as well as at some sites along p...

The most abundant terrestrial lavas, mid-ocean ridge basalt (MORB) and ocean island basalt (OIB), are commonly considered to be derived from a depleted MORB-mantle component (DMM) and more specific, variably enriched mantle plume sources. However, findings of oceanic lavas and mafic cumulates issued from melts, enriched in chlorine and having a rad...

The most abundant terrestrial lavas, mid-ocean ridge and ocean island basalt (MORB and OIB), are commonly considered to be derived from a depleted MORB-mantle component and more specific, variably enriched mantle plume sources. However, findings of oceanic lavas and mafic cumulates issued from melts, enriched in chlorine and having a radiogenic Sr...

Current theories suggest that on Earth and, possibly, on other terrestrial planets early in their history, the first continental crust may has been produced by direct melting of hydrated peridotite. However, the conditions, mechanisms and necessary ingredients of such production remain elusive. To fill this gap, we have conducted experiments of ser...

Mantle lithologies in orogenic massifs and xenoliths commonly display strikingly different Hf-and Nd-isotope compositions compared to oceanic basalts. While the presence of pyroxenites has long been suggested in the source region of mantle-derived magmas, very few studies have reported their combined Hf-Nd isotope compositions. We here report the f...

A stratiform chromite ore body crops out in the lower part of the dunitic mantle-crust transition zone (DTZ) that developed at the top of a mantle diapir in the Maqsad area in the Oman ophiolite. It is made of layers ranging in thickness from a few mm to a maximum of 3 m, and in modal composition from massive to antinodular and disseminated ore. Th...

The extent of slab contribution versus crustal assimilation in arc lavas is debated, as is the origin of their commonly radiogenic Os [1]. In the Cabo Ortegal Complex (Spain), the pyroxenite-rich Herbeira massif has been interpreted as a delaminated arc root exhumed during arc-continent collision [2, 3]. The pyroxenites exhibit a wide range of 187O...

Beneath oceanic spreading centres, the transition from the upwelling and partially molten peridotitic mantle and the accreting gabbroic lower crust appears as a major chemical, thermal and rheological interface. In most ophiolites worldwide, it is underlined by a dunitic horizon whatever the paleo-tectonic setting (mid-ocean ridges vs. supra-subduc...

This study is based on an integrated approach combining results from petrology, geophysics and modeling to explain the origin of continental alkaline magmatism in the Turkish-Iranian plateau (TIP). Synthesis of the petrological and chemical characteristics of the alkaline magmatism of the TIP, extending from 80 Ma to the present, shows that the alk...

This study is based on an integrated approach combining results from petrology, geophysics and modeling to explain the origin of continental alkaline magmatism in the Turkish-Iranian plateau (TIP). Synthesis of the petrological and chemical characteristics of the alkaline magmatism of the TIP, extending from 80 Ma to the present, shows that the alk...

This study aims at characterizing the subseafloor architecture of the Lucky Strike hydrothermal field (LSHF) based on an extensive chemical database of the various vents. Our analysis is motivated by the discovery in 2013 of a new active high-temperature site, named Capelinhos, approximately 1.5 km east of the LSHF. Capelinhos fluids display partic...

The nature, magmatic evolution, and geodynamic setting of both inner and outer Makran ophiolites, in SE Iran, are enigmatic. Here, we report mineral chemistry, whole-rock geochemistry, and Sr–Nd–Pb isotope composition of mantle peridotites and igneous rocks from the Eastern Makran Ophiolite (EMO) to assess the origin and tectono magmatic evolution...

In the Trinity Ophiolite, California, USA, mafic-ultramafic plutons with an arc petro-geochemical affinity intruded mantle peridotites that were accreted along a marginal oceanic spreading centre (Ceuleneer and Le Sueur, 2008). In this work, we report the microstructures of a consistent sequence of dunites and pyroxenite-rich layered cumulates (emb...

Petrological models accounting for the decoupling of Nd and Hf isotopes commonly invoke melt-peridotite interaction and ancient depletion. In the lower arc crust and sub-arc lithospheric mantle, melt-peridotite interaction and differentiation of primitive basaltic magmas are expected to produce abundant pyroxenites, which potentially can be recycle...

The igneous andmechanical processes controlling the formation of nodular chromite ore have been investigated through the study of a chromitite dyke emplaced in the uppermost part of the 330 m-thick dunitic mantle/crust transition zone that developed at the top of a mantle diapir in theMaqsad area of theOman ophiolite. The dyke is parallel to the pa...

The Maqsad area in the Oman ophiolite exposes a >300 m thick dunitic mantle-crust transition zone (DTZ) that developed above a mantle diapir. The Maqsad DTZ is primarily made of “pure” dunites (olivine with scattered chromite and chromite seams) and “impregnated” dunites, which exhibit a significant lithological variability, including various kinds...

How the Earth's continental crust was formed in the Hadean eon is a subject of considerable debates [1-4]. For example, shallow hydrous peridotites [2,5], in particular the Hadean Earth's serpentinites [6], are potentially important ingredients in the creation of the continental ptoto-crust, but the mechanisms of this formation remain elusive. In t...

The understanding of the petrological processes occurring in the mantle-crust transition zone beneath oceanic ridges can be studied in the Oman ophiolite. The Maqsad area in the Oman ophiolite evolved in a MORB-like magmatic environment and presently exposes a >300 m thick Dunitic Transition Zone (DTZ) above a paleo-mantle diapiric structure. It wa...

It is now accepted that significant volumes of pyroxenites are generated in the subduction factory and remain trapped in the mantle. In ophiolites and orogenic massifs the geometry of pyroxenite layers and their relationships with the host peridotite can be observed directly. Since a large part of what is known about the upper mantle structure is d...

Pyroxenites exposed in orogenic peridotite massifs illustrate the diversity of petrogenetic processes in supra-subduction environments. However, the source of their parental melts and the timing of their formation remain poorly constrained due to overprinting by metasomatism and metamorphism. We here report Sr-, Nd-, Hf-and Os-isotope compositions...

Pyroxenites exposed in ophiolites and orogenic peridotite massifs may record petrogenetic processes occurring in mantle domains generated and/or transferred in supra-subduction environments. However, the timing of their formation and the geochemical characteristics of their source region commonly are obscured by metamorphic and metasomatic overprin...

In the Herbeira massif, Cabo Ortegal Complex, Spain, a well exposed assemblage of deformed dunites and pyroxenites offers a unique opportunity to investigate key upper mantle tectonic processes. Four types of pyroxenites are recognized: clinopyroxenites with enclosed dunitic lenses (type-1), massive websterites (type-2), foliated and commonly highl...

Using a combined approach of seafloor mapping, MAPR and CTD survey, we report evidence for active hydrothermal venting along the 130°-140°E section of the poorly-known South-East Indian Ridge (SEIR) from the Australia-Antarctic Discordance (AAD) to the George V Fracture Zone (FZ). Along the latter, we report Eh and CH4 anomalies in the water column...

Determining which petrological processes build the mantle-crust dunitic transition zone (DTZ) in oceanic spreading settings has a direct impact on our understanding of thermal and chemical transfers on Earth. We report on understated but widespread mineral assemblages present in the DTZ at the top of a mantle diapir (Oman ophiolite), including parg...

The genesis of primitive arc magmas has had a major impact on continent formation through time, but the rarity of exposures of deep arc sections limits our understanding of the details of melt migration and differentiation. Abundant pyroxenites are exposed within a 600 m thick section of arc-related mantle harzburgites and dunites in the Herbeira m...

Travertine are found in ophiolite massifs in association with bicarbonate-depleted hyperalkaline spring waters (pH up to 11.9), in contrast with most continental carbonates (e.g., travertine, tufa, speleothems) that precipitate from calcium bicarbonate-enriched waters. Here travertines formed from bicarbonate-depleted hyperalkaline spring water wer...

We present observations of the SouthEast Indian Ridge (SEIR) collected during the STORM cruise (South Tas-mania Ocean Ridge and Mantle) on the N/O L'Atalante early 2015. The SEIR between Australia and Antarctica displays large variations of axial morphology despite an almost constant intermediate spreading rate. The Australia-Antarctic Discordance...

Abundant massive pyroxenites and dunites occur among harzburgites in the Herbeira massif of the Cabo Ortegal complex as part of the Variscan suture in Spain [1]. The formation and evolution of this assemblage have never been comprehensively understood due to a particularly complex tectonothermal history [2,3]. Our new whole-rock and in situ geochem...

Ophiolites expose gabbroic sections that are generally separated from the mantle section by a dunitic transition zone (DTZ). Our previously published data on the Oman Ophiolite DTZ demonstrated that two main magmatic processes may explain its genesis: 1) reaction melting between a mantle peridotite and a melt under-saturated with orthopyroxene; 2)...

Layering is a common feature in mafic and ultramafic layered intrusions and generally consists of a succession of layers characterized by contrasted mineral modes and/or mineral textures, including grain size and orientation and, locally, changing mineral compositions. The morphology of the layers is commonly planar, but more complicated shapes are...

Three harzburgitic massifs are exposed in the Cabo Ortegal Complex as part of the Variscan suture in Spain. Among these, the Herbeira massif has an unusually high volume of massive and layered pyroxenites whose formation has never comprehensively understood due to a particularly complex tectonothermal history (Ábalos et al., 2003). We use a detaile...

In most ophiolites, the contact between the mantle peridotites and the gabbroic cumulates from the lower oceanic crust is underlined by a horizon of dunite ranging in thickness from a few meters to a few hundred meters. The genesis of this dunitic transition zone (DTZ) can be attributed to different processes that are not necessarily mutually exclu...

The origin of mantle heterogeneities and their fate in subduction zones are keys for understanding the core to crust exchanges and their application for exploration targeting. The Herbeira massif of the Cabo Ortegal complex has an unusually high volume of pyroxenites associated with dunites in a sheet-shaped body [2]. The igneous features of these...

The Oman ophiolite is considered as a fossil analog of fast oceanic spreading centers, especially from the structure and composition of its lower crust. However, a glance at former studies reveals that this conclusion is based on observations conducted on a few spots in the ophiolite. A clear observational and sampling bias exists against areas whe...

Magmatic relics are ubiquitous in the mantle of the Oman ophiolite. They include discordant and concordant dykes showing sharp contact with their host. Their lithological nature is extremely variable but can be classified into four lithological types: troctolites, olivine gabbros, pyroxenites and gabbronorites with euhedral Opx (i.e. where Opx appe...

The Azarbayjan Magmatic Plateau (AMP) is a huge area of Tertiary alkaline volcanism in Iran. The main tectonic features of AMP were formed as a result of convergence between the northward-moving Afro-Arabian plate and the relatively stable Eurasian plate. The lithospheric mantle evolution beneath AMP is not well known due to the limited petrologica...

Magmatic relics are ubiquitous in the mantle of the Oman ophiolite. They include discordant and concordant dykes showing sharp contact with their host. Their lithological nature is extremely variable but can be classified into four lithological types: troctolites, olivine gabbros, pyroxenites and gabbronorites with euhedral Opx (i.e. where Opx appe...

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