Growth of chloritoid and garnet along a nearly isothermal burial path to 70 km depth: an example from the Bughea Metamorphic Complex,Leaota Massif,South Carpathians

Mineralogy and Petrology - Chloritoid-bearing micaschist occurs in the matrix of a subduction mélange (Bughea Complex) of the Leaota Massif (South Carpathians) containing blocks of...     

Alteration of Platinum-Group and Base-Metal Mineral Assemblages in Ophiolite Chromitites from the Dobromirtsi Massif,Rhodope Mountains (Bulgaria)

The Dobromirtsi Ultramafic Massif, located in the Rhodope Mountains (SE Bulgaria), is a portion of a Paleozoic sub-oceanic mantle affected by polyphase regional metamorphism. This massif contains several small, podiform chromitite bodies which underwent the same metamorphic evolution as their host peridotites. Like other ophiolite chromitites, those found in Dobromirtsi carry abundant platinum-group minerals (PGM) and base-metal minerals (BMM). The PGM consist mainly of Ru-, Os-, and Ir-based PGM (laurite RuS₂-erlichmanite OsS₂, Os-Ru-Ir alloys, irarsite [IrAsS], Ru-rich pentlandite, and an unknown Ir-sulfide) but minor Rh- and Pd-based PGM (hollingworthite [RhAsS] and a series of unidentified stannides and sulfantimonides) are also present. In contrast, the BMM are dominated by pentlandite (Ni,Fe)₉S₈, followed by heazlewoodite (Ni₃S₂), breithauptite (NiSb), maucherite (Ni₁₁As₈), godlevskite (Ni₇S₆), gersdorffite (NiAsS), millerite (NiS), undetermined minerals containing Ni, As and Sb, orcelite (Ni_5-XAs₂), awaruite (Ni₃Fe) and chalcopyrite (CuFeS₂). The detailed study of the textural relationships, morphology and composition of the PGM and BMM inclusions indicate the existence of two different PGM-BMM assemblages: (i) a primary or magmatic; and (ii) a secondary related with postmagmatic alteration. The PGM and BMM inclusions in unaltered zones of chromite crystals (mainly laurite-erlichmanite and pentlandite) are considered to be primary magmatic minerals formed under variable temperature (1200–1100°C) and sulfur fugacity (between −2 and −0.5 log fS₂). In contrast, PGM and BMM located along altered edges of chromite and serpentinised silicate matrix are considered to be secondary, formed from or re-equilibrated with altering fluids. Secondary PGM and BMM assemblages are considered as result of the combination of reducing and oxidising events related with regional metamorphism. Under low fO₂ states, fS₂ also drops giving place to the formation of S-poor Ni-rich sulfides and secondary Ru-alloys by desulfurisation of primary S-containing minerals. In contrast, predominance of platinum-group elements and/or base-metal arsenides and sulfarsenides associated with the altered edges of chromite (chromite strongly enriched in Fe₂O₃) is related with the fixing of remobilised PGE (mainly Ir, Rh and Pd) and base-metals (mainly Ni and Fe) when late oxidising fluids supplied As as well as Sb and Sn.     

High-Pressure Dehydration Melting of Metapelites: Evidence from the Migmatites of Yaounde (Cameroon)

The migmatites of Yaound? consist essentially of anatectic metapelitickyanite-garnet gneisses characterized by granulite-facies mineralassemblages. Several types of migmatitic rocks have been recognized:(1) leucosomes associated with garnet-rich melanosomes, conformablewith the regional metamorphic layering; some leucosomes aregranitic in composition whereas some others are granodioriticand characterized by low K and Rb and by the lack of HREE fractionation;(2) quartzo-feldspathic differentiations without the relatedmelanosomes, occurring as veins conformable with or cross-cuttingthe regional metamorphic layering or along shear-zones, andcorresponding mineralogi-cally to granitic or quartz-rich v?ins;(3) garnet-rocks mainly composed of garnet with abundant accessories,occurring as intrusive bodies within the migmatitic series. Structural and petrographic data suggest that the migmatitesare not derived from the surrounding granulite-facies gneissesbut that both types of rock result from a single dehydrationmelting event. The formation of migmatites or gneisses, interpretedin terms either of absence of melt extraction or of shear-inducedmelt segregation, is ascribed to variations in strain distributionwithin the metamorphic pile. The chemical characteristics of the rocks and petrogenetic modellingsuggest that the migmatites of Yaounde arose from the superimpositionof the following events: (1) subsolidus differentiation of biotite-gneisses;(2) dehydration melting of biotite-gneisses at temperaturesaround 800?C (P=10–12 kbX leading to low amounts of melt(F<0?2), which was either tectonically segregated (migmatites)or not (granulite-facies gneisses); (3) injection of anatecticmaterial comprising both partial melts and garnet-rich residues,corresponding to high melt fractions (F>0?5) and probablyformed at higher temperatures (850?C) and at deeper structurallevels. The REE signature of equilibrium partial melts (9?3<Ce_N/Yb_N78;l?2<Yb_N<5?4) indicates that granitic magmas cannot bederived from dehydration melting of biotite-bearing metapelitesonly. Several other possibilities are discussed.     

A possible UHP-eclogite in the Leaota Mts. (South Carpathians) and its history from high-pressure melting to retrograde inclusion in a subduction melange

An unusual eclogite pod containing impure jadeite to omphacite pyroxene with anti-phase domain (APD) visible under the optical microscope is hosted in a medium-grade matrix in the Leaota Massif. Textural relationships support the hypothesis of garnet formation by peritectic reactions involving high-jadeite clinopyroxene, while inclusions entrapped in garnet, mainly a wide range of amphibole compositions, seemingly crystallised from a fluid phase in disequilibrium with the garnet host. Thermobarometric estimates indicate UHP, HT peak conditions (2.8–3.2 GPa, 780–840°C) inconsistent with those of the associated rocks, followed by a complicated exhumation path. The P–T-array of the retrograde path suggests syn-subduction exhumation and tectonic inclusion in a melange with a matrix derived from the accretionary wedge. Partial melting of the subducting slab, which induces tectonic weakening, may be an effective mechanism in detaching and enclosing small eclogite pods in metamorphic terrains.     

湘中下石炭统粘土矿物组合特征

湖南中部下石炭统是一套以碳酸盐岩为主夹碎屑岩含煤岩系的沉积,根据粘土矿物在下石岩统剖面分布规律,结合各组段岩性岩相特征,可推断出粘土矿物组合特征及其环境分布,从滨岸碎屑沉积到滨外泥质陆棚、滨外浅水碳酸盐陆棚,到深水碳酸盐陆棚和浅海盆地,即从滨岸向盆地方向,高岭石含量急剧减少,伊利石逐渐增加,伊利石/蒙脱石混层矿物和绿泥石则先是增加,然后又趋于减少,其最高含量分别在浅水碳酸盐陆棚和滨外泥质陆棚。测水组含煤岩系粘土矿物以高岭石为主,伊利石次之,并有一定量的绿泥石和伊利石/蒙脱石混层矿物,它们在垂向上的变化反映了沉积环境水介质酸碱度和盐度的变化规律。     

Study of some allanites and monazites from the South Carpathians (Romania)

Summary Allanites and monazites from different rocks of the South Carpathians (Romania) are described, and 17 analyses are presented. The genetic relations are discussed.

---

Untersuchungen an Allaniten und Monaziten aus den Südkarpaten (Rumänien)

Zusammenfassung Allanite und Monazite aus verschiedenen Gesteinen der Südkarpaten (Rumänien) werden beschrieben und 17 chemische Analysen werden gebracht. Die genetischen Beziehungen werden diskutiert.

---

---

With 1 Figure     

徐-淮地区早侏罗世侵入杂岩中单斜辉石岩捕虏体的矿物组合及演化

对徐－淮地区早侏罗世侵入杂岩中尖晶石单斜辉石岩捕虏体的岩石学和矿物学研究表明，镁铁尖晶石和富铝单斜辉石矿物组合代表了更早期地幔岩浆在下部地壳或上地幔顶部的堆积体，其形成的温压条件为0.90GP和835℃；以尖晶石转变成石榴石和单斜辉石＋石榴石＋刚玉组合为代表的矿物组合（Ⅱ）反映了尖晶石单斜辉石岩形成后又经历了高压变质作用，所估算的温压条件为1.40-1.65GPa和900－1000℃；晚期退变角闪石的形成表明尖晶石单斜辉石岩又遭受了角闪岩相的退化变质作用，估算的温压条件为0.70GPa和670－740℃。该类捕虏体的发现对认识大别－苏鲁超高压变质带的深部俯冲方向及其范围具有重要意义。     

Ductile Thrusting Recorded by the Garnet Isograd from Blueschist-Facies Metapelites of the Ile de Groix, Armorican Massif, France

Mineral assemblages in the blueschist-facies metapelites fromthe Ile de Groix (Armorican Massif, France) permit the distinctionof two main units. The Upper Unit is characterized by: (1) highmodal proportions of garnet; (2) larger grain size; (3) therarity of graphite-bearing layers; (4) a single, although composite,foliation S₁. A Lower Unit is defined by: (1) low modal proportionsof garnet; (2) smaller grain size; (3) an abundance of graphite-bearinglayers; (4) a pervasive crenulation cleavage S₂. In the UpperUnit, coexisting garnet and chloritoid are more magnesian andless manganiferous than in the Lower Unit. The differences inmodal proportions and chemistry of coexisting minerals reflectdifferent P–T conditions. The P–T history of theblueschist-facies metapelites is estimated using a simplifiedpetrogenetic grid in the NFMASH system and thermodynamic calculations,which suggest peak P–T conditions at about P = 16–18kbar, T = 450–500°C and P = 14–16 kbar, T =400–450°C in the Upper and Lower Units, respectively.Peak P–T conditions were followed by a nearly isothermaldecompression for both units at slightly different temperatures(of the order of 50°C). The contact between the two units,i.e. the garnet isograd, is interpreted as a greenschist-faciesductile thrust. Thrusting of the higher-grade unit, i.e. theUpper Unit, over the Lower Unit occurred after the high-pressureevent, i.e. during the exhumation of both units. The observedsuperposition of higher-grade rocks over lower-grade rocks arguesagainst models where the exhumation history is entirely controlledby crustal-scale vertical shortening (i.e. extension). KEY WORDS: Armorican Massif; blueschist facies; Ile de Groix; metapelites; P–T path; garnet isograd     

Complex Growth Textures in a Polymetamorphic Metabasite from the Kraubath Massif (Eastern Alps)

Zoned garnet and amphibole occur in metabasites of the KraubathMassif, Eastern Alps, that contain relic magmatic clinopyroxene.The amphibole composition gradually changes from core (X_Mg =0·83) to rim (X_Mg = 0·6–0·7). A numberof compositional varieties of garnet occur in the metabasite.An older porphyroblastic garnet (Py_23–27, Alm_41–43,Grs_29–33) has two different compositional domains, onerelatively rich in Mg (Py_27–30) and the other rich inCa (Grs_35–38) with a low Mg (Py_20–25) content. Theyoungest variety, which forms rims on, or microveins in, theporphyroblastic garnet, has high Ca and low Mg (Grs_40–57,Py_2–7, Alm_46–51). The amphibole cores and garnetporphyroblasts are interpreted to represent minerals formedduring Variscan regional metamorphism under amphibolite-faciesconditions. Alpine metamorphism is represented by the most recentCa-rich and Mg-poor variety of garnet that coexists with theamphibole rims, epidote and chlorite. Fracturing in the porphyroblasticgarnet probably originated during retrogression of the Variscanamphibolite-facies assemblages. Textural relations suggest thatthe garnet in the microveins formed by dehydration of hydrousphases during an Alpine metamorphic overprint that reached P–Tconditions of 550–583°C at 1·0 GPa. KEY WORDS: microveins; garnet; metabasites; Kraubath Massif; Eastern Alps     

Pyroxene-Olivine-Quartz Assemblages in Rocks Associated with the Nain Anorthosite Massif, Labrador

Unusually iron-rich pyroxene and olivine occur in rocks associatedwith the Nain anorthosite massif, Labrador. Adamellite and granodioritecontain orthopyroxene (inverted from pigeonite) as iron-richas Ca₆Fe₈₂Mg₁₂; comparison with experimental data suggests aminimum pressure of crystallization of 5 kb. Some of these iron-richpyroxene crystals have broken down, apparently upon decreasingpressure, to yield intergrowths of less iron-rich orthopyroxene(near Ca₇Fe₇₂Mg₂₁), ferroaugite, fayalite (near Fo₉), and quartz.Other rocks, monzonites, contain pyroxenes with calcium-poorcores and ferroaugite rims, as well as crystals composed ofbroad lamellae of ferroaugite and orthopyroxene in sub-equalproportions. Analysis of one such crystal with unusually thinand closely spaced lamellae yielded a bulk composition of Ca₂₄Fe₅₈Mg₁₈.Such pyroxenes probably crystallized near or above the crestof the augite-pigeonite two-phase region, probably above 925°C. This high temperature suggests that the monzonites crystallizedfrom relatively dry magmas. If they represent a residual fractionderived from the same magma as the anorthosite, then that magmamust have been nearly anhydrous. Pigeonite rather than orthopyroxene was the primary magmaticCa-poor pyroxene in most of the Nain rocks studied here. Nucleationrates apparently were low under subsolidus conditions, and low-Capigeonite (Ca₂Fe₇₈Mg₂₀) is present in grains where orthopyroxenedid not nucleate as pigeonite cooled and exsolved ferroaugite.Iron-rich orthopyroxene (Ca₂Fe₇₉M₁₉) crystallized instead ofpigeonite in a Greenland quartz syenite that contains more abundanthydrous phases.     

The Key Influence of Fluid in the Preserves, Mineral Assemblages, Compositionsand Structures: Study from High-Pressure Eclogite and Its Amphibolization in the Western Dabie Mountains，Central China

正Pseudosection modeling for the garnet amphibolite samples from the Western Dabie Mountains show they have experienced similar HP metamorphic evolution with that of the adjected eclogites.The common assemblage of     

Characteristics of debris flows from the lower part of the Lotru River basin (South Carpathians,Romania)

This paper focuses on characteristics of debris flows from the lower part of the Lotru River basin (South Carpathians, Romania). The damage produced by these debris flows has included burial of agricultural land, roads covered by debris flows, and even the obstruction of the Lotru River. Simple statistical analysis has been used to emphasize the characteristics of the debris flow sites. The collected data show that heavy rainfall is the main triggering mechanism of debris flow events in the Lotru hydrographic basin. The daily rainfall data for this region show that important debris flow events generally occur when rainfall exceeds 40 mm in 24 h, while rainfall levels between 25 and 40 mm in 24 h result in hyperconcentrated flows. For 11 of 14 studied debris flow sites, the fan area is greater than the source area, probably due to the thickness of the regolith, which is up to 5–10 m deep. Both source area and deposition area are very dynamic. The retreat rate calculated for five debris flow sites ranges from 5 to 30 m in 30 years (from 1975 to 2005). Channel cross section measurements on one of the debris flows show that velocity values vary from 1.31 to 2.64 m/s; corresponding discharge values vary from 4 to 10.03 m³/s.     

Formation of Polycrystalline Graphite Aggregates in High-Pressure Metamorphic Rocks from the Kokchetav Massif,Northern Kazkhstan

Doklady Earth Sciences - An inclusion of graphite in zircon from the diamond- and tourmaline-bearing rocks of the Kokchetav massif (Northern Kazakhstan) has been studied. The inclusion, associated...     

The Role of Water Retention in the Anatexis of Metapelites in the Bushveld Complex Aureole, South Africa: an Experimental Study

Highly restitic metapelites occur at the contact of the RustenburgLayered Suite (Bushveld Complex). On the basis of previous experimentalstudies, the high (     

High-Pressure Granulites (Retrograded Eclogites) from the Hengshan Complex, North China Craton: Petrology and Tectonic Implications

Both high- and medium-pressure granulites have been found asenclaves and boudins in tonalitic–trondhjemitic–granodioriticgneisses in the Hengshan Complex. Petrological evidence fromthese rocks indicates four distinct metamorphic assemblages.The early prograde assemblage (M₁) is preserved only in thehigh-pressure granulites and represented by quartz and rutileinclusions within the cores of garnet porphyroblasts, and omphacitepseudomorphs that are indicated by clinopyroxene + sodic plagioclasesymplectic intergrowths. The peak assemblage (M₂) consists ofclinopyroxene + garnet + sodic plagioclase + quartz ±hornblende in the high-pressure granulites and orthopyroxene+ clinopyroxene + garnet + plagioclase + quartz in the medium-pressuregranulites. Peak metamorphism was followed by near-isothermaldecompression (M₃), which resulted in the development of orthopyroxene+ clinopyroxene + plagioclase symplectites and coronas surroundingembayed garnet grains, and decompression-cooling (M₄), representedby hornblende + plagioclase symplectites on garnet. The THERMOCALCprogram yielded peak (M₂) P–T conditions of 13·4–15·5kbar and 770–840°C for the high-pressure granulitesand 9–11 kbar and 820–870°C for the medium-pressuregranulites, based on the core compositions of garnet, matrixpyroxene and plagioclase. The P–T conditions of pyroxene+ plagioclase symplectite and corona (M₃) were estimated at     

The Key Influence of Fluid in Metamorphic Rock Preserves, Mineral Assemblages, Compositions and Structures: Study from High-Pressure Eclogite and Its Amphibolization in the Western Dabie Mountains，Central China

正The most of high/ultrahigh-pressure(HP/UHP)terranes of the world are characterized by the occurrence of numerous pods,lenses or layered blocks of eclogite and amphibolites(e.g.O’Brien,1997;Elvevold and Gilotti,2000;Zhang et al.,2003;and references there in).Field and petrological features suggest that amphibolites should     

Mineral Assemblages of Amphibolites Associated with Alpine-Type Ultramafics in the Dinaride Ophiolite Zone (Yugoslavia)

Amphibolites are frequently and characteristically associatedwith alpine-type ultramafics within ophiolite zones of differentgeological ages. Ultramafics of the Dinaridic ophiolite zoneare predominantly lherzolite, and are associated with differentvarieties of gabbro, dolerite, diabase, spilite, and amphibolite.Amphibolites commonly form narrow, interrupted zones aroundlarger ultramafic massifs, and, in some areas, they exceed theultramafics in size. All these rocks are members of the Jurassic(?)volcanic-sedimentary complex (‘Diabas-Hornstein Formation’)consisting predominantly of graywacke type sandstone and shale. The amphibolites characteristically have crystalloblastic texturesand are commonly banded and foliated, which distinguishes themfrom associated gabbros and dolerites. Different kinds and varietiesof metamorphic rocks can be found within the Dinaridic amphibolitecomplexes: amphibolite schists containing plagioclase, pyroxeniteschists containing diopside and plagioclase, monomineralic amphiboleschists, and eclogites. Samples of each of these rock typeswere collected from several localities and monomineralic fractionsof amphiboles, plagioclases, garnets, and clinopyroxenes wereseparated and examined in detail. Amphiboles range from kaersutite, pargasite, and edenite throughtransitional varieties enriched in tschermakite and ‘common’hornblende molecules. Plagioclase varies from anorthite to sodicoligoclase. Associated garnets are enriched either in pyropeor in almandine. Clinopyroxene is hedenbergitic diopside withabout 10–20 per cent of jadeite molecule and hypersthenecontains about 40 per cent FeSiO₃. Variations in mineral composition of the amphibolites demonstratestheir metamorphic origin. Although there is a continuous changein chemical composition, three mineral assemblages can be distinguished.Data from experimental petrology indicate that the amphibolitesassociated with alpine-type ultramafics can be stable underupper mantle PT conditions.     

Metapelites of the Kanskiy Granulite Complex (Eastern Siberia): Kinked P-T Paths and Geodynamic Model

The Southern Yenisey Range (Eastern Siberia) consists of thegranulite-facies Kanskiy complex bordered by the lower-gradeYeniseyskiy and Yukseevskiy complexes. Samples of metapeliteof the Kanskiy complex typically show characteristic garnet-formingreaction textures and near-isobaric cooling P–T paths.An important new result of this study concerns the differencein shape of the P–T paths from different parts of theKanskiy granulite complex: metapelites collected 8 km from theboundary with the Yeniseyskiy complex followed a linear pathwith dP/dT 0·006 kbar/°C; metapelites collected3 km from this boundary reveal a kinked P–T path withan interval of burial cooling (dP/dT –0·006 kbar/°C).The difference in the shape of the P–T paths is supportedby the chemical zoning of garnet studied in the second groupof samples. A mechanism of buoyant exhumation of granulite issuggested by comparison with the results of numerical modelling,which indicate that such a diversity of P–T paths mayresult from a transient disturbance of the thermal structureby rapid differential movement of material from different crustallevels. To arrive at a correct tectonic interpretation, thewhole assemblage of interrelated P–T paths of metamorphicrocks collected from different localities within the same complexmust be studied. KEY WORDS: crustal diapirism; exhumation; granulites; numerical modelling; P–T path     

Geochemistry of mafic rocks of the PGE-bearing Vurechuaivench Massif (Monchegorsk Complex,Kola region)

The platinum-bearing Paleoproterozoic Vurechuaivench Massif in the Monchegorsk Pluton is made up of amphibolized and saussuritized gabbronorites, anorthosites, and norites. The geochemical features of the massif rocks are considered at four detailed areas. It was confirmed that the Vurechuaivench and Nyud-Poaz massifs are geochemically similar. The rare-earth element (REE) distribution in the rocks of the Vurechuaivench Massif is peculiar in the low total REE content (9.4–27.6 ppm), negative REE slope, significant LREE enrichment [La/Yb] _n = 3.7–8.7), and distinctly expressed positive Eu anomaly ([Eu/Eu*] _n = 1.2–2.2). The REE distribution pattern remains unchangeable throughout the entire section, including the rocks of the Pt reef, with a gradual upsection REE increase. It is suggested that the PGE reef of the Vurechuaivench Massif, as the Platinova Reef (Skaergaard massif) and Sonju-Lake Intrusion (Duluth complex), was formed during fractional crystallization in a large magma chamber without new magma influx. It is conceivable that the Vurechuaivench Massif is the allochthonous fragment of a large loppolith-like body, the lower portions of which compose the Nyud-Poaz Massif, while the middle part was almost completely eroded.     

High-grade metamorphic rocks in the pre-Alpine nappe stack of the Getic-Supragetic basement (Median Dacides, South Carpathians, Romania)

Summary Metamorphic rocks in the pre-Alpine basement of the Getic-Supragetic units (Median Dacides of the Carpathian belt) are spatially related to different lithotectonic units, some of which contain high-pressure relicts reflecting an early stage of oceanic and continental subduction, locally synchronous with mylonitic shear zones. Kyaniteamphibole ± quartz-bearing eclogites preserve a complete metamorphic clockwise loop; the estimated peak conditions within the outer part of the Cumpana unit were at least 20 kb at 780–860 °C. Pre-eclogite-stage magmatic phases occur in some units with true equilibrated eclogites. Clinopyroxene-plagioclase inclusions in garnet of a garnet-clinopyroxene assemblage within a metagabbro indicate a temperature around 760–790 °C at a maximum pressure of about 19 kb. The units finally evolved together during stages of exhumation under metamorphic conditions ranging from the Barrovian-type (minimum age of 330 Ma) to the high-temperature/low-pressure type. The absolute age of the high-pressure stage and the eclogite protoliths is unknown. In comparison with other collision belts, it is likely that the gneiss units of the Median Dacides underwent a complete cycle of underthrusting and exhumation similar to other segments of the European Variscides, and that the formation of the eclogite occurred during the early stages of subduction.

---

Résumé Les roches métamorphiques du socle pré-alpin des domaines Gétiques et Supragétiques (Dacides médianes de la chaîne des Carpathes) appartiennent à des unités lithotectoniques différentes dont certaines contiennent des reliques de métamorphisme haute pression reflétant un stade précoce de subduction continentale et océanique, localement synchrone de zones de cisaillement mylonitiques. Des éclogites é disthène-amphibole ± quartz permettent de reconstituer un trajet PT horaire complet. Les conditions paroxysmales sont estimées au sein de l'unité de Cumpana é plus de 20 kb pour 780–860 °C. Des phases magmatiques pré-éclogitiques coexistent avec des phases de haute pression dans les éclogites de certaines unités et des inclusions de clinopyroxene-plagioclase dans les grenats d'un métagabbro indiquent une température de 760–790 °C pour une pression maximale de 19 kb. L'ensemble des unités évolue finalement durant les stades d'exhumation sous les mêmes conditions de métamorphisme barrovien (âge minimum de 330 Ma) puis de haute température-basse pression. L'âge du stade de haute pression et des protholithes reste inconnu. En comparaison avec d'autres chaînes de collision, il est vraisemblable que les Dacides médianes ont subi un cycle d'enfouissement et d'exhumation similaire é celui décrit dans d'autres segments de la chaîne varisque européenne, la formation des éclogites étant attribuée aux premiers stades de la subduction.

---

---

With 9 Figures