Search

The ultramafic rocks of the Herbeira Massif in the Cabo Ortegal Complex (NW Iberia) host chromitite bodies. The textural and compositional study of the host rocks and the chromitites classified them into: (1) Type-I chromitites, forming massive pods of intermediate-Cr chromite (Cr# = 0.60–0.66) within dunites; and (2) Type-II chromitites forming semi-massive horizons of high-Cr chromite (Cr# = 0.75–0.82) interlayered with dunites and pyroxenites. Minor and trace elements (Ga, Ti, Ni, Zn, Co, Mn, V and Sc) contents in the unaltered chromite cores from both types show patterns very similar to fore-arc chromitites, mimicked by the host dunites and pyroxenites. Calculated parental melt compositions suggest that Type-I chromitites crystallized from a melt akin to fore-arc basalt (FAB), while Type-II chromitites originated from a boninite-like parental melt. Both melts are characteristic of a fore-arc setting affected by extension during rollback subduction and have been related to the development of a Cambrian-Ordovician arc. These chromitites are extremely enriched in platinum-group elements (PGE), with bulk-rock PGE contents between 2,460 and 3,600 ppb. Also, the host dunites and pyroxenites exhibit high PGE contents (167 and 324 ppb, respectively), which are higher than those from the primitive mantle and global ophiolitic mantle peridotites. The PGE enrichment is expressed in positively-sloped chondrite-normalized PGE patterns, characterized by an enrichment in Pd-group PGE (PPGE: Rh, Pt and Pd) over the Ir-group PGE (IPGE: Os, Ir and Ru) and abundant platinum-group minerals (PGM) dominated by Rh-Pt-Pd phases (i.e. Rh-Ir-Pt-bearing arsenides and sulfarsenides, Pt-Ir-Pd-base-metal-bearing alloys, and Pt-Pd-bearing sulfides). The PGM assemblage is associated with base-metal sulfides (mostly pentlandite and chalcopyrite) and occurs at the edges of chromite or embedded within the interstitial (serpentinized) silicate groundmass. Their origin has been linked to direct cry

Medium and high grade kyanite-bearing graphitic metapelites of the basement of the Torrox Unit (Upper Alpujarride, Western Mediterranean) show kyanite-andalusite-kyanite replacements and coexisting garnet types with complex compositional zoning and growth-dissolution stages. This allows inferring two clockwise P-T paths associated with contrasted orogenic cycles of latest Carboniferous – earliest Permian and Eocene(?)-Miocene age, respectively. Dated (306 ± 77 Ma) prograde medium grade garnet cores with relatively low to moderate Ca content indicates pre-Alpine barrovian metamorphism in the kyanite stability field (ca. 600°C, 0.7–0.8 GPa). This implies a prograde pressurization of the sequence followed by decompression, as inferred from andalusite replacements after kyanite. Deeper in the sequence, anatectic granitic orthogneisses contain high-grade graphitic kyanite-bearing metapelitic restitic enclaves. Dating of rutile (with inclusions of kyanite) and monazite (shielded in biotite) from the pelitic enclaves provided pre-Alpine ages (ca. 300 Ma) rejuvenated due to Alpine overprint. Such pressurization event is not consistent with a late Variscan stage, commonly identified with a tectonic scenario characterized by orogenic collapse and decompression at ca. 300 Ma. Instead, we propose a post-Variscan collision event related to the closure of the western Paleotethys. On the other hand, Ca-rich cores of garnet porphyroblasts in the medium-grade metapelites formed at 1.1–1.2 GPa, 500°C, implying a metamorphic gradient of ca. 11.5°C/km related to Eocene (?) subduction. Kyanite+phengite replacements after andalusite are related to this stage. Late Mg-rich Ca-poorer overgrowths in garnet porphyroblasts document increasing temperature during the first stage of decompression (down to 0.9 GPa at ca. 650°C) with increasing thermal gradient up to ca. 20°C/km. These two complete metamorphic cycles of pressurization and heating followed by decompression allow reconciling previou

The Peltetec ophiolitic belt, exposed along the western margin of the Cordillera Real (Ecuador), comprises tectonic slivers of metamorphosed (greenschist facies) and variably deformed metaperidotites (serpentinites), gabbros (locally cumulate), greenschist and sub-greenschist rocks. New field data, deformation and petrographic observations, whole-rock major element, mineral composition and P-T determinations of the Peltetec metaophiolite allow determining the metamorphic-geodynamic events of a section of the active western margin of Gondwana during the Mesozoic. Two metamorphic events are proposed: (i) ocean-floor metamorphism during the formation of oceanic lithosphere under low-pressure amphibolite facies conditions (M0), followed by (ii) prograde metamorphism up to the greenschist facies along an intermediate (Barrovian) P/T gradient (M1; ~315°C and ~ 3.9 kbar, ca. 23°C/km). The first metamorphic event occurred under near-static stress conditions and rocks did not suffer significant deformation. During this event, pyroxenes were replaced by hornblende while plagioclase recrystallized. The second event produced strongly recrystallized and foliated greenschist facies rocks with a peak assemblage of actinolite + chlorite + albite + epidote + titanite ± phengite. We interpreted that this assemblage developed during the closure of a back-arc basin and the emplacement of the ophiolite onto the continental margin in the late Triassic or possibly by compressive events in the Early Cretaceous and/or Late Cretaceous. Later processes are related to the regional mostly strike-slip Peltetec fault/shear zone that produced displacement and mixing of blocks, as indicated by cataclastic structure present in most of the slivers, but without differentiable metamorphic recrystallization overprint.

The sedimentary successions of the Permian-Triassic rifting related to the Alpine Tethys in the easternmost Lower Alpujarride units (Internal Betic Zone, south Spain) host shallow-intrusive basic bodies of Mesozoic age. These gabbroic bodies experienced low-grade Alpine metamorphic overprint, singularly recorded in three outcrops nearby Alicante city in southeast Spain: Callosa and Orihuela Ranges and Nueva Tabarca Island. Overall, the metabasic bodies still preserve magmatic ophitic/subophitic texture and relicts of magmatic augite and ferropargasite-ferroedenite-edenite and kaersutite. In contrast, metamorphic minerals include magnesioriebeckite, actinolite, albite, stilpnomelane, phengite, and chlorite. Major and trace element geochemical data suggest crystallization of the igneous protoliths from subalkaline (tholeiitic) to alkaline within-plate (continental) basaltic magmas slightly enriched in incompatible elements. These magmas with E-MORB geochemical affinity very likely intruded at shallow crustal levels in an extensional-synrift-geodynamic setting related to the breakoff of Pangea in the region. Pressure-Temperature (P-T) conditions estimated by average P-T method and pseudosection calculations suggest metamorphic peak at ca. 6 kbar at 340°C consistent with burial metamorphism down to ca. 18 km depth with intermediate thermal gradients of ca. 18°C/km. These conditions are different to the typical subduction-related blueschist facies conditions of the Lower Alpujarride units and suggest, instead, a collisional (Barrovian) event. This can be explained by a late-stage accretion of the studied units after the main subduction-related event, pointing to the dispersion of the corresponding Lower Alpujarride sections along the margin in different palaeogeographic positions before deformation and movement to their actual structural position. The metamorphic correlation of the studied units with the accreted passive margin of South Iberia (Subbetic zone) is also dis

Exotic blocks of massive antigorite-serpentinite (antigoritite) document a deep-seated subduction channel in the Villa Clara serpentinite-matrix mélange, central Cuba. The petrological and geochemical characteristics of antigoritite allow distinguishing two types of rock: i) antigoritite and ii) dolomite-bearing antigoritite. Both types are intimately related in field exposures and represent deep peridotite infiltrated by H2O-CO2 fluid mixtures that triggered antigoritization and local carbonation. Fluid infiltration continued after antigoritization forming a vein network as a potential response to hydrofracturing that precipitated tremolitite in the veins and triggered fluid-antigoritite reaction forming blackwalls. The mineralogical and chemical zoning in the blackwalls (Atg + Chl + Tr adjacent to antigoritite and Chl + Tr adjacent to the tremolitite vein) attest for multi-step metasomatic processes during fluid-rock interaction characterized by advection of infiltrating fluid towards the blackwall and, possibly, by diffusion out of the blackwall towards the fluid-filled vein. Tentative thermodynamic modeling of the blackwall domain Atg + Chl + Tr points vein network formation at 400–500 °C and 5–10 kbar during exhumation in the subduction channel, suggesting the infiltration of deep-seated pressurized fluid that triggered hydrofracturing. The chemical compositions of antigoritites, veins and blackwalls indicate a LILE- and LREE-enriched fluid evolved from the subducting plate, while Srsingle bondNd isotope systematics are compatible with an external fluid composed of a mixture of fluids evolved from sediments and, probably to a lesser extent, altered oceanic crust.

A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.

A U-Pb zircon date of ∼113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.

The Neoproterozoic Bou Azzer ophiolite in the Moroccan Anti-Atlas Panafrican belt hosts numerous chromitite orebodies within the peridotite section of the oceanic mantle. The chromitites are strongly affected by serpentinization and metamorphism, although they still preserve igneous relicts amenable for petrogenetic interpretation. The major, minor and trace element composition of unaltered chromite cores reveal two compositional groups: intermediate-Cr (Cr# = 0.60 – 0.74) and high-Cr (Cr# = 0.79 – 0.84) and estimates of parental melt compositions suggest crystallization from pulses of fore-arc basalts (FAB) and boninitic melts, respectively, that infiltrated the oceanic supra-subduction zone (SSZ) mantle. A platinum group elements (PGE) mineralization dominated by Ir-Ru-Os is recognized in the chromitites, which has its mineralogical expression in abundant inclusions of Os-Ir alloys and coexisting magmatic laurite (RuS) and their products of metamorphic alteration. Unusual mineral phases in chromite, not previously reported in this ophiolite, include super-reduced and/or nominally ultra-high pressure minerals moissanite (SiC), native Cu and silicates (oriented clinopyroxene lamellae), but “exotic” zircon and diaspore have also been identified. We interpret that clinopyroxene lamellae have a magmatic origin, whereas super-reduced phases originated during serpentinization processes and diaspore is linked to late circulation of low-silica fluids related to rodingitization. Zircon grains, on the other hand, with apatite and serpentine inclusions, could either have formed after the interaction of chromitite with mantle-derived melts or could represent subducted detrital sediments later incorporated into the chromitites. We offer a comparison of the Bou Azzer chromitites with other Precambrian ophiolitic chromitites worldwide, which are rather scarce in the geological record. The studied chromitites are very similar to the Neoproterozoic chromitites reported in the Arabi

A U-Pb zircon date of ~113 Ma revealed that a variety of jadeitites and related omphacitite, chloritite and albite-rich rocks from the subduction-related Sierra del Convento block-in-serpentinite-matrix mélange (eastern Cuba) formed nearly synchronously with MORB metabasite-derived anatectic trondhjemitic liquids at high-temperature and pressure in a hot subduction environment. Field, petrologic and geochemical data indicate hydrothermal/metasomatic processes triggered by juvenile fluids likely evolved from the crystallizing hydrous trondhjemitic melts. These fluids, variably mixed with sediment-derived fluids and channelized along fractures in the supra-slab mantle, precipitated relatively pure jadeitite with geochemical patterns depleted in REE and HFSE and epidote-rich jadeitite with LILE- (notably Ba) enriched compositions with respect to N-MORB. The crystallization of jadeitite veins was accompanied by formation of chloritite blackwalls at the vein-ultramafic rock contact and omphacititic patches at the outer parts of the veins, denoting wall rock-fluid interactions. Further pervasive flow of external fluid within the rock bodies triggered modal and cryptic (geochemical) metasomatic transformation of earlier jadeitite, producing mica-rich jadeitite and albite-epidote (-chlorite) rocks. Altogether these rocks document a discrete episode of massive flow of fluid in the supra-slab mantle roughly coeval with hydrous melting of subducted MORB metabasite.

[EN] The aim of this PhD Thesis is to address the geodynamic evolution of the active Andean continental margin during the Mesozoic, centered in the Northern Andean branch of the chain, by means of a petrological approach. Initially, two mafic - ultramafic complexes of nominally Cretaceous age were selected. One related to an oceanic environment (oceanic lithosphere) obducted onto the continental margin termed the Peltetec ophiolitic belt (Peltetec Unit) and a continental volcanic arc intrusion termed the Tampamchi ultramafic – mafic complex, both located in the Cordillera Real of Ecuador. However, the Triassic U-Pb zircon age obtained in this work allow discarding the previous published Ar-Ar plagioclase (albite) Cretaceous age of the Peltetec ophiolite, which must be considered an overprinting age. This unexpected result prevents considering the potential geodynamic relationship of the selected complexes., [ES] El objetivo de esta tesis doctoral es abordar la evolución geodinámica del margen continental occidental de los Andes del Norte durante el Mesozoico mediante una aproximación petrológica. Para esto se seleccionaron dos complejos máficos-ultramáficos de edad nominalmente Cretácica, uno relacionado a un ambiente oceánico correspondiente a litósfera oceánica obductada sobre el margen continental, llamado Cinturón ofiolítico Peltetec (Unidad Peltetec), y el otro una intrusión de arco continental llamado Complejo ultramáfico-máfico Tampanchi, ambos localizados en la Cordillera Real de Ecuador. Sin embargo, la edad U-Pb en circón Triásica obtenida en este estudio descarta la edad Cretácica (Ar-Ar en plagioclasa/albita) previamente interpretada como edad de formación de la ofiolita Peltetec, la cual debe considerarse como una edad sobreimpuesta. Este resultado impide considerar la potencial relación geodinámica entre los complejos seleccionados.

The architecture and pressure-temperature conditions reached by a Cretaceous block-in-matrix serpentinite mélange exposed in the Zagros suture resemble those imaged in the active Mariana subduction zone. There, large magnitude-earthquakes (M>w9) have never been recorded but smaller events – of poorly-constrained physical origin – in the range M∼w3-6 are widespread. Field and petro-structural constraints led to a first report of blueschist-facies seismic fault-related rocks in the Zagros serpentinite melange, including breccias, foliated cataclasites and ultracataclasites; all observed within a foliated mafic metatuffaceous block embedded in serpentinite schists. Fine-scale petrological characterization of ultrafine-grained, fluidized cataclastic material reveals the presence of newly-formed glaucophane, lawsonite, phengite, albite and pumpellyite, an assemblage inferred (based on thermodynamic modelling) to have crystallized in the lower lawsonite-blueschist facies at ∼0.6-1.0 GPa and 230-300 °C. Extensional veins containing similar mineral assemblages are observed crosscutting the aforementioned rocks but are also identified as comminuted fragments in all fault-related lithologies. Crosscutting relationships among the multiple generations of fluidized ultracataclasites and brecciated blueschists suggest that episodic faulting and hydrofracturing were contemporaneous processes at ∼20-35 km depth, i.e., at similar conditions as reported for metabasalts expelled by Mariana serpentinite mud volcanoes. Mechanical modelling confirms that the studied fault-related features can only have formed under nearly lithostatic pore fluid pressure conditions, maintaining the system in a critically unstable regime that promoted recurrent seismic faulting, as monitored in the Mariana seismogenic zone. These fluids are likely associated with externally and deeply-generated fluid pulses that may have reached the seismogenic window, imprinting a Ta-Th-Nb-HREEs-enriched trace element sig

New field and petrographic observations, whole-rock major- and trace-element geochemical data, Nd and Sr isotope systematics and U-Pb SHRIMP zircon ages of the Peltetec metaophiolite and related rocks (Ecuador) allow the characterization of the igneous and sedimentary protoliths and the evaluation of the geodynamic evolution of the active western margin of Gondwana during the Mesozoic. The Peltetec ophiolitic belt, exposed along the western margin of the Cordillera Real (Ecuador) and previously considered of Cretaceous age, comprises slices of metamorphosed (greenschist facies) and variably deformed peridotites, gabbros (locally cumulate), basaltic lavas and dykes, hydrothermal breccias and sedimentary rocks. The geochemical characteristics of the tholeiitic basaltic rocks indicate a Sr-Nd isotope depleted mantle source with variable imprint of subduction zone-derived or continental crust-assimilated components, as indicated by enrichment in Th, negative anomaly of Nb and relative depletion in high field strength elements (HFSE). Geochemical diversity allows defining different groups of noncumulate igneous rocks with oceanic island arc and NMORB-like back-arc affinities. U-Pb zircon ages from a metabasite yielded 228.1 ± 1.7 Ma, interpreted as the crystallization age of the magma. These data allow proposing the generation of the Peltetec ophiolite in a back-arc setting as a consequence of late Triassic extension of the western continental margin of Gondwana. Granites located at the western margin of the Peltetec Unit with S-type affinity and equal Triassic age (U-Pb age of 228.2 ± 0.8 Ma) document coeval anatexis of the continental crust as a consequence of heating associated with the same extensional event that originated the ophiolite. Geologic correlation allows enlarging such tectonic scenario to include ophiolitic units of similar age in Colombia.

New field and petrographic observations, whole-rock major- and trace-element geochemical data, Nd and Sr isotope systematics and U-Pb SHRIMP zircon ages of the Peltetec metaophiolite and related rocks (Ecuador) allow the characterization of the igneous and sedimentary protoliths and the evaluation of the geodynamic evolution of the active western margin of Gondwana during the Mesozoic. The Peltetec ophiolitic belt, exposed along the western margin of the Cordillera Real (Ecuador) and previously considered of Cretaceous age, comprises slices of metamorphosed (greenschist facies) and variably deformed peridotites, gabbros (locally cumulate), basaltic lavas and dykes, hydrothermal breccias and sedimentary rocks. The geochemical characteristics of the tholeiitic basaltic rocks indicate a Sr-Nd isotope depleted mantle source with variable imprint of subduction zone-derived or continental crust-assimilated components, as indicated by enrichment in Th, negative anomaly of Nb and relative depletion in high field strength elements (HFSE). Geochemical diversity allows defining different groups of noncumulate igneous rocks with oceanic island arc and NMORB-like back-arc affinities. U-Pb zircon ages from a metabasite yielded 228.1 ± 1.7 Ma, interpreted as the crystallization age of the magma. These data allow proposing the generation of the Peltetec ophiolite in a back-arc setting as a consequence of late Triassic extension of the western continental margin of Gondwana. Granites located at the western margin of the Peltetec Unit with S-type affinity and equal Triassic age (U-Pb age of 228.2 ± 0.8 Ma) document coeval anatexis of the continental crust as a consequence of heating associated with the same extensional event that originated the ophiolite. Geologic correlation allows enlarging such tectonic scenario to include ophiolitic units of similar age in Colombia.

The “Medellín Dunite”, the main ultramafic body of the Central Cordillera of Colombia, constitutes a fragment of oceanic lithospheric mantle formed at a back–arc basin/incipient arc scenario emplaced onto the western continental margin of Pangaea during Triassic time. This body has been classically, and is still considered, mainly of dunite composition. However, in spite of two subsequent metamorphic imprints that obscure the primary mantle mineralogical composition, there is petrographic and geo-chemical evidence that points to a harzburgitic nature of the unit. In order to overcome the petrographic effects of medium–T metamorphism, metasomatism, and serpentini-zation, we analyzed published and new major–element geochemical data by means of algebraic methods to approximate the mantle mineralogical composition of ultramafic rocks. The restored mantle mineralogy clearly indicates that the body is mainly of harz-burgitic composition, and therefore we propose that the term “Medellín Dunite” should no longer be applied to avoid terminological confusion. Furthermore, a phase–relation approach in simple systems for the metamorphic evolution allows identifying the main reason for the contradictory terminology used so far: olivine is paragenetic (stable) with tremolite and talc during medium–T (ca. 600 °C) metamorphic imprint undergone by the body. During this initial metamorphic event, characterized by full hydration (as opposed to the late–stage serpentinization), mantle pyroxenes reacted out and medi-um–T olivine formed while high–T olivine persisted metastably as a likely consequence of moderate temperature and sluggish diffusion kinetics. On the other hand, we ana-lyze two likely geodynamic scenarios to provide a common context of metamorphism for the ultramafic body and associated metabasites (Aburrá Ophiolite): (i) ocean–floor metamorphism and (ii) intra–backarc subduction–initiation metamorphism. The latter allows a new tectonic view of the Aburrá Ophiolite, formed

The Havana–Matanzas Ophiolite contains one of the few examples of ophiolitic platinum group minerals (PGM)-rich chromitites associated with orthopyroxenites in the mantle section of ophiolitic complexes. The chromitites occur as veins hosted by orthopyroxenite bands within mantle peridotites. The peridotites are mostly harzburgites and their accessory chromite shows high-Al compositions (Cr# [Cr/(Cr+Al), atomic ratio] = 0.39–0.50), which are typical of spinels in abyssal peridotites. Conversely, chromite from the chromitite veins and their host orthopyroxenite are high-Cr (Cr# = 0.72–0.73 and 0.62–0.69, respectively), with lower Mg# [Mg/(Mg+Fe), atomic ratio]. This suggests that both the chromitite and the orthopyroxenite formed from melts with boninitic affinity. The abundant PGM inclusions found in the chromitites are mainly Os-rich laurite grains, which is also characteristic of chromitites formed from magmas with boninitic affinity. Therefore, we propose that the chromitite veins and the orthopyroxenite bands probably formed contemporaneously in the fore-arc setting of an intra-oceanic arc during subduction. The chromitite-orthopyroxenite pair of the Havana-Matanzas Ophiolite could form after the reaction of a Si-rich melt with boninitic affinity and mantle harzburgite, with the orthopyroxenite bands preserving fingerprints of the infiltration of boninitic-affinity melts within the mantle. The small volume of forming chromitite could maximize the efficiency for the mechanical collection of the PGM forming in the parental melt of these rocks, resulting in the anomalous enrichment of primary PGM in the chromitites., [ES] La ofiolita de Habana-Matanzas contiene uno de los pocos ejemplos de cromititas ricas en minerales del grupo del platino (MGP) asociadas a ortopiroxenitas de la sección mantélica de complejos ofiolíticos. Las cromititas ocurren como venas encajadas en bandas de ortopiroxenita dentro de la peridotita mantélica. Las peridotitas son mayoritariamente harzburgitas con cromita accesoria rica en Al (#Cr [Cr/(Cr+Al), cociente atómico] = 0.39–0.50), lo cual es típico de espinelas en peridotitas abisales. Por otro lado, la cromita perteneciente a las venas de cromitita y a la ortopiroxenita encajante es rica en Cr (#Cr = 0.72–0.73 y 0.62–0.69, respectivamente) y con bajo #Mg [Mg/(Mg+Fe2+), cociente atómico]. Esto sugiere que tanto las venas de cromitita como la ortopiroxenita se formaron a partir de fundidos de afinidad boninítica. Las abundantes inclusiones de MGP encontradas en las cromititas son principalmente granos de laurita ricos en Os, lo cual también es propio de cromititas formadas a partir de magmas con afinidad boninítica. Por lo tanto, proponemos que las venas de cromitita y las bandas de ortopiroxenitas se formaron contemporáneamente en un contexto de ante-arco en un arco intra-oceánico durante el proceso de subducción. El conjunto cromitita-ortopiroxenita de la ofiolita de Habana- Matanzas se formó por la reacción de fundidos ricos en Si con afinidad boninítica y la harzburgita mantélica. Las bandas de ortopiroxenitas sería la huella química que habrían dejado estos fundidos boniníticos al infiltrarse por el manto. El volumen reducido de las cromititas que se formaron maximizó la eficiencia del proceso de recolección mecánica de los MGP que se formaban en el fundido parental, dando lugar al enriquecimiento de MGP primarios como inclusiones en las cromititas.

New field and petrographic observations, whole-rock major- and trace-element geochemical data, Nd and Sr isotope systematics and U-Pb SHRIMP zircon ages of the Peltetec metaophiolite and related rocks (Ecuador) allow the characterization of the igneous and sedimentary protoliths and the evaluation of the geodynamic evolution of the active western margin of Gondwana during the Mesozoic. The Peltetec ophiolitic belt, exposed along the western margin of the Cordillera Real (Ecuador) and previously considered of Cretaceous age, comprises slices of metamorphosed (greenschist facies) and variably deformed peridotites, gabbros (locally cumulate), basaltic lavas and dykes, hydrothermal breccias and sedimentary rocks. The geochemical characteristics of the tholeiitic basaltic rocks indicate a Sr-Nd isotope depleted mantle source with variable imprint of subduction zone-derived or continental crust-assimilated components, as indicated by enrichment in Th, negative anomaly of Nb and relative depletion in high field strength elements (HFSE). Geochemical diversity allows defining different groups of noncumulate igneous rocks with oceanic island arc and NMORB-like back-arc affinities. U-Pb zircon ages from a metabasite yielded 228.1 ± 1.7 Ma, interpreted as the crystallization age of the magma. These data allow proposing the generation of the Peltetec ophiolite in a back-arc setting as a consequence of late Triassic extension of the western continental margin of Gondwana. Granites located at the western margin of the Peltetec Unit with S-type affinity and equal Triassic age (U-Pb age of 228.2 ± 0.8 Ma) document coeval anatexis of the continental crust as a consequence of heating associated with the same extensional event that originated the ophiolite. Geologic correlation allows enlarging such tectonic scenario to include ophiolitic units of similar age in Colombia.

Diamond is commonly regarded as an indicator of ultra-high pressure conditions inEarth System Science. This canonical view is challenged by recent data and interpre-tations that suggest metastable growth of diamond in low pressure environments.One such environment is serpentinisation of oceanic lithosphere, which produceshighly reduced CH4-bearing fluids after olivine alteration by reaction with infiltratingfluids. Here we report the first ever observedin situdiamond within olivine-hosted,CH4-rich fluid inclusions from low pressure oceanic gabbro and chromitite samplesfrom the Moa-Baracoa ophiolitic massif, eastern Cuba. Diamond is encapsulated invoids below the polished mineral surface forming a typical serpentinisation array,with methane, serpentine and magnetite, providing definitive evidence for its meta-stable growth upon low temperature and low pressure alteration of oceanic litho-sphere and super-reduction of infiltrated fluids. Thermodynamic modelling of the observed solid and fluid assemblage ata reference P-T point appropriate for serpentinisation (350 °C and 100 MPa) is consistent with extreme reduction of the fluidto logfO2(MPa)=¿45.3 (¿logfO2[Iron-Magnetite]=¿6.5). These findings imply that the formation of metastable diamond atlow pressure in serpentinised olivine is a widespread process in modern and ancient oceanic lithosphere, questioninga generalised ultra-high pressure origin for ophiolitic diamond.

The Upper Units of the allochthonous complexes of the NW Iberian Massif constitute a terrane with continental affinity. They represent the vestiges of a Cambrian magmatic arc developed in the periphery of Gondwana (West African Craton) which was involved in the Devonian Variscan collision, undergoing high-P, high-T metamorphism. This includes ultramafic rocks, high-P mafic rocks (eclogites and granulites) and high-P migmatitic paragneisses. The latter rocks show an extensive migmatization with the leucosomes oriented parallel to the regional foliation. The migmatitic paragneisses are composed of garnet, kyanite, biotite, quartz, plagioclase, K-feldspar, rutile and Ti-hematite. Thermodynamic modelling using the measured bulk composition in the NCKFMASTHO system indicates metamorphic peak conditions of ~15 kbar and ~800 to 835°C, followed by a significant cooling. The prograde evolution is assessed by means of a melt-reintegration approach, using the composition of the garnet and its inclusions. An appropriate composition of liquid is added to the measured bulk composition to emulate the pre-melting bulk composition. Modelling of this melt-reintegrated composition allows to identify a colder high-P episode below ~500°C. Zircon crystals extracted from the leucosomes show overgrowths crystallized from the partial melt at c. 389 Ma (U–Pb system). The P–T–t path proposed reveals a subduction of the peri-Gondwanan arc-derived section down to mantle depths. An isobaric heating stage occurred as a result of residence at great depths and/or inception of a transient oceanic basin at c. 395 Ma. The ensuing near-isothermal exhumation occurred due to the extension related to the inception of the basin, reaching the thermal peak shortly before c. 389 Ma. Subsequent cooling is related to the underthrusting of colder oceanic and transitional crust below the HP-HT Upper Units.

The exercise of paleogeographic/tectonic reconstruction of past orogenic belts is a complex task that includes the interpretation and integration of multi-technique approaches such as basin tectonics, structural geology, petrology, geochemistry, geochronology, and geodynamics. Proterozoic geologic records are fragmented and incomplete, which make efforts to reconstruct paleogeography and orogenic processes even more challenging. Therefore, for our understanding of the tectonic evolution of past orogenic systems to advance, it is essential that any existing model, including the ones proposed by Heilbron and Valeriano (2020, https://doi.org/10.1029/2019tc005897), are repeatedly exposed to debate and testing. In this reply we address the points raised by Heilbron and Valeriano in order to clarify the scientific foundations of our tectonic interpretation for one of the Neoproterozoic Brasiliano/Pan-African orogens in South America (the Central Ribeira Belt), presented in Meira, Garcia-Casco, Hyppolito, et al. (2019, https://doi.org/10.1029/2018TC004959). We also evaluate the proposed paleogeographic reconstructions for this part of West Gondwana and conclude that an intracontinental model better explains the currently available data and observations, including the space problem pointed out in recent publications, and that existing geochemical and geochronologic data by themselves are not conclusive with respect to an unequivocal tectonic environment.

The Moa-Baracoa ophiolite in eastern Cuba is one of the few known ophiolites that display sulfide mineralization attributable to a magmatic origin in association with podiform-chromite ores hosted in the mantle-crust transition. These sulfide ores chiefly consist of Fe-Ni-Cu sulfides, namely pyrrhotite, pentlandite, chalcopyrite and cubanite partly altered to valleriite. The sulfide mineralization is located along the contact between the podiform-like chromite ores and intruding pegmatitic gabroic dykes. The detailed mineralogical study of the sulfide mineralization coupled with the first ever laser ablation ICP-MS analysis reveals that this sulfide mineralization show contents of the precious metals (Os, Ir, Ru, Pt, Re, Au, Ag) and other (semi)-metals (Co, Ni, Cu, Se, Te, Bi, Pb, As Sb) comparable to those sulfides from the magmatic sulfide deposits associated with mafic complexes hosted in the continental crust. The results obtained from this study confirm that Fe-Ni-Cu sulfides at Potosí are magmatic in origin, and very likely derived from the solidification of droplets of sulfide melt segregated by immiscibility from the intruding mafic melts once they interacted with the pre-existing chromitite at the mantle-crust transition zone of the ophiolite. The immiscibility of sulfide melt was achieved as a result of a progressive increase of fS, very likely triggered by a set of circumstances, including the progressive fractionation of the intruding mafic melt leading to increase of aSiO and accumulation of volatiles as well as the crystallization of oxides. Two main generations of pentlandite were observed. One generation is primary in origin and it was locally exsolved along with pyrrhotite from monosulfide solid solution (MSS) during low-temperature cooling. The second type of pentlandite resulted from the reaction of MSS with coexisting droplets of Cu-and Ni-rich sulfide melt. LA-ICP-MS analysis reveals that most precious metals (Ru, Os, Ir, Re, Au, Ag) were concen

The Sierra del Convento mélange (Eastern Cuba) represents a well preserved fragment of the Cretaceous oceanic subduction channel in the Caribbean realm, developed by the subduction of the Protocaribbean basin below the Caribbean Plate. The mélange is formed by a serpentinite matrix, which contains a variety of tectonic blocks metamorphosed to high pressure and low to high temperature, including blueschists, pelitic gneisses, anatectic tonalitic–trondhjemitic rocks, epidote-garnet plagioclase-lacking amphibolites and sepertinites. This mélange has unique characteristics by showing evidence of partial melting of the slab developed by subduction of very young oceanic plate. Recently, in situ jadeitite blocks have been discovered in the Sierra del Convento mélange surrounded by sheared serpentinitic rocks. The combination of hot subduction and occurrence of jadeitite generates an exceptional scenario to decipher the interaction at intermediate to high-temperature of fluids in the subduction channel and its boundary with the mantle wedge. This PhD thesis is focused on the study of jadeitite and related rocks with emphasis in their petrogenesis by fluid-rock interaction in a subductive context. In addition, the serpentinitic rocks associated with jadeitites have been included in the study in order to decipher the context of formation of jadeitites. Serpentinite rocks preserve fertile protolith signatures, [ES] La mélange de la Sierra del Convento (Cuba Oriental) representa un fragmento bien conservado del canal de subducción oceánica del Cretácico en el ambiente Caribeño, desarrollado por la subducción de la cuenca oceánica protocaribeña bajo la placa del Caribe. La mélange está formada por una matriz serpentinítica, la cual contiene una variedad de bloques tectónicos metamorfizados a alta presión y de baja a alta temperatura, incluyendo esquistos azules, gneises pelíticos, rocas anatécticas trondhjemíticas y tonalíticas, anfibolitas de epidota y granate sin plagioclasa y serpentinitas. Esta mélange tiene características únicas por mostrar evidencias de fusión parcial de la lámina subducente gracias a la subducción de una placa oceánica muy joven. Recientemente, bloques in situ de jadeitita han sido descubiertos en la mélange de la Sierra del Convento rodeados por rocas serpentiníticas cizalladas. La combinación de subducción caliente y la aparición de jadeitita ofrece un escenario excepcional para descifrar la interacción de fluidos en el canal de subducción, y su límite con la cuña de manto. Esta tesis doctoral está focalizada en el estudio de la petrogénesis de jadeititas y rocas asociadas por interacción de fluido-roca en un contexto subductivo. Además, las rocas serpentiníticas asociadas a las jadeititas han sido incluidas en este estudio para descifrar el contexto de formación de las jadeititas.

Four artifacts from San Salvador Island, Bahamas, with affinities to jadeite jade were studied by mineralogical and petrographical techniques and compared to similar studies of jadeite rock (jadeitite) from sources in the greater Caribbean region: Guatemala (both north and south Motagua mélange occurrences); the Sierra del Convento Mélange, Cuba; and the Río San Juan Complex, Dominican Republic. Three of the four artifacts are jadeite jade. The fourth is a metavolcanic rock of greenschist facies metamorphism. Each of the three jadeitite objects is distinct in terms of mineral assemblage and microscopic minerals intergrowth textures. One artifact manifests strong similarities with a variety of jadeitite known from Cuba, the closest source geographically to the Bahamas. The other two artifacts display unique characteristics of either mineral assemblage or texture that have not been observed to date in rocks from the known sources. Consequently, search must continue for greater diversity within the documented sources or new sources of jadeite jade that conform to what was observed must be found.

Recent findings of diamonds in ophiolitic peridotites and chromitites challenge our traditional notion of Earth mantle dynamics. Models attempting to explain these findings involve incorporation of diamonds into chromite near the mantle transition zone. However, the occurrence of metastable diamonds in this context has not been considered. Here, we report for the first time in situ microdiamonds in chromite from ophiolitic chromitite pods hosted in the Tehuitzingo serpentinite (southern Mexico). Here, diamonds occur as fracture-filling inclusions along with quartz, clinochlore, serpentine, and amorphous carbon, thus indicating a secondary origin during the shallow hydration of chromitite. Chromite chemical variations across the diamond-bearing healed fractures indicate formation during the retrograde evolution of chromitite at temperatures between 670 °C and 515 °C. During this stage, diamond precipitated metastably at low pressure from reduced C-O-H fluids that infiltrated from the host peridotite at the onset of serpentinization processes. Diamond was preserved as a result of fracture healing at the same temperature interval in which the chromite alteration began. These mechanisms of diamond formation challenge the idea that the occurrence of diamond in ophiolitic rocks constitutes an unequivocal indicator of ultrahigh-pressure conditions.

Las ofiolitas de Sierra de Baza corresponden a uno de los pocos afloramientos dentro de las ofiolitas Béticas aún sin estudiar como tal. Esta Asociación ofiolítas Bética forman parte del Complejo del Mulhacén, junto a la Unidad de la Caldera infrayacente y la Unidad de las Sabinas suprayacente. Constituyendo dos mantos de corrimiento, de origen cortical, compuestos por basamentos principalmente Paleozóicos y coberteras mesozocias. El Complejo del Veleta, formado por varios miles de metros de micaesquistos con grafito aflora como una serie de ventanas tectónicas bajo el Complejo del Mulhacén y constituyen las unidades más profundas de la Cordillera Bética. El manto ofiolítico está compuesto por rocas básicas, ultramáficas y sedimentarias, afectadas en parte por metamorfismo de fondo oceánico, que durante la Orogenia Alpina, se vieron afectadas por el metamorfismo orogénico polifásico. Las rocas ultramáficas son serpentinitas con clinopiroxeno y harzburgitas secundarias, que en muchos afloramientos de la asociación ofiolítica Bética, contienen diques basálticos parcialmente rodingitizados y metamorfizados. Todos los magmas que forman parte de estas ofiolitas, como diques, gabros y basaltos, son de procedencia astenosférica y su ambiente geodinámico de génesis corresponde al de una dorsal oceánica, de tipo E-MORB y fueron generados a lo largo de una zona de acreción de placas oceánicas. Algunos de estos magmas atravesaron localmente, en su salida a la superficie oceánica, materiales corticales, produciéndose una asimilación local de los mismos, dilucidable por algunos rasgos químicos de la roca total, que indican que el suelo oceánico del que derivan estas ofiolitas se originó por aumento de la distensión de la litosfera y corteza continental, y ascenso de la astenosfera a partir del Jurásico inferior, prolongandose episódicamente a lo largo del cretácico. Las etapas prejurásicas de rifting y adelgazamiento cortical, que afectaron a las unidades de la Caldera y de las

[EN] This PhD is about the serpentinitic matrix, mafic crust and exotic ultramafic blocks of the Villa Clara serpentinitic mélange (VCSM) in central Cuba in an attempt to evaluate the evolution of oceanic lithosphere. Each of these units bears witness of mantle source composition, origin of oceanic crust and its relation to the mantle, ocean floor metamorphism, metasomatism and fluid flux in the subduction zone. The study of the serpentinitic matrix allowed the identification of two peridotite protoliths. Group A, with fertile compositions (high Al2O3 and low Cr# in pyroxene and spinel and enriched in heavy rare earth elements) and group B, displaying refractory compositions (low Al2O3 and higher Cr# in pyroxene and spinel compositions and depleted in middle and heavy rare earth elements). Group A can be related to typical abyssal/fracture zone peridotite, whereas group B is typical of forearc peridotite. Melting modelling shows that, group A resulted from low melting degrees (c. 4-8%) of a depleted mantle source, whereas group B reached up to c. 14-22% melting upon a two-stage melting of a depleted mantle followed by melting of a protolith similar to group A. The studied mafic crust includes rocks of sub-volcanic (diabase and microgabbro) and plutonic origin (cumulate gabbro and olivine gabbro). The sub-volcanic unit attests for two types of mafic magma: group 1 displays forearc basalts signature (FAB; low Ti/V ratio) and group 2 island arc tholeiite composition (IAT; medium Ti/V ratio), both with positive Th and negative Nb anomalies in comparison to N-MORB compositions. These compositions as well as the isotopic signature of the plutonic unit (low 143Nd/144Nd and low 87Sr/86Sr) point to a subduction-related imprint. Geochemical evidence supports a genetic relationship between the protoliths of the serpentinitic matrix rocks and the sub-volcanic mafic crust. An indirect evidence is the light rare earth element enrichment of group B peridotites, which is commonly i

The origin of the assemblage of ultra-high pressure (UHP), super-reduced (SuR) and several crustally derived phases in ophiolitic chromitites is still hotly debated. In this paper, we report, for the first time, this assemblage of phases in ophiolitic chromitites of the Caribbean. We studied the Mercedita chromitite deposit in the eastern Cuban ophiolitic complexes. The mineral phases were characterized using microRaman spectroscopy, energy-dispersive spectroscopy with a scanning electron microscope (SEM-EDS), X-ray microdiffraction and electron microprobe analyses. Mineral concentrates were prepared using hydroseparation techniques. We have identified oriented clinopyroxene lamellae in chromite, oriented rutile lamellae in chromite, moissanite hosted in the altered matrix of the chromitite, graphite-like amorphous carbon, corundum and SiO hosted in healed fractures in chromite grains, and native Cu and Fe–Mn alloy recovered in heavy-mineral concentrates obtained by hydroseparation. This assemblage may correspond to UHP-SuR conditions, implying recycling of chromitite in the mantle or formation of the chromite grains at deep mantle depths, followed by emplacement at a shallow level in the mantle. However, the chromitite bodies contain gabbro sills oriented parallel to the elongation of the chromitite lenses, and these show no evidence of HP/UHP metamorphism. Therefore, the identified “exotic” phases may not be indicative of UHP. They formed independently as oriented clinopyroxene lamellae in chromite during cooling (clinopyroxene and rutile), in super-reduced microenvironments during the serpentinization processes, and by transference of subducted crustal material to the mantle wedge via cold plumes.

La restauración arquitectónica patrimonial emplea la técnica de reintegración volumétrica en los soportes pétreos gravemente deteriorados. En la utilización de morteros de restauración y recrecido se requiere controlar aspectos importantes como: similitud cromática y textural respecto del entorno pétreo adyacente, menor o igual resistencia mecánica e igual o mayor porosidad/permeabilidad, respecto a la piedra original. Este último aspecto es particularmente complicado pues también se requiere que la distribución porcentual de rangos de poro no sea discordante con la que presenta el material pétreo original. A través de la patente de invención (con números de publicación ES2187245 A1 y B1 16. 06. 2004), con titularidad de la Universidad de Granada, se ha logrado una excelente piedra artificial porosa aplicable a trabajos decorativos en construcción y un mortero de restauración de materiales pétreos con porosidad controlada. Ambos están constituidos, en gran parte, por residuos de rocas ornamentales por lo que se da un uso concreto a este tipo de subproductos difícilmente reutilizables. En este trabajo presentamos el procedimiento para obtener estas piedras artificiales y morteros porosos con fines constructivos, decorativos y restauradores, a partir de la mezcla controlada de áridos de rocas ornamentales, aglomerantes inorgánicos, orgánicos, o sus mezclas y generador de porosidad. Tras el fraguado y endurecimiento se pone de manifiesto uno de los aspectos más relevantes del producto, que se basa en la generación de un complejo sistema poroso conectado gracias a la incorporación de poliestireno expandido molido, el cual se activa tras la puesta en obra mediante la aplicación de disolventes orgánicos., [EN] The technique of volumetric reintegration in severely deteriorated stone materials is of major importance for the restoration of architectural heritage. In using mortars for restoration it is important to control aspects such as the colour and textural similarity in relation to the adjacent stone, minor or equal strength and equal or greater porosity/permeability with respect to the original stone. This latter aspect is of particular complexity because the percentage distribution of pore-size ranges should not differ from that of the original stone material. The invention patent (with numbers of publication ES2187245 A1 and B1 16. 06. 2004), owned by the University of Granada, allows the production of excellent porous stones for decorative work in construction and mortar for restoration of stone materials with controlled porosity. Both materials consist of ornamental rock waste, so that a particular recycling purpose is given to this type of material which is difficult to reuse. In this paper we present the manufacturing process of these artificial stones and porous mortars with decorative and restorative purposes, from the controlled mixture of aggregates of ornamental rocks, organic and inorganic binders and generators of porosity. Once the curing and hardening has been done it is worth noting that one of the most important aspects of the product is the generation of a complex connected porous system as a result of the incorporation of crushed expanded polystyrene, which is activated after hardening through the application of organic solvents.