Las hornblenditas,gabros y dioritas del Macizo del Montnegre (Barcelona, Cordilleras costero catalanas)

En relación con los granitos tardihercínicos calcoalcalinos del Macizo del Montnegre aparecen rocas ultrabásicas-básicas a intermedias. Las más básicas son hornblenditas olivínicas, con espinela, clinopiroxeno, ortopiroxeno, anfíboles de varios tipos y flogopita. Hay además melagabros-gabros hornbléndicos y leucogabros, estos últimos con anfíbol minoritario. Las rocas más ácidas son cuarzodioritas y cuarzomonzodioritas biotítico-hornbléndicas, con cristales relictos de clinopiroxeno y ortopiroxeno. El contenido máximo en anortita de la plagioclasa en las dioritas es tan alto como en los gabros. Toda la asociación muestra una evolución típicamente calcoalcalina, pero las hornblenditas y algunos gabros podrían haberse formado a partir de diferentes tipos de magmas básicos. Las cuarzodioritas serían rocas híbridas, con participación de un magma más básico y otro más ácido. El primero estaría saturado en clinopiroxeno y ortopiroxeno, además de en plagioclasa de composición bitownita, y el otro magma sería más ácido

Spinels of Variscan olivine hornblendites related to the Montnegre granitoids revisited (NE Spain) : petrogenetic evidence of mafic magma mixing

Olivine hornblendites (cortlandtites) form part of the Montnegre mafic complex related to late-Variscan I-type granitoids in the Catalan Coastal Ranges. Two generations of spinel are present in these hornblendites: Spl1 forms euhedral crystals included in both olivine and Spl2. Spl2 forms euhedral to anhedral crystals associated with phlogopite and fibrous colourless amphibole forming pseudomorphs after olivine. Compositions of Spl1 are picotite-Al chromite (Fe#: 77.78-66.60; Cr#: 30.12-52.22; Fe3+/R3+: 6.99-21.89; 0.10< TiO2%<0.62). Compositions of Spl2 are pleonaste (Fe#: 37.86-52.12; Cr#: 1.00-15.45; Fe3+/R3+: 0.31-5.21; TiO2%<0.10). The two types of spinel follow a CrAl trend, mainly due to the substitution (Fe2+)-1Cr-1= MgAl, which is interpreted as the result of mixing between two different mantle-derived melts. The compositions of early Spl1 crystals included in olivine are characteristic of Al-rich basalts. More aluminous Spl2 would result from reaction of olivine with a less evolved, Al and K-rich mantle-derived melt after new refilling of the magma chamber or channel. As a whole, spinels from similar examples of Variscan olivine hronblendites also follow a CrAl trend with high Fe# and starting at higher Cr# than other trends of this type. Cr# heterogeneity in the early spinels from these Variscan hornblendites would be inherited from the variable Al content of the mafic melts involved in their genesis

Minerales 'exóticos' en cromititas ofiolíticas. Implicaciones para la geodinámica mantélica

Los depósitos ofiolíticos de cromita constituyen un rasgo característico de la secuencia mantélica de las ofiolitas (González-Jiménez et al., 2014 y referencias en éste). Los cuerpos de cromititas se encuentran en dunitas y harzburgitas distribuyéndose a lo largo de una zona de espesor variable, entre 1 y 2 km, debajo de los niveles de gabros bandeados de la corteza inferior oceánica. El origen de cuerpos monominerálicos de cromita en el manto, especialmente el mecanismo de concentración de cromita y el ambiente tectónico de formación, continúa siendo un tema sujeto a debate (e.g., Proenza et al., 1999; González-Jiménez et al., 2014). A tal efecto, se han propuesto hipótesis basadas en: i) cristalización cotéctica de cromita+olivino y su posterior separación mecánica; ii) procesos de mezcla o contaminación de magmas; iii) asimilación de piroxenitas y gabros; iv) aumento del grado de polimerización del fundido debido a la pérdida de agua; v) cambios en la fugacidad de oxígeno. Todas estas hipótesis asumen procesos a baja presión en el manto (<20 km profundidad)

The BCN-SGA student chapter: a tool for insertion to research and laboral world in metallogeny

The activity of the BCN-SGA Student Chapter is evaluated. Establishedin 2012 it has grown up to 69 members, organizing 2 international workshops, 8seminars, numerous visits to museums, activities stimulating the use of English in socialevents and microresearch projects. The results of these microprojects are 15presentations in scientific congresses. These activities enhance tea

Les col·leccions de mineralogia de la UB. Una eina d'aprenentatge i de participació dels estudiants

Les col·leccions de Mineralogia de la Universitat de Barcelona poden ser de litoteca (emprades en l'ensenyament presencial i no presencial) i sistemàtica (usades com a material de referència de recerca). Comprenen mostres de mà, làmines primes i probetes. Les col leccions de referència son controlades per estudiants, els quals comproven la identitat del mineral i en fan la catalogació. Així s'introdueix els estudiants en les tècniques de caracterització i en les tècniques de musealització

The Petrogenesis of the ophiolitic mélange of Central Cuba: origin and evolution of oceanic litosphere from abyssal to subduction and suprasubduction zone settings

[eng] 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 interpreted as a result of re-equilibration with percolating basaltic melts like those represented by the sub-volcanic mafic crust. Also, melting modelling of primitive melts of the mafic crust (group 1-FAB related) results in c. 8-10 % melting of an abyssal mantle source like group A peridotites that produced a residue like group B peridotites. On the other hand, ocean floor metamorphism affected the mafic crust, which displays greenschist to amphibolite facies assemblages that attest for low pressure/low to medium temperature at shallow depths. This process had an impact on the concentration of mobile elements. A different metasomatic/enrichment process is recorded by trace element geochemistry and stable and radiogenic isotopes (B, Nd, Sr and Pb) in the serpentinitic matrix. The isotopic relations point to a slab fluid formed after devolatilitzation of the subducting plate as the source of metasomatic agent. The slab fluid is composed of diverse proportions of altered oceanic crust fluid (AOCF), global subducting sediment fluid (GLOSSF) and terrigenous fluid (TERF). The combination of these three isotopic reservoirs with an already serpentinized mantle related to ocean floor hydration reproduces the isotopic signature of the serpentinitic matrix of the VCSM. This result is in agreement with evidence provided by the high-pressure exotic ultramafic block of the VCSM, which showssimilar isotopic composition indicating interaction with a similar fluid in a context of subduction. The petrological and geochemical characteristics of the exotic ultramafic block allow distinguishing two types of serpentinite: i) antigorite-serpentinite and ii) dolomite-bearing antigorite serpentinite. Both represented a subducted peridotite that derives from a peridotite protolith locally CaO-enriched as a result of infiltration of a H2O-CO2 fluid mixture. Fluid infiltration in the subduction channel triggered serpentinization /carbonation and formation of tremolite veins and associated blackwalls developed in host antigorite-serpentinite. Mineralogical and chemical zoning in the blackwall (Atg + Chl + Tr towards the host serpentinite and Chl + Tr towards the vein) attest for metasomatic changes in fluid composition during fluid-rock interaction. The differences in chemical composition between blackwall and antigorite-serpentinite show that the infiltrating fluid was enriched in Ca, Al, LILE and LREE. Pseudosection modelling in the vein structure indicates that their formation took place at c. 4S0QC and c. 10 kbar. All these findings allow constraining the geodynamic evolution of the Villa Clara serpentinitic mélange in the context of the Caribbean realm. The serpentinitic matrix attests for two contrasting geodynamic settings. Group A peridotites formed at an abyssal/fracture zone setting in the Proto-Caribbean oceanic basin, whereas group B peridotites, exotic ultramafic block and mafic crust are pointing to a forearc setting. Both scenarios are reconciled in a geodynamic model of Upper Jurassic-Lower Cretaceous oceanic lithosphere formation upon break-up of Pangea followed by subduction initiation, likely at a fracture zone setting, during the early Cretaceous, and further development of a serpentinized forearc mantle and associated subduction channel during Lower-Upper Cretaceous time until final emplacement of the ensemble (serpentinitic mélange) during the latest Cretaceous-Eocene.[cat] Aquesta tesi doctoral tracta sobre la matriu serpentinítica, escorça màfica i els blocs exòtics ultraàafics de la mélange serpentinítica de Villa Clara situada a Cuba Central. El propòsit és avaluar l'evolució de la litosfera oceànica. Cadascuna d'aquestes unitats proporciona informació sobre la composició original del mantell, l'orígen de la escorça oceànica i la seva relació amb el mantell, el metamorfisme de fons oceànic, el metasomatisme i el flux de fluids en la zona de subducció. L'estudi de la matriu serpentinítica ha permès l'identificació de dos protòlits de peridotita. El grup A, amb composicions fèrtils (alt Al2O3 i baix Cr# en piroxens i espinela, així com un enriquiment dels elements de les terres rares pesades) i el grup B, que mostra composicions refractàries (baix Al2O3 i alt Cr# en piroxens i espinela, així com un empobriment en els elements de les terres rares mitjanes i pesades). El grup A es pot relacionar amb peridotites abissals / zona de fractura, mentre que el grup B té composicions típiques d'avantarc. Els models de fusió mostren que el grup A és el resultat de la fusió a graus de fusió baixos (c. 4-8%), mentre que el grup B pot arribar fins a c. 14-22% de fusió després d'una fusió en dos passos, la primera a partir d'un mantell empobrit i la segona per una fusió d'un protòlit similar a les roques del grup A. L'escorça màfica aquí estudiada inclou roques d'origen subvolcànic (diabasa i microgabre) i plutònic (acumulats de gabre i gabre olivínic). La unitat subvolcànica mostra que hi ha dos tipus de magma màfic; grup 1 mostra una signatura típica de basalts d'avantarc (FAB; baix ratio Ti/V) i el grup 2 amb una composició de toleiites d'arc d'illes (IAT; ratio intermedia Ti/V), ambdòs amb anomalia positiva de Th i negativa de Nb en comparació a composicions N-MORB. Aquestes composicions a més de la composició isotòpica de la unitat plutonica (baix 143Nd/144Nd i 87Sr/86Sr) indica la presència d'un component subductiu. Hi ha evidències geoquímiques que recolzen una relació genètica entre els protòlits de la matriu serpentinítica i la unitat subvolcanica de l'escorça màfica. Una evidencia indirecta és l'enriquiment de terres rares lleugeres en les peridotites del grup B. Aquest enriquiment s'interpreta com a resultat de la reequilibració de fosos basàltics que percolen en el mantell, aquests podrien estar representats per la unitat subvolcànica de l'escorça màfica. També els models de fusió dels fosos primitius de la escorça màfica (grup 1- FAB) prediuen el c. 8-10 % de fusió d'un mantell abissal, com el de les peridotites tipus A que produeix un residu equivalent al de les peridotites tipus B. D'altra banda, el metamorfisme de fons oceànic afecta a l'escorça màfica, que mostra associacions minerals típiques de fàcies d'esquistos verds i amfibolites. Aixà permet establir una pressió baixa i una temperatura baixa a intermèdia típica de condicions someres. Aquest procés té un impacte directe en la concentració dels elements mòbils. Diferents processos metasomàtics/enriquiment es veuen registrats en la geoquímica dels elements traça i els isòtops estables i radiogènics (B, Nd, Sr i Pb) de la matriu serpentinítica. Les relacions isotòpiques apunten a la presència de fluids provinents de la desvolatilització de la placa subduent on es forma l'agent metasomatizador. Aquests fluids estan compostos per diferents proporcions de fluids provinents de l'escorça oceànica alterada, sediments subduïts i sediments terrígens. La combinació d'aquests tres reservoris isotòpics amb un mantell ja hidratat en el fons oceànic reprodueix la signatura isotòpica de la matriu serpentinítica de la mélange serpentinítica de Villa Clara. Aquest resultat està en consonància amb l'evidencia proveïda pels blocs exòtics ultramàfics d'alta pressió de la mélange serpentinítica de Villa Clara, ja que aquests mostren composicions isotòpiques similars indicant la interacció amb un fluid similar en un context de subducció. Les característiques petrològiques i geoquímiques dels blocs exòtics ultramàfics permeten distingir dos tipus de serpentinites: i) antigoritita i ii) antigoritita amb dolomita. Ambdues representen peridotites subduïdes que deriven d'un protòlit localment enriquit en CaO com a resultat de l'infiltració d'una mescla de fluids amb H2O-CO2. L'infiltració de fluids en el canal de subducció és el detonant per la serpentinització/carbonatació i formació de dominis de reemplaçament i venes de tremolita en la antigoritita. El zonat mineralògic i químic observat en els dominis de reemplaçament (domini de Atg + Chl + Tr en direcció a la antigoritita i el domini Chl + Tr en direcció a la vena) confirmen els canvis metasomàtics de la composició del fluid durant l'interacció fluid-roca. Les diferències de composició química entre els dominis i la antigoritita mostren que el fluid que s'infiltra estava enriquit en Ca, Al, elements litòfils de gran radi ionic i terres rares lleugeres. La modelització de la pseudosecció realitzada en el domini Atg + Chl + Tr indica que la seva formació va tenir lloc a c. 4S0QC i c. 10kbar. Tots aquests resultats permeten constrènyer l'evolució geodinàmica de la mélange serpentinítica en el context de la regió del Carib. La matriu serpentinítica demostra la presència de dos ambients geodinàmics diferents. Les peridotites del grup A format en un ambient abissal/zona de fractura en la conca oceànica del Proto-Carib, mentre que les peridotites del grup B, els blocs exòtics ultramàfics i l'escorça màfica apunten cap a un ambient d'avant arc. Els dos escenaris coexisteixen en un model geodinàmic del Juràssic Superior- Cretaci Inferior amb la formació de litosfera oceànica després del trencament de Pangea i el posterior inici de la subducció, en un ambient de zona de fractura. L'inici de la subducció en el Cretaci inferior i posterior desenvolupament de la serpentinització de la zona d'avantarc i el canal de subducció durant el Cretaci Inferior- Superior fins al final emplaçament del conjunt (mélange serpentinitic) durant Cretaci Superior-Eocè

The Petrogenesis of the ophiolitic mélange of Central Cuba: origin and evolution of oceanic litosphere from abyssal to subduction and suprasubduction zone settings

[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 interpreted as a result of re-equilibration with percolating basaltic melts like those represented by the sub-volcanic mafic crust. Also, melting modelling of primitive melts of the mafic crust (group 1-FAB related) results in c. 8-10 % melting of an abyssal mantle source like group A peridotites that produced a residue like group B peridotites. On the other hand, ocean floor metamorphism affected the mafic crust, which displays greenschist to amphibolite facies assemblages that attest for low pressure/low to medium temperature at shallow depths. This process had an impact on the concentration of mobile elements. A different metasomatic/enrichment process is recorded by trace element geochemistry and stable and radiogenic isotopes (B, Nd, Sr and Pb) in the serpentinitic matrix. The isotopic relations point to a slab fluid formed after devolatilitzation of the subducting plate as the source of metasomatic agent. The slab fluid is composed of diverse proportions of altered oceanic crust fluid (AOCF), global subducting sediment fluid (GLOSSF) and terrigenous fluid (TERF). The combination of these three isotopic reservoirs with an already serpentinized mantle related to ocean floor hydration reproduces the isotopic signature of the serpentinitic matrix of the VCSM. This result is in agreement with evidence provided by the high-pressure exotic ultramafic block of the VCSM, which showssimilar isotopic composition indicating interaction with a similar fluid in a context of subduction. The petrological and geochemical characteristics of the exotic ultramafic block allow distinguishing two types of serpentinite: i) antigorite-serpentinite and ii) dolomite-bearing antigorite serpentinite. Both represented a subducted peridotite that derives from a peridotite protolith locally CaO-enriched as a result of infiltration of a H2O-CO2 fluid mixture. Fluid infiltration in the subduction channel triggered serpentinization /carbonation and formation of tremolite veins and associated blackwalls developed in host antigorite-serpentinite. Mineralogical and chemical zoning in the blackwall (Atg + Chl + Tr towards the host serpentinite and Chl + Tr towards the vein) attest for metasomatic changes in fluid composition during fluid-rock interaction. The differences in chemical composition between blackwall and antigorite-serpentinite show that the infiltrating fluid was enriched in Ca, Al, LILE and LREE. Pseudosection modelling in the vein structure indicates that their formation took place at c. 4S0QC and c. 10 kbar. All these findings allow constraining the geodynamic evolution of the Villa Clara serpentinitic mélange in the context of the Caribbean realm. The serpentinitic matrix attests for two contrasting geodynamic settings. Group A peridotites formed at an abyssal/fracture zone setting in the Proto-Caribbean oceanic basin, whereas group B peridotites, exotic ultramafic block and mafic crust are pointing to a forearc setting. Both scenarios are reconciled in a geodynamic model of Upper Jurassic-Lower Cretaceous oceanic lithosphere formation upon break-up of Pangea followed by subduction initiation, likely at a fracture zone setting, during the early Cretaceous, and further development of a serpentinized forearc mantle and associated subduction channel during Lower-Upper Cretaceous time until final emplacement of the ensemble (serpentinitic mélange) during the latest Cretaceous-Eocene

Spinels of Variscan olivine hornblendites related to the Montnegre granitoids revisited (NE Spain) : petrogenetic evidence of mafic magma mixing

Olivine hornblendites (cortlandtites) form part of the Montnegre mafic complex related to late-Variscan I-type granitoids in the Catalan Coastal Ranges. Two generations of spinel are present in these hornblendites: Spl1 forms euhedral crystals included in both olivine and Spl2. Spl2 forms euhedral to anhedral crystals associated with phlogopite and fibrous colourless amphibole forming pseudomorphs after olivine. Compositions of Spl1 are picotite-Al chromite (Fe#: 77.78-66.60; Cr#: 30.12-52.22; Fe3+/R3+: 6.99-21.89; 0.10< TiO2%<0.62). Compositions of Spl2 are pleonaste (Fe#: 37.86-52.12; Cr#: 1.00-15.45; Fe3+/R3+: 0.31-5.21; TiO2%<0.10). The two types of spinel follow a CrAl trend, mainly due to the substitution (Fe2+)-1Cr-1= MgAl, which is interpreted as the result of mixing between two different mantle-derived melts. The compositions of early Spl1 crystals included in olivine are characteristic of Al-rich basalts. More aluminous Spl2 would result from reaction of olivine with a less evolved, Al and K-rich mantle-derived melt after new refilling of the magma chamber or channel. As a whole, spinels from similar examples of Variscan olivine hronblendites also follow a CrAl trend with high Fe# and starting at higher Cr# than other trends of this type. Cr# heterogeneity in the early spinels from these Variscan hornblendites would be inherited from the variable Al content of the mafic melts involved in their genesis

Cryptic alkaline magmatism in the oceanic Caribbean arc (Camagüey area, Cuba)

Mid and Late Cretaceous arc-related basaltic rocks in the Camagüey area, East Central Cuba, record an intriguing seemingly random enrichment in alkalis that suggests alkaline affinity, representing an oddity in the Greater Antilles. In this study, the petrology and geochemistry of volcanic rocks from the Camujiro, Piragua and La Mulata Formations have been investigated. The rocks bear a diverse mineral assemblage including feldspars (plagioclase and potassium feldspar), clinopyroxene, phlogopite and amphibole with both equilibrium and disequilibrium textures. Clinopyroxene porphyritic crystals show conspicuous oscillatory and convolute zoning and reveal events of mafic recharge and crystallization in equilibrium with alkaline and calc-alkaline basaltic magmas and their mixtures. Composition of fluorophlogopite xenocrystals is consistent with crystallization from mafic alkaline liquids. Unlike whole-rock major element composition, immobile trace element abundances suggest a systematic calc-alkaline affinity. Chondrite-normalized rare-earth element (REE) patterns are similar to those of calc-alkaline and high-K (and single bondTh) calc-alkaline rocks from the Caribbean Antilles. Geochemical modelling indicates that the parental basic magmas formed by a 5-10% hydrous partial melting of spinel-facies depleted mantle fluxed by fluids evolved from subducted oceanic crust and pelagic sediments, as well as fractional crystallization. Random enrichment in alkalis in studied samples is attributed to the entrainment during ascent of material derived from mafic alkaline melts injected in the upper mantle or the root of the island-arc. Our new data establish a mature stage in the evolution of the Caribbean island-arc by Cenomanian times capable of sourcing alkaline melts and the existence of a thickened island arc crust that favored fractional crystallization and magma chamber recharge processes unlike in previous stages of the island-arc construction