Geoquímica e Isotópos de Nd de Rochas Metavulcânicas da Antiforme Capané, Complexo Metamórfico Porongos, RS

The Capané Antiform, located in the northern part of the Neoproterozoic Porongos Metamorphic Complex (RS), is composed of a supracrustal sequence metamorphosed under greenschist (eastern flank) to amphibolite (western flank) facies. Four groups of rocks were recognized. Groups 1 and 2 are constituted of felsic and mafic rocks from the central and western part of the antiform, respectively. They show high LREE and LILE and low HREE and HFSE. The εNd (t) varies from strongly negative (-20) in felsic rocks to moderately negative (-6 to -11) in mafic rocks, with Nd TDM ages that varies from Paleoproterozoic to Mesoproterozoic. The Group 3 consists of metarhyolites from the eastern flank and is geochemically similar to former groups, but shows differences in Nd isotope composition. The εNd(t) is slightly negative (-2 to -4) and the model ages are restricted to the Mesoproterozoic. Group 4, constituted of metabasalts, shows chemical similarities with OIB-MORB and has juvenile isotope signature. The first three groups were interpreted as evolved from a magmatic arc, related probably to the collision of the São Gabriel block with the Encantadas microcontinent during the Neoproterozoic. The Nd differences observed were considered as a result of more or less interaction between mantle and crust components and, particularly, the characteristics observed in the Group 3 can point out a correlation with the syn-tangential granitoids from the eastern part of the Dom Feliciano Belt. The metabasalts of the group 4 were correlated to the antiform's previously described ophiolite remains.The Capané Antiform, located in the northern part of the Neoproterozoic Porongos Metamorphic Complex (RS), is composed of a supracrustal sequence metamorphosed under greenschist (eastern flank) to amphibolite (western flank) facies. Four groups of rocks were recognized. Groups 1 and 2 are constituted of felsic and mafic rocks from the central and western part of the antiform, respectively. They show high LREE and LILE and low HREE and HFSE. The εNd (t) varies from strongly negative (-20) in felsic rocks to moderately negative (-6 to -11) in mafic rocks, with Nd TDM ages that varies from Paleoproterozoic to Mesoproterozoic. The Group 3 consists of metarhyolites from the eastern flank and is geochemically similar to former groups, but shows differences in Nd isotope composition. The εNd(t) is slightly negative (-2 to -4) and the model ages are restricted to the Mesoproterozoic. Group 4, constituted of metabasalts, shows chemical similarities with OIB-MORB and has juvenile isotope signature. The first three groups were interpreted as evolved from a magmatic arc, related probably to the collision of the São Gabriel block with the Encantadas microcontinent during the Neoproterozoic. The Nd differences observed were considered as a result of more or less interaction between mantle and crust components and, particularly, the characteristics observed in the Group 3 can point out a correlation with the syn-tangential granitoids from the eastern part of the Dom Feliciano Belt. The metabasalts of the group 4 were correlated to the antiform's previously described ophiolite remains

SISTEMA PORFIRÍTICO YARUMALITO, ANTIOQUIA: PETROGRAFÍA Y CARACTERIZACIÓN DE LAS ALTERACIONES HIDROTERMALES

En este trabajo se presenta la descripción petrográfica de secciones de núcleos (YAR-06, YAR-017 y YAR019) pertenecientes al Sistema Porfirítico Yarumalito, con el objeto de identificar la litología y alteraciones hidrotermales asociadas con mineralizaciones de oro en este sistema, propiedad de Colombian Mines Corporatión, este proyecto se localiza a 4,3Km al sur del municipio de Valparaíso, Antioquia. La descripción de estas secciones se realiza mediante el análisis macroscópico de núcleos de perforación, petrografía y microscopia electrónica (SEM); petrográficamente los cuerpos hipoabisales corresponden a andesitas y dacítas con alteraciones potásica, propilítica, cuarzo-sericita y sericítica; estás alteraciones tienen distribución en halos de vetillas o al interior de estas y menormente se presenta con una distribución penetrativa. En las secciones analizadas, el pulso inicial corresponde pórfidos de composición andesítica, con alteraciones potásica, cuarzo-sericitica y propilítica, este pulso es seguido por pórfidos dacíticos que presenta las mismas alteraciones pero con una intensidad mayor y finalmente estos cuerpos hipoabisales son cortados por pequeños diques dacíticos cuya alteración principal es sericitica. La  mineralogía de los pórfidos aporta datos sobre las etapas evolutivas del sistema, así por ejemplo se observa como el pulso inicial es más básico y progresivamente va pasando a composiciones moderadamente más félsicas; de igual manera ocurre con las texturas de estos cuerpos, que sugieren niveles de profundidad relativamente diferentes para los pulsos identificados; por otra parte las texturas secundarias y las alteraciones presentes indican una prominente interacción con fluidos de origen magmático-hidrotermal.  This paper describes petrographically sections of drill core (YAR-06, YAR-017 and YAR-019) belonging to the Yarumalite Porphyritic System, in order to identify the lithology and hydrothermal alterations associated with gold mineralization in this system, owned of Colombian Mines Corporation, this project is located 4,3 Km south of the municipality of Valparaiso, Antioquia. The description of these sections bodies is made by the macroscopic analysis of drilling cores, optical petrography and electron microscopy (SEM); petrographically the hypoabisal bodies correspond to andesites and dacites with potassic, propylitic, quartz-sericite and serictic alterations; these alterations have distribution in halos of veins or to the interior of these and less occurs with a distribution pervasive in the rock. In the analyzed sections, the initial pulse corresponds to andesitic porphyries, with potassic, quartzsericitic and propylitic alterations, this pulse is followed by dacitic porphyries that presents the same alterations but with a greater intensity and finally these hypoabisal bodies are cut by small dacitic dykes whose main alteration is sericitic. The mineralogy of the porphyries provides data on   the evolutionary stages of the system, for example it is observed as the initial pulse is more basic and progressively goes to compositions moderately more felsic; similarly to the textures of these bodies, which suggest relatively different levels of depth for the identified pulses; on the other hand the secondary textures and hydrothermal alterations presents, suggest a prominent interaction with fluids of magmatic-hydrothermal origin. &nbsp

Petrology of Acandí´'s Batholith and associated bodies in Unguía, Chocó, Colombia

El Batolito de Acandí es un cuerpo intrusivo con amplias variaciones composicionales (González y Londoño, 2002) que data del Oligoceno (Restrepo y Toussaint, 1976), a su vez intruído por cuerpos subvolcánicos de andesitas, dacitas, y diques de basaltos. Debido a la diferencia composicional de este cuerpo en la cordillera Occidental, se realiza la integración e interpretación de datos del análisis petrográfico, geoquímico e isotópico de muestras recolectadas en la parte norte del Golfo de Urabá entre los municipios de Acandí y Unguía en el departamento de Chocó. En esta zona, las rocas del Batolito son gabros: rocas melanocráticas, masivas, equigranulares de grano fino a medio, subhedrales, de textura fanerítica; y las de los cuerpos subvolcánicos y diques son: rocas leucocráticas, masivas, inequigranulares, de grano fino a medio, subhedrales, con textura porfirítica y rocas melanocráticas afaníticas (basaltos). Petrografía detallada muestra que las rocas del Batolito son compuestas por plagioclasa, piroxenos y anfíboles, como accesorios pirita diseminada, apatita, magnetita e ilmenita. Son rocas holocristalinas, melanocráticas, inequigranulares, subhedrales, de fino a groso granulares, con presencia de texturas ofíticas y subofíticas, con coronas de reacción y zonación en plagioclasas. Las rocas subvólcanicas que intruyen el batólito son basaltos afaníticos, dacitas y andesitas con texturas porfiríticas, con plagioclasa y hornblenda como minerales principales. Son inequigranulares, de tamaño muy fino a grueso, con texturas cúmuloporfiríticas, vesiculares y amigdulares. Los análisis geoquímicos e isotópicos indican que tanto las rocas del batolito como las de los cuerpos que lo intruyen, son de afinidad subalcalina de la serie calco-alcalina de bajo a medio K, metaluminosas, con enriquecimiento en elementos de tierras raras leves en relación a las tierras raras pesadas. Los datos geoquímicos e isotópicos de Nd y Sr sugieren que estas rocas se forman a partir de procesos en arcos de islas, asociados a zonas de subducción, siendo posteriormente acrecionadas al margen continental.The Acandi’s batholith is a large intrusive body with a wide compositional variation (Gonzalez and Londoño, 2002) dating from the Oligocene (Restrepo and Toussaint, 1976), and intruded by subvolcanic andesites and dacites bodies and basalt dikes. Due to the compositional difference of this body in the Western Cordillera, it is performed integration and interpretation of new petrographic, geochemical and isotopic data from samples collected in the northern Gulf of Urabá between the towns of Acandí and Unguía it is done in Choco department. For this area, batholith rocks are gabbros: melanocratic rocks, massive, equigranular fine to medium grained, subhedral, phaneritic texture; and the subvolcanic bodies and dikes are: leucocratic, massive and inequigranular rocks, fine to medium grained, subhedral, with sporphyritic texture and aphanitic melanocratic rocks (basalts). Detailed petrography shows that the rocks from the Batolith are constituted by plagioclase, pyroxene and amphibole, with disseminated pyrite, apatite, magnetite and ilmenite as accessory phases. The batholith rocks are holocrystalline, melanocratic, inequigranular, subhedral, from fine to granular roughly, with the presence of ophitic and subophitic textures, with reaction rings (coronas) and zoning in plagioclase. The intrusive subvolcanic rocks that crosscut the Batholith are afanitic basalts, dacites, and andesites with porphiritic textures, having plagioclase and hornblende as main minerals. They are inequigranular, very fine to coarse grained, with glomeroporphyritic texture and also vesicular and amygdular textures. Geochemical and isotopic analyses indicate that both batholiths and intrusive rocks are sub-alkaline from the calc-alkaline series of low to medium K, metaluminous with light rare earth elements enrichment in relation to the heavy rare earth elements. The geochemical and Nd and Sr isotopic data suggest that these rocks are formed in island arcs, associated with subduction zones, being later added to a continental margin.&nbsp

RAPAKIVI MAGMATISM IN THE MIDDLE INIRIDA BASIN, GUAINÍA DEPARMENT, COLOMBIA

In eastern Colombia, the crystalline basement is intruded by several anorogenic granites of Mesoproterozoic age. One of these anorogenic granitic intrusions outcrops in the area of the indigenous Matraca and Danta communities, at the middle Inirida River Basin, and is mostly covered by Tertiary sedimentary rocks and Quaternary deposits. Petrographic and geochemical analyses reveal them as holocrystalline, leucocratic, and coarse-grained monzonite to granodiorite with Pyterlite-type rapakivi texture indicating anorogenic affinity. We named this plutonic body informally as Matraca rapakivi granite, which was initially correlated with the Parguazan Event (conventional method in zircons, 1550 Ma) described in Venezuela. However, LA-ICP-MS U/Pb zircon dating yields a concordant zircon enclosure age of 1343 ± 8 Ma for the magma crystallization, in other words a 100-200 Ma younger magmatism, but also shows a coincidence with our ages of the Parguaza Granite in Colombia (LA-ICP-MS U/Pb zircon, 1390-1400 Ma). These ages suggest episodic intrusions of A-type granites between 1300-1400 Ma, associated with Nb, Ta, REE and Sn mineralizations.Durante el Mesoproterozoico varios granitos rapakivi intruyeron el basamento cristalino en el oriente colombiano aflorando en varios sitios como en las comunidades indígenas de Danta y Matraca, en la cuenca media del río Inírida en el departamento de Guainía, donde están cubiertos con rocas sedimentarias del Terciario y depósitos cuaternarios. Análisis petrográficos y geoquímicos revelan que se trata de un cuerpo porfirítico, holocristalino, leucocrático, grosogranular y de composición monzonítica a granodiorítica con textura rapakivi tipo piterlita, indicando afinidad anorogénica. Hemos designado informalmente este cuerpo plutónico como granito rapakivi de Matraca e inicialmente fue asociado con el gran Evento Parguenze descrito en Venezuela (método convencional U/Pb en circones, 1.550 Ma). Sin embargo, las recientes dataciones U/Pb en circones con LA-ICP-MS establecen una edad concordante de 1.343 ± 8 Ma para su cristalización que marca un magmatismo de 100-200 Ma más joven, pero que a su vez representa mayor concordancia con las recientes edades mediante el mismo método para el Granito de Parguaza en Colombia de 1.390-1.400 Ma, lo cual nos permite suponer intrusiones episódicas de granitos tipo “A” emplazados entre 1.300-1.400 Ma y parcialmente enriquecidos en mineralizaciones de Nb, Ta, REE y Sn

Stratigraphy and geochronlogy of the Guarinos greenstone belt, Goiás, Brazil

O greenstone belt de Guarinos é uma das três faixas de rochas supracrustais de baixo grau metamórfico marginadas por ortognaisses do extremo norte do Bloco Arqueano de Goiás. A investigação da estratigrafia daquelas faixas iniciou no final da década de 1970, com modificações ao longo dos anos em decorrência de mapeamentos geológicos de detalhe. A proposta estratigráfica mais recente em vigor do greenstone belt de Guarinos reúne as rochas supracrustais no Grupo Guarinos, subdividido nas formações Serra do Cotovelo (metakomatiitos), Serra Azul (metabasaltos), São Patricinho (metaturbiditos máficos), Aimbé (BIF) e Cabaçal (filitos carbonosos e metarenitos impuros). O mapeamento de detalhe e os resultados de sondagens do programa de exploração mineral na área pela Yamana Desenvolvimento Mineral S.A. possibilitaram redefinir a Formação Cabaçal e desdobrá-la em um membro inferior de filitos carbonosos com intercalações de derrames de basalto e lentes de gondito; um intermediário de horizonte de gondito e formação ferrífera com metachert e barita maciça; e um superior de filito carbonoso com eventuais lentes de metachert. Os metarenitos impuros, por seu turno, são propostos sob a denominação de Formação Mata Preta, a qual está lateralmente interdigitada com as rochas da Formação Cabaçal. Dados geocronológicos U-Pb obtidos por LA-ICP-MS em cristais detríticos de zircão dos turbiditos máficos da Formação São Patricinho e dos metarenitos da Formação Mata Preta indicam área fonte dominada por rochas do Sideriano e Riaciano, com parcial participação de fonte Arqueana. A natureza dos litotipos das formações Cabaçal e Mata Preta e as relações de contato entre ambas sugerem que o estágio de bacia que representam evoluiu a partir de importante evento anóxico oceânico mundial de 2,2 a 2,06 Ga e responsável pela Formação Cabaçal. O ambiente euxênico foi contemporâneo com um arco magmático que atuou como fonte da carga clástica dos arenitos da Formação Mata Preta.The Guarinos greenstone belt is one of the three low metamorphic grade supracrustal rocks assemblage rimmed by orthogneisses of Central Brazil's Archean Block northern limits. The investigation of the stratigraphy of those greenstone belts started by the end of 1970's and underwent improvements during the years as a result of detailed geological mapping. The latest and accepted stratigraphic model for the Guarinos greenstone belt refers its supracrustal rocks under the Guarinos Group, which is subdivided into the Serra do Cotovelo (metakomatiites), Serra Azul (metabasalts), São Patricinho (mafic metaturbidites), Aimbé (BIF) and Cabaçal (carbonaceous phyllites and impure metarenites) formations. Detailed geologic mapping (1:10,000) and drill-cores during an exploration program by Yamana Desenvolvimento Mineral S.A. in the area allowed a better definition of the metasedimentary package of the Cabaçal Formation, which is here formally proposed to be subdivided into a Lower Member of carbonaceous phyllites with basalt lava flows and gondite lenses interlayers, an Intermediate Member of gondite, iron formation, metachert and massive barite lenses, and an Upper Member of carbonaceous phyllites with minor metachert lenses. The impure metarenites, formerly considered as part of the Cabaçal Formation, are proposed under the Mata Preta Formation, which is laterally interfingered with the Cabaçal Formation. U-Pb LA-ICP-MS geochronological data of detrital zircon grains from the São Patricinho mafic metaturbidites and the impure metarenites of the Mata Preta formations indicate that the major source-area of the clastic load had a Siderian to Rhyacian age, with minor contribution from Archean rocks. From the rock assemblage of both units and their contact relationships it is concluded that the basin stage they represent evolved during the world-wide Anoxic Oceanic Event (AOE) that took place during the 2.2 to 2.06 Ga, represented by the carbonaceous phyllites of the Cabaçal Formation, coeval with the erosion of a magmatic arc that derived the immature clastic load of the Mata Preta Formation

Caracterização da Alteração Hidrotermal Micácea do Tipo Greisen e dos Reequilíbrios de Baixa Temperatura em Áreas Graníticas: o Exemplo do Distrito Estanífero de Encruzilhada do Sul, RS

The hydrothermal alteration associated with the tin mineralization in the Encruzilhada do Sul Tin District is characterized by zones with different compositions. The most important of these hydrothermal zones are the phyllic and the argillic. The first one is composed mainly by white mica and quartz with tourmaline. The argillic alteration is composed by kaolinite. The phyllic zones represent associations with greisens and disseminated pervasive white mica on the granitic wall rocks. The argillic zones are constrained to the top zones of some granitic intrusions associated with greisens and quartz-veins in the stockworks. The hydrothermal fluids associated with the alteration show homogenization temperatures ranging from about 450˚C to 120˚C. The first temperature is the upper limit for the hydrothermal system, related with the white mica high temperature alteration. The second temperature is the lower limit of the argillic alteration under the hydrothermal conditions. The white mica related with the phyllic alteration range from phengite to muscovite. The argillic alteration has the presence of halloysite, probably as a weathering product.The hydrothermal alteration associated with the tin mineralization in the Encruzilhada do Sul Tin District is characterized by zones with different compositions. The most important of these hydrothermal zones are the phyllic and the argillic. The first one is composed mainly by white mica and quartz with tourmaline. The argillic alteration is composed by kaolinite. The phyllic zones represent associations with greisens and disseminated pervasive white mica on the granitic wall rocks. The argillic zones are constrained to the top zones of some granitic intrusions associated with greisens and quartz-veins in the stockworks. The hydrothermal fluids associated with the alteration show homogenization temperatures ranging from about 450˚C to 120˚C. The first temperature is the upper limit for the hydrothermal system, related with the white mica high temperature alteration. The second temperature is the lower limit of the argillic alteration under the hydrothermal conditions. The white mica related with the phyllic alteration range from phengite to muscovite. The argillic alteration has the presence of halloysite, probably as a weathering product

RAPAKIVI MAGMATISM IN THE MIDDLE INIRIDA BASIN, GUAINÍA DEPARMENT, COLOMBIA

In eastern Colombia, the crystalline basement is intruded by several anorogenic granites of Mesoproterozoic age. One of these anorogenic granitic intrusions outcrops in the area of the indigenous Matraca and Danta communities, at the middle Inirida River Basin, and is mostly covered by Tertiary sedimentary rocks and Quaternary deposits. Petrographic and geochemical analyses reveal them as holocrystalline, leucocratic, and coarse-grained monzonite to granodiorite with Pyterlite-type rapakivi texture indicating anorogenic affinity. We named this plutonic body informally as Matraca rapakivi granite, which was initially correlated with the Parguazan Event (conventional method in zircons, 1550 Ma) described in Venezuela. However, LA-ICP-MS U/Pb zircon dating yields a concordant zircon enclosure age of 1343 ± 8 Ma for the magma crystallization, in other words a 100-200 Ma younger magmatism, but also shows a coincidence with our ages of the Parguaza Granite in Colombia (LA-ICP-MS U/Pb zircon, 1390-1400 Ma). These ages suggest episodic intrusions of A-type granites between 1300-1400 Ma, associated with Nb, Ta, REE and Sn mineralizations.Durante el Mesoproterozoico varios granitos rapakivi intruyeron el basamento cristalino en el oriente colombiano aflorando en varios sitios como en las comunidades indígenas de Danta y Matraca, en la cuenca media del río Inírida en el departamento de Guainía, donde están cubiertos con rocas sedimentarias del Terciario y depósitos cuaternarios. Análisis petrográficos y geoquímicos revelan que se trata de un cuerpo porfirítico, holocristalino, leucocrático, grosogranular y de composición monzonítica a granodiorítica con textura rapakivi tipo piterlita, indicando afinidad anorogénica. Hemos designado informalmente este cuerpo plutónico como granito rapakivi de Matraca e inicialmente fue asociado con el gran Evento Parguenze descrito en Venezuela (método convencional U/Pb en circones, 1.550 Ma). Sin embargo, las recientes dataciones U/Pb en circones con LA-ICP-MS establecen una edad concordante de 1.343 ± 8 Ma para su cristalización que marca un magmatismo de 100-200 Ma más joven, pero que a su vez representa mayor concordancia con las recientes edades mediante el mismo método para el Granito de Parguaza en Colombia de 1.390-1.400 Ma, lo cual nos permite suponer intrusiones episódicas de granitos tipo “A” emplazados entre 1.300-1.400 Ma y parcialmente enriquecidos en mineralizaciones de Nb, Ta, REE y Sn

PETROGRAFÍA, GEOQUÍMICA Y GEOCRONOLOGÍA DEL GRANITO DE PARGUAZA EN COLOMBIA

El Granito de Parguaza aflora en el departamento de Vichada-(Colombia), hacia la margen del río Orinoco y es parte del gran batolito descrito en Venezuela como Granito del Parguaza. Este cuerpo en Colombia aflora como cerros aislados tipo inselberg y serranías de poca extensión con pendientes abruptas que sobresalen entre las extensas llanuras terciarias. Representa uno de los granitos anorogénicos aflorantes más grandes del mundo y puede ser distinguido como una de las unidades colombianas más antiguas (Mesoproterozoico) que no han sufrido deformación. Se caracteriza por presentar textura rapakivi tipo wiborgita y piterlita, su composición es granítica a granítica de feldespato alcalino. Además de las variaciones composicionales y texturales, se encuentran zonas de grano fino, diques pegmatíticos, aplíticos y venas de cuarzo. Geoquímicamente se clasifica como un granito tipo A, metaluminoso a peralcalino, formado en ambiente post-colisional a anorogénico. Nuevas mediciones de U/Pb con LA-ICP-MS en circones indican nuevas edades concordantes de 1.392 ± 5 Ma y 1.402 ± 2 Ma para las partes más distales, respectivamente, mucho más jóvenes que edades propuestas anteriormente en territorio venezolano 1.545 Ma, lo cual puede ser interpretado como un intrusivo más complejo o como procesos de cristalización muy lentos de núcleo a borde. Por otro lado, estas edades son correlacionadas con granitos anorogénicos similares en el W del Cratón Amazónico en Brasil y con otros afloramientos rapakivi estudiados en el departamento de Guainía al SE de Colombia.  The Parguaza Granite outcrops in the Vichada department of Colombia, towards the Orinoco River margin, where it conforms a portion of the large batholith described in Venezuela as Granito de El Parguaza. This intrusion outcrops in Colombia as isolated inselberg hills and moderately extended mountain chains with abrupt slopes that protrude through Tertiary plains. It represents one of largest anorogenic granites worldwide and is one of the oldest colombian units (Mesoproterozoic) without tectonic deformation. The granite exhibits both typical Wiborgite and Pyterlite rapakivi texture, with a monzogranitic to alkali feldspar granitic composition. Among the compositional and textural variations, we find fine-grain zones, pegmatitic and aplitic dikes as well as quartz veins. Geochemically, it conforms a metaluminous to peralkaline A-type granite, intruded under post-collisional to rifting anorogenic conditions. New U/Pb measurements with LA-ICP-MS in zircons show hither to unknown concordant ages of 1392 ± 5 My to 1402 ± 2 My, respectively in the more distal zones; much younger than 1545 My ages reported in Venezuela, which may be explained or by a more complex intrusion and crystallization history or by a very slow crystallization process from the core to the edge; on the other hand, these ages are in concordance to similar anorogenic granites from the W Amazonian Craton in Brazil and with other rapakivi outcrops studied in the Guainía Department in the south-east of Colombia. &nbsp

PETROGRAFÍA, GEOQUÍMICA Y GEOCRONOLOGÍA DEL GRANITO DE PARGUAZA EN COLOMBIA

El Granito de Parguaza aflora en el departamento de Vichada-(Colombia), hacia la margen del río Orinoco y es parte del gran batolito descrito en Venezuela como Granito del Parguaza. Este cuerpo en Colombia aflora como cerros aislados tipo inselberg y serranías de poca extensión con pendientes abruptas que sobresalen entre las extensas llanuras terciarias. Representa uno de los granitos anorogénicos aflorantes más grandes del mundo y puede ser distinguido como una de las unidades colombianas más antiguas (Mesoproterozoico) que no han sufrido deformación. Se caracteriza por presentar textura rapakivi tipo wiborgita y piterlita, su composición es granítica a granítica de feldespato alcalino. Además de las variaciones composicionales y texturales, se encuentran zonas de grano fino, diques pegmatíticos, aplíticos y venas de cuarzo. Geoquímicamente se clasifica como un granito tipo A, metaluminoso a peralcalino, formado en ambiente post-colisional a anorogénico. Nuevas mediciones de U/Pb con LA-ICP-MS en circones indican nuevas edades concordantes de 1.392 ± 5 Ma y 1.402 ± 2 Ma para las partes más distales, respectivamente, mucho más jóvenes que edades propuestas anteriormente en territorio venezolano 1.545 Ma, lo cual puede ser interpretado como un intrusivo más complejo o como procesos de cristalización muy lentos de núcleo a borde. Por otro lado, estas edades son correlacionadas con granitos anorogénicos similares en el W del Cratón Amazónico en Brasil y con otros afloramientos rapakivi estudiados en el departamento de Guainía al SE de Colombia.  The Parguaza Granite outcrops in the Vichada department of Colombia, towards the Orinoco River margin, where it conforms a portion of the large batholith described in Venezuela as Granito de El Parguaza. This intrusion outcrops in Colombia as isolated inselberg hills and moderately extended mountain chains with abrupt slopes that protrude through Tertiary plains. It represents one of largest anorogenic granites worldwide and is one of the oldest colombian units (Mesoproterozoic) without tectonic deformation. The granite exhibits both typical Wiborgite and Pyterlite rapakivi texture, with a monzogranitic to alkali feldspar granitic composition. Among the compositional and textural variations, we find fine-grain zones, pegmatitic and aplitic dikes as well as quartz veins. Geochemically, it conforms a metaluminous to peralkaline A-type granite, intruded under post-collisional to rifting anorogenic conditions. New U/Pb measurements with LA-ICP-MS in zircons show hither to unknown concordant ages of 1392 ± 5 My to 1402 ± 2 My, respectively in the more distal zones; much younger than 1545 My ages reported in Venezuela, which may be explained or by a more complex intrusion and crystallization history or by a very slow crystallization process from the core to the edge; on the other hand, these ages are in concordance to similar anorogenic granites from the W Amazonian Craton in Brazil and with other rapakivi outcrops studied in the Guainía Department in the south-east of Colombia. &nbsp

Caracterização geoquímica e isotópica das diferentes seqüências metavulcânicas da suíte metamórfica Porongos

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