O Magmatismo Granítico da Região Oriental do Escudo Sul-rio-grandense. Uma Revisão

A porção oriental do Escudo Sul-rio-grandense é constituída por rochas granitoides que têm sido agrupadas em três fases segundo sua relação com os dois principais eventos tectônicos registrados na área. O primeiro é marcado por folheações de baixo ângulo, com transporte segundo EW e metamorfismo de fácies anfibolito. Sua idade é supostamente brasiliana e é acompanhada por um magmatismo cálcico-alcalino onde predominam composições tonalíticas-granodioríticas, incluindo ainda trondhjemitos e granitos. O segundo evento tectônico é marcado pelo desenvolvimento de zonas de cisalhamento transcorrente de direção e transporte SW-NE. O magmatismo associado é constituído principalmente por rochas graníticas cálcico-alcalinas e granitoides peraluminosos produzidos por fusão crustal. Uma fase final de magmatismo granítico registra apenas reativações da tectônica transcorrente, ou evidências de uma tectônica trativa, e é composta por granitos muito diferenciados de afinidade cálcico-alcalina que evoluem para granitos alcalinos de caráter pós-orogênico. A evolução litoquímica do magmatismo granítico sugere sua associação com a evolução de um arco magmático desenvolvido sobre margem continental em um contexto tectônico similar, por exemplo, ao do botólito de Sierra Nevada. A diferenciação do magmatismo, possivelmente de derivação mantélica, foi dominada por mecanismos de fracionamento mineral e contaminação por líquidos ou rochas crustais. A presença de depósitos minerais e intenso hidrotermalismo sugerem uma considerável potencialidade do ponto de vista metalogênico

Litoquímica e Evolução de Granitóides Cálcio-alcalinos da Região Leste do Escudo Sul-rio-grandense

O magmatismo granítico Brasiliano foi estudado do ponto de vista geoquímico e petrogenético, em uma porção da região leste do Escudo Sul-rio-grandense. Com base em critérios estruturais estes granitoides foram agrupados em três fases distintas. A Fase 1 é sintectônica com o evento compressivo regional de maior intensidade e mostra metamorfismo de fácies anfibolito. É composta por rochas dominantemente granodioríticas com hornblenda e biotita, contendo enclaves de tonalitos e trondhjemitos. Na Fase 2 dominam os biotita monzogranitos afetados principalmente por zonas de cisalhamento restritas e por metamorfismo de fácies xistos verdes. A Fase 3, tardia pós-cinemática com relação ao evento gerador das zonas de cisalhamento restritas, é constituída predominantemente por biotita granitos equigranulares, observando-se uma evolução para termos com mineralogia indicativa de afinidade alcalina. Os dados químicos indicam para a maior parte dos granitoides estudados uma afinidade com a série cálcio-alcalina médio a alto potássio, comparável ao magmatismo do batólito de Sierra Nevada, EUA. Os teores relativamente elevados de Ba, Sr e ETR leves são sugestivos de magmatismo em margem continental espessa. Os termos mais altamente diferenciados, principalmente da Fase 3, apresentam tendência alcalina, relacionando-se com a fase pós-orogênica. De modo geral, a evolução magmática destas fases pode ser explicada pelo fracionamento de assembleias dominadas por plagioclásio, hornblenda ou clinopiroxênio, óxidos de ferro e titânio, e apatita, além de biotita e feldspato alcalino, que tornam-se dominantes na Fase 3. Os dados radiométricos existentes permitem correlacionar esta granitogênese com a descrita no Cinturão Damara, no sudoeste africano

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

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

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

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

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

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 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