. 2016. Magmatismo rapakivi en la cuenca media del río Inírida, departamento de Guainía, Colombia. Boletín de Geología, 38 (1): 17-32.
RESUMENDurante 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.
55Petrografía, geoquímica y geocronología U/Pb en circones de rocas ígneas y metamórficas a lo largo del Río Cuiarí en el sur del Departamento de Guainía, Colombia . (2019). Petrografía, geoquímica y geocronología U/Pb en circones de rocas ígneas y metamórficas a lo largo del Río Cuiarí en el sur del Departamento de Guainía, Colombia.
Petrography, geochemistry and zircon U/Pb geochronology in igneous and metamorphic rocks, Cuiarí River, south of Guainía department, Colombia
ABSTRACTIn order to archive a better understanding of the Rio Negro-Juruena Geochronological Province (1.55-1.8 Ga) of the Amazonian Craton in SE-Colombia, we performed analyses of metamorphic, igneous and metasedimentary rocks outcropping in vicinity of the Cuiarí-River in the south of Guainía Department, near the Brazilian border. Based on field observations, mineralogical, geochemical and U/Pb LA-ICP-MS analysis in zircons, we could identify in the study area a Statherian basement which forms the Mitú Complex. It is composed by Petrografía, geoquímica y geocronología U/Pb en circones de rocas ígneas y metamórficas a lo largo del Río Cuiarí en el sur del Departamento de Guainía, Colombia
The 1.80-1.76 Ga crystalline basement in Colombia as part of the W-Amazonian Craton is composed mainly of gneisses, granitoids and migmatites, affected later by several compressive and extensional events resulting for example in A-type granites, but also mafic intrusions and dikes. Here we present, after a revision of main geological features, research results obtained on the NW-SE trending ilmenite-apatite-rich Caño Viejita gabbro in the SW-Vichada department some 500 km east of Bogota. Petrographic and geochemical data hint to a metaluminous continental alkaline gabbro enriched in K, Ti and P, possibly due to continental crust reworking or magma mixing, as also confirmed by trace elements characteristics in the apatites like HREE enrichment (Ce/Yb)cn 12-13, negative Eu-anomaly, and Y, Th, Sr, Mn ratios. LA-ICP-MS U-Pb apatite geochronology suggests an early Neoproterozoic emplacement age between 975±9 and 1002±21 Ma related with rifting triggered by the Amazonia-Baltica-Laurentia collision during the Rodinia Supercontinent assembly and associated Grenvillian events. These events also caused mafic intrusions in other parts of the craton. Apatite fission track thermochronometry and thermal history modelling on one sample suggest the onset of the final exhumation stage during Jurassic (~180 Ma), which brought the rocks slowly to their current outcrop position.
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