Joan Carles Melgarejo Draper

U-Pb geochronology on zircon and columbite-group minerals of the Cap de Creus pegmatites, NE Spain

The Cap de Creus granitic pegmatites in the eastern Catalan Pyrenees were dated using in situ U-Pb geochronology by laser ablation ICP-MS on zircon and columbite-group minerals (CGM), which are present in the different types of pegmatites from type I (K-feldspar pegmatites, least evolved) to type IV (albite pegmatites, most evolved) and therefore allow dating the different pegmatitic pulses. In a type III pegmatite where zircon and CGM are co-genetically associated in the same sample, both minerals were dated using zircon and tantalite reference materials, respectively, to avoid laser-induced matrix-dependent fractionation. In one sample, xenotime genetically associated with zircon was also dated. Two ages were obtained for type I and three ages for type III pegmatites. Three of these 5 ages range from 296.2xa0±xa02.5 to 301.9xa0±xa03.8xa0Ma and are allocated to the primary magmatic stage of crystallization and therefore to the emplacement event. Two younger ages (290.5xa0±xa02.5 and 292.9xa0±xa02.9xa0Ma) obtained on secondary zircon and xenotime, respectively, are interpreted as late post-solidus hydrothermal remobilization. There is no age difference between type I and type III pegmatites. The mean 299xa0Ma primary magmatic age allows the main late Carboniferous deformation event to be dated and is also synchronous with other peraluminous and calc-alkaline granites in the Pyrenees. However, the youngest ages around 292xa0Ma imply that tectonics was still active in Early Permian times in the Cap de Creus area.

Phanerozoic Metallogeny in the Colombian Andes: A Tectono-magmatic Analysis in Space and Time

The Colombian Andes are a highly fertile although little documented metallogenic province. Time-space analysis has identified numerous metallotects containing a wide variety of mineral deposits, framed within five broad metallogenic epochs, defined by important changes in the Phanerozoic tectonic and magmatic evolution of the region. Mineral deposits of both syngenetic and epigenetic origins range from the products of orthomagmatic cumulate segregation and those related to hydrothermal processes associated with oceanic and continental rifting and subduction-related volcanism/magmatism to accumulations related to uplift, basin development, chemical sedimentation and the amagmatic migration of mineral-rich brines. Important secondary and residual deposits are related to the complex weathering and erosion history of the Northern Andean region. Significant deposits and mineral districts were formed in the peri-cratonic or intra-oceanic realm and are allochthonous to the Colombian cordilleras, a result of the complex Meso-Cenozoic accretionary history of the region. Numerous metal deposits and mineral districts are described in detail, and the sympathetic relationship between metal occurrences in the Colombian Andes and the tectonic development of the region as a whole is demonstrated.

Spatial-Temporal Migration of Granitoid Magmatism and the Phanerozoic Tectono-Magmatic Evolution of the Colombian Andes

Plutonic and hypabyssal porphyritic granitoids (and their volcanic equivalents) are important constituents of the composite geological record of the Colombian Andes, not only from a volumetric standpoint but more so as products of the complex Phanerozoic tectono-magmatic evolution of the region. Based upon U-Pb (zircon) age data circa 1995–2017, six principle periods of Phanerozoic granitoid magmatism have been identified, including early Paleozoic (ca. 485–439 Ma), Carboniferous (ca. 333–310 Ma), Permo-Triassic (ca. 289–225 Ma), latest Triassic-Jurassic (ca. 210–146 Ma), late Cretaceous to Eocene (ca. 100–42 Ma) and latest Oligocene to Mio-Pliocene (ca. 23–1.2 Ma). Mio-Pliocene granitoids of this last period, located within the physiographic Central Cordillera, are essentially coaxial with the Pleistocene to Recent Colombian (Northern Andean) volcanic arc. Major, trace and REE lithogeochemical data for Colombian granitoids are interpreted to reflect mantle vs. crustal magma source regions and variations in petrogenetic processes, including magmatic differentiation, partial melting, crustal anatexis/assimilation and magma mixing. Supported by Sr-Nd, Pb and Hf isotope analyses and regional geological and geophysical constraints, the lithogeochemical and isotopic compositions of Colombian granitoids are interpreted within the wide range of settings which characterize Phanerozoic tectonic evolution of the Northern Andean region. Mantle- and crustal-derived granitoids associated with subduction-related arcs, collision-type orogeny and post-orogenic collapse, regional taphrogenesis, back-arc extension, oceanic rifting and crustal anatexis related to slab delamination, asthenospheric upwelling and crustal underplating are all potentially represented. The analytical resolution of combined U-Pb (zircon), lithogeochemical and isotope data permits a detailed analysis of the temporal vs. spatial migration and petrogenetic variation of granitoid magmatism during the Phanerozoic. Major granitoid suites have herein been integrated into pre-Northern Andean, proto-Northern Andean and Northern Andean orogenic phases of Colombian tectonic evolution.