U-Pb LA-ICP-MS GEOCHRONOLOGY
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Boletín de Geología Vol. 32, N° 2, julio-diciembre de 2010 U-Pb LA-ICP-MS GEOCHRONOLOGY AND REGIONAL CORRELATION OF MIDDLE JURASSIC INTRUSIVE ROCKS FROM THE GARZON MASSIF, UPPER MAGDALENA VALLEY AND CENTRAL CORDILLERA, SOUTHERN COLOMBIA Camilo Bustamante1, Agustín Cardona1, Germán Bayona2, Andrés Mora3, Víctor Valencia4, George Gehrels5, Jeff Vervoort6 ABSTRACT New U-Pb zircon geochronology from four granitic units sampled along a southeast-northwest transect between the Garzón Massif and the Serranía de las Minas (Central Cordillera), records a Middle Jurassic magmatic activity with two different spatio-temporal domains at ca. 189 Ma and 180-173 Ma. Reconnaissance data suggest that the four granitoids are characterized by mineralogical and geochemical characteristics akin to a continental magmatic arc setting. The new results suggest that the southern Colombian continental margin includes remnants of tectono- magmatic elements formed by the subduction of the Farallon plate under the South American continental margin. This Middle Jurassic arc magmatism is part of the broader Andean scale arc province, and is significant for understanding the tectonic and paleogeographic scenario that characterized the Mesozoic tectonic evolution of the Northern Andes. Key words: U-Pb geochronology, Colombia, Jurassic, Intrusive rocks, Garzón Massif, Central Cordillera. GEOCRONOLOGÍA U-Pb LA-ICP-MS Y CORRELACIÓN REGIONAL DE LAS ROCAS INTRUSIVAS DEL JURÁSICO MEDIO DEL MACIZO DE GARZÓN, VALLE SUPERIOR DEL MAGDALENA Y LA CORDILLERA CENTRAL, SUR DE COLOMBIA RESUMEN Se presentan nuevas edades U-Pb en circones de cuatro unidades graníticas muestreadas a lo largo de una transecta SE-NW entre el Macizo de Garzón y la Serranía de las Minas (Cordillera Central), las cuales registran una actividad magmática en el Jurásico Medio en dos dominios espaciales y temporales diferentes: 189 Ma y 180 a 173 Ma. Estos cuatro granitoides tiene características mineralógicas y geoquímicas afines con un ambiente de arco magmático continental. Los nuevos resultados sugieren que la margen continental al sur de Colombia incluye remanentes de elementos tectono-magmáticos formados por la subducción de la placa Farallón bajo la margen continental suramericana. Este magmatismo de arco del Jurásico medio es parte de la provincia de arco que se presenta a lo largo de los Andes, y es importante para el entendimiento de la dinámica tectónica y la paleogeografía que caracterizó el Mesozoico de los Andes del Norte. Palabras clave: Geocronología U-Pb, Colombia, Jurásico, Rocas intrusivas, Macizo de Garzón, Cordillera Central. 1 Smithsonian Tropical Research Institute, Panamá, Panamá. [email protected], [email protected]; Cll 32D # 76-40 - Apto 402, Medellin, Colombia 2 Corporación Geológica Ares, Bogotá, Colombia. [email protected] 3 Instituto Colombiano del Petróleo-ECOPETROL, Piedecuesta, Colombia. [email protected] 4 Valencia Geoservices, Tucson AZ, USA. [email protected] 5 University of Arizona, Department of Geosciences, Tucson AZ, USA. [email protected] 6 Washington State University, School of Earth and Environmental Sciences, Pullman WA, USA. [email protected] 93 U-Pb LA-ICP-MS geochronology and regional correlation of Middle Jurassic intrusive rocks from the garzon massif, upper Magdalena Valley and Central Cordillera, Southern Colombia. INTRODUCTION GEOLOGICAL SETTING Early to Late Mesozoic tectonic evolution of the western The Colombian Andes consist of three mountain ranges margin of South America is related to successions of (Figure 1) built as a result of Paleozoic and Meso- different tectonic regimes that recorded the initial effects Cenozoic phases of terrane relate accretion interspersed of Pangea break-up, Pacific subduction, and in northern several periods of continuous subduction (Restrepo and South America the formation of the proto-Caribbean Toussaint, 1988; Toussaint, 1995; Cediel et al., 2003; ocean (Pindell, 1985; Jaillard et al., 1990; Toussaint, Pindell et al., 2005; Ordoñez et al., 2006). 1995; Ramos and Aleman, 2000; Ramos, 2009; 2010; Pindell and Keenan, 2010). The Western Cordillera includes volcanic rocks with intercalated marine sediments of Cretaceous age These events are responsible for overimposed tectonic formed in an oceanic plateau environment (reviews in scenarios of passive margin, rift and/or arc setting in the Kerr et al., 1997), whose accretion took place during Colombian Andes, and potential along strike and lateral the Late Cretaceous, linked to the advance of the segmentation of the different geological environments allocthonous Caribbean Plate (Toussaint, 1996; Kerr (Aspden et al., 1987; Toussaint, 1995; Ramos and and Tarney, 2005; Pindell et al., 2005). The Central Aleman, 2000; Cediel et al., 2003; Sarmiento-Rojas et Cordillera comprises a pre–Mesozoic polymetamorphic al., 2006; Vásquez et al., 2010). basement intruded by several Meso-Cenozoic plutonic rocks (Toussaint, 1993; Ordóñez-Carmona et al., 2006; Additional complexities include along strike translation Vinasco et al., 2006). Its major tectonic record reflect and juxtaposition of a variety of Mesozoic continental several collisional and subduction events between 290- magmatic related fragments (Bayona et al., 2006; 2010), 230 Ma link to the agglutination of Pangea (Ordóñez- that seems to be linked to the existence of an oblique Carmona and Pimentel, 2002; Vinasco et al., 2006; subduction configuration with the Colombian margin Cardona et al., 2010). Albian to Aptian rocks are as the final stop for the redistribution of continental discontinuously and limited exposed (Toussaint, 1996). para-authocthonous type terranes (Jaillard et al., 1990; Restrepo and Toussaint, 1988; Toussaint, 1993; Bayona Finally, the Eastern Cordillera includes Precambrian and et al., 2006; 2010; Keenan and Pindell, 2010). Paleozoic metamorphic rocks, with overlain deformed Paleozoic sediments (Toussaint, 1993; Restrepo-Pace In this contribution we present new U-Pb LA-ICP-MS zircon et al., 1997; Cediel et al., 2003; Cordani et al., 2005; geochronology and reconnaissance geochemistry from four Ordóñez-Carmona et al., 2006). Meso-Cenozoic plutonic bodies sampled along an east-west transect between sedimentary marine and continental successions are the Garzón Massif and the westernmost limit of the Upper registered within this cordillera, and record the changing Magdalena Valley in order to establish more precise time tectonic conditions from passive to active margin that constrains on the Jurassic plutonism in Southern Colombia end in the Andean orogeny (reviews in Cediel et al., and contribute to the discussion of its tectonic scenario. 2003; Mora et al., 2006; Bayona et al., 2008). Geochronological data for these rocks has not been published so far, and their precise interpretation has been JURASSIC MAGMATISM built on lithological correlations and geochronological data from plutonic rocks at the northern extension of Jurassic volcanic and plutonic rocks are widespread this batholiths, which have shown mainly cooling ages along the Colombian Andes (Figure 1), and can be that varies between ca. 177-136 Ma (Vesga and Barrero, related to a broader magmatic province that affect the 1978; Sillitoe et al., 1982; Brook, 1984; Aspden et al., entire western margin of South America (Aspden et al., 1987; Altenberger and Concha, 2005). 1987; Lucassen, et al., 1996; Noble, et al., 1997; Jaillard et al., 2000; Kramer et al., 2005; Oliveros et al., 2006; Therefore, the precise timing and tectonic implication 2007; Mpodozis and Ramos, 2008). of this Jurassic plutons provide insights on the Middle Jurassic tectonomagmatic regime of northwestern South Magmatic activity is recorded by an extensive series of American and serve as piercing point for understanding elongated batholithic bodies distributed along the eastern the variable Middle Mesozoic tectonic events (Ramos margin of the Central Cordillera, the margins of the Upper and Aleman; 2000; Sarmiento-Rojas et al., 2006; Magdalena Valley and the Garzón and Santander Massifs. Bayona et al., 2006, 2010; Vásquez et al., 2010). Similar elements are also found within several more isolated 94 Camilo Bustamante, Agustín Cardona, Germán Bayona, Andrés Mora, Víctor Valencia, George Gehrels, Jeff Vervoort massifs in northern Colombian, including the San Lucas and Dewey, 1982; Maze, 1984; McCourt et al., 1984; Serrania and the Caribbean massifs such as the Sierra Nevada Aspden et al., 1987; Ross and Scotese, 1988; Pindell de Santa Marta, Perijá and Guajira Serranias (Aspden et al., and Erikson, 1993; Bayona et al., 1994; Toussaint 1995; 1987; Alvarez, 1967; Tschanz et al., 1974; Toussaint, 1995 and Pindell and Tabutt, 1995; Meschede and Frisch, 1998; references therein). Available geochronological data mostly Cediel et al., 2003; Vásquez et al., 2006). However due obtained by the K-Ar method reveals the existence of at least to the changing nature of the Mesozoic tectonic regimes three major magmatic peaks of magmatic activity between c.a. in northern South America (reviews in Toussiant, 195-180 Ma, 167-160 Ma and 151-142 Ma (review in Aspden 1995; Pindell and Keenan, 2010; Ramos, 2010), the et al., 1987). Most of these rocks are spatially associated with apparent existence of significantly displaced crustal volcanic rocks of effusive and explosive character, which segments (Bayona et al., 2006; 2010) and the paucity of suggest a shallow level of emplacement and a protracted geochronological and geochemical data, a distinction on tectono-magmatic