Vulcanismo De Afinidad Adaquítica en El Miembro Inferior De La Formación Combia (Mioceno Tardío) Al Sur De La Subcuenca De Amaga, Noroccidente De Colombia

Abstract

RESUMENEn este trabajo se presenta la química de los depósitos volcaniclásticos del Miembro Inferior de la Formación Combia y los cuerpos sub-volcánicos que la intruyen, aflorantes en la parte sur de la subcuenca de Amagá, en el valle interandino del río Cauca, Colombia. Corresponden a una suite andesítica-dacítica calcoalcalina de medio K con contenido de SiO 2 entre 59,04 y 62,86%, y solo una muestra corresponde a un basalto toleítico (SiO 2 =50,6%). Las muestras se identifican por tener altas proporciones de LILE/HFSE, Ba/LREE, Sr/Nd, y empobrecimiento relativo en Nb y Ta, típicas de magmas de una zona de subducción. El diagrama multielemental de tierras raras indica que dos muestras tienen relaciones diferentes de MREE/HREE (Gd/Yb) >3,9 y de LREE/HREE (La/Yb) > 19,7 que las separa del resto de las muestras. La mayoría de las muestras presentan firmas adaquíticas caracterizadas por: Nd/ 144 Nd= 0,512849 -0,512907, los cuales sugieren una fuente manto derivada, previamente metasomatizada con fluidos del slab, sin descartar la fusión parcial de la misma, con generación de los magmas adaquíticos en niveles profundos de la corteza. Las rocas y depósitos aquí descritos corresponden a un segmento del arco magmático calcoalcalino de edad Mioceno que se extiende en el norte de los Andes. En el Miembro Inferior de La Formación Combia, en el sur de la subcuenca de Amagá, se debería incluir los cuerpos sub-volcánicos que la intruyen como una suite de afinidad adaquítica.Palabras clave: Formación Combia, magmatismo de arco, adaquitas, manto derivado, noroeste de Colombia ADAKITE-LIKE SIGNATURE IN THE LOWER MEMBER OF THE COMBIA FORMATION (LATE MIOCENE) AT THE SOUTHERN OF AMAGÁ SUB-BASIN,NORTHWEST COLOMBIA ABSTRACTIn this study, we report chemistry of samples of the volcaniclastic deposits from the Lower Member of the Combia Formation and the intruding sub-volcanic bodies. These rocks are located at the southern of Amagá sub-basin of the Cauca River, Colombia. Most of the samples correspond to a medium-K calc-alkaline andesitic-dacitic suite (SiO 2 =59, 04 -62,86 wt. %), and only one is a toleiitic basalt SiO 2 =50,6 wt%. The samples have high LILE/HFSE, Ba/LREE, Sr/ Nd ratios and Nb and Ta relative depletion, typical of magmas in a subduction system. The REE patterns show that two samples have high MREE/HREE and LREE/HREE ratios (Gd/Yb >3,9 and La/Yb > 19,7) in comparison with the rest of the samples. Nd= 0,512849 -0,512907 are indicative of melts from a mantle-derived source, although an interaction with slab melts is not discarded, and the adakitic magmas were generated at the base of the crust. The volcanic sequence described in this study is a segment of the Miocene magmatic arc extending along the northern Andes. According to our results, in the Lower Member of the Combia Formation, at the southernmost Amagá sub-basin sector, it must be included the intruding subvolcanic bodies as an adakitic suite.

Chapter 12

“…Additional geochemical research on the CSVI on the lower volcanic rocks from the Cauca and Amagá regions (Borrero & Toro-Toro, 2016) shows that adakitic signature magmas could be related to melts originated in a previously metasomatized mantle located in a subduction zone.…”

“…4º N) (Figure 3) are considered a continuous magmatic belt in the northern part of the Western Cordillera with an extension of ca. 100 km (Álvarez, 1983;Borrero & Toro-Toro, 2016;Leal-Mejía, 2011). The CSVIs are commonly distinguishable in the field due to their positive relief from the sedimentary country rocks (AF and CF) and the Romeral mélange (Cediel et al, 2003).…”

“…Although some authors have considered that the volcaniclastic sequence of the CF and CSVI may correspond to the same magmatic event (Borrero & Toro-Toro, 2016;Grosse, 1926;Jaramillo et al, 2019;Leal-Mejía, 2011), there is no agreement as to whether both the Amagá Basin-CSVI and Cauca River-CSVI were formed from the same magmatism (Borrero & Toro-Toro, 2016;Leal-Mejía, 2011).…”

“…The present work represents an effort to synthesize an essential amount of petrography, field relationships, mineral chemistry, geochronological, and geochemical data previously reported associated with volcanic, volcaniclastic, hypabyssal, porphyritic magmatism and sedimentary rocks of the Combia Formation found along the Cauca River valley. The authors here combine unpublished petrography, mineral chemistry, geochronological, and geochemical data with previous data available from Jaramillo (1976), Álvarez (1983), Marriner & Millward (1984), Ordóñez-Carmona (2001), Dunia (2005), Tejada et al (2007), Tassinari et al, (2008), Leal-Mejia (2011), Borrero & Toro-Toro (2016, Bissig et al (2017), Jaramillo et al (2019), and Bernet et al (2020) to better understand this unique geological occurrence in Colombia.…”

“…The CF mainly comprises basic tholeiitic magmas, linked to crustal thinning and basin extension (Bernet et al, 2020;Dunia, 2005;Jaramillo, 1976;Jaramillo et al, 2019). Furthermore, calc-alkaline, andesitic to dacitic, shallow, volcanic porphyries of the Cauca Shallow Volcanic Intrusions (CSVI) are spatially associated with the CF, even though some authors define them as a single, separate unit (e.g., Borrero & Toro-Toro, 2016;Tassinari et al, 2008). Moreover, the cartographic resolution of the volcanic products recorded in the CF does not record individual event levels.…”