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Andean orogenic processes controlled the spatial and temporal distribution of the magmatic and sedimentary record. This contribution integrates new U/Pb zircon ages, heavy mineral analyses and biostratigraphic constraints from the Neogene sedimentary record of the fore‐arc and intra‐arc basins and volcano‐plutonic rocks of southwestern Colombia, to reconstruct these orogenic processes. The results reveal continuous arc magmatism since the Late Oligocene, with a major post‐Middle Miocene magmatic peak and exhumation. When integrated with other geological constraints, the tectonic evolution of the margin includes Eocene‐Oligocene oblique convergence with limited magmatic activity, followed by the initiation of a Late Oligocene‐Early Miocene arc that migrated to the east in the Middle Miocene, when it experienced a major increase in magmatic activity, crustal deformation, exhumation and thickening. This orogenic evolution is related to the shallowing of the slab dip due to the subduction of the Neogene Nazca Plate.

ABSTRACT:The terms used to define the clastic deposits related to volcanic activity have important implications for the society in volcanic regions. Taking into account the importance of using a common terminology when considering natural hazards in the Spanish-speaking world, this study presents a classification of volcaniclastic deposits. This classification attempts to integrate the terminology related to the formational and depositional processes (eruptive and non-eruptive) taking place at volcanoes with the resulting volcaniclastic deposits and their constituent components. The classification emphasizes on how both physical and temporal variations in volcanic activity are responsible for observed differences in the related deposits. The purpose of this classification is to be a reference for the Spanishspeaking scientific community in order to avoid the numerous inconsistencies derived from the existing translations from multiple authors. Additionally, we present a flow diagram in both Spanish and English to illustrate that this classification system can be used to define and classify consolidated/lithified, and unconsolidated deposits. The appropriate classification of volcaniclastic deposits and their constituents can ultimately improve the definition and communication of potential volcanic hazards.

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.