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The Amagá basin between the Western and Central Cordilleras of the Northern Andes of Colombia host the Neogene volcanic and volcaniclastic Combia Formation. At this stage it is not clear how the formation of this unit is related to arc volcanism and which role the Nazca plate subduction beneath the western margin of South America plays. The timing, petrography and geochemical characteristics of Combia Formation rocks were studied in the western and eastern parts of the Amagá basin, in order to gain more information on the type of magma generation and volcanic activity that led to the deposition of the Combia Formation. Apatite and zircon fission-track dating largely confirm a 12-6 Ma age for the deposition of the Combia Formation. Petrographic and major element analyses show that mainly trachy-andesite ignimbrites with a calc-alkaline composition were deposited in the western Amagá basin, whereas the volcanic rocks of the eastern Amagá basin are lava flow and fallout deposits of basaltic andesites or of tholeiitic composition. Trace element and isotopic analyses show that slab dehydration and sediment melting were important in primary magma generation in the mantle wedge, but the primary magma was mixed with lower continental crustal melts, resulting in characteristic isotope signatures in the western and eastern Amagá basin. All this points to subduction driven arc volcanism with slab dehydration, sediment melting magma mixing.

In this contribution, DInSAR analysis, seismic/brittle strain rates, and seismic uplift estimations were used to evaluate ground deformation patterns of the 24 December 2019 Mw 5.8 Mesetas Earthquake that occurred in the Mesetas municipality (Meta, Colombia), on the eastern foothills of Colombian’s Eastern Cordillera, near the Serranía de la Macarena. According to the focal mechanisms computed for this earthquake, the right-lateral Algeciras Fault System was responsible for the rupture event. Primary and secondary SAR images from December 18/2019 and 30/2019, respectively, were used to calculate coseismic ground deformation of the study area. Geocoded line-of-sight (LOS) displacement image suggests that major ground deformation was on the order of 0.2 m for the 24 December discrete seismic event, while the accumulated seismic contribution to surface uplift during 1993 to 2020 reached values of ca. 0.14 m/yr. In contrast, seismic/brittle strain rates and seismic uplift estimations show that this part of South America is currently experiencing deformation at a rate of 4.1×10-16 ± 1.7×10-17s-1 and uplift at a rate of 81.5 ± 3.4 m/Ma during 2018-2020, whereas the deformation was 0.1×10-16 ± 0.2 ×10-17s-1 at a rate of 2.2 ± 0.5 m/Ma between 1993-2018.

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