Chapter 12

Abstract

A transtensional basin setting originated the Combia Volcanic Province in the northern Andes of Colombia. Volcanism is heterogeneous encompasses tholeiitic, calc-alkaline, and shoshonitic magmatic series. A review of existing geochemical and geochronological data suggests that all magma series coexisted between 12 and 6 Ma but originated from different processes. Tholeiites formed via the melting of a modified primitive mantle source, with limited sedimentary or continental-contaminant input. Calc-alkaline magmas are mainly adakitic and formed from fractionation of garnet and amphibole at high pressures from a hydrous melt from an enriched source. Petrographic and mineral chemistry of garnet-bearing rocks indicate that magmas underwent at least three ascent phases that include: (1) crystallization of high-pressure phenocryst phases at 900 °C and 1200 GPa in a mantle-derived melt, (2) stalling of differentiated magma at lower-pressure conditions, and (3) stalling at shallower conditions, where decompression occurred. Shoshonitic magmas formed via from a mantle with sedimentary or continental-contaminant input source in the plagioclase stability field. Finally, Combia Volcanic Province's formation was enhanced by the Caldas Tear, a slab window developed by the subduction of the Sandra Ridge beneath the South American Plate.

Chapter 3

“…Few studies have focused on the initial Miocene volcanism and that in the Pliocene -Pleistocene, on which the current volcanism developed; therefore, knowledge about the spatiotemporal evolution of this magmatism is lacking. The characterization of the Miocene volcanism is restricted to hy-potheses based on the Combia Formation of tholeiitic affinity (i.e., Ramírez et al, 2006;Weber et al, 2020), which crops out to the north of the Andes in the Inter-Andean Cauca Valley in the Department of Antioquia, and the rhyolitic volcanism associated with large caldera structures south of the Central Cordillera, which produced extensive ignimbrite plains on both sides of the cordillera.…”

Volume 1

“…The Combia Formation, exposed in the northwest of the Colombian Andes, is a unique occurrence of tholeiitic magmatism formed in an extensional basin and associated with calc-alkaline magmatic rocks. The review of geochemical and geochronological information by Weber et al (2020) described in chapter 12 indicates that the two magmas coexisted. The tholeiites were formed from a primitive mantle, with a limited supply of sedimentary or continental contaminants, and the calc-alkaline magmas, mainly adakitic, were formed from the fractionation of garnet and amphibole at high pressures from a hydrated melt from an enriched source.…”

Presentation

“…The Combia Formation, exposed in the northwest of the Colombian Andes, is a unique occurrence of tholeiitic magmatism formed in an extensional basin and associated with calc-alkaline magmatic rocks. The review of geochemical and geochronological information by Weber et al (2020) described in chapter 12 indicates that the two magmas coexisted. The tholeiites were formed from a primitive mantle, with a limited supply of sedimentary or continental contaminants, and the calc-alkaline magmas, mainly adakitic, were formed from the fractionation of garnet and amphibole at high pressures from a hydrated melt from an enriched source.…”