242-10 In-Situ Geochronology and Metamorphic Evolution of the Early Cretaceous Arquia Complex, Northern Andes: From Cold to Warm Subduction Regime?

Abstract:

Subduction-related complexes have the potential to act as geological archives of convergence history in active margins. In the Northern Andes, metamorphic units grouped in the Arquia Complex relate regionally to a subduction complex that records the Cretaceous convergent history in northwestern South America. Two main episodes of metamorphism associated with subduction and collisional tectonic events have been proposed during the Early Cretaceous and Late Cretaceous–Paleocene, however, few attempts have been made to understand the evolution of the metamorphic record associated to these events, especially timing and linkage to P-T conditions.

We present petrography, geochemistry, Raman spectroscopy of carbonaceous material (RSCM) and in-situ multi-geochronology to characterize the Arquia metamorphic rocks in the western flank of the Central Cordillera of Colombia (Filadelfia-Caldas) and evaluate their implications for the convergence evolution of the Colombian Andes during the Early Cretaceous.

In Filadelfia (Caldas-Colombia), the Arquia Complex comprises metabasic and pelitic schists, and amphibolites associated with serpentinites, exposed along a NNE-trending structural belt. Mafic protoliths are predominantly of MORB affinity. In the southwest, pelitic schists show white mica (Si: 3.4 apfu), quartz and epidote-group minerals, with or without chloritoid, graphite and garnet retrogressed to chlorite, while metabasic shists comprise actinolite, albite, chlorite, occasionally preserving inclusions of garnet and white mica (Si: 3.3–3.4 apfu) within plagioclase porphyroblasts. RSCM yields temperatures between 452–486 °C, indicating low- to moderate-temperature conditions. To the northeast, hornblende and oligoclase-bearing amphibolites record higher metamorphic conditions. In-situ white mica Rb-Sr, titanite U-Pb and garnet Lu-Hf ages from pelitic and metabasic schists in the southwest range within ca. 132–123 Ma, whereas to the northeast pelitic schists and amphibolites yield titanite U-Pb and white mica Rb-Sr ages of ca. 117 and 115 Ma, respectively. 

Our data suggest that rocks of the Arquia Complex underwent a diachronous thermal evolution tracking changes in the thermal regime of the subduction zone before Late Cretaceous collision, represented by an event at ca. 132-123 Ma under moderate-temperature conditions, followed by retrogression to lower-temperature conditions. Garnet and white mica inclusions in albite porphyroblasts suggest an earlier growth stage probably associated to higher pressure conditions. To the northeast, amphibolite-facies conditions at ca. 115 Ma suggest a shift toward a hotter thermal regime, possibly associated with a change in the subduction angle and roll back.

Geological Society of America Abstracts with Programs. Vol. 58, No. 5, 2026

doi: 10.1130/abs/2026AM-19337

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