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Geochemical Analysis of the Chinchín Formation in Southern Ecuador

The subduction of the Nazca Plate under the South American Plate has led to the uplift of the majority of the Andes Mountains, but in Ecuador, the Nazca Plate subducts underneath the North Andes Plate, which then collides with the South American Plate. This tectonic setting has formed two parallel mountain chains as well as a complex series of basins between them. However, the formations that make up these basins are poorly understood. This study focuses on the Chinchín Formation, an ~3.5 km thick, volcanic formation that serves as the bedrock of the Quingeo Basin in southern Ecuador. This study employs XRF analysis to determine the change in composition of an ~112 m elevation change within the Formation in order to better understand the history of basin development in this region. Eight bedrock samples from the southern portion of the Chinchín Formation were analyzed. The rocks range from basaltic andesite to dacite, although most are andesitic in composition. Two non-sequential samples are amygdaloidal, indicating that this section of the Formation was deposited in multiple volcanic events. These amygdules and the unusually high concentration of iron in all samples indicate secondary mineral deposition by low-temperature fluids.