Date of Award
2026-05-01
Degree Name
Master of Science
Department
Geological Sciences
Advisor(s)
James B. Chapman
Abstract
The modern continental arc system in Ecuador is well understood but less is known about arc systems in the past, hindering our understanding of the tectonic evolution of the northern Andes. The Macuchi arc, located in the Western Cordillera of Ecuador, was thought to be the main continental arc system during the Eocene, but new zircon U-Pb LA-ICPMS dates from intrusive arc rocks in central Ecuador indicate a more complex history. During the mid-Eocene, the footprint of arc magmatism broadened and expanded into the Inter-Andean Valley and Eastern Cordillera. During the late Eocene to Oligocene, the arc migrated back toward the trench at ~4 km/Myr, which is interpreted to be due to steepening of the subduction angle and/or slab rollback. New zircon Lu-Hf LA-ICPMS isotopic data and a compilation of previously published radiogenic isotope data show a clear spatial isotopic trend in Ecuador. Igneous rocks erupted or emplaced in the Western Cordillera, in Caribbean plateau basement, have strongly juvenile εHf isotopic compositions that approach depleted mantle values (+16 to 10). Magmatic rocks located farther from the trench have more evolved compositions (+5 to 0). This spatial isotopic trend can be observed in most Cenozoic igneous rocks regardless of specific age, including in the Quaternary to recent volcanic arc. Temporal trends in detrital zircon εHf data from modern rivers and sedimentary deposits primarily reflect position and migration of the arc. Zircon εHf values exhibit a broader range of values and an overall shift to more evolved composition when the arc broadened into the Inter-Andean Valley during the Eocene. As the arc migrated back toward the trench and into oceanic plateau basement, zircon εHf values shifted to more juvenile compositions.
Language
en
Provenance
Received from ProQuest
Copyright Date
2026-05
File Size
159 p.
File Format
application/pdf
Rights Holder
Muriel M. Sandoval Vazquez
Recommended Citation
Sandoval Vazquez, Muriel M., "Eocene To Oligocene Continental Arc Migration In Ecuador And The Origin Of Spatiotemporal Trends In Zircon Lu-Hf Radiogenic Isotopes" (2026). Open Access Theses & Dissertations. 4790.
https://scholarworks.utep.edu/open_etd/4790