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A HOT CHAPTER IN EARTH’S HISTORY: INSIGHTS FROM THE PALEOPROTEROZOIC ITABUNA-SALVADOR-CURAÇÁ OROGEN IN SOUTH AMERICA
Thesis

A HOT CHAPTER IN EARTH’S HISTORY: INSIGHTS FROM THE PALEOPROTEROZOIC ITABUNA-SALVADOR-CURAÇÁ OROGEN IN SOUTH AMERICA

Cole roy McGregor
Master of Science (MS), Washington State University
2026
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Thesis_CM (May-7-2026)(2)DownloadView
Open Access CC BY V4.0

Abstract

The Paleoproterozoic represents a pivotal interval in Earth’s evolution, marked by supercontinent assembly, globally distributed zircon age peaks, and the transition toward modern-style plate tectonics. Orogenic belts formed between ~2.1 and 1.8 Ga are widely recognized as hot to ultra-hot systems associated with the assembly of the supercontinent Nuna/Columbia. The Itabuna-Salvador-Curaçá Orogen (ISCO), with peak metamorphic temperatures up to 900–950 °C (Leite et al., 2009), represents a major tectono-thermal event responsible for an extensive 2.1–2.0 Ga magmatic and metamorphic record within the São Francisco Craton (SFC), Brazil. This study integrates garnet Lu-Hf and Sm-Nd geochronology, apatite Sm-Nd data, and zircon U-Pb ages to constrain the timing and duration of metamorphism in the ISCO. Samples include garnet-bearing and non-garnet-bearing gneisses from across the orogen and adjacent crustal domains. Garnet Lu-Hf ages range from ~2.12 to 2.04 Ga and record peak to near-peak metamorphic conditions, while garnet Sm-Nd ages (~2.05–2.02 Ga) track cooling. Apatite Sm-Nd ages extend to ~1.95 Ga. The persistence of high temperatures over tens of millions of years indicates that the ISCO represents a long-lived, regionally extensive metamorphic system. The prolonged thermal evolution is consistent with ultra-hot Precambrian orogens and supports models of early plate tectonics operating under higher geothermal gradients and slower cooling rates than those observed today.

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