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Unraveling the evolution of mineral deposits in rainbow hydrothermal field through micro-scale analysis of sulfide phases
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Orientador(es)
Resumo(s)
Seafloor hydrothermal fields are a key source of metals to the oceans, via interaction of seawater with deep underlying rocks (e.g. Ni, Cu, Zn, Fe). This study focuses on the mineralogical and chemical composition of sulfide-rich chimneys in the Rainbow Hydrothermal Field (RHF), an active and vigorous hydrothermal system hosted in ultramafic rocks located near the Mid-Atlantic Ridge (MAR). The RHF has a set of unique conditions (lowest pH, highest temperature and chlorinity among Atlantic hydrothermal systems). These characteristics reflect prolonged fluid-rock interactions, resulting in fluids heavily enriched in transition metals, while showing positive anomalies in other elements remobilized from the host rocks. Fourteen chimney samples of the RHF were collected during the SALDANHA oceanographic mission (1998) and were studied using detailed petrography, electron probe microanalysis (EPMA), SEM/EDS, whole-rock geochemistry, and in situ sulfur isotopic analysis (LA-MC-ICP-MS). The compositional data allowed to redefine the mineralization styles into three main typologies, each with a signature mineral/mineral assemblage: Cu-style (copper sulfides), Sph-style (sphalerite), and Postyle (pyrrhotite), with Cu-style proving to be more complex and thus requiring the subdivision into three different sub-styles. Each of these mineralization styles reflects distinct physicochemical precipitation conditions, allowing usto infer variations and distinguish between pre- and post-deposition processes in the temporal evolution of hydrothermal fluids in the RHF. The obtained δ34S values range from -2.77 ‰ to +3.82 ‰, reflecting the diversity of mineralization styles and the present minerals, with the highest values associated to the Cu-style and the lowest values belonging to the Sph-style. The obtained values, along with the petrographic and geochemical data also reiterate that both pre-depositional processes driven by changes in fluid dynamics, temperature and composition and post-depositional processes characterized by isotopic alteration and mineral transformation are fundamental factors to the evolution of hydrothermal fields.
Descrição
Tese de Mestrado, Geologia (Geodinâmica e Recursos Geológicos), 2026, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Rainbow Hydrothermal Field Mid-Atlantic Ridge Hydrothermal chimneys Sulfides δ 34S