Banca de DEFESA: Carolina Michelon Camarda

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Carolina Michelon Camarda
DATE: 15/12/2023
TIME: 14:00
LOCAL: Sala de videoconferência e Teams
TITLE:

Hydrous iron oxides in super-deep mantle and their implications for Earth’s dynamics.

KEY WORDS:

Super deep Diamonds, Iron oxy-hydroxy, Earth’s mantle, Synchrotron

PAGES: 119
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

Hydrated minerals present in the oceanic lithosphere are known as the main agents responsible for the transport of water into the Earth's mantle through subduction zones. In the upper mantle, water can be stored in the crystalline structure of minerals such as amphibole and mica, or in nominally anhydrous minerals such as olivine and pyroxenes. Additionally, the mantle transition zone has been recognized as a potential reservoir of water. Experimental studies have demonstrated that high-pressure polymorphs of olivine that mark this zone, wadsleyite and ringwoodite, have significant OH storage capacity, which has also been confirmed in two naturally hydrated ringwoodites found as inclusions in super-deep diamonds. On the other hand, the lower mantle has always been considered anhydrous due to its main mineralogy that has low storage capacity of OH. Hydrated minerals in the lower mantle, known as dense hydrous magnesium silicates (DHMSs), can only incorporate a small proportion of OH into their crystal structures and are relatively scarce phases. Recent experimental studies have shown that iron oxihydroxide phases can remain stable under lower mantle conditions, implying that water can be transported and stored inside the Earth by goethite polymorphs (α-FeOOH). These studies suggest that α-FeOOH, commonly present in subducted oceanic plates, partially decomposes into Fe2O3 and Fe3O4 at pressures of ~35 - 76 GPa (~1,155 – 2,500 km) and temperatures of 876,85- 2476,85 ºC, thus releasing H2O and O2 into the lower mantle. Notably, through investigations on inclusions in a super-deep diamond from Juína, Mato Grosso - Brazil, the first documented natural occurrence of stable ε-FeOOH in the lower mantle was found. This phase was observed in transition, with natural goethite (εFeOOH) decomposing into possibly hydrated high-pressure hematite (Fe2O3) and magnetite (Fe3O4). Through the crystalline structure of hematite, it was possible to identify that this phase transition occurs at a pressure of 56 GPa, corresponding to ~1,850 km depth in the lower mantle. With the transition, there is also the release of H2O and O2 into the deep mantle. Therefore, this discovery provides valuable information about the water cycle inside the Earth, suggesting that the lower mantle contains more water than previously believed and may exhibit compositional heterogeneities formed by redox reactions generated by the release of H2O and O2 in a predominantly reducing environment. The results are based on novel data obtained from three beamlines of the new 4th generation synchrotron radiation source - Sirius at the Brazilian National Synchrotron Light Laboratory (LNLS), which includes μ-tomography (MOGNO beamline), X-ray fluorescence (CARNAÚBA beamline), nano-tomography (CARNAÚBA beamline), XANES (CARNAÚBA beamline), and micro-X-ray diffraction (EMA beamline).

COMMITTEE MEMBERS:
Externa à Instituição - ADRIANA ALVES - USP
Interna - 2341034 - ROBERTA MARY VIDOTTI
Presidente - 1069348 - TIAGO LUIS REIS JALOWITZKI
Interno - 3043135 - WOLF UWE REIMOLD