Banca de DEFESA: Aline Alves dos Santos

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : Aline Alves dos Santos
DATE: 19/12/2023
TIME: 09:00
LOCAL: Sala de videoconferência e Teams
TITLE:

Mineral chemistry, Sr-Nd-Os isotopes and platinum group elements of the peridotites from Los Gemelos volcano, Meseta de Canquel, Argentine Patagonia.

KEY WORDS:

Spinel peridotites; Partial melting; Mesoproterozoic; Hydrous and high-K mantle metasomatism; Sr, Nd and Os isotopes; Patagonian mantle.

PAGES: 126
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

Mantle xenoliths from Canquel Plateau, Patagônia, are object of this study,which represent the first investigation of a new spinel-bearing suite dated from Mesoproterozoic (1.3–0.9 Ga). The composition vary between harzburgites and clinopyroxene-poor lherzolites characterized by typical indicators of partial melt extraction, such as low whole-rock Al2O3 and CaO contents (both <1.5 wt.%), high Mg# of silicate phases (90–95), and Cr-rich spinel (Cr# 0.20–0.42). The depletion of incompatible highly siderophile elements (Re, Ru, Pd) relative to the primitive upper mantle certify the high-degrees of melt extraction and the highly-depleted caracther of the samples. The existence of phlogopite, accompained by abundant alkaline glass veins containing high- and low-SiO2 compositions are undoubtable evidence of modal metasomatism. The light rare earth element (LREE) enrichment observed in clinopyroxene, as well as the whole-rock U-shaped REE pattern are evidence of cryptic metasomatism. The melt-rock interaction is corroborated by major (i.e., Mg# vs. basaltic elements) and trace (i.e., La/YbN vs. Sr/Y and Ti/Eu; and Sr vs. Ti/Eu) element contents of pyroxenes. Moreover, the calculated compositions of melts in equilibrium with clinopyroxene coexisting with phlogopite, as well as whole-rock SrNd isotopic ratios suggest interaction with subduction-related components. Remarkably, the metasomatic overprint is selectively prominent in the deeper (~70 km) mantle column compared to the shallower (~50 km). These features are consistent with the hybridization of the depleted lithosphere with a K-rich alkaline melt. Considering the long-lived subduction system established in the Patagonia back-arc throughout the Phanerozoic, it is most likely that the metasomatic event recorded by Los Gemelos mantle xenoliths is associated with the upwelling of asthenospheric material through a slab-window during the Paleocene-Eocene, wich promoted the partial melting of the oceanic crust.

COMMITTEE MEMBERS:
Interno - 1178074 - GUILHERME DE OLIVEIRA GONCALVES
Interna - 2697315 - MARIA EMILIA SCHUTESKY
Presidente - 1069348 - TIAGO LUIS REIS JALOWITZKI
Externo à Instituição - VALDECIR DE ASSIS JANASI - USP