First U-Pb age constraints from plutonic xenoliths preserved in alkaline volcanic rocks of the Brazilian Fernando de Noronha Archipelago, Southwest Atlantic Ocean

• Autor(a) principal: Júlia Mattioli Rolim
• Data de Publicação: 2022
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Institucional da UFMG
• Texto Completo: http://hdl.handle.net/1843/40979; https://orcid.org/0000-0003-0966-8974
• topic: PLUTONIC ROCKS; APATITE; TITANITE; ZIRCON; Rochas plutônicas; Apatita - Fernando de Noronha, Arquipélago (PE); Tempo geológico

Plutonic xenoliths are a potential wealth of information and evidence about magmatic processes that occur at depth, in the feeder zones of volcanic edifices. New petrographic, geochemical, isotopic, and geochronology data are presented for kaersutite diorite derived from a pyroclastic deposit from the basal unit of the Fernando de Noronha Archipelago (FNA), in the Southwest Atlantic Ocean. The kaersutite diorite consist primarily of andesine, diopside, kaersutite, phlogopite, and minor amounts of magnetite and ilmenite, along with accessory minerals such as apatite, titanite, and zircon. Major and trace element signatures from bulk-rock analyses yield silica under-saturated compositions and light REE enriched patterns (La/YbN = 13-14) that are similar to the other rocks from the FNA. Nd isotope analyses yield ƐNd values of +1.7 to +2.2. U-Pb analyses of zircon obtained from the kaersutite diorite provided a crystallization age of 13.69 ± 0.07 Ma, while a combined titanite-apatite U-Pb age record a younger U-Pb age at 9.76 ± 0.94 Ma, reflecting a younger thermal event, probably related to the explosive magmatism that formed the pyroclastic deposit of the basal unit of FNA. These ages also indicate that the FNA magmatism was coeval with onshore continental magmatism found in northeastern Brazil.