Banca de DEFESA: ADRIANO HENRIQUE ANDRADE DE AGUIAR

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : ADRIANO HENRIQUE ANDRADE DE AGUIAR
DATE: 13/08/2025
TIME: 14:30
LOCAL: Videoconferência
TITLE:

Mineralogy, chemistry, and textural characterization of Al-phosphates: examples from Samambaia intraplate fault system, Brazil 

KEY WORDS:

Al-phosphates; Paragenesis; Crack-seal mechanism; Fault-related mineralization

PAGES: 30
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

This study investigates the mineralogy, texture, and chemistry of secondary Al-phosphates (variscite, crandallite, millisite/wardite) from the Samambaia intraplate fault system, northeastern Brazil. Using petrography, X-ray diffraction, QEMSCAN, SEM/EDS, and EPMA analyses, we distinguish paragenetic relationships and precipitation sequences associated with multiple tectonic reactivations and fluid influx events. Results indicate that variscite is the dominant and most texturally diverse phosphate, precipitating both from direct alteration of kaolinite and by recrystallization of Ca-rich aluminophosphates under acidic conditions. Crandallite and millisite formed earlier under near-neutral to slightly alkaline conditions, later replaced as fluid pH decreased. Textural evidence such as zoned crystals, cockade breccias, and rhythmic Fe–Al banding reflects cycles of fracture opening, sealing, and renewed fluid flow, consistent with a crack-seal mechanism. Geochemical data highlight element mobility (P, Al, Fe, Ca) sourced from dissolution of primary minerals and weathered host rocks, suggesting precipitation mainly from meteoric fluids enriched in phosphorus and iron. This integrated approach reveals the interplay of tectonics, fluid evolution, and chemical conditions in shaping complex Al-phosphate assemblages, offering new insights into fluid–rock interaction in seismogenic fault zones.

COMMITTEE MEMBERS:
Externo à Instituição - FÁBIO RAMOS DIAS DE ANDRADE - USP
Presidente - 2042352 - FREDERICO CASTRO JOBIM VILALVA
Externa ao Programa - 1298966 - RAQUEL FRANCO DE SOUZA - null