Resumo

ARMSTRONG-ALTRIN, John S.. Provenance of sands from Cazones, Acapulco, and Bahía Kino beaches, Mexico. Rev. mex. cienc. geol [online]. 2009, vol.26, n.3, pp.764-782. ISSN 2007-2902.

Petrographic, major, trace, and rare-earth element geochemistry of sands from three beaches of México (Cazones, Acapulco, and Bahía Kino) were studied to determine their provenance. The textural study reveals that the proportion of quartz is higher in Bahía Kino (~48-83 %) than in Cazones (~22-48 %) and Acapuclo (~20-48 %) sands. Most of the sand samples are classified as felsic sands using SiO₂ content. The variations in SiO₂, Fe₂O₃, MgO, TiO₂ contents and Al₂O₃ / TiO₂, K₂O/ Na₂O, SiO₂/ Al₂O₃ ratios among the three study areas reflect differences in source rock characteristics. The low Chemical Index of Alteration values (CIA: ~38-58) suggest the prevalence of week weathering conditions in the source regions. A steady weathering trend identified in the A-CN-K diagram for Acapulco and Cazones sands is indicative of uplift along the source region and indicates that sands were derived from diverse sources. A major variation in ∑REE content is observed in Acapulco sands (~22-390 ppm) than in Cazones (~49-83 ppm) and Bahía Kino sands (~50-89 ppm), and is likely due to differences in fractionation of minerals. However, all the sand samples show similar REE patterns with enriched LREE, depleted HREE and a negative Eu anomaly. The comparison of REE data of sands with those of source rocks located relatively close to the study areas suggest that Cazones and Acapulco sands were derived from felsic and intermediate rocks, whereas Bahía Kino sands were derived from felsic rocks.

Palavras-chave : beach sand; provenance; weathering; geochemistry; hydraulic sorting; tectonic settings; zircon; ilmenite; rare-earth elements; Bahía Kino; Cazones; Acapulco; Mexico.

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