The effect of chemical and physical imperfections in zircon grains in influencing the U-Pb age analyses: Insights from zircon fission track etching

Autor(es)

Resende, Rosana Silveira ^[1] ; Tello Saenz, Carlos Alberto ^[1] ; Stuani Pereira, Luiz Augusto ^[1] ; Dantas, Elton Luiz ^[2]

Afiliação do(s) autor(es)

^[1] Univ Estadual Paulista, Dept Phys, UNESP, BR-19060900 Presidente Prudente, SP - Brazil

^[2] Univ Brasilia, Inst Geosci, Lab Geochronol Studies Geodynam & Environm, BR-70910900 Brasilia, DF - Brazil

• Tipo de documento: Artigo Científico
• Fonte: LITHOS; v. 346, NOV 15 2019.
• Citações Web of Science: 0

Resumo

Understanding the chemical etching effects in the crystalline structure of zircon grains is crucial to know their chemical composition, morphology and isotopic geochemistry. After chemical etching, the zircon grain can be classified as homogeneous heterogeneous, hybrid and anomalous depending on the surface fission-track density observed under an optical microscope. The complementary techniques such as optical microscopy, micro-Raman spectroscopy, scanning electron microscopy (imaging by cathodoluminescence and secondary electrons) and electron microprobe, were employed to characterize the zircon grain surfaces from Igneous, Metamorphic and Sedimentary rocks before and after chemical etching, except for Raman spectroscopy. Measurements of U-Pb age are concordant in areas on the grain surface with uniform fission-track density. The chemical and isotopic analyses show that the etching is capable of revealing the different layer imperfections of the zircon crystalline structure, which can be inherent in its crystallization or acquired during its geological history. Therefore, identification of crystallographic preserved areas on the zircon surface, which are associated with uniform fission-track density, helps to get highly concordant U-Pb ages. In general, the results showed that the U-Pb system depends significantly on the amorphization degree of the zircon crystalline structure, which in most cases can only be revealed by etching. (C) 2019 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 14/15838-2 - Método de Traços de fissão nos minerais, apatita, zircão e epídoto: termo-cronologia da porção norte da Bacia do Paraná e dos Andes peruanos
• Beneficiário: Carlos Alberto Tello Sáenz
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 11/14943-9 - Efeitos do ataque químico nos minerais apatita e zircão e suas implicações no Método de Traços de Fissão: Geocronologia da Serra da Canastra.
• Beneficiário: Rosana Silveira Resende
• Modalidade de apoio: Bolsas no Brasil - Doutorado