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

Author(s)

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

Affiliation

^[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

• Document type: Journal article
• Source: LITHOS; v. 346, NOV 15 2019.
• Web of Science Citations: 0

Abstract

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)

• FAPESP's process: 14/15838-2 - Apatite, zircon and epidoto fission track method: thermochronology of the northern part of Paraná Basin and the peruvian Andes
• Grantee: Carlos Alberto Tello Sáenz
• Support Opportunities: Regular Research Grants
• FAPESP's process: 11/14943-9 - Chemical etching effects in apatite and zircon minerals and their implications in the Fission Track Method: Canastra Mountain Range Geochronology.
• Grantee: Rosana Silveira Resende
• Support Opportunities: Scholarships in Brazil - Doctorate