FISSION TRACKS IN MONAZITE: INNOVATION AND PERSPECTIVES IN ULTRA-LOW-TEMPERATURE THERMOCHRONOLOGY

• Grant number: 24/17513-5
• Support Opportunities: Regular Research Grants
• Start date: July 01, 2025
• End date: June 30, 2028
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Airton Natanael Coelho Dias
• Grantee: Airton Natanael Coelho Dias
• Host Institution: Centro de Ciências e Tecnologias para a Sustentabilidade (CCTS). Universidade Federal de São Carlos (UFSCAR). Sorocaba , SP, Brazil
• Associated researchers: Antonio Said Webbe Sales ; David Chew ; Mauricio Parra Amézquita ; Sean Jones ; Vinicius de Queirós Pereira

Abstract

Fission Track Thermochronology (FT) has become one of the most useful techniques for reconstructing the thermal history of low-temperature rocks. In the case of sedimentary rocks, thermochronology allows for understanding evolutions of basins, as well as the regional cooling patterns of sediment source regions. The technique is based on the accumulation of tracks originating from the spontaneous fission of 238U over geological time, and on the feasibility of these tracks made visible in using optical microscopy when the mineral is subjected to an appropriate etching protocol. Widespread application of FT thermochronology in U-rich minerals like apatite and zircon have enabled documenting the rock cooling across a range of temperatures of 250-60°C, but have failed to illuminate cooling patterns at lower temperatures. Recently, new studies resulting from advances in mass spectrometry and laser technologies that allow direct quantification of U and empirical development of reliable etching protocols have identified monazite as a potential mineral for application in FT. Monazite, a phosphate-containing Rare Earth Element (REE), U, and Th, is commonly found as an accessory mineral in igneous, metamorphic, and sedimentary rocks. Despite containing U and Th, and being applied in dating systems such as U-Th-Pb and (U-Th)/He, that is, being a promising mineral for multimethod geochronology, little progress has been made in the application of FT on monazite (MFT) until few years ago. The main outcome obtained recently has been the realization that monazite is an ultra-low-temperature thermometer, with annealing temperatures in the range of 25-45 °C, which opens a new field of investigation to study rates of surface processes. Given the many technological and methodological advances that have been achieved in the last 10 years and the reality that we are facing a frontier technique, the objective of this project is: i) to implement MFT in the laboratories of the TRACKs Group - DFQM, CCTS/UFSCar, to evaluate the potential of monazite as an ultra-low temperature thermochronometer (25-45 ºC); ii) to perform a Proof of Concept based on the analysis in two geologically distinct regions in their exhumation rates: a rapidly exhuming Eastern Cordillera in Colombia (Colombian Andes) and the moderately slowly exhumed Brazilian continental margin (Búzios region, Rio de Janeiro). (AU)