Banca de QUALIFICAÇÃO: Ariela Oliveira Mazoz

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : Ariela Oliveira Mazoz
DATE: 05/09/2022
TIME: 09:00
LOCAL: Sala de videoconferência
TITLE:

 Characterization of titanite and monazite reference materials for U-Pb and Sm-Nd isotopes mycroanalyses by LA-ICP-MS

KEY WORDS:

 reference materials; titanite; monazite;  U-Pb; Sm-Nd; LA-ICP-MS

PAGES: 139
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUMMARY:

The use of LA-ICP-MS technique has increased in several laboratories around the world and is revolutionizing earth sciences studies. Recent advances in the LA-ICP-MS U-Th-Pb geochronology allows acquisition of U-Pb data at high spatial resolution (> 10 μm), with precision and reproducibility better than 3% on individual ²⁰⁶Pb/²³⁸U and ²⁰⁸Pb/²³²Th ages, at relatively fast throughput and low cost compared to other microanalytical techniques, such as SHRIMP or ID-TIMS. With the expansion of LA-ICP-MS laboratories around the world, the demand for reference materials for calibration and quality control has increased significantly. In this research, we have investigated two new potential titanites reference materials (Bear Lake and Khan River) for U-Pb geochronology by means of high precision (ID-TIMS) and high-spatial resolution methods (LA-ICP-MS and SHRIMP). We made use of the chemical abrasion technique - for the first time applied to titanites - to minimize the imperfect areas of the crystal fragments (e.g. fractures, damaged portions) and resulting in a more homogeneous translucent material. Bear Lake titanite shows a uniform pattern in a REE diagram and has high but relatively constant common Pb. For Khan River titanite, the REE content is variable and the common Pb concentration is low, but slightly variable. U-Pb ID-TIMS analyses yielded Pb_c-uncorrected intercept ages of 516.3 ± 1.3 Ma (2s) and 1067.81 ± 0.74 Ma (2s) for Khan River and Bear Lake titanites, respectively. Multiple U-Pb LA-SF/MC-ICP-MS analyses gave consistent Pb_c-uncorrected intercept ages for both, Khan River (517 ± 1/5 Ma, 2s) and Bear Lake (1070 ± 1/11 Ma, 2s). U-Pb SHRIMP analyses on both titanites samples returned consistent ages within uncertainty. LA-SF-ICP-MS runs, using Khan River and Bear Lake titanites as calibrant to correct the ²⁰⁶Pb/²³⁸U in non matrix-matched analyses reproduced the ages os other established RMs within <1% deviation. In this study, we have also investigated the Vermilion monazite as a potential reference material for U-Pb geochronology, using high-precision technique (ID-TIMS) and high-spatial resolution methods (LA-ICP-MS and SHRIMP), and for Sm-Nd microanalysis (LA-MC-ICP-MS). BSE images revealed that Vermilion monazite is relatively homogeneous and free from compositional zoning, showing uniform REE pattern with considerably small variations between the crystals. Our potential monazite reference material yielded ID-TIMS weighted mean ²⁰⁷Pb*/²⁰⁶Pb* age of 2667.5 ± 1.2 Ma (2s) with a slightly discordant concordia age. U-Pb SHRIMP data returned a ²⁰⁷Pb*/²⁰⁶Pb* weighted average age of 2662 ± 2/27 Ma (2s). U-Pb ²⁰⁷Pb/²⁰⁶Pb weighted average LA-MC-ICP-MS and LA-Q-ICP-MS data are 2666 ± 1/27 Ma (2s) and 2665 ± 5/27 Ma (2s), respectively. High-spatial resolution data are in agreement with the high precision ID-TIMS. Sm-Nd LA-MC-ICP-MS results from two laboratories returned an average ¹⁴⁷Sm/¹⁴⁴Nd ratio of 0.0854 ± 0.0027 (3.1 %RSD, 2SD) and a homogeneous average ¹⁴³Nd/¹⁴⁴Nd ratio of 0.51068 ± 0.00004 (0.01 %RSD, 2SD). The initial epilson Nd (εNd_i) varied from -0.8 ± 0.5 (2s) to 0.6 ± 0.4 (2s). The titanite and monazite reference materials can be applied to investigate crustal evolution process and to trace the source of hydrothermal fluids mineralization.

BANKING MEMBERS:
Interno - 1303786 - ELTON LUIZ DANTAS
Interno - 6404885 - NILSON FRANCISQUINI BOTELHO
Interna - 1644358 - PAOLA FERREIRA BARBOSA
Presidente - 418662 - ROBERTO VENTURA SANTOS
Interno - 1069348 - TIAGO LUIS REIS JALOWITZKI