In situ U-Pb dating of titanite by LA-ICPMS

Abstract

Titanite is an ideal mineral for U-Pb isotopic dating because of its relatively high U, Th and Pb contents. Here, we developed a technique for U-Pb dating of titanite using the 193 nm ArF laser-ablation system and Agilent 7500a Q-ICP-MS. Standards of titanite (BLR-1 and OLT-1) and zircon (91500 and GJ-1) were dated using single spot and line raster scan analytical methods. To check the matrix effect, titanite (BLR-1) and zircon (91500) standards were analyzed as the external standards. The weighted mean 206 Pb/ 238 U ages of OLT-1 titanite are 1015±5 Ma (2, n=24) and 1017±6 Ma (2, n=24) by single spot and line raster scan analyses, respectively, using BLR-1 titanite as the external standard. These ages are consistent with its reference age of about 1014 Ma. However, using 91500 zircon as the external standard, the weighted mean 206 Pb/ 238 U ages are 917±4 Ma (2, n=24) and 927±5 Ma (2, n=24) for BLR-1 titanite, and 891±4 Ma (2, n=24) and 901±5 Ma (2, n=24) for OLT-1 titanite by single spot and line raster scan analyses, respectively. It is evident that these ages are ~12% younger than their reference values. Our results reveal that significant matrix effect does exist between different kinds of minerals during LA-ICPMS U-Pb age determination, whereas it is insignificant between same minerals. Therefore, same mineral must be used as the external standard for fractionation corrections during in situ LA-ICPMS U-Pb age analysis. In addition, we determined U-Pb ages for titanites from the Early Cretaceous Fangshan pluton, which indicates a rapid cooling history of this pluton. Isotopic geochronology is the key to understand the temporal and special evolution of geological bodies and their related geodynamics. There are many analytical methods to date isotopic ages of geological bodies, while the most commonly used is U-Pb dating of accessory minerals [1]. Minerals such as zircon and monazite have high uranium concentration and U-Pb closure temperature (T c(zircon) >800°C[2]; T c(Monazite)~7 50°C [3]) with low common lead, which makes them to be the preferred target for U-Pb dating. However, zircon and monazite are relatively stable and cannot be reset by the later thermal and chemical processes, due to its physical and chemical resistance. Thus, they are hardly used to constrain the later metamorphic ages of metamorphosed and hydrothermally altered rocks [4,5].Furthermore, some rocks (e.g. ultramafic rocks) do not contain zircon and monazite. Titanite (CaTiSiO 5 ) is one of the common accessory minerals in igneous rocks, and also occurring in metamorphic, hydrothermal and some sedimentary rocks [5][6][7][8]. It usually has relatively high U content (10-100 ppm [7]), which is commonly hold in its crystal lattice. It also has a relatively high U-Pb closure temperature of 650-700°C [9,10], making it an attractive phase as a geochronometer. Moreover, different with zircon and monazite, titanite is mainly composed by major elements of rocks, which easily exchange with other minerals and react with fluid and melt. ...

Succession of Permian and Mesozoic metasomatic events in the eastern Pyrenees with emphasis on the Trimouns talc–chlorite deposit

“…As both titanite and allanite are silicates, we decided to use the GJ-1 zircon as the primary standard. As already explained in Fallourd et al (2014), Sun et al (2012) claimed that titanite can be up to 12 % younger than their known ages using either spot or raster analyses when a zircon standard is used. However, Storey et al (2006) and Darling et al (2012) concluded that the error related to the non-matrix matching between the unknown (titanite and allanite, respectively) and the external standard (zircon) is negligible.…”

Age determination of nephrite by in-situ SIMS U–Pb dating syngenetic titanite: A case study of the nephrite deposit from Luanchuan, Henan, China

“…Titanite is also very common in many nephrite deposits (Cooper, 1995;Ling, 2012;Liu et al, 2010;Lu, 2005;Qin, 2013;Simandl et al, 1999;Tao, 1992). Recent studies demonstrated that titanite U-Pb age determination using modern microbeam techniques (SIMS and LA-ICPMS) has great potential to provide robust constraints on the timing of highto intermediate-grade metamorphism (Li et al, 2014;Rasmussen et al, 2013;Sun et al, 2012). In this study, we present SIMS U-Pb titanite age data for the Luanchuan nephrite deposit in Central China.…”

Polygenetic titanite records the composition of metamorphic fluids during the exhumation of ultrahigh‐pressure metagranite in the Sulu orogen

“…Sample preparation and analytical method for titanite U–Pb dating followed those described by Sun et al . (). The ICP‐MS measurements were carried out using time‐resolved analysis.…”