In situ u-pb rutile dating by la-icp-ms
Reported errors on ratios and are used to calculate Zr, common Pb, Th, and U concen- ages for a single analysis are calculated by propagating trations of the samples, taking the simplified assumption of errors on the peak and background of standards and sam- identical matrix effects between standard and unknown ples, a 0.
- Rutile U-Pb Geochronology.
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Decay constants used correct for ablation yields. The same Luvizotto et al. Stoll is used as a standard which is analyzed twice For low Th phases like rutile, common Pb can be with a laser beam diameter of 50 lm for every 20 unknown accurately calculated by measuring Pb Pbmeas , know- analyses. It has been found that even with 15 s of ablation ing that most Pb is not derived from radioactive decay of at a laser beam size of 12 lm, all determined trace ele- Th within the phase.
Therefore, respectively and the Pb count rate: We for changes to the beam position from point to point. However, rutile contains 50 ppm U. Single fragments contamination, rather than that from the mineral, correc- from the R19 crystal were dissolved employing the pres- tions were made for present-day lead. Elemental separation was per- formed with HCl anion column chemistry to eliminate Ti Results and separate both Pb and U.
From this data set, we excluded 9 analyses due determined by standard runs on NBS common Pb to irregular ablation signals. As can be observed A mass fractionation of 0.
With U concentrations in the ana- less. Analytical conditions are similar to show common Pb concentrations, calculated from count those used for zircon Kelly et al. Analyses were made using a pri- 0.
As usual a field aperture was inserted to reduce range from 1 to more than 2, Please note that in the number of secondary ions coming from the outer part of crustal lead, Pb is ca. It was found that for rutile the O2 Pb, so that e. Under the analytical conditions used, Pb R10 was typically less than 0. Similar count the crystal Table 1; Fig.
Crystal 1, 1, 1, 1, 1, 1, rims at 0 and 8 mm. For this study, we obtained TIMS ages on four 0. Heaman; cited in Clark U ppm Th et al. Still, especially mg for large spots sizes 70—90 lm such changes during 30 s of ablation are minor. Bold horizontal line at Ma represents the TIMS age 2 s error within thickness of line Rutile in metamorphic rocks guarantees that any instability of the ablation process and any sample heterogeneity during a single analysis is All samples from metamorphic rocks analysed in this accounted for and also allows for a robust common Pb study have more than 10 large rutiles [ lm within correction see Eqs.
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Results Large numbers of laser ablation ages are often pooled from concentration measurements gave no U concentra- e. If applied to all results for rutile standard R19, we positions. However, close inspection of the data reveals that average ages for each analytical session Fig. Although subtle, results chemistry are described in Luvizotto and Zack Hence, errors are not 0.
Rutiles from eclogites from the few other local- biotite ages on the other side ca. The highly trace element enriched nature are in excellent agreement with results from this study. Werner and Lippolt , coincident with overgrowth zones in Saidenbach zircons The mineral assemblage is only slightly ret- detrital zircons and rutiles within a given sediment see rograded biotite, phengite and plagioclase formation and also Okay et al. Seventy-two rutile grains have consists mostly of the primary phases garnet—kyanite— been analyzed for trace elements with a lm laser spot quartz—rutile.
Rutile is always very fresh and occurs as Supplementary Material 2 , from which 28 grains ca inclusions in garnet and as a matrix phase. This result can be compared C20 ppm.
All 28 analyzed rutiles plot on the concordia, with other geochronological data, since this unique locality spanning an age range between 1, and 2, Ma, with has spurred extensive investigations. We concur with this conclusion and argue that the 10 single Ma rutile grain also derives from the Adelaide Fold Belt. This becomes clear when the differences are compared for rutile and material transported from the nearby Musgrave Block zircon in the age distribution Fig.
While rutile ages Belousova et al. This is however unlikely as the show only one marked peak at 1, Ma, zircon ages of Musgrave Block should also have provided detrital rutile. Such high temperatures episodes related to Grenvillian, Kimban, and Sleafordian are found both for the 1, Ma age group and for the older orogenic activities, respectively , while rutile ages reflect rutiles.
Sample tion of single rutiles are decoupled if derived from areas EGC-4 is from the middle of the Christie Domain. Here, with slow cooling histories as diffusion rates of Zr and Pb Tomkins et al. What can be concluded from the Zr data of were localized and did not lead to large-scale thermal detrital rutiles from EGC-4, however, is that most rutiles perturbations. Alternatively, it cannot be completely ruled likely originated at granulite-facies conditions, with no out that the 1, Ma age zircon population represents direct age information on their origin.
However, they come from very different lithologies. Furthermore rutiles in IVZ-R6 formed from biotite breakdown amphibolite-facies f i Luvizotto and Zack , while the hydrothermal rutiles R10 and R19 most likely precipitated directly out of a fluid.
Therefore, lated from Zr-in-rutile with the calibration of Tomkins et al. Gray areas indicate that both lithologies and at all temperature conditions with lower rutiles around 1, ages and rutiles significantly older have a temperatures accentuating this effect. Despite the frequent accessory phases like monazite are present in the reaction description of rutile as being a common Pb-rich phase, the domain Harley et al.
This seems et al. Sample IVZ-R6b from the Ivrea Verbano Zone has Instead, the Pb correction method will be invaluable in the youngest rutiles in this study and is therefore particu- future studies in which each spot analysis can be evaluated larly well suited to illustrate the common Pb correction independently.
Examples for such applications are found in based on Pb. To illustrate the having its own protolith.
Also, spot dating will make it power of Pb correction, uncorrected data are shown in a possible to investigate age zoning within single mineral Tera-Wasserburg plot in Fig. All data points are above grains. Rutile may prove to be the best candidate for studying the reverse concordia, forming a mixing line between a age zoning within single crystals see Kooijman et al. It can also be low initial common Pb single spot common Pb correction is observed that the degree of discordance is directly corre- difficult for titanite and apatite.
However, so far no fully in rutiles.
In-situ U/Pb rutile dating by LA-ICP-MS: Pb correction and prospects for ther
Rutiles included in garnet and from the matrix always yielded identical ages for Z and PD This is in striking contrast to knowledge about the timing of the last metamorphic episode. We would also one population and 2 are concordant an assumption that like to thank Dorrit Jacob, Klemens Link, Jasper Berndt-Gerdes, Ellen has to be made for titanites; see e.
Kooijman, and Klaus Mezger for discussions. This project was supported by 1. Blue and pink shaded regions are weighted mean with 1 sigma error for UO and UO 2 correction, respectively. Grey shaded area outlined in black represents published age of standard measured by TIMS Luvizotto et al. Individual rutile U-Pb analyses typically take minutes per spot. The spot size is approximately 45x45 microns. The run table for rutile includes the following: HfO, TaO, Pb, a background measured at 0. It is not practical to measure V, Cr, Nb, and Zr because they occur in high concentrations, and should be measured by electron microprobe or laser ablation.
Analytical depends heavily on U ppm and common Pb ppm. Age uncertainty decreases as rutile age and U concentration increases. However, TIMS destroys the grain and cannot resolve internal age zonation. Also, U-Pb and trace element concentrations can be performed in the same run. Small analytical spot size allows for high spatial resolution.