| 1. |
- Luvizotto, G. L., et al.
(författare)
-
Rutile crystals as potential trace element and isotope mineral standards for microanalysis
- 2009
-
Ingår i: Chemical Geology. - 0009-2541. ; 261:3-4, s. 346-369
-
Tidskriftsartikel (refereegranskat)abstract
- The present paper reports trace element concentrations of 15 elements (V, Cr, Fe, Zr, Nb, Mo, Sn, Sb, Hf, Ta, W, Lu, Pb, Th and U) as well as Ph and Hf isotope data for four relatively homogeneous and large (centimeter size) rutile grains. Methods employed are SIMS, EMP, LA-ICP-MS, ID-MC-ICP-MS and TIMS. For most elements homogeneity is usually within +/- 10% and occasionally variations are even narrower (+/- 5%), particularly in the core of two of the studied grains. The trace element concentrations of the grains span a broad compositional range (e.g., Zr concentrations are ca. 4, 100, 300 and 800 ppm). Provisional concentration values, calculated based on the homogeneity of the element and agreement between techniques, are presented for Zr, Nb, Sn, Sb, Hf, Ta, W and U. The present work represents a significant step forward in finding a suitable mineral standard for rutile microanalysis and encourages not only further search for mineral standards but also applications of rutile in the field of geochemistry and geochronology. In this sense, the rutiles presented here are useful as mineral standard in general in-situ rutile measurements, particularly for Zr-in-rutile thermometry, quantitative provenance studies (Nb and Cr concentrations as index of source rock type) and U-Pb dating. One of the studied grains has a relatively high U concentration (ca. 30 ppm) and rather constant U-Pb ages (1085.1 to 1096.2 Ma (207)Pb/(235)U ages and 1086.3 to 1096.6 Ma, (206)Pb/(238)U ages), favoring its application as an age standard for U-Pb rutile dating. Since Lu concentrations in rutile are very low and Hf concentrations can be relatively high (tens of ppm), detrital rutiles may be suitable for obtaining initial Hf isotope composition of source rocks, therefore the rutiles presented here can be used as calibration material for in-situ rutile Hf isotope studies. (C) 2008 Elsevier B.V. All rights reserved.
|
|
| 2. |
- Smye, A. J., et al.
(författare)
-
Episodic heating of continental lower crust during extension: A thermal modeling investigation of the Ivrea-Verbano Zone
- 2019
-
Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 521, s. 158-168
-
Tidskriftsartikel (refereegranskat)abstract
- Rheology of the continental lower crust plays an integral role in governing the style of continental extension. Temperature-dependent creep deformation in the lower crust decreases lithospheric strength and promotes coupling of deformation in the brittle crust and upper mantle; however, few constraints exist concerning the thermal evolution of extending lower crust. Here, we present a high-temperature thermochronological investigation of the Ivrea-Verbano Zone archetypal continental lower crust that was attenuated during opening of the Alpine Tethys oceanic basin. Rutile U-Pb dates collected from three samples spanning the bottom similar to 2-km of the crustal section are between similar to 160 and similar to 180 Ma, and exhibit near-rim zonations in Zr, Hf, Nb and Ta. Thermal-kinematic modeling of these data, combined with existing rutile U-Pb dates, show that the base of the Ivrea-Verbano Zone experienced heating on two timescales: conductive heating over similar to 10 Myr, associated with thinning of the lithospheric mantle, and advective heating over <0.1 Myr, associated with high-temperature infiltration of fluids during crustal exhumation. These constraints match the thermal predictions of geodynamic models that predict high-magnitude thinning of lithospheric mantle during the early stages of extension. Conductive heating of lower crust directly preceded mantle exhumation and crustal excision, suggesting that thermal weakening of the lithosphere promotes focusing of extensional strain. (C) 2019 Elsevier B.V. All rights reserved.
|
|
| 3. |
- Soares, C. J., et al.
(författare)
-
Characterisation of Apatites as Potential Uranium Reference Materials for Fission-track Dating by LA-ICP-MS
- 2015
-
Ingår i: Geostandards and Geoanalytical Research. - 1639-4488. ; 39:3, s. 305-313
-
Tidskriftsartikel (refereegranskat)abstract
- k crystal (6.9gg(-1)U). The relative standard deviation (1 RSD) of the U concentration determined by ID-ICP-MS of both apatite crystals was 1.5%, whereas 1 RSD for the We report homogeneity tests on large natural apatite crystals to evaluate their potential as U reference materials for apatite fission-track (AFT) thermochronology by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The homogeneity tests include the measurements of major element concentrations by electron probe microanalysis (EPMA), whereas for U concentration, isotope dilution (ID) ICP-MS and laser ablation (LA) ICP-MS were employed. Two apatite crystals are potential reference materials for LA-ICP-MS analysis: a 1cm(3) fraction of a Durango crystal (7.5gg(-1)U) and a 1cm(3) Mud TanLA-ICP-MS results was better than 4%, providing sufficient homogeneity for fission-track dating. The results on the U homogeneity for two different apatite samples are an important step towards establishing in situ dating routines for AFT analysis by LA-ICP-MS. Nous restituons des tests d'homogeneite sur des grands cristaux d'apatite naturelle afin d'evaluer leur potentiel en tant que materiaux de reference pour l'U en vue d'une application dans le domaine de la thermochronologie par traces de fission sur apatite (AFT) par spectrometrie de masse a plasma induit couplee a l'ablation laser (LA-ICP-MS). Les tests d'homogeneite incluent des mesures des concentrations en elements majeurs par microsonde electronique (EPMA), alors que pour la concentration en U, la dilution isotopique (ID) ainsi que l'ablation laser (LA) ICP-MS ont ete employees. Deux cristaux d'apatite sont des materiaux de reference possibles pour les analyses LA-ICP-MS: une fraction d'1 cm(3) d'un cristal de Durango (7,5 mu gg(-1)U) et un cristal d'1cm(3) de Mud Tank (6,9 mu gg(-1)U). L'ecart type relatif (1RSD) de la concentration en U determinee par ID-ICP-MS des deux cristaux d'apatite est 1,5%, tandis que celui pour les resultats LA-ICP-MS est inferieur a 4%, offrant ainsi une homogeneite suffisante pour les datations par la methode des traces de fission sur apatite. Les resultats concernant l'homogeneite de l'U pour deux echantillons differents d'apatite sont une etape importante vers la possibilite d'envisager des datations AFT in situ en routine par LA-ICP-MS.
|
|
| 4. |
- Zack, Thomas, 1968, et al.
(författare)
-
In situ U-Pb rutile dating by LA-ICP-MS: Pb-208 correction and prospects for geological applications
- 2011
-
Ingår i: Contributions to Mineralogy and Petrology. - 0010-7999. ; 162:3, s. 515-530
-
Tidskriftsartikel (refereegranskat)abstract
- Rutile is a common accessory mineral that occurs in a wide spectrum of metamorphic rocks, such as in blueschists, eclogites, and granulites and as one of the most stable detrital heavy minerals in sedimentary rocks. The advent of rutile trace element thermometry has generated increased interest in a better understanding of rutile formation. This study documents important analytical advances in in situ LA-ICP-MS U/Pb geochronology of rutile: (1) Matrix matching, necessary for robust in situ dating is fulfilled by calibrating and testing several rutile standards (R10, R19, WH-1), including the presentation of new TIMS ages for the rutile standard R19 (489.5 +/- A 0.9 Ma; errors always stated as 2 s). (2) Initial common lead correction is routinely applied via Pb-208, which is possible due to extremely low Th/U ratios (usually < 0.003) in most rutiles. Employing a 213 nm Nd:YAG laser coupled to a quadrupole ICP-MS and using R10 as a primary standard, rutile U/Pb concordia ages for the two other rutile standards (493 +/- A 10 Ma for R19; 2640 +/- A 50 Ma for WH-1) and four rutile-bearing metamorphic rocks (181 +/- A 4 Ma for Ivrea metapelitic granulite; 339 +/- A 7 Ma for Saidenbach coesite eclogite; 386 +/- A 8 Ma for Fjortoft UHP metapelite; 606 +/- A 12 Ma for Andrelandia metepelitic granulite) always agree within 2% with the reported TIMS ages and other dating studies from the same localities. The power of in situ U/Pb rutile dating is illustrated by comparing ages of detrital rutile and zircon from a recent sediment from the Christie Domain of the Gawler Craton, Australia. While the U/Pb age spectrum from zircons show several pronounced peaks that are correlated with magmatic episodes, rutile U/Pb ages are marked by only one pronounced peak (at ca 1,675 Ma) interpreted to represent cooling ages of this part of the craton. Rutile thermometry of the same detrital grains indicates former granulite-facies conditions. The methods outlined in this paper should find wide application in studies that require age information of single spots, e.g., provenance studies, single-crystal zoning and texturally controlled dating.
|
|
