| 1. |
- Fumes, R. A., et al.
(författare)
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Petrochronology of high-pressure granulite facies rocks from Southern Brasilia Orogen, SE Brazil: Combining quantitative compositional mapping, single-element thermometry and geochronology
- 2022
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Ingår i: Journal of Metamorphic Geology. - : Wiley. - 0263-4929 .- 1525-1314. ; 40:3, s. 517-552
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Tidskriftsartikel (refereegranskat)abstract
- We use a combination of several in situ techniques to assess the P-T-t path of high-pressure granulites from the Passos Nappe in the Southern Brasilia Orogen (SE Brazil). Quantitative element mapping and single-element thermometers (Zr-in-rutile and Ti-in-quartz) are coupled with P-T pseudosections and monazite and rutile dating. Compositional and temperature maps, based on cathodoluminescence mapping and in situ analyses of Ti-in-quartz, are presented as a novel approach to evaluate crystallization temperature. The studied rocks have a pelitic protolith and record a peak pressure assemblage of garnet + kyanite + rutile + K-feldspar + quartz + melt +/- plagioclase that formed at similar to 830 degrees C and 1.2 GPa. Retrograde conditions of similar to 560 degrees C and 0.6 GPa are determined based on the grossular content of garnet and the crystallization of biotite and ilmenite. Metamorphic peak conditions occurred ca. 635 Ma, according to monazite dating, with a younger date of ca. 615 Ma associated with later kyanite crystallization. Rutile ages of ca. 590 Ma are linked to the late retrograde stage (at similar to 600 degrees C). Results show that the distribution of Ti-in-quartz is heterogeneous, decreasing in abundance towards the rim of crystals, though the higher temperatures constrained with Ti-in-quartz thermometry are broadly consistent with peak conditions. The peak pressure conditions are consistent with continental collision setting in the Southern Brasilia Orogen and were followed by an early cooling/decompression stage and then by a slow cooling during exhumation and transport to shallower crustal levels.
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| 2. |
- Zack, Thomas, 1968, et al.
(författare)
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In situ U-Pb rutile dating by LA-ICP-MS: Pb-208 correction and prospects for geological applications
- 2011
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Ingår i: Contributions to Mineralogy and Petrology. - 0010-7999. ; 162:3, s. 515-530
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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.
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| 3. |
- Luvizotto, G. L., et al.
(författare)
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Nb and Zr behavior in rutile during high-grade metamorphism and retrogression: An example from the Ivrea-Verbano Zone
- 2009
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Ingår i: Chemical Geology. - 0009-2541. ; 261:3-4, s. 303-317
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Tidskriftsartikel (refereegranskat)abstract
- Detailed textural observations and in situ analyses (EMP, SIMS and LA-ICP-MS) are used to characterize trace element behavior during prograde and retrograde metamorphic reactions involving rutile. The Ivrea-Verbano Zone is a classic granulite area and rocks from the Strona and d'Ossola valleys are an example of the amphibolite to granulite facies transition. Although different rock types occur in the area, detailed sampling and petrographic work show that rutile only occurs in granulite facies paragneisses. These rocks show a rich inventory of textures that allow not only for the investigation of trace element behavior in response to prograde rutile growth, but also for the effect of post-peak processes on rutile chemistry. Nb concentrations in rutile from lower grade samples show a larger spread (from 500 to 5000 ppm within one sample) when compared to those from higher grades. This pattern can be modeled using prograde rutile growth formed from biotite breakdown. Zr concentrations in rutile are characterized by an anomalously large spread and a bimodal distribution. Maximum Zr concentrations increase according to the general metamorphic gradient known for this area. Temperatures (from Zr-in-rutile thermometry), although feasible, are considerably higher than previous calculations (increasing from ca. 850 to 930 degrees C). A second cluster of Zr concentrations in rutile occurs at rather constant concentrations (ca. 1000 ppm) for all localities and is interpreted to be related to intense fluid influx at high-temperature and/or to post-peak diffusional resetting favored by slow cooling rates. Alteration textures, characterized by a complex network of micro-veins, are evidence for the late fluid influx The fluid strongly affected the rutiles, which is evidenced by corrosion of older rutile grains and formation of rutile veinlets. (C) 2008 Elsevier B.V. All rights reserved.
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| 4. |
- Luvizotto, G. L., et al.
(författare)
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Rutile crystals as potential trace element and isotope mineral standards for microanalysis
- 2009
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Ingår i: Chemical Geology. - 0009-2541. ; 261:3-4, s. 346-369
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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.
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| 5. |
- Luvizotto, G. L., et al.
(författare)
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Rutile occurrence and trace element behavior in medium-grade metasedimentary rocks: example from the Erzgebirge, Germany
- 2009
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Ingår i: Mineralogy and Petrology. - 0930-0708. ; 97:3-4, s. 233-249
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Tidskriftsartikel (refereegranskat)abstract
- Metamorphic textures in medium-grade (similar to 500-550A degrees C) metasedimentary rocks from the Erzgebirge give evidence of prograde rutile crystallization from ilmenite. Newly-crystallized grains occur as rutile-rich polycrystalline aggregates that pseudomorph the shape of the ilmenites. In-situ trace element data (EMP and SIMS) show that rutiles from the higher-grade samples record large scatter in Nb content and have Nb/Ti ratios higher than coexisting ilmenite. This behavior can be predicted using prograde rutile crystallization from ilmenite and indicates that rutiles are reequilibrating their chemistry with remaining ilmenites. On the contrary, rutiles from the lowest grade samples (similar to 480A degrees C) have Nb/Ti ratios that are similar to the ones in ilmenite. Hence, rutiles from these samples did not equilibrate their chemistry with remaining ilmenites. Our data suggest that temperature may be one of the main factors determining whether or not the elements are able to diffuse between the phases and, therefore, reequilibrate. Newly-crystallized rutiles yield temperatures (from similar to 500 to 630A degrees C, Zr-in-rutile thermometry) that are in agreement with the metamorphic conditions previously determined for the studied rocks. In quartzites from the medium-grade domain (similar to 530A degrees C), inherited detrital rutile grains are detected. They are identified by their distinct chemical composition (high Zr and Nb contents) and textures (single grains surrounded by fine grained ilmenites). Preliminary calculation, based on grain size distribution of rutile in medium-grade metapelites and quartzites that occur in the studied area, show that rutiles derived from quartzites can be anticipated to dominate the detrital rutile population, even if quartzites are a minor component of the exposure.
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| 6. |
- Santos, C. A., et al.
(författare)
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Metamorphism of retroeclogites from the Passos Nappe, Southern Brasilia Orogen
- 2021
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Ingår i: Journal of South American Earth Sciences. - : Elsevier BV. - 0895-9811. ; 112
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure metamafic rocks from the Passos Nappe, Southern Brasilia Orogen, have been traditionally interpreted as highly retrogressed eclogites, even though no reliable P-T conditions were available thus far. In this work, samples from the least retrogressed sample were studied using petrography, mineral and whole-rock chemical analysis, thermodynamic modelling, and rutile U-Pb geochronology, with the objective of unravelling its metamorphic history. The studied rocks are, descriptively, hornblende-garnet-clinopyroxene schists. Garnet and hornblende occur in a matrix composed of clinopyroxene-plagioclase symplectite, with garnet being surrounded by plagioclase-hornblende coronas. A combination of thermodynamic modelling, Zr-in-rutile and Ti-in quartz thermobarometry suggests peak temperature to be 725 +/- 30 degrees C, attained at a minimum pressure of approximate to 16 kbar, and data from rutile and quartz crystals included in garnet qualitatively indicate an earlier stage at higher P and lower T, constraining a clockwise P-T path. No evidences of UHP metamorphism were found thus far. A lower intercept age of 579 +/- 23 Ma was calculated from rutile data, which is identical, within uncertainty, to rutile ages obtained previously in units immediately above the rocks studied here. The data suggests that these rocks were submitted to a different P-T path compared to the adjacent units, and that they were subducted to depths of at least approximate to 60 km and tectonically emplaced amid the surrounding metapelitic rocks before 579 Ma, which is compatible with current models for the evolution of the Southern Brasilia Orogen.
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| 7. |
- Triebold, S., et al.
(författare)
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Deducing source rock lithology from detrital rutile geochemistry: An example from the Erzgebirge, Germany
- 2007
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Ingår i: Chemical Geology. - 0009-2541. ; 244:3-4, s. 421-436
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the applicability of rutile trace element geochemistry to provenance studies. The study area is the Erzgebirge in eastern Germany, where metamorphic rocks ranging from lower greenschist facies conditions up to granulite facies conditions are exposed. We collected sand and rock samples from small catchment areas for a comparative analysis of rutile geochemistry using wavelength-dispersive electron microprobe. Our results show that rutile geochemistry is a powerful tool in provenance studies, allowing for the identification of source lithologies and an evaluation of the host orogen's metamorphic history. The log (Cr/Nb) ratio has proven to be decisive in discriminating between mafic and metapelitic lithologies. It is also useful for identifying different source rocks when plotted versus a third element or proxy. Furthermore, our results suggest that rutile thermometry can be applied to a much wider range of lithologies than previously assumed. A quantification of temperature populations within single sand samples shows that at high-grade metamorphic conditions, such as those found in the Erzgebirge, more than 65% of rutiles do not re-equilibrate during retrograde metamorphism and thus retain their peak temperature chernistry. Such samples, which have equilibrated at recent metamorphic conditions, can be identified by their 2-sigma standard deviations of less than 120 degrees C. Below 550-600 degrees C, no complete equilibration is reached. Rutiles from greenschist facies and lower metamorphic conditions in the Erzgebirge still inherit relict temperatures from a former metamorphic cycle. They partly record very high temperatures >950 degrees C and supposedly derive from erosion of the west African craton in Ordovician time. (C) 2007 Elsevier B.V. All rights reserved.
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| 8. |
- Triebold, S., et al.
(författare)
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Discrimination of TiO2 polymorphs in sedimentary and metamorphic rocks
- 2011
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Ingår i: Contributions to Mineralogy and Petrology. - 0010-7999. ; 161:4, s. 581-596
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Tidskriftsartikel (refereegranskat)abstract
- Investigation by Raman spectroscopy of samples from different geological settings shows that the occurrence of TiO2 polymorphs other than rutile can hardly be predicted, and furthermore, the occurrence of anatase is more widespread than previously thought. Metamorphic pressure and temperature, together with whole rock chemistry, control the occurrence of anatase, whereas variation of mineral assemblage characteristics and/or fluid occurrence or composition takes influence on anatase trace element characteristics and re-equilibration of relict rutiles. Evaluation of trace element contents obtained by electron microprobe in anatase, brookite, and rutile shows that these vary significantly between the three TiO2 phases. Therefore, on the one hand, an appropriation to source rock type according to Nb and Cr contents, but as well application of thermometry on the basis of Zr contents, would lead to erroneous results if no phase specification is done beforehand. For the elements Cr, V, Fe, and Nb, variation between the polymorphs is systematic and can be used for discrimination on the basis of a linear discriminant analysis. Using phase group means and coefficients of linear discriminants obtained from a compilation of analyses from samples with well-defined phase information together with prior probabilities of groupings from a natural sample compilation, one is able to calculate phase grouping probabilities of any TiO2 analysis containing at least the critical elements Cr, V, Fe, and Nb. An application of this calculation shows that for the appropriation to the phase rutile, a correct-classification rate of 99.5% is obtained. Hence, phase specification by trace elements proves to be a valuable tool besides Raman spectroscopy.
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