| 41. |
- Konrad-Schmolke, Matthias, 1970, et al.
(författare)
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Discrimination of thermodynamic and kinetic contributions to the heavy rare earth element patterns in metamorphic garnet
- 2022
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Ingår i: Journal of Metamorphic Geology. - : Wiley. - 0263-4929 .- 1525-1314. ; 41:4, s. 465-90
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Tidskriftsartikel (refereegranskat)abstract
- Variations of rare earth element (REE) concentrations in metamorphic garnet are an important source of information of geodynamic and geochemical processes in the deeper Earth. In order to extract this information, the thermodynamic equilibrium and kinetic contributions of the REE uptake in garnet must be distinguished and quantified. Utilizing high-resolution trace element and μ-Raman mapping together with combined thermodynamic–geochemical–diffusion models, we demonstrate that the equilibrium and kinetic aspects of the REE uptake in metamorphic garnet can be discriminated by interpreting 2D trace element mapping in a single sample. The heavy (H) REE (Tb to Lu) zoning in the investigated garnet from a high-pressure blueschist comprises an inner part with an overall decrease from core to inner rim, followed by a concentric zone of HREE enrichment and a drastic HREE decrease towards the outermost rim. The central peak in the garnet core decreases in intensity with decreasing atomic number of the REE. The broad overall shape of this pattern resembles those often observed in metamorphic garnet from different rock types and tectonic settings. Superimposed on this trend is a concentric pattern of minor recurring fluctuations in the HREE concentrations with at least six regularly spaced sets of peaks and troughs along the entire garnet radius. Comparison of the observed inclusion suite, the trace element maps and thermodynamic–geochemical models show that the inner part with decreasing HREE concentrations results from fractional garnet growth in an unchanged mineral assemblage, whereas the REE enrichment zone is caused by the breakdown of titanite. We suggest that the width of the central peak is controlled by the bulk permeability of the interconnected transport matrix and the fraction of matrix minerals that the garnet equilibrates with. The superimposed REE fluctuations result from changing element transport properties of the host rock and mark recurring changes from equilibrium REE uptake to transport-limited REE uptake in garnet. Such fluctuating element transport properties can be best explained by pulse-like fluid fluxes that rhythmically change the interconnectivity of the intercrystalline transport matrix. Increasing numbers of published spatially highly resolved REE analyses show that such trace element fluctuations are common in metamorphic garnet indicating that recurring changes in rock permeabilities due to pulsed fluid fluxes are a common phenomenon during metamorphism.
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| 42. |
- Marks, Michael A. W., et al.
(författare)
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The F, Cl, Br and I Contents of Reference Glasses BHVO-2G, BIR-1G, BCR-2G, GSD-1G, GSE-1G, NIST SRM 610 and NIST SRM 612
- 2017
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Ingår i: Geostandards and Geoanalytical Research. - : Wiley. - 1639-4488 .- 1751-908X. ; 41:1, s. 107-122
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Tidskriftsartikel (refereegranskat)abstract
- Halogen contents for the widely distributed reference glasses BHVO-2G, BIR-1G, BCR-2G, GSD-1G, GSE-1G, NIST SRM 610 and NIST SRM 612 were investigated by pyrohydrolysis combined with ion chromatography, total reflection X-ray fluorescence analysis, instrumental neutron activation analysis, the noble gas method, electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Glasses BHVO-2G, GSD-1G and GSE-1G have halogen contents that can be reproduced at the 15% level by all bulk techniques and cover a significant range in halogen mass fractions for F (~ 20–300 μg g−1), Cl (~ 70–1220 μg g−1) and Br (~ 0.2–285 μg g−1) and I (~ 9–3560 ng g−1). The BIR-1G glass has low F (< 15 μg g−1), Cl (~ 20 μg g−1), Br (15 ng g−1) and I (3 ng g−1). The halogen contents for the silica-rich NIST SRM 610 and 612 glasses were poorly reproduced by the different techniques. The relatively high Cl, Br and I abundances in glasses GSD-1G and GSE-1G mean that these glasses are well suited for calibrating spatially resolved micro-analytical studies on silicate glasses, melt and fluid inclusions. Combined EPMA and laser ablation-inductively coupled plasma-mass spectrometry data for glass GSE-1G demonstrate homogeneity at the 10% level for Cl and Br.
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| 43. |
- Rösel, D, et al.
(författare)
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LA-ICP-MS U–Pb dating of detrital rutile and zircon from the Reynolds Range: A window into the Palaeoproterozoic tectonosedimentary evolution of the North Australian Craton
- 2014
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 255:1, s. 381-400
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Tidskriftsartikel (refereegranskat)abstract
- The Palaeoproterozoic Reynolds Range of the Arunta Region, central Australia, comprises a series of shallow marine clastic sediments (Reynolds Range Group) which overlies deeper water sequences of turbidites (Lander Rock Formation) and minor sandstones (“unnamed sandstone”). U–Pb age data collected from detrital rutile and zircon in these rocks indicates these sequences contain very similar age spectra, although with a notable and important shift to younger ages within the stratigraphically younger Reynolds Range Group. Detrital zircons from the “unnamed sandstone” directly underlying the unconformity with the Reynolds Range Group contain a major age component at ca. 1860 Ma, together with a wide spread of ages between ca. 3.2 and 2.0 Ga and a minor age component of 1830–1805 Ma. Detrital rutile from the same rock yield a unimodal age spectrum with a mean age of ca. 1840 Ma. The detrital zircon age spectrum from the Reynolds Range Group is similar, although the youngest cluster of ages is younger and dates to between 1800 Ma and 1780 Ma. Detrital rutile from these rocks yield a unimodal age spectrum with a mean age of ca. 1790 Ma. Although the observed differences in ages are subtle, we suggest these nevertheless mark a significant change in provenance. We attribute the predominance of 1860–1820 Ma detrital zircon and 1840 Ma detrital rutile within the “unnamed sandstone” and the characteristic ca. 1860 Ma detrital zircon age cluster in previously published provenance studies from the Lander Rock Formation to uplift and erosion of the Halls Creek–Pine Creek Orogen. This orogenic belt marks collision between the North Australian and Kimberley cratons, an event dated to between 1835 Ma and 1810 Ma and which incorporates marginally older rocks dating to 1860 Ma from the foreland of the Kimberley Craton. By contrast we attribute the influx of younger rutile and zircon, together with a distinct facies change observed with the onset of the deposition of the Reynolds Range Group, to a shift in provenance region to the Yapungku Orogen, which marks the collision between the West Australian and North Australian cratons and is dated to ca. 1800–1765 Ma. A change in provenance is additionally consistent with significant differences in rutile trace element composition. The Lander Rock Formation and the Reynolds Range Group are stratigraphically correlated with sedimentary rocks that overly large parts of the North Australian Craton. We suggest this indicates spatially continuous basinal conditions within the North Australian Craton between ca. 1840 Ma and 1780 Ma, although the erosion and drainage systems feeding this basin were strongly influenced by the collision and orogenesis along the northwest and southwest margins of the North Australian Craton.
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| 44. |
- Sengun, Firat, et al.
(författare)
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Trace element composition of rutile and Zr-in-rutile thermometry in meta-ophiolitic rocks from the Kazdag Massif, NW Turkey
- 2016
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Ingår i: Mineralogy and Petrology. - 0930-0708. ; 110, s. 547-560
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Tidskriftsartikel (refereegranskat)abstract
- In northwest Turkey, ophiolitic meta-gabbros are exposed on the Kazdağ Massif located in the southern part of the Biga Peninsula. Trace element composition of rutile and Zr-in-rutile temperatures were determined for meta-gabbros from the Kazdağ Massif. The Zr content of all rutiles range from 176 to 428 ppm and rutile grains usually have a homogeneous Zr distribution. The rutile grains from studied samples in the Kazdağ Massif are dominated by subchondritic Nb/Ta (11–19) and Zr/Hf ratios (20–33). Nb/Ta and Zr/Hf show positive correlation, which is probably produced by silicate fractionation. The Nb/Ta and Zr/Hf ratios increase with a decrease in Ta and Hf contents. The core of rutile grains are generally characterized by low Nb/Ta ratios of 17–18 whereas the rims exhibit relatively high Nb/Ta ratios of 19–23. Trace element analyses in rutile suggest that these rutile grains were grown from metamorphic fluids. The P-T conditions of meta-gabbros were estimated by both Fe–Mg exchange and Zr-in-rutile thermometers, as well as by the Grt-Hb-Plg-Q geothermobarometer. The temperature range of 639 to 662 °C calculated at 9 kbar using the Zr-in-rutile thermometer is comparable with temperature estimates of the Fe-Mg exchange thermometer, which records amphibolite-facies metamorphism of intermediate P-T conditions. The P-T conditions of meta-ophiolitic rocks suggest that they occur as a different separate higher-pressure tectonic slice in the Kazdağ metamorphic sequence. Amphibolite-facies metamorphism resulted from northward subduction of the İzmir-Ankara branch of the Neo-Tethyan Ocean under the Sakarya Zone. Metamorphism was followed by internal imbrication of the Kazdağ metamorphic sequence resulting from southerly directed compression during the collision.
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| 45. |
- Smit, Matthijs, et al.
(författare)
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Early evolution of the Pamir deep crust from Lu-Hf and U-Pb geochronology and garnet thermometry
- 2014
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Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 42:12, s. 1047-1050
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Tidskriftsartikel (refereegranskat)abstract
- Determining early orogenic processes within the Pamir-Tibet orogen represents a critical step toward constructing a comprehensive model on the tectonic evolution of the region. Here we investigate the timing and cause of prograde metamorphism of Cenozoic metamorphic rocks from the Pamir plateau through Lu-Hf geochronology, U-Pb rutile thermochronology, and garnet thermometry. Regional prograde metamorphism and heating to 750–830 °C, as constrained by thermometry, occurred between 37 and 27 Ma. Prograde growth of garnet first occurred in the South Pamir and spread to the Central Pamir during the following 10 m.y. The early metamorphism is attributed to high mantle heat flow following the ca. 45 Ma break-off of the Indian slab south of the Pamir. Our investigation confirms a long-lived thermal history of the Pamir deep crust before the Miocene, and provides a causal link between break-off, enhanced mantle heat flow, and prograde heating of the subduction hanging wall.
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| 46. |
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| 47. |
- Zhang, Yi Ge, et al.
(författare)
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Refining the alkenone-pCO2 method II : Towards resolving the physiological parameter ‘b’
- 2020
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 281, s. 118-134
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Tidskriftsartikel (refereegranskat)abstract
- Haptophyte algal biomarkers called alkenones are widely used to reconstruct atmospheric CO2 in Earth’s Cenozoic history. This method is based on the notion that the algal carbon isotope fractionation during photosynthesis, as represented by ep37:2, is a function of seawater CO2 concentration and algal physiology. Constraining the algal physiological parameter, known as the ‘b’ term, is the key for successful applications of the alkenone-CO2 method. Using sensitivity analyses, we show that the growth rate (µ), cell size (r), and membrane permeability (P) are the most important variables to determine b. For all life on Earth, body size is a key factor that regulates metabolic rates. Exploiting the interdependence between phytoplankton cell size and growth rate, and specifically, the r – µ relationship for coccolithophores, we show that the length of fossil coccoliths (Lcoccolith) produced by ancient alkenone-synthesizers can be used to estimate r and therefore µ. Combining our new Lcoccolith data and published ep37:2 from the South China Sea Site MD01-2392, existing results from ODP Site 925, and ice core CO2, we determined the cell membrane permeability (P = 5.09 10-5 m s-1) for the Pleistocene community employing a bootstrap resampling technique. These new methods of constraining r, µ and P, combined with proxy-derived temperature (T), led us to rebuild b as a variable for each sample individually, which is subsequently used for alkenone-CO2 calculations. Application of this approach established pCO2 of the last 3 glacial-interglacial cycles, which turns out to be comparable with the ice core data in both the amplitude of changes and absolute values. It also reconciles the published Eocene – Oligocene alkenone-CO2 data which showed large geographical differences, with the new estimates much more consistent among different sites, and in line with other proxy-based results and ice sheet model predictions.
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| 48. |
- Brinkmann, Inda, et al.
(författare)
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Drought recorded by Ba/Ca in coastal benthic foraminifera
- 2022
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 19:9, s. 2523-2535
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Tidskriftsartikel (refereegranskat)abstract
- Increasing occurrences of extreme weather events, such as the 2018 drought over northern Europe, are a concerning issue under global climate change. High-resolution archives of natural hydroclimate proxies, such as rapidly accumulating sediments containing biogenic carbonates, offer the potential to investigate the frequency and mechanisms of such events in the past. Droughts alter the barium (Ba) concentration of near-continent seawater through the reduction in Ba input from terrestrial runoff, which in turn may be recorded as changes in the chemical composition (Ba/Ca) of foraminiferal calcium carbonates accumulating in sediments. However, so far the use of Ba/Ca as a discharge indicator has been restricted to planktonic foraminifera, despite the high relative abundance of benthic species in coastal, shallow-water sites. Moreover, benthic foraminiferal Ba/Ca has mainly been used in open-ocean records as a proxy for paleo-productivity. Here we report on a new geochemical data set measured from living (CTG-labeled) benthic foraminiferal species to investigate the capability of benthic Ba/Ca to record changes in river runoff over a gradient of contrasting hydroclimatic conditions. Individual foraminifera (Bulimina marginata, Nonionellina labradorica) were analyzed by laser-ablation ICP-MS over a seasonal and spatial gradient within Gullmar Fjord, Swedish west coast, during 2018-2019. The results are compared to an extensive meteorological and hydrological data set, as well as sediment and pore-water geochemistry. Benthic foraminiferal Ba/Ca correlates significantly to riverine runoff; however, the signals contain both spatial trends with distance to Ba source and species-specific influences such as micro-habitat preferences. We deduce that shallow-infaunal foraminifera are especially suitable as proxy for terrestrial Ba input and discuss the potential influence of water-column and pore-water Ba cycling. While distance to Ba source, water depth, pore-water geochemistry, and species-specific effects need to be considered in interpreting the data, our results demonstrate confidence in the use of Ba/Ca of benthic foraminifera from near-continent records as a proxy for past riverine discharge and to identify periods of drought.
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| 49. |
- Moldan, Filip, et al.
(författare)
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Bedömningsgrunder försurning - tester av MAGIC-biblioteket
- 2022
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Rapport (refereegranskat)abstract
- IVL Svenska Miljöinstitutet har tillsammans med Sveriges lantbruksuniversitet (SLU) på uppdrag av Havs-och vattenmyndigheten undersökt ett antal frågeställningar angående bedömningsverktyget MAGIC-biblioteket baserade på synpunkter och data från kalkningsansvariga handläggare på länsstyrelserna.MAGIC-biblioteket är ett försurningsbedömningsverktyg som gör att sjöar och vattendrag kan bedömas utifrån ett liknande vatten. På det sättet har tiotusentals sjöar och vattendrag bedömts. I samband med bedömningarna har det identifierats ett antal fall där beräknade referensvärden bedömts vara orealistiska utifrån annan kunskap som användarna av MAGIC-biblioteket besitter. Ett utskick gjordes till kalkningsansvariga handläggare på länsstyrelserna där det efterfrågades underlag på sådana objekt där försurningsbedömning med MAGIC-biblioteket anses vara felaktig. Så mycket relevant bakgrundsinformation som möjligt efterfrågades för att möjliga förklaringar till de olika bedömningarna skulle kunna undersökas. Svar kom in från åtta länsstyrelser. Utifrån det insamlade materialet jämfördes MAGIC (Model of Acidification of Groundwater in Catchments)-modellerade objekt och MAGIC-bibliotekets resultat med historiska fiskdata, med uppmätt vattenkemi inklusive trender över tid och en jämförelse med uppmätt och modellerat atmosfäriskt nedfall gjordes.I studien jämfördes förekomst av mört från slutet av 1800-talet i Värmland med modellerad vattenkemi. Mört har förekommit i merparten av sjöarna, inklusive sjöar med lågt modellerat pH. Det är dock en tydligt minskande andel sjöar med förekomst av mört ju lägre modellerat pH vattnen har. Detta skiljer sig från till exempel den betydligt mindre försurningskänsliga abborren, där inget samband mellan förekomst och historiskt modellerat pH kunde urskiljas. Sjöar med lågt pH och där mört förekom i slutet av 1800-talet har i genomsnitt högre halt av löst organiskt kol än sjöar med högre pH.En jämförelse mellan uppmätta tidsserier från sjöar samt modellerade värden för samma sjö i MAGIC-biblioteket visar att magnituden av den modellerade trenden i många fall större än den observerade trenden. Bilden är inte helt entydig och skillnaderna är större för sulfat än för ANC (syraneutraliserande förmåga), men att modellen överskattar trenden förekommer betydligt oftare än tvärt om. Detta beror till största delen på att det finns en tendens för modellen att överskatta sulfathalten i sjöarna vid den tidpunkt då vattenförekomsterna började provtas. Orsaken till detta kan variera, men korrekt modellering av tidstrender i avrinningen förutsätter att tidsutvecklingen av nedfallet av svavel, kväve och baskatjoner som användes i modelleringen följt verkligheten även på platser och under tidsperioder där det inte finns data att grunda modellberäkningar på.
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| 50. |
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