ORCID Profile
0000-0003-1083-4730
Current Organisation
Universität Bern
Does something not look right? The information on this page has been harvested from data sources that may not be up to date. We continue to work with information providers to improve coverage and quality. To report an issue, use the Feedback Form.
Publisher: Elsevier BV
Date: 10-2016
Publisher: European Association of Geochemistry
Date: 10-2022
Publisher: Elsevier BV
Date: 06-2016
Publisher: Copernicus GmbH
Date: 09-03-2021
DOI: 10.5194/GCHRON-3-123-2021
Abstract: Abstract. Epidote – here defined as minerals belonging to the epidote–clinozoisite solid solution – is a low-μ (μ=238U/204Pb) mineral occurring in a variety of geological environments and participating in many metamorphic reactions that is stable throughout a wide range of pressure–temperature conditions. Despite containing fair amounts of U, its use as a U−Pb geochronometer has been hindered by the commonly high contents of initial Pb, with isotopic compositions that cannot be assumed a priori. We present a U−Pb geochronology of hydrothermal-vein epidote spanning a wide range of Pb (3.9–190 µg g−1), Th (0.01–38 µg g−1), and U (2.6–530 µg g−1) contents and with μ values between 7 and 510 from the Albula area (eastern Swiss Alps), from the Grimsel area (central Swiss Alps), and from the Heyuan fault (Guangdong Province, China). The investigated epidote s les show appreciable fractions of initial Pb contents (f206=0.7–1.0) – i.e., relative to radiogenic Pb – that vary to different extents. A protocol has been developed for in situ U−Pb dating of epidote by spot-analysis laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) with a magmatic allanite as the primary reference material. The suitability of the protocol and the reliability of the measured isotopic ratios have been ascertained by independent measurements of 238U/206Pb and 207Pb/206Pb ratios, respectively, with quadrupole and multicollector ICP-MS applied to epidote micro-separates digested and diluted in acids. For age calculation, we used the Tera–Wasserburg (207Pb/206Pb versus 238U/206Pb) diagram, which does not require corrections for initial Pb and provides the initial 207Pb/206Pb ratio. Petrographic and microstructural data indicate that the calculated ages date the crystallization of vein epidote from a hydrothermal fluid and that the U−Pb system was not reset to younger ages by later events. Vein epidote from the Albula area formed in the Paleocene (62.7±3.0 Ma) and is related to Alpine greenschist-facies metamorphism. The Miocene (19.2±4.3 and 16.9±3.7 Ma) epidote veins from the Grimsel area formed during the Handegg deformation phase (22–17 Ma) of the Alpine evolution of the Aar Massif. Identical initial 207Pb/206Pb ratios reveal homogeneity in Pb isotopic compositions of the fluid across ca. 100 m. Vein epidote from the Heyuan fault is Cretaceous in age ( 107.2±8.9 Ma) and formed during the early movements of the fault. In situ U−Pb analyses of epidote returned reliable ages of otherwise undatable epidote–quartz veins. The Tera–Wasserburg approach has proven pivotal for in situ U−Pb dating of epidote, and the decisive aspect for low age uncertainties is the variability in intra-s le initial Pb fractions.
Publisher: Elsevier BV
Date: 2022
Publisher: Copernicus GmbH
Date: 20-05-2022
DOI: 10.5194/EGUSPHERE-2022-311
Abstract: Abstract. Deformation of polymineralic aggregates can be accommodated by viscous granular flow, a process mediated by the interplay among intracrystalline plasticity and dissolution–precipitation, each active in specific minerals at given P–T conditions. Common rock-forming minerals like quartz, feldspars and sheet silicates have been intensively studied in terms of deformation processes. Instead, the deformation behavior of epidote and its role during viscous granular flow is not well investigated, although this mineral is ubiquitous in granitic rocks deforming at greenschist-facies conditions. In this contribution, we provide microstructural and geochemical evidence for the occurrence of dissolution–precipitation of epidote during deformation of an epidote-quartz vein. The main part of the vein is deformed producing a fold, which is visible due to relicts of primary-growth layering inside the vein. The deformation mechanisms active during deformation include dynamic recrystallization of quartz by subgrain rotation recrystallization, producing grain-size reduction of the primary vein quartz. This occurs contemporaneously with dissolution and (re)precipitation of epidote, and grain-boundary sliding, leading to a combined process described as viscous granular flow. The combination of intracrystalline plasticity, grain boundary sliding and dissolution locally and repeatedly produce creep cavities. These represent not only loci for nucleation of new epidote grains at the expenses of dissolved one, but they also allow fluid-mediated transport of elements. The same trace element patterns between old epidote relicts and newly formed grains, with much narrower variability, indicate a process of chemical homogenization. The nature of the fluid mediating deformation is investigated using Pb–Sr isotope data of epidote, which suggest that deformation is assisted by internally recycled fluids with the addition of a syn-kinematic external fluid component.
Publisher: American Geophysical Union (AGU)
Date: 28-10-2022
DOI: 10.1029/2022GL099154
Abstract: Chromium stable isotope composition (δ 53 Cr) is a promising tracer for redox conditions throughout Earth's history however, the geochemical controls of δ 53 Cr have not been assessed in modern redox‐stratified basins. We present new chromium (Cr) concentration and δ 53 Cr data in dissolved, sinking particulate, and sediment s les from the redox‐stratified Lake Cadagno (Switzerland), a modern Proterozoic ocean analog. These data demonstrate isotope fractionation during incomplete (non‐quantitative) reduction and removal of Cr above the chemocline, driving isotopically light Cr accumulation in euxinic deep waters. Sediment authigenic Cr is isotopically distinct from overlying waters but comparable to average continental crust. New and published data from other redox‐stratified basins show analogous patterns. This challenges assumptions from δ 53 Cr paleoredox applications that quantitative Cr reduction and removal limits isotope fractionation. Instead, fractionation from non‐quantitative Cr removal leads to sedimentary records offset from overlying waters and not reflecting high δ 53 Cr from oxidative continental weathering.
Publisher: Elsevier BV
Date: 05-2018
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-2497
Abstract: & & Recently, the application of LA& #8211 ICP& #8211 MS has enabled U& #8211 Pb dating of epidote minerals within the epidote& #8211 clinozoisite solid solution series (Peverelli et al., 2020). Epidote crystallization ages can provide an absolute time frame of deformation sequences when combined with detailed microstructural and metamorphic P& #8211 T analysis. Epidote deformation occurs in a brittle manner over a wide range of conditions below its closure temperature for Pb diffusion (685& #8211 & #176 C Dahl, 1997) hence, such deformation will not affect its formation U& #8211 Pb age. Nevertheless, the possibility of isotopically resetting epidote via fluid& #8211 mineral interaction has to be taken into account even at low deformation temperatures.& & & & We investigated the geochemical and Sr& #8211 Pb isotopic characteristics of epidote in one hydrothermal vein in the Aar Massif (central Swiss Alps). The vein is associated with an Alpine shear zone and it is composed of aggregates of 0.1& #8211 mm anhedral to subhedral epidote grains (epidote-A) + green biotite within a quartz matrix. This quartz dynamically recrystallized by subgrain rotation at temperatures above 400 & #176 C (Stipp et al., 2002) along with crystallization of a second epidote generation (epidote-B) made of tiny (& 0.1 mm) anhedral epidote grains in part mantling epidote-A and defining a fold. We address whether interaction with the fluid that precipitated epidote-B chemically affected epidote-A, i.e. whether the U& #8211 Pb age measured by LA& #8211 ICP& #8211 MS in epidote-A still dates its crystallization upon vein formation or displays age disturbance.& & & & LA& #8211 ICP& #8211 MS Sr and Pb concentration data overlap between epidote-A and epidote-B, as do their REE patterns, with (La/Yb)& sub& N& /sub& ratios of 0.03& #8211 .92. Lead and Sr isotopic signatures were measured respectively by solution MC& #8211 ICP& #8211 MS and by TIMS in epidote-A and in separates mixing different proportions of epidote-A and -B (no pure mechanical separates of epidote-B possible), and they are different. This requires open-system conditions during deformation, i.e., introduction of an external fluid with higher & sup& & /sup& Sr/& sup& & /sup& Sr and & sup& & /sup& Pb/& sup& & /sup& Pb ratios during crystallization of epidote-B. Despite the presence of an external fluid and the incorporation of external Sr and Pb in epidote-B, LA& #8211 ICP& #8211 MS U& #8211 Pb isotopic data for epidote-A define a regression in a Tera& #8211 Wasserburg plot indicating an age of 19.2 & #177 4.3 Ma, consistent with epidote-A crystallization during original vein opening. The preservation of the crystallization age in epidote-A indicates that interaction with the fluid that formed epidote-B did not geochemically and isotopically affect epidote-A. The consistency in trace element contents between epidote-A and -B hints that the epidote-forming cations were inherited by the fluid from epidote-A, and thus suggests dissolution-precipitation as the formation process for epidote-B.& & & & & & & & & Dahl, Earth Planet. Sci. Lett. 150, 277& #8211 , 1997.& & & & Peverelli et al., Geochronology Discuss. [preprint], 0.5194/gchron-2020-27, in review, 2020.& & & & Stipp et al.,& Geological Society, London, Special Publications,& (1), 171-190, 2002& &
Publisher: Wiley
Date: 12-08-2020
DOI: 10.1111/GBI.12410
Publisher: Elsevier BV
Date: 12-2015
Publisher: Elsevier BV
Date: 08-2021
Publisher: Informa UK Limited
Date: 09-02-2019
DOI: 10.1080/01635581.2018.1542011
Abstract: Combination gemcitabine and nab-paclitaxel (Gem-Nab-P) is a common regimen used to treat metastatic pancreatic ductal adenocarcinoma (PDAC). Toxicity from this regimen is associated with significant morbidity. Currently, Gem-Nab-P is dosed using estimated body surface area, derived from height and weight. This study investigates whether skeletal muscle assessment could be a useful tool in the dosing of Gem-Nab-P in metastatic PDAC. This study included 52 patients who had received first-line treatment with Gem-Nab-P for PDAC. Demographic and chemotherapy treatment information was gathered from medical records and body composition analysis was performed using single slice computed tomography methods, at spinal level L3. Patients who experienced first-cycle chemotherapy-associated toxicity did not have a different median skeletal muscle area (SkMA) to those who did not (128.6 cm
Publisher: Elsevier BV
Date: 10-2018
Publisher: Elsevier BV
Date: 08-2010
Publisher: Copernicus GmbH
Date: 30-09-2020
Abstract: Abstract. Monoclinic epidote is a low-µ (µ = 283U / 204Pb) mineral occurring in a variety of geological environments, participating in many metamorphic reactions and stable throughout a wide range of pressure–temperature conditions. Despite containing fair amounts of U, its use as a U–Pb geochronometer has been hindered by the commonly high contents of initial Pb with isotopic compositions that cannot be assumed a priori. We present U–Pb geochronology of hydrothermal-vein epidote spanning a wide range of Pb (3.9–190 µg g−1), Th (0.009–38 µg g−1) and U (2.6–530 µg g−1) contents and with µ values between 7–510 from the Albula area (eastern Swiss Alps), from the Grimsel area (central Swiss Alps) and from the Heyuan fault (Guangdong province, China). The investigated epidote s les show appreciable fractions of initial Pb that vary to different extents. A protocol has been developed for in situ U–Pb dating of epidote by spot-analysis laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) with a magmatic allanite as primary reference material. The suitability of the protocol and the reliability of the measured isotopic ratios have been ascertained by independent measurements of 238U / 206Pb and 207Pb / 206Pb ratios respectively by quadrupole and multicollector ICP–MS applied to epidote micro-separates digested and diluted in acids. For age calculation, we used the Tera–Wasserburg (207Pb / 206Pb–238U / 206Pb) diagram, which does not require corrections for initial Pb and provides the initial 207Pb / 206Pb ratio if all intra-s le analyses are co-genetic. Petrographic and microstructural data indicate that the calculated ages date the crystallization of vein epidote from a hydrothermal fluid and that the U–Pb system was not reset to younger ages by later events. Vein epidote from the Albula area formed in the Paleocene (62.7 ± 3.0 Ma) and is related to Alpine greenschist-facies metamorphism. The Miocene (19.1 ± 4.0 Ma and 16.9 ± 3.7 Ma) epidote veins from the Grimsel area formed during the Handegg phase (22–17 Ma) of the Alpine evolution of the Aar Massif. Identical initial 207Pb / 206Pb ratios reveal homogeneity in Pb isotopic compositions of the fluid across ca. 200 m. Vein epidote from the Heyuan fault is Cretaceous in age (108.1 ± 8.4 Ma) and formed during the early movements of the fault. In situ U–Pb analyses of epidote returned reliable ages of otherwise undatable epidote-quartz veins. The Tera–Wasserburg approach has proven pivotal for in situ U–Pb dating of epidote and the decisive aspect for low age uncertainties is the variability in intra-s le initial Pb fractions.
Publisher: Copernicus GmbH
Date: 15-05-2023
DOI: 10.5194/EGUSPHERE-EGU23-732
Abstract: Crustal rocks involved in orogenic processes frequently bear evidence for widespread fluid circulation. The hydration history of the granitic continental crust in inverted passive continental margins is of particular interest, as granitoids experience rheological weakening by fluid-rock interaction processes. Regrettably, it is often unclear if hydration occurs during rifting or during tectonic inversion. Hence, it is difficult to appreciate the interplay of pre- and syn-orogenic fluids inside continental crustal segments of rifted margins. The geochemical fingerprint of ancient hydration events is stored in hydrous minerals that crystallized directly from circulating paleo-fluids. Thus, such minerals can shed light on the nature of these ancient fluids, as well as provide temporal constraints if they can be dated. Hence, advances in geochronological methods applied to hydrous minerals may prove pivotal in untangling the history of fluid circulation in the granitic continental crust in orogens.We applied U& #8211 Pb geochronology of epidote [i.e., Ca2Al2(Al,Fe3+)Si3O12(OH)] in hydrothermal veins hosted by a late Carboniferous/early Permian calc-alkaline granodiorite in the inverted Adriatic passive continental margin (hereafter & #8220 Err nappe& #8221 ), both located in the eastern Swiss Alps. During Jurassic rifting leading to the break-up of Pangea, the continental crust in the Err nappe was hydrated, as seawater-derived fluids percolated along syn-rift faults. However, geochronological data of epidote reveal that the hydration of the granitic continental crust in the Err nappe occurred also later during inversion. Epidote U& #8211 Pb geochronology returned two age clusters: (1) 85.2 & #177 9.7 Ma, related to Late Cretaceous compression and (2) 59.9 & #177 2.7 Ma, related to subsequent Paleocene extension. These age clusters unveil two distict events of fluid circulation, which are consistent with the timing of tectonic inversion and deformation proposed in the literature. As confirmed by Pb& #8211 Sr& #8211 O& #8211 H isotope geochemistry of epidote, Late Cretaceous fluid circulation was likely mediated by fluids released by underlying units undergoing metamorphism during Eo-Alpine compression. Notably, the Paleocene fluids circulating during extension were most likely surficial in origin (i.e., meteoric water and/or modified/connate seawater), and they percolated into the granitic continental crust by exploiting extensional faults.In the context of existing data, our results show that the hydration of the granitic continental crust of the Adriatic passive continental margin was mediated by a repeated series of fluid circulation events. Our work advocates that the use of a multi-methodological approach, combining new geochemical and geochronological, tools provides unprecedented insight into complex processes of fluid circulation in the continental crust, and beyond.
Publisher: Proceedings of the National Academy of Sciences
Date: 27-04-2021
Abstract: The fate and transport of tungsten (W) in aquatic environments is still poorly constrained. To identify the processes that control the abundance of dissolved W, we applied a sophisticated analytical approach that enables the accurate determination of the seawater W isotopic composition. Our results indicate that the removal of W from seawater mainly occurs via adsorption onto oxide minerals. The marine inventory of W is therefore intimately linked to the areal extension of oxic marine conditions. Concurrently, the limited scavenging of W in anoxic marine settings seems a unique characteristic of W, highlighting that W isotopes can help to reconstruct the earliest rise of oceanic oxygen in Earth’s history.
Publisher: Copernicus GmbH
Date: 22-11-2022
Abstract: Abstract. Deformation of polymineralic aggregates can be accommodated by viscous granular flow, a process mediated by the interplay among intracrystalline plasticity and dissolution–precipitation, each active in specific minerals under given P–T conditions. Some rock-forming minerals like quartz and feldspars have been intensively studied in terms of deformation processes. Instead, the deformation behavior of epidote and its role during viscous granular flow is not well investigated, although this mineral is ubiquitous in granitic rocks deforming under greenschist-facies conditions. In this contribution, we provide microstructural and geochemical evidence for the occurrence of dissolution–precipitation of epidote during deformation of an epidote–quartz vein. The main part of the vein is deformed, producing a fold, which is visible due to relicts of primary-growth layering inside the vein. The deformation mechanisms active during deformation include dynamic recrystallization of quartz by subgrain rotation recrystallization, producing grain size reduction in the primary vein quartz. Recrystallization occurs contemporaneously with dissolution and (re)precipitation of epidote and quartz grain boundary sliding, leading to a combined process described as viscous granular flow. The combination of grain boundary sliding and dissolution locally and repeatedly produces creep cavities. These represent not only loci for nucleation of new epidote grains at the expense of dissolved ones, but they also allow fluid-mediated transport of elements. The same trace element patterns between old epidote relicts and newly formed grains, with much narrower variability in the latter, indicate a process of chemical homogenization. The nature of the fluid that mediates deformation is investigated using Pb–Sr isotope data of epidote, which suggest that deformation is assisted by internally recycled fluids with the addition of a syn-kinematic external fluid component.
Publisher: Elsevier BV
Date: 09-2021
Publisher: Elsevier BV
Date: 04-2010
Publisher: American Association for the Advancement of Science (AAAS)
Date: 19-11-2010
Abstract: Silicon is a major structural component of many marine organisms, whose chemistry is affected by oceanic nutrient distributions. To constrain nutrient changes since the last glacial period, Ellwood et al. (p. 1088 , published online 21 October) measured the isotopic compositions of silicon obtained from the skeletons of deep-sea sponges found in deep cores from the Atlantic and Pacific sectors of the Southern Ocean and compared them to the silicon signatures in the skeletons of modern sponges. The results indicate that nutrient redistribution, related to iron fertilization from dust deposition, boosted the growth of organisms that transferred silicon to mid-latitudes during the last glacial period.
Publisher: Springer Science and Business Media LLC
Date: 06-2009
DOI: 10.1038/NATURE08049
Publisher: Elsevier BV
Date: 10-2007
Publisher: European Association of Geochemistry
Date: 12-2021
Publisher: Elsevier BV
Date: 05-2013
DOI: 10.1016/J.ACA.2013.03.020
Abstract: Stable copper (Cu) isotope geochemistry provides a new perspective for investigating and understanding Cu speciation and biogeochemical Cu cycling in seawater. In this work, s le preparation for isotopic analysis employed solvent-extraction with amino pyrollidine dithiocarbamate/diethyl dithiocarbamate (APDC/DDC), coupled with a nitric acid back-extraction, to concentrate Cu from seawater. This was followed by Cu-purification using anion-exchange. This straightforward technique is high yielding and fractionation free for Cu and allows precise measurement of the seawater Cu isotopic composition using multi-collector inductively coupled plasma mass-spectrometry. A deep-sea profile measured in the oligotrophic north Tasman Sea shows fractionation in the Cu isotopic signature in the photic zone but is relatively homogenised at depth. A minima in the Cu isotopic profile correlates with the chlorophyll a maximum at the site. These results indicate that a range of processes are likely to fractionate stable Cu isotopes in seawater.
Publisher: Elsevier BV
Date: 10-2014
Publisher: Springer Science and Business Media LLC
Date: 28-05-2008
DOI: 10.1038/NATURE07072
Abstract: Animal-like multicellular fossils appeared towards the end of the Precambrian, followed by a rapid increase in the abundance and ersity of fossils during the Early Cambrian period, an event also known as the 'Cambrian explosion'. Changes in the environmental conditions at the Precambrian/Cambrian transition (about 542 Myr ago) have been suggested as a possible explanation for this event, but are still a matter of debate. Here we report molybdenum isotope signatures of black shales from two stratigraphically correlated s le sets with a depositional age of around 542 Myr. We find a transient molybdenum isotope signal immediately after the Precambrian/Cambrian transition. Using a box model of the oceanic molybdenum cycle, we find that intense upwelling of hydrogen sulphide-rich deep ocean water best explains the observed Early Cambrian molybdenum isotope signal. Our findings suggest that the Early Cambrian animal radiation may have been triggered by a major change in ocean circulation, terminating a long period during which the Proterozoic ocean was stratified, with sulphidic deep water.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Copernicus GmbH
Date: 27-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-4660
Abstract: & & Variation in molybdenum (Mo) concentration and isotope composition is an established tracer for redox changes in marine environments. Here we apply Mo as a proxy of past water column oxygenation in ancient ferruginous and hyposulfidic Lake Towuti. Lake Towuti is & .2 Myrs old, up to 200m deep, weakly stratified and anoxic below ~100 m water depth, and surrounded by an ultramafic bedrock-dominated catchment in South Sulawesi, Indonesia. Despite the current permanent stratification, deeper water mixing and oxygenation occurred periodically in the past due to Towuti& #8217 s sensitivity to climate change. To better reconstruct the redox changes through time, we present Mo concentration and isotope data from laterite profiles overlying ultramafic bedrock, lake surface sediments, and a ~30 kyr sediment piston core from Lake Towuti, Indonesia.& & & & Although Mo concentrations in laterite profiles are overall higher compared to the underlying bedrock, the absence of a significant Mo isotopic variability with values close to the unweathered ultramafic protolith, varying from & #8211 .16& #8240 to & #8211 .04& #8240 & #948 & sup& & /sup& Mo& sub& NIST3134& /sub& , suggests low aqueous mobility of Mo during weathering due to the formation of laterite Fe-oxides. In contrast to the laterite s les, Mo isotopic variability in lake surface sediments show a larger variability varying from & #8211 .15& #8240 to & #8211 .13& #8240 & #948 & sup& & /sup& Mo& sub& NIST3134& /sub& with a significantly lighter Mo isotopic composition in sediments deposited under oxic bottom water conditions. This light Mo isotopic composition is likely caused by early diagenetic redox cycling of Mo and Fe at the sediment-water interface. In the deeper, anoxic parts of the basin, Mo isotopic compositions show values close to the laterite input with elevated sedimentary Mo concentrations which are likely the result of an authigenic Mo enrichment from the water column. Mo isotope variability in sediments taken from a piston core in the deep part of the lake is in the range of Mo isotope compositions from modern surface sediments, varying from & #8211 .14& #8240 to & #8211 .66& #8240 & #948 & sup& & /sup& Mo& sub& NIST3134& /sub& . Interestingly, this variability is well correlated with local and global indicators of climate change from previous studies. Sediments deposited between ~30 kyr and ~10 kyr exhibit Mo isotope signatures similar to present-day oxygenated shallow water sites, thereby suggesting enhanced lake mixing and bottom water oxygenation under drier and colder climate conditions of the last glacial period. Sediments deposited since ~10 kyr under wetter and warmer climate conditions exhibit Mo isotope signatures similar to present-day anoxic deeper water settings. These suggest that Mo isotope compositions of lake sediments are potential quantitative indicators of past climate-driven water column oxygenation.& &
Publisher: Elsevier BV
Date: 09-2015
Publisher: Elsevier BV
Date: 2019
Publisher: Elsevier BV
Date: 2010
Publisher: Elsevier BV
Date: 07-2020
Publisher: Proceedings of the National Academy of Sciences
Date: 20-03-2019
Abstract: Episodic development of “oxygen oases” during the Archean Eon characterizes the hundreds of millions of years transition to permanent oxygenation in the atmosphere–hydrosphere system at the Great Oxidation Event (∼2.4–2.3 Ga). One of these well-characterized oxygen oases is recorded in Mesoarchean sediments of the Pongola Supergroup. We show that in contrast to the Neoarchean, biological oxygen production in a shallow ocean having Mo-based nitrogen fixation was not sufficient to result in a dissolved nitrogen reservoir that would carry the isotopic effects of an aerobic nitrogen cycle. Nevertheless, it appears that low concentrations of bioavailable phosphorus, rather than nitrogen, suppressed the growth and expansion of oxygenic photosynthesizers and may explain why pervasive and permanent oxygenation was delayed during the Archean Eon.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-11903
Abstract: & & Significant Mo mobility and isotope (& #948 & sup& /95& /sup& Mo) fractionation is induced during prograde metamorphism at present-day subduction zones. Depending on the redox conditions during early subduction and accompanied slab dehydration, isotopically heavy Mo is released towards the overlying mantle wedge, leaving behind a depleted, and isotopically light subducted slab. This isotopically light Mo signature has been detected in slab-melt influenced volcanic rocks and potentially will be traceable in ocean-island basalts, if their geochemical signatures are affected by previously subducted lithologies (i.e. slab and overlying sediments). Thus, the isotope composition of mantle plume-influenced volcanic rocks might reveal the nature of subducted and re-incorporated lithologies and possibly redox conditions during subduction.& & & & In this study, we present new Mo isotope data for South-Mid Atlantic Ridge basalts that partly interacted with the enriched Discovery and Shona mantle plumes. Isotopically heavier Mo isotope ratios (& #948 & sup& /95& /sup& Mo & ambient depleted mantle) are observed in s les tapping a more enriched mantle source. Furthermore, & #948 & sup& /95& /sup& Mo correlates with radiogenic isotopes (Sr, Nd, Hf) indicating recycling of a Proterozoic sedimentary components with a Mo isotopic composition that was not modified during and before subduction by Mo mobility under oxidising conditions. Rather, the new Mo isotope data supports and expands on previous stable Se and S isotope evidence that suggests the incorporation of subducted anoxic Proterozoic deep-sea sediments into the mantle of the South-Mid Atlantic Ridge basalts.& &
Publisher: Geological Society of America
Date: 2007
DOI: 10.1130/G24563Y.1
Publisher: Springer Science and Business Media LLC
Date: 15-01-2018
Publisher: Elsevier BV
Date: 08-2016
Publisher: Elsevier BV
Date: 02-2013
Publisher: Elsevier BV
Date: 08-2021
Publisher: American Geophysical Union (AGU)
Date: 06-2021
DOI: 10.1029/2020PA004207
Abstract: The worldwide recognition of the Toarcian carbon isotope excursion (T‐CIE) in organic‐rich sedimentary rocks has been linked to an oceanic anoxic event (OAE) which implies the world's deep oceans were anoxic ∼183 Ma. The majority of independent redox observations used to build this argument were mainly obtained from T‐CIE organic‐rich sediments deposited on northern European epicontinental shelf. However, increasing evidence has shown that this shelf had limited connection with the open ocean, making it unsuitable for reconstructing the T‐CIE ocean redox structure. To unveil such controversy, we present integrated δ 15 N bulk and δ 15 N ker from Dotternhausen profile, Germany, combined with literature data from other T‐CIE profiles. Both δ 15 N bulk and δ 15 N ker values are predominantly between +0.3 and +2.5‰. These positive near‐zero δ 15 N values imply enhanced N 2 fixation by cyanobacteria using molybdenum (Mo)‐based nitrogenase to compensate bioavailable N loss following quantitative denitrification and/or anammox in a strongly redox‐stratified marine setting. Such N isotope composition contradicts the typical sedimentary δ 15 N values ( ‰) induced by partial water‐column denitrification and/or anammox in modern‐ocean oxygen minimum zones. We rather propose the existence of local oxygen‐deficient basins on northern European epicontinental shelf where dissolved N underwent extensive denitrification and/or anammox causing bioavailable N deficiency. Mo‐based diazotrophy thus played a critical role in discriminating N isotope compositions among multiple hydrographically restricted T‐CIE marginal basins. Restricted oxygen‐depleted environments on the northern European epicontinental shelf unlikely represent the open‐ocean redox landscape. The existence of the global OAE thus needs comprehensive redox investigations on Tethys and/or Panthalassa deep‐sea T‐CIE successions to validate.
Publisher: Elsevier BV
Date: 2013
Publisher: Elsevier BV
Date: 06-2012
Publisher: Elsevier BV
Date: 03-2018
Publisher: Elsevier BV
Date: 04-2021
Publisher: Elsevier BV
Date: 12-2015
Publisher: Geological Society of America
Date: 2007
DOI: 10.1130/G23543A.1
Publisher: Elsevier BV
Date: 05-2007
Publisher: Elsevier BV
Date: 09-2013
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-11833
Abstract: & & Lake Cadagno, a meromictic, redox stratified lake located in Val Piora in Switzerland has extensively been studied serving as a modern analogue of the Archean/Proterozoic ocean. Euxinic conditions were established after a short transition interval immediately following lake formation ~10& #8217 years ago. Overall elevated but very variable Mn concentration during this transition period have been thought to reflect fluctuating bottom water redox condition with authigenic accumulation of sedimentary Mn from the water column in line with observation from deep basins of the Baltic Sea.& & & & To test this hypothesis we measured the Mo isotopic composition of Lake Cadagno sediments with a focus on the transition interval following lake formation between 7.4 and 7.8 m depth. With a & #948 & sup& /95& /sup& Mo& sub& NIST+0.25 & /sub& composition ranging from -1.72 to +3.77& #8240 the Mo isotopic variability of the transition interval sediments is significantly larger compared to Cadagno sapropels deposited under euxinic conditions and significant larger compared to the entire Mo isotopic variability observed in marine reservoirs. Aside this large variability in & #948 & sup& /95& /sup& Mo& sub& NIST+0.25 & /sub& a gradual change from isotopically very light to very heavy Mo isotopic composition upcore is observed. This transient sedimentary Mo isotope pattern cannot be explained by fluctuating bottom water redox conditions at the beginning of the lake and cannot be a primary signature caused by changes in the depositional environment. Likely, the inflow of oxic groundwater from subsurface karst aquifers present in Cadagno into organic-matter-rich lake sediments, a likely active and currently ongoing process, causes the formation of a chemocline at depth in the sediment column. Here the reduction of sulphate and the precipitation of isotopically light Mo from the dissolved oxic groundwater reservoir causes progressively higher & #948 & sup& /95& /sup& Mo& sub& NIST+0.25 & /sub& upwards in the sediment column.& sub& & /sub& & & & &
Publisher: Elsevier BV
Date: 09-2021
Publisher: Elsevier BV
Date: 09-2015
Publisher: Copernicus GmbH
Date: 03-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-1235
Abstract: & & Molybdenum (Mo) isotopes are known as sensitive recorders for changes in redox conditions because the oxidized form of Mo (Mo VI) is more soluble, whereas its reduced form is more particle reactive. Previous studies suggest that Mo isotopic fractionation during the weathering process is controlled by atmospheric input, Mo host, and bedrock composition. However, Mo isotopic variation and processes influencing fractionation in weathering profiles overlying ultramafic bedrock, the early Earth analog, have yet to be explored. This study explores for the first time (1) Mo behavior and (2) isotopic fractionation in two representative and intensely-weathered lateritic profiles overlying ultramafic bedrock of the East Sulawesi Ophiolite, Indonesia. Mo concentrations measured on s les obtained from laterite successions studied here range between 60 - 537 ppb and are overall higher compared to bedrock values ranging between 9 - 45 ppb. The Mo isotope compositions of laterite s les vary between -0.043& #8240 to -0.161& #8240 & #948 & sup& & /sup& Mo& sub& NIST3134& /sub& . The overall close to mantle Mo isotopic composition of the laterite s les, their small Mo isotope variability, and the covariation between Mo and Ti concentrations suggest low mobility of Mo during chemical weathering and laterite formation. This low Mo mobility is likely a consequence of a) the low Mo concentration of the ultramafic protolith and b) adsorption of Mo to secondary Fe-Oxides during laterite formation under oxic weathering conditions.& &
No related grants have been discovered for Martin Wille.