New constraints on the Sulfur isotope signature of the sub-continental lithospheric mantle wedge: in situ δ34S analyses of pentlandite from the exhumed orogenic garnet-bearing peridotite of the Ulten Zone, Eastern Italian Alps

Orogenic peridotites associated with high-grade felsic rocks record mass exchange between crust and mantle reservoirs at convergent plate margins. In this geodynamic framework, fluids released by submerging slabs can mobilize redox-sensitive elements such as carbon (C) and sulfur (S) and percolate the mantle wedge, eventually forming hydrate minerals associated with carbonate and sulfide phases at appropriate T, P and f O2&#160;conditions.&#160;The introduction of sulfur into the sub-continental lithospheric mantle (SCLM) wedge and its mobilization at grain-scale can be investigated by means of in situ &#948;34S analyses of mantle wedge sulfides, which may have inherited the composition of the fluid sources. To date, the impact of the S transfer through the SCLM wedge is poorly known and limited in situ S isotope values of sulfides from mantle wedge peridotite are available in literature. Our study focuses on the Ulten Zone (UZ) orogenic-garnet peridotites, which provide an ideal case to investigate the S mobilization through the SCLM wedge and the effects of crustal fluids on the sulfide &#948;34S signature, especially during the exhumation stage. We therefore integrate a well-constrained paragenesis with mineral chemistry and in situ S isotope signature of sulfides. The UZ peridotites were involved in a collisional setting during the Variscan orogenesis, recording HP-eclogite-facies conditions and exhumation after their incorporation in a m&#233;lange with the associated garnet-kyanite gneisses. A suite of coarse to fine-grained peridotites was investigated in order to cover all the metasomatic stages preserved in these rocks, considering the grade of serpentinization and the occurrence of carbonates. Microstructural observations and major element compositions indicate that pentlandite (&#177;&#160;chalcopyrite &#177;&#160;chalcocite &#177;&#160;sphalerite) is the ubiquitous primary sulfide, which is commonly replaced by secondary heazlewoodite and millerite in medium to highly serpentinized peridotite. Pentlandite occurs in different textural positions related to several metasomatic stages: (i) polycrystalline aggregates (pentlandite + Cl-apatite + phlogopite + ilmenite + calcite-brucite intergrowths) included in spinel (in garnet); (ii) interstitial in matrix; (iii) in carbonate and serpentine veins. Overall, the S isotope signature of pentlandite exhibits a relatively narrow range between -1.62 and +3.76 &#8240;. The relatively low S isotope values require a mantle-like source for the metasomatizing fluids enriched in sulfur, with possible contamination with fluids of other different sources. These new results show that sulfur was introduced into the lithospheric mantle and mobilized by influxes of late metasomatic fluids, in part related to the serpentinization, and provide additional constraints on the S isotope composition of the SCLM wedge.

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Denudation systematics inferred from in situ cosmogenic 10Be concentrations in fine (50–100 µm) and medium (100–250 µm) sediments of the Var River basin, southern French Alps

Earth Surface Dynamics ◽

10.5194/esurf-7-1059-2019 ◽

2019 ◽

Vol 7 (4) ◽

pp. 1059-1074 ◽

Cited By ~ 1

Author(s):

Apolline Mariotti ◽

Pierre-Henri Blard ◽

Julien Charreau ◽

Carole Petit ◽

Stéphane Molliex ◽

...

Keyword(s):

Glacial Cycles ◽

Size Fractions ◽

French Alps ◽

Fine Grained ◽

Denudation Rates ◽

Variable Morphology ◽

Cosmogenic 10Be ◽

The Impact ◽

Quartz Grains

Abstract. Marine sedimentary archives are well dated and often span several glacial cycles; cosmogenic 10Be concentrations in their detrital quartz grains could thus offer the opportunity to reconstruct a wealth of past denudation rates. However, these archives often comprise sediments much finer (<250 µm) than typically analyzed in 10Be studies, and few studies have measured 10Be concentrations in quartz grains smaller than 100 µm or assessed the impacts of mixing, grain size, and interannual variability on the 10Be concentrations of such fine-grained sediments. Here, we analyzed the in situ cosmogenic 10Be concentrations of quartz grains in the 50–100 and 100–250 µm size fractions of sediments from the Var basin (southern French Alps) to test the reliability of denudation rates derived from 10Be analyses of fine sands. The Var basin has a short transfer zone and highly variable morphology, climate, and geology, and we test the impact of these parameters on the observed 10Be concentrations. Both analyzed size fractions returned similar 10Be concentrations in downstream locations, notably at the Var's outlet, where concentrations ranged from (4.02±0.78)×104 to (4.40±0.64)×104 atoms g−1 of quartz. By comparing expected and observed 10Be concentrations at three major river junctions, we interpret that sediment mixing is efficient throughout the Var basin. We resampled four key locations 1 year later, and despite variable climatic parameters during that period, interannual 10Be concentrations were in agreement within uncertainties, except for one upper subbasin. The 10Be-derived denudation rates of Var subbasins range from 0.10±0.01 to 0.57±0.09 mm yr−1, and spatial variations are primarily controlled by the average subbasin slope. The integrated denudation rate of the entire Var basin is 0.24±0.04 mm yr−1, in agreement with other methods. Our results demonstrate that fine-grained sediments (50–250 µm) may return accurate denudation rates and are thus potentially suitable targets for future 10Be applications, such as studies of paleo-denudation rates using offshore sediments.

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Mineral chemistry, bulk rock geochemistry, and S-isotope signature of lode-gold mineralization in the Bétaré Oya gold district, south-east Cameroon

Geological Journal ◽

10.1002/gj.3093 ◽

2017 ◽

Vol 53 (6) ◽

pp. 2579-2596 ◽

Cited By ~ 6

Author(s):

Akumbom Vishiti ◽

Cheo Emmanuel Suh ◽

Bernd Lehmann ◽

Elisha Mutum Shemang ◽

Njumbe Lionel Junior Ngome ◽

...

Keyword(s):

Gold Mineralization ◽

Mineral Chemistry ◽

Bulk Rock ◽

Lode Gold ◽

Isotope Signature ◽

S Isotope

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New insights into the Re–Os systematics of sub-continental lithospheric mantle from in situ analysis of sulphides

Earth and Planetary Science Letters ◽

10.1016/s0012-821x(02)00799-9 ◽

2002 ◽

Vol 203 (2) ◽

pp. 651-663 ◽

Cited By ~ 167

Author(s):

Olivier Alard ◽

William L. Griffin ◽

Norman J. Pearson ◽

Jean-Pierre Lorand ◽

Suzanne Y. O’Reilly

Keyword(s):

Lithospheric Mantle ◽

In Situ Analysis ◽

Continental Lithospheric Mantle

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An igneous-textured clast in the Peace River meteorite: insights into accretion and metamorphism of asteroids in the early solar system

Canadian Journal of Earth Sciences ◽

10.1139/e2012-078 ◽

2013 ◽

Vol 50 (1) ◽

pp. 14-25 ◽

Cited By ~ 5

Author(s):

Christopher D.K. Herd ◽

Jon M. Friedrich ◽

Richard C. Greenwood ◽

Ian A. Franchi

Keyword(s):

Solar System ◽

Isotope Composition ◽

Parent Body ◽

Early Solar System ◽

Element Abundances ◽

Fine Grained ◽

Peace River ◽

Petrology And Geochemistry ◽

Mineral Compositions ◽

The Impact

The mineralogy, petrology, and geochemistry of an igneous-textured clast in the Peace River L6 chondrite meteorite was examined to determine the roles of nebular processes, accretion, and parent-body metamorphism in its origin. The centimetre-scale clast is grey and fine grained and is in sharp contact with the host chondrite. Two sub-millimetre veins cut across both the clast and host, indicating that the clast formed prior to the impact (shock) event(s) that produced the numerous veins present in the Peace River meteorite. The clast and host are indistinguishable in terms of mineral compositions. In contrast, there are differences in modal mineralogy, texture, as well as trace element and oxygen isotope composition between the clast and host. These differences strongly suggest that the clast was formed by impact melting of LL-group chondritic material involving loss of Fe–FeS and phosphate components, followed by relatively rapid cooling and incorporation into the Peace River host meteorite. Subsequent metamorphism on the Peace River parent body caused recrystallization of the clast and homogenization of mineral compositions and thermally labile element abundances between the clast and host. Shock metamorphism, including formation of shock melt veins, occurred post-metamorphism, during fragmentation of the L chondrite parent body. The results suggest that the formation of the Peace River parent asteroid included the incorporation of material from other asteroids and that the pre-metamorphic protolith was a breccia. Accordingly, we propose that the Peace River meteorite be reclassified as a polymict breccia.

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Electrical Conductivity and pH in Surface Water as Tool for Identification of Chemical Diversity

Ecological Chemistry and Engineering S ◽

10.2478/eces-2020-0006 ◽

2020 ◽

Vol 27 (1) ◽

pp. 95-111

Author(s):

Joanna Potapowicz ◽

Danuta Szumińska ◽

Małgorzata Szopińska ◽

Sebastian Czapiewski ◽

Żaneta Polkowska

Keyword(s):

Surface Runoff ◽

Physicochemical Parameters ◽

Morphological Changes ◽

Chemical Diversity ◽

Fine Grained ◽

Ph Values ◽

Glacier Front ◽

Western Shore ◽

The Impact

AbstractIn the present study, the creeks and lakes located at the western shore of Admiralty Bay were analysed. The impact of various sources of water supply was considered, based on the parameters of temperature, pH and specific electrolytic conductivity (SEC25). All measurements were conducted during a field campaign in January–February 2017. A multivariate dataset was also created and a biplot of SEC25 and pH of the investigated waters was performed. The average temperatures of the investigated waters were 0.10-8.10 °C. The pH values indicate that most of the water environments of the analysed area are slightly acidic to alkaline (5.26–8.50) with two exceptions: Siodlo II Creek (9.26) and Petrified Forest Creek (8.95), which are characterised by greater alkalinity. At the measurement points closest to the Baranowski Glacier and Ecology Glacier, SEC25 values were the lowest (26.8–61.1 µS·cm–1), while the remaining values ranged from 79.0 to 382 µS·cm–1 for the whole studied area. Based on the results it is concluded that the periodic intensive inflow of ablation waters, combined with morphological changes in the glacier front, causes a significant variability in the outflow network, creating the conditions for changes in basic physicochemical parameters. Moreover, it is observed that local depressions in the terrain form sedimentation traps in which, alongside fine-grained deposits, compounds can accumulate that originate from in situ sedimentation and that are also associated with surface runoff from the melting of snow cover, buried ice and permafrost.

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Combining volatiles measurements in fluid inclusions with petrology of ultramafic xenoliths: new insights on the evolution of the West Eifel and Siebengebirge (Germany) Sub-Continental Lithospheric Mantle

10.5194/egusphere-egu21-13422 ◽

2021 ◽

Author(s):

Barbara Faccini ◽

Andrea Luca Rizzo ◽

Federico Casetta ◽

Luca Faccincani ◽

Theodoros Ntaflos ◽

...

Keyword(s):

Fluid Inclusions ◽

Lithospheric Mantle ◽

Mineral Chemistry ◽

The Other ◽

Gaseous Emissions ◽

Melt Extraction ◽

Other Hand ◽

Ultramafic Xenoliths ◽

Continental Lithospheric Mantle ◽

West Eifel

Integrating petrography and mineral chemistry data with the determination of volatiles concentration and isotopic fingerprint in fluid inclusions (FI) in ultramafic xenoliths opens a new window on the study of the Sub-Continental Lithospheric Mantle (SCLM). This frontier approach is crucial for understanding nature, evolution and volatiles recycling within the lithosphere, being particularly important in active or dormant volcanic areas, where the signature of the surface gaseous emissions can be compared to that of the deep mantle domains.Five distinct populations of ultramafic xenoliths brought to the surface in West Eifel (~0.5-0.01 Ma) and Siebengebirge (~30-6 Ma) volcanic fields (Germany) were investigated by combining petrographic and mineral chemistry analyses with noble gases + CO2 determinations in olivine-, orthopyroxene- and clinopyroxene-hosted FI. Xenoliths from West Eifel are modally and compositionally heterogeneous, as testified by the large forsterite range of olivine, the Cr# range of spinel and the variable Al and Ti contents of pyroxene. Siebengebirge rocks, on the other hand, are quite homogeneous, having mostly refractory composition and reflecting high extents (up to 30%) of melt extraction. Equilibration temperatures vary from 900 to 1180 &#176;C in West Eifel and from 880 to 1060&#176;C in Siebengebirge xenoliths, at comparable oxygen fugacity values. In all xenoliths populations, FI composition is dominated by CO2, with olivines being the most gas-poor phases and reflecting a residual mantle that experienced one or more melt extraction episodes. The 3He/4He ratio corrected for air contamination (Rc/Ra values) in all phases varies from 6.8 Ra in harzburgites to 5.5 Ra in lherzolites and cumulates rocks, suggesting a progressive modification of an original MORB-like mantle signature via interaction with crustal-related components with 3He/4He and 4He/40Ar* signature similar to magmatic gaseous emissions. The mineral phase major element distribution, together with the systematic variations in FI composition, the positive correlation between Al-enrichment in pyroxene and equilibration temperatures, and the concomitant Rc/Ra decrease at increasing temperature, suggest that the SCLM beneath Siebengebirge represented the German lithosphere prior to the massive infiltration of melts/fluids belonging to the Quaternary Eifel volcanism. On the other hand, West Eifel xenoliths bear witness of multiple heterogeneous metasomatism/refertilization events that took place in the German SCLM between ~6 and ~0.5 Ma. According to Ne and Ar isotope systematics, the FI composition in the studied xenoliths can be explained by mixing between recycled air and a MORB-like mantle, being irreconcilable with the presence of a lower mantle plume beneath the Central European Volcanic Province.

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