The recent discovery of heavy Si isotopic compositions in both high-Na Tonalite-Trondhjemite-Granodiorite (TTG) and High-K Granite-Monzonite-Syenite (GMS) suites of early continental crust requires that a notable seawater-derived silica-rich component had been added to their respective protoliths prior to melting. Here we use the Ge/Si ratio as a complementary tracer to delta Si-30 in order to delineate the exact role of modal quartz and silicified basalts from the Archean seafloor among the primary controls of the early appearance of felsic melts on Earth. We have approached the question by (1) specifying the Ge/Si signatures of various Archean and post-Archean rock types by compiling the Ge-SiO2 data stored within the GEOROC database; (2) coupling Ge/Si investigation to silicon isotopes on a large selection of silicified and unsilicified altered mafic and ultramafic greenstones, felsic volcanics, TTG and GMS granitoids and mineral separates from TTGs of the Barberton Greenstone Belt (BGB) of South Africa. The GEOROC compilation demonstrates that Archean TTGs and granites display much lower Ge/Si (1.15 +/- 0.10 and 1.13 +/- 0.11 mu mol/mol, respectively) than post-Archean adakites, granites, tonalites and granodiorites (with average Ge/Si in the range of 1.64 to 1.85 mu mol/mol). This result is corroborated by the Ge/Si ratios we report from BGB rocks that formed prior to Kaapvaal craton stabilisation, including 3.5 Ga Theespruit Formation felsic volcanic rocks, 3.5-3.2 Ga TTGs and 3.2-3.1 Ga GMSs, all of which exhibit low ratios (0.68 +/- 0.23; 0.92 +/- 0.17; 1.05 +/- 0.19 mu mol/mol, respectively). Based on their low TTG-like Ge/Si, precratonic GMSs are dismissed as being derived from melting of both TTG and metasedimentary sources. Instead, TTGs and GMSs originated from similar Ge-depleted sources. Low Ge/Si ratios, coupled to heavy Si isotopic signatures (-0.14 parts per thousand & nbsp;& nbsp;< delta Si-30 < +0.27 parts per thousand & nbsp;) are also a characteristic feature of mafic and ultramafic BGB greenstones subjected to low-temperature hydrothermal seafloor alteration, especially at the interface between silicified (0.2 < Ge/Si < 1.2 mu mol/mol) and unsilicified (1.8 < Ge/Si < 3.1 mu mol/mol) portions of the altered Archean seafloor. We infer that both Na-rich and K-rich Archean felsic melts are derived from a unique class of protoliths: Ge-depleted metabasalts containing a significant modal proportion of supracrustal quartz generated by the silicification of the Eo-Paleoarchean basaltic seafloors. The transition from Na-rich to K-rich felsic melts in the BGB is assumed to be connected to a gradual increase of potassium as a key element associated with seafloor silicification. In contrast, younger (3.07-2.69 Ga), post-cratonic BGB granites have higher Ge/Si (1.93 & PLUSMN;0.23 mu mol/mol) and were generated through the reworking of a TTG-like basement, by incongruent melting of biotite and hornblende (1.79 < Ge/Si < 2.97 mu mol/mol) leaving an oligoclase-rich (0.64 < Ge/Si < 0.72) residue. The Earth changed from a prevalent Ge-depleted felsic crust in early-middle Archean times to a widespread Ge-enriched post-Archean crust, which emphasizes the importance of late Archean changes in the Earth dynamics. In particular, our data suggest the likelihood of generating primitive felsic continents by rather shallow melting processes, without the need for inducing high pressures by subduction, as long as Archean ocean floors were silicified. (c) 2022 Elsevier B.V. All rights reserved.

SummaryWikis are one of the most important tools of Web 2.0 allowing users to easily edit shared data. However, wikis offer limited support for merging concurrent contributions on the same pages. Users have to manually merge concurrent changes, and there is no support for an automatic merging. Real‐time collaborative editing reduces conflicts as the time frame for concurrent work is very short. In this paper, we propose extending wiki systems with real‐time collaboration. We propose an automatic merging solution adapted for rich content wikis. Our solution relies on an operational transformation algorithm defined for high level operations that capture user actions such as move, merge, and split.

The lasers used for the telecom industry associated with the focal plane embedded in LIDAR for automotive could pave the way to robust yet low cost Spatially Resolved Diffuse Reflectance Spectroscopy in the SWIR range.

Late Cenozoic volcanic activity in the Udokan ridge is related to reactivation of the Kodar-Udokan and Chukchudu weak zones. The former locates in the area of the Baikal Rift System (BRS) overlapping the Proterozoic foredeep in the Aldan shield. The latter joins the Stanovoy suture which belongs to the Olekma-Stanovaya Orogenic System (OSOS) reactivated due to collision of the Bonin and Honshu arcs. Diverse volcanic pulses in the weak zones indicate independent tectonic activity in the BRS and OSOS. Trace element abundances in lavas from both zones have been studied by ICP-MS technique. The initial 14 Ma olivine melaleucetite magmas in the Kodar-Udokan zone were inferred to represent phlogopite-bearing mantle source depleted in Pb and Y (Ce/Pb = 20; Y/Ho = 22). Alkali olivine basalts and basanites erupted between 3.2 and 2.4 Ma exhibited hybrids of two or three end-members including, beside the Pb-Y depleted component, those of the lower crust and similar to the primitive mantle. In the Chukchudu zone, the 4.0–3.5 Ma basanites were dominated by the OIB-like component. During the last 1.8 Ma, the low-Y material melted. It is suggested that lavas of the Kodar-Udokan zone represent the continental mantle which underlain the Aldan shield in the Archean, but partly or completely modified by the Proterozoic processes of deep tectono-thermal reactivation. Lavas of the Chukchudu zone exhibit lithospheric mantle material formed during deep Phanerozoic convection and/or mantle material of the Baikal-Vitim terrane subducted beneath the Archean crust of the Aldan shield in the Paleozoic.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Editorial: Biogeochemistry and Genomics of Silicification and Silicifiers Brivaëla Moriceau, Marion Gehlen, Paul Tréguer, Stephen Baines, Jacques Livage, Luc André

Series of lherzolite xenoliths from two nearest locations of deep seated inclusions have been analyzed to receive the information about the variations in petrography PTfo2 conditions and construction of the mantle column.Bereya picrite basalt-tuff lherzolite xenoliths represent starting period of mantle activity referred to the formation of lava plateau.The most common Gtf-lherzolites are very similar to Ga-Sp Iherzolites but less oxidized and more fertile Na, Ti, Al enriched (fig.l).Ga lherzolites features are subdivided to the several groups gradually reducing in grain size and changing in structure from coarse grained porphyric Iherzolites through mean grained foliated or deformed to fine-equal -grained varieties together with temperature decreasing from 1150°C to 950°C.The rims on the garnet changing from presumably Opx to Cpx and Sp in this sequence also demonstrate temperature decrease.The lower T° interval (750-900°C) is constructed by coarse grained slightly depleted lherzolites with Phi or Al-rich Px and Sp possibly representing lithospheric mantle.REE and geochemical features manifest the Cpx and Ga formation from moving melts.Gradual rise of Sm/Nd, Gd/Yb ratios, positive correlation of LREE and negative of HREE in lherzolite Cpx with estimated temperatures in Ga lherzolites reveals Ga control while low T° Sp lherzolites have no Ga influence.Phlogopite bearing Iherzolites are the most REE enriched but slightly depleted varieties show crystallization from the carbonatite -like liquid remaining after the migration of more differentiated melt and mixing the remaining liquid.The natural distributions of REE in Cpx (Ionov et al.,1993) are modeling by simple removing of more differentiated melt (Fig. 3).In Dzhilinda site the following groups varying in structural features were distinguished.According to PT estimates and their projection on geotherm three temperature intervals and depth levels were found.1) Most primitive and H-T° (1030-1200 C°) and deep seated peridotites are represented by pseudogamet and spinel lherzolites, close to them in mineral chemistry with protogranular or porphyroclastic structure with dunite lenses.They represent the jut of the oxidized and undifferentiated asthenospheric material.2) Next temperature interval 900-760° is exemplified by mean and fine grained lherzolites varying in oxidizing conditions -\

The Archaean continental crust comprises two major groups of silicon-rich granitoids: the tonalite–trondhjemite–granodiorite and granite–monzonite–syenite suites, which differ in their sodium-to-potassium ratios. How these felsic granitoids evolved from their mafic precursors remains elusive and the subject of great debate. Here, we present silicon isotopic constraints on the formation of representative trondhjemitic and granitic plutons from the Kaapvaal craton that range in age from 3.51–2.69 billion years ago. We identified very consistent silicon isotopic signatures, all uniformly 0.1–0.2‰ heavier than rocks of the modern continental crust. This unusual composition is explained by the melting of a mafic source that included significant proportions (15–35 wt%) of silicified basalts, which were common supracrustal rocks before 3 billion years ago. Before the melting event that formed the granitoid magmas at depth, portions of the mafic source rocks were enriched in silica by interaction with silica-saturated seawater. The addition of silica depresses the stability of amphibole at similar water activity, allowing trondhjemitic and granitic melt production at lower temperatures from protoliths with contrasting silica contents: 52–57 and ≥60 wt%, respectively. This explains why granitoids were able to form very early in Earth history but did not emerge in significant amounts on other rocky planets.

OCEANIC CRUST ?S. Elfadili(l), D. Demaiffe(l) and L. Andr6(2) (1) Univ.Libre de Bruxelles, P6trologie (CP 160/02) 50,

There is increasing evidence that abrupt vegetation shifts and large-scale erosive phases occurred in Central Africa during the third millennium before present. Debate exists as to whether these events were caused by climate change and/or intensifying human activities related to the Bantu expansion. In this study, we report on a multi-proxy investigation of a sediment core (KZR-23) recovered from the Congo submarine canyon. Our aim was to reconstruct climate, erosion and vegetation patterns in the Congo Basin for the last 10,000 yrs, with a particular emphasis on the late Holocene period. Samples of modern riverine suspended particulates were also analyzed to characterize sediment source geochemical signatures from across the Congo watershed. We find that a sudden increase of bulk sediment aluminium-to-potassium (Al/K) ratios and initial radiocarbon ages of bulk organic matter occurred after 2,200 yrs ago, coincident with a pollen-inferred vegetation change suggesting forest retreat and development of savannas. Although hydrogen isotope compositions of plant waxes (delta D-wax) do not reveal a substantial hydroclimate shift during this period, neodymium isotopes and rare earth elements in detrital fractions indicate provenance changes for the sediment exported from the Congo Basin at that time, hence suggesting a reorganization of spatial rainfall patterns across Central Africa during this event. Taken together, these findings provide evidence for changing landscapes in Central Africa from about 2,200 yrs ago, associated with synchronous events of vegetation changes and enhanced erosion of pre-aged and highly weathered soils. These events coincided remarkably well with the arrival of Iron Age communities into the rainforest, as inferred from comparison to regional archaeological syntheses. While the human impact on the environment remains difficult to quantify at the scale of the vast Congo Basin, we tentatively propose that strengthening of El Nifio-Southern Oscillation (ENSO) variability at that time played a key role in triggering the observed environmental changes, and possibly acted as a driver for the eastward migration of Bantu-speaking peoples across Central Africa. (C) 2018 Elsevier B.V. All rights reserved.

converge to demonstrate that K can reside in the cpx structure at high-pressures (4-14 GPa).To investigate the role of K-rich cpx in controlling the alkali, Sr, Ba, Nd and Pb contents in upper mantle, these elements were determined with REE, Th and U on specimens from two reported geological occurrences: K-rich diopsides from the ultra-high pressure (UHP) Kokchetav Massif and K-rich omphacites inclusions from the Argyle lamproitic diamonds.The Laserprobe ICP-MS was

Silicon (Si) is the second most abundant element in the Earth's crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, delta C-13, delta N-15, delta O-18, delta Si-30) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies.

Silicon (Si) is the second most abundant element in the Earth’s crust and is an important nutrient in the ocean. The global Si cycle plays a critical role in regulating primary productivity and carbon cycling on the continents and in the oceans. Development of the analytical tools used to study the sources, sinks, and fluxes of the global Si cycle (e.g., elemental and stable isotope ratio data for Ge, Si, Zn, etc.) have recently led to major advances in our understanding of the mechanisms and processes that constrain the cycling of Si in the modern environment and in the past. Here, we provide background on the geochemical tools that are available for studying the Si cycle and highlight our current understanding of the marine, freshwater and terrestrial systems. We place emphasis on the geochemistry (e.g., Al/Si, Ge/Si, Zn/Si, δ13 C, δ15 N, δ18 O, δ30 Si) of dissolved and biogenic Si, present case studies, such as the Silicic Acid Leakage Hypothesis, and discuss challenges associated with the development of these environmental proxies for the global Si cycle. We also discuss how each system within the global Si cycle might change over time (i.e., sources, sinks, and processes) and the potential technical and conceptual limitations that need to be considered for future studies.

The delta Si-30 stable isotopic composition of silicon in soils and fine-grained sediments can provide insights into weathering processes on continents, with important implications on the Si budget of modern and past oceans. To further constrain the factors controlling the distribution of Si isotopes in sediments, we have analysed a large number (n = 50) of separate size-fractions of sediments and suspended particulate materials collected near the mouth of rivers worldwide. This includes some of the world's largest rivers (e.g. Amazon, Congo, Mackenzie, Mississippi, Murray-Darling, Nile, Yangtze) and rivers from the case study areas of the Congo River Basin and Northern Ireland. Silt-size fractions exhibit a mean Si isotopic composition (delta Si-30 = -0.21 +/- 0.19%; 2 s.d.) similar to that previously inferred for the upper continental crust. In contrast, clay-size fractions display a much larger range of delta Si-30 values from -0.11 parts per thousand to -2.16 parts per thousand, which yield a global delta Si-30(clay) of -0.57 +/- 0.60 parts per thousand (2 s.d.) representative of the mean composition of the average weathered continental crust. Overall, these new data show that the Si isotopic signature transported by river clays is controlled by the degree of chemical weathering, as inferred from strong relationships with Al/Si ratios. At a global scale, the clay-bound Si isotopic composition of the world's largest river systems demonstrates a link with climate, defining a general correlation with mean annual temperature (MAT) in corresponding drainage basins. While the distribution of Si isotopes in river sediments also appears to be influenced by the tectonic setting, lithological effects and sediment recycling from former sedimentary cycles, our results pave the way for their use as paleo-weathering and paleo-climate proxies in the sedimentary record. (C) 2018 Elsevier Ltd. All rights reserved.

The remineralisation of sinking particles by prokaryotic heterotrophic activity is important for controlling oceanic carbon sequestration. Here, we report mesopelagic particulate organic carbon (POC) remineralisation fluxes in the North Atlantic along the GEOTRACES-GA01 section (GEOVIDE cruise; May–June 2014) using the particulate biogenic barium (excess barium; Baxs) proxy. Important mesopelagic (100–1000 m) Baxs differences were observed along the transect depending on the intensity of past blooms, the phytoplankton community structure, and the physical forcing, including downwelling. The subpolar province was characterized by the highest mesopelagic Baxs content (up to 727 pmol L−1), which was attributed to an intense bloom averaging 6 mg chl a m−3 between January and June 2014 and by an intense 1500 m deep convection in the central Labrador Sea during the winter preceding the sampling. This downwelling could have promoted a deepening of the prokaryotic heterotrophic activity, increasing the Baxs content. In comparison, the temperate province, characterized by the lowest Baxs content (391 pmol L−1), was sampled during the bloom period and phytoplankton appear to be dominated by small and calcifying species, such as coccolithophorids. The Baxs content, related to oxygen consumption, was converted into a remineralisation flux using an updated relationship, proposed for the first time in the North Atlantic. The estimated fluxes were of the same order of magnitude as other fluxes obtained using independent methods (moored sediment traps, incubations) in the North Atlantic. Interestingly, in the subpolar and subtropical provinces, mesopelagic POC remineralisation fluxes (up to 13 and 4.6 mmol C m−2 d−1, respectively) were equalling and occasionally even exceeding upper-ocean POC export fluxes, deduced using the 234Th method. These results highlight the important impact of the mesopelagic remineralisation on the biological carbon pump of the studied area with a near-zero, deep (> 1000 m) carbon sequestration efficiency in spring 2014.

Constraining the continental silicon cycle is a key requirement in attempts to understand both nutrient fluxes to the ocean and linkages between silicon and carbon cycling over different time scales. Silicon isotope data of dissolved silica (delta Si-30(DSi)) are presented here from Lake Baikal and its catchment in central Siberia. As well as being the world's oldest and voluminous lake, Lake Baikal lies within the seventh largest drainage basin in the world and exports significant amounts of freshwater into the Arctic Ocean. Data from river waters accounting for similar to 92% of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river delta Si-30(DSi) composition. The absence of a change in delta Si-30(DSi) within the Selenga Delta, through which 62% of riverine flow passes, suggests a net balance between biogenic uptake and dissolution in this system. A key feature of this study is the use of delta Si-30(DSi) to examine seasonal and spatial variations in DSi utilization and export across the lake. Using an open system model against deepwater delta Si-30(DSi) values from the lake, we estimate that 20-24% of DSi entering Lake Baikal is exported into the sediment record. While highlighting the impact that lakes may have upon the sequestration of continental DSi, mixed layer delta Si-30(DSi) values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilization with lower rates in the north relative to south basin.

We estimate the magnesium stable isotopic composition (delta Mg-26) of the major compartments involved in the biomineralisation process of euryhaline bivalve the manila clam Ruditapes philippinarum. Our aim is to identify the fractionation processes associated with Mg uptake and its cycling/transport in the bivalve organism in order to better assess the controlling factors of the Mg isotopic records in bivalve shells. delta Mg-26 were determined in seawater in hemolymph extrapallial fluid (EPF) soft tissues and aragonitic shell of adult clams collected along the Auray River estuary (Gulf of Morbihan France) at two sites showing contrasted salinity regimes. The large overall delta Mg-26 variations (4.16 parts per thousand) demonstrate that significant mass-dependent Mg isotopic fractionations occur during Mg transfer from seawater to the aragonitic shell.Soft tissues span a range of fractionation factors relative to seawater (Delta Mg-26(soft tissue-seawater)) of 0.42 +/- 0.12 parts per thousand to 0.76 +/- 0.12 parts per thousand and show evidence for biological isotopic fractionation of Mg. Hemolymph and EPF are on average isotopically close to seawater (Delta Mg-26(hemolymph-seawater) = -0.20 +/- 0.27 parts per thousand; 2 sd; n = 5 and Delta Mg-26(EPF-seawater) = -0.23 +/- 0.25 parts per thousand; 2 sd; n = 5) indicating (1) a predominant seawater origin for Mg in the intercellular medium and (2) a relatively passive transfer route through the bivalve organism into the calcifying fluid. The lightest isotopic composition is found in shell with delta Mg-26 ranging from -1.89 +/- 0.07 parts per thousand to -4.22 +/- 0.06 parts per thousand. This range is the largest in the dataset and is proposed to result from a combination of abiotic and biologically-driven fractionation processes. Abiotic control includes fractionation during precipitation of aragonite and accounts for Delta Mg-26(aragonite-seawater) approximate to 1000 ln alpha(aragonite-seawater) = -1.13 +/- 0.28 parts per thousand at 20 degrees C based on literature data. Deviations from inorganic precipitate (expressed as Mg-26(Physiol)) appear particularly variable in the clam shell ranging from 0.03 parts per thousand to -2.20 parts per thousand, which indicates that bivalve shell formation can proceed either under fractionation similar to inorganically-precipitated aragonite or under variable physiological influences. These physiological isotopic effects may be consistent with a regulation of dissolved Mg content in hemolymph and/or EPF due to Mg incorporation into soft tissue and/or Mg fixation by organic macromolecules. Using closed- and open-system models we estimate that Delta Mg-26(Physiol) can be satisfactorily resolved with a remaining Mg fraction in hemolymph and/or EPF of 74% down to 2%. However this feature is not reflected in our hemolymph and EPF data and may indicate that regulation processes and isotopic fractionation may take place in self-contained spaces located close to calcification sites. The potential role of the shell organic matrix which may host non-lattice-bound Mg in the shell is also discussed but remains difficult to assess with our data.Regarding the large physiological effects the delta Mg-26 record in the Manila clam shell offers limited potential as a proxy of temperature or seawater Mg isotopic composition. In contrast the sensitivity of its delta Mg-26 to the salinity regime may offer an interesting tool to track changes in clam biological activity in estuarine environments. (c) 2013 Elsevier Ltd. All rights reserved.

The hafnium and neodymium radiogenic isotope systems behave differently during Earth surface processes, causing a wide dispersion of Hf and Nd isotopic compositions in sediments and other sedimentary rocks. The decoupling between Hf and Nd isotopes in sediments is generally attributed to a combination of preferential sorting of zircon during sediment transport and incongruent weathering processes on continents. In this study, we analysed size-fractions of sediment samples collected near the mouth of 53 rivers worldwide to better understand the factors controlling the distribution of Hf and Nd isotopes in sediments. Our results for rivers draining old cratonic areas and volcanic provinces demonstrate that both granite and basalt weathering can lead to significant grain-size dependent Hf isotopic variability. While silt-size fractions mainly plot along the Terrestrial Array, World river clays are systematically shifted towards more radiogenic Hf isotopic compositions, defining together with published data a new Clay Array (εHf=0.78×εNd+5.23). The Hf–Nd isotope decoupling observed in volcanogenic sediments is best explained by selective alteration of Lu-rich mineral phases (e.g. olivine) and preferential enrichment of resistant unradiogenic minerals, such as spinel and ilmenite, in silt fractions. We also show that the extent to which World river clays deviate from the Clay Array (ΔεHfclay) is not linked to the presence of zircons. Instead, it correlates positively with weathering indices and climatic parameters (temperature, rainfall) of the corresponding drainage basins. Overall, these findings demonstrate that the distribution of Hf–Nd isotopes in clay-size sediments is related to a large extent to weathering conditions on continents, although the precise mechanisms controlling this relationship remain unclear. We finally propose that the Hf–Nd isotope pair proxy could be used in palaeoenvironmental studies to provide semi-quantitative information on past climates.