scholarly journals Compositional Variability of Lignin in Biomass

2018 ◽  
Author(s):  
Ana Lourenço ◽  
Helena Pereira
Keyword(s):  
Compositional Variability

scholarly journals Serpentine–Hisingerite Solid Solution in Altered Ferroan Peridotite and Olivine Gabbro

Minerals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 47 ◽  
Author(s):  
Benjamin Tutolo ◽  
Bernard Evans ◽  
Scott Kuehner
Keyword(s):  
Iron Formation ◽  
Olivine Gabbro ◽  
Banded Iron Formation ◽  
Silicate System ◽  
Duluth Complex ◽  
Sheet Silicate ◽  
Structure Modulation ◽  
Compositional Variability ◽  
Common Observation ◽  
End Members

We present microanalyses of secondary phyllosilicates in altered ferroan metaperidotite, containing approximately equal amounts of end-members serpentine ((Mg,Fe2+)3Si2O5(OH)4) and hisingerite (□Fe3+2Si2O5(OH)4·nH2O). These analyses suggest that all intermediate compositions can exist stably, a proposal that was heretofore impossible because phyllosilicate with the compositions reported here have not been previously observed. In samples from the Duluth Complex (Minnesota, USA) containing igneous olivine Fa36–44, a continuous range in phyllosilicate compositions is associated with hydrothermal Mg extraction from the system and consequent relative enrichments in Fe2+, Fe3+ (hisingerite), Si, and Mn. Altered ferroan–olivine-bearing samples from the Laramie Complex (Wyoming, USA) show a compositional variability of secondary FeMg–phyllosilicate (e.g., Mg–hisingerite) that is discontinuous and likely the result of differing igneous olivine compositions and local equilibration during alteration. Together, these examples demonstrate that the products of serpentinization of ferroan peridotite include phyllosilicate with iron contents proportionally larger than the reactant olivine, in contrast to the common observation of Mg-enriched serpentine in “traditional” alpine and seafloor serpentinites. To augment and contextualize our analyses, we additionally compiled greenalite and hisingerite analyses from the literature. These data show that greenalite in metamorphosed banded iron formation contains progressively more octahedral-site vacancies (larger apfu of Si) in higher XFe samples, a consequence of both increased hisingerite substitution and structure modulation (sheet inversions). Some high-Si greenalite remains ferroan and seems to be a structural analogue of the highly modulated sheet silicate caryopilite. Using a thermodynamic model of hydrothermal alteration in the Fe–silicate system, we show that the formation of secondary hydrothermal olivine and serpentine–hisingerite solid solutions after primary olivine may be attributed to appropriate values of thermodynamic parameters such as elevated a S i O 2 ( a q ) and decreased a H 2 ( a q ) at low temperatures (~200 °C). Importantly, recent observations of Martian rocks have indicated that they are evolved magmatically like the ferroan peridotites analyzed here, which, in turn, suggests that the processes and phyllosilicate assemblages recorded here are more directly relevant to those occurring on Mars than are traditional terrestrial serpentinites.

scholarly journals Compositional Variability and Mutation Spectra of Monophyletic SARS-CoV-2 Clades

2021 ◽  
Author(s):  
Xufei Teng ◽  
Qianpeng Li ◽  
Zhao Li ◽  
Yuansheng Zhang ◽  
Guangyi Niu ◽  
...  
Keyword(s):  
Compositional Variability ◽  
Mutation Spectra

Coupled substitutions in PGE-enriched cobaltite: new evidence from the Rio Jacaré layered complex, Bahia state, Brazil

2015 ◽  
Vol 79 (5) ◽  
pp. 1185-1193 ◽  
Author(s):  
Andrei Y. Barkov ◽  
Yana Fedortchouk ◽  
Robert A. Campbell ◽  
Tapio A.A. Halkoaho
Keyword(s):  
Layered Intrusion ◽  
Fluid Phase ◽  
Primary Phase ◽  
Sulfur Fugacity ◽  
Type Molecule ◽  
Substitution Mechanism ◽  
Compositional Variability ◽  
New Evidence ◽  
Layered Complex ◽  
Grain Core

AbstractMicrocrystals of platinum-group element (PGE)-bearing cobaltite occur in the Gulcari A deposit of vanadiferous titanomagnetite in the lower zone of the Rio Jacaré mafic-ultramafic layered intrusion, Brazil. Aggregates of cobaltite and sperrylite are cluster-like and developed generally along the boundary of Fe-Ti oxide grains with deuteric silicates. Our observations of cryptic zoning, compositional variability and interelement correlations are based on 37 analytical points (wavelength-dispersion spectrometry mode) of cobaltite, and indicate that Ir and Rh behave uniformly with Ni and antipathetically with Co which, in turn, correlates directly with S content. Iridium, Rh and Ni apparently substitute for Co in the As-enriched grain core, and the substitution mechanism invokes solid solution with a cattierite-type molecule: (Ni + Ir + Rh) + (AsS) = Co + (S2). The PGE-bearing cobaltite probably crystallized as a primary phase at 500 to 300°C, from microvolumes of a late fluid phase. The observed enrichment in S and decrease in the As:S ratio at the cobaltite grain margins is a reflection of the increase in sulfur fugacity (fS2) with decrease in temperature of crystallization.

Effect of RP-1 Compositional Variability on Thermophysical Properties

2009 ◽  
Vol 23 (11) ◽  
pp. 5550-5555 ◽  
Author(s):  
M.L. Huber ◽  
E.W. Lemmon ◽  
T.J. Bruno
Keyword(s):  
Thermophysical Properties ◽  
Compositional Variability

scholarly journals Sinking particles promote vertical connectivity in the ocean microbiome

2018 ◽  
Vol 115 (29) ◽  
pp. E6799-E6807 ◽  
Author(s):  
Mireia Mestre ◽  
Clara Ruiz-González ◽  
Ramiro Logares ◽  
Carlos M. Duarte ◽  
Josep M. Gasol ◽  
...  
Keyword(s):  
Surface Waters ◽  
Deep Ocean ◽  
Rrna Gene ◽  
Carbon Export ◽  
Size Fractions ◽  
Sinking Particles ◽  
Prokaryotic Diversity ◽  
Compositional Variability ◽  
Organic Particles ◽  
Community Connectivity

The sinking of organic particles formed in the photic layer is a main vector of carbon export into the deep ocean. Although sinking particles are heavily colonized by microbes, so far it has not been explored whether this process plays a role in transferring prokaryotic diversity from surface to deep oceanic layers. Using Illumina sequencing of the 16S rRNA gene, we explore here the vertical connectivity of the ocean microbiome by characterizing marine prokaryotic communities associated with five different size fractions and examining their compositional variability from surface down to 4,000 m across eight stations sampled in the Atlantic, Pacific, and Indian Oceans during the Malaspina 2010 Expedition. Our results show that the most abundant prokaryotes in the deep ocean are also present in surface waters. This vertical community connectivity seems to occur predominantly through the largest particles because communities in the largest size fractions showed the highest taxonomic similarity throughout the water column, whereas free-living communities were more isolated vertically. Our results further suggest that particle colonization processes occurring in surface waters determine to some extent the composition and biogeography of bathypelagic communities. Overall, we postulate that sinking particles function as vectors that inoculate viable particle-attached surface microbes into the deep-sea realm, determining to a considerable extent the structure, functioning, and biogeography of deep ocean communities.

Hydrous mafic-ultramafic intrusives in a nascent arc (Massif du Sud, New Caledonia ophiolite).

2021 ◽  
Author(s):  
Arianna Secchiari ◽  
Alessandra Montanini ◽  
Dominique Cluzel ◽  
Elisa Ferrari
Keyword(s):  
Trace Element ◽  
Transition Zone ◽  
New Caledonia ◽  
Incompatible Trace Element ◽  
Coarse Grained ◽  
Main Body ◽  
Distinctive Features ◽  
First Occurrence ◽  
Ultramafic Cumulate ◽  
Compositional Variability

<p>The New Caledonia ophiolite hosts one of most complete sections of a nascent arc, representing an excellent natural laboratory for investigating the origin and the evolution of subduction systems. The sequence, originated during the onset of the Eocene subduction [1, 2], is composed of ultra-depleted forearc harzburgites [3] overlain by a dunite-dominated transition zone (500m thick), in turn overtopped by mafic-ultramafic cumulate lenses. The ultramafic rocks of the transition zone (mainly dunites and wehrlites) most likely resulted from melt-peridotite reactions involving primitive arc tholeiites and boninitic magmas [2]. By contrast, dunite-pyroxenite and gabbronorite cumulates derive from H<sub>2</sub>O-poor depleted melts transitional between boninites and arc-tholeiites [2, 4].</p><p>In this contribution, we report the first occurrence of amphibole-bearing ultramafic lithologies in the New Caledonia arc sequence. Our study deals with a petrological and geochemical characterisation of a 2.5km x 5km composite, roughly snowball-shaped, intrusive body, consisting of pyroxenite, dunite, wehrlite, hornblendite and associated mafic-ultramafic, locally sheared, dikes from the Plum area (Massif du Sud).  The pyroxenite component, which forms the core of the intrusion, consists of coarse-grained websterites, mainly composed of weakly oriented orthopyroxene (~ 30-75 vol.%) and clinopyroxene (~ 20-40 vol.%), with variable amounts of edenitic amphibole (~ 2-30 vol.%). The amphibole generally occurs as poikilitic crystals or develops as coronas on pyroxenes. Highly calcic plagioclase (An= 83-96 mol %) is scarce in the pyroxenite body (~ 2 vol. %), but more abundant in the associated dikes (~ 10-50 vol.%). Clinopyroxene shows variable Mg# (0.82-0.92) and low Al<sub>2</sub>O<sub>3 </sub>(0.99-2.00 wt%). Likewise, amphibole yields high Mg# (0.712-0.865). Estimated equilibrium temperatures based on conventional pyroxene thermometry range between 870-970°C, whereas amphibole-plagioclase pairs provide slightly lower values (800-910 °C).</p><p>Whole rocks have moderately high Mg# (71-82) and REE concentrations one to five times chondritic values. The websterites of the main body show LREE-depleted (La<sub>N</sub>/Nd<sub>N</sub> = 0.5-0.8), weakly concave downward patterns, with flat HREE segments (Lu<sub>N</sub>/Tm<sub>N</sub> = 1.1-1.3). The mafic-ultramafic dikes display similar patterns, bearing depleted to flat LREE segments (La<sub>N</sub>/Nd<sub>N</sub> = 0.6-1) and positive Eu anomalies. For all the investigated lithologies, extended trace element diagrams indicate enrichments for FME (i.e. Rb, Ba, U) and Th, coupled to Zr-Hf depletion. Strong Sr positive spikes are only observed for the crosscutting dikes, while the pyroxenite body yields Sr negative anomalies.</p><p>Geochemical modelling shows that the putative liquids in equilibrium with the websterites have intermediate Mg# (57–63) and incompatible trace element patterns sharing remarkable similarities with the New Caledonia CE-boninites [5]. However, they significantly differ from the equilibrium melts reported for the other intrusive rocks of the sequence [1, 4], suggesting greater compositional variability for the liquids ascending into the Moho transition zone and lower crust. Our results support the notion that petrological and geochemical heterogeneity of magmatic products may be distinctive features of subduction infancy.</p><p> </p><p>References</p><p>[1] Marchesi et al., Chem. Geol., 2009, 266, 171-186.</p><p>[2] Pirard et al., J. Petrol., 2013, 54, 1759–1792.</p><p>[3] Secchiari et al., Geosc. Front., 2020, 11(1), 37–55.</p><p>[4] Secchiari et al., Contrib. Mineral. Petrol., 2018, 173(8), 66.</p><p>[5] Cluzel et al., Lithos, 2016, 260, 429–442.</p>

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