scholarly journals Melting of sediments in the deep mantle produces saline fluid inclusions in diamonds

2019 ◽  
Vol 5 (5) ◽  
pp. eaau2620 ◽  
Author(s):  
Michael W. Förster ◽  
Stephen F. Foley ◽  
Horst R. Marschall ◽  
Olivier Alard ◽  
Stephan Buhre
Keyword(s):  
Marine Sediments ◽  
Fluid Inclusions ◽  
Subduction Zones ◽  
Experimental Results ◽  
Mantle Lithosphere ◽  
Earth’S Mantle ◽  
Deep Mantle ◽  
Solid Phases ◽  
Alkali Chlorides ◽  
Low Pressures

Diamonds growing in the Earth’s mantle often trap inclusions of fluids that are highly saline in composition. These fluids are thought to emerge from deep in subduction zones and may also be involved in the generation of some of the kimberlite magmas. However, the source of these fluids and the mechanism of their transport into the mantle lithosphere are unresolved. Here, we present experimental results showing that alkali chlorides are stable solid phases in the mantle lithosphere below 110 km. These alkali chlorides are formed by the reaction of subducted marine sediments with peridotite and show identical K/Na ratios to fluid inclusions in diamond. At temperatures >1100°C and low pressures, the chlorides are unstable; here, potassium is accommodated in mica and melt. The reaction of subducted sediments with peridotite explains the occurrence of Mg carbonates and the highly saline fluids found in diamonds and in chlorine-enriched kimberlite magmas.

scholarly journals Abyssal Serpentinites: Transporting Halogens from Earth’s Surface to the Deep Mantle

Minerals ◽  
2019 ◽  
Vol 9 (1) ◽  
pp. 61 ◽  
Author(s):  
Lilianne Pagé ◽  
Keiko Hattori
Keyword(s):  
Mass Balance ◽  
Subduction Zones ◽  
Hydrothermal Fluids ◽  
Igneous Rocks ◽  
The Other ◽  
Ultrahigh Pressure ◽  
Conservative Estimate ◽  
Mantle Lithosphere ◽  
Deep Mantle ◽  
Subducting Slab

Serpentinized oceanic mantle lithosphere is considered an important carrier of water and fluid-mobile elements, including halogens, into subduction zones. Seafloor serpentinite compositions indicate Cl, Br and I are sourced from seawater and sedimentary pore fluids, while F may be derived from hydrothermal fluids. Overall, the heavy halogens are expelled from serpentinites during the lizardite–antigorite transition. Fluorine, on the other hand, appears to be retained or may be introduced from dehydrating sediments and/or igneous rocks during early subduction. Mass balance calculations indicate nearly all subducted F is kept in the subducting slab to ultrahigh-pressure conditions. Despite a loss of Cl, Br and I from serpentinites (and other lithologies) during early subduction, up to 15% of these elements are also retained in the deep slab. Based on a conservative estimate for serpentinite thickness of the metamorphosed slab (500 m), antigorite serpentinites comprise 37% of this residual Cl, 56% of Br and 50% of I, therefore making an important contribution to the transport of these elements to the deep mantle.

scholarly journals Metamorphic devolatilization of subducted marine sediments and the transport of volatiles into the Earth's mantle

Nature ◽  
2001 ◽  
Vol 411 (6835) ◽  
pp. 293-296 ◽  
Author(s):  
D. M. Kerrick ◽  
J. A. D. Connolly
Keyword(s):  
Marine Sediments ◽  
Earth’S Mantle

VAPOR DENSITY OF SULPHUR DIOXIDE

1934 ◽  
Vol 11 (4) ◽  
pp. 530-538 ◽  
Author(s):  
W. W. Stewart ◽  
O. Maass
Keyword(s):  
Molecular Weight ◽  
Equation Of State ◽  
Sulphur Dioxide ◽  
Apparent Molecular Weight ◽  
Experimental Results ◽  
Vapor Density ◽  
Straight Line ◽  
Low Pressures

The technique developed in this laboratory for measuring gas densities has been made still more sensitive by using a 50-litre volume. The experimental results obtained showed that the apparent molecular weight-pressure isothermal for sulphur dioxide is not a straight line. This is in agreement with the equation of state for gases at low pressures, the study of which has been the main object of this investigation. From the data on sulphur dioxide its true molecular weight was found to be 64.075.

Continental mantle lithosphere, and shallow level enrichment processes in the Earth's mantle

1990 ◽  
Vol 96 (3-4) ◽  
pp. 256-268 ◽  
Author(s):  
C.J. Hawkesworth ◽  
P.D. Kempton ◽  
N.W. Rogers ◽  
R.M. Ellam ◽  
P.W. van Calsteren
Keyword(s):  
Mantle Lithosphere ◽  
Shallow Level ◽  
Earth’S Mantle

Evolution of deep mantle sourced carbonated melt in the mantle lithosphere

2020 ◽  
Author(s):  
Guoliang Zhang
Keyword(s):  
Rare Earth ◽  
Field Strength ◽  
Rare Earth Elements ◽  
Lithospheric Mantle ◽  
High Field ◽  
Volcanic Rocks ◽  
Mantle Lithosphere ◽  
High Field Strength ◽  
Alkali Basalts ◽  
Deep Mantle

<p>Deep sourced magmas play a key role in distribution of carbon in the Earth’s system. Oceanic hotspots rooted in deep mantle usually produce CO<sub>2</sub>-rich magmas. However, the association of CO<sub>2</sub> with the origin of these magmas remains unclear. Here we report geochemical analyses of a suite of volcanic rocks from the Caroline Seamount Chain formed by the deep-rooted Caroline hotspot in the western Pacific. The most primitive magmas have depletion of SiO<sub>2</sub> and high field strength elements and enrichment of rare earth elements that are in concert with mantle-derived primary carbonated melts. The carbonated melts show compositional variations that indicate reactive evolution within the overlying mantle lithosphere and obtained depleted components from the lithospheric mantle. The carbonated melts were de-carbonated and modified to oceanic alkali basalts by precipitation of perovskite, apatite and ilmenite that significantly decreased the concentrations of rare earth elements and high field strength elements. These magmas experienced a stage of non-reactive fractional crystallization after the reactive evolution was completed. Thus, the carbonated melts would experience two stages, reactive and un-reactive, of evolution during their transport through in thick oceanic lithospheric mantle. We suggest that the mantle lithosphere plays a key role in de-carbonation and conversion of deep-sourced carbonated melts to alkali basalts. This work was financially supported by the National Natural Science Foundation of China (91858206, 41876040).</p>

A preliminary assessment of the application of Sr, Nd, Pb, He and N isotope analysis to fluid inclusions in kimberlite olivine: A new approach to trace deep-mantle sources

2020 ◽  
Author(s):  
Andrea Giuliani ◽  
Janne M. Koornneef ◽  
Peter Barry ◽  
Patrizia Will ◽  
Henner Busemann ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Trace Element ◽  
Mass Spectrometer ◽  
Fluid Inclusions ◽  
Noble Gas ◽  
Isotope Analysis ◽  
Helium Isotope ◽  
New Approach ◽  
Deep Mantle ◽  
Mantle Sources

<p>Kimberlites are the deepest melts that reach Earth’s surface and, therefore, can provide unique insights into the composition and evolution of the convective mantle through time. Application of isotope geochemistry to trace the composition of kimberlite sources has thus far been hindered by the ubiquitous alteration and incorporation of xenocrystic material in kimberlite rocks. Bulk-kimberlite analyses are typically considered reliable for Nd and Hf isotopes due to their overwhelmingly higher concentrations in kimberlite melts compared to common mantle and crustal contaminants. Conversely, Sr and Pb isotope compositions of bulk kimberlite samples are seldom considered representative of their parental melts thus requiring analysis of robust magmatic phases, primarily perovskite. Addressing the primary (i.e. magmatic) isotopic composition of volatile elements, such as N and noble gases, requires analyses of volatile-rich phases, and fluid inclusions in olivine represent a typical primary target in mantle-derived magmas. However, fluid inclusions in kimberlitic olivine are dominantly secondary in origin. Secondary inclusions can form at any time after crystallisation of their mineral host, which requires assessment of the origin of trapped fluids (i.e. pristine magmatic fluids, crustal fluids of external derivation, or combination thereof) before their isotopic composition can be used to make inferences about kimberlite mantle sources.</p><p>Here we present trace-element and Sr-Nd-Pb-He-N isotopic compositions of multiple olivine aliquots representing two different magmatic units of the ~88 Ma Wesselton kimberlite (Kimberley, South Africa). The Sr and Nd isotopic composition of olivine analysed by isotope-dilution (ID) TIMS are within the narrow range of perovskite <sup>87</sup>Sr/<sup>86</sup>Sr (0.7043-0.7046) and whole-rock <sup>143</sup>Nd/<sup>144</sup>Nd (eNd<sub>i</sub> = 0.4–2.2) for the Kimberley kimberlites. These results indicate that the secondary fluid inclusions, which dominate the incompatible trace-element budget of olivine separates, have a pristine magmatic origin devoid of crustal contribution.</p><p>Helium isotope compositions were measured by laser heating of 1.6 to 9.8 mg of olivine using an ultrahigh-sensitivity compressor-source noble gas mass spectrometer. <sup>3</sup>He/<sup>4</sup>He ratios are between 1.6 R<sub>A</sub> and 3.7 R<sub>A</sub> (where R<sub>A</sub> indicates the atmospheric <sup>3</sup>He/<sup>4</sup>He ratio), values more radiogenic than MORBs but comparable to HIMU OIBs. These results indicate a high time-integrated (U+Th)/He ratio in the source of the Kimberley kimberlites, which is consistent with the moderately high (i.e. HIMU-like) time-integrated U/Pb ratio implied by elevated initial <sup>206</sup>Pb/<sup>204</sup>Pb in Wesselton olivine (19.1-19.5), Kimberley kimberlites (up to 19.9) and megacrysts in southern African Cretaceous kimberlites (up to 20.5). The combination of low <sup>3</sup>He/<sup>4</sup>He, moderately radiogenic <sup>87</sup>Sr/<sup>86</sup>Sr, and negative d<sup>34</sup>S values (-2.6‰ to -5.7‰) require a contribution from subducted recycled material in the source of the Kimberley kimberlites. Conversely, a preliminary N isotope analysis of Wesselton olivine by in-vacuo crushing using a noble gas mass spectrometer returned a mantle-like d<sup>15</sup>N of -2.9‰, which might suggest limited recycling of surface N (d<sup>15</sup>N >0‰) in the source of these kimberlites. We conclude that the combination of Sr-Nd-Pb and He-N isotope tracing of fluid inclusions in olivine can provide a robust new approach to address the composition of kimberlite sources and, therefore, the evolution of the deep mantle through time.</p>

The stability of Fe–Ni carbides in the Earth's mantle: Evidence for a low Fe–Ni–C melt fraction in the deep mantle

2014 ◽  
Vol 388 ◽  
pp. 211-221 ◽  
Author(s):  
Arno Rohrbach ◽  
Sujoy Ghosh ◽  
Max W. Schmidt ◽  
Clazina H. Wijbrans ◽  
Stephan Klemme
Keyword(s):  
Earth’S Mantle ◽  
Deep Mantle ◽  
The Stability

Composition of fluids released along a subduction interface with increasing depth: insights from fluid inclusions analysis on the Schistes Lustrés - Monviso transect (Western Alps)

2020 ◽  
Author(s):  
Clément Herviou ◽  
Anne Verlaguet ◽  
Philippe Agard ◽  
Hugues Raimbourg ◽  
Michele Locatelli ◽  
...  
Keyword(s):  
Oceanic Crust ◽  
Fluid Inclusions ◽  
Subduction Zones ◽  
Shear Zones ◽  
Free Fluid ◽  
Accretionary Wedge ◽  
Continuous Increase ◽  
Dehydration Reactions ◽  
Eclogite Facies ◽  
Fluid Sources

<p>Important amounts of fluids are released in subduction zones by successive dehydration reactions occurring both in the previously hydrated oceanic crust (and mantle) and overlying sedimentary cover. The release and circulation of such fluids in rocks have major consequences on both their mechanical and chemical behavior. Indeed, the presence of a free fluid phase strongly modifies the rock rheology, fracturing properties, and could be implicated in both intermediate-depth earthquake and slow slip events nucleation. Moreover, the scale of mass transfer, associated chemical changes in infiltrated rocks and element recycling in subduction zones are controlled by both the rock permeability and the amount and composition of such fluids. Thus, there is a crucial need to identify the major fluid sources, amounts and pathways to better constrain their impact on subduction dynamics.</p><p>Metamorphic veins, as well as mineralized fractures and shear zones in exhumed fossil subduction zones are the best witnesses of fluid-rock interactions and fluid circulation pathways. However, their interpretation in terms of fluid sources, residence time, scale of circulation requires a good knowledge of the composition of potential fluid sources. In order to determine the composition of the fluid released by both oceanic crust and sediments at various depth along their subduction, we analyzed the composition of fluid inclusions contained in vein minerals formed at peak P-T conditions, in rock units buried at various depths in the Alpine subduction zone.</p><p>The Schistes Lustrés complex is a slice-stack representing the deep, underplated part of the former Alpine accretionary wedge. These Alpine Tethys rocks are mainly composed of oceanic calcschists with fewer mafic and ultramafic rocks, buried to various depths before exhumation. From West to East, the juxtaposed Schistes Lustrés units show increasing peak P-T conditions from blueschist (300-350°C - 1.2-1.3 GPa) to eclogite facies (580°C - 2.8 GPa). This study focuses on the Schistes Lustrés - Monviso transect, which shows an almost continuous increase in metamorphic grade.</p><p>In the Schistes Lustrés blueschist-facies sediments, fluid inclusions were analyzed in quartz from high-pressure veins, i.e. quartz that co-crystallized with prograde to peak metamorphic minerals such as lawsonite and Fe-Mg carpholite. In the metamorphosed mafic rocks, we analyzed fluid inclusions from the peak metamorphic assemblages, i.e. glaucophane +/- omphacite in blueschist facies rocks, omphacite in eclogite-facies slices. Raman spectroscopy data on these fluid inclusions suggest that fluids released during dehydration of calcschists in blueschist-facies conditions are aqueous fluids with low-salinity and small amounts of CO<sub>2</sub> and CH<sub>4</sub>. In contrast, eclogitic fluids released from metagabbros are highly saline brines with low N<sub>2 </sub>content. These results, which will be associated with LA-ICP-MS analysis of fluid inclusions in metasedimentary quartz veins, will contribute to better constrain the evolution of composition of the fluids liberated by dehydration reactions with depth and protolith composition along the subduction interface.</p>

On the diffusion of gases through metals

1936 ◽  
Vol 32 (4) ◽  
pp. 657-662 ◽  
Author(s):  
Jwu-Shi Wang
Keyword(s):  
High Pressures ◽  
Adsorbed Layer ◽  
Experimental Results ◽  
The Other ◽  
Important Process ◽  
Low Pressures ◽  
Diffusion Of Hydrogen ◽  
Diffusion Of Gases

The results of experiments on the diffusion of hydrogen through metals from a pressure p on one side to a vacuum on the other show that at high pressures the amount diffusing varies linearly with p½ but that at low pressures it varies more rapidly. The difficulty usually encountered when diffusion from an adsorbed layer into the solid is considered theoretically is that the theory indicates that saturation should be reached. In this paper it is shown that this difficulty is due to the omission of an important process at the surface and that by including this process the experimental results can be explained.

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