Upper mantle metasomatism: Chemical and physical consequences

1987 ◽  
pp. 155-159 ◽  
Author(s):  
J. B. Dawson
Keyword(s):  
Upper Mantle ◽  
Mantle Metasomatism ◽  
Physical Consequences

Upper-mantle metasomatism beneath a continental rift: clinopyroxenes in alkali mafic lavas and nodules from Sruth West Uganda

1981 ◽  
Vol 44 (335) ◽  
pp. 315-323 ◽  
Author(s):  
F. E. Lloyd
Keyword(s):  
Upper Mantle ◽  
Significant Proportion ◽  
Mantle Metasomatism ◽  
Continental Rift ◽  
Published Data ◽  
East African ◽  
South West ◽  
Mafic Lavas ◽  
Bulk Chemistry

AbstractClinopyroxenes are dominant in highly potassic, silica undersaturated mafic volcanics occurring on the western rim of the uplifted, rifted East African craton. A kimbcrlite style of eruption provides nodules of alkali clinopyroxenite (clinopyroxene + titaniferous phlogopite+titanomagnetite, apatite, sphene, and rare corroded olivine) which have similar bulk chemistry to the feldspathoid-bearing lavas. Many nodules display metasomatic textures supporting a formation from the alteration of pre-existing material; clinopyroxene growth is characterized by complex, non-oscillatory colour zoning. Comparison of natural clinopyroxene chemistry with published data for elinopyroxenes crystallized from synthetic potassium-rich mafic material, suggests that a significant proportion of the nodules crystallized at upper-mantle pressures. Neither garnet- nor orthopyroxene-bearing nodules have ever been recorded from south-west Uganda, suggesting that metasomatism of the local mantle has proceeded far enough to obliterate all recognizable remnants of four-phase lherzolite.

First assessment of the noble gas and CO2 isotopic composition of fluid inclusions hosted in mantle xenoliths from El Hierro (Canary Islands) 

2021 ◽  
Author(s):  
Andres Sandoval Velasquez ◽  
Andrea Luca Rizzo ◽  
Alessandro Aiuppa ◽  
Maria Luce Frezzotti ◽  
Samantha Remigi ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Oceanic Crust ◽  
Canary Islands ◽  
Fluid Inclusions ◽  
Upper Mantle ◽  
Noble Gas ◽  
Mantle Metasomatism ◽  
Mantle Xenoliths ◽  
Local Source ◽  
El Hierro

<p>Studying the isotopic composition of fluids trapped in mantle xenoliths opens avenues to understanding the origin and cycling of volatiles in the Earth’s upper mantle. Here, we present the first isotopic results for noble gases and CO<sub>2</sub> in fluid inclusions (FI) trapped in mantle xenoliths from El Hierro the youngest island of the Canarian archipelago. Our results are based on 6 mantle xenolith samples (3 Spinel-lherzolites and 3 Spinel-harzburgites) collected from the El Julan cliff valley (Oglialoro et al., 2017), from which we hand-picked crystals of Ol, Opx, and Cpx. Isotopic determinations were performed at the INGV (Sezione di Palermo) noble gas and stable isotopes laboratories, following the preparation methods and analytical procedures described in Rizzo et al. (2018 and references therein).</p><p>The Ne-Ar isotopic compositions reveal the presence of an atmospheric component in the FI. Most of the samples exhibit <sup>4</sup>He/<sup>20</sup>Ne ratios > 60, <sup>20</sup>Ne/<sup>22</sup>Ne ratios between 9.84 and 10.49, <sup>21</sup>Ne/<sup>22</sup>Ne ratios from 0.0295 to 0.0330, and <sup>40</sup>Ar/<sup>36</sup>Ar > 800, suggesting mixing between MORB-like mantle fluids and an air-derived component. We argue this latter may (at least in part) derive from upper mantle recycling of atmospheric fluids via paleo-subduction event(s). Excluding samples possibly affected by diffusive fractionation processes, the average Rc/Ra ratio (<sup>3</sup>He/<sup>4</sup>He ratio corrected for atmospheric contamination) measured in El Hierro xenoliths is ~7.45 + 0.26 Ra, within the MORB range (8 + 1 Ra; Graham, 2002). The He homogeneous signature of these xenoliths agrees well with the <sup>3</sup>He/<sup>4</sup>He compositions previously reported in lava phenocrysts and cumulates (Day and Hilton, 2011) and is slightly below the maximum ratios measured in groundwater samples during the 2012 volcanic unrest (~8.2 Ra; Padron et al., 2013). All these pieces of evidence argue against a primordial source involved in the local lithospheric mantle. Putting these data in the context of previous literature results for FI and surface gases in the Canary Islands (La Palma, La Gomera, Tenerife, Gran Canaria, and Lanzarote), we identify an eastward <sup>3</sup>He/<sup>4</sup>He decreasing trend that parallels a corresponding increase of the oceanic crust thickness. In addition to the mantle heterogeneity, we propose that part of the <sup>3</sup>He/<sup>4</sup>He east-to-west variation along the archipelago is caused by the variable thickness of the oceanic crust (and hence, different interactions with <sup>4</sup>He-rich crustal fluids during emplacement).</p><p>The FI δ<sup>13</sup>C(CO<sub>2</sub>) isotopic composition ranges from -2.38 to -1.23‰ in pyroxenes and -0.2 to +2.0‰ in olivine. These unusually positive δ<sup>13</sup>C compositions support the existence of a recycled crustal carbon component in the local source mantle, likely pointing to mantle metasomatism (Oglialoro et al., 2017) from fluids carrying carbon from subducted sediments and/or altered oceanic crust (AOC).</p>

scholarly journals Experimental study of formation of chromian priderite and yimengite as products of modal mantle metasomatism

2019 ◽  
Vol 486 (6) ◽  
pp. 709-713
Author(s):  
V. G. Butvina ◽  
S. S. Vorobey ◽  
O. G. Safonov ◽  
D. A. Varlamov ◽  
G. V. Bondarenko ◽  
...  
Keyword(s):  
Experimental Study ◽  
Upper Mantle ◽  
Mantle Peridotite ◽  
Mantle Metasomatism ◽  
Mantle Minerals ◽  
Silicate Inclusions ◽  
Chromium Spinel ◽  
Series Of Experiments ◽  
Indicator Minerals ◽  
The Relationship

The article presents the data of a series of experiments on the synthesis of exotic titanates (priderite and yimengite) as a result of the reproduction of metasomatic conditions of transformation of mantle minerals (chromite, ilmenite). It was first synthesized chromian priderite not containing Ba. The experiments showed the possibility of crystallization of this mineral as a reaction product of high-chromium spinel and rutile with potassium aqueous carbonate fluid (melt) in the upper mantle. In particular, the obtained experimental data allow us to interpret the relationship between K-Cr-priderite and carbonate-silicate inclusions in chromites of Bohemian garnet peridotites. In the experimental study of the reaction of chromite and ilmenite with aqueous potassium-carbonate fluid (melt) obtained both phases of titanates (priderite and yimengite) - indicator minerals, mantle metasomatism, which directly confirms the possibility of formation of yimengite and K-Cr-priderite and other titanates, the result of mantle metasomatism of upper mantle peridotite under conditions of the highest activity of potassium.

Metasomatism-controlled hydrogen distribution in the Spitsbergen upper mantle

2020 ◽  
Vol 105 (9) ◽  
pp. 1326-1341
Author(s):  
Wenting Tang ◽  
Hejiu Hui ◽  
Dmitri A. Ionov ◽  
Wei Chen ◽  
Lisha Zhang ◽  
...  
Keyword(s):  
Trace Elements ◽  
Upper Mantle ◽  
Mantle Metasomatism ◽  
Hydrogen Distribution ◽  
Nd Isotope ◽  
Basaltic Rocks ◽  
Incompatible Trace Elements ◽  
Island Basalt

Abstract Hydrogen concentrations in minerals of peridotite xenoliths in alkali basaltic rocks from Quaternary volcanoes in northwest Spitsbergen were measured using polarized Fourier transform infrared spectroscopy (FTIR) to trace the effects of geologic processes on hydrogen distribution in the continental lithospheric mantle. The mineral grains show hydrogen profiles with lower concentrations at rims suggesting diffusive hydrogen loss during the entrapment and transport of the xenoliths in magma. However, hydrogen concentrations in the centers of the grains are uniform and appear to represent hydrogen abundances in the Spitsbergen upper mantle. The olivine, orthopyroxene, and clinopyroxene contain 1–10, 130–290, and 350–560 ppm H2O, respectively. Hydrogen abundances away from metasomatic melt conduits recorded by Type 1 xenoliths are correlated with the concentrations of incompatible trace elements, indicating that hydrogen distribution is related to mantle metasomatism. By contrast, hydrogen near the melt conduits, recorded by Type 2 xenoliths, shows no regular correlations with incompatible trace elements (except Nb in clinopyroxene) and may be affected by fractional crystallization of amphibole in the conduits. Hydrogen contents decrease away from the melt conduits and are controlled by the interaction between the depleted host mantle and percolating metasomatic melts. Therefore, the metasomatic melt could have variably hydrated the Spitsbergen upper mantle via different processes. The H2O/Ce ratios of the melt in equilibrium with clinopyroxene near the metasomatic melt conduits range from 93 to 218, i.e., within the oceanic island basalt (OIB) range. This is consistent with that the metasomatic melt could have been derived from OIB-type sources evidenced by the Sr-Nd isotope compositions of the xenoliths.

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