Carbonatite Melts and Electrical Conductivity in the Asthenosphere

Gaillard, Fabrice; Malki, M.; Iacono-Marziano, Giada; Pichavant, Michel; Scaillet, Bruno

doi:10.1126/science.1164446

Cited by 292 publications

(263 citation statements)

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“…On the other hand, the high melt ascent velocity may simply be achieved with liquid of much lower viscosity than that of basalt melt, such as carbonaterich melt. Faul 46 argued for the possibility of volatile-rich melts at the deeper part of the mid-ocean ridge to explain high melt ascent rate at low porosities, and recent experimental 10 and electrical conductivity 12,53 results suggest the existence of a small amount of carbonate-rich melt in the asthenosphere beneath the midocean ridge. In addition, a geochemical study by Dasgupta et al 54 suggested that the 230 Th and 231 Pa excesses observed in erupted mid-ocean ridge basalt are a consequence of contributions of carbonate-rich melt.…”

Section: Article Nature Communications | Doi: 101038/ncomms6091mentioning

confidence: 99%

“…Kimberlite magma is characterized by low silica with high magnesium and a C-O-H volatile-rich composition [5][6][7][8] , and is thought to be formed in the presence of H 2 O and CO 2 under conditions close to the carbonate-peridotite solidus in the Earth's mantle [9][10][11] . Small amounts of carbonate-rich melt may also be present in the asthenosphere beneath mid-ocean ridges, according to recent electrical conductivity studies 12,13 and high-pressure and hightemperature experiments 10,[14][15][16] . In addition, strongly carbonated silicate melt is thought to be partly responsible for the presence of oceanic low-velocity zones 10,17 .…”

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confidence: 99%

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Ultralow viscosity of carbonate melts at high pressures

et al. 2014

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Knowledge of the occurrence and mobility of carbonate-rich melts in the Earth's mantle is important for understanding the deep carbon cycle and related geochemical and geophysical processes. However, our understanding of the mobility of carbonate-rich melts remains poor. Here we report viscosities of carbonate melts up to 6.2 GPa using a newly developed technique of ultrafast synchrotron X-ray imaging. These carbonate melts display ultralow viscosities, much lower than previously thought, in the range of 0.006-0.010 Pa s, which are B2 to 3 orders of magnitude lower than those of basaltic melts in the upper mantle. As a result, the mobility of carbonate melts (defined as the ratio of melt-solid density contrast to melt viscosity) is B2 to 3 orders of magnitude higher than that of basaltic melts. Such high mobility has significant influence on several magmatic processes, such as fast melt migration and effective melt extraction beneath mid-ocean ridges.

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Section: Article Nature Communications | Doi: 101038/ncomms6091mentioning

confidence: 99%

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confidence: 99%

Ultralow viscosity of carbonate melts at high pressures

et al. 2014

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“…Aside from the chemical composition, other available alternative causes for high conductivity anomalies can be considered, such as water in nominally anhydrous minerals (Wang et al, 2006;Yang, 2011;Karato, 2009, 2014a), interconnected saline (or aqueous) fluids (Hashim et al, 2013;Shimojuku et al, 2014;Sinmyo and Keppler, 2017;Guo et al, 2015;Li et al, 2018), partial melting (Wei et al, 2001;Maumus et al, 2005;Gaillard et al, 2008;Ferri et al, 2013;Laumonier et al, 2015Laumonier et al, , 2017Ghosh and Karki, 2017), interconnected secondary high conductivity phases (e.g., FeS, Fe 3 O 4 ; Jones et al, 2005;Bagdassarov et al, 2009;Padilha et al, 2015), dehydration of hydrous minerals (Wang et al, 2012(Wang et al, , 2017Manthilake et al, 2015Manthilake et al, , 2016Hu et al, 2017;Sun et al, 2017a, b;Chen et al, 2018) and graphite films on mineral grain boundaries (Freund, 2003;Pous et al, 2004;Chen et al, 2017). In consideration of the similar formation conduction and geotectonic environments, the Himalaya-Tibetan orogenic system was compared with the Dabie-Sulu UHPM belt and explained high electrical conductivity anomalies.…”

Section: Geophysical Implicationsmentioning

confidence: 99%

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

Dai

Sun

et al. 2018

Solid Earth

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Abstract. The electrical conductivity of gneiss samples with different chemical compositions (W A = Na 2 O + K 2 O + CaO = 7.12, 7.27 and 7.64 % weight percent) was measured using a complex impedance spectroscopic technique at 623-1073 K and 1.5 GPa and a frequency range of 10 −1 to 10 6 Hz. Simultaneously, a pressure effect on the electrical conductivity was also determined for the W A = 7.12 % gneiss. The results indicated that the gneiss conductivities markedly increase with total alkali and calcium ion content. The sample conductivity and temperature conform to an Arrhenius relationship within a certain temperature range. The influence of pressure on gneiss conductivity is weaker than temperature, although conductivity still increases with pressure. According to various ranges of activation enthalpy (0.35-0.52 and 0.76-0.87 eV) at 1.5 GPa, two main conduction mechanisms are suggested that dominate the electrical conductivity of gneiss: impurity conduction in the lower-temperature region and ionic conduction (charge carriers are K + , Na + and Ca 2+ ) in the higher-temperature region. The electrical conductivity of gneiss with various chemical compositions cannot be used to interpret the high conductivity anomalies in the Dabie-Sulu ultrahigh-pressure metamorphic belt. However, the conductivity-depth profiles for gneiss may provide an important constraint on the interpretation of field magnetotelluric conductivity results in the regional metamorphic belt.

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“…It is difficult to reconcile rapid emplacement of crystal-rich lavas with an estimated viscosity that are five to six orders of magnitude higher than ever measured in the field and/or in laboratory experiments (Dawson et al 1995b;Pinkerton et al 1995;Norton and Pinkerton 1997). However, the extremely low melt viscosities and high diffusion rates that characterize natrocarbonatitic magmas (Gaillard et al 2008) could favor rapid crystallization during emplacement of lava flows (e.g., the crystal content of a solidified lava flow is not identical to the crystal content during emplacement). Previous experimental studies focused on the crystallization of natrocarbonatitic magmas have been conducted at 100 and 20 MPa confining pressure (Cooper et al 1975;Petibon et al 1998).…”

Section: Introductionmentioning

confidence: 93%

Experimental constraints on the crystallization of natrocarbonatitic lava flows

Mattsson

Caricchi

2009

Bull Volcanol

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Natrocarbonatitic magmas are characterized by their extremely low viscosities and fast elemental diffusion, and as a consequence of this, their chemistry and crystallinity can change significantly during residence in shallow reservoirs or even due to cooling during lava flow emplacement. Here, we present the results of a series of crystallization experiments conducted at 1-atm confining pressure and in a temperature range between 630°C and 300°C. The experiments were set up to characterize the chemistry and growth processes of the phenocryst phases present in natrocarbonatites. The results are applicable to (1) processes occurring during residence in shallow magma reservoirs and/or (2) during lava flow emplacement. We show that during crystallization of natrocarbonatites at atmospheric pressure, gregoryite is the first mineral to crystallize at 630°C, followed by nyerereite at 595°C. Crystal size distributions of the gregoryites show that the crystals grow rapidly by textural coarsening (i.e., Ostwald ripening). As the crystallization is a continuous process at this pressure, the composition of the residual melt changes in response to the crystallization. However, the experiments also show that individual crystals completely reequilibrate with the changes in melt composition in as little time as <11 min. We therefore conclude that crystallization and diffusion are extremely fast processes in the natrocarbonatitic system and that the measured chemical variations in phenocrysts from Oldoinyo Lengai can be explained by different cooling histories. Finally, we model the rheological control on the emplacement of highly crystallized natrocarbonatitic lavas at Oldoinyo Lengai.

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Carbonatite Melts and Electrical Conductivity in the Asthenosphere

Cited by 292 publications

References 34 publications

Ultralow viscosity of carbonate melts at high pressures

Ultralow viscosity of carbonate melts at high pressures

Effect of chemical composition on the electrical conductivity of gneiss at high temperatures and pressures

Experimental constraints on the crystallization of natrocarbonatitic lava flows

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