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Geochemical and geodynamic perspectives on the origin and evolution of deep-seated mantle melts and their interaction with the lithosphere

The origin and evolution of the continental lithosphere is closely linked to changes in mantle dynamics through time, from its formation through melt depletion to multistage reworking and reorganisation related to interaction with melts formed both beneath and within it. Understanding this history is critical to constraining terrestrial dynamics, element cycles and metallogeny. We welcome contributions dealing with: (1) Reconstructions of the structure and composition of the lithospheric mantle, and the influence of plumes and subduction zones on root construction; (2) Interactions of plume- and subduction-derived melts and fluids with continental lithosphere, and the nature and development of metasomatic agents; (3) Source rocks, formation conditions (P-T-fO2) and evolution of mantle melts originating below or in the mantle lithosphere; (4) Deep source regions, melting processes and phase transformation in mantle plumes and their fluids; (5) Modes of melt migration and ascent, as constrained from numerical modelling and microstructures of natural mantle samples; (6) Role of mantle melts and fluids in the generation of hybrid and acid magmas.These topics can be illuminated using the geochemistry and fabric of mantle xenoliths and orogenic peridotites, mantle-derived melts and experimental simulations.

Co-organized by GMPV2
Convener: Igor Ashchepkov | Co-conveners: Sonja Aulbach, Kate Kiseeva, Evgenii Sharkov
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Tue, 27 Apr, 09:00–10:30

Chairpersons: Kate Kiseeva, Evgenii Sharkov, Sonja Aulbach

09:00–09:05
5-minute convener introduction

09:05–09:10
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EGU21-9325
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ECS
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solicited
Aleksei Kruk and Alexander Sokol

We study the reaction of garnet lherzolite with carbonatitic melt rich in molecular CO2 and/or H2O in experiments at 5.5 GPa and 1200-1450°C. The experimental results show that carbonation of olivine with formation of orthopyroxene and magnesite can buffer the CO2 contents in the melt, which impedes immediate separation of CO2 fluid from melt equilibrated with the peridotite source. The solubility of molecular CO2 in melt decreases from 20-25 wt.% at 4.5-6.8 wt.% SiO2 typical of carbonatite to 7-12 wt.% in more silicic kimberlite-like melts with 26-32 wt.% SiO2. Interaction of garnet lherzolite with carbonatitic melt (2:1) in the presence of 2-3 wt.% H2O and 9-13 wt.% molecular CO2 at 1200-1450°С yields low SiO2 (<10 wt.%) alkali‐carbonatite melts, which shows multiphase saturation with magnesite-bearing garnet harzburgite. Thus, carbonatitic melts rich in volatiles can originate in a harzburgite source at moderate temperatures common to continental lithospheric mantle (CLM).

Having separated from the source, carbonatitic magma enriched in molecular CO2 and H2O can rapidly acquire a kimberlitic composition with >25 wt.% SiO2 by dissolution and carbonation of entrapped peridotite. Furthermore, interaction of garnet lherzolite with carbonatitic melt rich in K, CO2, and H2O at 1350°С produces immiscible kimberlite-like carbonate-silicate and K-rich silicate melts. Quenched silicate melt develops lamelli of foam-like vesicular glass. Differentiation of immiscible melts early during ascent may equalize the compositions of kimberlite magmas generated in different CLM sources. The fluid phase can release explosively from ascending magma at lower pressures as a result of SiO2 increase which reduces the solubility of CO2 due to decarbonation reaction of magnesite and orthopyroxene.

The research was performed by a grant of the Russian Science Foundation (19-77-10023).

How to cite: Kruk, A. and Sokol, A.: Lherzolite - carbonatite melt interaction in the presence of additive CO2 and H2O: Experimental data at 5.5 GPa and 1200-1450°C, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9325, https://doi.org/10.5194/egusphere-egu21-9325, 2021.

09:10–09:12
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EGU21-1251
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Highlight
Jussi S Heinonen et al.

Some studies on basaltic and more primitive rocks suggest that their parental magmas have assimilated more than 50 wt.% (relative to the initial uncontaminated magma) of crustal silicate wallrock. But what are the thermodynamic limits for assimilation by primitive magmas? This question has been considered for over a century, first by N.L. Bowen and many others since then. Here we pursue this question quantitatively using a freely available thermodynamic tool for phase equilibria modeling of open magmatic systems — the Magma Chamber Simulator (MCS; https://mcs.geol.ucsb.edu).

In the models, komatiitic, picritic, and basaltic magmas of various ages and from different tectonic settings assimilate progressive partial melts of average lower, middle, and upper crust. In order to pursue the maximum limits of assimilation constrained by phase equilibria and energetics, the mass of wallrock in the simulations was set at twice that of the initially pristine primitive magmas. In addition, the initial temperature of wallrock was set close to its solidus at a given pressure. Such conditions would approximate a rift setting with tabular chambers and high magma input causing concomitant crustal heating and steep geotherms.

Our results indicate that it is difficult for any primitive magma to assimilate more than 20−30 wt.% of upper crust before evolving to intermediate/felsic compositions. However, if assimilant is lower crust, typical komatiitic magmas can assimilate more than their own weight (range of 59−102 wt.%) and retain a basaltic composition. Even picritic magmas, more relevant to modern intraplate settings, have a thermodynamic potential to assimilate 28−49 wt.% of lower crust before evolving into intermediate/felsic compositions.

These findings have important implications for petrogenesis of magmas. The parental melt composition and the assimilant heavily influence both how much assimilation is energetically possible in primitive magmas and the final magma composition. The fact that primitive mantle melts have potential to partially melt and assimilate significant fractions of (lower) crust may have fundamental importance for how trans-Moho magmatic systems evolve and how crustal growth is accomplished. Examples include generation of siliceous high-magnesium basalts in the Precambrian and anorogenic anorthosite-mangerite-charnockite-granite complexes with geochemical evidence of considerable geochemical overprint from (lower) crustal sources.

How to cite: Heinonen, J. S., Spera, F. J., and Bohrson, W. A.: Thermodynamic constraints on assimilation of silicic crust by primitive magmas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1251, https://doi.org/10.5194/egusphere-egu21-1251, 2021.

09:12–09:14
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EGU21-523
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Highlight
Mousumi Roy and Lang Farmer

This study explores how thermal disequilibrium during channelized melt-infiltration modifies the continental lithosphere from beneath. For this purpose, a 1D model of thermal disequilibrium between melt-rich channels and surrounding melt-poor material was developed, allowing us to estimate heat exchange across channel walls during melt transport at the lithosphere-asthenosphere boundary (LAB).  For geologically-reasonable values of volume fraction of channels (φ), relative velocity across channel walls (v), channel spacing (d), and timescale of episodic melt-infiltration (τ), disequilibrium heating may contribute >10-3 W/m3 to the LAB heat budget. During episodic melt-infiltration, a thermal reworking zone (TRZ) associated with spatio-temporally varying disequilibrium heat exchange forms at the LAB. The TRZ grows by the transient migration of a disequilibrium-heating front at material-dependent velocity, reaching a maximum steady-state width δ∼[φvd-2τ2]. The model results have implications for the Cenozoic evolution of the western US, specifically during the time period following the middle-Cenozoic ignimbrite flareup, and can be used to interpret a disparate set of previously published geophysical and geologic observations from the western US. The spatio-temporal scales associated with establishment of the TRZ in the models are found to be comparable with those inferred for the migration of the LAB based on geologic and petrologic observations within the Basin and Range province. More generally, the geochemistry of Cenozoic basalts across the region indicate a process in which melt-infiltration may have hastened the thinning and weakening of the lithosphere during and following the mid-Cenozoic ignimbrite flare-up, prior to Neogene extension.

How to cite: Roy, M. and Farmer, L.: Implications of thermal disequilibrium during channelized melt-transport for the evolution of the lithosphere-asthenosphere boundary in intraplate settings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-523, https://doi.org/10.5194/egusphere-egu21-523, 2021.

09:14–09:16
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EGU21-15256
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ECS
Georgii Vasilev and Yury Perepechko

The paper presents a non-stationary model of heat-mass transfer of heterophase media in application to the study of the intrusion processes of magmatic melts in permeable zones of the lithospheric mantle and crust. Special emphasis is given to the study of the change in rheological properties of the fluido-magmatic mixture in the process of magmatic channel formation. The increased compressibility of the fluid phase is taken into account in the model by setting the Van der Waals equation of state. The calculated values of thermodynamic parameters of the fluid-magmatic system such as pressure, temperature, volumetric phase content, are the basis for the analysis of metasomatic changes in mantle matter. The Numerical model is based on the Runge-Kutta-TVD method. Verification of the numerical model on standard tests shows good accuracy of the program code and the possibility of using it for investigations of the currents of fluid-magmatic flows. The study of variation in interphase interaction parameters during melt movement in permeable zone, including change in interphase viscous friction, demonstrates a significant change in temperature distribution in the section of fluid-magmatic system. The work was financially supported by the Russian Foundation for Basic Research, grants No. 19-05-00788.

How to cite: Vasilev, G. and Perepechko, Y.: Heat-mass transfer simulation of fluid media in the magma channel, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15256, https://doi.org/10.5194/egusphere-egu21-15256, 2021.

09:16–09:18
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EGU21-14200
Yuri Perepechko et al.

The paper presents a non-isothermal model of hydrodynamic heating of lithospheric rocks above magma chambers in application to the seismic focal zone of the Kamchatka region and associated volcanic arcs. The effect of convective heating of mantle and crustal rocks on dynamics of metasomatic changes and convective melting was studied. In the existing models of ore-forming systems, fluid mass transfer is determined mainly by the retrograde boiling of magmas in meso-abyssal intrusive chambers. Analysis of the manifestations of deposits of the porphyry formation of the Pacific Ocean active margins shows the decisive participation in their formation of mantle-crust ore-igneous systems. The model of convective heat-mass transfer in fluid mantle-crust systems coupled with magma chambers is designed with the consideration of effects of interphase interaction in rocks of permeable zones above igneous fluid sources. Numerical simulation of the dynamics of fluid systems under the volcanoes of the frontal zone of Kamchatka shows altered ultramafic rocks in metasomatic zoning and the presence of facial changes in the mineral composition of wehrlitized rocks. In the mantle wedge of the northwestern margin of the Pacific Ocean, over which epicontinental volcanic arcs developed in the post-Miocene stage, there is possible combination of the products of different-time and different-level igneous systems in the same permeable "earth's crust-lithospheric mantle" transition zones. Assuming that the "cratonization" of volcanic sections of the continental Earth's crust follows the "metasomatic granitization" pattern, the initial element of which is the wehrlitization of mantle wedge ultramafic rocks, the processes of metasomatic fertilization of mantle wedge rocks were investigated using a flow-through multiple-reservoir reactor. In the seismically active regions of the Pacific transition lithosphere, specific conditions for heating of areas of increased permeability above mantle fluid sources should be recorded. Metasomatic columns in such fluid systems can describe the formation of at least three levels of convective melting of metasomatized mantle wedge substrates, as well as the formation of a region of high-temperature fluid change of mafic intrusion rocks in the Earth's crust. The work was financially supported by the Russian Foundation for Basic Research, grants No. 19-05-00788.

How to cite: Perepechko, Y., Sorokin, K., Mikheeva, A., Sharapov, V., and Imomnazarov, S.: Modeling of convective heat-mass transfer in permeable parts of seismic focal zones of the Kamchatka region and associated volcanic arcs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14200, https://doi.org/10.5194/egusphere-egu21-14200, 2021.

09:18–09:28
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EGU21-3313
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solicited
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Highlight
Maya Kopylova et al.

The study reports petrography, bulk major and trace element compositions of lamprophyric Devonian dykes in three areas of the Kola Alkaline Carbonatite Province (N Europe). Dykes in one of these areas, Kandalaksha, are not associated with a massif, while dykes in Kandaguba and Turij Mys occur adjacent (< 5 km) to coeval central multiphase ultramafic alkaline-carbonatitic massifs. Kandalaksha dyke series consists of aillikites - phlogopite carbonatites and monchiquites. Kandaguba dykes range from monchiquites to nephelinites and phonolites; Turij Mys dykes represent alnoites, monchiquites, foidites, turjaites and carbonatites. Some dykes show extreme mineralogical and textural heterogeneity and layering we ascribe to fluid separation. The crystallization and melt evolution of the dykes were modelled with Rhyolite-MELTS and compared with the observed order and products of crystallization. Our results suggest that the studied rocks were related by fractional crystallization and liquid immiscibility. Primitive melts of alkaline picrites or olivine melanephelinites initially evolved at P=1.5-0.8 GPa without a SiO2 increase due to abundant clinopyroxene crystallization controlled by the CO2-rich fluid. At 1-1.1 GPa the Turij Mys melts separated immiscible carbonate melt, which subsequently exsolved carbothermal melts extremely rich in trace elements. Kandaguba and Turij Mys melts continued to fractionate at lower pressures in the presence of hydrous fluid to the more evolved nephelinite and phonolite melts. The studied dykes highlight the critical role of the parent magma chamber in crystal fractionation and magma diversification. The Kandalaksha dykes may represent a carbonatite - ultramafic lamprophyres association, which fractionated at 45- 20 km in narrow dykes on ascent to the surface and could not get more evolved than monchiquite. In contrast, connections of Kandaguba and Turij Mys dykes to their massif magma chambers ensured the sufficient time for fractionation, ascent and a polybaric evolution. This longevity generated more evolved rock types with the higher alkalinity and an immiscible separation of carbonatites.

How to cite: Kopylova, M., Nosova, A., Sazonova, L., Vozniak, A., Kargin, A., Lebedeva, N., Volkova, G., and Pereseckaya, E.: Magmatic diversification of dykes is controlled by adjacent alkaline carbonatitic massifs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3313, https://doi.org/10.5194/egusphere-egu21-3313, 2021.

09:28–09:30
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EGU21-8725
Irina Sotnikova and Nikolay Vladykin

Lamproites of the Aldan Shield were found (Vladykin 1985) at the beginning of 80-es (for the first time in the USSR), being mainly the intrusive varieties of lamproites, though there occur among them some dyke and volcanic varieties. The general geological and geochemical features of lamproites of the Aldan shield were reported at the VI International Kimberlite Conference at Novosibirsk in 1995 (Vladykin 19971).

In  Aldan Shield there are known 14 locations of lamproites mostly referred to the Mesozoic rifting. This zone stretches out over all Aldan Shield, from the Murun massif in the Western part of the shield up to the Konder massif in the Eastern part of the shield. These occurrences of lamproites are of Jurassic age (120-150 m.a.). Only lamproites of Khani massif in the SW part of the Aldan Shield are more ancient. At first (according to the data of V.V.Arkhangelskaya) the Khani massif was considered to be Paleozoic, then using K-Ar method (VSEGEI) it was established Proterozoic age of biotite pyroxenites of the massif 1800 m.a. We found the dyke of olivine lamproites of the massif that crosses the biotite pyroxenites. We obtained even more ancient age – 2700 m.a. by zircons from these lamproites with a device SHRIMP (VSEGEI) (Vladykin, Lepekhina - 2005).

New data on Sr-Nd – systematization of the lamproites of the Aldan Shield have been obtained. The ratios 87Sr/86Sr in lamproites of Aldan vary from 0.703 to 0.708, whereas έ Nd – from -6 to -25. The source of Aldan Shield lamproites is enriched mantle ЕМ-1 (рис.1), that is consistent with their geological position (Vladykin -1997). They are situated between the Aldan Shield and the Siberian platform, where did not occur subduction. The North American lamproites (Leucite Hills, Smoky Bewt, Prery Creak ecc) have a similar position between the Canadian shield and the North-American platform and the same mantle source.

Compared to the Australian lamproites, the lamproites of the Aldan Shield have lower concentrations of rare-earth elements. The TR spectra for the Aldan lamproites (fig. 2) are rather uniform. A slight slope of the spectrum curves and slight Eu-anomaly are typical. For the earlier olivine lamproites lower TR concentrations are typical as compared with more differentiated leucite and sanidine lamproites.

The lamproites of the Aldan Shield originated from the enriched mantle source ЕМ-1, the age of that, according to Pb isotopic data, obtained for the rocks of the Murun massif (Vladykin 19972) is estimated as 3200 m.a. The dykes of the olivine lamproites of the Khani massif are the oldest lamproites in the world (2700 m.a.). The TR spectrum of the same type is indicative of similar genesis of the lamproites from various massifs of the Aldan Shield. In spite of the deep mantle source of the Aldan lamproites, they don’t bear diamonds actually, since the diamonds were likely burnt during their crystallization (at t- 1200-1000o C).

RFBR 09-05-00116, 08-05-9000.

References:

Vladykin N.V. First occurence of lamproites in the USSR.//Doklady Academii Nauk SSSR, 1985, Vol..208, N 3, p.718-722. (in Russia).

How to cite: Sotnikova, I. and Vladykin, N.: Trace element geochemistry and isotopy (Sm, Nd) of lamproites of the Aldan Shield, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8725, https://doi.org/10.5194/egusphere-egu21-8725, 2021.

09:30–09:32
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EGU21-8395
Sergey Zhmodik et al.

In the Eastern margin of the  Anabar shield the Proterozoic alkaline pipes, dikes, and stocks are widespread. The largest Talakhtakh diatreme cut Middle-Upper Riphean dolomites (MP3-NP2) at the left bank of Kuonamka River (Fig. 1). The Talakhtakh diatreme includes alkaline basaltoids, ultra-K-trachytes, lamproites, olivine leucitites, tephrites, (Vishnevsky et al., 1986). TRE distribution indicates the proximity of sanidine trachytes to lamproites.

 The 40Ar/39Ar laser dating show two age maxima 1476 ± 17 (N = 14) and 1321 ± 17 (N = 9) Ma. If 10 points form a linear regression, with an age value of 1497 ± 40 million years, an initial ratio of 189 ± 100, then most of the remaining points are located along the abscissa axis. This arrangement may be associated with different degrees of rejuvenation of the K/Ar isotope system within the dating sites. The weighted average of 1476 ± 17, as more accurate, corresponds to the age of sample formation.

Ernst et al (2016) identified a new Kuonamka Large Igneous Province (LIP), based on U-Pb dating of baddeleyites from dolerite dikes and sills of the Anabar shield. The age of Kuonamka LIP is ~ 1501 ± 3 Ma. The resulting 40Ar/39Ar is the age of leucite trachytes (lamproites) The Talakhtakh diatreme fully corresponds to the time of occurrence of the Kuonamka LIP and indicates the formation of high-K effusions of the Talakhtakh complex during this period.

This work supported by RFBR grants: No. 18-05-70109 and the Russian Ministry of Education and Science

Gusev N.I., et al. State Geological Map of the Russian Federation. Sheet R-49-Olenek. An explanatory Memorandum. Saint Petersburg: Map factory VSEGEI. . 2016. 448 с.

Vishnevskiy S.A., Dolgov Yu. A., Sobolev N. V.  Geology&Geophysics, 1986. № 8. P. 17-27.

Ernst R. E., Okrugin A.V. et al.  Russian Geology&Geophysics. 2016. № 5. P. 653,-671.