GMPV2.1

EDI
Evolution of the Earth's upper mantle: a petrological, geochemical and geodynamic perspective on lithospheric mantle xenoliths, orogenic and ophiolitic peridotites

The nature of Earth’s lithospheric mantle is largely constrained from the petrological and geochemical studies of xenoliths. They are complemented by studies of orogenic peridotites and ophiolites, which show the space relationships among various mantle rock types, missing in xenoliths. Mantle xenoliths from cratonic regions are distinctly different from those occurring in younger non-cratonic areas. Percolation of melts and fluids through the lithospheric mantle significantly modifies its petrological and geochemical features, which is recorded in mantle xenoliths brought to the surface by oceanic and continental volcanism. Basalts and other mantle-derived magmas provide us another opportunity to study the chemical and physical properties the mantle. These various kinds of information, when assembled together and coupled with experiments and geophysical data, enable the understanding of upper mantle dynamics.
This session’s research focus lies on mineralogical, petrological and geochemical studies of mantle xenoliths, orogenic and ophiolitic peridotites and other mantle derived rocks. We strongly encourage the contributions on petrology and geochemistry of mantle xenoliths and other mantle rocks, experimental studies, the examples and models of mantle processes and its evolution in space and time.

Co-organized by GD2
Convener: Jacek Puziewicz | Co-conveners: Costanza Bonadiman, Michel Grégoire, Karoly Hidas, Petros Koutsovitis
Presentations
| Thu, 26 May, 08:30–11:30 (CEST)
 
Room K1

Presentations: Thu, 26 May | Room K1

Chairpersons: Jacek Puziewicz, Theodoros Ntaflos
08:30–08:37
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EGU22-517
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ECS
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On-site presentation
Dariusz Marciniak, Ciążela Jakub, Jesus Ana, Pieterek Bartosz, Koepke Jürgen, Strauss Harald, Lazarov Marina, Horn Ingo, Słaby Ewa, Prell Marta, and Blutstein Konrad

Holes CM1A and CM2B of the International Continental Scientific Drilling Program (ICDP) Oman Drilling Project (OmanDP, https://www.omandrilling.ac.uk/)  drilled  through  the Moho  Transition  Zone  (MTZ).  CM1A is composed  of layered gabbro (0–160 meters below surface, mbs), dunite (160–310 mbs), and harzburgites (310–405 mbs), whereas CM2B contains dunite (20–120 mbs) and harzburgites (120–300 mbs). The drillholes provided an unprecedented opportunity to study the behavior of metals in the MTZ, where arriving primitive MORB melts  extensively  react  with  the  mantle.  Here,  melts, typically  enriched  with  sulfur and  chalcophile  elements,  are supposed to enrich the mantle and lower crust with sulfides (Gonzalez-Jimenez et al., 2020 – Ore Geol. Rev.; Ciążela et al., 2018 - GCA).          

            Modal sulfide content increases downwards the gabbro sequence from ~0.004 vol.‰ to ~1.0 vol.‰ but decreases again from 0.8 vol.‰ to 0.01 vol.‰ in the lower part of the MTZ and in the harzburgite of the upper mantle. This is reflected in the S concentration increasing from 341 ± 17 ppm, 2sd (standard deviation = σ) to  832  ±  37  ppm,  2sd,  in  the  gabbro  section  and  decreasing  downwards  from  the middle part of  Moho into harzburgites from 475 ± 21, 2sd ppm to 63 ± 3 ppm, 2σ. The sulfides in olivine gabbro from MTZ are mostly (56–87% of all sulfides) pyrrhotite-pentlandite-chalcopyrite assemblages indicating the magmatic origin. Sulfides in layered gabbro sequence are consisted of similar magmatic assemblages (36-100%) with minor chalcopyrite, bornite, heazlewoodite, chalcocite, millerite, siegenite and sphalerite with secondary origin. In dunite and harzburgite sequences sulfides are exclusively hydrothermal.

Based on EMPA and LA-ICPMS measurements, Zn, Co and Cu seem to reach their maximum concentrations in magmatic sulfides from the MTZ. Although, no significant differences are observed between the Fe isotope signatures in magmatic pyrrhotites from the lower crust (–0.73 to –0.24, 2sd [‰] of δ56Fe) and the MTZ (–0.73 to –0.53, [‰] of δ56Fe), we found different δ56Fe for pyrrhotite (–0.24‰) and chalcopyrite +0.36‰ within the same sulfide grain. The bulk signature of δ56Fe for this grain is –0,12‰ being in accordance with the mass balance calculated δ56Fe 0.025‰ ± 0.025‰ of the mantle (Craddock et al., 2013 – Earth Planet. Sci. Lett).

            The  enrichment in sulfides and selected metals (Zn, Co, Cu) towards the  MTZ  might  result  from  melt-mantle  reaction  as  we  proposed previously for the slow-spread oceanic lithosphere based on the Kane Megamullion Ocean Core Complex (Ciążela et al., 2018 - GCA).  In the CM1A/2B ultramafic rocks: dunites and harzburgites, most sulfides are, however, secondary, formed by the same secondary fluids which caused the pervasive serpentinization. To verify whether these sulfides replaced the primary magmatic sulfides or were brought from late-stage seawater-derived fluids, we plan to measure sulfur in whole-rocks and in situ and more iron isotopes in sulfides in situ. Preliminary δ56Fe signature isotope data give us evidence for magmatic origin of the sulfides from upper part of the MTZ section.

How to cite: Marciniak, D., Jakub, C., Ana, J., Bartosz, P., Jürgen, K., Harald, S., Marina, L., Ingo, H., Ewa, S., Marta, P., and Konrad, B.: Metal migration and ore minerals across the crust-mantle transition zone (Oman DP ICDP holes CM1A, CM2B), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-517, https://doi.org/10.5194/egusphere-egu22-517, 2022.

08:37–08:44
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EGU22-328
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ECS
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On-site presentation
Bartosz Pieterek, Jakub Ciążela, Riccardo Tribuzio, Magdalena Matusiak-Małek, Andrzej Muszyński, Harald Strauss, Marina Lazarov, Stefan Weyer, Ingo Horn, Thomas Kuhn, and Izabella Nowak

Copper deposits or sulfide enrichment have been found along the crust-mantle transition zones in ophiolites and along the oceanic Moho. However, scarcity of suitable exposures limits our knowledge on the migration of chalcophile metals across the subcontinental crust-mantle boundary. This study aims to provide new constraints on the migration of sulfide-associated chalcophile metals at the transition between the subcontinental mantle peridotites of the Balmuccia massif and lower crustal gabbronorites of the Mafic Complex (Ivrea-Verbano Zone, NW Italy).

An ~80-m-thick zone composed of interlayered pyroxenites and gabbronorites (Contact Series; CS) showing igneous contact with the mantle peridotites was sampled along the Val Sesia river, near the Isola village. We investigated a transect from the mantle peridotites (rich in pentlandite) through the CS to the lower crustal gabbronorites (rich in pyrrhotite or pyrite). The CS zone comprises three sampling sites located 0–5 m (CS1), 65–70 m, and 75–80 m from the mantle peridotites and is characterized by the along-transect Mg# variations (Mg# of 71–57). The mantle peridotites are sulfide poor (average of 0.12 vol.‰), in contrast to the CS rocks (up to 7.8 vol.‰). The enhanced sulfide abundances in mafic rocks of the CS correlate with higher S, Cu, Ag, and Cd contents. This sulfide- and chalcophile-rich metal zone within the CS ends ~75 m away from the margin of mantle peridotites implying a probable thickness of the enrichment zone. Sulfides from mantle peridotites and CS1 are pyrrhotite-(troilite)-chalcopyrite-(cubanite)-pentlandite assemblages of magmatic origin, which is supported by δ34S ranging from –0.6‰ to +1.8‰ (average of 0.0‰; cf., Oeser et al., 2012 – Chemical Geology).

The in-situ Fe isotope signatures of polyphasic sulfide grains from CS1 show a strong fractionation between the various phases. The δ56Fe values of pyrrhotites are negative ranging from –0.8‰ to 0.0‰, whereas chalcopyrite exhibit positive values of 1.3–1.7‰. The mass balance calculations of the δ56Fe for the bulk composition of the sulfide grains from CS1 show unfractionated (magmatic or mantle) values of 0.0 ± 0.2‰ (cf., Craddock et al., 2013 – EPSL).

The stagnant melts at the crust-mantle boundary extensively react with the mantle yielding enrichment in sulfides and chalcophile elements, which is known to yield enrichment in sulfides (Ciazela et al., 2018 - GCA; Patkó et al., 2021 - Lithos). However, the contact between the Balmuccia mantle peridotites and the lower continental crust of the Mafic Complex is highly heterogeneous with alternating layers of pyroxenites and gabbronorites. These layers may have formed from distinct magma batches as suggested by the along-transect Mg# variations. Therefore, the mechanism of observed enrichment in sulfides and chalcophile elements probably involves several stages of melt-peridotite and melt-pyroxenite reactions. These might explain the exceptionally large ~75-m-thick sulfide-rich horizon observed at the CS. Our results indicate that substantial chalcophile metal inventory is trapped at the CS. Assuming they behave the same at the Moho level, this would explain the relative deficit of these elements in the continental crust when compared its bulk composition to the composition of primitive mantle melts.

This research was funded by the NCN Poland (2018/31/N/ST10/02146)

How to cite: Pieterek, B., Ciążela, J., Tribuzio, R., Matusiak-Małek, M., Muszyński, A., Strauss, H., Lazarov, M., Weyer, S., Horn, I., Kuhn, T., and Nowak, I.: New constraints on the origin of metal enrichment at the crust-mantle boundary from the Ivrea-Verbano Zone, NW Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-328, https://doi.org/10.5194/egusphere-egu22-328, 2022.

08:44–08:51
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EGU22-2217
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ECS
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On-site presentation
Hubert Mazurek, Magdalena Matusiak-Małek, Jakub Ciazela, Bartosz Pieterek, Jacek Puziewicz, and Sylvin S.T. Tedonkenfack

Sulfides hosted by peridotites from Befang (Oku Volcanic Group, Cameroon) xenolith suite can play an important role in tracking migration of strategic metals such as Au, Ag, or Cu through the subcontinental lithospheric mantle (SCLM) beneath the Central African Orogenic Belt. Most peridotites are lherzolites, which are subdivided into two main groups differing by crystallographic preferred orientation (CPO) and rare-earth element (REE) composition of clinopyroxene. Group I is characterized by light REE (LREE)-depleted clinopyroxene (re-)crystallized during percolation of metasomatic melt. Group II contains LREE-enriched clinopyroxene with the CPO representing deformation before percolation of the melt (Tedonkenfack et al., 2021). Lherzolites of group I  are interpreted to be metasomatized by MORB-like melts coming from  Depleted MORB Mantle (DMM). Peridotites of  group II are interpreted to be a protolith for the group I ones.

The sulfides form oval to slightly elongated grains enclosed usually in orthopyroxene, or rarely in clinopyroxene and olivine. They are composed of pyrrhotite (Po), pentlandite (Pn), and chalcopyrite (Ccp). Pyrrhotite is mostly predominant, whereas Pn forms exsolution lamellae in Po or massive crystals separating Po from Ccp. Chalcopyrite is present on the rims of grain or penetrates through the entire grain, occasionally containing cubanite exsolutions. The Group I lherzolites contain more sulfides (up to 0.031 vol.‰), with larger grains (range: 14−250 µm, 57 µm on average) compared to the Group II sulfides (up to 0.002 vol.‰, range: 12−45 µm, 27 µm on average respectively). Sulfides from Group I are richer in Po, and especially Ccp (Po77Pn12Ccp11 on average) compared to Group II (Po72Pn23Ccp4 on average). Ni/(Ni+Fe) in pyrrhotite from Group I (0.14–0.43) is more heterogeneous compared to group II (0.20–0.37).

Enrichment in Po and Ccp in the Befang Group I xenoliths suggests a significant role of melts in transporting sulfur and metals. Observed refertilization by DMM-derived melts may affect the chalcophile and highly siderophile metal budget of the SCLM. The degree of refertilizaton seems to depend on temperature and therefore is moderate in Befang (up to 0.031 vol.‰) with moderate temperatures of orthopyroxene-clinopyroxene equilibration (938–997°C; Tedonkenfack et al, 2021). In lower temperatures of Opx-Cpx equilibration (810–970°C), we observe higher sulfide abundances (up to 0.062 vol.‰), whereas in higher temperatures (1010–1120°C) lower sulfide abundances (up to 0.00048 vol.‰; Mazurek et al., 2021).

 

This study was supported by the Diamond Grant project 093/DIA/2020/49.

 

References

Mazurek, H., Ciazela, J., Matusiak-Małek, M., Pieterek, B., Puziewicz, J., Lazarov, M., Horn, I., Ntaflos, T.: Metal enrichment as a result of SCLM metasomatism? Insight from ultramafic xenoliths from SW Poland., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15992, https://doi.org/10.5194/egusphere-egu21-15992, 2021

Tedonkenfack SST., Puziewicz J., Aulbach S., Ntaflos T., Kaczmarek M-A., Matusiak-Małek M., Kukuła A., Ziobro M.: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Contributions to Mineralogy and Petrology, 176: 37.

How to cite: Mazurek, H., Matusiak-Małek, M., Ciazela, J., Pieterek, B., Puziewicz, J., and Tedonkenfack, S. S. T.: Metal enrichment in refertilized subcontinental lithospheric mantle: insight from the ultramafic xenoliths from the volcanic rocks of the Oku Volcanic Group (Cameroon) , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2217, https://doi.org/10.5194/egusphere-egu22-2217, 2022.

08:51–08:58
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EGU22-6901
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ECS
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On-site presentation
Jakub Ciazela, Bartosz Pieterek, Dariusz Marciniak, Hubert Mazurek, Levente Patko, and Ewa Slaby

Cu-rich sulfide deposits of economic importance in ophiolites such as Troodos in Cyprus or Semail in Oman often occur along the crust-mantle transition zones (e.g. Begemann et al., 2010). Although secondary sulfides formed during serpentiniztion now prevail, the relicts of primary magmatic sulfides indicate the igneous nature of enrichment in sulfides at the oceanic Moho level. Crust-mantle transition zones in situ in the oceans are suggested to be enriched in sulfides and many chalcophile (e.g. Cu, Zn, Pb, Se, Te) metals via melt-mantle reaction (Ciazela et al., 2017; 2018). The enrichment in sulfides seems to be ubiquitous along the crust-mantle transition zone (Ciazela et al., 2018) and might be expected even at the continental Moho. This is possible as sulfides precipitate during melt-mantle reaction independently on pressure. The process seems to work at low pressures of the oceanic crust-mantle transition zone (0.1–0.2 GPa) (Marciniak et al., this session; Ciazela et al., 2018), medium pressures of the continental crust-mantle transition zone (~1.0 GPa) (Pieterek et al., this session), and in high pressures related to various melt-metasomatized mantle xenoliths (up to 2.5 GPa) (Mazurek et al., this session; Patkó et al., 2021). Metal refertilization due to variable melt-peridotite reactions at the crust-mantle transition zone and along melt channels in the upper mantle may affect the local, regional, and even global metal mass balance of the oceanic and continental lithosphere. The distribution of mantle sulfides is heterogeneous. The zones of enrichment in metals occur mostly at the crust-mantle transition or in melt-modified mantle rocks along melt channels in the upper mantle. These zones are important for subsequent ore formation in secondary processes. In the oceans, especially along slow-spreading ridges, shallow magmatic sulfide horizons are penetrated by hydrothermal fluids operating along faults to form massive sulfides on the seafloor. On land, the re-mobilization of the mantle sulfides horizons by sulfide-undersaturated melts or by buoyant CO2 bubbles can contribute to the formation of porphyry and related epithermal mineral deposits.

Begemann F., Hauptmann A., Schmitt-Strecker S. and Weisgerber G. (2010) Lead isotope and chemical signature of copper from Oman and its occurrence in Mesopotamia and sites on the Arabian Gulf coast. Arab. Archaeol. Epigr. 21, 135–169.

Ciazela J., Dick H. J. B., Koepke J., Pieterek B., Muszynski A., Botcharnikov R. and Kuhn T. (2017) Thin crust and exposed mantle control sulfide differentiation in slow-spreading ridge magmas. Geology 45, 935–938.

Ciazela J., Koepke J., Dick H. J. B., Botcharnikov R., Muszynski A., Lazarov M., Schuth S., Pieterek B. and Kuhn T. (2018) Sulfide enrichment at an oceanic crust-mantle transition zone: Kane Megamullion (23°N, MAR). Geochim. Cosmochim. Acta 230, 155–189.

Patkó L., Ciazela J., Aradi L. E., Liptai N., Pieterek B., Berkesi M., Lazarov M., Kovács I. J., Holtz F. and Szabó C. (2021) Iron isotope and trace metal variations during mantle metasomatism: In situ study on sulfide minerals from peridotite xenoliths from Nógrád-Gömör Volcanic Field (Northern Pannonian Basin). Lithos 396397, 106238.

How to cite: Ciazela, J., Pieterek, B., Marciniak, D., Mazurek, H., Patko, L., and Slaby, E.: Melt metasomatism and enrichment in metals in the uppermost Earth’s mantle, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6901, https://doi.org/10.5194/egusphere-egu22-6901, 2022.

08:58–09:05
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EGU22-9560
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ECS
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On-site presentation
Jakub Mikrut, Magdalena Matusiak-Małek, and Jacek Puziewicz

The Mirdita Ophiolite in northern Albania forms a ~240 km long and ~40 km wide zone within Dinaric-Hellenic belt. It marks suture after Neo-Tethyan Ocean closure. The chemical diversity of volcanic crustal rocks led to its division into two zones: the eastern one is interpreted to have Supra-Subduction Zone (SSZ) origin, whereas the western zone exhibits Mid-Ocean Ridge (MOR) affinity. More than a dozen of ultramafic massifs occur along the entire length of the ophiolite.

In this study we focus on chemical diversity of peridotites from two adjacent massifs, Kukes and Puka, which have SSZ and MOR affinities, respectively. The Kukes Massif is composed of a sequence from harzburgites at its base to clinopyroxene-poor dunites at the top, followed by pyroxenitic and peridotitic cumulates at the mantle/crust transition zone. The Puka massif is a mantle dome, composed of harzburgites and plagioclase/amphibole lherzolites (locally mylonitzed) and it is interpreted as a former oceanic core complex (OCC; Nicolas et al. 2017). Both massifs are pervasively penetrated by pyroxenitic and gabbroic veins and are serpentinised to variable degree.

Chemical composition of minerals varies between samples and lithologies, as well as between massifs. Olivine from the Kukes harzburgites has higher Fo values and NiO contents than that from dunites (Fo89.5-92 and NiO 0.31-0.52 wt.% vs. Fo88.1-91.2 and NiO 0.15-0.30 wt.%, respectively). Clinopyroxene has Mg#92.5-95.1 and Al=0.03-0.08 apfu in harzburgite, while interstitial dunite clinopyroxene has Mg#94-98 and Al below 0.03 apfu. Harzburgite orthopyroxene has Mg#90.1-91.8 and Al=0.03-0.08 apfu. Chromian-spinel has Cr#0.55-0.72 and Mg#0.46-0.56 in harzburgites and Cr#0.63-0.86 and Mg#0.25-0.48 in dunites, moreover in dunites it often exhibits chemical zonation with Cr# increasing to core. Chemical composition of minerals changes gradually in the scale of single outcrop, with Fe content increasing toward veins.

The Puka peridotites have more enriched composition. Olivine has Fo87.8-90.8 and NiO=0.25-0.43 wt. %, clinopyroxene has Mg#90.1-93.3 and Al=0.05-0.15 apfu, orthopyroxene has Mg#88.5-91.0 and Al=0.03-0.1 apfu, while spinel has Cr#0.38-0.55 and Mg#0.42-0.57, with single sample of Cr#0.60-0.75 and Mg#0.33-0.52. Plagioclase is Ca-rich (77-95 An), amphibole – occurring in some lherzolites – has composition of pargasite-tremolite.

Differences in lithological and chemical composition are visible between peridotites from both massifs, which correspond with diversity of crustal rocks and suggest that also mantle sections of the ophiolite record different origin. Peridotites from Kukes are harzburgites and dunites pointing to their refractory nature. The depleted peridotites were further affected by intensive magmatic veining. Infiltration of the melt triggered gradual enrichment in Fe of the silicates and chemical zonation of spinel. This process is well visible in dunites, where changes of Fe contents can be followed on distances of few meters. As metasomatic modification has a limited range, most of chemical differences have to be related with different protolith, but further studies are required to reconstruct rocks evolution.

Protolith of Puka peridotites is more fertile compared with Kukes, but reaction between veins and host lherzolite was not observed, and mylonitization led to Al depletion in pyroxenes.

This study was financed from scientific funds for years 2018-2022 as a project within program “Diamond Grant” (DI024748).

How to cite: Mikrut, J., Matusiak-Małek, M., and Puziewicz, J.: Preliminary insights into lithological and chemical diversity in Mirdita Ophiolite peridotite massifs – Kukes and Puka case studies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9560, https://doi.org/10.5194/egusphere-egu22-9560, 2022.

09:05–09:12
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EGU22-13175
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On-site presentation
Dmitri Ionov, Zhe Liu, Paolo Nimis, Yigang Xu, and Alexander V. Golowin

Many aspects of structure and thermal state of >200 km thick cratonic lithospheric mantle (CLM) remain unclear because of insufficient sampling and uncertainties of pressure (P) and temperature (T) estimates. An exceptionally detailed record of equilibration temperature and composition for the central Siberian craton in the 60–230 km depth range was obtained using new and published petrographic and in-situ chemical data for ~200 garnet peridotite xenoliths from the Udachnaya kimberlite. The thermal profile is complex with samples between 35 and 40 mW/m2 model conductive geotherms as well as hotter layers in the middle and at the base (190–230 km) of the CLM. A previously unknown mid-lithospheric zone includes rocks up to 150° hotter than ambient geotherm, with high modal garnet and cpx, low-Mg# and melt-equilibrated REE patterns. We posit that hot domains with enriched compositions may form at depths where ascending melts stall (e.g., due to loss of volatiles and/or redox change) and react with wall-rock harzburgites. By contrast, we find no rocks rich in volatile-rich metasomatic amphibole, mica or carbonate, nor layers composed of peridotites with distinct melt-extraction degrees. The CLM base contains both coarse and variably deformed rocks heated and re-worked (Mg#Ol down to 0.86) by localized interaction with asthenospheric melts.

How to cite: Ionov, D., Liu, Z., Nimis, P., Xu, Y., and Golowin, A. V.: Xenolith-based thermal and compositional lithospheric mantle profile of the central Siberian craton, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13175, https://doi.org/10.5194/egusphere-egu22-13175, 2022.

09:12–09:19
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EGU22-7935
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ECS
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On-site presentation
Tereza Zelinková, Martin Racek, and Rainer Abart

Uncommon Ba-Cl-rich phases including Ba-Cl micas and Cl-phosphates have been found in garnet pyroxenites as a part of the matrix or in polyphase inclusions in garnets. Polyphase inclusions are rich in carbonates (dolomite, magnesite, norshetite), phosphates (Cl-apatite, goryainovite (Ca2PO4Cl), monazite) and other silicates (spinel, amphibole, orthopyroxene, clinopyroxene, margarite, aspidolite, scapolite, cordierite). The inclusions appear as chains crosscutting garnet crystals and their presence is not linked with any chemical zoning in the host garnet.

The Ba-Cl-rich mica has composition ranging from Ba-rich phlogopite to chloroferrokinoshitalite and to oxykinoshitalite. The mica present in the matrix correspond to Ba-rich phlogopite with low Cl contents and occur together with celsian and low-Cl hydroxyl apatite. The mica in the polyphase inclusions ranges to almost pure chloroferrokinoshitalite and oxykinoshitalite endmembers and coexists either with Cl-apatite (Cl = 1.2 apfu) or rarely goryainovite containing up to 2.5 wt% of SrO. This is second world occurrence of goryainovite and first evidence that Ca can be partially replaced by Sr in this mineral.

Special attention was paid to the composition trends of the Ba-Cl-rich micas. These are mainly related to the XFe ratio, which correlates positively with Cl, Ba, and Al and negatively with Si and Na. Positive correlation of Cl with Ba and XFe leads to the formation of mica with composition Ba0.95K0.03Fe2.69Mg0.37Al1.91Si2.02Cl1.98, XFe0.88, which is the most Cl-rich mica so far described from natural samples (10.98 wt% Cl) and is very close to the theoretical formula of chloroferrokinoshitalite BaFe3Al2Si2O10Cl2. The positive correlation of Ba with Al and their negative correlation with Si and K is corresponding to the coupled substitution Ba1Al1K-1Si-1 linking the composition of phlogopite and kinoshitalite. Composition trend related with the Ti-content shows that Ti correlates positively with Ba but negatively with Cl, XFe, and with the sum of Mg and Fe. It implies that Ti is incorporated into mica in coordination with O (Ti1O2(Mg,Fe2+)-1(OH)-2) and it leads to the formation of oxykinoshitalite (BaMg2TiSi2Al2O12). Since the incorporation of either Cl or Ti + O correlates with XFe content of mica, XFe ratio can be the crucial factor controlling the ability of mica to incorporate Cl into its crystal lattice. In some cases, two micas with contrasting composition corresponding closer to chloroferrokinoshitalite or oxykinoshitalite coexist in one polyphase inclusion, demonstrated by distinct content of XFe, Ti and Cl (for example: XFe0.20:0.77, Ba0.48:0.63, Ti0.35:0.02, Cl0.27:1.45). This could imply the existence of an immiscibility between the composition trends of chloroferrokinoshitalite and oxykinoshitalite .

Such Ba, Cl and K-rich phases are atypical for garnet pyroxenite. Their presence may be caused by the injection of fluid/melt of crustal source during subduction and subsequent exhumation processes or may be related to earlier mantle metasomatism. The presence of Cl-rich phases together with carbonates indicates extremely high activity of Cl and CO2 in the metasomatizing fluid/melt that interacted with garnet pyroxenites.

How to cite: Zelinková, T., Racek, M., and Abart, R.: Compositions of Ba-Cl-rich micas and other uncommon phases related to metasomatism of garnet pyroxenite (Gföhl unit of the Moldanubian Domain, Bohemian Massif), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7935, https://doi.org/10.5194/egusphere-egu22-7935, 2022.

09:19–09:26
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EGU22-1865
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On-site presentation
Jacek Puziewicz, Sonja Aulbach, Mary-Alix Kaczmarek, Anna Kukuła, Theodoros Ntaflos, Magdalena Matusiak-Małek, Sylvin S. T. Tedonkenfack, and Małgorzata Ziobro-Mikrut

The Wum maar is located in the Oku Volcanic group, part of continental sector of the Cameroon Volcanic Line (CVL) in west Africa, which consists of volcanoes active from Eocene to recent. The continental part of the CVL is located on the metamorphic-igneous basement of the Neoproterozoic Central African Orogenic Belt (CAOB), which originated during Gondwana assembly. Some of the CVL lavas contain spinel-facies peridotite and pyroxenite xenoliths giving insight into the mantle lithosphere underlying the CAOB.

We studied xenolith suite (19 xenoliths) from the Wum maar, comprising 14 lherzolites and 5 websterites. The half of lherzolites (7) consist of minerals with fertile composition (olivine Fo89, orthopyroxene Al 0.16-0.19 atoms per formula unit, clinopyroxene Al 0.28-0.31 a pfu, spinel Cr# 0.08-0.13). Clinopyroxene is REE-depleted and has 87Sr/86Sr ratios of 0.7017-0.7021. A reconnaissance study of crystal preferred orientation (CPO) by EBSD shows that at least in part of the rocks the clinopyroxene fabric is very weak, suggesting that its crystallization post-dates the primary deformation event recorded by the olivine-orthopyroxene framework. A smaller part of lherzolites (5) contains clinopyroxene the CPO of which fits that of the olivine-orthopyroxene framework, is LREE-enriched and has 87Sr/86Sr ratios of 0.7027-0.7028. One of these lherzolites contains amphibole (pargasite), which forms aggregates and schlieren and texturally is later than olivine-pyroxene host. CPO of amphibole, ortho- and clinopyroxene is decoupled from that of olivine in that rock. Two lherzolites have slightly depleted mineral compositions (olivine Fo90-91, orthopyroxene Al 0.15 apfu, clinopyroxene Al 0.25 a pfu, spinel Cr# 0.18).

Websterites are dominated by orthopyroxene (Al 0.20-0.21 a pfu) whereas clinopyroxene (Al 0.30-0.31) is subordinate, and is characterized by LREE-depletion and 87Sr/86Sr ratios of 0.7019-0.7020. Spinel occurring in websterites is aluminous (Cr# 0.04-0.06), in some samples subordinate olivine (Fo90) occurs. One of the xenoliths consists of millimetric monomineral layers of pyroxenes and olivine chemically identical to those occurring in websterites.  

The mineral chemical data coupled with mineral fabrics suggest that lherzolites with LREE-depleted clinopyroxene could have originated by late crystallization caused by melt metasomatism. The metasomatic agent is probably best represented by websterites, which contain LREE-depleted clinopyroxene with similar, depleted 87Sr/86Sr of 0.7019-0.7020 (compare to DM value of 0.7026, Workman and Hart 2005), confirming earlier findings of refertilization of the regional lithospheric mantle by highly depleted melts (Tedonkenfack et al. 2021). The addition of amphibole was connected with recrystallization of ortho- and clinopyroxene and with significant change of its 87Sr/86Sr signature to more radiogenic values.

Funding. This study originated thanks to the project of Polish National Centre of Research NCN 2017/27/B/ST10/00365 to JP. The bilateral Austrian-Polish project WTZ PL 08/2018 enabled extensive microprobe work.

References:

Tedonkenfack SST, Puziewicz J, Aulbach S, Ntaflos T., Kaczmarek M-A, Matusiak-Małek M, Kukuła A, Ziobro M: Lithospheric mantle refertilization by DMM-derived melts beneath the Cameroon Volcanic Line – a case study of the Befang xenolith suite (Oku Volcanic Group, Cameroon). Contributions to Mineralogy and Petrology 176: 37.

Workman RK, Hart SR (2005) Major and trace element composition of the depleted MORB mantle (DMM). Earth and Planetary Science Letters 231: 53-72.

How to cite: Puziewicz, J., Aulbach, S., Kaczmarek, M.-A., Kukuła, A., Ntaflos, T., Matusiak-Małek, M., Tedonkenfack, S. S. T., and Ziobro-Mikrut, M.: Preliminary data on mantle xenoliths from the Wum maar, Oku Volcanic Group, Cameroon Volcanic Line (West Africa), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1865, https://doi.org/10.5194/egusphere-egu22-1865, 2022.

09:26–09:33
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EGU22-4351
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ECS
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On-site presentation
Małgorzata Ziobro-Mikrut, Jacek Puziewicz, Sonja Aulbach, Theodoros Ntaflos, and Magdalena Matusiak-Małek

The 3.5-0.5 Ma Devès volcanic field consists mainly of nepheline basanite rocks. The underlying Variscan basement is a part of the western Moldanubian Zone (an allochton of the European Variscan orogen, probably the Gondwana margin). The Devès volcanic field is located in the “southern” mantle domain of Massif Central (MC), which consists of fertile lithospheric mantle (LM) little affected by partial melting [1]. These characteristics probably resulted from intense metasomatism by melts coming from the upwelling asthenosphere [2].

Despite the rich literature dealing with the LM beneath the Devès volcanic field, some textural and geochemical details remain obscure. We studied a large xenolith population (n – 21) from Mt.Briançon (NW of the Devès volcanic field) with extensive use of EMPA and LA-ICP-MS in order to obtain a comprehensive and representative data set, and here present the preliminary findings.

The Mt.Briançon xenoliths are typically oval in shape and vary in size from 4 to 13 cm. The host rocks are tuff and scoria deposits. The xenoliths are mostly anhydrous spinel lherzolites rich in clinopyroxene (cpx, modal content up to 28%) and scarce harzburgites. One xenolith consists of olivine clinopyroxenite in contact with peridotite. The peridotites exhibit serial texture or different stages of porphyroclastic texture. In some xenoliths elongated spinel is arranged in streaks.

Most of the three major phases in the peridotites are homogenous at the grain and xenolith scale. Olivine Fo is typically 88.5-90.4% in the whole suite, and NiO content is 0.35-0.43 wt.%. Orthopyroxene (opx) has Mg# 0.89-0.91 and 0.128-0.217 atoms of Al per formula unit (apfu). Cpx has Mg# 0.88-0.91 and Al content of 0.208-0.316 apfu and spinel Cr# is highly variable in the whole suite (0.09-0.28). In contrast, one harzburgite (sample 4025) has olivine with higher Fo (~91.2%), opx with higher Mg# (~0.92) and lower Al content (0.111-0.116 apfu), cpx with Mg# ~0.92 and Al content of ~0.145 apfu, and spinel Cr# of ~0.43 and Mg# of ~0.75.

The main observed REE pattern in peridotite cpx is relatively flat Lu-Eu and slightly, but variably depleted in lighter REE. In several xenoliths cpx exhibits various REE patterns, transitioning from LREE-depleted to relatively flat or slightly LREE-enriched, while a few samples contain cpx with REE abundances moderately increasing Lu-Sm and steeply increasing towards La. The majority of peridotite opx REE patterns are moderately decreasing in Lu-Sm and more steeply decreasing towards La, whereas a less common opx pattern is similar to the previous one in Lu-Nd, but much less depleted in lighter REE. This opx coexists with LREE-rich cpx.

This study confirms that the LM beneath Mt.Briançon is mostly lherzolitic and quite fertile in terms of major elements. Ongoing work, utilizing the diversity of lithologies and pyroxene REE patterns, combined with detailed major-element and REE thermometry and with textural observations, will provide detailed insights into the microstructural, thermal and metasomatic history of the LM beneath the MC.

 

This study was funded by Polish National Science Centre to MZM (UMO-2018/29/N/ST10/00259).

 

References

[1] Uenver-Thiele L. et al. (2017). JPetrol 58, 395–422.

[2] Puziewicz J. et al. (2020). Lithos 362–363, 105467.

How to cite: Ziobro-Mikrut, M., Puziewicz, J., Aulbach, S., Ntaflos, T., and Matusiak-Małek, M.: Preliminary characteristics of mantle xenoliths from Mt. Briançon (Massif Central, France) - missing information about the lithospheric mantle beneath Devès volcanic field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4351, https://doi.org/10.5194/egusphere-egu22-4351, 2022.

09:33–09:40
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EGU22-5617
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On-site presentation
Camilla Sani, Alessio Sanfilippo, Alexander A. Payve, Felix Genske, and Andreas Stracke

In Nd-Hf isotopic space the great majority of the global abyssal peridotites plot in the field defined by global MORBs. However, Hf isotope ratios by far exceeding those in ridge basalts, are locally observed in abyssal peridotites showing that the Earth’s mantle is more heterogeneous that inferred from ridge basalts [1]. Mantle peridotites exposed at the Doldrums Fracture Zone at the Mid Atlantic Ridge (7-8° N) reveal that such heterogeneity coexists on a kilometre-scale. Abyssal peridotites from the northern part of the Doldrums FZ domain can be grouped into residual peridotites and melt-modified (refertilized) samples [2]. New Nd-Hf isotopic data show that the refertilized peridotites preserve highly radiogenic Hf values (εHf up to 101) associated with MORB-like Nd isotopes (εNd up to 12), reflecting partial resetting of ancient highly depleted mantle by recent melt-rock interaction. On the other hand, despite a very depleted incompatible element compositions, the residual peridotites have Nd-Hf isotope ratios similar to the local MORB (εNd = 7-12 and εHf =12-19). They most likely reflect highly depleted mantle that has been entirely reset by reaction with extracted or retained melts, and hence developed with only modest incompatible element depletion until recent melting at the Mid Atlantic ridge axis, which led the strong incompatible element depleted of these peridotites. The kilometre-scale association of such isotopically heterogeneous domains suggests that the upper mantle exposed in this portion of Atlantic formed by a combination of ancient melting and melt-rock reaction processes, preceding its emplacement below the present-day Mid Atlantic ridge axis.

 [1] Stracke, A., et al., 2011. Abyssal peridotite Hf isotopes identify extreme mantle depletion. Earth and Planetary Science Letters, 308(3-4), pp.359-368. [2] Sani, C., et al., 2020. Ultra-depleted melt refertilization of mantle peridotites in a large intra-transform domain (Doldrums Fracture Zone; 7–8° N, Mid Atlantic Ridge). Lithos, 374, p.105698.

How to cite: Sani, C., Sanfilippo, A., Payve, A. A., Genske, F., and Stracke, A.: Kilometre-scale isotopic heterogeneity in abyssal peridotites from the Doldrums Fracture Zone (Mid Atlantic Ridge, 7-8ºN)., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5617, https://doi.org/10.5194/egusphere-egu22-5617, 2022.

09:40–09:47
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EGU22-5414
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ECS
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On-site presentation
Mélanie Ballay, Marc Ulrich, and Gianreto Manatschal

Keywords: magma-poor rifted margin, refertilization, partial melting, mantle-melt interaction

Although magmatic processes are of primary importance for the understanding of lithospheric breakup, many first order questions remain, such as: how, when, where and how much magma is produced during final rifting; what are the conditions and controlling processes of magma production; how does magma percolate and interact with the lithospheric mantle; and how and when does magma focus, how is it extracted and how does it interact with the extensional processes during final rifting and breakup? Answering to these questions is a prerequisite to understand lithospheric breakup and formation of a new plate boundary, which is among the least understood plate tectonic processes at present.

In this study we present preliminary petrological results from mantle rocks dredged from the SW Australia ocean-continent transition (OCT, Diamantina zone). We analyzed pyroxene and spinel compositions from these peridotites to identify mantle domains and mantle-melt reactions during rifting and breakup. The chemical composition of clinopyroxenes shows two distinct populations: a first generation characterized by low (Sm/Yb)N ratios and no Eu anomalies, while a second generation shows interstitial textures and flat HREE patterns with a deep negative Eu anomaly. These two populations of clinopyroxenes suggest that the peridotites from the Diamantina zone record two distinct events: a first cooling event that is followed by magma infiltration. This is further supported by equilibrium temperatures calculated on the two clinopyroxene generations showing that the first population equilibrated at lower temperatures (900°C ± 30°C) corresponding to a subcontinental geotherm, while the second generation equilibrated at higher temperatures (1100°C ± 100°C), and was likely liked to the entrapment of MORB-type melts in the plagioclase stability field at low pressure (~5kbar) during magma infiltration.  

The exhumation path of the Diamantina peridotites determined in our study is similar to those of refertilized peridotites from the present-day Iberia and fossil Alpine Tethys OCTs, suggesting that refertilisation processes occurring at magma-poor rifted margins during final rifting and breakup are not dependent from the inherited nature of the subcontinental mantle.

How to cite: Ballay, M., Ulrich, M., and Manatschal, G.: Magmatic processes at rifted margins: Preliminary results from peridotites of the Diamantina zone (SW Australia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5414, https://doi.org/10.5194/egusphere-egu22-5414, 2022.

Coffee break
Chairpersons: Theodoros Ntaflos, Małgorzata Ziobro-Mikrut, Petros Koutsovitis
10:20–10:27
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EGU22-9331
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On-site presentation
Petros Koutsovitis, Alkiviadis Sideridis, Pavlos Tsitsanis, Federica Zaccarini, Basilios Tsikouras, Christoph Hauzenberger, Tassos Grammatikopoulos, Luca Bindi, Giorgio Garuti, and Konstantin Hatzipanagiotou

Nea Roda and Gomati ultramafic bodies (east Chalkidiki, north Greece) consist of both Cr- and Al- podiform chromitites, which are highly altered. Their PGE geochemistry and subsequently PGE-mineralogy (PGM) demonstrate abnormal element concentrations with an enrichment in PPGE (Pd, Pt), leading to high Pd/Ir ratios. Secondary PGM and base metal assemblages are dominated by Sb and As, whereas primary phases form sulphides. At a more mature stage, desulphurization of the aforementioned phases led to formation of native metals. Diopside hosted within diopsidite and chromitite show both an alkaline melt- and a fluid- rock interaction, depicted by LREE enrichment. The temperature of the metasomatic fluids was lower than 600oC, as recorded by chlorite and garnet geothermometry. A raise in fluid mobile elements (FME: B, Sb, Li, As, Cs, Pb, U, Ba and Sr) is noted in the whole rock and clinopyroxene analysis. All these characteristics along with the distinctive spinel textures (porous, zoned grains) point to a metasomatic event during subduction that led to the post-magmatic modification of the chromitites and the mantle section causing a LREE, Pb, As, Sb, Pd and Pt enrichment. 

How to cite: Koutsovitis, P., Sideridis, A., Tsitsanis, P., Zaccarini, F., Tsikouras, B., Hauzenberger, C., Grammatikopoulos, T., Bindi, L., Garuti, G., and Hatzipanagiotou, K.: Mantle metasomatism recorded upon bimodal chromitites (E. Chalkidiki, Greece): a tool to unravel metasomatic processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9331, https://doi.org/10.5194/egusphere-egu22-9331, 2022.

10:27–10:34
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EGU22-3865
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ECS
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Virtual presentation
Shivani Harshe, Mallika Jonnalagadda, Raymond Duraiswami, Mathieu Benoit, Michel Grégoire, and Nitin Karmalkar

Well-developed corona structures are observed and described in detail in the cumulate troctolites from Chainigund village, Kargil. The gabbro-troctolite unit is situated 5 km NW of Kargil city and consists of gabbros, troctolites, and anorthosites with doleritic dykes cross-cutting the unit at places. The host gabbros are fresh and display both fine and coarse-grained varieties. Troctolites occur as pods and veins within the gabbro and are composed of plagioclase (77-80 vol%), olivine (10-16 vol%), pleonaste spinel (6-8 vol%), amphiboles (2 -3 vol%) and opaques (0.5-2vol %). Both olivines and plagioclases are unzoned with spectacular coronas around the olivines (Fo 74.9-76.7) at the contact with plagioclase feldspar (An90.6-95.2). From center outwards, the discontinuous reaction series consists of the following members: Olivine, enstatitic orthopyroxene, magnesio-hornblende (Amph1) enclosed by a symplectitic rim of pargasite (Amph2) and pleonaste spinel and concludes at the plagioclase interface i.e. Ol-Opx-Amph1-Amph2-Spl-Plg. The mineral textures of the corona structure indicate formation in the presence of an interstitial fluid trapped between cumulus olivine and plagioclase. The reaction of this fluid with the olivine resulted in a rim of peritectic orthopyroxene around olivine which was subsequently replaced to form Amph 1 between the orthopyroxene and plagioclase. This is evident by the horse-shoe shaped outline and intermingling boundary shared by orthopyroxene and Amph 1. The formation of outer Amph 2 and spinel symplectite layers could be attributed to the replacement of precursor clinopyroxene and plagioclase at high temperatures (1050-1150° C ± 40° C). The Amph-Spl symplectites, presence of oxidizing conditions (magnetite and ilmenite), discontinuous reactions and local or short-range diffusion phenomena thus indicate that the corona structures are a result of metasomatic interaction of cooling magma with the previously formed minerals.

Keywords: Corona structures; troctolite gabbro; olivine- plagioclase contact; Kargil; Ladakh; India.

How to cite: Harshe, S., Jonnalagadda, M., Duraiswami, R., Benoit, M., Grégoire, M., and Karmalkar, N.: Formation of corona structures from the troctolitic gabbros of Chainigund, Kargil, Ladakh, NW Himalayas, India: Petrological implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3865, https://doi.org/10.5194/egusphere-egu22-3865, 2022.

10:34–10:41
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EGU22-199
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ECS
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Virtual presentation
Yuuki Hagiwara, Ross Angel, Mattia Gilio, Junji Yamamoto, and Matteo Alvaro

The determination of the pressure and temperature (P-T) history experienced by mantle xenoliths, especially the pressure, is essential for elucidating the physicochemical layering structure of the uppermost mantle. However, the lack of continuous reactions between solid solution minerals with large volume changes in spinel-lherzolites makes it difficult to apply conventional geobarometry based on mineral chemistry. Here, elastic geobarometry (Angel et al., 2014; Angel et al., 2017), a complementary technique for determining equilibrium P-T conditions of rocks, was applied to spinel inclusions in olivine in a spinel-lherzolite xenolith.

To utilize elastic geobarometry, reliable equations of state (EoS) for the host mineral and inclusion are essential. Although the EoS for mantle olivine is well constrained by Angel et al. (2018), detailed studies on the EoS for spinel are scarce. Therefore, we firstly conducted a comprehensive review of previous studies investigating the temperature and/or pressure dependence of volume, bulk modulus, and heat capacity, and then determined the EoS for end member spinel using EoSfit7c (Milani et al., 2017).

Next, using Raman spectroscopy, we attempted to estimate the residual pressure of spinel inclusions (Pinc) trapped in olivine in a mantle xenolith from Ennokentiev, Sikhote-Alin, Far Eastern Russia (see Yamamoto et al. (2012) for the chemical composition of the sample). As a result, the peaks of the spinel inclusions were always shifted to higher wavenumbers than those of the unstrained reference spinel crystal from the same xenolith, but only Eg (~410 cm-1) and A1g (~750 cm-1) peak positions could be measured with sufficient accuracy for quantitative analysis of residual pressure. When Pinc was estimated using relation between spinel peak position and pressure reported by Chopelas and Hofmeister (1991), the data obtained from the center of the inclusion showed positive Pinc from both A1g and Eg peaks, and they agreed within error. However, it is desirable to use the A1g peak for the calculation of Pinc because 1) the Eg peak has low Raman scattering intensity, 2) depending on the crystal orientation of the host olivine, the Eg peak of spinel could interfere with the B3g peak of olivine, and 3) the Eg peak is expected to be sensitive to the differential stress because the Pinc calculated from the Eg peak obtained from the edge of the inclusion is unusually higher than that calculated from the A1g peak. Since positive residual pressures were obtained from all the inclusions investigated, by combining the EoS of spinel constrained in this study and measured Pinc, spinel inclusions trapped in olivine can be expected to be a new method for estimating the depth provenance of spinel-bearing peridotite.

 

References

Angel et al. (2014) Am Mineral, 99, 2146-2149; Angel et al. (2017) Am Mineral, 102, 1957-1960; Angel et al. (2018) Phys Chem Miner, 45, 95-113, Chopelas and Hofmeister (1991) Phys Chem Miner, 18, 279-293; Milani et al. (2017) Am Mineral, 102, 851-859; Yamamoto et al. (2012) Tectonophysics, 554-557, 74-82.

How to cite: Hagiwara, Y., Angel, R., Gilio, M., Yamamoto, J., and Alvaro, M.: Evaluation of elastic geobarometry of spinel inclusions in olivine and its application to mantle xenoliths, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-199, https://doi.org/10.5194/egusphere-egu22-199, 2022.

10:41–10:48
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EGU22-9457
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Virtual presentation
Magdalena Matusiak-Małek, Jakub Mikrut, Jacek Puziewicz, Anna Kukuła, Theodoros Ntaflos, Sonja Aulbach, Leif Johansson, and Michél Grégoire

Southern Sweden (Scania region) is located in the peripherical parts of the East European Craton (EEC). In the Mesozoic, up to three pulses of volcanic activity took place between 191 and 110 Ma (Bergelin et al., 2006, IJES; Tappe et al., 2016, GCA). Some of the alkali basaltoids carry ultramafic, mafic and felsic xenoliths (Rehfeldt et al, 2007, IJES). In this study, we focused on the evolution of the lithospheric mantle sampled by anhydrous, spinel-facies lherzolites, harzburgites, and subordinate dunites.

Based on the Fo content in olivine, the peridotites were classified into three groups. Group X peridotites are characterized by Ca-rich olivine (890-1470 ppm) with Fo=91.1-91.7.  Enstatite has Mg#=91.5-91.9 and Al=0.16-0.22 atoms per formula unit (apfu), while the Cr-augite has Mg#= 90.8-91.2 and Al=0.21-0.28 apfu. Clinopyroxene is chemically homogenous in terms of trace elements and is LREE-enriched with positive Eu-anomaly. The Nd and Sr isotopic ratios in clinopyroxene are 143Nd/144Nd=0.512548 (εNd=2.63) and  87Sr/86Sr=0.704237, respectively. Olivine in group Y peridotites is Ca-poor (<951 ppm) and has Fo=89.5-91.1, enstatite has Mg#=89.7-91.7, and Al content of 0.084-0.169 apfu. The Cr-diopside has Mg#=90.8-93.5 and Al=0.118-0.232 apfu. Trace element patterns in clinopyroxene allow subdivision of this group into two subgroups: subgroup Y1 – with heterogeneous LREE-enriched clinopyroxene, and subgroup Y2 – with homogenous LREE-enriched clinopyroxene; both groups are characterized by a positive Eu anomaly, but in subgroup Y1 it is significantly more pronounced. The Nd and Sr isotopic ratios in clinopyroxene from subgroup Y1 are 143Nd/144Nd=0.512624–0.512644 (εNd=4.13-4.52) and 87Sr/86Sr=0.703027–0.703100, therefore significantly more depleted than group X. In group Z peridotite the Fo content in olivine is 88.1-89.1, the Mg# in enstatite is 89.1-89.5 and its Al content is 0.19-0.20 apfu. The Mg# of Cr-diopside is 88.5-89.4 and the Al content is 0.24-0.25 apfu. The trace elements contents in clinopyroxene is homogenous and the REE pattern is flat at values double that in the primitive mantle.         

 The highest equilibration temperatures were estimated for the group X xenoliths, where TWES=1101-1110 °C (Witt-Eickschen and Seck, 1991, CMP) and TBK=1214-1241 °C (Brey and Köhler, 1990, JoP).  The temperatures calculated for group Y xenoliths are TWES=875-1033 °C and TBK=872-1027 °C and do not significantly differ between subgroups. Temperatures recorded by the group Z sample are TWES=1040-1056 °C and TBK=1065-1081 °C.

The composition of group X peridotites suggests their metasomatism by a high-temperature mafic melt resembling the basaltoids from Scania. Alternatively, they may represent high-pressure cumulates, as suggested by their coarse-grained texture. The group Y peridotites record cryptic metasomatism of a significantly depleted peridotite (melt extraction ranging typically between 25 and 30%) by a carbonatitic melt. The carbonatitic metasomatic agent was fractionating chromatographically from REE-, Th- and U-rich in subgroup Y2 to -poor in those elements in subgroup Y2. The group Z peridotite possibly represents depleted peridotite which was further metasomatized by a mafic melt. The lithospheric mantle beneath the marginal part of EEC has a complex composition, which is however different from a typical cratonic mantle.

 

Founded by Polish National Science Centre grant no. UMO-2016/23/B/ST10/01905 and WTZ PL 08/2018.

How to cite: Matusiak-Małek, M., Mikrut, J., Puziewicz, J., Kukuła, A., Ntaflos, T., Aulbach, S., Johansson, L., and Grégoire, M.: Composition of lithospheric mantle beneath southern margin of East European Craton evidenced by peridotitic xenoliths from Scania, S Sweden., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9457, https://doi.org/10.5194/egusphere-egu22-9457, 2022.

10:48–10:55
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EGU22-4679
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ECS
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Virtual presentation
Levente Patkó, Zoltán Kovács, Nóra Liptai, László E. Aradi, Márta Berkesi, Jakub Ciazela, Károly Hidas, Carlos J. Garrido, and István J. Kovács

The Bakony-Balaton Highland Volcanic Field (BBHVF), where Neogene alkali basalts and their pyroclasts host a great number of upper mantle xenoliths, is situated in the western part of the Pannonian Basin. One of the barely investigated xenolith localities of the BBHVF is Mindszentkálla. In the BBHVF, most of the xenoliths have lherzolitic modal composition, however, the Mindszentkálla locality is dominated by harzburgites. In addition to the homogeneous coarse-grained harzburgite xenoliths, we collected composite and multiple composite (with more than two different domains) xenoliths that represent small-scale heterogeneities. Harzburgite, interpreted as the host rock, is crosscut by dunitic, orthopyroxenitic, apatite-bearing websteritic, and amphibole-phlogopite-bearing veins.

To understand the evolution of the conspicuously complex mantle beneath Mindszentkálla, in situ major and trace element analyses were carried out on all rock-forming minerals. The major element chemistry of silicate minerals in the harzburgite wall rock and dunite veins show lower basaltic element (Fe, Mn, Ti, Na) contents with respect to the orthopyroxenitic and websteritic veins. The rare earth elements display flat or spoon-shaped patterns in the harzburgitic clinopyroxenes, whereas the websteritic clinopyroxenes and the amphiboles of the amphibole-phlogopite vein are enriched in light rare earth elements.

The observed textural and geochemical features indicate that the Mindszentkálla xenoliths could have gone through significant mineralogical and compositional modifications in at least two events. During the first event, the lherzolitic mantle was metasomatized most likely by a silica-rich melt, which could have resulted in orthopyroxene-rich peridotitic lithology. The metasomatizing Si-rich melt is likely related to a former subduction event.

The second metasomatic event led to the formation of dunite, orthopyroxenite, apatite-bearing websterite, and amphibole-phlogopite-bearing veins. These lithologies are likely the products of interactions between volatile-enriched, asthenosphere-derived basaltic melts and the peridotite wall rock, or they represent the high-pressure crystallization of such melts. The ascent of these mafic melts may have happened shortly before the xenolith entrapment during the Neogene basaltic volcanism.

How to cite: Patkó, L., Kovács, Z., Liptai, N., Aradi, L. E., Berkesi, M., Ciazela, J., Hidas, K., Garrido, C. J., and Kovács, I. J.: Deciphering multiple metasomatism beneath Mindszentkálla (Bakony-Balaton Highland Volcanic Field, western Pannonian Basin) revealed by upper mantle peridotite xenoliths, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4679, https://doi.org/10.5194/egusphere-egu22-4679, 2022.

10:55–11:02
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EGU22-3733
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ECS
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Virtual presentation
Valentina Brombin, Edoardo Barbero, Emilio Saccani, Nicola Precisvalle, Sonja Lepitkova, Ivica Milevski, Igor Ristovski, Igor Milcov, Gorgi Dimov, Costanza Bonadiman, and Gianluca Bianchini

In the upper mantle, volatiles control its composition, partial melting conditions, as well as the ascent rate of the formed melts. As consequence, volatile composition of the mantle is, in turn, recorded in the melts and, therefore, in the erupted basaltic rocks. Despite their importance, origin, budget, and fluxes of the volatiles in the upper mantle are poorly constrained. It is well known that the main input of mantle volatiles, such as carbon (C) and sulphur (S), represents components released from the subducting slab, e.g., oceanic rocks and sediments, whose have characteristic isotopic signatures. In this view, studies of isotopic ratios of volatiles of subduction-related magmatic rocks could be used to identify the chemical components released by the subducting slab metasomatizing the upper mantle. To confirm this hypothesis, we investigated the major and trace element composition, as well as the C and S elemental contents and isotopic ratios of subvolcanic and volcanic rocks of the Vardar ophiolites of North Macedonia, which represent remnants of the Mesozoic Tethyan oceanic lithosphere formed in supra-subduction zone tectonic settings.

The ophiolites were sampled at Lipkovo and Demir Kapija localities, in the northern and southern part of North Macedonia, respectively. Based on whole-rock major and trace element composition, two main groups of rocks can be distinguished: i) Group 1 rocks, which are subalkaline basalts with backarc affinity and ii) Group 2 rocks, which are calc-alkaline basalts with arc affinity. The petrogenetic modelling based on trace and Rare Earth Elements, indicates that Group 1 mantle sources were affected by limited metasomatic processes by slab-released components, in particular aqueous fluids and sediment melts, whereas the Group 2 mantle sources were strongly metasomatized by sediment melts and adakitic melts. Accordingly, the Group 1 rocks exhibit C-enriched and S-depleted isotopic signature, indicating a minor involvement of melts from the subducting sediments. On the other hand, the C-depleted and S-enriched isotopic signatures of the Group 2 rocks suggest a major involvement of melts derived from the subducting sediments rich in organic matter and sulphate phases Therefore, both geochemical and isotopic data of the subvolcanic and volcanic samples of the North Macedonia ophiolites show that the sub-arc mantle sources are more affected by slab-released fluids than those of the backarc basin, which are more distal from the trench. Thus, combining the geochemical and isotopic data of subvolcanic and volcanic samples of complex geological framework can contribute to reconstruct the geodynamic scenarios, such as that of the Vardar ophiolites in the Dinaric-Hellenic belt. In addition, this approach may be useful to better understand the global geodynamic cycles of volatiles reconstructing their origin, budget, and isotopic composition, and understand the impacts on climate and environment from local to global scale.

How to cite: Brombin, V., Barbero, E., Saccani, E., Precisvalle, N., Lepitkova, S., Milevski, I., Ristovski, I., Milcov, I., Dimov, G., Bonadiman, C., and Bianchini, G.: Basaltic rocks from the Vardar ophiolite (North Macedonia): new insights on the metasomatism of sub-arc upper mantle using geochemical and stable isotope data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3733, https://doi.org/10.5194/egusphere-egu22-3733, 2022.

11:02–11:09
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EGU22-13428
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ECS
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Virtual presentation
Abimbola Chris Ogunyele, Tommaso Giovanardi, Mattia Bonazzi, Maurizio Mazzuccheli, Alessandro De Carlis, Anna Cipriani, and Alberto Zanetti

Dyke swarms intruding the mantle–continental crust transition of the Adria plate as documented by the Ivrea-Verbano Zone (IVZ, Southern Alps) represent a unique opportunity to investigate the evolution of mantle melts from Late Paleozoic to Mesozoic in the post-collisional Variscan realm. Thus, we present new petrological and geochemical data of dyke swarms cropping out in the Finero Phlogopite Peridotite mantle unit. Dykes are from a few cm to >1 m thick and cut at a high angle the mantle foliation.

The dyke swarms are composed of cumulus phlogopite-bearing amphibole peridotite, hornblendite, diorite and anorthosite. Many dykes are composite, showing variable proportions of melanocratic and leucocratic layers. Volatiles overpressure during the late magmatic stage is testified by plastic flow and development of a porphyroclastic structure by deformation of early cumulates and by the widespread segregation of a fine-grained mica matrix. The dyke swarms show mineralogical and geochemical features varying between two end-member series.

A dyke series is characterized by Al-rich pargasite (Al2O3 up to 18 wt.%) and phlogopite, associated with apatite, calcite, sulphides and sometimes sapphirine. The amphiboles show i) large LILE and LREE contents, ii) negative Nb, Ta, Zr and Hf anomaly and iii) isotopic oxygen composition heavier than the mantle interval, which support the occurrence of recycled continental crust components in the parent melts and impart an overall “orogenic” affinity.

The second series mainly consists of Al-poorer pargasite, phlogopite and albite (An 8-10), associated with apatite, monazite, ilmenite, zircon, Nb-rich oxides and carbonates. Mineral compositions and assemblages indicate that the parent melts were strongly enriched in Fe, Na, H2O, P and C. Amphiboles are still enriched in LILE and LREE, but show extreme enrichments in Nb, Ta, Zr and Hf. As a whole, the petrochemical features point to an “anorogenic” alkaline affinity. Zircons from the “anorogenic” dykes are mostly anhedral, with homogenous internal structure or sector zoning. The strongly positive εHft (average of +10) of zircons and the Sr isotopic composition of amphiboles (0.7042) point to a derivation of such “anorogenic” melts from mildly enriched mantle sources. Concordant 206Pb/238U zircon ages for “anorogenic” dykes vary from 221 ± 9 Ma to 192 ± 8 Ma. Some dykes show both “orogenic” and “anorogenic” affinities, thus recording different pulses of mantle melts and metasomatic overprinting. As a whole, the dyke swarms show a transition from “orogenic” to “anorogenic” affinity indicating re-opening of dykes’ conduits for the melt ascending, pointing to a progressive change of the mantle sources of the Mesozoic magmatism of the Southern Alps.

How to cite: Ogunyele, A. C., Giovanardi, T., Bonazzi, M., Mazzuccheli, M., De Carlis, A., Cipriani, A., and Zanetti, A.: Transition from “orogenic-like” to “anorogenic” geochemical affinity in Mesozoic post-collisional magmatism: evidence from alkali-rich dykes from Ivrea-Verbano Zone (Southern Alps), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13428, https://doi.org/10.5194/egusphere-egu22-13428, 2022.

11:09–11:16
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EGU22-1863
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Virtual presentation
Nikolay Bonev, Zornitsa Dotseva, and Petyo Filipov

In the Alpine orogen of the north Aegean region, the eastern Rhodope Zone consists of widespread high-grade metamorphic basement exposed in Bulgaria and Greece. In this high-grade basement, the lithologically variegated upper unit contains meta-ultramafic bodies, which are considered as dismembered Precambrian meta-ophiolite association (Kozhoukharova 1984). In the same unit, the voluminously predominant amphibolites, having mafic igneous precursors of boninitic-tholeiitic affinity, are in turn considered of Precambrian-Paleozoic island arc origin (Haydoutov et al. 2004), or part of the amphibolites of Ordovician age have back-arc origin (Bonev et al. 2013). The upper unit, together with the overlying Circum-Rhodope belt Jurassic ophiolite, constitutes the hanging wall of the Eocene extensional system consisting of meta-granitoids with Carboniferous protoliths in the footwall. Here, we report on the geochemistry of the amphibolites from the upper unit in Bulgaria and Greece, and discuss their composition and tectonic setting, which might shed a light on the mid-late Paleozoic-early Mesozoic tectonic architecture of the region.

The amphibolites occur intercalated with para- and ortho-metamorphic lithologies within the upper unit. Texturally, they are represented mainly by massive or banded amphibolite and garnet-bearing amphibolite. The bulk mineral assemblage contains amphibole and plagioclase ± quartz ± garnet ± epidote-clinozoisite ± chlorite ± sphene ± rutile, which resulted from the main metamorphic overprint in amphibolite-facies and variable retrogression to greenschist-facies. The meta-mafic rocks cover the range of basalt to andesite composition, with elevated MgO, variable alkali and low-K contents, having mainly tholeiitic to weak calc-alkaline affinity. The range of TiO2 defines two groups of high-Ti (>1%) and low-Ti (<1%) meta-mafic rocks. Mostly flat to slightly LREE-depleted chondrite-normalized patterns characterize the high-Ti group, which overlaps N-MORB and E-MORB compositions. The low-Ti group exhibits pronounced LREE-depleted and fractionated REE patterns, rarely U-shaped boninitic-like pattern. N-MORB-normalized trace element profiles define high LILE/HFSE ratios, moderate to strong HFSE and HREE depletion of the low-Ti group, and close to N-MORB to slightly enriched HFSE-HREE trend of the high-Ti group. A negative Nb anomaly characterizes part of the low-Ti group, whereas other samples from both groups show no Nb anomalies and have contents higher than N-MORB. On various trace element discrimination diagrams the majority of high-Ti group meta-mafic rocks display clear MORB affinity and few samples plot in the WPB field of oceanic island tholeiites, whereas low-Ti meta-mafic rocks show island arc tholeiite (IAT) affinity or have transitional MORB/IAT signature. 

The compositional diversity of the meta-mafic rocks from the upper unit with MORB, transitional MORB/IAT and IAT affinity, in turn call for the origin of the protoliths in a paired ocean ridge-island arc environment, and thus could hints their supra-subduction zone origin in an island arc/back-arc setting.

 

References

Bonev, N., Ovtcharova-Schaltegger, M., Moritz, R., Marchev, P., Ulianov, A. 2013. Geod Acta 26, 3-4, 207-229.

Haydoutov, I., Kolcheva, K., Daieva, L., Savov, I., Carrigan, Ch.  2004. Ofioliti, 29, 2, 145-157.

Kozhoukharova, E. 1984. Geologica Balc., 14, 4, 9-36.

 

Acknowledgements: The study was supported by the NSF Bulgaria KP-06-N54/5 contract.

How to cite: Bonev, N., Dotseva, Z., and Filipov, P.: Geochemistry and tectonic significance of meta-ophiolitic mafic rocks in the high-grade metamorphic basement of the eastern Rhodope Zone, Bulgaria-Greece, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1863, https://doi.org/10.5194/egusphere-egu22-1863, 2022.

11:16–11:23
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EGU22-9103
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ECS
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Virtual presentation
Igor Iakovlev, Vladimir Malkovets, and Anastasia Gibsher

Peridotite xenoliths are of great interest for research, since their composition is closest to the simulated compositions of the upper mantle, and they also make it possible not only to determine the conditions for the formation of these rocks, but also the degree of metasomatic processing of the diamondiferous keel, as well as the thickness and distribution area of diamondiferous rocks in the lithospheric mantle.

The Middle Paleozoic (D3-C1) diamondiferous kimberlite pipe Komsomolskaya-Magnaya was chosen as the object of research. This is one of the diamondiferous pipes of the Siberian platform, which contains many unchanged xenoliths of peridotite rocks.

We studied a collection of 180 peridotite xenoliths of the Komsomolskaya-Magnitnaya pipe, of which 104 belong to dunite-harzburgite paragenesis, 74 to lherzolite and 4 websterites. Also, we studied a large number of minerals from the concentrate material of the Komsomolskaya-Magnitnaya kimberlite pipe.

A high proportion (~ 30%) of peridotites with high magnesian olivines (Mg #> 93 mol%) indicates the presence of a block of highly depleted rocks in the lithospheric mantle.

We noted a high proportion of garnets with S-shaped REE distribution spectra (~ 60%), as well as garnets belonging to the harzburgite-dunite paragenesis in accordance with the CaO-Cr2O3 diagram. It indicates a moderate role of metasomatic changes associated with silicate melts, as well as interaction with carbonatite melts enriched in LREE.

In addition, kimberlite indicator minerals (KIM) (garnets, chrome spinels, ilmenites) were studied, sampled directly from 7 geophysical anomalies, 6 new kimberlite bodies, and kimberlite pipes Interkosmos, Kosmos-2, 325 years of Yakutia, belonging to the Upper Muna field. These data provide more information on the composition of the lithospheric mantle within the entire Upper Muna field.

For several kimberlite bodies, a high proportion of KIM of the diamond association is noted, however, for most kimberlite bodies, signs of a high degree of secondary metasomatic processes are noted, which negatively affect the preservation of diamond in the lithospheric mantle.

Cr-spinels from various kimberlite bodies of the Upper Muna field attract special attention. In addition to the typical peridotite Cr-spinels, there are Cr-spinels that follow the magmatic trend (Sobolev, 1974) and have extremely low contents of aluminum and titanium. The genetic identity of these Cr-spinels is still unknown.

Was done precise pressure (P)-temperature (T) estimation using single-clinopyroxene thermobarometry (Nimis, Ta). Was obtained mantle paleogeotherm.  Data was received about surface heat flux ~34–35mW/m2, 225–230 km lithospheric thickness, and 110–120 thick “diamond window” for the Upper Muna field (Dymshits et al, 2020).

  • Dymshits A. M., Sharygin I. S., Malkovets V. G., Yakovlev I. V., Gibsher A. A., Alifirova T. A., Vorobei S. S., Potapov S. V., Garanin V. K. Thermal state, thickness, and composition of the lithospheric mantle beneath the Upper Muna kimberlite field (Siberian Craton) constrained by clinopyroxene xenocrysts and comparison with Daldyn and Mirny fields // Minerals. 2020. V. 10. P. 549.
  • Sobolev N.V., Deep inclusions in kimberlites and the problem of the composition of the upper mantle // Novosibirsk: Nauka, 1974.

How to cite: Iakovlev, I., Malkovets, V., and Gibsher, A.: Features of the composition and structure of the lithospheric mantle of the Upper Muna field., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9103, https://doi.org/10.5194/egusphere-egu22-9103, 2022.

11:23–11:30
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EGU22-3525
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ECS
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Virtual presentation
Multi-mineral study of lithospheric metasomatism in N-Tanzania: Mantle source characterization of the carbonatite magmas 
(withdrawn)
Valentin Casola and Lydéric France