Crystallisation of trapped carbonate-silicate melts terminating at the carbonated solidus ledge: a record of carbon immobilisation mechanism in the lithospheric mantle

HAIFLER, Jakub, Jana KOTKOVÁ and Renata ČOPJAKOVÁ. Crystallisation of trapped carbonate-silicate melts terminating at the carbonated solidus ledge: a record of carbon immobilisation mechanism in the lithospheric mantle. CONTRIBUTIONS TO MINERALOGY AND PETROLOGY. NEW YORK: SPRINGER, 2024, vol. 179, No 4, 27 pp. ISSN 0010-7999. Available from: https://dx.doi.org/10.1007/s00410-024-02108-1.

Basic information

• Original name: Crystallisation of trapped carbonate-silicate melts terminating at the carbonated solidus ledge: a record of carbon immobilisation mechanism in the lithospheric mantle
• Authors: HAIFLER, Jakub, Jana KOTKOVÁ and Renata ČOPJAKOVÁ.
• Edition: CONTRIBUTIONS TO MINERALOGY AND PETROLOGY, NEW YORK, SPRINGER, 2024, 0010-7999.

Other information

• Original language: English
• Type of outcome: Article in a journal
• Confidentiality degree: is not subject to a state or trade secret
• WWW: URL
• Impact factor: Impact factor: 3.500 in 2022
• Organization unit: Faculty of Science
• Doi: http://dx.doi.org/10.1007/s00410-024-02108-1
• UT WoS: 001187646000001
• Keywords in English: Orogenic garnet peridotites; Bohemian Massif; Multiphase solid inclusions; Carbonated peridotite solidus; Pseudosection; Mantle melt
• Tags: International impact, Reviewed

Abstract

Orogenic peridotites in the crystalline basement of the northwestern Bohemian Massif contain multiphase solid inclusions (MSI), which are interpreted to be crystallisation products of trapped former carbonate-silicate melts metasomatizing their host rocks. We applied conventional thermobarometry and forward thermodynamic modelling to constrain the P-T evolution ranging from the peak metamorphic conditions of the investigated harzburgite and lherzolite, through entrapment of the melts in the outer parts of garnets, to the (re)-equilibration of the MSI assemblages. The peak conditions of c. 1100 degrees C/4.5-5.5 GPa are recorded by garnet cores and large pyroxene porphyroclasts. The melt entrapment, during which garnet outer parts grew, was associated with influx of the metasomatizing liquids and probably took place during the early stage of the exhumation. Thermodynamic model of amphibole-free MSI assemblage comprising kinoshitalite/Ba-rich phlogopite (approximated by phlogopite in the model), dolomite, magnesite, clinopyroxene, orthopyroxene, garnet and chromite provided robust estimate of P and T of its (re)-equilibration, c. 900-1000 degrees C, 1.8-2.2 GPa. Furthermore, the lack of olivine reflects co-existence of COH fluid with high X(CO2) = CO2/(CO2 + H2O) >= 0.6. Models employing identical P-T-X(CO2) parameters successfully reproduced the other two amphibole-bearing assemblages observed. The modelled stability fields show perfect alignment with a characteristic isobaric segment of the solidus curve of carbonated peridotite. This co-incidence implies that the (re)-equilibration corresponds to the termination of the melt crystallisation once the near-isothermal exhumation path intersected the solidus. Decreased solubility of silicates at the carbonated peridotite "solidus ledge", inferred from the published experimental data, as well as concentric textures of some MSI indicates sequential crystallisation from the early silicates to late dolomite. The carbonated "solidus ledge" is a relatively narrow boundary in the lithospheric mantle capable of an abrupt immobilisation of fluxing or transported carbonated melts. The investigated rocks are estimated to store approximately 0.02 kg C/m3 (or 6 ppm C) occurring as carbonates in the MSI.