Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient
Abstract The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensiv...
| Main Authors: | , , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Nature Portfolio
2021-06-01
|
| Series: | Scientific Reports |
| Online Access: | https://doi.org/10.1038/s41598-021-90844-w |
| _version_ | 1831572643228155904 |
|---|---|
| author | Costanza Bonadiman Valentina Brombin Giovanni B. Andreozzi Piera Benna Massimo Coltorti Nadia Curetti Barbara Faccini Marcello Merli Beatrice Pelorosso Vincenzo Stagno Magdala Tesauro Alessandro Pavese |
| author_facet | Costanza Bonadiman Valentina Brombin Giovanni B. Andreozzi Piera Benna Massimo Coltorti Nadia Curetti Barbara Faccini Marcello Merli Beatrice Pelorosso Vincenzo Stagno Magdala Tesauro Alessandro Pavese |
| author_sort | Costanza Bonadiman |
| collection | DOAJ |
| description | Abstract The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity. |
| first_indexed | 2024-12-17T13:31:03Z |
| format | Article |
| id | doaj.art-840c784f6ced414882045257231e3c6a |
| institution | Directory Open Access Journal |
| issn | 2045-2322 |
| language | English |
| last_indexed | 2024-12-17T13:31:03Z |
| publishDate | 2021-06-01 |
| publisher | Nature Portfolio |
| record_format | Article |
| series | Scientific Reports |
| spelling | doaj.art-840c784f6ced414882045257231e3c6a2022-12-21T21:46:34ZengNature PortfolioScientific Reports2045-23222021-06-0111111710.1038/s41598-021-90844-wPhlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambientCostanza Bonadiman0Valentina Brombin1Giovanni B. Andreozzi2Piera Benna3Massimo Coltorti4Nadia Curetti5Barbara Faccini6Marcello Merli7Beatrice Pelorosso8Vincenzo Stagno9Magdala Tesauro10Alessandro Pavese11Dipartimento di Fisica e Scienze della Terra, Università degli Studi di FerraraDipartimento di Fisica e Scienze della Terra, Università degli Studi di FerraraDipartimento di Scienze della Terra, Sapienza Università di RomaDipartimento di Scienze della Terra, Università degli Studi di TorinoDipartimento di Fisica e Scienze della Terra, Università degli Studi di FerraraDipartimento di Scienze della Terra, Università degli Studi di TorinoDipartimento di Fisica e Scienze della Terra, Università degli Studi di FerraraDipartimento di Scienze della Terra e del Mare (DiSTeM), Università di PalermoDipartimento di Fisica e Scienze della Terra, Università degli Studi di FerraraDipartimento di Scienze della Terra, Sapienza Università di RomaDipartimento di Matematica e Geoscienze, Università di TriesteDipartimento di Scienze della Terra, Università degli Studi di TorinoAbstract The occurrence of phlogopite and amphibole in mantle ultramafic rocks is widely accepted as the modal effect of metasomatism in the upper mantle. However, their simultaneous formation during metasomatic events and the related sub-solidus equilibrium with the peridotite has not been extensively studied. In this work, we discuss the geochemical conditions at which the pargasite-phlogopite assemblage becomes stable, through the investigation of two mantle xenoliths from Mount Leura (Victoria State, Australia) that bear phlogopite and the phlogopite + amphibole (pargasite) pair disseminated in a harzburgite matrix. Combining a mineralogical study and thermodynamic modelling, we predict that the P–T locus of the equilibrium reaction pargasite + forsterite = Na-phlogopite + 2 diopside + spinel, over the range 1.3–3.0 GPa/540–1500 K, yields a negative Clapeyron slope of -0.003 GPa K–1 (on average). The intersection of the P–T locus of supposed equilibrium with the new mantle geotherm calculated in this work allowed us to state that the Mount Leura xenoliths achieved equilibrium at 2.3 GPa /1190 K, that represents a plausible depth of ~ 70 km. Metasomatic K-Na-OH rich fluids stabilize hydrous phases. This has been modelled by the following equilibrium equation: 2 (K,Na)-phlogopite + forsterite = 7/2 enstatite + spinel + fluid (components: Na2O,K2O,H2O). Using quantum-mechanics, semi-empirical potentials, lattice dynamics and observed thermo-elastic data, we concluded that K-Na-OH rich fluids are not effective metasomatic agents to convey alkali species across the upper mantle, as the fluids are highly reactive with the ultramafic system and favour the rapid formation of phlogopite and amphibole. In addition, oxygen fugacity estimates of the Mount Leura mantle xenoliths [Δ(FMQ) = –1.97 ± 0.35; –1.83 ± 0.36] indicate a more reducing mantle environment than what is expected from the occurrence of phlogopite and amphibole in spinel-bearing peridotites. This is accounted for by our model of full molecular dissociation of the fluid and incorporation of the O-H-K-Na species into (OH)-K-Na-bearing mineral phases (phlogopite and amphibole), that leads to a peridotite metasomatized ambient characterized by reduced oxygen fugacity.https://doi.org/10.1038/s41598-021-90844-w |
| spellingShingle | Costanza Bonadiman Valentina Brombin Giovanni B. Andreozzi Piera Benna Massimo Coltorti Nadia Curetti Barbara Faccini Marcello Merli Beatrice Pelorosso Vincenzo Stagno Magdala Tesauro Alessandro Pavese Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient Scientific Reports |
| title | Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient |
| title_full | Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient |
| title_fullStr | Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient |
| title_full_unstemmed | Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient |
| title_short | Phlogopite-pargasite coexistence in an oxygen reduced spinel-peridotite ambient |
| title_sort | phlogopite pargasite coexistence in an oxygen reduced spinel peridotite ambient |
| url | https://doi.org/10.1038/s41598-021-90844-w |
| work_keys_str_mv | AT costanzabonadiman phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT valentinabrombin phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT giovannibandreozzi phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT pierabenna phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT massimocoltorti phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT nadiacuretti phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT barbarafaccini phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT marcellomerli phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT beatricepelorosso phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT vincenzostagno phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT magdalatesauro phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient AT alessandropavese phlogopitepargasitecoexistenceinanoxygenreducedspinelperidotiteambient |