An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism

Michael W. Förster, Dejan Prelević, Stephan Buhre, Regina Mertz-Kraus, Stephen F. Foley

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed "orogenic lamproites" and are compositionally distinct from K-rich "anorogenic lamproites" that show lower 87Sr/86Sr and a trace element pattern that resembles that of primary mantle melts. For both groups the processes of K-enrichment within their source are uncertain and are thought to be linked to melts of sedimentary rocks for "orogenic lamproites" and low-degree melts of ultramafic mantle rocks for "anorogenic lamproites". In both cases, metasomatism of the mantle lithosphere is the precursor to K-rich magmatism. In this study we experimentally determine the effects of mantle metasomatism by sediment- and hydrous mantle melts. The experiments simulate the interaction of refractory lithospheric mantle and metasomatizing melt in a 2-layer reaction experiment. The sediment/dunite reaction experiments lead to formation of a strongly K-enriched phlogopite-pyroxenite layer sandwiched between the two starting materials. The low temperature of the sediment/dunite reaction runs at <1000 °C simulates a fore-arc subduction environment, in which the melts of sediment are consumed during interaction with dunite as the temperature is below the solidus of the produced phlogopite-pyroxenites. The hydrous mantle melt/dunite reaction run is simulated by reacting a hydrated basanite with dunite. Since the temperature of the reaction is higher than the solidus of the resulting phlogopite-pyroxenites (1200 °C), the hydrous melt is not consumed but flows further, increasing in K2O and K/Na as it reacts with the refractory peridotite. In both cases, melts are enriched in K and K/Na increases by crystallizing a low K and low K/Na eclogitic residue. Compositions of glass and phlogopite from both types of reactions are comparable to glasses and phlogopites found within post-collisional lavas. Since the enrichment of K within the reaction zone is strongly controlled by the formation of low K/Na and low-K residues, metasomatic enrichment of the mantle lithosphere in K does not need a highly K-enriched metasomatic agent.

LanguageEnglish
Pages76-88
Number of pages13
JournalJournal of Asian Earth Sciences
Volume177
DOIs
Publication statusPublished - 15 Jun 2019

Fingerprint

magmatism
experimental study
melt
mantle
dunite
phlogopite
sediment
metasomatism
lithosphere
glass
trace element
basanite
pyroxenite
experiment
mantle source
peridotite
sedimentary rock
isotopic composition
subduction
potassium

Keywords

  • Lamproite
  • High-pressure experiments
  • Metasomatism
  • Post-collisional magmatism
  • Mediterranean magmatism
  • High-K lavas

Cite this

Förster, Michael W. ; Prelević, Dejan ; Buhre, Stephan ; Mertz-Kraus, Regina ; Foley, Stephen F. / An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism. In: Journal of Asian Earth Sciences. 2019 ; Vol. 177. pp. 76-88.
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abstract = "Potassium-rich lavas with K/Na of >2 are common in orogenic and anorogenic intraplate magmatic provinces. However, in the primitive mantle, the concentration of Na exceeds that of K by 10 times. The source of K-rich lavas thus needs to be either K-enriched or Na-depleted to account for high K/Na ratios. The geochemical and isotopic compositions of high 87Sr/86Sr post-collisional lavas show that their mantle source contains a recycled crustal component. These highly K-enriched lavas with crustal like trace element patterns are termed {"}orogenic lamproites{"} and are compositionally distinct from K-rich {"}anorogenic lamproites{"} that show lower 87Sr/86Sr and a trace element pattern that resembles that of primary mantle melts. For both groups the processes of K-enrichment within their source are uncertain and are thought to be linked to melts of sedimentary rocks for {"}orogenic lamproites{"} and low-degree melts of ultramafic mantle rocks for {"}anorogenic lamproites{"}. In both cases, metasomatism of the mantle lithosphere is the precursor to K-rich magmatism. In this study we experimentally determine the effects of mantle metasomatism by sediment- and hydrous mantle melts. The experiments simulate the interaction of refractory lithospheric mantle and metasomatizing melt in a 2-layer reaction experiment. The sediment/dunite reaction experiments lead to formation of a strongly K-enriched phlogopite-pyroxenite layer sandwiched between the two starting materials. The low temperature of the sediment/dunite reaction runs at <1000 °C simulates a fore-arc subduction environment, in which the melts of sediment are consumed during interaction with dunite as the temperature is below the solidus of the produced phlogopite-pyroxenites. The hydrous mantle melt/dunite reaction run is simulated by reacting a hydrated basanite with dunite. Since the temperature of the reaction is higher than the solidus of the resulting phlogopite-pyroxenites (1200 °C), the hydrous melt is not consumed but flows further, increasing in K2O and K/Na as it reacts with the refractory peridotite. In both cases, melts are enriched in K and K/Na increases by crystallizing a low K and low K/Na eclogitic residue. Compositions of glass and phlogopite from both types of reactions are comparable to glasses and phlogopites found within post-collisional lavas. Since the enrichment of K within the reaction zone is strongly controlled by the formation of low K/Na and low-K residues, metasomatic enrichment of the mantle lithosphere in K does not need a highly K-enriched metasomatic agent.",
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year = "2019",
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An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism. / Förster, Michael W.; Prelević, Dejan; Buhre, Stephan; Mertz-Kraus, Regina; Foley, Stephen F.

In: Journal of Asian Earth Sciences, Vol. 177, 15.06.2019, p. 76-88.

Research output: Contribution to journalArticleResearchpeer-review

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T1 - An experimental study of the role of partial melts of sediments versus mantle melts in the sources of potassic magmatism

AU - Förster, Michael W.

AU - Prelević, Dejan

AU - Buhre, Stephan

AU - Mertz-Kraus, Regina

AU - Foley, Stephen F.

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KW - High-pressure experiments

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KW - Post-collisional magmatism

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