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Journal Article

Quenching of basaltic melts by volatile exsolution

Authors

Ballhaus,  Chris
External Organizations;

Pakulla,  Josua
External Organizations;

/persons/resource/wirth

Wirth,  R.
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/roddatis

Roddatis,  Vladimir
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

/persons/resource/schreib

Schreiber,  Anja
3.5 Interface Geochemistry, 3.0 Geochemistry, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum;

Münker,  Carsten
External Organizations;

Wombacher,  Frank
External Organizations;

Kronz,  Andreas
External Organizations;

Fonseca,  Raúl O. C.
External Organizations;

Cieszynski,  Hanna
External Organizations;

Friedrich,  Hans-Henning
External Organizations;

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Fulltext (public)

5023230.pdf
(Publisher version), 4MB

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Citation

Ballhaus, C., Pakulla, J., Wirth, R., Roddatis, V., Schreiber, A., Münker, C., Wombacher, F., Kronz, A., Fonseca, R. O. C., Cieszynski, H., Friedrich, H.-H. (2023): Quenching of basaltic melts by volatile exsolution. - Contributions to Mineralogy and Petrology, 178, 57.
https://doi.org/10.1007/s00410-023-02041-9


Cite as: https://gfzpublic.gfz-potsdam.de/pubman/item/item_5023230
Abstract
Normally, volatiles in silicate melts are ephemeral components that escape as gases when the melt reaches fluid saturation. When fluid saturation occurs at elevated pressure, magmatic fluids may have large amounts of oxide solute dissolved, are less volatile, and may resemble viscous gels. In Cyprus we have the rare case that solutes of a magmatic fluid coexist with H2O saturated basaltic to boninitic glasses. Quenching of the melts and fluid solutes was induced by fluid segregation. When the fluids exsolved, the liquidus temperature was raised and the melts were left supercooled, while the system temperature remained ± constant. Quenching rates deduced from the morphologies and compositions of quench crystals were high. We analyzed coexisting glasses and fluid solutes for major and trace elements. The fluid mobile trace elements (Rb, K, Pb, Sr) are enriched in both the glasses and fluid solutes. Both endmembers (melt and fluid) have a common parentage and originated within a hydrous mantle source. The glasses have 2.5 ± 0.25 wt.% H2O and record residual H2O contents left after fluid exsolution was completed. Water contents in glasses correspond to an H2O partial pressure (pH2O) of 65 ± 10 MPa and an emplacement depth on the seafloor of 6500 ± 1000 m, provided equilibrium was reached between the pH2O imposed by the melts and the seawater column. Following fluid exsolution, the degree of supercooling ∆T of the melts relative to the dry MgO-in-melt liquidus temperature was  – 65 ± 10 °C. The cooling rate ∆T/t at the time of crystallization of dendritic clinopyroxene crystals can be semi-quantified from the distribution of Al2O3 between metastable clinopyroxene dendrites and melt, to at least  – 50 °C h−1. Toward the end of the article we speculate if other cases exist where quenching was triggered by fluid exsolution. A possible example are spinifex textures deep inside komatiite flows where quenching rates by conductive cooling did not exceed 0.3 to 1 °C h−1. Our proposition assumes that many spinifex-textured komatiites were hydrous, that they contained H2O in quantities sufficient to reach fluid saturation at emplacement pressure, and that spinifex textures formed as a result of supersaturation by fluid loss.