Carbonatite-melilitite-phosphate immiscible melts from the aragonite stability field entrained from the mantle by a Pliocene basalt

Autor(en)

Vratislav Hurai, Monika Huraiová, Gerlinde Habler, Monika Horschinegg, Rastislav Milovský, Stanislava Milovská, Miroslav Hain, Rainer Abart

Abstrakt

A plagioclase megacryst containing composite crystal-glass inclusions was ejected in a Pliocene basaltic diatreme in the Carpathian back-arc basin (Pannonian Basin). The megacryst grew from phonolitic melt, relics of which are preserved in the crystal-glass inclusions. Most of the pristine melt has undergone substantial compositional resetting by interaction with several batches of a low-viscosity carbonated, P-rich melilitite melt, which infiltrated and largely replaced the original inclusion content. The melilitite melt also caused partial resorption of the host megacryst and crystallisation of new calcic plagioclase forming stringers and palisades. A P-rich calcic carbonatite melt exsolved from the melilitite and later crystallised to aragonite at ~ 800 °C and 1.9 GPa. The phosphate melt fraction exsolved from the carbonatite and solidified as CO₃²⁻-rich A-B type apatite. At a very late evolutionary stage, K- and Si-rich fluids caused potassic and silicic alteration of the solidified melilitite glass along cracks and interfaces between calcic carbonate globules and glass at temperatures below 680 °C. The oxygen isotope composition of the plagioclase megacryst (6.2 ‰ V-SMOW; Vienna Standard Mean Ocean Water) and the ⁸⁷Sr/⁸⁶Sr isotope ratio of carbonates in the inclusions (0.7034) are consistent with a mantle-derived melt. ⁸⁷Sr/⁸⁶Sr isotope ratios (0.7047–0.7051) in interstitial carbonates from associated syenite and carbonatite xenoliths indicate a metasomatised mantle source contaminated with radiogenic crustal material or altered marine carbonate. The O-isotope ratios in the carbonates, 22.7 ± 0.6 ‰ V-SMOW in calcite and 23.6 ± 0.7 ‰ V-SMOW in aragonite, are also consistent with a sedimentary precursor. Contrasting δ¹³C values in the calcite, -12.7 ± 0.5 ‰ V-PDB (Vienna PeeDee Belemnite), and the aragonite (-4.6 ± 0.5 ‰ V-PDB) indicate low-temperature modification of calcite assisted by δ¹³C-depleted CO₂ and preservation of primary magmatic δ¹³C values in aragonite. The microstructural and geochemical evidence points towards heterogeneous silicate-carbonate melt fractions generated during the metasomatism and partial melting of a supra-subduction mantle wedge.

Organisation(en)

Department für Lithosphärenforschung

Externe Organisation(en)

Slovak Academy of Sciences (SAS), Slovenian Academy of Sciences and Arts, Univerzita Komenského v Bratislave

Journal

Mineralogy and Petrology

Band

117

Seiten

467-496

Anzahl der Seiten

30

ISSN

0930-0708

DOI

https://doi.org/10.1007/s00710-022-00783-1

Publikationsdatum

2022

Peer-reviewed

Ja

ÖFOS 2012

105120 Petrologie

Schlagwörter

ASJC Scopus Sachgebiete

Geophysics, Geochemistry and Petrology

Sustainable Development Goals

SDG 14 – Leben unter Wasser

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/6c4753a3-c63e-4eea-a605-f02a94876feb