Abstract
AbstractA 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 $$\delta$$
δ
13C-depleted CO2 and preservation of primary magmatic $$\delta$$
δ
13C 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.
Publisher
Springer Science and Business Media LLC
Subject
Geochemistry and Petrology,Geophysics
Reference173 articles.
1. Amundsen HEF (1987) Evidence for liquid immiscibility in the upper mantle. Nature 327:692–695
2. Anderson UB, Eklund O (1994) Cellular plagioclase intergrowths as a result of crystal-magma mixing in the Proterozoic Aland rapakivi batolith, SW Finland. Contrib Mineral Petrol 117:124–136
3. Andreeva IA, Naumov VB, Kovalenko VI, Kononkova NN (1999) The magma composition and genesis of theralite from the Mushugai Khuduk carbonatite-bearing complex in Southern Mongolia. Geokhimiya 8:826–841
4. Araújo DP, Griffin WL, O’Reilly SY (2009) Mantle melts, metasomatism and diamond formation: Insights from melt inclusions in xenoliths from Diavik, Slave Craton. Lithos 112:675–682
5. Ardia P, Giordano D, Schmidt MW (2008) A model for the viscosity of rhyolite as a function of H2O-content and pressure: A calibration based on centrifuge piston cylinder experiments. Geochim Cosmochim Acta 72(24):6103–6123. https://doi.org/10.1016/j.gca.2008.08.025
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