Publication Date:
2013-05-11
Description:
We describe the first observation of primary magmatic aragonite in carbonatite and carbonated syenite, occurring as xenoliths in a Pliocene basaltic diatreme located near the Hungary–Slovakia border. The aragonite-hosting matrix consists of disordered P-rich calcite, occasionally associated with trachyte glass. We interpret the aragonite growth as evidence of supra-lithostatic overpressure in the magmatic plumbing system that connected the crustal basaltic reservoir with the partial melting zone of the lithospheric mantle, and the disordered calcite ± trachyte as quenched residual, immiscible melts, generated close to the solidus of the carbonated alkali basalt differentiated in the crustal reservoir. The quenching event was a phreato-magmatic eruption within the stability field of the low-pressure calcite; this was triggered by advective overpressure, caused by expanding gas bubbles in a quasi-incompressible silicate melt system. The high-pressure, pre-eruption origin of aragonite is indicated by enrichment in 13 C compared to the associated calcite interpreted as a record of CO 2 degassing at T 〉 500 °C. The oxygen ( 18 O ranges of 22.1–24.5 V-SMOW in aragonite, 21.6–22.7 in calcite) and carbon ( 13 C ranges of –4.4 to –5.9 V-PDB in aragonite, –11.9 to –12.7 in calcite) isotope signatures are consistent with a degassed carbonatite melt primarily derived from a subduction zone.
Print ISSN:
0003-004X
Electronic ISSN:
1945-3027
Topics:
Geosciences
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