2004/02/01 by E. Mariani, Lorenzo Toscani, Danilo Bersani · 13 citations
Chemistry · Earth and Planetary Sciences · Materials Science · #Chemistry #Clay minerals and soil interactions #Geochemistry #Geological and Geochemical Analysis #Geology #High-pressure geophysics and materials #Leucite #Magma #Mantle (geology) #Melt inclusions #Mineralogy #Olivine #Peralkaline rock #Phenocryst #Phlogopite #Volcanic rock #Volcano
paper · doi:10.1180/0026461046810173
published in Mineralogical Magazine 68(1), 83-100 (Cambridge University Press)
openalex publication_date 2004/02/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/11
Abstract The lamproite of Gaussberg is an ultrapotassic rock where leucite, olivine and clinopyroxene microphenocrysts occur in a glass-rich groundmass, containing microliths of leucite, clinopyroxene, apatite, phlogopite and rare K-richterite. Abundant silicate melt inclusions occur in olivine, leucite and, rarely, in clinopyroxene microphenocrysts. Raman investigations on melt inclusions showed the presence of pure CO 2 in the shrinkage bubbles. On the other hand, the glass of the groundmass is CO 2 -poor and contains up to 0.70 wt.% of dissolved H 2 O, as estimated by infrared spectra. It is inferred that CO 2 was released at every stage of evolution of the lamproite magma (CO 2 -rich shrinkage bubbles), whereas H 2 O was retained for longer in the liquid. At Gaussberg, CO 2 seems to have a major role at relatively high pressure where it favoured the crystallization of H 2 O-poor microphenocrysts; the uprise of the magma to the surface decreased the solubility of CO 2 and caused a relative increase in water activity. As a consequence, phlogopite and K-richterite appeared in the groundmass. The glass composition of both the groundmass and melt inclusions suggests different evolutions for the residual liquids of the investigated samples. Sample G886 shows the typical evolution of a lamproite magma, where the residual liquid evolves toward peralkaline and Na-rich composition and crystallizes K-richterite in the latest stage. Sample G895 derives from mixing/mingling of different batches of magma; effectively glasses from melt inclusions in leucite and clinopyroxene are more alkaline than those found in early crystallized olivine. Leucite and clinopyroxene crystallized early from a relatively more alkaline batch of lamproite magma and, successively, a less alkaline, olivinebearing magma batch assimilated them during its rise to the surface.