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CO_2-rich glass, round calcite crystals, and no liquid immiscibility in the system CaO-SiO_2-CO_2, at 2.5 GPa

Lee, Woh-Jer and Wyllie, Peter J. and Rossman, George R. (1994) CO_2-rich glass, round calcite crystals, and no liquid immiscibility in the system CaO-SiO_2-CO_2, at 2.5 GPa. American Mineralogist, 79 (11-12). pp. 1135-1144. ISSN 0003-004X.

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Following reports that the miscibility gap between silicate and carbonate liquids located experimentally on feldspar-calcite joins extended to the alkali-free side of the system CaONa_2O-Al_2O_3-SiO_2-CO_2, the melting of a mixture of calcite (70 wt%) and quartz was investigated at 2.5 GPa. The isobaric reaction, calcite (CC) + quartz (Qz) = liquid (L) + vapor (V), was reversed at 1350 ºC. Quartz and rounded calcite crystals were concentrated at the bottom of the capsule, and CO_2, was distributed in large vapor bubbles in the glass layer and at the top of the capsule. The liquid quenched to transparent glass, which is unusual in carbonate-rich systems. In two-stage reversal experiments, a sample of L + V that was heated to the subsolidus temperature of 1300, ºC produced a few rounded calcite grains organized in dendritic patterns; at 1200 ºC, dendritic intergrowths of CC + Qz were produced with some coarser-grained areas. The glass was found to contain about 20 wt% CO_2, on the basis of the geometry of phase boundaries and EDS analysis. There was no evidence for immiscible liquids. The round calcite crystals are equilibrium mineral phases, not quenched CaCO_3. liquids, and surface tension effects control their shapes. Infrared spectroscopic studies indicated that (CO_3)^(2-), is the dominant CO_2, species in the glass, and the silicate structure is partially polymerized, probably as a result of interaction between Ca^(2+) and SiO_4 tetrahedra. The phase relationships in the CaCO_3-SiO_2, system, the simplest model for subducted oceanic crust with limestone (or for basalt altered by sea water), show that subducted crust potentially could transport calcite to great depths for long-term storage in the mantle and could also yield low-SiO_2, carbonate-rich magmas under some thermal conditions. Such carbonate-rich melts may be efficient agents for mantle metasomatism.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1994 Mineralogical Society of America. Manuscript received December 23, 1993. Manuscript accepted July 11, 1994. This research was supported by the Earth Science section of the U S. National Science Foundation, with grants EAR-9218806 (P.J.W.) and EAR-9104059 (G.R.R.). This is contribution no. 5412 of the Division of Geological and Planetary Sciences California Institute of Technology.
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NSF Earth SciencesEAR-9218806
NSF Earth SciencesEAR-9104059
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Caltech Division of Geological and Planetary Sciences5412
Issue or Number:11-12
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Official Citation:CO2-rich glass, round calcite crystals, and no liquid immiscibility in the system CaO-SiO2-CO2 at 2.5 GPa WOH-JER LEE, PETER J. WYLLIE, GEORGE R. ROSSMAN 1135-1144
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44122
Deposited By: Ruth Sustaita
Deposited On:04 Mar 2014 19:27
Last Modified:03 Oct 2019 06:14

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