37 research outputs found
Effect of fluorine on near-liquidus phase equilibria of an Fe–Mg rich basalt
Author Posting. © The Author(s), 2012. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Chemical Geology 312-313 (2012): 118-126, doi:10.1016/j.chemgeo.2012.04.015.Volatile species (H2O, CO2, F, Cl, etc) have important effects on the formation and crystallization history of basaltic magmas. Here, we have experimentally investigated the effects of F on phase equilibria of Fe-Mg-rich basalt. Our results show that fluorine has large effects on the liquidus temperature and the chemistry of crystallizing minerals. Compared to the F-free system, addition of ~2 wt.% F moves the olivine-pigeonite liquidus point down ~2 kbar and 95 °C (from 12 kbar, 1375 °C to 10 kbar, 1280 °C). With increasing fluorine concentrations, dramatically increases for both pyroxene and olivine, suggesting that fluorine in basaltic magmas complexes primarily with MgO. Complexing with MgO in the melt decreases its MgO activity, and forces the crystallizing minerals to greater Fe/Mg, and so increases . Models of basalt generation, where the magma is fluorine-rich, need to include the effect of not only water but fluorine on liquidus depression and minerals crystallizing/melting. Our results suggest that fluorine may significantly aid in the petrogenesis of silica-poor, alkali-rich magmas in the Earth and Mars.This work was supported by NASA MFR grant # NNX09AL25G to A.H. Treiman and J. Filiberto, a Lunar and Planetary Institute summer internship to J. Wood, and a Packard fellowship for science and engineering to R. Dasgupta
NMR parameters in alkali, alkaline earth and rare earth fluorides from first principle calculations
19F isotropic chemical shifts for alkali, alkaline earth and rare earth of
column 3 basic fluorides are measured and the corresponding isotropic chemical
shieldings are calculated using the GIPAW method. When using PBE exchange
correlation functional for the treatment of the cationic localized empty
orbitals of Ca2+, Sc3+ (3d) and La3+ (4f), a correction is needed to accurately
calculate 19F chemical shieldings. We show that the correlation between
experimental isotropic chemical shifts and calculated isotropic chemical
shieldings established for the studied compounds allows to predict 19F NMR
spectra of crystalline compounds with a relatively good accuracy. In addition,
we experimentally determine the quadrupolar parameters of 25Mg in MgF2 and
calculate the electric field gradient of 25Mg in MgF2 and 139La in LaF3 using
both PAW and LAPW methods. The orientation of the EFG components in the
crystallographic frame, provided by DFT calculations, is analysed in term of
electron densities. It is shown that consideration of the quadrupolar charge
deformation is essential for the analysis of slightly distorted environments or
highly irregular polyhedra.Comment: 18 pages, 8 figures, 4 tables and ES
A tetranuclear fluorido-bridged iron compound: Fluoride abstraction from the tetrafluoridoborate anion
Metals in Catalysis, Biomimetics & Inorganic Material