First results from a new experimental technique to determine fluid/solid trace element partition coefficients using diamond aggregate extraction traps
Stalder, R.; Foley, S. F.; Brey, G. P.; Forsythe, L. M.; Horn, I.
published: Sep 10, 1997
ArtNo. ESP154017201007, Price: 29.00 €
Partitioning of representative members of the LFSE, LREE, HREE and HFSE trace element groups between fluid (H20 and 1.5 M HCl) and garnet have been determined experimentally at 50 kbar and 1000 °C, corresponding to the depth of the upper part of a subducting plate beneath active island arc volcanoes. Partition coefficients were determined by direct analysis of solid residues and the fluid solute which was trapped in a diamond aggregate during quenching of the experiment. Each capsule contained 50 percent of diamond crystals (grain size ~50 mu-m) in the upper half of the capsule; the pore space between the diamonds aggregates is preserved even at 50 kbar, so that the fluid was able to communicate with the solid residual phases throughout the duration of the experiment. Trace element concentrations in the fluid trap and crystalline residues were determined by laser ablation microprobe (LAM). Results indicate that equilibrium is reached within two days. REE are fractionated by a fluid effectively, D (fluid/gt)Sm/D (fluid/gt)Yb is around 50. Neither in the presence of pure water nor after addition of hydrochloric acid do partition coefficients for Nb and Ta seem to be decoupled from La and Ceo Therefore, we conclude that a Cl-solution cannot produce negative HFSE anomalies during selective enrichment in subduction zone infiltration processes.