The structure of silicate melts in the system Na(2)O center dot 4SiO(2) saturated with reduced C-O-H volatile components and of coexisting silicate-saturated C-O-H solutions has been determined in a hydrothermal diamond anvil cell (HDAC) by using confocal microRaman and FTIR spectroscopy as structural probes. The experiments were conducted in-situ with the melt and fluid at high temperature (up to 800 degrees C) and pressure (up to 1435 MPa). Redox conditions in the HDAC were controlled with the reaction, Mo + H(2)O = MoO(2) + H(2), which is slightly more reducing than the Fe + H(2)O = FeO + H(2) buffer at 800 degrees C and less.|The dominant species in the fluid are CH(4) + H(2)O together with minor amounts of molecular H(2) and an undersaturated hydrocarbon species. In coexisting melt, CH(3) - groups linked to the silicate melt structure via Si-O-CH(3) bonding may dominate and possibly coexists with molecular CH(4). The abundance ratio of CH(3) - groups in melts relative to CH(4) in fluids increases from 0.01 to 0.07 between 500 and 800 degrees C. Carbon-bearing species in melts were not detected at temperatures and pressures below 400 degrees C and 730 MPa, respectively. A schematic solution mechanism is, Si-O-Si + CH(4) (sic) Si-O-CH(3)+H-O-Si. This mechanism causes depolymerization of silicate melts. Solution of reduced (C-O-H) components will, therefore, affect melt properties in a manner resembling dissolved H(2)O. (C) 2010 Elsevier Ltd. All rights reserved.