Li, Be, B, and their isotopes are powerful tools for studies of fluid processes in subduction zones, mainly because of their distinct isotopic composition in different reservoirs and their potential mobilization at elevated temperatures. Laboratory hydrothermal experiments, utilizing an autoclave rocking apparatus, were used to investigate the basic chemical behavior of these elements and isotopes under various temperatures and pressures and to mimic sediment-water interaction during the early oceanic crust subduction. In addition, an extensive survey was conducted of their distributions in submarine hydrothermal vents, in mud volcanoes on land and on the seafloor, in tectonically expelled waters, mud pot waters in the Salton Sea, and in the DSDP/ODP sediments and pore waters.; Significant mobilization of Li, Be, and B at elevated temperatures was observed in the hydrothermal experiments. Li is readily mobilized at temperatures above 150{dollar}spcirc{dollar}C. The dissolved {dollar}deltasp6{dollar}Li appears to be a function of smectite or chlorite formation and the exchange process is reversible. The fluid pH exerts a dominant control on Be mobilization, especially, while the fluid acidity is generated at elevated temperatures. This partitioning behavior can be understood in terms of oxy-beryllium species re-distribution. Bulk B (exchangeable + lattice bound) in sediment were released at relatively low temperature. The K{dollar}sb{lcub}rm D{rcub}{dollar} becomes essentially zero at temperatures above 100{dollar}spcirc{dollar}C, indicating no surface adsorption. Large mobilization of the lattice bound B occurs at temperatures above 300{dollar}spcirc{dollar}C.; These experimental data agree well with the surveyed natural fluid samples and emphasize the importance of slab derived fluids to explain the B-{dollar}sp{lcub}10{rcub}{dollar}Be and B-{dollar}deltasp{lcub}11{rcub}{dollar}B systematics in arc volcanics. In addition, the K{dollar}sb{lcub}rm D{rcub}{dollar} information of B was applied for a correction of temperature squeezing artifacts in pore water B and {dollar}deltasp{lcub}11{rcub}{dollar}B.; Mobilization of B, Li, and possibly Be at elevated temperatures provide critical contraints for a better understanding of their oceanic mass balance, as well as in subduction zones. For instance, the B budget in the ocean is in better shape after taking into account the "re-flux B" in accretionary prism and the potential volatilization during arc magmatism.
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