EXPERIMENTAL SIMULATION OF AMPHIBOLITE AND ULTRABASIC ROCK INTERACTION IN SUBDUCTION ZONES

This paper presents the results of an experimental study of the compos itions of fluids, glasses, and minerals in the systems amphibolite-H2O , Iherzolite-H2O, and amphibolite-lherzolite-H2O. The former two syste ms represented the composition of oceanic crust and mantle rocks, whil e the latter was assumed to simulate the interaction between the hot m antle wedge and the colder rocks of the subducted oceanic plate. Exper iments were carried out using a high gas-pressure apparatus under 5-8 kbar at temperatures of 800-1000 degrees C. The systems amphibolite-H2 O and Iherzolite-H2O were investigated under isothermal conditions, wh ile the system amphibolite-Iherzolite-H2O was studied under conditions of temperature gradient along the axis of the capsule. All experiment s were run in gold ampules to prevent iron loss into the walls. The co mposition of fluid was governed by amphibolite solubility. High-Mg alu minous amphibole developed in the Iherzolite, and a small amount of me lt was produced as a result of the fluid effect on Iherzolite. The com position of the melt approximated the composition of andesite. The flu id phase produced during the experiments contained 0.2 wt % Na2O and 0 .1-0.2 wt % SiO2 on average.