Pressure-temperature Stability Studies of Talc and 10-Å Phase Using X-ray Diffraction.

We investigated the behavior of talc plus water to 10-Å phase formation. This phase is capable of transporting water from subducted oceanic lithosphere into the Earth's mantle. Knowing more about the stability field of 10-Å phase across the slab-mantle interface can help to determine the Earth's water budget. X-ray diffraction measurements of natural talc plus water at combined temperatures of 27°C-400°C and pressures of 0-15 GPa were made at the Advanced Light Source beamlines 12.2.2 and 11.3.1. Elevated temperatures and pressures were achieved with a resistively heated, membrane driven diamond-anvil cell. Data were collected along isotherms and modeled using a monoclinic unit cell. Our data suggest that water is incorporated into the talc structure at room temperature while at elevated pressures. Elevated temperature data show pressure-temperature path dependence and time-dependence for in situ data collection. All temperature data suggest a change in the compression mechanism of talc starting at approximately 2 GPa.