What are volatiles?
Volatiles are chemical species that under normal
conditions of pressure and temperature exist in the gaseous phase.
The main volatiles associated with volcanoes are water (H2O),
in the form of steam, and carbon dioxide (CO2) gas.
Volatiles from the Mantle>>
There are 3 possible reservoirs that can contribute volatiles to
subduction zone volcanoes: 1)
the subducting slab, 2) the mantle wedge, and 3) the crust. The
subducting slab has a veneer of marine sediments on its surface,
which are taken into the mantle as part of the subduction process.
The sediments, in particular, tend to be very water and carbonate
rich. Thermal breakdown of the carbonate as the subducting plate
enters the mantle produces CO2. Another source of volatiles
is the mantle trapped between the downgoing plate and the over-riding
plate or crust upon which the volcano is built. This region of the
mantle is called the mantle wedge. Finally, the arc crust itself
can release volatiles by thermal contact with ascending magmas from
the mantle. Distinguishing between these possible sources of volatiles
in subduction zone volcanoes is a primary objective of our study
in Costa Rica.