  We present an analysis of the gas-poor circumstellar material in the HD
113766 binary system (F3/F5, 10 - 16 Myr), recently observed by the Spitzer
Space Telescope. For our study we have used the infrared mineralogical model
derived from observations of the Deep Impact experiment. We find the dust
dominated by warm, fine (~1 um) particles, abundant in Mg-rich olivine,
crystalline pyroxenes, amorphous silicates, Fe-rich sulfides, amorphous carbon,
and colder water-ice. The warm dust material mix is akin to an inner main belt
asteroid of S-type composition. The ~440 K effective temperature of the warm
dust implies that the bulk of the observed material is in a narrow belt ~1.8 AU
from the 4.4 L_solar central source, in the terrestrial planet-forming region
and habitable zone of the system (equivalent to 0.9 AU in the solar system).
The icy dust lies in 2 belts, located at 4-9 AU and at 30 - 80 AU. The lower
bound of warm dust mass in 0.1 - 20 um, dn/da ~ a^-3.5 particles is very large,
at least 3 x 10^20 kg, equivalent to a 320 km radius asteroid of 2.5 g cm^-3
density. Assuming 10m largest particles present, the lower bound of warm dust
mass is at least 0.5 M_Mars The dust around HD 113766A originates from
catastrophic disruption of terrestrial planet embryo(s) and subsequent grinding
of the fragments, or from collisions in a young, extremely dense asteroid belt
undergoing aggregation. The persistence of the strong IR excess over the last
two decades argues for a mechanism to provide replenishment of the
circumstellar material on yearly timescales.
