  (abridged) We present Spitzer infrared observations to constrain disc and
dust evolution in young T Tauri stars in MBM 12, a star-forming cloud at high
latitude with an age of 2 Myr and a distance of 275 pc. The region contains 12
T Tauri systems, with primary spectral types between K3 and M6; 5 are weak-line
and the rest classical T Tauri stars. We first use MIPS and literature
photometry to compile spectral energy distributions for each of the 12 members
in MBM 12, and derive their IR excesses. The IRS spectra are analysed with the
newly developed two-layer temperature distribution (TLTD) spectral
decomposition method. For the 7 T Tauri stars with a detected IR excess, we
analyse their solid-state features to derive dust properties such as
mass-averaged grain size, composition and crystallinity. We find a spatial
gradient in the forsterite to enstatite range, with more enstatite present in
the warmer regions. The fact that we see a radial dependence of the dust
properties indicates that radial mixing is not very efficient in the discs of
these young T Tauri stars. The SED analysis shows that the discs in MBM 12, in
general, undergo rapid inner disc clearing, while the binary sources have
faster discevolution. The dust grains seem to evolve independently from the
stellar properties, but are mildly related to disc properties such as flaring
and accretion rates.
