  We present new analysis of 11 intermediate-age (1-2 Gyr) star clusters in the
Large Magellanic Cloud based on Hubble Space Telescope imaging data. Seven of
the clusters feature main sequence turnoff (MSTO) regions that are wider than
can be accounted for by a simple stellar population, whereas their red giant
branches indicate a single value of [Fe/H]. The star clusters cover a range in
present-day mass from about 1E4 to 2E5 solar masses. We compare radial
distributions of stars in the upper and lower parts of the MSTO region, and
calculate cluster masses and escape velocities from the present time back to a
cluster age of 10 Myr. Our main result is that for all clusters in our sample
with estimated escape velocities > 15 km/s at an age of 10 Myr, the stars in
the brightest half of the MSTO region are significantly more centrally
concentrated than the stars in the faintest half AND more massive red giant
branch and asymptotic giant branch stars. This is not the case for clusters
with escape velocities < 10 km/s at an age of 10 Myr. We argue that the wide
MSTO region of such clusters is mainly caused by to a 200 - 500 Myr range in
the ages of cluster stars due to extended star formation within the cluster
from material shed by first-generation stars featuring slow stellar winds.
Dilution of this enriched material by accretion of ambient interstellar matter
is deemed plausible if the spread of [Fe/H] in this ambient gas was very small
when the second-generation stars were formed in the cluster.
